1
2476-6763
Tarbiat Modares University
9184
Seismic capacity and possibility of collapse of tall steel buildings with outrigger system using failure curves and damage profiles]
دانشجو
ا
1
11
2017
17
4
1
13
03
04
2016
10
10
2016
forms of the outrigger or belt truss structure have high performance in reducing the response of tall structures against side loads. However outriggers system are not considered as a seismic system in design codes. In this paper seismic behavior of tall buildings with outriggers will be checked and the effect of adding outrigger on the seismic behavior of steel tall structures in term of capacity of seismic intensity corresponding to the level of performance of collapse, Distribution of seismic requirements in high of structures demand curves corresponding to the general instability of structures and Fragility curves will be studied. Therefore, in the first three buildings of 20, 25 and 30 floors in three dimensions are designed so that the effects of outriggers not considered in the initial design and in terms of members resistance and the relative displacement (drift) have passed some regulations. To do this, the three structures is designed using 3D model So that the effects of outrigger are not considered in the initial design and in terms of resistance members as well as the relative displacement of stories have passed limits of design code. and then one of main frame of structure is analyzed using “Opensees” software and moment frame structural system and CBF with regard to inelastic behavior in both the presence and absence of outrigger checked by IDA analysis. The results show Keywords: Tall Building, Outrigger and Belt Truss, Seismic behavior, Incrimental Daynamic Analysis. forms of the outrigger or belt truss structure have high performance in reducing the response of tall structures against side loads. However outriggers system are not considered as a seismic system in design codes. In this paper seismic behavior of tall buildings with outriggers will be checked and the effect of adding outrigger on the seismic behavior of steel tall structures in term of capacity of seismic intensity corresponding to the level of performance of collapse, Distribution of seismic requirements in high of structures demand curves corresponding to the general instability of structures and Fragility curves will be studied. Therefore, in the first three buildings of 20, 25 and 30 floors in three dimensions are designed so that the effects of outriggers not considered in the initial design and in terms of members resistance and the relative displacement (drift) have passed some regulations. To do this, the three structures is designed using 3D model So that the effects of outrigger are not considered in the initial design and in terms of resistance members as well as the relative displacement of stories have passed limits of design code. and then one of main frame of structure is analyzed using “Opensees” software and moment frame structural system and CBF with regard to inelastic behavior in both the presence and absence of outrigger checked by IDA analysis. The results show Keywords: Tall Building, Outrigger and Belt Truss, Seismic behavior, Incrimental Daynamic Analysis. To do this, the three structures is designed using 3D model So that the effects of outrigger are not considered in the initial design and in terms of resistance members as well as the relative displacement of stories have passed limits of design code. and then one of main frame of structure is analyzed using “Opensees” software and moment frame structural system and CBF with regard to inelastic behavior in both the presence and absence of outrigger checked by IDA analysis. The results show Keywords: Tall Building, Outrigger and Belt Truss, Seismic behavior, Incrimental Daynamic Analysis.
11138
An Investigation of the Effect CFRP Post Tensioned Cables on Seismic Behavior of Steel Braced Frames with Controlled Rocking System
amirzehni
hasan
shafei
erfan
1
11
2017
17
4
15
25
17
01
2016
10
10
2016
Conventional lateral force resisting systems, dissipate seismic energy through plastic deformation in primary structural members that results in significant damage in buildings. In most cases, repair of these induced damages are impossible from the structural viewpoint, or have not economic justification. Recent research works are to localize the induced damage to specific elements (as fuse, dampers and etc.) without plasticization of primary load-carrying elements that ensure the stability of structure. In steel structures, the self-centering rocking braced system is an innovative type of seismic lateral force resisting systems that is developed with aim to minimize structural damages, residual drifts and enable repair or replace of damaged elements with minor expense after experiencing earthquakes. Steel braced frame with controlled rocking system consists of three primary components: (1) steel braced frame with rigid joints and no connections to base foundation at the column bases that is free to rock cyclically during excitation; (2) post tensioning cables which are connected to the frame top and foundation base in order to provide retreat back or self-centering capability of the system. Expressed mechanism plays an important role in restoration of quake-imposed displacement into its initial position; and (3) the replaceable energy dissipating elements that act as structural fuses to absorb seismic energy through undergoing of inelastic deformations and provide the required ductility of the system prior to instability or collapse. In this type of lateral force resisting systems, the post tensioned cables and the members of the braced frame are design to remain elastic during excitation and provide high stiffness, strength and global stability of the structure with minor local deformations. In this design concept, post tensioned strands are the key members known in providing self-centering capability of the system and occurrence of any plastic deformation in these elements endangers overall stability of system. Probable exceedance of seismic force may result in yield of post-tensioned cables and consequent elimination of restoring functionality of self-centering mechanism. In current research work, the steel material is replaced by carbon fiber reinforced plastic (CFRP) fabric in post tensioning strands, and the consequent effects of proposed substitution is investigated on the behavior of braced frame and linked structural components. The research was conducted on two steel braced frames with controlled rocking system equipped with steel and CFRP cables and the models are analyzed using nonlinear dynamic time history analysis (NLTHA) procedure. The frames are subjected to JMA-Kobe ground motion record, that is scaled to 69%, 100% and 120% intensity groups which corresponds to unit, 1.45 and 1.74 times of maximum considered earthquake (MCE) ground motion level. Extracted results show that using CFRP post tensioned cable instead of steel cables, can protect the system against instability even under 100% Kobe ground motion record scale and leads to a more reliable type of controlled rocking systems. This study also revealed that remaining the CFRP cable on elastic region not only controls the frame lateral displacement, also prevents early failure in fuses under severe earthquakes and ensures the seismic energy dissipating capability of the structure.
7139
Study of the SBAR performance in COD removal of Petroleum and MTBE
Taghipour
Shabnam
Ayati
Bita
^{
h
}
Razaei
Mina
^{
h
}Tarbiat Modares Univ.
1
11
2017
17
4
17
27
09
01
2016
10
10
2016
The petroleum refineries, water are used for different purposes, such as extraction of contaminants. Some of these pollutants such as petroleum and Methyl Tertiary Butyl ether (MTBE) can be noted that have less biodegradability than other organic compounds. Discharge of these pollutants into water, and the presence of them in drinking water make huge environmental concerns. A sequencing airlift reactor (SBR) along with an internal riser is called sequencing batch airlift reactor (SBAR); it has a similar structure to SBR and purifies wastewater with a certain temporal cycle in a single reactor. The SBAR system, which is used along with granules to treat wastewater, is known as granule sequencing batch airlift reactor (GSBAR). Using this system for biodegrading requires a high concentration of biomass (aerobic granules. In recent years, several studies have been conducted on the use of aerobic biogranules. Mousavi et al., examined the removal of phenol with an initial concentration of 1000 mg/L from saline wastewater using GSBAR with aerobic granules 2 mm in size. The results indicated that 99% of phenol was removed. Bao et al., studied the effect of temperature on the formation of aerobic granules and on the removal of nutrients by SBAR system. The granules had an average diameter of 3–4 mm, density of 1.036 g/mL, sludge volume index of 37 mL/g, and sedimentation rate of 18.6–65.1 cm/min. The input load rate of COD, NH4–N, and PO4–P was 1.2–2.4, 0.122, and 0.012–0.024 kg/m3/day, respectively and the removal efficiency at low temperatures was 90.6–95.4, 72.8–82.1, and 95.8–97.9%, respectively. Taheri et al., examined the formation of aerobic granules in SBR for treating saline wastewater. In this study, the granules were 3–7 mm in size, had a fall speed of 0.9–1.35 cm/s, and density of 32-60 g/L. Using aerobic granules with a diameter of 1–2 mm to biologically restore 2, 4-di-chlorophenol with an initial concentration of 4.8 mg/L, Wang et al., achieved the removal efficiency of 95% and 94% for COD and di-chlorophenol, respectively. Siroos Rezaei et al. reported that COD removal efficiency of synthetic wastewater was 95% with the glucose carbon source in six 4-h cycles with a loading rate of 1500 mg/L in SBAR system using aerobic granules. The new granules had different diameters in the range of 0.5–5 mm, high sedimentation ability, and SVI of 100 mL/g. Ghaderi et al., investigated the performance of the biofilm reactor and SBR in removing formaldehyde from wastewater. The results revealed that removal efficiency of CODs less than 200 mg/L was 100% and removal efficiency of CODs between 200–450 mg/L was 90% after 48 h. The aim of this study was evaluating the ability of SBAR system in quick produce of granules and achieving high removal of petroleum and MTBE in a short time. For this purpose, 2 similar SBAR systems with Circular cross-section were used. Outer Cylinder's diameter and length was respectively 8cm and 110 and the internal riser's diameter and length was respectively 4 cm and 90 cm. In the first system (R1) petroleum was treated in 6 hours and in the second system (R2) MTBE wastewater was treated in 4 hours. In COD equivalent to 600 mg/L, the removal efficiency of R1 and R2 were equal to 81.1 and 84.2%. These values were respectively 82.8 and 90% in COD equivalent 500 mg/L. Consider to granules changes, optimal COD was respectively equivalent to 600 and 500 mg/L in R1 and R2. By reducing retention time to 5 and 3 hours in R1 and R2, removal efficiency of pollutants in optimal COD of each system was respectively 77.8 and 90 %. The first granules were observed in the seventh day of operating system. During this period, the size of the granules increased to 1.3 and 0.6 mm in R1 and R2. Density and velocity of the granules were in the range of 0.0252-1.1998 gr/mL and 3.02-3.32 cm/s in R1 and 0.05-0.06502 gr/mL and 0.4-0.9 cm/s in R2. SVI was in the range of 42-65 mL/g, pH and DO was in the range of 6.8-7.2 and 2-6 mg/L and ORP was always above 100 mV.
7736
Experimental study on impact behaviour of high performance concrete with statistical approach
dalvand
ahmad
^{
j
}
^{
j
}Assistant Professor, Dep. Eng., Lorestan University, khorramabad,iran
1
11
2017
17
4
39
49
15
12
2015
07
01
2017
High-performance concrete (HPC) exceeds the properties and constructability of normal concrete. Normal and special materials are used to make these specially designed concretes that must meet a combination of performance requirements. Special mixing, placing, and curing practices may be needed to produce and handle high-performance concrete. Extensive performance tests are usually required to demonstrate compliance with specific project needs (ASCE 1993, Russell 1999, and Bickley and Mitchell 2001). High-performance concretes are made with carefully selected high-quality ingredients and optimized mixture designs; these are batched, mixed, placed, compacted and cured to the highest industry standards. Typically, such concretes will have a low water-cementing materials ratio of 0.20 to 0.45. Plasticizers are usually used to make these concretes fluid and workable. High-performance concrete has been primarily used in tunnels, bridges, and tall buildings for its strength, durability, and high modulus of elasticity. High Performance concrete (HPC) are a class of fiber cement composites with fine aggregates that exhibit tensile strain hardening response under uni-axial loading. These materials are characterized by pseudo-ductile tensile strain hardening behavior and multiple cracking prior to failure. This figure emphasizes the transition from brittle concrete to quasi-brittle FRC (strain softening behavior after first cracking) to ductile HPFRCC with strain hardening behavior after first cracking. In recent years, a new class of HPFRCC has emerged as ECC. Engineered Cementitious Composite (ECC) which was developed at University of Michigan had a typical moderate tensile strength of 4-6 MPa and ductility of 3-5%.Since there is not enough available information to give mechanical characteristics and also to calculate the mean, standard deviation and coefficient of variation, some statistical evaluations are necessary to obtain accurate results of the effect of inclusion of PP fiber on absorbed energy and impact resistance of concrete. Concrete is a heterogeneous material, and that is why results obtained from several tests are often significantly scattered. There is a few quantitative statistical data about the effect of PP fiber on compressive, flexural strength of HPC at the other research work; therefore it shows a necessity to study the effects of PP fiber on mentioned parameters.Gotten data were statistically analyzed. 240 concrete specimens were prepared in three series with different mix designs, containing 0.5, 0.75 and 1 percent of PP fibers. Twenty 100×100×100mm cubic specimens, twenty 320×80×60mm beam specimens andforty150×64mm discs were cast from each mixture. Cubic specimens were used to determine the compressive strength, beam specimens were tested to obtain flexural strength and cylindrical cutting specimens (discs) were subjected to the drop-weight test following the ACI committee 544 to determine impact strength of mixed concretes. Statistical analysis done based on these experimental tests showed that in comparison with data of impact strength, data of mechanical properties have less dispersion. Also while increasing percentage of fibers, dispersion in data increases. According to results of compressive strength test on cubic specimens, adding fibers to specimens increased the coefficient of variations of compressive strength. The coefficient of variations of compressive strength for HPFRCC was increase from 4.96 % to 8.42 %. Also Statistical data for flexural strength are almost normally distributed. Mean flexural strength in HP-1 group (1% fiber) was 6.24 MPa, which is 29 % and21 % more than HP-0.5 group (0.5 % fiber) andHP-0.75 group(0.75 % fiber), respectively. HP-1 group's coefficient of variation is 9.88 % which is 11 % and 8 % more than the same parameter in HP-0.5 and HP-0.75 groups, respectively.
7253
Behavior assessment of common shear walls in iran with steel boundary element
Dehghani
Ehsan
^{
m
}
Allameh Najafi
S. Mahdi
^{
n
}
Allameh Najafi
S. Ali
^{
o
}
^{
m
}University of Qom
^{
n
}University of Qom
^{
o
}University of Qom
1
11
2017
17
4
51
62
26
01
2016
13
03
2017
Abstract: Composite construction in steel and concrete offers significant advantages for use as the primary lateral resistance systems in building structures subjected to seismic loading. While composite construction has been common for over half a century through the use of composite beam and joist floor systems, over the past decade a substantial amount of research has been conducted worldwide on a wide range of composite lateral resistance systems. These systems include unbraced moment frames consisting of steel girders with concrete-filled steel tube (CFT) or steel reinforced concrete (i.e., encased steel sections, or SRC) beam-columns; braced frames having concrete-filled steel tube columns; and a variety of composite and hybrid wall systems. Structural walls are widely used in building structures as the major structural members to provide substantial lateral strength, stiffness, and the inelastic deformation capacity needed to withstand earthquake ground motions. In recent years, steel reinforced concrete (SRC) walls have gained popularity for use in high-rise buildings in regions of high seismicity. SRC walls have additional structural steel embedded in the boundary elements of the reinforced concrete (RC) walls. Walls with additional shapes referred as composite steel-concrete shear walls, contain one or more encased steel shapes, usually located at the ends of the wall. Composite shear walls with steel boundary element are known as the structural members able to withstand high in-plane lateral forces at low displacement levels. Reinforced concrete shear walls with steel boundary element being performed in Iran are joined to the foundation, in boundary element section, usually through bolts and base plates. Most reliable codes of the world have nothing to say about the behavior of this type of shear walls, and no experimental studies or analyses have been conducted on the behavior of this type of shear walls. In the past decade, great effort has been devoted to the study of seismic behavior of SRC walls, for Design provisions for SRC walls have also been included in some leading design codes and specifications, for example, AISC 341-10 , Eurocode 8, and JGJ 3-2010 Exposed baseplates together with anchor bolts are the customary method of connection of steel structures to the concrete footings . In this paper, the influence of cross section of base plate’s joint bolts to the foundation and the wall’s longitudinal bars embedding within the area of boundary element in the foundation, on the behavior of this type of shear walls have been investigated. The finite element software is first calibrated and the accuracy of its results is validated through modeling the experimental samples. In this research, the concrete’s nonlinear finite element analysis method and concrete damage plasticity model have been used for the concrete’s behavior modeling. The results show that increasing in the level of bolt’s cross section and also the embedding of longitudinal bars of boundary element in the foundation cause an improvement of the capacity of these walls. However, these walls’ resistance against the normal axial loads is considered to be less than reinforced concrete shear wall. Keywords: Reinforced concrete shear wall, Steel boundary element, Concrete damage plasticity model, Finite element model.
1051
Investigation behavior of bearing 3D Panel wall developed by lateral load in independent and system states
1
11
2017
17
4
63
75
08
03
2016
10
10
2016
The three dimensional panels are one of the modern building systems which can be placed in the category of industrial buildings. It has always been tried to conduct many studies for identifying the behavior and upgrading the capacity of panels due to their earthquake resistance and high speed performance. In this regard, in this research a comparative study of structural components behavior of the upgraded three-dimensional panels under lateral load in independent and system mode, is investigated. At the same time it is tried to study the effect of strengthening the three dimensional panels and system mode (independent wall, L-shaped and BOX-shaped walls) on the three-dimensional panels. In order to verify, the results of panel were compared with dimensions of 120 × 120 with laboratory results of Kabir and Jahanpour and the results indicate the validity of the model. In the following, twenty-four models with dimensions close to reality (360 × 360〖cm〗^2), are built with Abaqus software. Overall, six independent wall model, L-shaped, roofed L-shaped, BOX-shaped walls with symmetric loading, BOX -shaped wall with asymmetrical loading and roofed BOX-shaped wall were built. Then the models are strengthened without strengthened reinforcement and with strengthened reinforcements ( 10) with an angle of 30, 45 and 60 degrees. The applied lateral loading, is exerted by changing the location on the end wall. After applying the loading, the pushover curve is plotted from which the maximum lateral load bearing capacity, the absorbed energy are obtained. It is warth mentioning for drawing the push over curve the target displacement is determind by ATC 24 guideline. And also for drawing the histories careature ATC40 guidline is used. The evaluation of results showed that the lateral load bearing capacity of L-shaped wall without strengthened reinforcement is not more than independent wall, but also it will be less. But by adding roof to the structure, the load bearing capacity will be increased due to reducing twisting effect. If strengthening the wall occurs, in roofed and without roofed modes, the capacity will be increased about 50 and 100 %. In BOX-shaped wall, in symmetric and asymmetric loading, the load bearing capacity will be increased about 200 and 50 % respectively. Now, if strengthened, the load bearing capacity in symmetric and asymmetric loading will be increased 3.5 and 2 times respectively. The effective angle of placement of strengthened reinforcement in the independent wall is 45 and 60 degrees. But in BOX-shaped and L-shaped walls, the use of strengthened reinforcement 45 degrees is recommended. In the L-shaped wall alone (not the entire system), the capacity will be increased 21 % and by adding roof, the load bearing capacity will be approximately two times. This mode in the BOX-shaped wall with symmetrical loading will be 63 %. By generally comparing the histories cerratures it is resulted that the L-shaped wall wich has the torsion originated from loading, has a lower energy dissipation in comparison with the models. And also if the exsting story loads to the integrated performance of the walls, it can.
3531
Modeling and optimization of fast degradation of contaminated soil with 2-methylpropane-2-thiol by modified Fenton process
Roohi
Pejman
^{
}
Fatehifar
Esmaeil
^{
}
Alizadeh
Reza
^{
}
^{
}Researcher in environmental Engineering Research center
^{
}Head of Environmental Engineering Research Center
^{
}Head of chemical engineering department
1
11
2017
17
4
77
88
04
06
2016
10
10
2016
The pollution of soil with 2-methylpropane-2-thiol as an odorant hydrocarbon is an environmental problem. It also causes secondary impacts such as social dissatisfaction and economic problems due to tourist revenue reduction. 2-methylpropane-2-thiol is a hazardous material and remediation of soil polluted by this material with a fast method is important to study. In this study, modified Fenton treatment is investigated for oxidation of 2-methylpropane-2-thiol. Central Composite Design (CCD) based on Response Surface Methodology (RSM) was used to obtain appropriate effects of the main factors (initial H2O2 concentration, FeSO4 to soil ratio and stirring time interval percentage) and their interactions on the removal efficiency. Treatments were set up to monitor 2-methylpropane-2-thiol removal efficiency for initial contaminant concentration of 64690 part per million by weight. Samples were analyzed by gas chromatograph equipped with FID and TCD detector and HP-Plot Q column. Design of experiment in the three-factor with five-level matrix include 20 experiment. Randomization technique is used to guard against unknown and uncontrolled factors as lurking nuisance factors. Moreover, blocking technique is used for investigation of probable effect of initial soil temperature on results. Analysis of variance and Pareto analysis show that all main factor are effective. Also, stirring time interval percentage was the most influential factors on 2-methylpropane-2-thiol removal efficiency. Results of the experiments shows that at low concentration levels removal efficiency increases with hydrogen peroxide concentration up to the certain level. For higher concentration of hydrogen peroxide concentration, the removal efficiencies decreased which could be due to scavenging. Also, increasing in FeSO4:Soil ratio increases removal efficiency up to the certain level because Fe2+ is an alternative to enable more extensive and greater contaminant oxidation; however a greater ratio (greater than 0.0040) causes decrease in the removal efficiency. This phenomena could be due to side reactions which affect reactive radicals such as OH• radicals. Furthermore, investigation of the results demonstrates that 2-methylpropane-2-thiol removal efficiency rises with increasing stirring time interval percentage. This phenomena could be due to uniform distribution of oxidation agent and Fe2+ and better desorption of contaminant from soil to liquid phase. Moreover, based on analysis of variance, the interaction between hydrogen peroxide and FeSO4: Soil ratio was significant with positive effect on the removal efficiency. This interaction could be the result of reaction between H2O2 and Fe2+. By considering main and interaction effects, with the raising H2O2 and Fe2+ concentration up to a certain level, the removal efficiency increase and with further concentration increasing the removal efficiency will be dropped. Analysis of variance indicate that initial soil temperature (21 and 25 0C) were not effective factors during the time interval of the experiments which could be due to the exothermic reaction between hydrogen peroxide, FeSO4 and contaminant. P-value of lack-of-fit (0.064) indicates that suggested model adequately fits the data with good correlation coefficient (R2=95.12%). Optimum condition suggested for maximum 2-methylpropane-2-thiol removal efficiency (94.412%) shows that concentration of H2O2 and Fe2+ ion must be at the certain level and maximum stirring time for remediation in the studied intervals. CCD model predict 94.084% for the removal efficiency at optimum condition which is good agreement with the predicted value.
5769
Development of a Vertical Design Spectrum for Iranian Plateau Using V/H Spectral Ratio
1
11
2017
17
4
89
100
23
04
2016
10
10
2016
In last two decades, some earthquakes like Kobe (1995), Chi-chi (1999) and Bam (2003) have shown the importance of vertical component of ground motion in inflicting damage on a variety of structural systems. Moreover, it has been shown that the effects of vertical component of earthquake in structural responses are more pronounced in the near fault regions. Therefore, It seems that, both horizontal and vertical design spectra are required in structural design procedure to reduce the vulnerability of structural systems to seismic loads. However, some of the existing design codes or guidelines are providing the designers only with the horizontal spectrum. In some others, the vertical spectrum is defined using a unified ratio of 2/3 with respect to the horizontal one. A new trend in design codes approaches is to introduce vertical design spectrum for the ground motion. Typically, there are two approaches in obtaining the vertical component of response spectrum using Ground Motion Prediction Equations (GMPEs). The differences between these approaches are based on the method of using GMPEs in development of vertical spectrum. The first approach is a direct application of GMPEs for vertical component of earthquake and in the second one; the attenuation model is in the form of vertical to horizontal spectral ratio function (V/H). The attenuation model in this case is used to scale the horizontal spectrum to the vertical one. While V/H ratio usually scales down the horizontal spectrum, it may scale up the spectrum in near distances particularly for the short period range of the response spectrum. GMPEs have a key role in seismic hazard evaluation for site-specific spectra. To propose a GMPE for any specific region the magnitude, source-to-site distance and peak ground characteristics of earthquakes in that region are required. In addition, some other parameters such as site class, faulting mechanism and so on might be considered necessary in development of GMPEs for a particular region. Although, various GMPEs have been developed for horizontal component of earthquake, there are no reliable GMPEs for vertical component of earthquake in Iranian plateau. In this study, after selecting the required GMPEs (GMPEs for horizontal and vertical component as well as GMPE for vertical to horizontal spectral ratio), the integrity of the results for development of vertical spectrum is evaluated. The sensitivity analyses for the V/H model show the relative independancy of this ratio to the magnitude and faulting mechanism of earthquakes (as well as site classes). Therefore, the source-to-site distance parameter is chosen as the sole contributor in defining the V/H ratio. Later, a simplified model for V/H ratio in terms of distance (source to site) is proposed in this study. Seismic hazard analysis for vertical component of earthquake is performed using V/H at a desired site and compared with the results of uniform hazard spectrum (UHS) analysis for the same component of earthquake in the region. Later, a vertical design spectrum for the Iranian plateau based on V/H ratio is proposed. At the end, using a calibration technique that can convert the horizontal uniform hazard spectrum to the design code horizontal spectrum is used to find the disgn response spectrum for vertical component of earthquake for Iranian plateau.
2457
Approximate Nonlinear Seismic Evaluation of Frame Buildings by Static and Dynamic Analysis Methods and Comparison with the Exact Solutions
^{
}
^{
}Civil Eng. Department, University of Kashan
1
11
2017
17
4
101
112
14
03
2016
08
06
2016
Performance-based earthquake engineering requires accurate estimation of the seismic demand and capacity of structures. In recent years, various kinds of nonlinear static and dynamic analyses have been developed for the seismic evaluation of structures. Nonlinear dynamic time history analysis method is not only very time consuming, but also needs a proper skill and proficiency in order to interpret its results. For the performance evaluation of the structures, the speed and also the precision of conducting different analyses are very significant criteria. This issue has led to the creation of various new methods based on the principles of nonlinear and incremental static and dynamic analysis. One of the methods that has been proposed to tackle this task is incremental dynamic analysis (IDA). This procedure requires non-linear time history analyses (NL-THA) of the structure for an ensemble of ground motions, each scaled to many intensity levels, selected to cover a wide range of structural response; all the way from elastic behaviour to global instability. From the results of such computation, it is possible to determine structural capacities (or ground motion intensities) corresponding to various limit states; immediate occupancy (IO), life safety (LS), or collapse prevention (CP). Another approach to reduce the computational effort required for IDA is to estimate seismic demands for the practical structures by modal pushover analysis (MPA), an approximate procedure, instead of non-linear RHA. Thus, each of the many non-linear RHA required in IDA is replaced by a MPA. In addition, a more recent proposed method logically combines two different techniques, IDA and MPA is employed, presented by modal incremental dynamic analysis (MIDA). Using MIDA procedure, simple approximate curves that present a realistic linear and non-linear seismic behavior of the structure headed for the calculation of the damage measure (DM) due to the applied scaled level of earthquakes can easily be extracted. In this study, the capability, limitation and precision of MPA in comparison with NL-THA and also MIDA in comparison with IDA method are evaluated. For this purpose, two steel building models of 5 and 15-story with special moment resisting frame (MRF) in X direction and simple frame with X-bracing in Y direction has been designed. Furthermore, seven far field earthquake records are used for nonlinear analyses. In the current article, acceleration spectral intensity of the first mode of vibration with 5% damping, i.e. Sa(T1, %5) factor, are used as of intensity measure (IM). The story deflection and story drift are chosen as of the most important DM parameters to estimate the seismic vulnerability of structures in design practice. Comparison of the numerical results reveals that the MPA method has good accuracy in building seismic demands evaluation for 5-story frames (MRFs and braced frames) and 15-story MRF. However, no exact response is obtained for 15-story braced frame, considering the first three vibration modes of the structure. It is also shown that the results from MIDA simple method compares favorably to the IDA method. Thus, MIDA can be served by design engineers for seismic analysis in order to evaluate structural performance due to its relative simplicity and minimal computational effort.
8220
Predicting Maximum Horizontal Displacement of the Wall and the Maximum Tensile Force in Reinforcements for Geogrid Reinforced Soil Wall under Overturning Mechanism
Asakereh
Adel
Ahang
Masoud
1
11
2017
17
4
113
126
28
01
2016
13
03
2017
Soil reinforcement is a new technique to improve the mechanical properties of soil. Geosynthetic reinforced soil walls are usually designed based on limit equilibrium methods, ignoring the effects of foundation, reinforcement stiffness, facing, and other parameters. However, design procedures do not consider the deformation of the walls explicitly. Recently, numerical methods are used for the design and analysis of reinforced soil walls, and the programs written on this basis are used. Usually in limit methods, design of reinforced soil structures control for external stability or total stability or internal stability. After design of reinforcement elements, the overall stability of wall, i.e. overturning, sliding, and bearing capacity should be controlled. But in numerical methods, stress distribution and deformation can be achieved in reinforced soil walls. In this study, the finite difference method is used to perform analysis. According to the deformation manner of the wall and boundary conditions imposed on the structure in the reference study, so that the wall is joint at the heel (wall cannot slide) and taken into account its foundation in the rigid (insufficient bearing capacity does not happen), it can be said that obtained results of this modeling are used only for the overturning mode. In this numerical study, the effect of various system parameters on the performance of the wall, especially the maximum tensile force in the reinforcements and the horizontal displacement of the wall, is merely investigated for the external overturning instability mode. The important parameters of reinforced soil wall structure were studied including the reinforcement stiffness (J), the backfill soil friction angle (∅), the elasticity modulus of backfill soil (Es), the facing wall rigidity (EI), the reinforcement length (L), and wall height (H). Among investigated parameters, the most important parameters effective on the amount of deformation of the wall and maximum tensile force in reinforcements are reinforcement stiffness (J) and backfill soil friction angle (∅) regarding the material properties, respectively; other parameters do not have significant effect on the cases studied. The effect of stiffness on the maximum tensile force in the reinforcements is minimal and negligible. In the wall geometry which includes the reinforcement length (L) and wall height (H), the reinforcement length was the most effective and the most important factor to design reinforced soil walls. Based on the numerical results, the best range of L/H ratio to design reinforced soil walls is between 0.5 and 0.8 since for L/H ratio equal to 0.8 and more, the horizontal displacement of the wall is considered almost the same. Due to the importance of the project and the cost, it is suggested to consider L/H equal to 0.7. In this numerical study, curves are provided for predicting the maximum horizontal displacement of the wall and the maximum tensile force in the reinforcements. The numerical analyses show that there is a particular pattern between the maximum horizontal displacements of the walls and maximum tensile forces in the reinforcements. The results are presented in the form of graphs; using these graphs, the maximum horizontal displacement of the facing wall and the maximum tensile force in the reinforcement for walls with different heights can be predicted.
1179
Two-Phase Numerical Simulation of Flow Pattern in Three-sided Spillways, Considering Scale Effect
Farhoudi
Mahdiar
Salehi Neyshabouri
Seyed Ali Akbar
Safarzade
Akbar
1
11
2017
17
4
127
140
17
11
2013
23
11
2016
Regarding significant reduction in costs and operating problems, three-sided spillway in comparison with other spillways, attracts crucial attention of designers of these structures. Three-side spillways are a type of outlet works at dams that despite their hydraulic limitations and construction problems, under specific topographical conditions selected as one of the best options in storage dams. This spillway is applicable in areas concerned with limitation of available space for overall width of spillway and where excess volume for flood overload. Also when modification and capacity increase in existing spillways are necessary, this structure is recommended. On the other hand, inappropriate conditions in water channel, such as flow turbulence and impact of water on bed and lateral walls of channel result in poor performance of these structures. In the present study, firstly 3D flow pattern of a U-shaped spillway, the channel and the end sill have been evaluated using computational fluid dynamics software (FLOW-3D). RNG k-ɛ model was implemented for simulation of turbulence. Comparison of numerical results with experimental data showed that this model has a good ability to predict three dimensional flow patterns over this kind of spillways. Hydraulic performance with targeting to reduce pressure fluctuations in side channel is an important issue in this type of spillways design. Regarding important effect of air entrance in hydraulic structures, two-phase analysis has been performed in this study. Numerical results show that two-phase analyses have a better performance compared to one-phase simulations. Studies show that by changing the inlet flow rate, the maximum error in the estimation of water level and pressure profiles at bottom of the channel occurred at low discharges. Also the maximum numerical error in computing observed in the area where bulge is. Then, taking into account the actual dimensions of the model, scale effects have been studied on physical model scales. The findings have some major implications of civil, environmental and sanitary engineering, because most hydraulic structures, storm water systems and water treatment facilities operate with Reynolds numbers within ranging from 106 to over 108. In a physical model, the flow conditions are said to be similar to those in the prototype flow conditions if the model displays similarity of form, similarity of motion and similarity of forces. The present results demonstrated quantitatively that the dynamic similarity of two-phase flows cannot be achieved with a Froude similarity unless working at full-scale. So that physical models are not good at predicting air entrainment and the amount of air entering is dependent on Reynolds number and does not follow Froude similarity. The largest amount of free surface profile variation due to aforementioned reason has been observed in air entrance and bulge formation zones. This variation decreases as flow moves toward downstream or as discharge value increases.
1002
Suitable Remote Range Strong Motion Accelerograms for three-dimensional non-linear analysis for Tehran,Iran
Ghassemieh
Mehdi
^{
}
hasani sokhtesarae
mohamad
bastami
morteza
^{
}Professor of Structural Engineering
School of Civil Engineering
University of Tehran
1
11
2017
17
4
141
152
29
01
2016
13
03
2017
In regions that are susceptible to earthquake occurrence, designing large and engineering developed structures such as tall buildings, dams and bridges most often requires quantitative dynamic analysis. Engineers discuss important questions on possible magnitude of earthquake in the zones under construction and require knowledge on the movements or the spectrums enforces and/or defining parameters. Time history analysis is the most natural analytical method compatible with the physical behaviors in the course of earthquake in a way that structures are performed by including the effects of earth acceleration as a function of time being applied in the structural base. The accelerograms which are used in analyzing the chronological history in determining the impacts of earth movement must reveal the actual movements of earth in the construction site of the structure during earthquake; As a result, selecting accelerogram is very important in analyzing the chronology. Unfortunately, the point that suitable records must be selected with respect to the conditions that govern seismic source, the geological characteristics, tectonic distance from fault and the largeness of the zone is usually neglected. Our country is located in one of the most active seismic regions in the world. According to the scientific information and documents, Iran is one of the riskiest regions of the world and is exposed to serious damage from earthquake. In the recent years, there has been an earthquake with large physical and financial casualties in one of the regions of the country once every five years in average. Presently, Iran is on top of the list of countries where earthquake is associated with life casualties. It is very difficult to fully prevent damages caused by high magnitude earthquakes. This is especially important in the city of Tehran with the very large population that lives in it, and is encircled by several active faults. The main goal of this research is to prepare a suitable list of remote range strong motion accelerograms to be used in nonlinear analysis in Tehran. The main focus of this research is to study all parameters that are effective in selecting suitable strong motion accelerogram in Tehran and for this purpose, 1000 strong motion accelerograms from earthquakes that occurred in Iran between 1978 through 2007 were studied and the entire parameters effective in selecting suitable strong motion accelerograms for the city of Tehran including distance, magnitude, frequency contents, earthquake mechanism, soil and specifications of earth strata were reviewed. Ultimately, a suitable list of strong motion accelerograms is presented to be used in nonlinear three-dimensional analysis. To achieve this goal, the geological and geotechnique features of the region were studied. In addition, the mechanism of active faults in the region were studied as well and by considering the parameters of magnitude, the focal depth, the distance of registry stations to the earthquake place, the geology studies of the records registry stations, mechanism and the frequency contents of a series of the accelerograms are suggested to reveal the actual movement of earth in Tehran as much as possible; if modeling and chronological history analysis are bi-dimensional, it will be possible to use 28 categories alongside and orthogonal with the faults in the suggested list. It should be noted that to analyze the chronology, only those accelerograms were used which could be scaled with the spectrum of the standard plan of the region and prove compatible with the frequency period of the structure. Minimum moment magnitude in the mentioned list is equal to 5.6 and maximum moment magnitude is 7.4. The mean magnitude in this list is 6.45. The mean maximum earth acceleration for the list was equal to 0.191g. The dominant mean period in the list is 0.64 seconds. The dominant frequency in this collection of accelerogram includes a large frequency range; therefore, suitable stimulation could be anticipated from this list for various structures.
10935
Multi-objective Optimization Design of Tuned Mass Damper System Subjected to Critical Excitation
Kamgar
Reza
^{
}
Khatibinia
Mohsen
^{
}
^{
}Room 57, Department of Civil Engineering, Shahrekord University, Shahrekord, Iran
^{
}Department of Civil Engineering, University of Birjand, Birjand, Iran
1
11
2017
17
4
153
164
11
07
2016
21
05
2017
Controlling the maximum acceleration and displacement of the roof within the acceptable range is important and essential. In order to control structures, a number of control systems have been introduced that are categorized into four system including active, passive, semi active and hybrid system. One of the most used passive systems is the tuned mass damper system which is placed on the roof of structure for controlling the behavior of building. In addition, the optimization of structures subjected to the earthquake load is an essential task for the safe and economic design of structures. It must be noted that earthquakes are random phenomena and the precise prediction of forthcoming events is a hard task. However, in seismic design codes, the static and modal seismic methods for the seismic design of structures are adopted by the design spectrum produced based on previous earthquakes. Hence, in order to overcome this problem, the concept of critical excitation as a robust method has been presented and developed to generate worst–case critical excitations. The critical excitation method have been presented in the framework of an optimization problem to maximize the structural responses subjected to some constraints. In this paper, an effective method is presented to determine the optimum values for the parameters of the tuned mass damper system subjected to critical earthquakes. The critical earthquakes are unique and are computed based on the dynamical properties of the structure. For this purpose, based on the obtained information from the past occurred earthquakes the critical earthquakes of a ten story shear building are established subjected to the constraints. The constraint scenarios include some computable properties of the ground motion such as energy, peak ground acceleration an upper bound Fourier amplitude spectrum. In fact, in this stage, to compute the critical earthquakes an inverse nonlinear constraint optimization problem must be solved for each time step. Then, the building equipped by a tuned mass damper system at roof of the structure (controlled building) is considered and the optimal design of tuned mass damper subjected to critical earthquakes are implemented. The maximum absolute displacement and acceleration of the roof are considered as the objective functions. Finally, among the computed earthquakes, one of them which produces the maximum objective functions is selected as the critical earthquake. In the optimization procedure, the mass, damping and stiffness of the tuned mass damper (TMD) system are adopted as the design variables. Multi-objective particle swarm optimization method is used to optimize the parameters of the tuned mass damper system. Since, the optimal design of the tuned mass damper system is presented as a multi-objective optimization problem, a set of optimal solutions are obtained. Numerical examples demonstrate the ability and efficiency of the proposed method in the optimal design of the tuned mass damper system subjected to the critical earthquakes. In addition, the numerical results show that the maximum absolute values of the displacement and acceleration of the roof efficiently decreases when the building is controlled by the optimum tuned mass damper system. Also, the results show that the severe earthquake needs a bigger mass for tuned mass damper in order to control the displacement and acceleration of the roof.
1194
Application of Edge Based Smoothed Finite Element Method in Solution of Seepage and Foundation Settlement Problems
Karimian
Erfan
^{
}
o
m
^{
}
^{
}Ph.D. Candidate in Geotechnical Eng., Faculty of Civil and Environmental Eng., Tarbiat Modares University
^{
}1
1
11
2017
17
4
165
174
13
02
2017
21
05
2017
Smoothed finite element method (SFEM) was introduced by application of the strain smoothing technic in the conventional finite element method (FEM). The strain smoothing technic was previously used in mesh-free methods to overcome the numerical instabilities due to nodal integration. SFEM has three main types: 1-Cell-based SFEM (CSFEM), 2-Node-based SFEM (NSFEM) and 3-Edge-based SFEM (ESFEM). In these methods, problem domain is first discretized into a mesh of elements, similar to the FEM, and then based on these elements, domains are created to perform the strain smoothing operation on them. These domains are called “Smoothing Domains”. The difference between SFEM types is in the method of creating these smoothing domains. Different smoothing domains, can give results with different qualities. Among them, the edge-based method can give results that are ultra-accurate and super-convergent. Due to their interesting features, SFEMs have been used to solve different problems. Problems such as, mechanics of solids and piezoelectrics, fracture mechanics and crack propagation, heat transfer, structural acoustics, nonlinear and contact problems, adaptive analysis, phase change problem and many more. In this paper, first idea and formulation of SFEM is reviewed, with special consideration on the edge-based method. Detailed instructions are given for creation of edge-based smoothing domains, and strain and stiffness matrices for this method are derived. After that, the algorithm for creation of a SFEM code is introduced. Based on these formulations and algorithm, an edge-based smoothed finite element code is created, that is used for analysis of some numerical examples. Two problems, based on two different practical geotechnical engineering applications, are solved using the ESFEM and also FEM with 3-node and 6-node triangular elements. Using same mesh for all three methods, makes comparison possible, and performance of the ESFEM will be investigated. First problem, is a steady state seepage problem, where seepage below a sheet pile barrier is modeled, with the assumption of plane strain condition. Since there is no analytical solution for this problem, FEM results using 6-node triangular elements are considered as the more accurate results for comparison. Investigating the results reveals that implementation of the strain smoothing technic in FEM using 3-node triangular elements, can make the results closer to those of the FEM using 6-node triangular elements, while the degrees of freedom remain constant. Edge-based smoothed finite element method can give results for steady state seepage problem, that have errors less than half of the conventional FEM results errors, with the same mesh and number of degrees of freedom. The other problem, is calculating the elastic settlement of a circular foundation, to investigate the performance of the ESFEM in axisymmetric problems, compared with the FEM. Again, the problem is solved using three methods: ESFEM, FEM with 3-node triangular elements, and FEM with 6-node triangular element, with the latter as the most accurate. Surface deformation of the problem domain, after imposition of the foundation load is studied. It is seen that ESFEM results match the FEM results. A closer look reveals that the ESFEM results for settlement of the foundation, is closer to the FEM results using 6-node triangular elements, than the FEM using 3-node elements and are more accurate.
7261
Assessing absolute maximum dynamic response of a single span beam acted upon by an accelerated moving object
m.nikbin
iman
^{
}
Javadi
Shima
^{
}
^{
}Assistant Professor, Islamic Azad University, Rasht Branch.
^{
}MSc Student, Civil Eng. Dept., Noor Branch, Islamic Azad University, Noor, Iran.
1
11
2017
17
4
175
186
02
02
2016
07
01
2017
In structural dynamics, loads having varying positions has been broadly studied. Such loads are so called moving loads which appears in various applications in industry. High speed machining systems, overhead cranes, cable ways, pavements, computer disc memories and robot arms are a few examples of moving load dynamic problems. Vibration of bridge structures subject to moving vehicles is often referred to as an application of moving load problems. A great number of researchers proposed numerical and analytical methods to deal with the vibration of solids and structures under travelling loads. A famous classic approach in the simulation of moving loads is the moving force. In moving force model, a constant traveling force is assumed to act upon the base structure. However, this assumption yields to reasonable structural analysis if the mass of the moving object is negligible. Nowadays, with ongoing advances of transportation technology, the mass, speed and acceleration of moving vehicles are notably increased. In this regard, during the last few decades, many researchers showed that the moving force is no longer valid for large moving masses. Therefore, the moving mass simulation has been proved to be closer to the physical model of vehicle bridge interaction. As a common practice, bridges carrying moving vehicles has been assumed as vibrating beams excited by point moving masses. It has been very customary to consider the midspan or center point of the base beam as the reference point in order to assess the maximum dynamic response of the structure under moving mass; therefore, most of the existing computed design envelopes are related to the values occurring at the midpoint of the structure. However, the location of the maximum values occurrence is not necessarily at midspan. To shed light on this issue, in this research an analytical-numerical method is established to capture dynamic response of an Euler-Bernoulli beam traversed by a moving mass. Most of the available literature on moving load problem is concerned with the travelling loads having constant speeds. To remove this restrictive presumption, in this paper, the considered moving mass is assumed to move at non-zero constant acceleration. The beam is considered to be undamped and initially at rest. The moving mass is assumed to maintain full contact condition with the base beam while sliding on it. By exploiting a series of continuous shape functions having time varying amplitude factors, a norm space is provided by which the beam spatial domain is discretized. The problem is then transformed into time domain for which a time integration method is utilized. Absolute maximum dynamic response of the supporting beam under the passage of accelerated moving mass is extensively sought over the beam length. In this manner, whole beam length is being monitored for the maximum values at each time step of time integration procedure. The beam absolute maximum dynamic response is comprehensively computed considering different mass ratios and extensive range of linearly time varying velocities. Parametric studies are carried out on the absolute maximum values of dynamic flexural moments and deflections and compared to those captured at midspan. Finally, it highlighted that the midspan of the beam cannot be a valid reference to obtain the true maximum deflections and flexural moments of the base beam.
9247
The Effect of nano-silica and polypropylene fibers on mechanical properties and durability of normal and light weight concretes
Mohammadi
Yaghoub
^{
}
Seifollahi
Farid
^{
}
^{
}Associate Prof. of Civil Engineering, University of Mohaghegh Ardabili
^{
}Ph.D student of Civil Engineering Department, University of Mohaghegh Ardabili
1
11
2017
17
4
187
198
26
04
2016
07
01
2017
Over the course of time into the 21th century, concrete has been known as one of the most high usage materials in the construction industry. As a consequence, trying to produce light concrete is an active and developing area within the new field of construction science. This technology consists of lowering the whole weight of structure by using new bulding techniques, new materials and optimizing ways of manufacture. Lowering the weight not only economizes on the expenses, time and energy but also decreases the damages of earthquakes. Furthermore, it keeps the constructions safe and minimizes the damages resulting from the overweight of the structure during different waves of shocks and aftershocks. In spite of considerable amount of compressive strength, low tensility strength and relatively high fragility of the concrete, there are limitations in using it in some parts which are partially or fully under forces of tention in different parts of structures. This fundamental defect of concrete in practice can be eliminated by reinforcing it through using steel tabs in the direction of traction forces. Having in mind that the armature just constitues a small part of the whole cross section of the structure, it will not be correct to conceive of the cross section of concrete as an isotropic and homogeneous surface. In recent decades, in order to come up with the isotopic condition and decrease the fragility, weakness and retrogression of concrete new techniques and trends of applying slender fibers running through the internal section of the bulk of concrete has become prevalent and common practice. The concrete containing nano materials compared with the normal concrete affected by nono chemical materials with cement particles and clcium hydroxide crystals which exist in cement, has a severe effect on the performance of concrete composites while such mixtures come into each others’ contact. In this study,we examined the effect of Nano-silica and polypropylene fibres on mechanical properties and durability of normal and light weight concretes. In the design of light weight concrete, lecalight weight aggregates were used. More than 384 cubic and cylindrical samples were made based on ASTM standards and compressive strenght, indirect tensile strength, ultrasonic and electrical resistance experiments were done. The results of the experiments showed considerable increase in mechanical characteristics and durability of normal and light weight concretes. Nano-silica contributes to the proper spread of the fibers. Compressive strength, indirect tensile strength, and the dynamic elasticity module of the ordinary concrete were higher than those of the light weight concrete, while the electrical resistance of the light weight concrete was higher compared to the corresponding samples. Compressive strength and indirect tensile strength increased to 71 and 55 percent in normal concrete and to 43 and 47 percent in light weight concrete respectively. Considerable increase in electrical resistance indicates high durability of these kinds of concretes. Of course, economic considerations of using nano-silica and polypropylene fibers require special attention. Finally, the right amount of utilization of the polypropylene fibers and nano silica were determined in order to achieve normal concrete and light weight concrete with optimal properties.
1452
Effects of Soil Washing by Fe3O4 Nanoparticles in the Batch and Continouse Flow Configurations on the Physicochemical Characteristics of Soil and Nanofluid
dahrazma
behnaz
^{
}
^{
}Associate professor/Shahrood University o
1
11
2017
17
4
199
212
04
06
2016
13
03
2017
Remediation of contaminated soil by heavy metals is an important environmental issue which attracted many attentions and was evaluated by several methods. It is highly desirable to apply suitable remedial methods to reduce the risk of heavy metal contamination in soils. Development of new low-cost, efficient and environmental friendly remediation technologies is the main goal of the recent research activities in environmental science and technology. Using nanotechnology in removal of environmental pollutions is of modern and applicable methods. One of the early generations of nanoscale technologies in the field of environment is the use of iron nanoparticles as a ground for sorption of pollutants. These nanoparticles are nontoxic, inexpensive, and very strong absorbents.The aim of this study was to assess the effects of cadmium removal by soil washing with iron (III) oxide nano particles (Fe3O4), stabilized with Polyacrylic Acid (PAA) as nanofluid, on physicochemical characteristics of nanofluid and soil in two defined systems including batch and continuous flow configurations. For this purpose, after complete removal of Cd from the soil in both systems under the optimized conditions, the effects of removal on the physicochemical characteristics of soil and nanofluid including pH, electrical conductivity, and total dissolved solid were assessed. The results of XRD and SEM of soil samples and also zeta potential and size distribution of nanofluid, before and after the removal were investigated. To ensure the absence of other pollutants and elimination of any interaction between soil pollutants, the soil was prepared with clean standard materials and afterwards it was contaminated with cadmium solution prepared by cadmium nitrate. The optimum conditions for cadmium removal in the batch system was as follows: nanofluid concentration=500 ppm, pH=6.5, contact time=24 hr and the ratio of contaminated soil mass (gr) to nanofluid volume (mL) =1:150 . completely Cd removal in continouse flow configuration obtained in the following conditions: nanofluid concentration=500 ppm, pH=6.5, contact time=24 hr, and the flow rate =0.5 mL/min. Cadmium content in the nanofluid after remediation was determined with UV spectrophotometer by using APDC complexes in Tween 80 media. As per the results of this study, pH of the soil samples in the both batch and continuous flow configuration increased from 7.8 to 8.55 and 8.35 respectively. pH of nanofluid increased from 6.5 to 6.8 in the continuous flow configuration and 7.59 in the batch system. EC and TDS of the nanofluid decreased from 1.66 mS/cm and 1110 mg/L to 1.049 mS/cm and 699 mg/L in the continuous flow configuration and these parameters also reached respectively to 0.952 mS/cm and 635 mg/L in the batch system. Soil washing using Fe3O4 nanoparticle did not changed remarkably EC and TDS of the contaminated soil. Nanoparticles size with highest frequency in nanofluid before removal was 205 nmand after Cd removal reached to 23 nm and 29 nm in the continuous flow configuration and batch system respectively, which was an indication of the sorption of nanoparticles with grater size to the soil during the soil washing process. Zeta potential values of influent and effluent of nanofluid from continuous flow configuration and batch system were -61.5, -51.3, and -37.4 mV respectively. The structural changes of soil samples after removal in the both systems were assessed by XRD and SEM tests which confiremed the sorption of nanoparticles through the soil washing.
5782
Assessment of concrete core strength with and without steel bars
MOMENI
KOMEIL
^{
}
Madandoust
Rahmat
^{
}
Ranjbar
Malek Mohammad
^{
}
^{
}Ph.D. student
Faculty of Engineering
University of Guilan,
Rasht- Iran
^{
}Associate professor
Faculty of Engineering
University of Guilan,
Rasht- Iran
^{
}Associate professor
Faculty of Engineering
University of Guilan,
Rasht- Iran
1
11
2017
17
4
213
228
16
05
2017
23
10
2017
The concrete compressive strength is a suitable index to ensure the quality of concrete while the construction is underway. The core samples, which represent the potential strength of concrete, are prepared, cured, and tested according to the relevant standard codes and specifications. On the other hand, determination of the actual strength of concrete in a structure is not easy because it depends on the history of the curing procedure, the adequacy of concrete compaction, and the casting method. Therefore, the question that has always attracted the attention of designers is if the standard test specimens can represent the in-situ strength of concrete. Arriving at the answer to this question becomes even more important when the strengths of standard test specimens are lower than the specified strength. In this case, either the strength of concrete in the structure is lower than the design value or the specimens do not actually represent the concrete strength in the structure. In such cases, the problem would be addressed by drilling and testing some core specimens from the suspected structural member. In addition, there may be no standard specimens at a late age, and it may be necessary to determine the current strength of the structure.Concrete core test is always regarded as an important issue in the area of concrete industry to evaluate the in-situ concrete strength, and sometimes it becomes the unique tool for safety assessment of existing concrete structures. Core test is, therefore, introduced in most building codes. The presence of rebar in the cores affects the results of testing; accordingly, some codes specify that no bars are allowed to be present in the cores, while others account for the bars by introducing a correction factor. In the present experimental research, the parameters that exert significant effects on the strength of the cores containing rebar are examined. To that end, 112 plain and reinforced concrete beams with the bars of 10- and 16-mm diameter (with different arrangements) and water-to-cement ratios of 0.4 and 0.55 have been created. The beams have been kept and cured under air-dried conditions. In order to perform the compression tests, 988 concrete cores of 7.5- and 10-cm diameters with aspect ratios of 1 and 2 have been drilled at 14, 28, and 56 days of age. In the majority of cases, as the water-to-cement content increases from 0.4 to 0.55, there is a larger amount of strength loss in the cores containing the rebar as compared to those without any rebar. The strength of the cores declines by increasing the concrete cover for the bars. For the cores containing a single bar, the reduction which is resulted in the strength in comparison to that of the plain concrete cores is more dramatic in the cores having a bar of larger diameter. On the other hand, the amount of strength drop increases by increasing the number of bars. The largest drop in the strength values, amounting to 23 percent of the plain-concrete core strength, is observed in the concrete cores having two 16-mm bars. Furthermore, the cores containing eccentric rebar show a greater reduction in comparison to the cores with no eccentric rebar.
11876
Modification and improvement of equations to estimate the scour hole formation due to 2D wall jets using PSO algorithm
1
11
2017
17
4
229
239
16
11
2014
10
03
2016
Abstract: The interaction between the jets and the loose beds may cause scour hole formation. The scour hole developments may cause structural instability of the structures and increases the damage probability of the structures. Hence the scour hole dimensions estimation is an important subject for engineers. Many investigators worked on the effective parameters on scour hole dimensions due to plane wall jets. They have presented many different equations to estimate the scour hole dimensions. The equations may be used on a specific range of the effective parameters. Using the width range of the available experimental data the appropriate equations are developed. Using the dimensional analysis the non dimensional parameters such as Froude densimetric, Reynolds number, non-dimensional form of the sediment size, standard deviation of the sediment mixture, tailwater depth, non dimensional form of the channel width and non dimensional form of the time were obtained. Authors tried to use an optimization procedure to develop the equations. As, generally, solving the optimization models is impossible using the analytical procedure, recently new metaheuristic methods are used to find the optimum results. So, in this research PSO algorithm was used to find of the unknown exponents and coefficients leading to the best result of proposed equations. Two different algorithms local PSO (LPSO) and Global PSO (GPSO) were used to find the unknown coefficients and exponents. Sensitivity analysis of the algorithms showed that the algorithms proposed different coefficients and exponents for different values population. Among the proposed coefficients and exponents one set of them are the best with minimum error. Comparsion between the experimental data and previouse prposed equations confirms strong scatter. Hence, in this type of problem using the metaheuristic algorithm and sensitivity analysis are recommended. The analysis of the results showed that the scour hole depth due to plane wall jets, is increasing funcions of densimetric Froude number, tailwater depth, time, and non dimensional form of the channel width. However, this parameter is a decreasing function of sediment gradation and non dimensional form of the sediment size. Similar trends were also observed for maximum ridge height formed at the downstream of the scour hole. The distance of the maximum height of the ridge is also an increasing function of densimetric Froude number, time, non dimensional form of the channel width, and Reynolds number of the jet. However this parameter is an decreasing function of standard deviation of the sediment mixture and tailawter depth. The sensitivity analysis of the effective parameters on scour hole dimension to find the more effective parameters were conducted. The latter analysis showed that Reynolds number, non dimensional form of the sediment size and non dimensional form of time has secondary effect on scour hole dimensions due to plane wall jets. However, the jet Reynolds number has the secondary effect on temporal variations of scour hole dimensions. The latter parameters were omitted from the effective parameters on scour hole dimensions without sensitive decreasing of equation accuracy.
11944
Effects of URM infill panels on the progressive collapse of steel structures with moment resistant frames
mirtaheri
maseoud
1
11
2017
17
4
241
250
04
05
2016
13
03
2017
When one or more vertical elements of a structure fail due to defects in construction stages or over loading or etc., load distribution path of the structure changes and local failure arises in the damaged area. This kind of damage is not considered by engineers and can cause local collapse. The local collapse can spread vertically or horizontally to the other areas of the building if no alternate path exists to redistribute the loads. Therefore, limiting the local collapse in the damaged area is major idea to mitigate progressive collapse in the buildings. Nowadays, analyzing the structures which are designed based on the current standards, against progressive collapse and offering ways to improve and strengthen them is leading to part of the designing stages of the special buildings. Thus, some standards and codes in this field are being produced or updated. The most common method to analyze the structure against progressive collapse is the alternate path method. In this direct design method, the critical columns be removed immediately and stability of the remaining structure is investigated. But there is no references talk about the effect of lateral resistant of the infill panels. This is one of the simplifier assumptions which are used in numerical studies of progressive collapse phenomenon in structures indicate inconsistency between the numerical and experimental full-scale results. Unlike numerical studies, experimental studies showed that the structure remain stable even if more than one column removed. As a case study, in this research, a steel structure with 8 stories with moment resistant frame is analyzes and designed considering effect of unreinforced masonry infill panels (URM). URM infill panels in full contact with the frame elements on all four sides shall be considered as primary elements of a lateral force-resisting system. Recognizing this behavior, the stiffness contribution of the infill is represented with an equivalent compression strut connecting windward upper and leeward lower corners of the infilled frames. So, analytical macro-model based on the equivalent strut approach is used to simulate the effective infill panels. Potential of progressive collapse of the one of the peripheral frames is evaluated with the Opensees program based on the nonlinear dynamic analysis. Researchers found that linear static analysis might result in non-conservative results since it cannot reflect the dynamic effect caused by sudden removal of columns. So, time-history analysis should be applied to seek dynamical response of the structure. Results indicate that considering effect of the infill panels increase axial force of the columns and decrease bending moment of the beams and nodes displacements. So results are closer to the experimental studies and prove stability of the structure after column removal and increase resistant of the building against progressive collapse. As it distinct, modeling the infill panels in the analysis is complex and time-consuming, so in this research, the coefficients are proposed to apply to the load combinations instead of modeling the infill panels in order to closer the results together. The proposed coefficients are larger than one for columns forces and smaller than one for the beams forces.
4350
Effect of Rectangular Strip Roughness on Hydraulic Jump Characteristic in Diverging Rectangular Sections With FLOW-3D Software
1
11
2017
17
4
251
262
19
05
2016
07
01
2017
The hydraulic jump phenomenon is one of the most common phenomena in open channels. Hydraulic jump is a transition state from supercritical to subcritical flow regime, which normally occurs in conjunction with hydraulic structures, such as spillways, weirs, and sluice gates. A hydraulic jump phenomenon serves a variety of purposes, for instance, to dissipate the energy of flow to prevent bed erosion and aerate water or to facilitate the mixing process of chemicals used for the purification of water. Stilling basins are one of the most common structures for energy dissipation of flow with high velocities.The stilling basin has been accepted to be the most powerful hydraulic structure for the dissipation of the flow energy. The size and geometry of the stilling basin affect the formation of flow patterns, which can be influential for hydraulic performance of the whole system. The depth of water after the jump is related to the energy content of the flow, and any reduction in energy content with increased energy dissipation in the jump will reduce the required depth of flow after the jump. Sometimes these basins are supplied with appurtenances that increase the overall roughness of the basins. This in turn increases the energy dissipation, decreases the sequent depth, and requires a shorter basin for the full development of the hydraulic jump. There are plenty of research studies in the literature regarding the classical hydraulic jump in the usual rectangular straight stilling basin, but less for the hydraulic jump in other cross section shape of basins. Expanding gradually basin with the rectangular cross section acts as two separate hydraulic structures including stilling basin and transition. In this type of structures not only the transition can be eliminated, but the length of the basin will be also much smaller than what is designed for the usual straight basins. Researchers’ studies show that divergence in stilling basins reduce the sequent depth and the length of the jump while increasing the energy losses compared to the classic jumps. In this research, numerical simulation of the hydraulic jump was performed in divergence rectangular sections, and compared with the results of the laboratory, making use of the FLOW-3D software and the standard k-ԑ and RNG k-ԑ turbulence models. The effects of rectangular Strip roughness on the specification of hydraulic jump were evaluated. The results showed that the standard k-ԑ turbulence model was able to predict the water level profiles in the hydraulic jump in divergence rectangular sections with appropriate and acceptable coincidence. Results showed that the mean relative error of water surface obtained from numerical model and measured values is about 3.55 percent. Also the numerical model showed the vortices that were accrued because of diverging walls as well as experiment investigations. The results show that creating the rectangular Strip roughness, reduces the sequent depth as much as 13.65 % and the length of the hydraulic jump as much as 11.39%, while increasing the energy loss as much as 9.12%, compared to Smooth divergent stilling basin. The results also show that creating the rectangular Strip roughness, reduces the sequent depth as much as 24.63 % and the length of the hydraulic jump as much as 17.64%, while increasing the energy loss as much as 14.46%, compared to the classic hydraulic jumps. Consequently, the use of roughness in stilling basins would be economical.
9048
Quantitative solution of 2-D inverse elastodynamics problems using hybrid FDM-FEM and PSO
Nikpoo
Bahador
1
11
2017
17
4
263
275
27
02
2016
07
01
2017
It is clear that, having a exact knowledge about the geometry and properties of the materials and the domain that engineering problems are involved are very important specially in structural health monitoring, geotechnical earthquake engineering and other related field in civil engineering; in many cases, it might be useful if a suitable inverse solution is applied in order to detect the characteristics of the problems domain. The main purpose of this paper is to development of the hybrid finite element- finite difference method for solving inverse elastodynamic and elastostatic scattering problems and combining that with particle swarm optimization algorithm as a quantitative approach fo solving these types of the problems. This hybrid method has been used in order to preparing the forward solution of the problems and by defining a suitable cost function and minimizing that using PSO algorithm, various kind of inverse problems are solved. In general, an inverse scattering problem can be solved using qualitative or quantitative approaches. In some branches of quantitative techniques, usually, a forward solution is required and then using heuristic algorithm, the goal will be achieved. In this study, a hybrid FE-FD method is used as forward solver (which has the flexibility of finite element method and low computational cost of finite difference method); so, the domain inside and outside of the inclusion will be dicretized using finite difference method and the boundaries near the inclusion will be discretized by finite element method, and in this condition, the solution will be more flexible near the scatterer. In each solution step, first the finite element will be solved and the results will be transferred to the finite difference code and when the result is prepared in it, again, the response of the problem will go to finite element region. In this research, at first, a geometry and related location will be assumes, randomly and then regarding that, using an OpenSees program code, the boundaries of the inclusion will be discretized and using the MATLAB program the related to finite difference region is discretized, then the results from these two codes will go and back until the response goes converge. Then, the PSO code which is developed in MATLAB will qualify the results and evaluate the cost function (e.g., the cost function is defined by minimizing the the error between the displacement that is from the main model and the predicted model), and if the cost function is large, the PSO algorithm will propose the new location and/or geometry of the inclusion and again, the loop will be repeated until the cost function be near the zero and the solution procedure will be terminated. In order to evaluate, the efficiency and accuracy of the proposed approach, several problems are solved, where this algorithm could find the location and geometry of the inclusions (e.g., regular and irregular inclusion), the non-homogeneity of the inclusion and also detecting the soil layers by both static and dynamic loading.; the results show a very good accuracy as well as efficiency of the proposed approach for solving inverse problems in bounded and smi-infinite domains.
6911
Determination of clayey soil compression index (Cc) using adaptive neuro-fuzzy inference system
Hashemi Jokar
Mehdi
^{
}
mirasi
sohrab
Rahnema
Hossein
^{
}phd. candidate
1
11
2017
17
4
277
287
16
11
2015
26
04
2017
Construction of buildings and structures causes to compact of soil particles and soil settlement. Hence, determination and prediction of soil settlement in the stability of structures, resulting from the applied loads, is necessary before construction. As a result of consolidation test that is relatively time-consuming and costly testing, compression index (Cc) is used to get the amount of settlement. In fact, soil settlement can cause extensive damage to a project in some cases. In order To prevent these damages, correct prediction can be useful for safe designing of structures. Cc may be as a function of various parameters such as initial void ratio of soil, moisture of liquid limit, moisture of plastic limit, plasticity index, relative density, and so on. By considering the longtime of consolidation test, researchers have tried to find relationship between these parameters and Cc from the past until now. For this reason they tried to connect Cc to other physical measurable properties of the soil. In the past, some researchers have indirectly tried to measure these parameters. In this regard, several empirical single-parameter approaches are proposed to estimate Cc. Due to non-linear relationship between Cc and relevant parameters, Adaptive Neuro-Fuzzy Inference System (ANFIS) has found as an application to solve such non-linear problems and cases where an accurate understanding of the problem is required. ANFIS is a multilayer feed forward networks that is combination of Fuzzy Inference System (FIS) and Neural Network (NN). NN has ability to learn the input and output data and FIS is also capable for map the input space to the output space. ANFIS is a powerful tool to solve complex and nonlinear problems using the two mentioned features and also language power of FIS and numerical power of adaptive nervous system. In this paper, Compression index (Cc) is modeled by ANFIS. Two ANFIS model were created by subtractive clustering (SC) and Fuzzy c-means clustering (FCM), respectively, and then trained. By data clustering, collection of training data is divided into a number of fuzzy clusters and each cluster representing the system behavior. The data were collected from the Soil Mechanics Laboratory of Mashhad city. ANFIS input parameters are taken according to the same parameters that commonly chosen in most of empirical models for determining Cc that easily determined in the laboratory. These input parameters include initial void ratio (e0), liquid limit (LL) and plastic limit (PL). The number of required iterations for training (Epochs) in two ANFIS model, neighborhood radius (ra) in SC and number of clusters (NC) in FCM are optimized using trial and error method. After the end of solving and optimization of ANFIS models, the SC-FIS model was found in ra = 0.25 and NC =18 and the FCM-FIS model was obtained in NC = 20 with highest accuracy for prediction. Results showed both ANFIS model have a high capacity and appropriate forecasting for Cc prediction with chosen inputs parameters. Compared to the SC-FIS model, FCM-FIS is conducted prediction with higher accuracy. Using presented ANFIS models, can be predict the Cc of soils whose characteristics are within the specifications soils that used in this modeling with high accuracy and do not need to conduct consolidation tests that are very time consuming and costly.