Showing 3 results for Shear Capacity
Amin Mohebkhah, Ahmad Sarvecheraghi,
Volume 15, Issue 3 (9-2015)
Abstract
The majority of building population in Iran and other developing countries consists of unreinforced masonry buildings and sometimes confined masonry (CM) buildings. In such buildings, masonry shear walls are the main earthquake resistant components. The Iranian seismic standard IS2800 provides some specifications for seismic design and construction of confined and reinforced masonry buildings which all are based on the observed behavior of them during the past destructive earthquakes. In other words, the specifications are merely qualitative. This shows the necessity of assessment of masonry buildings behavior both experimentally and numerically. Despite the extensive numerical studies available in the literature, it seems that the lateral load behavior of masonry buildings cannot be properly investigated by continuum mechanics based methods such as traditional finite element method. As an alternative to the available finite element methods, a distinct/discrete element method (DEM) can be used to investigate the nonlinear lateral load behavior of masonry buildings. Distinct element method has the capability to con-sider large displacements, shear sliding and complete joints openings between bricks as well as automatic detection of new contacts during the analysis process. In this paper a two-dimensional numerical model is developed using distinct element method using the specialized distinct element software UDEC (Itasca, 2004) for the nonlinear static analysis of unreinforced masonry buildings subjected to in-plane monotonic loading. The Univer-sal Distinct Element Code (UDEC) is a 2D program based on the DEM to simulate the behavior of jointed materials subjected to either static or dynamic loading. The developed DEM model is validated using the results of a two-story unreinforced masonry building designed and tested based on the Iranian seismic standard IS2800 regulations at the Building and Housing Research Center (BHRC). Due to low intensity of gravitational normall stresses in conventional masonry buildings, the bricks were built using an elastic material model. In order to develope a DEM micro-model based on interface elements with zero thickness, the size of the bricks was expanded by the mortar thickness in both directions and the elastic properties of the expanded brick were assumed to be the same as that of the real brick. Howevr, For the joints, simulating the characteristics of the mortar, a Mohr–Coulomb slip model was employed. It was found that the model can be used confidently to simulate nonlinear behavior of unreinforced masonry buildings for parametric studies. The Iranian seismic standard IS2800 specifications pertain mainly to the masonry shear walls percentage need in each direction. In other words, the perpendicular shear walls are not taken into account in masonry buildings’ lateral load capacity calculations. However, unreinforced masonry buildings resist lateral loads through box action behavior of all constituent components (i.e. walls, foundation and diaphragms). Therefore, a parametric study was conducted to investigate the contribution of perpendicular masonry shear walls on buildings’ lateral load capacity. Parametric study showed that perpendicular masonry shear walls contribute considerably to the shear capacity of the masonry building.
Mohammad Mohammad Zakerinejad, Masoud Soltani Mohammadi,
Volume 21, Issue 2 (5-2021)
Abstract
Classic one-way shear design provisions began with 45 degrees truss analogy introduced by Ritter and then rectified by addition of a concrete contribution term (Vc) which was basically based upon the results of some academic tests of simply supported RC beams with concentrated loadings. There are some strong evidence and examples that this empirical approach and the difference between its experimental base and the effective mechanisms in many of existing applications can be disastrous. Shear failure of reinforced concrete falls in the category of brittle and undesirable failure modes and has caused unrectifiable incidents in structures and infrastructures throughout the world. Some of such examples are the shear failures observed in the event of Kobe earthquake, shear failure of US air force warehouse, fatal highway bridge failure in Laval, Canada, and damage of Sleipner offshore platform. After such observations, there have been some good efforts in development of methods based on the physical description of main mechanisms influencing the shear behavior of RC members and especially RC panels under in-plane stresses that led to development of theoretical approaches such as modified compression field theory (MCFT), softened truss model (STM), and critical shear crack theory (CSCT). These theories made some breakthrough in nonlinear analysis of RC structures and become the basis for shear design in some of advanced codes like AASHTO LRFD, fib model code and CSA. Due to the complex nature of shear behavior in reinforced concrete, consensus in this field has not been reached among researchers, yet. In this study, through a parametric study on shear capacity of reinforced concrete panels based on Local Stress Field Approach (LSFA), and assumption of a thorough and compatible physical description, an efficient method for shear capacity analysis of reinforced concrete members is introduced. The principal effecting input parameters in parametric study were selected randomly within a reasonable range in the n-dimensional space of variables. These variables included: ratio of longitudinal stress to shear stress, ratio of longitudinal reinforcement, yield stress of longitudinal reinforcement, characteristic strength of concrete, maximum aggregate size, transverse reinforcement amount, and yield strength of transverse reinforcement. The remaining input parameters, like concrete tensile strength, fracture energy, rebar size, etc. were picked reasonably, in accordance with main parameters. Using an immense and strong experimental database of reinforced concrete slender beams failed in shear alongside with a database of reinforced concrete panels failed under in-plane loads, it is shown that the proposed method is a reliable, simple and easy to use approach that possesses high accuracy in calculation of shear capacity of slender reinforced concrete beams with or without transverse reinforcement, in comparison with existing reputed methods, and leads to safe and economic designs. Continuous transverse reinforcement (CTR) with a rectangular or polygonal shape is a relatively new technique that has been introduced in order to accelerate and facilitate the construction of RC structures. Studies show that rectangular continuous transverse reinforcement can improve the shear behavior and shear capacity of reinforced concrete beams, although existing shear design provisions, even the most advanced ones, are unable to predict this enhancement in capacity. It is shown that the proposed method is able to predict the aforementioned improved shear capacity of reinforced concrete beams with rectangular continuous transverse reinforcement.
F. Homaei, E. Vosoughi Rahbari,
Volume 23, Issue 4 (10-2023)
Abstract
In today's, the preservation and maintenance of masonry structures in historical areas have become very important. A significant part of this issue is rooted in the use of non-reinforced construction materials in the building of such structures. In Iran, most of the historical buildings were built using masonry materials. The buildings were designed according to the special architecture of this region. The existing structures mostly consist of masonry walls as well as some openings with arched configurations. In these types of walls, the wall consists of two piers and an arch on top of them. Since Iran is located in a highly seismic zone, investigating the performance of these types of structures is essential under the action of earthquakes and lateral loadings. Therefore, in this paper, a numerical investigation is accomplished on the in-plane behavior of traditional brick arches under the action of lateral loads. To this end, the numerical model of a sample of an existing arch (in Kerman’s Mesgari bazaar) was considered. The model was developed on STKO software. In this regard, the nonlinear response of bricks and mortar joints was simulated by using the DamageTC3D material. As well, the geometry of the wall was constructed with four-node plane-stress elements. The lateral capacity of the wall was assessed under the action of gravity loads. To this end, the wall was analyzed under gravity loads with intensities of 0.0 to 0.2 MPa. Next, it was pushed laterally through the pushover analysis and the shear force-displacement capacity curve of the wall was obtained. Through a specific procedure, the obtained capacity curves were estimated with a bilinear graph. By using this graph, the performance points corresponding to the wall’s capacity were extracted and a complete discussion was made regarding the shear capacity and the corresponding displacement to each performance point. Based on the obtained results from the analysis, it was observed that with an increase in the intensity of the applied gravity load, the maximum shear capacity of the walls increases. However, a higher increase in gravity load intensity (over a specific limit) would cause more damage to the arch which leads to a smaller shear capacity. Also, it is observed that the distribution of cracks and their pattern along the walls follow a similar outline. However, crack widths are affected strongly by the intensity of the applied gravity load on the wall.