بررسی تحلیلی و آزمایشگاهی رفتار تیرهای بتن مسلح تقویت شده در برش به روش NSM همراه با مطالعات موردی

نوع مقاله : پژوهشی اصیل (کامل)

نویسندگان
امیر شمالی 1
داوود مستوفی نژاد 2
محمد رضا اصفهانی 3
1 دانشجوی دکتری سازه دانشکده مهندسی عمران دانشگاه صنعتی اصفهان
2 استاد دانشکده مهندسی عمران دانشگاه صنعتی اصفهان
3 استاد دانشکده مهندسی عمران دانشگاه فردوسی مشهد
چکیده
مقاله ی حاضر، عمل کرد تیرهای بتن مسلح تقویت شده در برش را به روش آزمایشگاهی مورد بررسی قرار داده و به کمک تحلیل اجزای محدود شبیه سازی می­کند. سپس با انجام تحلیل های موردی، تاثیر استفاده از بتن با مقادیر متفاوت مقاومت فشاری و نسبت های متفاوت آرماتورهای عرضی مورد بررسی قرار خواهد گرفت. در بخش آزمایشگاهی 4 نمونه ی تیر بتن مسلح به دو گروه با و بدون خاموت تقسیم شده و در آن اثر استفاده از نوارهای پلیمری تقویت شده با الیاف کربن به روش نصب در نزدیک سطح تحقیق می­شود. برای این منظور، تیرهایی با ابعاد 200 300 2000 میلی متر ساخته شده و تحت بار استاتیکی قرار گرفتند و منحنی های بار- تغییر مکان وسط دهانه و نحوه ی گسیختگی آن ها مورد مقایسه قرار گرفتند. شیارهای مورد استفاده در تکنیک NSM، مجموعه هایی از دو شیار هستند که در فواصل منظم در دهانه های برشی ایجاد شده اند. نتایج آزمایشگاهی نشان می دهد که استفاده از روش NSM باعث افزایش ظرفیت برشی به میزان 41 درصد و 69 درصد به ترتیب در تیرهای با و بدون خاموت می شود. به علاوه، شبیه سازی نمونه های آزمایشگاهی با مدل کردن احتمال جدا شدگی نوارهای کامپوزیتی با استفاده از المان چسبنده نشان می دهد که نتایج حاصل از روش پیشنهادی مدل سازی، انطباق خوبی با نتایج آزمایشگاهی دارد. هم چنین تحلیل های اجزای محدود موردی نشان میدهد که با کاهش مقاومت فشاری بتن، احتمال جدا شدگی نوارهای CFRP بیش تر است و با افزایش درصد آرماتورهای برشی، کرنش محوری نوارهای CFRP کاهش پیدا می کند.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

Analytical and experimental investigation of the RC beams shear-strengthened with NSM Method along with Case studies

نویسندگان English

amir shomali 1
DAVOOD MOSTOFINEJAD 2
mohammad reza esfahani 3
1 Department of Civil Engineering, Ferdowsi University of Mashhad, Mashhad, Iran
2 Department of Civil Engineering, Isfahan University of Technology (IUT), Isfahan, Iran
3 2 Department of Civil Engineering, Ferdowsi University of Mashhad, Mashhad, Iran
چکیده English

Analytical and experimental investigation of the RC beams shear-strengthened with NSM Method along with Case studies



Abstract

This paper examines the structural behavior of the reinforced concrete beams strengthened in shear experimentally and simulates using finite element analysis. Then, the effect of employing concrete with different compressive strengths and different ratios of transverse reinforcements is studied using the case analyses. In the experimental part, four reinforced concrete beams are divided into two series of with and without internal steel reinforcements and the effect of carbon-fiber-reinforced polymer (CFRP) laminates is investigated by near-surface mounted (NSM) technique as the shear strengthening method. For this purpose, rectangular beams with the dimensions 2000×300×200 mm are designed and monolithically tested in four point loading test up to failure and the load-displacement curves of the mid-span as well as their failure modes are compared with each other. All the beams were reinforced with 3 steel tension bars of 20 mm at the bottom and 2 steel compression bars of 12 mm at the top with end hooks. If stirrups are applicable, 6 mm diameter steel closed hoops spaced at designated distances, are applied. For strengthening using the NSM method, thin slots with 8 mm width and 10 mm depth are made on lateral faces of concrete cover. In order to install composite laminates, the CFRP strips after impregnating with strong epoxy resin are folded and embedded in these grooves. After curing the specimens, all the beams are subjected to a 2000 kN capacity hydraulic jack with the loading rate of 2.5 kN/Min. The ready-mix commercially concrete was delivered to the structural laboratory for casting the specimens with 28-day concrete strength of 30 MPa. The ACI code formulations were used for calculating the shear capacity of the beams before their casting and a suitable span to depth ratio was selected to inhibit deep beam failure. The experimental results indicate that using NSM technique enhances the shear capacity up to 41% and 69% in the beams with and without stirrups, respectively. Test results show that the NSM shear strengthened specimens failed by CFRP laminate rupture. Moreover, simulation of the test specimens by modeling the probability of FRP de-bonding using interface element and orthotropic behavior of laminates shows that the results of the proposed model are consistent with experimental results. In the numerical part, two case studies are carried out; in the first case analysis, three concrete compressive strengths of 20, 30 and 50 MPa are selected and in the second one, three steel stirrup spacing of 65, 130 and 190 mm are applied. Numerical case analyses show that as the compressive strength of concrete decreases, the failure mode the probability of de-bonding increases and as the stirrup percentage increases, the axial strain of CFRP laminates decreases. Numerical case analysis clarifies that by decreasing the distance of internal shear reinforcements from 195 mm to 65 mm, the maximum axial strain of CFRP laminate decreases about 45%. Load-deflection curves in the case analysis also show that by increasing the transverse steel ratio, ultimate displacement enhances and deformability capacity improves.

کلیدواژه‌ها English

NSM shear strengthening
CFRP
finite element method
Concrete strength
Stirrup
[1] Mofidi, A. and Chaallal, O. (2014), “Effect of steel stirrups on shear resistance gain due to externally bonded fiber sheets”, ACI Struct. J., 111(2), 353-362.
[2] Teng, J.G., Chen, J.F., Smith, S.T. and Lam, L. (2002), FRP Strengthened RC Structures, John Wiley & Sons, USA.
[3] Chen, J.F. and Teng, J.G. (2003), “Shear capacity of FRP- strengthened RC beam: FRP de-bonding”, Constr. Build.Mater., 17 (1), 27-41.
[4] Rita, S.Y., Wong, F. and Vecchio, J. (2003), “Towards modeling of reinforced concrete members with externally bonded fiber-reinforced polymer composites”, ACI Struct. J., 100 (1), 47-55.
[5] De Lorenzis, L. and Teng, J.G. (2007), “Near-surface mounted FRP reinforcement: an emerging technique for strengthening structures”, Compos. :Part B Eng., 38 (2), 119-143.
[6] Galal, K. and Mofidi, A. (2010), “Shear strengthening of RC T- beams using mechanically anchored un-bonded dry carbon fiber sheets”, J. Perform. Constr. Facil., 24 (1): 31-39.
[7] Mostofinejad, D. and Mahmoudabadi, E. (2010), “Grooving as an alternative of surface preparation to postpone de-bonding of FRP lamination in concrete beams”, J. Compos. Constr., 14 (6), 804-811.
[8] Mostofinejad, D. and Shameli, SM. (2013), “Externally bonded reinforcement in grooves (EBRIG) technique to postpone de-bonding of FRP sheets in strengthened concrete beams”, Constr. Build. Mater., 38, 751-758.
[9] Mostofinejad, D. and Tabatabaei Kashani, A. (2013), “Experimental study on effect of EBR and EBROG methods on de-bonding of FRP sheets used for shear strengthening of RC beams”, Compos. Part B Eng., 45, 1704-1713.
[10] Akter Hosen, Md., Zamin Jumaat, M., Saiful Islam, A. B. M., Abdus Salam, Md. and Hung Mo, K. (2017), “Side-nsmcomposite technique for flexural strengthening of RC beams”, Computers and Concrete, 20 (4), 439-448.
[11] Ramezanpour, M., Morshed, R. and Eslami, A. (2018), “Experimental investigation on optimal shear strengthening of RC beams using NSM GFRP bars”, Structural Engineering and Mechanics, 67 (1), 45-52.
[12] De Lorenzis, L. and Rizzo, A. (2009), “Behavior and capacity of RC beams strengthened in shear with NSM FRP Reinforcement”, Constr. Build. Mater., 23, 1555-1567.
[13] Dias, S.J.E., Barros, J.A.O. (2012), “NSM shear strengthening technique with CFRP laminates applied in high-strength concrete beams with or without pre-cracking”, Composites: Part B , 43, 290–301.
[14] Almassri, B., Barros, J.A.O., Al Mahmoud, F., Francois, R. (2015), “A FEM-based model to study the behaviour of corroded RC beams shear-repaired by NSM CFRP rods technique”, Composite Structures, 131, 731-741.
[15] Kuntal, V.S., Chellapandian, M, and Prakash, S.S. (2017), “Efficient near surface mounted CFRP shear trengthening of high strength pre-stressed concrete beams – An experimental study”, Compos. Struct., 180, 16-28.
[16] Lee, D., Cheng, L. (2013) “Bond of NSM systems in concrete strengthening – Examining design issues of strength, groove detailing and bond-dependent coefficient”, Constr. Build. Mater., 47, 1512-22.
[17] Mofidi, A., Chaallal, O. and Cheng, L. (2016), “Investigation of near surface–mounted method for shear rehabilitation of reinforced concrete beams using fiber reinforced–polymer composites”. J. Compos. Constr., 20 (2), 201-214.
[18] Chen, G.M., Chen, J.F. and Teng, J.G. (2012), “On the finite element modelling of RC beams shear-strengthened with FRP”, Construction and Building Materials, 32, 13-26.
[19] Hordijk, DA. (1991), “Local approach to fatigue of concrete”, Ph.D. Dissertation; Delft University of Technology, The Netherlands.
[20] Saenz, LP. (1964), “Discussion of equation for the stress-strain curve of concrete-by Desayi, P. and Krishan, S.”, ACI Structural Journal, 61, 1229-35.
[21] Lu, X.Z., Teng, J.G., Ye, L.P. and Jiang, J.J. (2005), “Bond-slip models for FRP sheets/plates bonded to concrete”, Engineering structures, 27(6), pp. 920-937.
[22] Sayed, A.M., Wang, X. and Wu, Z. (2014), “Finite element modelling of shear capacity of RC beams strengthened with FRP sheets by considering different failure modes”, Construction and Building Materials, 59, 169-179.
[23] Obaidat, Y.T., Heyden, S. and Dahlblom, O. (2010), “The effect of CFRP and CFRP/concrete interface models when modeling retrofitted RC beams with FEM”, Composite Structures, 92, 1931-8.
[24] Obaidat, Y.T., Heyden, S. and Dahlblom, O. (2013), “Evaluation of parameters of bond action between FRP and concrete”, J. Compos. Constr., 17, 626-635.
[25] ACI 318R-4 (2014), Building Code Requirements for Structural Concrete and Commentary, American Concrete Institute; Farmington Hills, Michigan, USA.
[26] ABAQUS 6.13. (2013), ABAQUS/theory user manual, Dassault Systemes, Providence, RI, USA.
[27] Coronado, C. (2006), “Characterization modeling and size effect of concrete-epoxy interfaces”, PhD Thesis; Pennsylvania State University, USA.
[28] CEB-FIP (1990), International Recommandations for the Design and Construction of Concrete Structures, CEB-FIP model code 1990; Design code, Paris.
fib Bulletin 14. (2001), Externally bonded FRP reinforcement for RC structures, technical report on the design and use of FRP EBR for reinforced concrete structures, International Federation for Structural Concrete; Lausanne.
مهندسی عمران مدرس
دوره 19، شماره 6
آذر و دی 1398
صفحه 115-127