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Title: Shear Stiffness of Earthquake-Resistant Concrete Squat Walls Reinforced with Glass Fiber-Reinforced Polymer Bars

Author(s): Islam Shabana, Ahmed Sabry Farghaly, and Brahim Benmokrane

Publication: Structural Journal

Volume: 120

Issue: 2

Appears on pages(s): 19-32

Keywords: fiber-reinforced polymer (FRP); reinforced concrete; seismic; shear stiffness; squat walls; strut and tie; variable-angle truss.

DOI: 10.14359/51738345

Date: 3/1/2023

While evaluating the stiffness properties is crucial for developing the response spectra of structures, none of the North American codes/standards—including ACI 318-19, ASCE/SEI 41-06, ASCE/SEI 43-05, and CSA A23.3-19—offer an explicit analytical approach for estimating the shear stiffness of cracked concrete squat walls. Furthermore, the paucity of experimental research has led to the lack of seismic design provisions for concrete structures reinforced with fiber-reinforced polymer (FRP) bars. Therefore, this study is focused toward investigating the stiffness characteristics of concrete squat walls reinforced with glass FRP (GFRP) bars, aiming at proposing a straightforward method of analysis that can be used to estimate the post-cracking shear stiffness. Four wall specimens with an aspect ratio (height-to-length ratio) of 1.14 were constructed and tested under simultaneous axial and reversed-cyclic lateral loads. Test results were analyzed in terms of stiffness degradation trends and decoupled flexural and shear deformations. An analytical model was developed for evaluating the secant shear stiffness at any load level in the post-cracking range. The model was achieved by idealizing the shear-transfer mechanism of the web reinforcement using a variable-angle truss, and that of the web concrete using a direct strut-and-tie system representing the tied arch action developed through the web. A simple analytical expression was formulated for predicting the magnitude of average strain in the web horizontal reinforcement at failure. The validity of the derived model and expressions was examined by reproducing the load-shear displacement response of the tested walls. Further verification was also conducted by reproducing the response of steel-reinforced concrete squat walls available in the literature, considering only their pre-web yielding range.