An Analytical Model for Shear Capacity Assessment of RC panels and Application to RC Beams

Document Type : Original Research

Authors
M. Mohammad Zakerinejad
M. Soltani Mohammadi
Tarbiat Modares University
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.

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Modares Civil Engineering journal
Volume 21, Issue 2
May and June 2021
Pages 119-132