Shear Behavior Of Squat Ultra-high Performance Fiber Reinforced Concrete Shear Wall

Squat ultra-high-strength concrete shear walls are considered one of the major lateral resisting members in various engineering structures.The behavior of these walls is frequently controlled by the shear response leading to brittle failure.Lately,ultra-high performance fiber reinforced concrete(UHPFRC)materials are sophisticated materials that are distinguished by high tensile and compressive strength,durability,and ductility.As a result of the brittle materials have difficulties gaining a ductile response,thence UHPFRC materials are utilized in the shear wall to improve ductility.Therefore,this study is concerned with evaluating the nonlinear shear behavior of squat UHPFRC shear walls reinforced with light transverse reinforcement using the finite element method,and based on the outputs of finite element analysis for models,is proposed statistical equation for predicting peak shear strength capacity.A nonlinear finite element method dependent upon the ABAQUS/Standard software and the concrete damaged plasticity model.The mechanical properties of materials obtained from previous laboratory tests were implemented in the concrete damaged plasticity model to develop a three-dimensional finite element model for simulating the behavior of squat UHPFRC shear walls.The ABAQUS model was corroborated by experimental findings of one of the prior experiment shear walls conducted by Hung et al.(2017).The analytical modeling of the shear wall model indicated that a 3D finite element model with mesh size(50 x 50)mm is capable of simulating the response of the squat UHPFRC shear wall reasonably.Dependent upon the validated model,analytical modeling consisting of 27 squat UHPFRC models with rectangular cross-sections under in-plane monotonic lateral loading was carried out.Nine ABAQUS models were subjected to constant axial load before lateral loading.All models were designed according to the provisions of the ACI 318-14 as reinforced concrete shear walls without considering the presence of steel fibers and utilized the actual strengths of the material.The parametric studies were adopted to investigate the shear response of squat shear walls were transverse reinforcement ratio,concrete compressive strength,steel fibers volume fraction,shear stress level,and axial load.Shear strength capacity,drift capacity,deformation,damage progression,and shear force against displacement response of the models were measured.The analytical modeling results showed that an increase or decrease transverse reinforcement ratio had no significant effect on the secant stiffness and shear strength capacity but affected the failure mode and ductility,while an increase in the longitudinal reinforcement ratio increased in the failure load and stiffness.It was found that models containing steel fiber amount of 2 % were more resistant to deformations than 1.5 %.It was also found that the models under moderate-level shear stress showed more damage compared to those subjected to higher levels.It was noticed that the presence of axial load had a significant influence on enhancing and increasing the stiffness and strength capacity.Furthermore,it also significantly influenced changing the response of models,the deformations and damage patterns,ductility,and failure manners.The axially loaded models exhibited a brittle response regardless of reinforcement ratio,while the models without axial load had a lower strength but higher ductility.The axially loaded models had a similar brittle response,and the diagonal compression shear failure was dominant.Based on the parameters that influenced the numerical modeling of finite element models,regression analysis was implemented to produce the empirical equation.The purpose of this statistical equation is to predict the peak shear strength capacity and be the future focal point for developing physics-based models ability to predict the response of squat UHPFRC shear walls under various conditions loading.The empirical expression was calibrated by comparing the predicted value of ultimate shear strength capacity with the measured value of previous laboratory specimens of squat UHPFRC shear walls.The evaluation results of the empirical equation indicated that it could be employed to predict the peak shear strength capacity of squat UHPFRC shear walls.It can be applied for all squat UHPFRC shear walls with rectangular cross-sections and surrounded by boundary elements,provided that the characteristics of the wall are within the characteristics of the finite element models used in the regression analysis.