Shear Behavior Of Reinforced ECC Beams

To enhance the structural and seismic resistance,as well as durability of concrete structures,an ultra-ductile fiber reinforced cementitious composites called Engineered Cementitious Composite(ECC)was developed.ECC has a similar compressive and tensile strength to conventional concrete,but its ultimate tensile strain can exceed3%,which is 300 times higher than that of normal concrete.Since ECC can bend like steel,it is always named as“bendable concrete”.Since it alters the fundamental brittle characteristics of concrete,ECC has already been widely applied for various field constructions including buildings,transportation,water and other infrastructures.As for the shear behavior of R/ECC members,the assumption"plane remains plane"is no longer applicable,and the shear cracking path is affected by quite a lot of factors.Therefore,it is difficult to predict the shear carrying capacity of R/ECC members.Like the classical shear problem of reinforced concrete(R/C)during the past century,the shear behavior of R/ECC members has also become a challenging problem which attracts continuous interest from the research community.To figure out the shear transfer mechanism of R/ECC beams,several innovative testing methods were used in this research,which could help quantify various shear strength components separately and show the structural behavior with a new level of detail.Furthermore,the discrete lattice model was adopted to simulate the shear behavior of R/ECC beams at macroscale.Finally,an analytical model for predicting shear carrying capacity of R/ECC beams was established.Details of this study are summarized as follows:(1)The mechanical properties of ECC with high volumes of fly ash Grade II are improved by incorporating cenosphere,and several factors affecting the strain capacity and compressive strength of ECC were studied,including the particle size and content of cenosphere,water/binder ratio and so on.Then,an optimal mix proportion was determined,which could help reduce the material cost but enhance its mechanical performance.(2)To evaluate the variation of shear resisting contribution from stirrups((1_s)and ECC((1_c),a continuously-distributed strain gauging system was adopted to measure the strain along full length of stirrups and longitudinal rebars.It provided a new insight into the mechanical interaction between ECC and steel reinforcement when shear failure predominates.(3)Through three-dimensional digital image correlation technology(3D-DIC),the combined opening and sliding displacement of shear crack could be measured.A phenomenological model for describing the shear crack kinematics was established,which can reflect the shear failure mechanism of R/ECC and R/C beams.(4)A total of 24 beam specimens were tested under shear with aforementioned strain and crack measuring system.The effects of matrix type,shear span-to-depth ratio,longitudinal reinforcement ratio and stirrup ratio on the shear performance of R/ECC beams were studied,including load-deflection response,failure mode,crack kinematics,reinforcement strain development,and the variation of shear strength components.(5)To upscale the application of discrete lattice model to simulate the macroscopic structural behavior of R/C and R/ECC members,a generic approach for modelling the rebar-matrix(ECC or concrete)interface in the discrete type random lattice model was proposed.Considering the randomness of the distributed matrix nodes and interface elements as well as the mesh size,the elemental properties were derived for aligned and non-aligned interface elements based on stochastic analysis.Then,a general method for simulating the structural behaviors of R/C and R/ECC members were established.(6)Based on the"truss-strut"shear transfer mechanism in R/ECC beams,an analytical model for predicting the shear strength of R/ECC beams was established.Furthermore,a shear test database for R/ECC beams was established,and a simplified empirical formula for calculating the shear carrying capacity of R/ECC beams was proposed through nonlinear regression analysis,which is more convenient for the shear design of R/ECC beams.