Study On Tension Stiffening Of Reinforced ECC

In recent years,the whole world surfer from the deterioration and damage of building structures.Cement-based composites,such as concrete,are extensively used in a variety of structural applications.However,concrete exhibits a brittle tensile behavior that could lead to reduced durability and structural performance in the long term.The use of discontinuous fibers to reduce the brittleness of the concrete,and improves its post-cracking tensile behavior,has been a focus of structural materials research since the 1960’s.This paper mainly studies the tensile stiffiness of reinforced ECC members under uniaxial tensile load.In this paper,12 kinds of components with different reinforcement ratios and cross-section sizes are designed and tested by pseudo-static loading.In addition to the use of sensors and displacement gauges,the digital speckle technology is also used to capture the strain change above specimen and the development of cracks.Based on the load-strain relationship of reinforced ECC member at different stages under uniaxial tension,this paper deduces the calculation model of each stage and carries on the calculation fitting with the assumption of deformation compatibility,obtaining a relatively good fitting result.The tensile strength,cracking strength and minimum reinforcement ratio of ECC were calculated by derivation.It is found that the formula for calculating the cracking strength of ordinary concrete is generally lower than the actual value of ECC cracking strength.By analyzing the load-strain curves and the strain distribution along the steel in elastic and plastic stages,it is observed that even after the initial cracking of the specimen,the strain distribution is uniform along the steel,which proves that the fiber has an obvious bridging effect in the crack.After the main crack is formed,the strain of reinforcement is concentrated in the main crack area.This test also observed that ECC could continue to bear loads and exhibit multiple cracking behaviors after the initial cracking.The range of reinforcement ratio conducive to crack development was summarized by observing the crack development morphology.Finally,a two-dimensional plane element model was established by using the finite element software Diana.Based on the total strain crack model,the tensile stiffiness performance of reinforced ECC member was considered.The finite element calculation results show that the finite element simulation results are in good agreement with the experimental results.Based on this,the parameter analysis of reinforced ECC members with the same reinforcement ratio but different section sizes is carried out in this paper.The finite element simulation results show that the larger the section size,the higher the bearing capacity,but the section size has no obvious effect on the development of cracks.