Research On Shear Behavior Of Concrete-ECC Composite Beam

The shear failure of beam usually is a brittle failure,which is much more harmful than its flexural failure,so it is commonly noted that overcoming the shear failure is an essential topic in the field of concrete.ECC(Engineered Cementitious Composites,ECC)is a kind of fiber reinforced cementitious composite material,which exhibits ultra-high toughness and superior crack control ability.Concrete-ECC beam is a new type of reinforced concrete composite member with ECC replacing the concrete in the tensile zone of reinforced concrete(RC)beam and using high strength steel bars.Compared with RC beams,ECC not only has the competence to make up such short slabs as low toughness and poor crack control performance,but also is capable of improving the shear resistance of the constructs.In addition,the design of assembly form and the useage of high strength steel bars are beneficial for energy conservation and emission reduction,meanwhile they can provide research direction for structural design.The major research contents of this study can be drawn as follows:(1)Through the shear tests of 78 concrete-ECC beams,the stress characteristics and failure patterns of concrete-ECC beams are analyzed.The results show that concrete-ECC composite beams with high strength reinforcement are similar to RC beams in the stress characteristics and the failure type,but this new type of composite beams are obviously superior to the ordinary RC beams in the ability of controlling crack and maintaining the integrity of components.(2)Based on analyzing the shear test data of reinforced ECC(RECC)beams,the relationship between the shear capacity of RECC beams and the main variables is explored the RECC data is verified and compared with the shear formula in Chinese and American specifications.The results show that the shear performance of RECC beams decreases with the increase of shear span ratio and section size,but the decrease is less than that of RC beam Although there is a certain gap between the calculation results and the test results of the Chinese standard and the American standard,the prediction results of the Chinese standard are better than that of the American standard.(3)The influences of different variables(shear span ratio,the interface form,concrete concrete strength,stirrup ratio,thickness of ECC)on bearing capacity of concrete-ECC beams are analyzed.It is argued that the influence of shear span ratio is greater;secondly,the influence of form processing interface is relatively small;thirdly,the thickness of the ECC is greater than 70 mm(the ratio of the replacement height to the section height is about 0.35)after the effect is weaker;fourthly,stirrup ratio is bigger when the shear effect is bad;finally,70mm thick ECC and stirrup ratio of 0.29%combined shear effect is best.Moreover,On the condition of the shear characteristics of RC and RECC beams,the stress characteristics of concrete-ECC is analyzed,and the the calculation formula of shear bearing capacity of concrete-ECC composite beams is preliminarily established.(4)The Abaqus software is used to carry out finite element analysis of the concrete-ECC beams,the stress process and failure form of composite beam are studied,and the load displacement curve and other results are obtained.By comparing the simulation results with the test results,it is found that the two failure forms are basically consistent,and the simulated load result is close to the test result,which verifies the rationality of concrete-ECC beam finite element model.