Research On Seismic Performance And Damage Model Of UHTCC Coupling Beams

Coupling beam is an important energy dissipation component in coupled shear wall structures system.Small span-to-depth and high shear-compression ratio of coupling beams,due to the size limit of the door holes on the walls,cannot meet the requirements of shear-compression ratio in code for design of concrete structures and technical specification for concrete structures of tall building.When the structural system is subjected to strong earthquakes,coupling beams are easy to have shear failure,which cannot meet the requirement of seismic ductility and energy dissipation.For this purpose,ultra high toughness cementitious composites(UHTCC)were used to replace concrete in coupling beams,and seismic performance tests are carried out.On basis of this,seismic damage model of UHTCC coupling beams was studied.In this paper,low-reversed cyclic loading tests were performed on four coupling beams with span-to-depth ratio of 1.5,in which two UHTCC coupling beams and two conventional RC coupling beams were contained.Analysis were done in terms of cracks development,failure modes,hysteretic response,shear capacity,ductility,stiffness degradation and energy dissipation.Results showed that shear capacity,ductility,energy dissipation can be improved effectively with UHTCC coupling beams,compared to conventional RC coupling beams.The development stage of diagonal cracks is longer.In the case of low stirrup ratio and no tied bars between diagonal reinforcements,UHTCC beams still have a high ductility and deformation.With superior damage tolerance,no serious damage occurred in specimens and it is possible to repair after earthquake.UHTCC specimen may delay the yielding of steel reinforcement,present lateral restrain effect,and degree of buckled diagonal reinforcement is lower than concrete specimen.At the component level,the damage behavior of UHTCC coupling beams was studied.On basis of test results,the damage status of UHTCC coupling beams in shear failure was divided into "intact","light damage","moderate damage","serious damage" and "destruction".Park-Ang damage model and Kratzig damage model were selected to evaluate the seismic damage,and both models with different parameters as the index were compared.Results showed that Park-Ang model has relatively clear index ranges,but presents a damage index greater than 1.The curves calculated using hystersis curve-based Kratzig damage model seem more reasonable,but the damage status levels are difficult to distinguish due to too large the damage index.Finally,Kratzig damage model is modified,and the modified damage index can clearly distinguish damage status levels of UHTCC coupling beams.