Experimental Study On Seismic Behavior Of Small Span-to-Height Ductile Cement-based Material Coupling Beams With Different Reinforcement Forms And Theoretical Analysis Of Nonlinear Loading Process

As a common energy dissipation component in high-rise buildings,the seismic performance of connecting beams is of great significance to the safety of buildings.The small span ratio coupling beams,which are common in structures,have the characteristics of high shear-compression ratio and insufficient ductility.Under strong earthquakes,shear failure occurs too early to meet the needs of earthquake resistance.In order to improve the brittleness of concrete,UHTCC is used as the base material of connecting beams.At the same time,the seismic performance of UHTCC coupling beams is studied by comprehensive reinforcement scheme.Five specimens were tested in this experiment.The Span-to-height ratio(1.0,1.5),base material(ordinary concrete,UHTCC)and reinforcement form(diagonal oblique bars,composite reinforcement)were taken as variables to study the seismic performance from the aspects of failure mode,steel strain,hysteretic curve,stiffness degradation and energy dissipation calculation.The following conclusions were drawn:1)X-shaped shear failure occurs in all specimens,while cracks in the composite reinforced concrete beams are sparsely distributed,and concrete spalling occurs in a large area at the later stage of loading.The RUHTCC beams,whether diagonal oblique reinforcement or composite reinforcement,have uniform crack distribution,good integrity at the later stage of loading,and no large-area spalling phenomenon.Moreover,using UHTCC as the base material,the yield of steel bars is delayed,the peak deformation and ductility are improved,the hysteretic curve is full,the energy dissipation capacity is improved,and the cumulative energy dissipation capacity is improved.It is more than 1.8 times higher.2)The yield displacement and ductility of RUHTCC beams with the same reinforcement form increase with the increase of span-height ratio,but the bearing capacity of RUHTCC coupling beams with span-height ratio of 1.0 is higher than that of RUHTCC coupling beams with span-height ratio of 1.5,and RUHTCC beams with span-height ratio of 1.5 is better than that of RUHTCC coupling beams with span-height ratio of 1.0.3)For RUHTCC coupling beams with the same Span-to-height ratio and different reinforcement forms,the rhombic reinforcement can improve the peak load and peak deformation,and the larger the Span-to-height ratio,the more obvious the improvement effect is.As far as the cumulative energy dissipation capacity is concerned,there is little difference between the two reinforcement forms.Based on the analysis of the experimental phenomena and results,the stress and deformation of the coupling beam are rationally simplified,and the stress process of the coupling beam is analyzed nonlinearly.The shear deformation calculated by the model basically coincides with the measured shear deformation in the experiment.After the analysis of the shear deformation proportion,the skeleton curve calculated by the model and the skeleton curve obtained by the analysis of the experimental data have a high coincidence.