Experimental And Analytical Studies On Damage-controllable RC Coupling Beams

The coupling beam is one of the key components to resist lateral forces in a shear wall system.However,during recent earthquake disasters it is often observed a severe shear damage on coupling beams with smaller aspect ratios,difficult to meet the strength and ductility requirements of practical engineering.In particular,once the RC parts are damaged,it is rather difficult to be repaired.In order to improve the seismic resilience of shear wall systems,this paper introduces the energy dissipative damper into the coupling beam.The better energy dissipation capacity of damper efficiently improves the seismic performance of coupling beams.Nine RC coupling beam specimens are first tested to examine the influence of aspect ratio,diagonal reinforcement,and RC slab on the seismic behavior of coupling beams.Results show that all specimens yield in flexure modes,while finally failed in shear modes or flexural-shear mixed modes.The maximum shear strength of the diagonally reinforced coupling beams are 20% larger than those without diagonal reinforcements.It is found that the slab has a little impact on the maximum shear strength.Both the diagonal reinforcement and the slab increase the flexural yield strength but have slight improvement on the ultimate deformation capacity.The initial effective stiffness of RC coupling beams ranges from 0.24 EIg to 0.3EIg,and the effective stiffness at yield is nearly 0.15 EIg,much smaller than the code recommended value,0.5 EIg.With the increase of deformation,the RC coupling beam and the RC slab are damaged subsequently,which cannot be easily repaired after earthquakes.In order to control the damage of RC coupling beams,an energy dissipative coupling beam equipped with steel plate dampers with slits at the mid-span is proposed.Four specimens having the same aspect ratio as RC coupling beams are tested.They are finally damaged with either fracture of metallic dampers or anchoring failure.Before the metallic fracture,the over-strength ratio of the damper reaches 2.5.The design values of the yield strength and the stiffness have 10% and 15% difference from the tested values,respectively,which are taken reasonable.The reasons for these differences are due to the deformation of anchoring,the slip of the bolts and the inconsistent deformation between dampers.For the specimens with the identical aspect ratio,the deformation capacity and the accumulated energy-dissipating capacity of energy dissipative coupling beams are larger than those of RC coupling beams.For the energy dissipative coupling beam,the deformation and the energy dissipation of dampers account for nearly 80% of the total values.The crack development on the energy dissipative coupling beam can be well controlled within an acceptable level.The dampers can be quickly replaced.A simplified numerical model of energy-dissipative coupling beams is finally developed.The mechanical behavior of dampers,the flexural and shear behavior of RC parts are simulated in simplified pattern.The inconsistent deformation between dampers in a coupling beam is represented by a zeroLength element.The error between numerical results and test results of the maximum shear strength and the cumulative dissipated energy are both less than 10%,while the stiffness difference reaches to 20% because of the loading boundary cannot be well reproduced by the numerical models.Parametric studies on the span ratio,the flexibility ratio and the strength ratio are conducted.The result indicates that those parameters shall be carefully selected to achieve a good bearing capacity,the energy dissipation capacity and the deformation capacity.They are suggested as 0.3 to 0.4,0.6 to 0.7 and 0.6 to 0.7,respectively for the span ratio,the flexibility ratio,and the strength ratio.