Role of dampers on the seismic performance of pin-supported wall-frame structures

Pin-supported(PS)walls have been proven effective in avoiding weak story failure of frame structures by increasing the height-wise continuous stiffness and producing uniform distribution of story drifts.However,little attention has been given to the floor velocity or acceleration responses of PS wall-frame structures,which predominate the seismic damage of various nonstructural components that are critical to the immediate occupancy and quick recovery of buildings.This paper presents a numerical evaluation of the floor velocity and acceleration responses of PS wall-frame structures,highlighting the effects of different types of dampers accompanying the PS walls.The results show that the PS walls alone significantly increase the peak floor velocity(PFV)and peak floor acceleration(PFA)responses.PS wall-frame structures with either steel or viscoelastic(VE)dampers are much less effective in reducing the PFV or PFA responses than they are in reducing the peak inter-story drift ratio(PIDR).The impact of this behavior is demonstrated by a seismic fragility analysis that incorporates demand parameters combining the maximum PIDR,average PFV and PFA.The results show that the use of VE dampers rather than hysteretic dampers results in better protection of nonstructural components in PS wall-frame structures.

Seismic force modification factor for ductile structures

The earthquake forces used in design codes of buildings should be theoretically determinable. This work examines the seismic force modification factor R based on elastic-plastic time-history earthquake analysis of SDOF systems, wherein the hys-teresis models are elastic-perfectly-plastic (EPP), elastic-linearly-hardening (ELH), shear-slipped and bilinear-elastic. The latter two models are analysed for separating the effect of the ductility and the energy-dissipating capacity. Three-hundred eighty-eight earthquake records from different site conditions are used in analysis. The ductility is taken to be 2, 3, 4, 5 and 6, with the damping ratio being 0.02, 0.035 and 0.05 respectively. The post-yield stiffness ratios 0.0, 0.1 and 0.2 are used in the analysis. The R spectra are standardized by the characteristic period of the earthquake records, which leads to a much smaller scatter in averaged numerical results. It was found that the most important factor determining R is the ductility. R increases more than linearly with ductility. The energy-dissipating capacity, damping and the post-yield stiffness are the less important factors. The energy dissipating capacity is important only for structures with short period and moderate period (0.3≤T/Tg<5.0). For EPP and ELH models, R for 0.05 damping is 10% to 15% smaller than for 0.02 damping. For EPP and ELH models, greater post-yield stiffness leads to greater R, but the influence of post-yield stiffness is obvious only when the post-yield stiffness is less than 10% of the initial stiffness. By means of statistical regression analysis the relation of the seismic force modification factor R with the natural period of the system and ductility for EPP and ELH models were established for each site and soil condition.

Analysis on seismic performance of a new type of joint in steel structures

To examine the seismic performance of a newly fabricated weakened joint at the beam end position,four groups of energy-consuming steel plates with different weakening depths and thicknesses were subjected to horizontal cyclic reciprocating loading tests on beam ends.The tests were designed to evaluate the beams'hysteresis curve,skeleton curve,bearing capacity degradation curve,stiffness degradation curve,and ductility and the nodes'energy dissipation capacity.The test results show that a newly fabricated joint will not undergo brittle damage when the beam-column joint is welded at a displacement of 105 mm.Thus,the hysteresis curve will show an inverse S shape,and an obvious slip phenomenon will occur,which is mainly due to splicing.The diameter of the bolt connecting the slab to the beam flange is slightly smaller than the aperture.Due to the existence of slippage,the skeleton curve has no evident yield point.The joint ductility coefficient is less than 3.0,and the initial rotational stiffness of the joint is also small.The buckling of the splicing panel causes a rapid decrease in the joint bearing capacity.The main approaches,appropriately reducing the weakening depth and increasing the thickness of the splicing plate,can delay the occurrence of buckling and improve the ductility of the joint.

Application of Viscoelastic Material in Structures Control

The factors influencing mechanical performances of viscoelastic material are studied.The proper finite element model for dynamical calculating the passive control of wind-earthquake resistance is constructed.A combined element stiffness matrix of damper-brace system is deduced.At last,the theoretical deduction is verified by comparing the theoretical results with experimental ones.

Energy-dissipative dual-crosslinked hydrogels for dynamically super-tough sensors

In the fields of electronic skin and soft wearable sensors,intrinsically stretchable conductors undergo rapid development;however,practical applications of artificial skinlike materials/devices have not been realized because of the difficulty in combining the electromechanical properties and sensing performance.Contrarily,insoluble inorganic conductive domains in the hydrogel matrix are generally incompatible with surrounding elastic networks,decreasing the mechanical strength.Usually,the hydrogels are vulnerable either to severe mechanical stimuli or large deformation,especially when notches are induced.In this study,based on an energy-dissipative dual-crosslinked conductive hydrogel,a mechanically durable and super-tough strain sensor was developed.The highly soft yet dynamically tough hydrogel demonstrated high ionic conductivity(30.2 mS cm^(-1)),ultrastretchability(>600%strain),and superior linear dependence of strain sensitivity with a maximum gauge factor of 1.2 at 500%strain.Because of these advantageous synergistic effects,the resultant hydrogel strain sensor demonstrated reliable and stable detection of a large range of human motion and subtle vibrations.Moreover,it impressively exhibited super toughness that could endure consecutive treading pressure and even retain normal operation after 20 times of car run-over on the road.These demonstrations highly confirm the sensor’s superior mechanical durability and reliability,displaying great potential in developing next-generation mechanically adaptable sensors.

Aseismic smart building isolation systems under multi-level earthquake excitations： Part II, energy-dissipation and damage reduction

Based on the performance results of the previously suggested smart building isolation systems （lst companion paper）, this following study verifies the control effects of the systems from the view point of energy dissipation and damage level metrics. Several different model cases of the strategically isolated multi-story building structures utilizing passive dampers and semi-active resettable devices are analyzed and the energy-based target indices are compared. Performance comparisons are conducted on statistically calculated story/structural hysteretic energy and story/structural damage demands over realistic suites of earthquake ground motion records, representing seismic excitations of specific return period probability. Again, the semi-active solutions show significant promise for applications ofresettable device, offering advantages over passive systems in the consistent damage reductions. The specific results of this study include the identification of differences in the mechanisms by which smart building isolation systems remove energy, based on the differences in the devices used. Less variability is also seen for the semi-active isolation systems, indicating an increased robustness.