Higher mode effects in hinged wall with BRBsin base-frame structures using distributed parameter models

To investigate the effect of higher modes on the displacement and inner forces in HWBB(hinged wall with buckling-restrained braces in base)-frame structure,distributed parameter models for both the HWBB-hinged frame structure and the HWBB-MRF(moment resisting frame)structure are built.The hinged wall is simplified as a flexural beam.BRBs(bucking-restrained braces)are simplified to a rotational spring.MRF is simplified to a shear beam.Vibration equations of distributed parameter models are derived.Natural periods,natural modes of vibration,inner forces and displacements of the distributed parameter models are derived based on the vibration equations using numerical methods.The effect of the relative stiffness ratio and the rotational stiffness ratio on the higher mode effects is investigated.For elastic structures,the global displacement and shear in MRF are predominantly controlled by the first mode,while the shear and bending moment in the wall are significantly affected by higher mode effects.The effect of the yielding of BRB on the inner forces distribution in the HWBB-hinged frame is investigated.The results indicate that the first mode will no longer contribute to the inner forces and the contribution from higher modes to inner forces increases after the BRBs yield.Displacement is not sensitive to higher mode effects and it is controlled by the first mode after the BRBs yield.Parameter analysis demonstrates that the displacement amplitudes are reduced with the increase in the flexural stiffness of the wall before the flexural stiffness reaches a certain value.The first three periods decrease with the increase in the rotational stiffness.With the increase in the rotational stiffness ratio,the contribution from the first mode decreases while contributions from both the second mode and third mode increase.

Estimation of relations among hysteretic response measures and design parameters for RC rectangular shear walls

Seismic design of RC structures requires estimation of structural member behavioral measures as functions of design parameters. In this study, the relations among cyclic behavioral measures and design parameters have been investigated for rectangular RC shear walls using numerical simulations calibrated based on the published laboratory tests. The OpenSEES numerical simulations modeling of plastic hinge hysteretic behavior of RC shear walls and estimation of empirical relations among wall hysteretic indices and design parameters are presented. The principal design parameters considered were wall dimensions, axial force, reinforcement ratios, and end-element design parameters. The estimated hysteretic response measures are wall effective stiffness, yield and ultimate curvatures, plastic moment capacity, yield and ultimate displacements, flexural shear capacity, and dissipated energy. Using results of numerous analyses, the empirical relations among wall cyclic behavioral measures and design parameters are developed and their accuracy is investigated.

Seismic performance of HWBBF considering different design methods and structural heights

Previous research has shown that using buckling-restrained braces(BRBs)at hinged wall(HW)base(HWBB)can effectively mitigate lateral deformation of steel moment-resisting frames(MRFs)in earthquakes.Forcebased and displacement-based design methods have been proposed to design HWBB to strengthen steel MRF and this paper comprehensively compares these two design methods,in terms of design steps,advantages/disadvantages,and structure responses.In addition,this paper investigates the building height below which the HW seismic moment demand can be properly controlled.First,3-story,9-story,and 20-story steel MRFs in the SAC project are used as benchmark steel MRFs.Secondly,HWs and HWBBs are designed to strengthen the benchmark steel MRFs using force-based and displacement-based methods,called HWFs and HWBBFs,respectively.Thirdly,nonlinear time history analyses are conducted to compare the structural responses of the MRFs,HWBBFs and HWFs in earthquakes.The results show the following.1)HW seismic force demands increase as structural height increases,which may lead to uneconomical HW design.The HW seismic moment demand can be properly controlled when the building is lower than nine stories.2)The displacement-based design method is recommended due to the benefit of identifying unfeasible component dimensions during the design process,as well as better achieving the design target displacement.