| The buckling restrained brace(BRB)&the buckling restrained braced frame(BRBF)are widely used in the shock absorbing structure because of their full and stable hysteresis energy dissipation characteristics.Time history analysis method for BRBF analysis has been adopted by researchers because of its fewer calculation assumptions and the reliable results,but its time-consuming character and the professional requirements to the design staffs are not suitable for common engineering designers.The recommended seismic design method "Equivalent Lateral Force Method",ELF-method for short,is relatively simple and easy to be mastered to the engineering designer.However,the adoption by ELF-method must meet the assumption of "building height must be within 40m,the main deformation must be the shear one,the gravity and stiffness along the structural height must distribute more uniform",this restricts the application of ELF-method for BRBF structure.Based on the strength theory,this paper presents two new concepts as "BRB average story horizontal bearing shear ratio,?-value",and "BRB base shear-bearing ratio,CB-Value" for the first time,then the second-order nonlinear analysis program named as CLAP,which could describe the geometric and material nonlinearity of the model and which is reccomended by"Steel Structural Committee" from Japanese Architecture Institute,is used for the nonlinear static and nonlinear dynamic analysis of the BRBF.The ranges of ?-value and CB-Value which meets the ELF-method assumptions are studied,and the suggestions are proposed for the design simplification corresponding to the condition which differ from the ELF-method assumptions with national seimic code.This article has carried out the following work:1)Based on the strength parameter ?-value and CB-value,nine multi-story BRBF steel frame models with ?=20%,30%,40%,50%,60%and 90%are designed.The plastic hinge mechanics with BRBs,Beams,and Columns are analyzed with pushover method.The maximum ductility demand and maximum cumulative plastic ductility demand of BRB are analyzed by the elastic-plastic time history analysis method to comprehensively verify the rationality of design model.2)The study both on the applicable assumption of the ELF-method for analysis the multi-story steel BRBF and values range with ? and CB are carried out by using the time history method under the 27 seismic energy inputting,considering the following parameters.The parameters are "the ratio of story stiffness to the initial stiffness by the pushover method",story drift ratio by story shear and story moment along the structural height,the correspondence between the vibration mode and the ?-value.For a multi-layer BRBF steel frame with a specific?-value and CB-value that satisfies the conditions of the ELF-method,it is recommended that the project could be simplified by using the ELF-method.3)The multi-story steel BRBF models which commonly used in the engineering application with some ?-value,which assumed to be inconsistent with the ELF-method,are calculated by the elastic-plastic time-history method and by the ELF-method.Both the calculation results are for analysis comparison to verify the valid for simplified ELF-method with selective verification,then the corresponding recommendations are given.The innovation of this paper is mainly reflected in the following aspects:1)The seismic design method of multi-story BRBF steel frame based on the strength parameter is proposed after the nine multi-story BRBF steel frames are analyzed by 27 kinds of seismic conditions.2)Seismic Simplification Design method of BRBF Steel Frame Based on the ELF-method is proposed from the following analysis parameters,such as the hinge mechanism,ductility demand,plastic energy consumption,stiffness change,story drift from story shear or from story bending,shear force distribution and vibration mode change of structural members.3)The range of ? and CB values meets ELF-method assumption for the multi-story BRBF steel frame design are given.For the assumption that the ELF-method is not satisfied.a simplified correction model and a simplified suggestion formula based on the ELF-method are given for a commonly used multi-story BRBF steel frame. |
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