Theoretical And Experimental Study On Innovative High-performance Steel Braced Frame Structures

The high-strength steel can be used to manufacture the beams and columns of steel frames so as to utilize its strength advantage.Consequently,the bearing capacity can be effectively enhanced,while the self-weight and steel consumption of the structure can be reduced.However,in most cases the high-strength steel could not satisfy the mandatory provisions in the Code for Seismic Design of Buildings(GB50011-2010)with respect to the structural steel that the ratio of the yield strength to the ultimate strength should not be larger than 0.85 and the elongation rate should not be smaller than 20%.Therefore,when used in seismic zones,it is suggested by the Specification for Design of High Strength Steel Structures(draft for comment)that structural components manufactured using the high-strength steel should remain elastic even in rare earthquakes.Obviously,it requires higher seismic performance for steel structures manufactured with high-strength steel.In order to provide a practical solution to the above problem,an innovative high-performance steel braced frame(HPSBF)structure is proposed,whose columns are manufactured using high-strength steel,while beams are manufactured using regular steel.Moreover,steel energy dissipaters(SEDs)with braces are incorporated into the structure.As a result,the HPSBF forms three fortification lines against the earthquake.In case of an earthquakes,the SEDs yields first,which makes the first fortification line;then the beams manufactured using regular steel yields,which makes the second fortification line;the columns manufactured using high-strength steel makes the third fortification line,which is not allowed to yield.Based on the above working mechanism,the performance-based seismic design method of the HPSBF is proposed in this dissertation,and key problems related to components,structure and design methods of the HPSBF are studied in this dissertation.The main research contents and achievements are as follows:1.In order to solve the existing problems in traditional SEDs,an improved shear-type SED,an improved bending-type SED and an improved shear-bending combined SED are proposed.The basic mechanical characteristics are studied by theoretical analysis,and the hysteretic performance and energy dissipation capacity are verified by pseudo-static cyclic tests.Results of the study show that the improved shear-type SED can effectively avoid stress concentration and welding residual stress on the web plate caused by the stiffener weld by adopting contact stiffeners.Consequently,the energy dissipation capacity and low-cycle fatigue performance can be enhanced.The improved bending-type SED can facilitate manufacture and assembling while avoiding adverse effects such as sudden stiffness increase by proper structure improvement.The improved shear-bending combined SED is constructed by combining the shear-type SED and bending-type SED in a reasonable way so that they work interactively rather than independently,where the bending plates not only dissipate energy,but also prohibit buckling of the web plate.Therefore,the overall hysteretic performance and energy dissipation capacity can be effectively enhanced.2.A normalized Bouc-Wen hysteresis model is studied so as to overcome the disadvantages of the traditional bilinear hysteresis model and the traditional Bouc-Wen hysteresis model,which features a normalized hysteresis variable and has no redundant parameters.The relations between the model parameters and the hysteretic characteristics of the SEDs are revealed by theoretical study.Furthermore,a parameter fitting method is proposed to identify the model parameters.It provides the basis for implementing time history analyses of the structure using the normalized Bouc-Wen model to describe the restoring forces of the SEDs,and identifying the mechanical parameters of SEDs using the normalized Bouc-Wen model.3.A simplified modeling method is proposed for the HPSBF structure.A comparison is drawn between the simplified model and the complete model with respect to dynamic characteristics,time history analysis results and computational efficiency.Results of the study indicate that the simplified model is not only computationally efficient,but also capable of achieving satisfying accuracy.By using the proposed simplified model in the optimal seismic design process,the efficiency of the optimization can be significantly enhanced,and the total time consumption can be greatly reduced.4.Two different methods are proposed to achieve optimal seismic design of the HPSBF structure,namely the increasing iterative method(IIM)and the modified genetic algorithm(MGA),and a comparison is drawn between them in terms of optimization results and time consumption.Results of the study indicate that both methods can provide economic and reasonable placement schemes for SEDs in the structure,while achieving the target inter-story drift ratios at different levels of seismic hazard.Furthermore,the inter-story drift ratios of the HPSBF structure can be more uniformly distributed along the height after the optimization.Additionally,the HPSBF structure is compared with the conventional steel braced frame(CSBF)structure.Results show that the HPSBF structure exhibits better seismic performance and is more economic than the CSBF structure.5.The seismic performance objectives and performance-based seismic design method are proposed for the HPSBF structure,and technical solutions are provided for the problems involved in the design process.Finally,the proposed design procedures and relevant technical solutions are demonstrated by a practical example.It is shown that the performance-based seismic design of the HPSBF structure can be well implemented through the proposed design procedures and relevant technical solutions,achieving the desired level of seismic performance.