| With the improvement of the manufacturing technology,the development trend of steel is progressing towards the high performance(HP)steel.Nowadays,modern engineering structures face challenges in terms of various disasters,such as fire,earthquake and corrosion,which naturally requires the steel to have multiple advanced properties.China now has the ability to produce superior high-performance(SHP)steel with combined benefits of high strength,seismic-performance,fire-resistance and corrosion-resistance.However,there is still a lack of fundamental mechanism and engineering techniques for its use in structural engineering,especially the lack of reliable conclusions and design methods for the mechanical analysis and bearing capacity of the bolted connections and beam-to-column joints,which prevents its further application in practical engineering.In this thesis,based on extensive experimental investigations,numerical simulations and theoretical analyses on the material properties and bolted connections at elevated temperatures as well as seismic behavior of beam-to-column joints using SHP steel,their mechanism is clarified,and design methods are proposed accordingly.The main research works are carried out herein as follows:(1)Material properties of 54 HP bolt tensile coupons and 18 SHP690 steel tensile coupons at elevated temperatures are carried out,and their stress-strain curves are obtained,with the temperature-dependent elastic modulus,yield strength,tensile strength,elongation after fracture are determined.Based on the extensive experimental data,constitutive models at elevated temperatures are proposed.(2)Fourteen tests on shear-resistant performance of bolted connections are conducted in the temperature range of 20-900℃,considering the influence of different steel strength grades and friction surface treatments.The slip load,ultimate load and failure mode at different temperatures are obtained.Combining numerical simulation technology,the variation ofpretension within bolt at elevated temperatures are theoretically analyzed,and a three-stage shear mechanism model is proposed.Based on the test and finite element analysis results,the design method of shear resistance of the bolted connection at elevated temperatures is proposed.(3)Cyclic loading tests of three beam-to-column joints are carried out,considering the influence of the axial compression ratio and the shape of the welding hole.The resistance,ductility,stiffness and energy dissipation are analyzed.A finite element model is developed and furher validated against the test results,and the effect of the behavior of panel zone on the whole performance of the joint is discussed.Based on the balance of the shearing yield in panel zone and the bending yield in beam,a strength and ductilitybased design strategy is proposed.The SHP steel and its use in structures are investigated herein at the levels of material,bolted connection and beam-to-column joint.It is indicated that the SHP steel has excellent performance in fire-resistance and seismic-resistance,and has strong comprehensive performance to meet the current requirements for seismic and fire design in accordance with national standards.At the same time,the research outcomes herein provide recommended values for the requirements of higher strength steel for fire resistance,as well as the fire-resistance matching between the bolt and the steel plate in the high-strength bolted connection,which contributes to further improve the performance-based design strategy as well as development of advanced steel. |
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