Research On The Damage Behavior And Calculation Model Of Welded Connections In Steel Frames Under Earthquakes

The steel moment resisting frame is widely used in high-rise buildings asits higher strength, better aseismic performance and easier manufacturecompared to the concrete structure. However, in Northridge and Kobeearthquake a number of welded connections in steel frames were found crackingat welds, resulting in the frame damage or collapse. A majority of the researcheson steel welded connections focus on the materials and construction detailsrather than the damage theory and calculation method, so the influence of theconnection damage is hardly taken into account in the aseismic design ofhigh-rise steel buildings.In this paper, two tests focusing on welds and full-scale connectionsseparately are conducted. The damage mechanism and finite element analysismethodology are studied. Finally a simplified calculation model is proposed forthe damage process of the welded connections. The main contents aresummarized as follows:1.20specimens originating from the welding zone of the bottom beamflange are tested under monotonic and cyclic loads, studying the influences ofthe material strength, geometry parameters and loading procedures on theconnection damage behavior.2. The finite element analyses are used to investigate the crack mechanismof the connection welds and the damage evolution equation based on the plasticstrain is proved to be credible.3.9full-scale welded flange-bolted web connections are tested undercyclic loads to investigate the effects of different loading procedures and peakloads for connection damage. The damage characters are concluded and threetypes of damage models are used to analyze the test results.4. Based on the metal ductile tearing theory, the "effective plastic strain" isproposed to describe the connection damage behavior. The evolution equationfor connection damage under cyclic loads is derived.5. The finite element method analyzing the connection cracking anddamage process under cyclic loads is proposed and the subroutine used inABAQUS is developed. The finite element analyses are checked by the testresults. 6. The indicator "effective plastic rotation" is proposed for the simplifiedmodel of welded connections based on the effective plastic strain. Thesimplified model for backbone and hysteretic curves of connections is derivedand verified with other experimental data. The comparison between thecalculation results and test data reveals that the damage model proposed in thispaper is favorable for predicting the damage behaviors of welded connectionsunder cyclic loads.7. A method for the non-linear dynamic analyses of steel frames usingdamage model of weled connections is explored and verified. The subrountie isdeveloped based on the damage model proposed in this paper.