Analytical and Experimental Investigation of the Effects of Member Deterioration on Seismic Response of Steel Frame Systems

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Until recently, steel frame buildings have been considered to be among the very best structural systems for use in regions subjected to earthquakes. However, the brittle fracture of many welding steel frame buildings as a result of the Northridge, Loma Prieta and other earthquakes in California, the serious damage, including collapse, of similar buildings during the Kobe Japan earthquake, and recent research have led many to question this assertion. Research has been initiated on the basic properties of steel weldments and connections. However, the impact of local fracture and strength deterioration on the overall performance of a system is still not understood.An integrative experimental and analytical assessment will be conducted in this project of the effects on overall system behavior of various forms of member strength deterioration. Models of two-dimensional frame systems representative of welded steel frame buildings are investigated to understand the relative contribution of various types of strength deterioration and ground motions on overall performance and to assess the effect of the dynamic redistribution of force caused by strength deterioration, and assess the role of system redundancy on global performance. Particular attention is directed at the consequences of (a) sudden loss of strength associated with brittle connection failures and (b) gradual deterioration of post-yield strength that may be associated with ductile response due to local buckling or lateral torsional buckling. Analytical studies will be conducted on a variety of framed systems. Shaking table tests with planer frame specimens made of replaceable plastic hinge regions which exhibit various forms of deterioration, including brittle fracture will be carried out and the test results will be integrated with analytical results to formulate designs recommendations.