Risk evaluation of steel frames with welded connections under earthquake

Numerous failures in welded connections in steel moment-resisting building frames (SMRF)<br />were observed when buildings were inspected after the 1994 Northridge Earthquake. These observations<br />raised concerns about the effectiveness of such frames for resisting strong earthquake ground motions.<br />The behavior of SMRFs during an earthquake must be assessed using nonlinear dynamic analysis, and<br />such assessments must permit the deterioration in connection strength to capture the behavior of the<br />frame. The uncertainties that underlie both structural and dynamic loading also need to be included in the<br />analysis process. This paper describes the analysis of one of approximately 200 SMRFs that suffered<br />damage to its welded beam-to-column connections from the Northridge Earthquake is evaluated.<br />Nonlinear static and dynamic analysis of this SMRF in the time domain is performed using ground<br />motions representing the Northridge Earthquake. Subsequently, a detailed uncertainty analysis is conducted<br />for the building using an ensemble of earthquake ground motions. Probability distributions for<br />deformation-related limit states, described in terms of maximum roof displacement or interstory drift, are<br />constructed. Building fragilities that are useful for condition assessment of damaged building structures<br />and for performance-based design are developed from these distributions.