The objective of the work described in this report was to analyze the global response of WTC 7 to initial failure events due to fire and to analyze the resulting sequence of component and subsystem failures to determine the events that led to the global collapse. The modeling approach began with collapse analyses of a multi-floor subassembly, leading to a global collapse analysis of WTC 7 using a model of the entire building. The floor model was used to test modeling methods and to test initiating event hypotheses. Experience from the previous WTC tower modeling effort was utilized to aid in modeling WTC 7. Steel material models formulated for the tower models formed the basis for those used in WTC 7. Also, meshing and model construction techniques were adapted from the tower models, where steel models from the WTC 1&2 analyses were modified wither thermally dependent properties to predict damage due to fire induced heating. Connection models were developed for the column-to-column connections as well as beam framing shear, moment, and seated connections that were used throughout the WTC 7 building construction. The WTC 7 finite element model used in the analyses was developed based on the original structural drawings as well as construction fabrication shop drawings for connections. The models included the primary structural components throughout the building, including exterior and core columns, floor framing beams and girders, floor slabs, column transfer truss structures, wind bracing truss members, and penthouse structures. A uniform finite element mesh was used throughout to provide the same level of fidelity in the entire structure. The global model contained approximately 3 million nodes and required approximately 8 weeks to process 25 seconds of simulated time, while using 12 processors in parallel. A model initialization sequence was developed to sequentially apply 1) gravity loads, 2) WTC 1 impact debris damage,and 3) fire induced temperatures.
Citation: NIST NCSTAR - 1-9
Pub Type: NIST Pubs
World Trade Center, WTC 7, progressive collapse, finite element analysis