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Reference Structural Models and Baseline Performance Analysis of the World Trade Center Towers. Federal Building and Fire Safety Investigation of the World Trade Center Disaster.


pdf icon Reference Structural Models and Baseline Performance Analysis of the World Trade Center Towers. Federal Building and Fire Safety Investigation of the World Trade Center Disaster. (6880 K)
Faschan, W. J.; Garlock, R. B.

NIST NCSTAR 1-2A; 230 p. September 2005.

Keywords:

World Trade Center; high rise buildings; building collapse; disasters; fire safety; fire investigations; terrorists; terrorism; structural models; columns; floors; gravity; wind load; performance evaluation; structural analysis

Abstract:

This report establishes the baseline performance of the North and South World Trade Center Towers (WTC 1 and WTC 2) under design gravity and wind loading conditions. Baseline performance results include basic information about the towers behavior under design loading conditions. These include total and inter-story drift under wind loads, floor deflections under gravity loads, demand/capacity ratios for the primary structural components of the towers, exterior columns response (shear lag effects and presence of tensile forces), performance of connections, and resistance of the towers to shear sliding and overturning. The primary tasks that were undertaken to establish the baseline performance include the following: (*) Development of structural databases of the primary components of WTC 1 and WTC 2 towers. These electronic databases were developed from original computer printouts of the structural design documents, including modifications made after construction. The task included the scanning and digitization of the original drawing books, a four-step quality control procedure, cross section property calculations, and development of the relational databases to link the generated database files into a format suitable for the development of the structural models. (*) Development of reference structural analysis models that capture the intended behavior of each of the two towers using the generated databases. These reference models were used to establish the baseline performance of the towers and also serve as a reference for more detailed models for other phases of the investigation, including aircraft impact damage analysis, and thermal-structural response and collapse initiation analysis. The main types of models developed were: Two global models of the major structural components and systems for the towers, one each for WTC 1 and WTC 2. The models included all primary structural components in the towers, including exterior walls (columns and spandrel beams), core columns, exterior wall bracing in the basement floors, core bracing at the mechanical floors, core bracing at the main lobby atrium levels, hat trusses, and rigid and flexible diaphragms representing the floor systems. One model each of the typical truss-framed floor (floor 96 of WTC 1) and typical beam- framed floor (floor 75 of WTC 2). The models included all major structural components in the floor system, including primary and bridging trusses, beams, strap anchors and horizontal trusses, concrete slabs, and viscoelastic dampers.