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.
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.
