We report on a simulation study of the performance of the North Tower (WTC-I) of the World Trade Center complex during the impact of American Airline Flight 11, on September 11, 2001. We discuss impact damage the structural core might have sustained and its possible behavior under structural and thermal loading. Our simulations indicate that the worst damage to the core structure was in stories 95 through 97 of the tower. We estimate that a core collapse mechanism could be initiated if the tower core column temperatures were elevated to about 700 o C.
SUMMARYA general framework for multi-criteria optimal design is presented which is well suited for performancebased design of structural systems operating in an uncertain dynamic environment. A decision theoretic approach is used which is based on aggregation of preference functions for the multiple, possibly con#icting, design criteria. This allows the designer to trade o! these criteria in a controlled manner during the optimization. Reliability-based design criteria are used to maintain user-speci"ed levels of structural safety by properly taking into account the uncertainties in the modelling and seismic loads that a structure may experience during its lifetime. Code-based requirements are also easily incorporated into this optimal design process. The methodology is demonstrated with a simple example involving the design of a three-storey steel-frame building for which the ground motion uncertainty is characterized by a probabilistic response spectrum which is developed from available attenuation formulas and seismic hazard models.
Several school buildings were surveyed in the disaster areas of the Marmara (17 August 1999, [Formula: see text]), Düzce (12 November 1999, [Formula: see text]), and Bingöl (1 May 2003, [Formula: see text]) earthquakes in Turkey. Among them, 21 reinforced concrete buildings were found to have an identical floor plan. Lateral load resisting structural system consisted of reinforced concrete frames (moment-resisting frame) in 16 of the buildings and structural concrete walls integrated with the moment-resisting frame (dual system) in the remaining five buildings. The number of stories above ground in these buildings ranged from two to four. These school buildings provide a nearly ideal test of the effect of a single important structural characteristic on the performance of buildings with structural designs that are uniform in all other respects. Our observation is that the presence of structural walls improves the behavior of reinforced concrete systems drastically.
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