Journal of Performance of Constructed Facilities

On February 26, 1993, a bomb explosion rocked the World Trade Center complex in New York City—killing six, injuring over one thousand people, casting tens of thousands into a life‐threatening situation, and causing hundreds of millions of dollars in damage. This paper is a personal account of what happened to eight people who, unaware of the catastrophe, found themselves trapped in a smoke‐filled express elevator for over three hours. The elevator was located in One World Trade Center, one of the two 110‐story‐tall towers in the complex. The paper describes the circumstances that brought the eight people together, the emergence of a leader and the efforts he marshaled to assure survival of the group in the hostile environment, and the events following the rescue, and provides a follow‐up of how the explosion affected the lives of some occupants in the following days. The account emphasizes the human‐interest aspects of the event and is not meant to be an objective or a technical report.

On Friday, February 26, 1993, a van loaded with explosives entered the underground parking garage of the World Trade Center. The van was parked on the B2 underground level, next to the south wall of Tower A. At 12:18 p.m., the van exploded, instantly destroying a large portion of the garage under the Vista Hotel, blasting out a 38‐mm (1.5‐in.) thick steel double‐tee tower cross brace, and sending $44\times {10}^3\mathrm{kN}$ (5,000 tons) of debris crashing onto the heating and refrigeration plant for the World Trade Center complex. Evacuation of the complex commenced, with some office workers making their way down the smoke‐filled stairs while others were trapped in elevators until rescued. Structural damage assessment, emergency repairs, and construction of temporary supports began soon after the explosion.

To quantify the global damageability of a structure, the weighted‐average function defined in terms of damage condition and the importance or weightages of structural elements has generally been used in literature. Judgment of structural importance of a structural element is a difficult task. The opinion provided by experts could have different perspective or bias, which may reflect in the overall assessment process. Structural analysis being precise these days, structural importance of a member could be realistically estimated using standard structural procedures. In this paper it is proposed that the weightage computation could be linked to damage sensitivity of the element response. It is argued that the weighted‐average computation based on damage sensitivity is a more realistic index for integrity assessment. In this perspective, the concept of damage sensitivity and its computational aspects based on the finite‐element method are also presented. Finally, examples of weighted‐average computation comprising fuzzy sets and importance factor obtained from normalized damage sensitivity are illustrated.

The paper describes a case history of severe damage to a house due to the settlement of fill containing organic matter. As the organic matter in the fill decomposed, the house settled, causing 10 cm. (4 in.) of foundation differential movement. The fill settled so much that open voids developed beneath the footings and the rear yard flatwork. One‐dimensional compression tests were performed on soil samples with different percentages of organic matter, where the organic matter was allowed to decompose, and the corresponding settlement was measured. The laboratory tests indicate an empirical relationship in which percent organics equals percent settlement, for a condition of complete decomposition. The amount of settlement was similar for organic matter distributed throughout the sample or placed as one layer at the center. The detrimental effects of organics in fill include a reduction in soil density, increased compressibility during loading, and time dependent settlement as the nonhumic substances decompose and compress.

The use of cohesive soils in geogrid‐reinforced backfills requires consideration of the performance of these materials under both as‐compacted and long‐term conditions. Depending on the as‐compacted conditions, the long‐term performance, as a result of in service saturation, can lead to strength loss and failure of such structures. This paper documents the case history of a geogrid reinforced retaining wall, constructed with cohesive backfill, that failed. Several different failure modes were observed along the wall. The results of extensive field and laboratory testing programs and engineering analyses to investigate the causes of failure are presented. These studies permit the different observed failure modes to be explained. Deficiencies in design and construction quality control are identified. The need for site‐specific design considerations rather than generic design procedures for such structures is demonstrated.