Journal of Performance of Constructed Facilities

This paper summarizes a structural evaluation of the posttensioned floor lift slabs of L'Ambiance Plaza, Bridgeport, Connecticut. The evaluation has been conducted to investigate, among other factors, the effect on slab stresses of the unorthodox horizontal splay of posttensioned tendons around column 4.8E and the effect of shear wall openings that existed during the lifting operation, for ideal lifting conditions (slab perfectly level), and for scenarios less than ideal. Initially, hand computations are made using simplified beam models to examine two areas of the west‐tower slab design that appeared particularly suspicious. Those computations reveal that a more refined stress analysis is warranted. To investigate the slab stresses more precisely, linear elastic finite element analyses of a typical west‐tower floor slab are conducted. Results from the analyses indicate that the anomalous layout of the posttensioning tendons in the west tower could be considered a possible cause that triggered the failure or, at a minimum, was clearly a factor in the propagation of the collapse after it had begun. The inclusion of nominal amounts of auxiliary bonded mild reinforcement (structural integrity steel) in the bottom of the slabs, continuous through the column strips, might have confined the slab failure, assuming the column supports and jacks could sustain the redistributed load.

Investigations of the collapse of the partially completed L'Ambiance Plaza, a 16‐story residential project under construction in Bridgeport, Connecticut, revealed four major structural deficiencies that may have triggered the collapse, along with at least five other design or construction conditions that negatively impacted structural reliability. The major deficiencies were: improper drape of posttensioning tendons adjacent to elevator openings, overstressed concrete slab sections adjacent to two temporary floor slots for cast‐in‐place shear walls, overstressed and excessively flexible steel lifting angles during slab lifting, and unreliable and inadequate temporary slab‐column connections to assure frame stability. The existence of so many deficiencies in one project raises fresh concern whether public safety is being adequately protected in the U.S. system for design and construction of major buildings. This project used a design concept that transferred major design responsibilities to the contractor via performance specifications, permitted construction procedures that were not backed up by proof of adequacy for temporary conditions, and provided quality‐assurance measures that did not include adequate review by the engineer of record. These system deficiencies led to the collapse. Recommendations for improving U.S. regulatory and structural design practice to help avoid future disasters like L'Ambiance Plaza are given.

During the past 30 years, the use of thin marble panels as building cladding has increased markedly, but there have been many costly durability problems associated with this nontraditional cladding material. The writers present a historical overview of the mechanical and chemical durability of marble. Results dating from the 1800s, from the first scientific research on the properties of marble, are reviewed. Available guideline references for marble cladding design and detailing are cited. The influences of chemical reactions and temperature cycles on marble durability are outlined. A standard definition of durability is presented, and its relationship to persistent time‐dependent problems is discussed. Some of the theories and alleged causes for one of the more publicized durability problems, permanent out‐of‐plane bowing of thin marble cladding panels, are given. State‐of‐the‐art knowledge with respect to permanent bowing is summarized. The need for further research is stated. The paper concludes that there is a need to examine marble cladding design as an engineering problem in the area of structural mechanics and material.

A unique structural system was constructed to enclose an existing football stadium at the University of Idaho, Moscow. Shortly after completion the roof began to leak, allowing the establishment of a serious strength‐reducing decay fungus in the structural wood components. This paper reviews the initial attempts to correct the leakage, the problems associated with determining the cause, and the subsequent replacement of the entire 4 acres (1.62 ha) of roof covering. The actual cause of the roof's failure to keep out water was never determined, though the new roof was designed to correct either a condensation problem or a point‐source leak in the exterior membrane. The initial cost of construction was $4,160,000, and an additional $2,120,000 was spent to replace the roof. The high cost for replacement of the unsatisfactory roof system illustrates the need to include an inspection or monitoring program for facilities that utilize new methods of construction or untested materials.

The performance of orthotropic steel bridge decks in North America is investigated, and the performance of the wearing surface of these bridges is the focal point of the study. Concrete deck deterioration has become a national concern in the past few years. Orthotropic steel decks have a relatively long life span and are generally economical to maintain. Because of higher initial costs and lack of performance data, their use has not been widespread. Twelve bridges with orthotropic decks in the U.S. and Canada were studied through a questionnaire survey and telephone interviews with the responsible authorities. It was found that steel decks require very little maintenance. Furthermore, corrosion of steel and fatigue of welded connections have not created major problems. Surface overlay has performed relatively poorly in some instances, especially under adverse weather conditions. It was found that adverse climate, excessive deck flexure, excessive traffic loads, and poor paving procedures were the main causes for the problems associated with the wearing course performance.