Content area
Abstract
The subject of this dissertation is the concept of preventing failures in long span structures. Recent collapses of long span structures have raised concerns in the minds of designers and contractors. Characteristics of long span structures which differ from those of simple and moderate spans have been frequently overlooked in design and construction procedures.
Recognizing problems evident in our past experience is the first stage of the study through a macroscopic study of occurrences and causes of structural failures in the past five years. Common trends and events that enabled the collapses and distresses of long span structures, as well as their relative comparison to other types of failures are identified. A more in-depth evaluation of sources of secondary stresses/factors as well as modes, sequence and causes of failure are conducted in the microscopic study. For this purpose, 22 cases have been reviewed, investigated, and analyzed.
Based on the above studies, institutional and procedural concepts to prevent failures in long span structures are presented in two categories. The first is improvements in design, construction and maintenance procedures. The subject encompasses design and loading criteria, design verification procedures, construction and post-construction monitoring, and interlinkages among parties involved in the building process.
The second category of preventive measures is the application of fault tree analysis. The fault tree diagrams illustrate the sequence and interrelationships of events contributing to the collapse of a structure. The qualitative analysis generates min cut sets, consisting of primary events illustrating possible "weak links" in the system. The application of this method in real example case is also presented.
In conclusion, while technical evaluations of past failure mechanisms of long span structures have enabled us to identify those events contributing to distresses and collapses, they also show these events have primarily stemmed from inadequacies in the design and construction procedures. Preventive measures should then be specifically directed to these procedural matters in order to efficiently reduce the number of failures of long span structures in the future.