Progressive collapse analysis of four existing reinforced concrete buildings using linear procedure

ABSTRACT: Progressive collapse occurs when local failure in a structural element spreads to the adjoining members, this might promote additional failure. The damage will propagate till the structure reaches to new static equilibrium configuration. Otherwise, entire collapse will happen. On the other hand, local damage in the structural system will be arrested if the facility has an adequate design to bridge over the damage and redistribute the loads. In general, buildings are designed to resist the normal anticipated loads like gravity, occupancy, wind and seismic. However, some structures occasionally are being exposed to unforeseen loads due to natural, man-made, intentional or unintentional reasons. These unexpected loads induce progressive collapse event. In the last few decades several catastrophic events were occurred. Those accidents have instigated vital debate amongst the structural engineering society in respect to the structural behavior under abnormal loading situations, such as collision, intense fire and explosion. Consequently, numerous studies have been conducted to improve the structural performance against extreme load hazards and progressive collapse phenomenon. These investigations proposed many suggestions to design and assess the new and the existing buildings in order to survive such unpredicted incidents and assure life safety of the occupants of those buildings. More concern was given to structures that are prone to progressive collapse event, such as military and federal offices besides skyscrapers. The recommendations have been specified by several researches and codes related to the progressive collapse issue, such as British Standard, Eurocode, ACI and AISC were not sufficient to prevent the disproportionate collapse since it is not easy to predict the spread of progressive collapse and the structural behavior under various triggered events in their sort and magnitude. Nevertheless, two governmental agencies in the United States have released detailed guidelines to mitigate the likelihood of progressive collapse. First document was published by the United States General Service Administration (GSA) in November 2000 and revised in June 2003. It was entitled “Progressive collapse analysis and design guidelines for new federal office buildings and major modernization projects”. The second guideline was the UFC 4-023-03 (DoD, 2010). In this research DoD 2010 labeled as “Design of Buildings to Resist Progressive Collapse” that was issued by the United States Department of Defense has been followed as a guideline to analyze and re-design the case study buildings. This document addresses the numbers and locations of the removed column according to the alternate load path method (sudden column loss). It stipulates that a column should notionally be removed from the middle of the short side, middle of the long side and from the corner of the building. Yet, it did not declare which one from the three cases is the most significant besides the influence of the building height. As a result, the prime objective of this study is to find out the impact of the building height and the most critical location of the removed vertical-support element. In order to accomplish this, four existing apartments have been selected. They are located in Famagusta, Northen Cyprus. Two of them have four-stories and the other two have eight-stories. Additionally, Linear static analysis of the three-dimensional (3-D) computer models of each selected building was carried out by using SAP2000 program. The failed members were identified and re-designed. Ultimately, observations from this research demonstrate that the increase in the height of the structure and the removal of column from the middle or near the middle of the short side of the building is more significant to progressive collapse event. …………………………………………………………………………………………………………………………………………………………………………………………………………