Evaluation of Progressive Collapse Resistance of High Rise Building with Different Structural Systems

Abstract

Structural safety has always been a key concern responsible for the design of civil en- gineering projects. One of the mechanisms of structural failure that has accumulated increased attention over the past few decades is referred to as progressive collapse. Progressive collapse of building structure is initiated when one or more vertical load carrying members particularly columns are seriously damaged or collapse during any of the abnormal loads i.e. vehicle impact, fare, earthquake, or other man-made or natural hazard. As a result, a substantial part of the structure may collapse, causing greater damage to the structure than the initial impact. Thus it is necessary to pre- vent progressive collapse of the building structure. The aim of present study is to evaluate the progressive collapse resistance of multi storied building with different structural systems. Various causes for progressive col- lapse are presented. After the collapse of the World Trade Center (WTC) Tower many government and private authorities worked on developing design guidelines for progressive collapse resistant structures. Among all the guidelines the U.S. General Service Administrator (GSA)and Department of Defense (DoD)are most widely used by structural engineers. Various criteria to be considered to perform progressive col- lapse analysis as specified in these guidelines are discussed. These guidelines have suggested three different analysis methods. Comparison between these two guidelines is also presented. Complete analysis and design of 10-storey concrete building is presented. A regular

oor plan of 20 m x 16 m is considered. Linear static analysis is performed using analysis program Midas Gen-2012. The DCR (Demand Capacity Ratio) is calculated using linear static analysis. It is important to mitigate the vulnerability of progres- sive collapse if building is having high potential of progressive collapse. To reduce the progressive collapse three types of structural systems are explored i.e. bracing at top storey level of the building, bracing at side face of the building and bracing at top storey level and side face of the building. The DCR (Demand Capacity Ratio) is calculated using linear static analysis and compared with different structural systems. Also, displacement is compared with different structural systems. For 10-storey building DCR in case of exure exceeds the permissible limit of 2.0 in case of GSA and UFC load case which reveals that beams are not safe in exure as per GSA guidelines and UFC guidelines. Also, DCR in case of shear exceeds the permissible limit of 1.0 in case of UFC load case which reveals that beams are safe in shear as per GSA guidelines but fails as per UFC guidelines.Demand capacity ratios for column exceed the allowable limit of 1.0 at bottom two to four stories.Displacement under column removal point for GSA loading and UFC loading is compared for all the cases and case 4 of column removal creates worst effect on the building structure. The three alternative structural systems are presented from which provision of bracing at top storey level and side face of the building is most economical solution to reduce the potential of progressive collapse.