Blast Resistant Design Of R.C.C. Structure

Abstract

In modern days many civilian structures need shielding against blast effects. Past incidences of terrorist activities have increased the awareness towards the structural design to mitigate the effect of explosion and prevention of collapse of the building. The objective of blast resistant design is to prevent the collapse of the structural system and to maintain structural integrity through ductile and redundant behavior. The aim of present work is to study the effects on building due to blast and to study progressive collapse potential of reinforced concrete building designed for gravity loading only and building designed for seismic loading. Present study includes the structural and non structural aspects for blast resistant building. Depending on building dimensions and blast load parameters, blast pressure on each face of the rectangular building is calculated. Blast load parameters includes scaled distance, peak overpressure, peak reflected pressure, and positive phase duration. The comparison of blast overpressure suggested by different authors is presented. The calculation of blast load on the faces of the building, as per ASCE manual for petrochemical buildings and IS 4991 criteria for blast resistant structures for explosion above ground is included in this work. Progressive collapse analysis method and criteria to be considered for analysis as given by the U.S. General Services Administration (GSA) are discussed. The key aspect of structural design to resist blast effects is to mitigate progressive collapse. To avoid progressive collapse three methods are available like indirect method, specific local resistance method and alternate load path method. One symmetrical four storey and ten storey building are studied for progressive collapse analysis. Evaluation of progressive collapse potential of gravity designed building and building designed for seismic loading is carried out using linear static, linear dynamic and nonlinear static analysis. Progressive collapse analysis is performed using SAP2000. In progressive collapse analysis guidelines of the U.S. General Services Administration (GSA) are followed. The comparison of linear static and linear dynamic analysis procedures for progressive collapse is carried. The demand capacity ratios found using linear IV static analysis are compared with the demand capacity ratio (DCR) calculated from linear dynamic analysis at all storey. The displacement at the column failure point, as obtained from static analysis and dynamic analysis are compared. Nonlinear behaviour can significantly affect the progressive collapse behaviour of a structure since before reaching the collapse condition a structure and its member components must have exceeded its elastic limits. Nonlinear static analysis is performed for gravity designed building and building designed for seismic loading. Comparison of DCR calculated from linear static analysis procedure with the sequence of hinge formation as obtained from nonlinear static analysis are carried out. The content of major project is divided in to various chapters. Chapter 1 includes general introduction of blast load and progressive collapse. Chapter 2 gives review of literature about blast resistant design. Parameters affecting blast load, blast load calculation as per ASCE guidelines and IS 4991 are presented in chapter 3. Chapter 4 discusses various analysis methods considering blast loading and progressive collapse analysis. Chapter 5 deals with the linear static progressive collapse analysis of the symmetrical building. Comparisons of linear dynamic (time history) analysis and linear static analysis for the symmetrical framed building are presented in chapter 6. Chapter 7 includes comparisons of linear static and nonlinear static approaches. Summary, conclusion and future scope of work is included in Chapter 8.