Adaptive nonlinear modeling procedure for progressive collapse analysis of reinforced concrete frame structures
Date of Issue2017
School of Civil and Environmental Engineering
Due to increasing threats from terrorism in the past decades, progressive collapse modeling of buildings is gaining popularity with objective of simulating collapse process of the whole or partial structural system, in order to give useful insight to improve existing design for the structure against progressive collapse. In this thesis, a novel modeling framework for progressive collapse of reinforced concrete (RC) frame structures is proposed. A set of damage assessment criteria to identify and quantify flexural, shear and axial damages and failures of RC members is suggested. This set of damage criteria incorporates axial-shear-flexural interactions of the structure during the analysis and it is capable of tracing cracking and crushing of concrete, yielding and fracture of reinforcement as well as final failures of cross-sections within RC members. Direct member removal algorithm is developed to simulate the process of collapse at member level, based on combined flexural/shear/axial failures of RC members. With developing a specially designed searching scheme, a new algorithm to monitor substructure collapse is also proposed. Locations and magnitudes of impact loads of the collapsed partial structure are also identified and calculated, according to rigid-body kinematics and energy principle. In addition, inelastic and oblique impact effects are properly considered. To efficiently simulate progressive collapse of large-scale buildings, superelement technique which separates the structure into linear and nonlinear zones is employed to reduce the computational time. As buildings in progressive collapse may undergo large rigid-body rotations of the structure, a rigid-body rotation correction to improve conventional superelement formulation is proposed for a more accurate large deformation analysis using superelement. Further, in order to consider nonlinearity spread during progressive collapse analysis, an adaptive superelement algorithm to automatically identify the propagation of nonlinear zone and then update the definition of superelement is proposed. By incorporating direct member removal algorithms as well as model regeneration procedure, an efficient adaptive superelement modeling procedure is developed for progressive collapse of RC frame structures. Numerical examples are given to show the advantages and effectivity of the suggested damage criteria and modeling procedures, through comparison with the results obtained from physical tests or standard nonlinear finite element analysis.