Seismic performance and failure mechanisms of infilled RC frames : numerical simulation and theoretical modelling

Abstract

Reinforced concrete infilled-frame structures are recognised as amongst the most common structural forms of buildings in the world. Although this structural form has been adopted for buildings for many years, it has been extensively reported that in every single disastrous earthquake during the past decades relatively poor seismic performance and severe damage of a considerable amount of concrete infilled-frame buildings, including many newly designed ones, were observed, particularly in the 1999 Izmit earthquake in Turkey and the 2008 Great Sichuan earthquake in China. It has revealed that inherent problems relating to the design and analysis methods of reinforced concrete infilled-frame buildings are not yet solved. The primary objective of the research presented in this thesis is to investigate thoroughly the seismic behaviour and performance of reinforced concrete infilled-frame structures under realistic three-dimensional loading conditions with consideration of the infill effects. Extensive numerical and computational investigations are conducted to assess the seismic performances and identify the vulnerabilities of infilled reinforced concrete frame buildings. The development of analytical models is strictly based on scientific approaches in order to retain the generality and applicability of the of analysis results. A discrete modelling approach for infilled RC frame structures is firstly developed and verified. The approach employs the surfaced-based interaction modelling technique to simulate the mixed-modes of fracture, crack propagation, post-fractured behaviour and finite sliding and separation of the bonded surfaces behaviour of mortar joints. A series of thorough investigation on the structural behaviour of masonry-infilled RC frame structures under seismic effects are performed. The dynamic characteristic, vulnerabilities, hysteresis behaviour, local infill/frame interaction, failure mechanisms and force transfer mechanisms of RC frames infilled with regular or irregular arranged masonry infill panels of different configurations and anchorage conditions are rigorously studied by nonlinear response analyses with the discrete modelling method. Based on the study results, comprehensive design recommendations, special considerations and performance criteria to mitigate and identify the vulnerabilities of reinforced concrete infilled frames to seismic effects are developed and proposed. Although the discrete approach successfully replicates varied nonlinear and complex structural behaviour under different loading patterns, high computational effort and the complicated model assembly of the discrete modelling approach may inhibit it in routine design utilisation for high-rise infilled frame structures. Therefore, addressing the need of a modelling approach that can save computational time, yet model assembly efforts, and is able to retain sufficient accuracy in macroscopic response analyses of infilled frame structures, a continuum model based on the Fourier-based incremental homogenisation strategy is successfully developed and verified. The continuum model can be an effective analysis tool for further research on infilled RC frame structures provided that the detailed local responses of infill materials are of less interest than the macroscopic structural responses. The contributions of the research are as follows: (1) from an academic point of view, the research fill in the blank areas in the research field of infilled frames through comprehensive investigation of the local infills/frame interaction and the global dynamic characteristics of infilled RC frame buildings under seismic excitations. The proposed modelling techniques/methods of infilled frames are derived and verified based on rigorous and scientific approaches, which can be applied to different complicated analysis problems of infilled frames; (2) from a practical point of view, the proposed analysis tools, results and design recommendations of the study presented in this thesis are also expected to provide crucial guidance for designing safer and better-performing frame buildings with infills under seismic effects in many countries and regions in the world, including Hong Kong, which has recently been classified as a region of moderate seismicity on the national earthquake zoning map, that are threatened by earthquake disasters.

Date of Award	2012
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology