Seismic Performance and Failure Mechanisms of Infilled RC Frames: Numerical Simulation and Theoretical Modelling

Reinforced concrete infilled-frame structures are recognised as amongst the mostcommon structural forms of buildings in the world. Although this structural form has beenadopted for buildings for many years, it has been extensively reported that in every singledisastrous earthquake during the past decades relatively poor seismic performance and severedamage of a considerable amount of concrete infilled-frame buildings, including many newlydesigned ones, were observed, particularly in the 1999 Izmit earthquake in Turkey and the2008 Great Sichuan earthquake in China. It has revealed that inherent problems relating tothe design and analysis methods of reinforced concrete infilled-frame buildings are not yetsolved. The primary objective of the research presented in this thesis is to investigatethoroughly the seismic behaviour and performance of reinforced concrete infilled-framestructures under realistic three-dimensional loading conditions with consideration of the infilleffects. Extensive numerical and computational investigations are conducted to assess theseismic performances and identify the vulnerabilities of infilled reinforced concrete framebuildings. The development of analytical models is strictly based on scientific approaches inorder to retain the generality and applicability of the of analysis results. A discrete modelling approach for infilled RC frame structures is firstly developed andverified. The approach employs the surfaced-based interaction modelling technique tosimulate the mixed-modes of fracture, crack propagation, post-fractured behaviour and finitesliding and separation of the bonded surfaces behaviour of mortar joints. A series of thorough investigation on the structural behaviour of masonry-infilled RCframe structures under seismic effects are performed. The dynamic characteristic,vulnerabilities, hysteresis behaviour, local infill/frame interaction, failure mechanisms andforce transfer mechanisms of RC frames infilled with regular or irregular arranged masonryinfill panels of different configurations and anchorage conditions are rigorously studied bynonlinear response analyses with the discrete modelling method. Based on the study results,comprehensive design recommendations, special considerations and performance criteria tomitigate and identify the vulnerabilities of reinforced concrete infilled frames to seismiceffects are developed and proposed. Although the discrete approach successfully replicates varied nonlinear and complexstructural behaviour under different loading patterns, high computational effort and thecomplicated model assembly of the discrete modelling approach may inhibit it in routinedesign utilisation for high-rise infilled frame structures. Therefore, addressing the need of amodelling approach that can save computational time, yet model assembly efforts, and is ableto retain sufficient accuracy in macroscopic response analyses of infilled frame structures, acontinuum model based on the Fourier-based incremental homogenisation strategy issuccessfully developed and verified. The continuum model can be an effective analysis toolfor further research on infilled RC frame structures provided that the detailed local responsesof 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, theresearch fill in the blank areas in the research field of infilled frames through comprehensiveinvestigation of the local infills/frame interaction and the global dynamic characteristics ofinfilled RC frame buildings under seismic excitations. The proposed modellingtechniques/methods of infilled frames are derived and verified based on rigorous andscientific approaches, which can be applied to different complicated analysis problems ofinfilled frames; (2) from a practical point of view, the proposed analysis tools, results anddesign recommendations of the study presented in this thesis are also expected to providecrucial guidance for designing safer and better-performing frame buildings with infills underseismic effects in many countries and regions in the world, including Hong Kong, which hasrecently been classified as a region of moderate seismicity on the national earthquake zoningmap, that are threatened by earthquake disasters.