This thesis is concerned with the modelling, behaviour and design of steel-concrete composite members and moment frames under seismic loading conditions. Such composite structures offer various behavioural and constructional advantages over their bare steel and reinforced concrete counterparts. In particular, the enhanced mechanical properties of composite members enable the use of floors with larger spans and reduced depths compared to other structural systems. Although numerous previous studies have investigated the behaviour of typical steel and reinforced concrete systems, composite frames have received much less attention due to the inherent complexities involved in their modelling and response assessment. For composite members and frames, various simplifications and idealisations are therefore typically employed in current analysis and design procedures. Importantly, there is a need for improved understanding and quantification of the inelastic cyclic response of composite members with due account for inherent degradation phenomena. To this end, this research aims to provide detailed studies into the inelastic cyclic behaviour of composite members and moment frames. The work includes the development of representative and computationally efficient nonlinear cyclic models for composite members consisting of steel members and reinforced concrete slabs. These models are then employed to provide detailed insights into the influence of key structural parameters and ground motion characteristics on the response of composite moment frames designed to European seismic design code provisions.
The research presented in this thesis is divided into two main parts. The first part involves the development of detailed continuum models that can simulate the asymmetric behaviour and cyclic degradation characteristics of composite members. These models are then employed in detailed parametric assessments in order to investigate and quantify the influence of key geometric and material properties on the inelastic cyclic response. Nonlinear relationships for modelling the response of composite members are proposed and can be used in nonlinear static pushover analysis and simplified cyclic modelling. The synthetically generated database from the parametric studies is also utilised for the calibration of uniaxial lumped plasticity models, with cyclic degradation, and which are suitable for computationally efficient frame analysis.
In the second part of the research, the seismic response of composite frames designed to European code provisions is examined by means of nonlinear analysis incorporating the calibrated degrading model. The behaviour is evaluated using detailed nonlinear static pushover procedures as well as dynamic response history analyses, with particular focus on the assessment of global and inter-storey drift demands. The study includes a set of 25 composite moment frames with various numbers of storeys and structural properties, and the loading includes a suite of 56 ground motion records which are used in incremental dynamic analysis. In addition to providing detailed insights into the key inelastic cyclic response characteristics of composite structures, the nonlinear frame analysis results are used to assess the global and local drift demands under realistic seismic loading conditions. The implications of the results of this research on typical design and assessment procedures adopted in practice are discussed. Finally, the thesis concludes with a summary of the main observations and findings of the research as well as suggestions for future work in related areas.