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Secondary structures are the members that are not part of the primary load-bearing components in a structural system. Although not intended to bear loads, secondary structures could be subjected to earthquake loading that may lead to failures. Damage to secondary structures could pose significant threats to life safety, prevent buildings from functioning and result in major economic loss. During past decades, a considerable amount of research efforts has been dedicated to develop rational approaches for seismic analysis of secondary structures. This paper aimed to assess these developments to today's knowledge as a reference for more accurate design. The review began with a brief description of the response characteristics of secondary structure under seismic loading, especially focusing on the factors that influence the responses. An appraisal of current numerical and experimental analysis methods of secondary structure is presented. Results from experimental work are used to validate the reliability of floor response spectrum and current design provision. Finally, an outlook of future possible research direction for more realistic design of secondary structures is given.

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In current seismic design, earthquake-induced forces in secondary structures are estimated from the acceleration of the primary structure at the support of the secondary structure. However, recent studies had shown that the response of the secondary structure can significantly affect that of the primary structure, which will simultaneously modifies that of the secondary structure. To accurately estimate the response of the secondary structure, the interaction at the interface of the two structures needs to be considered. In this study, a scaled model consisting of primary and secondary structures was designed to capture the interacting forces. The degree of fixity of the secondary structure was varied. Two types of dynamic loading, that is, impact and harmonic loads, were applied to the model structures. The relationship between the interacting force and the response of the secondary structure is discussed. Empirical formulae for predicting the maximum displacement of the secondary structure based on the displacement spectrum at its base were proposed. The formulae provided more accurate prediction of the top displacement of the secondary structure considered, in comparison with that obtained from a conventional floor response spectrum.

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