Quantification of seismic performance factors for modular corner-supported steel bracing system

Modular construction, using steel corner-supported modular units, is an impressive and environmentally friendly construction technique. It leverages off-site factory-controlled fabrication of volumetric units, including beams, columns, braces, and their intra-connections, as well as their on-site assembly through the use of so-called inter-connections, to form a building as a whole. The seismic detailing of both inter-connections and intra-connections deviates from current seismic design provisions, thereby affecting the seismic behaviour of a modular structure as a whole. Despite their widespread application, seismic design and detailing of corner-supported modular structures mostly relies on the available provisions, adopted for traditional lateral load-bearing systems due to their limited research data available. This paper aims to evaluate the seismic performance factors of modular corner-supported steel bracing systems using a rational nonlinear simulation technique. A nonlinear mathematical model which simulates the stiffness/strength deteriorated and pinched hysteretic response of both intra-connection beam-column elements and braced elements is adopted according to available data in literature, whereas the capacity-protected behaviour is assumed for inter-connections. The modelling technique is implemented into nonlinear mathematical models of corner-supported modular steel buildings with four, eight, and twelve storeys. A parametric study is firstly performed to evaluate the influence of inter-connection stiffness parameters on the nonlinear response of the structures. A set of incremental dynamic analyses is secondly conducted to generate data required to quantify seismic performance factors. The results are finally compared with the seismic performance factors recommended by the ASCE/SEI standard for code-approved connections. It is found that a static overstrength factor is close to 2.5 for the four-storey building whereas for taller buildings lower values than 2.5 is achieved. However, the dynamic overstrength factor showing inelastic force redistribution due to dynamic loading achieves values well above 2.5 regardless of building heights. Further, the response modification coefficient of 9.5 is suggested for braced corner supported modular systems which is well above the value for the equivalent code-specified system.