In modular construction, individual modules are constructed at a controlled industrial environment before being transported to site. They are then connected horizontally and vertically to form a structure. The vertical connections can be achieved by welding or bolting the columns of stacked modules. This study investigates the seismic performance of modular steel-braced frames (MSBFs) connected vertically using superelastic shape memory alloy (SMA) bolts. The study also identifies the required locations of SMA connections, in a typical MSBF, to optimize its seismic performance in terms of maximum inter-story drift (MID), maximum residual inter-story residual drift (MRID), and damage scheme.

In modular construction, individual modules are constructed at a controlled industrial environment before being transported to site. They are then connected horizontally and vertically to form a structure. The vertical connections can be achieved by welding or bolting the columns of stacked modules. This study investigates the seismic performance of modular steel-braced frames (MSBFs) connected vertically using superelastic shape memory alloy (SMA) bolts. The study also identifies the required locations of SMA connections, in a typical MSBF, to optimize its seismic performance in terms of maximum inter-story drift (MID), maximum residual inter-story residual drift (MRID), and damage scheme.

Modular steel buildings (MSBs) are widely used for one to six storey schools, apartments, and similar buildings, where repetitive units are required. Modular units are first built and finished under a controlled manufacturing environment. They are then transported to the building site, where they are connected horizontally and vertically. The lateral load resisting system for MSBs usually relies on steel braced frames, which dissipate the seismic energy through steel yielding. This behaviour leads to residual drifts complicating the repair of seismically damaged buildings or rendering them as irreparable. Systems that can minimize the seismic residual drifts are thus needed. Superelastic Shape Memory Alloys (SMAs) have the ability to undergo large plastic deformations and recover them upon unloading. Their utilization in steel structures can significantly reduce seismic residual deformations, which will facilitate post-seismic retrofitting. The purpose of this study is to examine the seismic performance of modular steel braced frame (MSBF) that utilizes SMA braces. A six-storey buckling restrained MSBF was considered as a case study. Nonlinear dynamic analysis was conducted to compare the seismic performance of this MSBF when it is fitted with steel and SMA braces. The use of SMA braces was found to improve the seismic performance of MSBs in terms of maximum residual inter storey drift (MRID) and damage scheme.

The hysteretic characteristics of a structural system of a building must be well understood in order to effectively mitigate the damage caused by seismic activities. Modular steel construction is fast evolving as an effective alternative to traditional on-site construction, especially in low to medium-rise buildings where repetitive units are required. In this building form, modular units are built and finished under controlled environment and are combined on-site to form larger building structures. The lateral resistance of this steel building type is often achieved by adding diagonal braces but the detailing requirements differ significantly from the traditional counterpart. This may be critical to its performance under earthquake ground motions. In this study, key response and performance characteristics such as the available strength, stiffness, ductility, and energy dissipation in braced frames of modular steel buildings are evaluated under reversed cyclic loading. Comparison is drawn with the hysteretic behaviour of concentrically braced frames in regular steel buildings. The analysis suggests that the unique vertical connection of different units would need to be carefully addressed in design in order to fully develop the lateral seismic resistance of the modular steel braced system.

Contemporary seismic design is based on dissipating earthquake energy through significant inelastic deformations. This study aims at developing an understanding of the inelastic behavior of braced frames of modular steel buildings (MSBs) and assessing their seismic demands and capacities. Incremental dynamic analysis is performed on typical MSB frames. The analysis accounts for their unique detailing requirements. Maximum inter-story drift and peak global roof drift were adopted as critical response parameters. The study revealed significant global seismic capacity and a satisfactory performance at design intensity levels. High concentration of inelasticity due to limited redistribution of internal forces was observed.

Several studies have shown that the lateral response of concentrically-braced frames is dominated by the inelastic behavior of the bracing members. However, the overall performance of the entire frame depends on the frame configuration including its connections. In this study, the hysteretic characteristics of modular steel-braced frames under reversed cyclic loading are evaluated. The design and construction of the test specimen accounted for the unique detailing requirements of these frames. A regular concentrically-braced frame with similar physical characteristics was also tested for comparison. Both test specimens consisted of a one-storey X-braced system with tubular brace cross-section. This paper describes the behavior characteristics and provides a detailed comparison of the two systems to assess the strength, stiffness, inelastic force and deformation, and energy dissipation characteristics of the modular system. An analytical model capable of capturing the effect of the system’s unique detailing requirements is proposed and validated using the test results.

Modular Steel Buildings (MSBs) are fast evolving as an effective alternative to conventional on-site steel construction. An explanation of the concept of modular steel design, including its unique detailing requirements is given in this paper. The paper also focuses on a typical MSB floor system which is achieved by welding the webs of the stringers directly to the floor beams. A typical modular floor grid structure is designed using conventional methods. The floor is then modelled using the finite element method and analyzed under the effect of dead and live service loads. This allows an assessment of the effect of direct welding between stringers and floor beams on the analysis and design of floor beams, stringers, and welded connections. The results reveal that consideration of the true behaviour of direct welding leads to a distribution of forces and moments which is different from those found in conventional steel buildings. A simplified analytical model is proposed to capture such behaviour. Regression functions have been developed to describe the model. In practice, the proposed model can predict the actual forces and moments, leading to a reliable design of modular steel floors.

The seismic behavior factor, R, is a critical parameter in contemporary seismic design. In the 2005 edition of the National Building Code of Canada, the R factor consists of ductility related force modification factor, Rd, and overstrength-related force modification factor, Ro. The choice of these factors for design depends on the structural system type. In this investigation, typical braced frames of Modular Steel Buildings (MSBs) are designed and modeled. Nonlinear static pushover analyses are conducted to study the inelastic behavior of these frames. Structural overstrength resulting from redistribution of internal forces in the inelastic range, design assumptions, and strain hardening behavior of steel and displacement ductility are evaluated and their relationships with some key response parameters are assessed. The results show that the reserve strength of MSB-braced systems is greater than that prescribed by the Canadian code for regular braced systems. It also appears that R depends on building height, contrary to what has been prescribed in many seismic design codes. It is concluded that some unique detailing requirements of MSBs need to be considered during design to eliminate undesirable seismic response.

Structural overstrength and ductility are two key characteristics that affect a reasonable assessment of the vulnerability of a building to seismic events. Overstrength results from sources inherent in the structural system and its response mechanism under loading, as well as design assumptions and simplifications. Ductility on the other hand is tied to the inelastic characteristics of the structural system, such as energy dissipation and strength degradation. In this paper, these parameters are assessed for a braced frame of a four-storey modular steel building using nonlinear static analyses. The design of the frame, particularly of columns, considers two widely used assumptions/simplifications; the Square Root of the Sum of the Squares (SRSS) approach and the Direct Summation approach. Analytical modeling of the modular braced frame takes into account the unique detailing requirements of this structural system. The implication of the results obtained from the analyses to the design of modular steel building braced frames is presented.

Capacity design procedure for regular steel braced frames is reasonably established. For concentrically braced frames, the general implication is to allow the diagonal braces to yield and buckle while protecting other frame members and components from inelastic deformation. These frame members and components are therefore designed to support induced forces due to yielding and buckling braces. In this study, conventional capacity design procedure is adopted for the design of typical braced frames of Modular Steel Buildings. The SRSS approach of accumulating brace induced forces as well as the “Direct Summation” approach are both considered in the capacity design of their columns. The frames are modeled and analysed by the nonlinear static pushover method. The analyses results are verified against the expected behaviour based on the design philosophy. It is concluded that some unique detailing requirements of modular steel buildings need to be considered during design in order to avoid undesirable seismic response.

The Modular steel building technique is fast evolving as an effective alternative to conventional on-site construction. A modular steel building, while generally designed using conventional methods, is unique in its method of construction as a result of special connections and details required to facilitate lifting and other construction handling operations. An analytical investigation using the finite element method is conducted on a stringer-to-beam connection of a typical floor-system of a modular steel school, designed using the Canadian steel design code. The results of the analysis revealed a number of issues that would need to be considered in any reliable prediction of structural response of modular steel floor framing. The rigidity of the connection partially restrains the rotation of the supported beam. This leads to force distribution between adjoined beams different from the case in conventional steel construction. Observations made from these results are expected to be incorporated into design guidelines that can be used by designers for an optimal design of modular steel buildings.