Experimental study on interior connections in modular steel buildings

Highlights

• An innovate interior connection design for modular steel buildings was proposed.

• The connection consists of the plug-in device and beam-to-beam bolted systems as horizontal and vertical connecting parts.

• The proposed connection design can solve working access problems at inner connecting regions.

• Static uniaxial loading tests, quasi-static cyclic loading tests and finite element analyses were performed.

• Deforming pattern, mechanical mechanisms, and effect of connection details were compared and discussed.

Abstract

In modular steel buildings, traditional architectures are separated into prefabricated room-sized volumetric units that are manufactured offsite and installed onsite. The connections between the modules are important for load transfer. Conventional inter-module connections mainly use direct plates and connect them using bolts; however, this may prove problematic for the inner connecting regions. A new type of design with beam-to-beam bolted connections is proposed in this paper; this design provides easy working access without being affected by the structural members. The static performance, hysteretic performance, skeleton curves, ductile performance, energy dissipation capacity, and stiffness degradation patterns of the joints are obtained by experiments and finite element analyses. The results showed that because of the construction between two unit joints, gaps would be formed between the upper and bottom columns, and this gap can influence the deformation patterns and distribution of bending loads at each unit joint. The weld quality at the unit joints is critical to ensure overall safety. Stiffeners can effectively increase the stiffness and load bearing capacity, but may reduce ductility performance. The deforming ability of the connection is also closely influenced by the stiffness of the floor beam column joint and ceiling beam column joint and their relative intermediate magnitudes.

Introduction

Modular construction involves an assembled structure in which the entire structure or building comprises prefabricated room-sized volumetric units or structural units that are manufactured offsite and installed onsite [1]. The modular units are often fully equipped with the required facilities and transported to the construction site; then they are connected onsite to form a complete and permanent residential or commercial building [2] (Fig. 1(a)). Compared to the conventional construction approaches, the off-site modular construction replaces the slow unproductive site activities by more efficient and faster factory processes. The perceived benefits of off-site manufacture are speed of construction, higher quality, lower cost, less wastage, and higher reliability [3]. Further, the modular steel structures are especially suitable for industrial production [4]. In recent years, off-site modular construction has been receiving increasing attention in high-density urban areas, where the construction practices are often constrained by limited working spaces and high requirements on low disturbance during operations [5]. In general, there are mainly two types of modules: continuous four-side support modules where the vertical loads are transmitted through the walls, and corner-supported modules where the vertical loads are transmitted through the corner and intermediate posts. The structural skeleton of the four-side support module mainly comprises light steel C-sections inside the walls, and is normally used for low-rise modular buildings, while the corner-supported modular form often uses hot rolled steel members that can withstand larger vertical loads in mid-rise or high-rise buildings.

Furthermore, these module forms have the units connected at their corners, so that they can structurally work together to transfer wind loads and to provide an alternative load path in the case of damage to a single module [6]. Lawson introduced the common bolted connection method normally used in the UK, and displayed the application exploration of high-rise modular steel buildings (MSBs) [1], [6]. The corner columns or angles in adjacent modular units are normally connected together with single bolted connector plates or side plates [7], [8]. Lee [9] later reported a rigid connection between vertically adjacent modules, through an extended bracket end at the lower ceiling beam to ensure fastening of bolts to the upper floor beams. Annan [4], [10], [11] presented a welded inter-module connection design with the upper and lower modular columns directly welded together, and performed seismic evaluation of the welded corner-supported MSBs. Using a similar method, Fathieh [12] also conducted seismic evaluation of MSBs having bolted steel plates as the inter-module connections. However, most of the reports or references cover only the connecting styles or simplification methods, with limited information on the mechanical performance of the inter-module connections.

At present, most of the (MSBs) have a single array arrangement or a simple layout in which most of the inter-module connections would be located in the perimeter region [13], [14]. However, for the inner connections, as shown in Fig. 1(b), the fourth module to be placed cannot be easily connected at its base, unless there is enough working access or a special opening. The modular construction features; its convent on-site erection assembly, and a safe and convenient inter-module connection is needed. In the present paper, a new type of inter-module design for the inner connecting regions is proposed. A series of static and cyclic loading tests were performed to understand the load bearing mechanism and seismic behaviour of the structure. The results can provide useful guidance and serve as reference to modular building design in the future.