Experimental and numerical investigation of mechanical properties on novel modular connections with superimposed beams

Highlights

• A novel modular connection with superimposed twin-beams is introduced.

• Continuity is defined as the rotation difference between up and down columns.

• The gap and twin-beams properties are critical to the overall joint response.

Abstract

The use of lightweight modular construction becomes increasing popular all around the world today. The benefits of off-site prefabrication include consistent quality, shorter construction time, eco-friendly function which are being realized in both residential and commercial building construction. The connection of modular building plays a critical role in ensuring the stability, robustness and seismic resistance of buildings. However, conventional connection design for modular buildings (e.g. blind flange gaskets, on-site welding or open large access holes) ignores the potentiation of composite effect on the stability of the modular buildings. This study presents a novel modular connection configuration (i.e. Type A modular connection) for connecting modular units to columns in both vertical and horizontal directions by an in-build component. The proposed connection can bring the floor beam of upper units and ceiling beam of bottom units into an integrated system with the advantages of easy installation without on-site welding. The mechanical behavior of modular connection was firstly experimentally investigated. An experimentally validated numerical model was then developed to further investigate the mechanical and deformation behavior of the joint. The results show that the proposed novel connection could allow the twins beam to rotate identically. In addition, they demonstrate that the twin beams’ flexural stiffness ratio and gap between in-build component and column are two critical factors that govern the continuity of the overall joint.

Introduction

Modular buildings system has been adapted world widely in the past few decades and is becoming more and more popular because of their rapid construction flexibility and worker friendly operation [1], [2]. The modular technology allows the productive process to be conducted in factories and then transported to sites and to be easily assembled. This process is not only good at schedule and budget controlling but also reducing environmental pollution [3]. Modular buildings can be applicable for schools, apartments, dormitories, hotels, and other architectural forms that contain repetitive units [4]. More than that, it can also be used in high-rise buildings which are combined with concrete core tube construction or additional braced structures [5].

The material of modular units can be various. While compared to concrete and timber framed modules, steel-based modules have characteristics of being more flexible in architectural design, longer span, lighter weight, and easier in connection [6], [7]. Light steel modular units are usually composed of floor beam, ceiling beam, corner column, wall, floor panel and ceiling panel. These components are assembled into a module off-site and constructed on-site through crane lifting. The typical modular unit installation procedure is shown in Fig. 1. According to R.M.Lawson [8], the generic forms of modular units can be classified into load-bearing modules in which loads are transferred through side walls and corner supported modules in which loads are transferred from edge beams to corner columns. The paper will focus on the connection system in steel-based corner supported modules.

Although the modular system has been widely used in practice, it is not difficult to find that the height of the modular building remains limited [9] without the help of outside braced systems such as concrete core and steel skeleton. This is partially due to the lack of strong structural systems and joining techniques to ensure structural integrity and the corresponding design guidelines [10]. Moreover, walls and floor cassettes in modular units can separate the space between adjacent units which limits the connecting access space as shown in Fig. 2 [11], [12].

In modular buildings, the connections between modular units play very important roles because they ensure the structural integrity, overall stability and robustness of the entire building[13], [14]. Many researchers have therefore sought for higher system strength and more efficient construction in perspective modular connection. A new type modular connection developed by Zhihua Chen et al [15], [16] utilizes a plug-in device and a group of through bolts to guarantee the load transfer between modules. This connection can avoid on-site welding and provide enough workspace for multiple unit connection. In addition, their research group also developed an innovative rotary inter-module connection [17], [18] applied at the end of modular columns with corner fitting. It is not necessary to open holes in beams or columns and it has a simple configuration, convenient operation, and no on-site welding. En-Feng Deng et al [19] proposed a bolted connection with a weld cover plate. Seven full-scale tests were conducted under monotonic and cyclic load and the results show that the connection has sufficient deformation capacity and ductility. Also, the twin-beams were found to have individual bending behavior and this kind of connection still needs on-site welding. Jeung-Hwan Doh et al [20] introduced a steel bracket connection, which allowed the modular units to be connected by a hollow cube through bolts. Wang, Yongrui et al [21] came up with a column joint for modular construction that connects work can operate externally by a long twisting tool. Lee, Seungjae, et al [22] changed the ceiling beam into a bracket type to fasten bolts so that the unit can be connected and disconnect easily. Dhanapal, et al [23] came up with a cast steel modular connection. The connection was weld in factories and installed inside the module units. It also has wide suitability due to its various construction form. Xiao-Meng Dai et [24] al proposed a self-lock modular connection which is a perfect solution to the limited workspace during the installation procedure.

The current research can solve the vast majority of modular construction problems. However, existing modular connections still preserve gaps between floor beams and ceiling beams, which will cause the underutilization of twin-beams. The potentiation of the composite effect to modular buildings has been proved by several researchers. Choi, Kyung-Suk, et al [25] showed that the interaction modeling of beams strongly affects the structural stiffness and strengths capacity of modular construction. The numerical study of Sharafi et al [26] shows that the continuous connection system between modular units can improve the integrity of modular construction significantly. Xu, Bo, et al [27], [28] raise a new modular construction system with laminated channel steel beams to enhance the interaction between adjacent beam components. And the bearing capacity and stiffness of the laminated channel steel beam are much higher than that of the single one.

Based on the previous study on laminated channel double beams by Xu, Bo, this paper aims to develop a novel modular connection that allows the ceiling beam and floor beam to fit naturally. Three full-scaled monotonic tests were conducted to analyze the mechanical properties including initial stiffness, bending strength, rotational capacity, and ductility. The parametric analysis was then conducted to obtain the main influencing factors to the mechanical behaviors on the novel modular connection.