Numerical analysis of corner-supported composite modular buildings under wind actions

Highlights

• A novel corner-supported composite module is proposed for multi-storey applications.

• The stiffness and strength of the module are improved by 21% and 33%, respectively.

• The proposed inter-module connections are sufficient in tying the connected modules.

• A 3-D FEA model is created for system-level analyses of the composite modular building.

• 12-storey modular buildings are potentially satisfactory under wind actions per AS 1170.

Abstract

This paper proposes a novel design of a corner-supported steel-concrete composite module that is suitable for multi-storey modular buildings. The strength and stiffness of the individual modules are improved through the designs of concrete-filled steel tubular (CFST) columns, laminated double beams, and integrated concrete slabs. The overall structural integrity of the modular buildings is improved through the designs of tenon-connected inter-module connections combined with beam-to-beam bolt connections. Analyses on modules reveal the effects of CFST columns on the failure mode and the lateral resistance of individual modules. Average increases of 21% in elastic stiffness and 33% in capacity under lateral loads are evident. The inter-module connections are proved to be effective in tying the modules together under lateral loads. A simplified FEA model is then developed for simulations of 12-storey modular buildings with various designs, of which the behaviours under wind actions are assessed according to the Australian Standards AS 1170.0–2. The drawbacks of the modular buildings are discussed, and the corresponding design recommendations are proposed.

Introduction

Prefabricated modular building is an innovative construction technique that manufactures building modules through flow line production in a factory and then installs them on-site to form a complete functioning structure or the major parts of a structure [[1], [2], [3]]. It modernises the construction process with automated machinery. Up to 70% to 95% of the manufacturing work could take place in a factory environment [4]. Modular buildings are expected to provide a wide range of economic and sustainability benefits in their life cycles [[5], [6], [7]]. Around 30–50% reduction in construction duration and over 10% cut down in total capital cost are often achieved when using the modular technique in comparison to conventional building methods [1]. A case study in Hong Kong has indicated an average wastage reduction level of around 52% when using prefabrication in buildings compared to conventional construction [8]. According to Global Alliance for Buildings and Construction, currently the buildings and construction together account for 36% of global final energy use and 39% of energy-related carbon dioxide (CO₂) emissions when upstream power generation is included [9]. The environmental impacts in the building and construction sector could be minimised by maximising the use of the modular technique [10]. Over the last decade, prefabricated modular buildings have established themselves with a growth rate of 10% each year in major building markets worldwide [11]. Successful applications have been demonstrated globally [[12], [13], [14], [15], [16], [17]].

Historically, the primary use of modular construction was in portable or temporary buildings, but this modular technique is now used in a wide range of multi-storey buildings, including schools, hospitals, commercial and residential buildings. This demand has been driven by the off-site nature of the manufacturing process and its substantial benefits discussed above. However, the market shares of modular buildings in the high-rise sectors are still less than 1% [12]. This is greatly due to the fact that multi-storey modular building is still an emerging technique, which requires more systematic research and studies to overcome the challenges [18], e.g., (1) with the increasing of the building height, the strength demands of the individual modules are increased, especially for the lower storey modules; (2) the increased building height also introduce the higher structural integrity requirement, which is an inherent shortcoming of most modular designs.

Recently, a series of studies have been conducted to design safer multi-storey modular buildings [4,20]. In particular, corner-supported steel modular buildings attract great attention since they apply direct and straight-forward load transfer mechanisms, and their open-wall designs provide more flexibility for meeting architectural requirements. As shown in Fig. 1, unlike continuously supported modules that have structural walls installed at the perimeter to transmit load, corner-supported modules resist load by their columns positioned at corners. In conventional designs of corner-supported modules, columns are commonly designed with steel hollow sections. However, it is difficult for these slender columns to achieve adequate strength for larger-scale or multi-storey applications and their material efficiency is often reduced by undesirable buckling phenomena. In this study, the modules are designed with concrete-filled steel tubular (CFST) columns. CFST is a promising structural element that utilises concrete and steel structural advantages and promotes composite effects through material confinement [21]. CFST possesses outstanding structural performance such as excellent stability, favourable ductility, great fire resistance, and large energy absorption capacity [22,23]. In the novel steel-concrete composite modules, the loading capacity can be significantly improved without increasing the columns' sectional dimensions. Moreover, using CFST can avoid variation of columns size along with the building height due to the change in capacity requirements, since one can change the strength of the infilled concrete or simply leaving the concrete out for upper-storey columns. As shown in Fig. 2, Fig. 3, the plug-in tenon connection is particularly effective when the connected columns are closed sections with identical cross-sectional dimensions.

Moreover, as shown in Fig. 2, in conventional designs of modular buildings, there is often a gap between the ceiling beams of the lower module and the floor beams of the upper module to facilitate inter-module connections and operating space for connection installation. This gap reduces the efficiency of the modular designs in two aspects. Firstly, the flexural rigidity of the two independent beams is substantially lower than that of two laminated beams bending together [24]. Secondly, the additional gap will increase the total building height or sacrifice the floor-to-floor height. To address this common issue in modular buildings, this study proposes the configuration of laminated parallel flange channels combined with an integrated concrete slab to increase the floor system's flexural rigidity without compromising the floor-to-floor heights [25], as shown in Fig. 3(b).

When it comes to system-level analyses of multi-storey modular buildings, experimental tests become extremely costly and dependent on access to large-scale industrial facilities. Hence the well-validated numerical simulation is the most widely used alternative in studies of building responses. The paper herein presents a systematic numerical study on multi-storey modular buildings using novel corner-supported steel-concrete composite modules. The proposed design aims to overcome several inherent shortcomings of existing multi-storey modular buildings. CFST columns and composite beam-floor systems are introduced to improve the strength and stiffness of individual modules, while the tenon-connected inter-module connections combined with beam-to-beam bolts are used to ensure the overall structural integrity. Detailed numerical models are created using the FEA software ABAQUS [26] to study the structural behaviour of the newly designed composite modules, in which the in-depth details such as the material nonlinearity, the manufacturing tolerance of plug-in tenons, and the frictional interfaces between each part are all taken into account. The differences in failure modes are discussed, and the improvements in both elastic stiffness and maximum load capacity are quantified for the novel composite modules. A simplified modelling method is developed and validated to facilitate the studies on larger-scale modular buildings. The lateral behaviour of four 12-storey modular buildings with SHS and CFST column designs and different floor plans are assessed under wind actions according to Australian Standards AS 1170.0–2. Finally, design recommendations for multi-storey modular buildings against wind actions are proposed based on the obtained numerical results.