Modular Steel Buildings Research Articles

Tensile and shear performance of rotary inter-module connection for modular steel buildings

Because of the advantages of construction speed and efficiency, modular steel buildings (MSBs) have been increasingly used in mid-to high-rise buildings with repetitive units. Different form of connection and mechanical performance of the inter-module connection of MSBs from the traditional structure have always been remained a research hotspot. In this study, the mechanical performance of an innovative rotary inter-module connection was studied mainly through two tensile and two shear resistance tests. Then, the parametric analysis was carried out through the finite element analysis. The critical components of the connection under the tensile load were the corner fitting and the bottom plate of the lower rotating part, whereas, during the shear performance, the top plate of the lower corner fitting played a vital role. The edge yield of the bottom plate of the lower rotating part was used as the basis for deriving the formula of the tensile bearing capacity of the connection. Finally, a simplified calculation model was developed, and the formulas for tensile and shear bearing capacities were derived and verified.

Lateral stiffness evaluation on corner-supported thin walled modular steel structures

Corner-supported modular steel buildings (CMSBs) are mainly composed of repetitive room-sized modules and inter-module connections. However, there is a lack of relevant understanding on the structural performance of CMSBs such as lateral stiffness. This study therefore investigated the lateral stiffness of the two-storey planar modular structure taken from CMSBs with the vertical rotary inter-module connections. Three full-scale monotonic experiments representing container-type modules, framed modules and their combination, were carried out to evaluate their lateral performance. The results indicated that all the three structures showed the satisfactory ductile behavior but the container-type modular structure could possess much higher initial stiffness when subjected to lateral load. Two lateral-force resistance mechanisms with different structural configurations were clarified including the framed moment resisting mechanism and the membrane tension action mechanism. The load transferring mechanism of inter-module connections was analyzed where modules stiffness as well as inter-module connections rotational stiffness were considered. In this way, theoretical modellings were developed to estimate the initial lateral stiffness of such two-storey modular structures and verified by the experimental results. Furthermore, the bending moment transferred by inter-module connections was obtained from the theoretical derivation and used to demonstrate the above load transferring of inter-module connections.

Three-storey modular steel building with a novel slider device: Shake table tests on a scaled down model and numerical investigation

A 0.25-scale three-storey stacked modular steel structure with a novel slider device used at each floor level was built and subjected to seismic biaxial base excitation. This was tested in a shake table and performed well, satisfying the desired characteristics of the slider device and the modular steel structure. The test structure was then modeled and analyzed numerically, and the analysis results were compared with the test data. This paper presents the details of shake table tests, numerical models, the comparison of tests and numerical results and the feasibility of using the proposed slider device in multi-storey modular steel structures.

Flexural behaviour of pairs of laminated unequal channel beams with different interfacial connections in corner-supported modular steel buildings

Abstract In this study, the combined bending action of pairs of laminated unequal channel beams with different interfacial connections were introduced into corner-supported modular steel buildings with the aim of enhancing the interactions between the adjacent beams and modules in modular buildings. These laminated beams consist of C sections acting together by bolts through their flanges. First, a series of experiments were conducted on three laminated beams, i.e. a channel beam with simple interfacial contact interactions (LB-C), a channel beam with four additional shear bolt connections (LB-C-4B) and a channel beam with eight shear bolt connections (LB-C-8B). Mechanical testing on an independent bending channel beam (ICB) was also performed as a control specimen to evaluate the structural performance of LB-C, LB-C-4B and LB-C-8B, respectively. To further understand the flexural behaviour of the laminated unequal channel beams, finite element models of the beams were developed and validated by using the experimental results. The results show that mechanical performance of LB-C, LB-C-4B and LB-C-8B is significantly better than that of ICB. In addition, the failure modes of the laminated beams are largely dependent on the stiffness of the interfacial connection between the floor and ceiling beams. Strengthening the interfacial interactions could enhance the flexural performance of the laminated beams. Most importantly, this study presents an analytical procedure for rapid prediction of the initial bending stiffnesses of the laminated beams.

Study on the stability bearing capacity of multi-column wall in modular steel building

Modular steel building is an innovative structural system composed of volumetric units that are manufactured with full decoration in factory and assembled on site like building blocks. As one type of steel modular structural system, load-bearing modular structural system of the steel multi-column wall has already been put into engineering practice. However, as the stabilizing mechanism of steel multi-column wall is unclear, effective length factor of column in the existing structural design is conservatively taken as 1.0. In this paper, eight tests were performed to investigate the axial stability performance of modular multi-column walls. The results indicated that the modular wall showed good ductility especially for the one that only experienced overall instability; the greater the width-to-thickness ratio of stand column, the easier it’s for local buckling to occur; panel and foamed concrete had minor effects on axial stiffness and ultimate bearing capacity of wall, so they could be neglected in the design. In the end, based on the finite element parametric analysis of steel multi-column wall modular wall, effective length factor of stand columns in the multi-column wall, which could be used in the design, could be obtained. This research could provide a preliminary study on the assessment of the stability capacity of multi-column wall in modular steel building.

Anti-collapse resistance mechanisms in corner-supported modular steel buildings

Due to different integration strategies and stability requirements, the robustness analysis of multi-story modular buildings, made of volumetric units, requires collapse capacity analysis of various scenarios, corresponding to the loss of supports and notional removal of a part of ground floor modules. In this paper the results of a parametric analysis on the progressive collapse response of typical corner supported modular steel buildings are presented. The focus is on the effects of inter-modular connections' design on the anti-collapse resistance of these buildings. To that end, the effects of inter-modular connections translational behaviour, rotational stiffness of inter-modular connections, their removal time, and the rigidity of modules on the buildings' response are studied. Various module loss scenarios are imposed to a six-story modular building and its dynamic progressive collapse responses are investigated through alternative load path method. The collapse modes and anti-collapse resistance capacity of the building are studied, and some design considerations are proposed accordingly. The results show the significant effect of the translational behaviour of the connections, especially in shear. The rotational stiffness is shown not to have considerable contribution to maintaining the overall stability, provided that the modules individually act as complete rigid moment frames. On the other hand, while increasing the removal time, to the level of vertical natural period of the building, can considerably reduce its dynamic collapse response, the modules' rigidity shows no significant effect on the gravity-induced collapse resistance of the modular buildings.

Effect of inter-module connection stiffness on structural response of a modular steel building subjected to wind and earthquake load

Despite the increasing popularity of modular buildings, there are relatively few published case studies considering the overall structural responses to wind and earthquake load. As a result, there is limited structural performance data for the overall behaviour of modular buildings, which in turn impedes the development of appropriate design standards. At the same time, different inter-module connections exhibit different structural behaviours, and the overall response of a building assembled from interconnected modules may be influenced by the inter-module connection. However, the structural behaviours of inter-module connections in modular building structures subjected to lateral dynamic loads are not well known in the existing literature. This paper, therefore, presents a numerical investigation into the overall structural behaviour of a selected case study building. In particular, the moment-rotation and force-displacement behaviours of the inter-module connection were simplified, and incorporated in the overall structural model. The numerical technique was verified by comparison with a previous study, and the verified technique was then extended to the selected six storey case study building. The results showed that the overall response was affected by the inter-module connection stiffness, especially the translational stiffness in the along load direction.

Collapse capacity of modular steel buildings subject to module loss scenarios: The role of inter-module connections

In modular buildings made of volumetric units, robust structural action may be established by considering various scenarios for localisation of damage, corresponding to loss of supports at the ground floor, such as notional removal of ground floor modules. This paper studies the role of inter-module connections in resisting capacity of modular steel buildings against gravity-induced progressive collapse scenarios, through removing individual or combinations of entire modules at the ground floor. For this purpose, some typical modular buildings are modelled using the macro-model based finite element method. In order to investigate the role of inter-modular connections solely and separate from the effects of other elements, the modules are assumed volumetric rigid bodies, connected through horizontal and vertical interconnections, which are modelled employing translational axial and shear nonlinear springs. Different module loss scenarios are instantaneously imposed to the building models, and their nonlinear dynamic response is monitored in the context of alternate path method analysis. Then the ultimate collapse capacity of the modular buildings along with the collapse mechanism and failure modes are determined through the nonlinear static pushdown analysis. It is shown that the modular buildings possess considerable collapse resisting capacity and are able to offer high level of robustness compared to their conventional counterparts.

Finite Element Analysis on Seismic Behaviour of Novel Joint in Prefabricated Modular Steel Building

In prefabricated modular steel building, joint plays an important role in the structural behaviour and transfer of load among connected modules. In this paper, a new type of bolted joint with tenon-gusset plate as horizontal connection and long beam bolts as vertical connection has been proposed. The nonlinear structural behaviour of the novel joint was analysed against static and quasi-static cyclic loadings by using finite element (FE) software ABAQUS. Numerical study was carried out to predict the lateral load carrying capacity, bending moment capacity, rotational stiffness, failure modes and seismic behaviour of the joint. Connection was simplified with nonlinear spring connector and 3-D beam elements. Parametric study was carried out on the length of column tenon and gap between adjacent modular units. The results revealed that against lateral loads, the gap was generated between the upper and lower parts of joint which resulted in the bearing failure of floor beam (FB). The length of column tenon has obvious while gap between modules showed marginal effect on load carrying capacity and structural behaviour of joint. The simplified joint accurately mimicked load–displacement curve and structural behaviour of detailed joint. Then, FE analysis was justified by analysing test results of innovative connection in the reference. With these evidences, the veracity of the FE analysis for studying nonlinear behaviour of novel joint was confirmed.

Experimental study on seismic behavior of two-storey modular structure

Due to the unique construction method of modular steel buildings (MSBs) with units prefabricated fully off the site and assembled quickly on the site, the inter-module connection for easy operation and overall performance of the system were key issues. However, it was a lack of relevant research on the system-level performance of MSBs. This study investigated the seismic performance of two-storey modular steel structure with a proposed vertical rotary inter-module connection. Three full-scale quasi-static tests, with and without corrugated steel plate and its combination, were carried out to evaluate and compare their seismic behaviour. The hysteretic performance, skeleton curves, ductile performance, stiffness degradation, energy dissipation capacity, and deformation pattern were clarified. The results showed that good ductility and plastic deformation ability of such modular steel structures. Two lateral-force resistance mechanisms with different layout combinations were also discussed in detail. The corrugated steel plate could significantly improve the lateral stiffness and bearing capacity of the modular steel structure. The cooperative working mechanism of modules and inter-module connections was further analyzed. When the lateral stiffness of upper and lower modular structures was close, limited bending moment transfer may be considered for the inter-module connection. While a large lateral stiffness difference existed initially between the upper and lower structures, an obvious gap occurred at the inter-module connection, and this gap may significantly influence the bending moments transferred by the inter-module connections. Meanwhile, several design recommendations of inter-module connections were also given for the application of MSBs.

Modelling of connections and lateral behavior of high-rise modular steel buildings

Prefabricated Prefinished Volumetric Construction (PPVC), which is a form of modular construction, has been promoted recently for high-rise buildings to raise construction productivity. The flexibility of the inter-module connections and discontinuity of floor slabs of individual modules need to be modelled correctly in the structural analysis since they have direct effect on the building stiffness and its corresponding responses under lateral loads. In this paper, translational spring models are proposed to model the load transfer behavior of the vertical modules connections which are crucial for the structural behavior of high-rise modular buildings. The accuracy of the proposed spring models is investigated by comparing the force distribution and load displacement behavior of modular braced frames with conventional frame model established based on assumptions that the beams are either pin or rigidity connected to the columns. To enhance the productivity and work efficiency of high-rise modular construction, the feasibility of connecting the modules at the corners rather than tying the abutting beams or slabs is proposed. A more realistic approach of modelling the floor slab consisting of multiple modules inter-connected at the corners is recommended. The effectiveness of the corner connected modules in transferring the horizontal forces to the building's lateral load resisting systems is evaluated.

Multi-storey Modular Cold-Formed Steel Building in Hong Kong: Challenges & Opportunities

Modular building construction has become widely popular across the continents, such as in America, Europe (United Kingdom), Asia (Singapore), and more recently in Australia. Promoting sustainability in construction, the application of modular construction has been successfully implemented in very broad range building functionalities. These include student residences, private housings, hotels, commercial buildings, military accommodation, health facilities, as well as other services units attached to the main buildings. Several low-rise buildings (6 to 10 stories) as well as high-rise buildings (20 to 30 stories) have used this type prefabricated off-site building system as an alternative construction method. Among those existing projects, modular steel building brings significant advantage on the manufacturing process and erection speed. These will be beneficial for Hong Kong which has very high pressure on housing demands. Due to its excellence on strength and durability, the modular integrated construction (MiC) in Hong Kong is looking to the direction of using cold-formed steel as structural component. Some challenges and opportunities are exist and these will be discussed in this paper.

Experimental Study on the Flexural Behavior of an Innovative Modular Steel Building Connection with Installed Bolts in the Columns

Modular buildings have the highest levels of precasting in the current building system. There are some defects in present modular connections, such as the difficulties of construction, the weakening of the bearing capacity of beams or columns, and damage to decorations. This paper presents an innovative modular connection with installed bolts in the columns. Two symmetrical monotonous static loading tests were conducted to explore the flexural behavior of the innovative connection. Meanwhile, the moment–rotation relations, destruction process, ultimate bearing capacity, stiffness classification and internal stress distribution were analyzed. The results showed that the specimen S1 with smaller diagonal stiffeners lost its bearing capacity due to the failure of the welding seam, and the extreme moment was 169 kN·m. The failure mode of S2 with large diagonal stiffeners was beam buckling, and the extreme moment was 209 kN·m. The stress of diagonal stiffeners and the join between the upper beam and stiffeners increased rapidly. Stiffeners can increase the stiffness and load-bearing capacity. The connection failures occurred on the beam or beam–column joints, while the connection between modules remained undamaged, which showed that the new connection has a good bearing capacity under the action of bending moment and pressure.

Shear behaviour of post-tensioned inter-module connection for modular steel buildings

In modular steel buildings the inter-module connections are key to the successful site installation of modules and the overall structural behaviour of the assembled building. The existing connection details such as site welding typically require external access during site install, which is not always possible or practical. Post-tensioned bolted steel connections are an enticing solution because they minimise the requirement for site work, allowing for easier internal assembly. However, the existing shear force-displacement model for inter-module connections is inadequate, and the initial load-slip behaviour is not accurately predicted. In this study, a new post-tensioned bolted steel connection is proposed and the prototypes are manufactured. The shear force-displacement and load-slip behaviours are investigated experimentally. The proposed connection is shown to have good initial stiffness in shear, which can be well controlled by the parameters of preload and slip factor. In addition, numerical simulation is conducted and the influence of the preload and slip factor on the load-slip behaviour is investigated. An improved empirical model is developed, and its application is demonstrated for the proposed connection.

Rotational stiffness of inter-module connection in mid-rise modular steel buildings

The inter-module connection used for the assembly of prefinished modules is a unique key issue for modular steel buildings (MSBs). Previous types of inter-module connection require additional operation spaces and have conflicts with architecture decoration. To overcome these limitations, this study proposed an innovative rotary inter-module connection applied at the end of modular columns with corner fitting. The working mechanism of the rotary connection was introduced through a bending resistance test. Then, finite element analysis (FEA) and theoretical derivation were conducted to investigate the initial rotational stiffness obtained through the preceding test. In terms of the feature of double beams in MSBs and the results obtained, the influence of the stiffness ratio of double beams on the internal force distribution was investigated via FEA and theoretical calculation. Some recommendations for the design were also presented. Finally, the manner in which stiffness characteristics of the inter-module connection is considered accurately in the structural design was discussed and the conceptual design procedure of the inter-module connection was given accordingly. The results obtained could serve as a reference for the design of mid-rise MSBs.

Experimental study of a pretensioned connection for modular buildings

Modular steel buildings consist of prefabricated room-sized structural units that are manufactured offsite and installed onsite. The inter-module connections must fulfill the assembly construction requirements and soundly transfer the external loads. This work proposes an innovative assembled connection suitable for modular buildings with concrete-filled steel tube columns. The connection uses pretensioned strands and plugin bars to vertically connect the adjacent modular columns. The moment-transferring performance of this inter-module connection was studied through monotonic and cyclic loading tests. The results showed that because of the assembly construction, the connected sections were separated under lateral bending, and the prestressed inter-module connection performed as a weak semirigid connection. The moment strength at the early loading stage originated primarily from the contact bonding mechanism with the infilled concrete, and the postyield strength depended mainly on the tensioned strands. The connection displayed a self-centering-like behavior that the induced deformation was reversed during unloading. The energy dissipation originated primarily from frictional slipping of the plugin bars and steel strands. The moment transferring ability was closely related to the section dimension and the arrangements of the plugin bars and steel strands. A simplified strength calculation and evaluation method was also proposed, and the effectiveness was validated with the test data.

Investigation on Architectural Adaptability for a New Kind of Column-Supported Modular Steel Buildings

Investigation on Architectural Adaptability for a New Kind of Column-Supported Modular Steel Buildings

Experimental investigations of vertical post-tensioned connection for modular steel structures

Modular construction is an off-site construction technique. In this method, structural volumetric modular components are produced in a factory and assembled on-site to form a larger, permanent building. Typical vertical connections of modular steel buildings (MSBs) are provided by on-site welding. Welding may interfere with the finishing of the modules and also when several modules are placed together at a given floor level complete access for welding is compromised. As an alternative to on-site welding, the present paper proposes a new vertical post-tensioned (PT) connection for MSBs. This connection is comprised of a post-tensioned threaded rod installed inside hollow structural sections (HSS) columns and a steel box placed between two modules. In order to evaluate the general and the seismic performance of the proposed connection, eight quasi-static cyclic loading tests were performed in T-shaped subassemblies. A combination of three different steel boxes and three initial post-tensioning loads levels were considered. Additionally, two quasi-static cyclic loading tests were performed using standard welded connections. No local buckling was observed in any of the specimens and no welding fractures occurred up to 3% drift demand. Results indicated that in comparison to the welded connection the proposed PT connection have similar lateral stiffness and strain distribution, and a higher cumulative energy dissipation capability. Therefore, the proposed connection has the potential to eliminate on-site welding in the assembly of the modules while providing the lateral resistance required.

Seismic performance of modular steel frames equipped with shape memory alloy braces

The demand for modular steel buildings (MSBs) has increased because of the improved quality, fast on-site installation, and lower cost of construction. Steel braced frames are usually utilized to form the lateral load resisting system of MSBs. During earthquakes, the seismic energy is dissipated through yielding of the components of the braced frames, which results in residual drifts. Excessive residual drifts complicate the repair of damaged structures or render them irreparable. Researchers have investigated the use of superelastic shape memory alloys (SMAs) in steel structures to reduce the seismic residual deformations. This study explores the potential of using SMA braces to improve the seismic performance of typical modular steel braced frames. The study utilizes incremental dynamic analysis to judge on the benefits of using such a system. It is observed that utilizing superelastic SMA braces at strategic locations can significantly reduce the inter-storey residual drifts.

Numerical study on the effects of diaphragm stiffness and strength on the seismic response of multi-story modular buildings

Modular building construction relies on prefabricated modules which are assembled onsite to form complete buildings. The assembly requires modules to be connected at discrete locations and results in the formation of discontinuous diaphragms. Diaphragm discontinuities could potentially lead to structural instability or possible diaphragm failure if unaccounted for. Therefore, the primary objective of this study is to evaluate the influence of in-plane diaphragm stiffness and strength on the seismic performance of multi-story modular buildings. A simplified method is presented to establish diaphragm service stiffness considering shear deformation of individual module diaphragms as well as shear and axial deformation of diaphragm connections. This method is used to construct numerical models of a four-by-four bay four-story modular steel building. Three diaphragm stiffness levels, namely rigid, stiff and flexible, are considered for these models and were each subjected to 44 horizontal ground motions relating to seismic events having a return period of 500 years. The results show that increased diaphragm flexibility leads to inter-story drifts that are dramatically large and inertial forces that are considerably different from calculated values using the equivalent lateral force procedure described in current seismic codes. This study is extended further to evaluate performance targets for both elastic and inelastic diaphragm response under a seismic event having a return period of 2500 years. The results are used to propose new seismic design factors, which include force and ductility amplification, and could be implemented for the design of diaphragm connections in multi-story modular buildings.