Modular Steel Buildings Research Articles

Experimental and theoretical study on axial compression behaviour of the modular combined column

Between the modular units of the modular steel building, there exists a combination of the adjacent modular columns. Due to the gaps between the modular columns and the lack of horizontal connections, the integrity of the modular steel structure is weak, which limits the use of modular steel structures in high-rise buildings. This paper proposes a kind of modular combined column realized the connection of modular single columns through the connectors and concrete, which can improve the integrity of the modular steel building. The assembly process of this new modular combined column is described. For axial compressive performance tests, four modular combined column specimens were designed, each with different height or different number of connecting plates. The axial compressive bearing capacity, ductility, stiffness, and other mechanical parameters of the specimens were analyzed according to the phenomena and load-displacement curves of the test. Then, the axial compression failure mode of the modular combined column specimens is compared and analyzed in conjunction with the finite element model. The results indicate that the axial compressive performance and ductility of the combined column suggested in this research are exceptional. The connector can enhance the overall mechanical qualities of the combined column by augmenting the restraining impact of concrete. Finally, the theoretical equation of the axial compression bearing capacity of the modular combined column is obtained by employing the superposition principle, and the equation's reliability is confirmed, along with the test results and the results of the numerical analysis.

Damage mitigation strategies for progressive collapse of modular steel buildings following sudden corner module removal

AbstractThis study evaluates gravity‐induced progressive collapse performance and damage mitigation strategies in modular steel buildings (MSBs) A typical three‐dimensional six‐story structure was modeled and analyzed using the finite element method, focusing on the instantaneous removal of a corner module. The study includes a parametric evaluation of the influence of beam moment capacity on progressive collapse and investigates the effect of using concrete as an infill for square hollow section columns. Additionally, the effectiveness of short K‐shaped braces in limiting gravity‐induced collapse was assessed. A response/damage index (DI) was proposed to quantify the overall structural response. The findings indicate that semirigid beam‐column connections outperform fully rigid connections. Both concrete‐filled columns and K‐shaped braces mitigate structural damage, with K‐shaped braces proving more effective in preventing collapse. Although increasing the beam moment‐resisting capacity reduced the DI, improvements were marginal beyond 50% of the fully rigid connection capacity. Higher beam moment capacities reduced local vertical displacement at the corner joint but led to undesirable lateral deformations. Reducing beam rigidity/capacity by 25% mitigated global structural deformations. The optimal beam moment capacity was identified as 75% of the total section capacity when using concrete‐filled columns. K‐shaped braces applied at the column midpoint entirely prevented progressive gravity‐induced collapse and no lateral deformations were observed in braced structures with fully rigid beam‐column connections, unlike unbraced structures. Concrete‐filled columns offer a cost‐effective solution for preliminary production of MSBs, while K‐shaped braces are suitable for retrofitting existing buildings. Further research is necessary to address other parameters influencing the mitigation of progressive collapse in MSBs.

Effect of inter-module connection properties on structural sway of high-rise modular buildings

The modular steel building is a rapidly evolving prefabricated structural system, consisting of discrete volumetric modules assembled with inter-module connections. Despite numerous studies on the design optimization of inter-module connections, research on the development of realistic connection models and the correlation between connection properties and the overall structural behavior is relatively scarce. This paper introduces a multiple-spring inter-module connection model and supplies detailed property calculations of different load transfer components. The model can effectively simulate different stiffness and strength levels at inter-module connections and predict relative dislocations between assembled modules. The model is then applied to analyze the structural sway of modular buildings under seismic loads. Influences of connection modelling methods and the real connecting abilities on structural sway responses are investigated through comparative analysis of connection and module drift deformations when using conventional pin or rigid constraint connection models and the proposed realistic multiple spring model. Results indicate that simplified pin or rigid constraints cannot accurately represent the actual load transfer mechanisms at inter-module connections. The horizontal link determines the composition extent of horizontally assembled columns and modules. The horizontal shear resistance is closely related to column loads and follows the downwardly increased mode, which induces different structural sway and module drift levels in modular buildings.

Optimising Plate Thickness in Interlocking Inter-Module Connections for Modular Steel Buildings: A Finite Element and Random Forest Approach

Interlocking Inter-Module Connections (IMCs) in Modular Steel Buildings (MSBs) have garnered significant interest from researchers. Despite this, the optimisation of plate thicknesses in such structures has yet to be extensively explored in the existing literature. Therefore, this paper focuses on optimising the thickness of interlocking IMCs in MSBs by leveraging established experimental and numerical simulation methodologies. The study developed various numerical models for IMCs with plate thicknesses of 4 mm, 6 mm, 10 mm, and 12 mm, all subjected to compression loading conditions. The novelty of this study lies in its comprehensive parametric analysis, which evaluates the slip prediction model. A random forest regression model, trained using the ‘TreeBagger’ function, was also implemented to predict slip values based on applied force. Sensitivity analysis and comparisons with alternative methods underscored the reliability and applicability of the findings. The results indicate that a plate thickness of 11.03 mm is optimal for interlocking IMCs in MSBs, achieving up to 8.08% in material cost reductions while increasing deformation resistance by up to 50.75%. The ‘TreeBagger’ random forest regression significantly enhanced slip prediction accuracy by up to 7% at higher force levels.

The flexural mechanical response of a novel plug-in self-locking inter-module connection for modular steel buildings

The bending-deformation resistance of a proposed plug-in self-locking inter-module connection was investigated. Firstly, bending tests were conducted on three foot-size plug-in self-locking inter-module connections. Secondly, the corresponding finite element model (FEM) was established with ABAQUS finite element software, and then verified through tests. A parametric analysis of the connection was also performed to estimate the influences of the construction clearance on the mechanism of synergistic strengthening between an inner insert and a lock cylinder. Finally, design recommendations are given for this self-locking connection. The results show that: firstly, the damage modes of the unreinforced insert specimens all involved shearing fracture at the lower part of the insert, and the slope-reinforced insert specimens underwent necking at the interface of a locking core plate and an insert plate with a ductility coefficient of 1.134. In addition, the load direction had no effect on the flexural capacity of the connection, while the initial flexural stiffness of the slope-reinforced interpolated plate connection was improved by 3.6% compared to the connection with unreinforced interpolated plate. And the flexural ultimate loads of all three specimens reached 5% of the design flexural load of the modular column. Secondly, the complete M-θ curve of the slope-reinforced inset plate connection is divided into the elastic phase, elasto-plastic phase and inner insert-reinforced phase. Thirdly, the initial flexural stiffness of the connection with g = 0 mm is 1.8 times higher than the connection with g ‡ 0 mm. When g = 2 mm, the connection had the extreme values of the reserve load capacity (27%) and the ductile deformation capacity (μⅡ = 1.36). In addition, at the stiffness enhancement point of the M-θ curve, there is a linear relationship between the rotation angle and construction clearance. Finally, the results found that a negative correlation between the flexural ultimate load and the construction clearance.

Numerical-analytical investigation on bending performance of laminated beams in modular steel buildings

It is well-known that the laminated channel beams can significantly strengthen the combination of adjacent beam components and further enhance the structural integrity of modular steel buildings. In present study, the superimposed bending performance of laminated channel beams was comprehensively investigated using the numerical and analytical methods. Firstly, FE models were developed and validated by the experimental data. Then, a series of numerical parametric studies combining the orthogonal and univariate analysis were successively conducted to identify the sensitivity of design parameters including interfacial bolt number (n), interfacial friction (f), layer height ratio (β), load type (p) and boundary condition (b), and further clarify the influence of key parameters on the cooperative bending properties. Finally, the analytical procedure was proposed to evaluate the equivalent bending stiffness of laminated channel beams. The results showed that the effect degrees of design factors on EIe and Pu were as follows: n > β > f > b > p and p > b > β > f > n, respectively. n and β were selected as the key design parameters for the modular laminated beams. The bending responses were nonlinearly promoted by n, while the linear regularity was observed for β. The influencing mechanism of n indicated that the bolt connections induced the additional internal forces, which caused the transferring of neutral axes and the superimposition effect of laminated beams. Quantifying the neutral axis deviations, the analytical models were developed and reasonably assessed the superimposed bending stiffness of laminated beams in modular steel buildings.

Tensile behavior of a novel self-locking inter-module connection in modular steel buildings

Modular steel buildings (MSBs) consist of complete steel modules and inter-module connections; the latter plays a crucial role in assembly efficacy on-site and in resisting the tension load at the base of a high-rise modular building subjected to lateral loads. This paper investigates the tensile performance of the proposed self-locking inter-module connection. Two full-scale experiments were conducted to evaluate the axial tensile behavior of this innovative connection. The mechanical properties of the self-locking inter-module connection were obtained and analyzed, including the failure modes, ultimate bearing capacity, and strain distribution. Under axial tension load, the self-locking inter-module connection exhibited adequate load-carrying capacity and ductility, as evidenced by the results. The refined finite element (FE) model of the self-locking inter-module connection was developed and validated against experimental data. Then, FE modeling was used to further investigate the working mechanism of the self-locking inter-module connection under axial tensile force. Two essential parameters were considered, including the bottom plate thickness of the upper corner fitting and the top plate thickness of the lower tenon. The numerical results demonstrated that the failure mode of such a self-locking inter-module connection was dependent on the relative relationship of the aforementioned two key parameters, which is reflected by the ratio (Kt) of the vertical shear area of the bottom plate of the upper corner fitting and the top plate of the lower tenon. Considering tensile resistances and material strength utilization, a range of values for the parameter Kt and design recommendations were provided.

Working mechanism evaluations of full-scale joints with bolted-cover plate connection for modular steel buildings

The force-reliability of the modular structural joints is crucial for ensuring the structural integrity of modular steel buildings. However, the welds connecting the beam and column within the module are susceptible to tear during seismic events. This mode of failure greatly undermines the ability of these joints to withstand seismic forces. Four full-scale modular structural joints with bolted-cover plate connection were designed and conducted for seismic performance testing, emphasizing the significance of methods such as reinforcing diagonal braces and strengthening flanges on the protective effect of beam–column welds in the module. The simplified modular structural joint and frame finite element model were proposed based on experimental data, refined finite element modeling, and theoretical analysis. The findings suggest that the seismic behavior of the modular structural joint remains unaffected by variations in axial compression ratio within the designed range of parameters. The beam–column weld of the module in the reinforced joint exhibits almost no weld tearing, and both strengthening methods demonstrate exceptional capacity for energy dissipation. The proposed simplified modeling method facilitates the efficient determination of the modular structural joint bearing capacity and the lateral stiffness of the modular frame. The research findings presented in this paper can serve as a valuable reference point for the engineering design of modular steel structures.

Analysis of Seismic Performance and Applicable Height of a Cooperative Modular Steel Building

As an innovative building system, the modular steel structure demonstrates a high degree of industrialization and assembly efficiency. However, no linkage exists between the components of modular units, leading to issues such as diminished load capacity and excessive steel usage in modular construction. In order to tackle these challenges, finite element numerical simulations are employed to examine the inter-column connectors and the cooperative modular steel buildings. This simulation calculates the initial stiffness across various degrees of freedom in these connectors. In addition, it analyzes the displacement response, changes in internal forces, and height of cooperative modular steel structures under varying seismic precautionary intensities. The results revealed that cooperative modular steel buildings substantially improve overall stiffness and lateral performance compared to their non-cooperative counterparts. There is a maximum reduction in the inter-story displacement angle of up to 36.1%, and the maximum reduction of the top displacement can reach 16.2%. This enhancement also increases structural stiffness, a shortened natural vibration period, and an augmented bottom shear force. Based on these findings, it is advised that the height of cooperative modular steel buildings should not exceed 21 m at 7 degrees (0.10 g), 21 m at 7 degrees (0.15 g), and 12 m at 8 degrees (0.20 g).

Research on seismic behavior of tapered-head bolted inter-module connection of modular steel buildings

Modular steel buildings (MSBs), which comprise prefabricated modular units, are a new type of assembled buildings. The inter-module connection of MSBs plays an important role in the connection between modular units and structural safety. At present, several types of inter-module connections are in use, such as welded, bolted, prestressed, or self-locking. However, they present problems such as poor welding quality, low construction efficiency and no operation space for the internal connection. To solve these problems, this study proposes an innovative tapered-head bolted inter-module connection. Cyclic tests were conducted considering three different parameters: the modular beam section form, axial compression ratio, and thickness of the modular floor beam. Seismic behavior indicators such as stiffness degradation and energy dissipation of the specimens were investigated. Subsequently, a refined finite element model (FEM) was established to verify the corresponding test results. Finally, based on test fitting and nonlinear regression analysis, a restoring force model of the tapered-head bolted connection was established. The results indicated that the calculated ratios of the restoring force model to test results were within 0.07 on the yield, maximum, and failure points and the coefficient of variation (COV) was 0.03, with high accuracy and application. This research provides a reference to some extent for designing MSBs.

Pull-out performance of grouting sleeve connection with short studs shear keys in modular steel building

In this paper, a new type of grouting sleeve connection joint with short studs shear key is proposed for the connection of high-rise modular steel structures. To study the tensile properties of the grouting connection in the modular structure, seven groups of 21 specimens were tested by push-out test. The results show that: (1) The axial bearing capacity of the specimen with a diameter of 16 mm studs is between 3549.2 kN and 3922.4 kN, and the anchorage strength is between 15.07 MPa and 16.66 MPa; (2) The bearing capacity of the connection consists of four parts, including the shear capacity of the studs, the shear capacity of the studs weld collar, the friction and bonding force of the interface. The shear capacity of the stud provides about 65 % of the bearing capacity; (3) The ultimate displacement ranges from 4.69 mm to 6.93 mm, and the ductility coefficient is 2.42–3.05. Then, combined with the test and simulation, the force mechanism of the connection is analyzed, and the design suggestion and the calculation method of the bearing capacity of the connections are put forward. Compared with the existing grouting connection joints, the bond strength of the connection proposed in this paper is 26.7 % higher, showing stronger pull-out resistance.

Robustness of Corner-Supported Modular Steel Buildings with Core Walls

This paper studies the dynamic response of corner-supported modular steel buildings with a core wall system, under progressive collapse scenarios, associated with corner module removals. Since using secondary systems such as concrete core in mid- to high-rise buildings is currently unavoidable, understanding their impact on load transfer between modules during collapse scenarios becomes essential. The designated four-, eight-, and twelve-story buildings were modelled using the macro-model-based finite element method in Abaqus. In addition, three different locations are considered for the concrete shear core within the building plan, leading to nine various case scenarios. Each vertical and horizontal inter-module connection was modelled by one axial and two shear springs with predefined nonlinear force-displacement behavior. The local and global buckling, which plays an essential role in the building’s stability, was considered to obtain accurate results. Finally, parametric studies on the building response were carried out, including the intra-module connection rigidity and inter-module connection stiffness. The results demonstrated that the core wall could maintain the robustness of a modular steel building through two mechanisms dependent on its location within the plan. In addition, preventing plastic hinges from forming in beams could be introduced as an anti-collapse mechanism in the corner module removal scenarios.

Seismic behavior of a novel liftable connection for modular steel buildings: Experimental and numerical studies

Modular steel buildings (MSBs) have achieved considerable popularity in multi-to-high rise constructions due to the favorable mechanical characteristic, eco-friendliness, cost-effectiveness, and enhanced construction efficiency. As the critical part of MSBs, the inter-module connection has an important influence on determining the seismic performance of MSBs. This study presented an experimental-numerical investigation on an innovative fully prefabricated liftable connection (FPLC) for MSBs. To study the seismic performance of the FPLC, quasi-static tests were conducted on four full-scale specimens. The seismic behavior of the specimens, including failure mode, hysteretic response, strength and stiffness degradation, deformation characteristic, etc. was evaluated and compared in detail. The effect of the section of the twin-beams, the dog-bone weakening of the beam and the connecting method between the corner fitting and twin-beams on the seismic behavior of the FPLC was revealed. Moreover, the feasibility for seismic application of the FPLC was evaluated according to Chinese code GB 50,011–2010 and Eurocode 3 Part 1–8. The results indicated that the proposed FPLC met the limit of elastic and elastic-plastic inter-story drift ratios required by GB 50,011–2010. According to Eurocode 3 Part 1–8, the FPLC with welded beams should be classified as “semi-rigid” connections, while the FPLC, whose beams were connected to the column walls by the steel angles and bolts, was classified as a “pinned” connection. Then, a refined finite element model (FEM) was developed and verified by the test results. Furthermore, the verified FEM was utilized to analyze the distribution of the equivalent plastic strain, the stress variation path, and the yielding area of the twin-beams to further reveal the energy dissipation and damage mechanism of the FPLC. Finally, a simplified FEM was established and the comparison with the test results proved its reliability and efficiency. The present study will contribute to provide a comprehensive understanding on seismic performance and design of the inter-module connection for MSBs.

Failure mechanisms of hexagonal-shaped intra-module connections in modular steel building

Modular construction has gained popularity for its cost-effectiveness, time savings, and environmental benefits. This research delves into innovating modular buildings to enhance their aesthetic value in contemporary architectural designs. Traditional rectangular modules have lost architectural significance in the modern era. The study focuses on the failure mechanisms of hexagonal intra-module connections under nonlinear static analysis, aiming for advanced structural design and performance in modular construction. The study tested a control model, a Welded Flange Bolted Web (WFBW) connection, and three variations with different parameters: boundary condition, bolt arrangement, and steel grade. For the boundary condition, the tie constraint between the beam's flanges and the diaphragm was removed. Bolt arrangement was assessed with staggered and non-staggered bolts. Steel grade variations included S275 and S355. Results showed that the WFBW connection outperformed the Bolted Web (BW) connection in load resistance. The most damaged component was the beam, with bearing failure at the upper bolt hole. Non-staggered bolts exhibited larger displacements than staggered bolts. The study emphasized the significance of steel material strength in terms of stress and strain on bolt capacity. It highlights the importance of intra-module connections in modular steel structures and the need to consider design parameters carefully. The findings offer insights into improving modular connections' performance and failure mechanisms, facilitating the creation of aesthetically pleasing and structurally sound modular structures. This nonlinear static analysis aids in developing advanced modular construction designs, enhancing architectural significance in the modern era. By merging structural performance and aesthetics, the study promotes innovative modular construction to meet contemporary architectural demands.

Seismic performance of self-centring connections with two energy dissipation stages for reusable modular steel buildings

This paper presented a feasibility study on a self-centring connection with two energy dissipation stages for use as a combined inter-module and intra-module connection in reusable modular steel buildings. The proposed connection was equipped with shape memory alloy (SMA) disc washers and friction dampers, the former for self-centring and the latter for energy-dissipation functions. The design concept of two energy dissipation stages was to achieve structural longevity and member reuse by 1) enabling rapid recovery after small and medium earthquakes, and 2) facilitating prompt repair if at all needed after large earthquakes. A spring analytical model was proposed, wherein each connection component was symbolised as a rotational spring. Based on the model, a design methodology to meet the two-stage performance goals was derived, where the critical story drift ratio between the two stages was expressed as a function of the properties of friction dampers and SMA disc washers. Detailed finite element simulations were used to validate the proposed design concept and the spring model and to assess the influence of the friction dampers and SMA disc washers on the hysteresis behaviour of the connection. The results demonstrated that the proposed connection would facilitate the design objectives when designed based on the proposed spring model to ensure structural longevity, member reuse, and efficient recovery and repair after seismic events.

A Study on Mechanical Performance of an Innovative Modular Steel Building Connection with Cross-Shaped Plug-In Connector

Modular steel buildings show high assembly degree and fast installation speed. The inter-module connection (IMC) is one of the key technologies that restrict the robustness of modular steel buildings. An innovative IMC with a cross-shaped plug-in connector is proposed, and the connection consists of end plates of columns, the cross-shaped plug-in connector, bolts, cover plates, and one-side bolts. The proposed IMC is easily constructed, and the cross-shaped plug-in connector can improve the shear resistance of the core area. The mechanical model of the proposed IMC is presented, and the panel zone volume modified factor and initial rotational stiffness modified factor are proposed for calculating the shear capacity of the panel zone and the initial rotational stiffness. Numerical simulation was conducted considering the influences of axial compression ratios, sections of beams and columns, and the thickness of the tenon plate of the connector. The bearing capacity of the proposed IMC was analyzed, and the values of the two factors mentioned above were calculated, and their regression formulas are presented. The results show that the sections of beams and columns and the axial compression ratios show great influences on the bearing capacity of the proposed IMC, while the thickness of the tenon of the cross-shaped plug-in connector shows almost no effect. In addition, the sections of beams and columns show great influences on the shear capacity of the panel zone, as well as the initial rotational stiffness of the proposed IMC, while the thickness of the tenon of the cross-shaped plug-in connector and the axial compression ratios show little effect and almost no effect, respectively. Furthermore, the bending moment limit of the beam end of the proposed IMC is suggested to be 0.6 times the resistance bending moment, and the proposed IMC is considered to be a rigid connection or inclined to a rigid connection The proposed IMC has good mechanical performance, and design recommendations are presented.

Numerical Assessment of The Robustness of a Corner‐supported Modular Steel Building

AbstractThis paper investigates the robustness of a 6‐storey corner‐supported Modular Steel Building (MSB) under notional ground floor corner column removal (i.e. alternate path method). The robustness assessment investigates the following structural effects that were frequently ignored for the sake of simplicity in existing numerical modelling approaches: (1) semi‐rigidity in the beam‐to‐column connections, and (2) initial out‐of‐straightness (geometric imperfection) in the compression members. Commonly, the welded connections between the beams and square hollow section columns are modelled as fully rigid, however, this may overestimate the actual robustness of MSBs as fully rigid connections often have a higher energy absorption capacity. Similarly, modelling a perfectly straight column could overestimate the actual robustness of MSBs. Comparing the model with semi‐rigid connections to that with fully rigid connections, an additional 30% vertical displacement was observed at the point of removal. However, geometric imperfections in the columns and diagonal braces did not cause any increase in building displacement/drift after removal. This highlights the importance of modelling the semi‐rigidity in the connections especially when the connections involve joining hollow sections.

Experimental-numerical investigation and design of bolted-cover plate connections under bending for modular steel buildings

Experimental-numerical investigation and design of bolted-cover plate connections under bending for modular steel buildings

Mechanical Behaviors of Inter-Module Connections and Assembled Joints in Modular Steel Buildings: A Comprehensive Review

Modular steel buildings offer the advantages of time-saving construction, reduced on-site work, and less resource waste. The mechanical behavior of modular connections is complex, depending on the type of connecting method and the load-transferring path. The aim of this paper is to offer an overview of the methods for creating inter-module connections. First, we discuss the existing inter-module connections, including vertical connections, horizontal connections, and module-to-concrete-core-wall connections. Then, the mechanical performance and simplified models of the inter-module connections are reviewed in detail; these have a significant influence on the development of modular steel buildings. Finally, the prospects of module-to-module connection are summarized. Despite the increasing amount of research that explores module-to-module connections, fully modular buildings have not yet been achieved, hindering the further development and use of modular steel buildings. In this context, self-locking connections and laminated double-beam connections are proposed, with the aim of promoting the increased use of modular steel buildings.

Collapse mechanism of three-dimensional modular steel buildings: Effect of steel wall and difference with traditional steel frame

This paper presents a numerical study on the collapse performance of 3-D MSB (modular steel building) in four module-removal scenarios: removals of a single corner module, single edge module, single interior module, and two edge modules. The final global deformation, resistance-displacement relationship, inter-module connection force, and contribution of the steel wall of the MSB structure are reported. The difference of the collapse mechanism between the MSB structure and traditional steel frame structure is also elaborated. It is found that using a 2-D model will significantly overestimate the deformation of the MSB structure in corner module loss due to the neglect of the floor slab, ceiling slab, and steel wall in the orthogonal direction. Under the interior and edge module loss circumstances, significant compression buckling can be observed in steel walls of the structure. In the condition of corner module loss, however, diagonal tension zones are found in the steel walls. The contribution of the steel wall to the resistance of the MSB structure in different module-removal scenarios is about 35%–66%. The existence of the steel wall delays the development of the tensile force and even results in compression force in the connection. In the two-edge module-removal scenario, when the steel wall is not considered, the MSB structure performs as a traditional steel frame, in which all connections between the adjacent modules are in tension. However, when the wall thickness increases, the tension in connections at the upper storey of the MSB structure decreases and may even changes to be in compression.