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2017, Journal of Steel Structures & Construction
Modular construction methods have been adapted globally for the past few decades and are becoming more common due to their ease of use and flexibility. Structural connections between modules are required for integrity and robustness but details vary depending on the form of the module and the particular application. The behaviour of connections in analysis and design of modular buildings should particularly be taken into account in detail because of their effects on the distribution of internal forces and on structural deformations. The purpose of this paper is to present and analyse the behaviours of an innovative steel bracket connection. Experiments, including shear loading and simply supported tests, were carried out to establish directly the ultimate resistance as well as failure modes of the connections. The finite element software, Strand7, was subsequently utilised to produce models for comparison with test results. A parametric study has been carried out to investigate the effects of varying bolthole dimension and bolthole spacing on the structural behaviours of the steel bracket connection using linear analysis. The model presented in this paper was formed as a baseline for future in-depth investigations to ensure design optimisation of the steel bracket connection.
Journal of Constructional Steel Research, 2020
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 interconnected 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.
Heliyon
Steel modular building structures are being increasingly adopted for a variety of building applications since their method of construction, despite being relatively new, offers many benefits over conventional constructional methods. Even though their behaviour under gravity (dead and live) loads is generally well understood, their response to lateral dynamic loads such as seismic and wind loads, is relatively less known. Due to their unique structural detailing, their structural response and failure patterns under lateral dynamic loading can vary considerably from that exhibited by conventional structures. Limited research has shown that under lateral loadings, modular structures tend to fail at the columns which are critical members whose failure can lead to partial or total collapse of the structure. This paper aims to mitigate this by shifting the failure away from the columns to inter-modular connections which can be allowed to deform in a ductile manner. Towards this end, this paper proposes two innovative inter-modular connections and investigates their performance under monotonic and cyclic lateral loading using comprehensive validated numerical techniques. The proposed connections have an additional steel plate and resilient layers to provide increased ductility and dissipation of seismic energy with desired ductile failure mechanisms. Three-dimensional numerical models of the proposed connections are developed in ABAQUS software considering geometric and material nonlinearities, as well as contact formulations to accurately capture their response to the lateral loads and failure propagations. The numerical model is verified based on experimental results in the literature and used for extensive parametric studies. Seismic reliance of the proposed connections in terms of ductility, failure patterns, and energy absorption are compared with those of a standard inter-modular connection currently used in modular buildings. The outcome of this study demonstrates that the proposed connections have superior dynamic performances compared to the standard inter-modular connections in use today. New information generated through this study will enable to improve life safety and dynamic performance of modular building structures under typical gravity loads as well as under seismic loading.
The Modular steel building technique is fast evolving as an effective alternative to conventional on-site construction. A modular steel building, while generally designed using conventional methods, is unique in its method of construction as a result of special connections and details required to facilitate lifting and other construction handling operations. An analytical investigation using the finite element method is conducted on a stringer-to-beam connection of a typical floor-system of a modular steel school, designed using the Canadian steel design code. The results of the analysis revealed a number of issues that would need to be considered in any reliable prediction of structural response of modular steel floor framing. The rigidity of the connection partially restrains the rotation of the supported beam. This leads to force distribution between adjoined beams different from the case in conventional steel construction. Observations made from these results are expected to be incorporated into design guidelines that can be used by designers for an optimal design of modular steel buildings.
Structures, 2021
Steel modular constructions involve the manufacture of fully equipped three-dimensional prefabricated modules in factory-controlled settings which are then transported to construction sites and assembled to form a complete structure. Adjacent modules are attached to each other only at their corners at inter-modular connections. Typical inter-modular connections are incapable of providing resistance against lateral dynamics loads. Current research shows that under lateral dynamic loads, steel modular buildings with rigid unyielding connectors are vulnerable to failure of the columns which result in either partial or complete collapse of the structure. Modular systems would therefore require additional in-situ lateral load resisting systems, such as shear cores, which would devalue the benefits of purely modular construction as they would need to be built in-situ. To address this shortcoming, this research proposes a novel steel inter-modular connection, with two variations, to achieve safe, reliable and ductile dynamic performance of a modular building under seismic actions. An extensive experimental program was undertaken to study the feasibility of the strength hierarchy and expected ductile failure patterns of the newly proposed inter-modular connections under monotonic and cyclic lateral loads. The experimental study revealed that the proposed inter-modular connections display superior dynamic behaviour with respect to response parameters such as moment-carrying capacity, energy dissipation and ductility. Ductile failure patterns within the connection region and away from the columns, which are critical members, were observed. This information will contribute to the design of safe and efficient inter-modular connections and enable enhanced lateral performance of steel modular buildings under dynamic loads. A comprehensive numerical model of the connection was also developed and validated for use in future parametric studies.
Journal of Constructional Steel Research, 1994
This paper presents the second part of the results of a study devoted to the analysis of heavy steel bracing connections, and to the effects of those connections on the behavior of braced frames subjected to static loads. The paper deals initially with the finite element analysis of one type of bracing connection, in which the structural fasteners such as bolted clip angles and fillet welds are modeled using the two-dimensional nodal interface element developed in a previous companion paper. Next, two series of full-scale tests of bracing connections subjected to tensile loading are described and the responses measured during the tests compared with the predictions. Good agreement was found between tests and predictions when the overall performance of the bracing connection is not strongly influenced by slip in the bolted fasteners. Lastly, one series of tests on beam-to-column connections made up of friction-bolted double clip angles is presented to validate the finite element model for this type of connection. Once validated, the finite element analysis is used to derive fundamental bracing connection flexibilities and the relative strength interaction domain to be used in a companion paper.
A combination of simple fabrication techniques and speedy site erection have made bolted endplates one of the most popular methods of connecting members in structural steelwork frames. Although simple in their use bolted endplates are extremely complex in their analysis and behaviour. In 1995 the Steel Construction Institute (SCI) and the British Constructional Steelwork Association (BCSA) jointly published a design guide for moment resisting connections [1]. The Green Book design method offers increased connection capacity using a combination of theoretical overstress in the beam compression zone and plastic bolt force distribution. This paper reports on a PhD research program at the University of Teesside which uses a combination of full scale testing and materially non-linear three dimensional finite element analyses (FEA) in order to investigate extended end plate beam-to-column connections. The FEA analyses, incorporating MYSTRO and LUSAS software [2], use enhanced strain solid and contact gap elements to model the connection behaviour.
MATEC Web of Conferences, 2018
The analysis of steel-framed building structures with full strength beam to column joints is quite standard nowadays. Buildings utilizing such framing systems are widely used in design practice. However, there is a growing recognition of significant benefits in designing joints as partial strength/semi-rigid. The design of joints within this partial strength/semi-rigid approach is becoming more and more popular. This requires the knowledge of the full nonlinear moment-rotation behaviour of the joint, which is also a design parameter. The rotational behaviour of steel semi rigid connections can be studied using the finite element method for the following three reasons: i) such models are inexpensive; ii) they allow the understanding of local effects, which are difficult to measure accurately physically, and iii) they can be used to generate extensive parametric studies. This paper presents a three-dimensional finite element model using ABAQUS software in order to identify the effect of different parameters on the behaviour of semi rigid steel beam to column end plate connections. Contact and sliding between different elements, bolt pretension and geometric and material non-linearity are included in this model. A parametric study is conducted using a model of two end-plate configurations: flush and extended end plates. The studied parameters were as follows: bolts type, end plate thickness and column web stiffener. Then, the model was calibrated and validated with experimental results taken from the literature and with the model proposed by Eurocode3. The procedure for determining the moment-rotation curve using finite element analysis is also given together with a brief explanation of how the design moment resistance and the initial rotational stiffness of the joint are obtained.
Buildings
Corner-supported modular structures are made of repetitive prefurnished, prefinished modular units, which are fabricated in a factory and transported to the site of a building to form a permanent building block. The modular units are then tied together through the use of so-called inter-modular connections, or inter-connections, which form a different configuration at joints compared to conventional steel structures. The presence of inter-connections in these structures, in addition to beam-to-column connections or intra-connections, may change their dynamic characteristics, including natural frequencies, mode shapes, and damping ratios. This paper aims to investigate the dynamic characteristics of a modular building through the use of operational modal analysis (OMA). A half-scaled three-storey modular structure, designed and instrumented with highly sensitive accelerometers, was experimentally tested under pure and randomly generated vibrations. The time history of the response ac...
2018
In multi-story steel frames, the beam-to-column connections should allow the transfer of the forces both in normal loading condition and also prevent progressive collapse when subjected to accidental loads. This paper studies the mechanical performance of a beam-to-column connection using different bolt configurations, under extreme loading situation, for which the connection’s ductility and post-flexural behaviour should provide an adequate level of robustness to the original structure. The study presents a parametric 3D FEM analysis, developed in order to assess the performance of several geometric configurations.
Journal of Constructional Steel Research, 1994
This paper presents the third part of the results of a study devoted to the analysis of heavy steel bracing connection, alut to the effects of those connections on the behavior of braced frames subjected to static loads. The paper presents initially a model compatible with standard frame analysis computer programs and capable of capturino the basic behavior of bracing connections. This is accomplished by representing the bracing connection by an equivalent three-member truss whose behavior can simulate relevant stiffness and strength of the prototype connection. This equivalent truss model is applied to the analysis of a single-story braced frame under service loads, and the sensitivity of the frame to different bracing connection stiffnesses, beam~to-column connection rotational rigidities and brace eccentricities is explored. Lastly, a more complex eight-story braced structure is analyzed under factored loads by yielding of connections and members to demonstrate the inelastic capabilities of the approach.
Materials (Basel, Switzerland), 2017
Modular systems have been mostly researched in relatively low-rise structures but, lately, their applications to mid- to high-rise structures began to be reviewed, and research interest in new modularization subjects has increased. The application of modular systems to mid- to high-rise structures requires the structural stability of the frame and connections that consist of units, and the evaluation of the stiffness of structures that are combined in units. However, the combination of general units causes loss of the cross-section of columns or beams, resulting in low seismic performance and hindering installation works in the field. In addition, the evaluation of a frame considering such a cross-sectional loss is not easy. Therefore, it is necessary to develop a joint that is stable and easy to install. In the study, a rigidly connected modular system was proposed as a moment-resisting frame for a unit modular system, and their joints were developed and their performances were com...
Connections are a key part of a steel structure and carrying them out properly is critical to achieve a safe and economical structure. Thus, establishing a solution requires knowledge of structural mechanics, ability to trace the flow of load in the beam and through the connection, experience and rational analysis of the design engineer. This paper presents a very brief history of connections, then types of connections usually used in design practice are described: angle connections, end plate connections and welded connections. In conventional analysis and design of steel framed structures joints are usually carried out under the assumption that they are either ideally pinned or fully rigid. However, experimental research shows that most connections used in current practice are semi-rigid type and their behaviour lies between these two idealized situations. Structural analysis models allow the joint representation with semi-rigid behaviour (ASRO, 2006). Eurocode 3 establishes three...
Journal of Constructional Steel Research, 2018
In this study, the seismic performance and inelastic behavior of joints were investigated using the bracket thickness, depth, and stiffener of the ceiling-bracket-type modular system as parameters. The performances of the joints were evaluated through a cyclic loading test and the nonlinear FEA. The initial stiffness, maximum flexural strength, failure mode at the ultimate stage, energy dissipation capacity, and inelastic behavior were analyzed, and it was determined whether the strong-column/weak-beam-type mechanism occurs at the joint. The results of the analysis were compared with those of the theoretical and FE models, respectively. For the comparison of the seismic performances, the flexural strength of the joint at the 0.04 and 0.05 rad inter-story drift ratios, which exceed the plastic moment, was investigated. From the comparison results, the standard specimen had a sufficient structural performance compared to the reference model, which was a welded joint. The joint was shown to be capable of maintaining a seismic performance higher than 80% of the plastic moment, and showed strain curves pointing to a strong column-weak beam behavior. In the joints, the initial stiffness was increased with a higher bracket thickness. In addition, the maximum flexural strength showed a large change in the loading direction due to the ceiling bracket. If the number of stiffeners is reduced, the joint will have both reduced initial stiffness and reduced maximum flexural strength. The bracket-type modular building was shown to be an effective and dependable modular system for resisting seismic loads, and the energy dissipation capacity of the standard specimen was shown to be higher than those of the other modular joints
Connections are a key part of a steel structure and carrying them out properly is critical to achieve a safe and economical structure. Thus, establishing a solution requires knowledge of structural mechanics, ability to trace the flow of load in the beam and through the connection, experience and rational analysis of the design engineer. This paper presents a very brief history of connections, then types of connections usually used in design practice are described: angle connections, end plate connections and welded connections. In conventional analysis and design of steel framed structures joints are usually carried out under the assumption that they are either ideally pinned or fully rigid. However, experimental research shows that most connections used in current practice are semi-rigid type and their behaviour lies between these two idealized situations. Structural analysis models allow the joint representation with semi-rigid behaviour . Eurocode 3 establishes three new categories of joints, according with both stiffness and strength criteria, required in structural modeling CEMSIG, 2010) namely: continuous, semi-continuous and simple joints. There are also presented the possibilities of modeling joints depending on the method of analysis.
Engineering Structures, 1989
A major part of this paper is devoted to a discussion of joints and connections for Moment Resisting Frames (MRFs). The demand placed on such joints for different earthquakes is examined using time-history analyses for a low-rise and a high-rise building with perimeter framing; this is compared with the experimentally determined capacities of such joints. A brief discussion of column splices indicating the proposed AISC specification for jumbo sections follows. The paper concludes with recommended details for brace-to-beam link and link-to-column connections for Eccentrically Braced Frames (EBFs) based on some recently completed analyses and tests.
Journal of Constructional Steel Research, 2020
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.
2021
In steel structures,the connections in the joints are idealized as either rigid or pinned. However in reality the connections display characteristics over a wide range of spectrum between these two idealisations. Rigid connections have some degree of flexibility, whereas pinned connections have some stiffness. Connection stiffness has a considerable effect on forces developed in the frame members as well as the lateral displacements of joints. This paper aims in determining the effects of the semi-rigid behaviour of the beam-column connection in the response of the frames. The semi-rigid connections are specified by their moment-rotation relationship. Linear moment-rotation relationship based on secant stiffness corresponding to 0.01 rad rotation has been considered in this paper. Based on this moment rotation relationship,the moment resisting frame is modelled considering rigid connections as well as semi-rigid connections. Response parameters like lateral dislacement and frame ben...
Applied Sciences, 2024
Structures must provide strength, stability, and stiffness to buildings and at the same time be efficient. This study addressed the effect of design elements and parameters on the strength of bolted lateral connections in steel beams under bending using the component-based finite element method. The variables evaluated were plate thickness, horizontal and vertical spacing between bolts, and geometric arrangement of bolts. Finite element software was used to evaluate the stress state of the junction plate, its plastic deformation, and bolt shear. A sensitivity analysis was performed to determine which bolt arrangements result in safer and more efficient designs using the same components. Stress distribution within the junction plate and plastic deformation values were used to evaluate the structural performance of the joints according to EuroCode 3. The results showed that placing bolts near the edge of a plate affected the bolts’ utilization, especially with thinner plates. Additionally, introducing an offset between central and outer bolt rows is not recommended as it worsened the stress distribution and the structural performance.
International Journal of Engineering, Transactions B: Applications
Following the Northridge earthquake of 1994, a significant number of steel moment resisting structural systems were damaged. Several studies have been conducted to improve the seismic performance of steel structures and specially their beam-to-column connections. One of the proposed connections for special moment-resisting frames included AISC-358 is Kaiser bolted bracket moment connection, briefly named, KBB. The brackets in these connections are precast steel elements. In this study, the seismic behavior of moment connection KBB has been examined under standard loading history and near-fault loading history according to ATC and FEMA codes. The results show that KBB connection has acceptable seismic performance except for deep beams. In deep beams a high prying force may occurs in upper rows of the bolts. the main reason for such phenomenon is rigidity of the bracket. Moreover use of Tapered Wedge Shims reduces pre-tensioned force in bolts and increases pinch in hysteresis curve of...
ANCHORAGE STRENGTH OF BEAM-PILLAR CONNECTIONS IN REINFORCED CONCRETE WITH BARS AND TYPE L CONNECTORS (Atena Editora), 2023
The conventional technique of anchoring in reinforced concrete beam-column connections by simple adhesion with straight steel bars can result in extensive anchorage length, according to the amplitude of the requests, harming the economy and aesthetics of the architectural project by forcing the enlargement of the column. Known solutions for transferring stresses between steel and concrete include anchoring combined adhesion with mechanical devices: pins, hooks or bends. The design of the connections of structural elements is done by applying mathematical models proposed by the technical standards, whose different calculation methodologies can result in discrepancies in the predictive analysis of the anchorage resistance with potential impacts on the costs and safety of the building. This work investigates the factors that influence the resistant capacity of beam-column connections molded with right-angle bending bars, confronting the accuracy of the ACI 318 (2019) and NBR 6118 (2014) standards for estimating the resistance of the set to the stresses. After analyzing the test data collected in the specialized literature and comparing their results with the values estimated analytically by the calculation models of the aforementioned standards, it was concluded that both codes meet the safety requirements, with the NBR being more conservative. The anchorage length proved to be the main factor influencing the anchorage efficiency, together with coverage and the compressive strength of the concrete.
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