Moment-resisting Connections Research Articles

Experimental and analytical evaluation of semi-rigid timber connection with screwed-in threaded rods and steel coupling part

A major challenge for mid and high-rise timber buildings is fulfilling serviceability requirements. Moment-resisting timber frames with semi-rigid moment-resisting connections as the primary lateral load-resisting system can be an alternative to buildings with wind bracing or shear walls, allowing for more free space, enhanced building performance, and architectural flexibility. Moreover, introducing semi-rigid timber connections can improve the performance of floors against human-induced vibrations and potentially decrease the material used. The performance of moment-resisting frames depends mainly on the properties of their beam-to-column connections. The paper presents an experimental investigation of semi-rigid moment-resisting connections with long screwed-in threaded rods and a steel coupling part. Long threaded rods (i.e., screwed-in threaded rods with wood screw threads) feature high axial stiffness and resistance and allow for immediate load transfer without initial slip. Due to these properties, threaded rods are preferred over conventional dowel-type fasteners such as bolts and dowels. Five full-scale moment-resisting timber connections were tested under cyclic and monotonic loading to investigate moment resistance, rotational stiffness, and energy dissipation. The stiffness obtained by cyclic and monotonic tests was compared with numerical and analytical methods. The beam-to-column moment-resisting connections demonstrated a high moment resistance of 92.2 kNm and rotational stiffness of 8049 kNm/rad without initial slip. The experimental results and analytical calculations of rotational stiffness differed only by 5 %, whereas the finite element model exhibited a discrepancy of approximately 35 %. The equivalent viscous damping was determined based on cyclic load tests at service load levels and was found to be in the range of 5.5 %–10.0 %. Finally, a parametric study is presented to discuss the effect of semi-rigid connections on the performance of the timber floors and material savings. The increase in rotational stiffness of the beam-to-column connections could lead to up to 13 % material savings.

A New Moment-Resisting Glulam Beam-End Connection Utilizing Mechanically Fastened Steel Rods—An Experimental Study

A new moment-resisting mass timber connection was designed based on the principles of force equilibrium in applied mechanics. The connection configuration utilizing two mechanically fastened threaded steel rods embedded into the end of a glulam beam section was experimentally investigated in this study. A gradually increasing transverse load was applied to the free end of a cantilevered beam, causing a bending moment on the beam-end connection until failure. Four different connection configurations were examined, each replicated twice to verify results. The beam connection parameters investigated were rod anchorage length (200 and 250 mm) and square washer size (38.1 and 50.8 mm). Test results show that increasing the washer size increased the connection bending strength by increments more significantly than those due to increasing the rod anchorage length. However, the connection configurations with the smaller-size washer, which failed mainly due to wood crushing under the washer, had higher ductility ratios than those with the larger-size washer, which failed due to steel rod yielding. In a real-life scenario, a structural element such as a glulam beam is usually loaded to approximately 50% to 70% of its design capacity, considering a reasonable margin of safety. The study estimates a maximum possible bending moment utilization factor for the strongest connection configuration that ranged between 34% and 48% compared to the maximum moment resistance of a supported glulam beam spanning an average length of 4.0 m to 6.0 m (a common span length in framed timber buildings) and has a cross-section size same as the one utilized in this study. This utilization factor is quite large for a timber connection, and thus, confirms a considerable moment-resisting capability of the new configuration developed in this study.

Experimental and Numerical Investigation on Flexural Strengthening of Precast Concrete Corbel Connections with Fiber-Reinforced Plastic Sheet

This paper presents the results of experimental and numerical investigations aimed at enhancing the flexural capacity of Precast Concrete Corbel Beam–Column Connections (PC-CBCCs) using Fiber-Reinforced Plastic (FRP) sheets. The experimental study primarily focused on assessing the flexural capacity of pinned PC-CBCCs reinforced with FRP layers, comparing them to a moment-resisting connection. A series of half-scale specimens, including three PC-CBCCs with varying FRP configurations, were tested alongside one in situ concrete fixed connection. The first specimen (PC-1) utilized L-shaped and full-wrap FRPs, whereas PC-2 and PC-3 employed both U-shaped and full-wrap layers. The objective is to quantify the ultimate flexural capacity of PC-CBCCs reinforced by FRP sheets. In PC-3, the external anchorage is introduced to assess its influence on delaying the FRP layer debonding under lateral loading. The effects of the FRP layer thickness, locations, and potential debonding are examined under unidirectional static tests while applying a constant axial compressive load to the columns and subjecting the beams to lateral loads until fracture. The test results illustrate that strengthening the corbel connection with L-shaped FRP or spiral U-shaped FRP sheets without mechanical anchorage cannot result in a significant bending capacity due to debonding. However, with the incorporation of mechanical anchors, the connection manages to enhance the moment capacity to 81% of a fixed connection’s flexural capacity. Additionally, a finite element model of the PC-CBCCs and a fixed joint is developed to simulate nonlinear static analyses of the connections using ANSYS 19.2 software. The simulation model is precise in predicting the initial stiffness and ultimate capacity of the beam–column joints, as verified by the experimental results. A comprehensive comparison is conducted to determine their responses by employing various FRP configurations and properties. Moreover, design parameters such as bond length and thickness of the FRP sheets, along with appropriate mechanical anchorage, are identified as effective in preventing debonding, and delamination. However, wrapping the beam far away from the joint interface has a minimal impact on the failure mode, stress reduction, and load-bearing capacity.

An investigation and design of novel moment-resisting beam-column connections for precast concrete construction

This study investigates the behavior of hybrid beam-column connections with numerous detailing methods to be incorporated into precast concrete moment-resisting frames under simulated reversed cyclic loading, and ultimately develops a design procedure. Seismic performance of moment-resisting precast concrete beam-column connections was investigated through simulated reversed cyclic load tests. In addition, nonlinear finite element analysis (FEA) of typical monolithic and precast concrete connections was carried out using a modified concrete damage plasticity model. Good agreement was achieved between experimental and numerical results, which indicates that the FEA model is capable of capturing failure modes of the investigated precast concrete connections. Simple detailing modifications resulted in major improvements in the performance of connections in terms of load-displacement curves, stiffness, and energy dissipation. Finally, a design procedure was developed for the investigated connections based on failure modes and investigated limit states.

A Timber–Concrete–Composite Edge Connection for Two-Way Spanning Cross-Laminated Timber Slabs—Experimental Investigations and Analytical Approach

This paper introduces a method to create a moment-resisting edge connection between two cross-laminated timber (CLT) panels. With this connection, two-way spanning cross-laminated timber slabs can be realised, where the span exceeds the manufacturing and transport-related width of the individual CLT panels. Until now, mostly on-site gluing solutions have been suggested for such connections. In this study, a solution using a timber–concrete–composite (TCC) system is proposed. For this, self-tapping screws are inserted along the edge face of the CLT component, enabling the formation of a lap splice between two adjacent CLT elements. This lap splice is reinforced by additional rebars and filled with concrete. This means that only familiar, easy-to-handle materials are used on-site, and there is no need for adhesives, which can be difficult to apply. To evaluate the load-bearing capacity of the connection, it was subjected to a pure bending load in four-point bending tests, where load-bearing capacities of up to 70% of the characteristic load-bearing capacity of the solid CLT elements were achieved. An analytical approach for a simplified engineering calculation model is introduced to determine the load acting upon the screws. Based on the experimental results, it is shown that the analytical approach is able to adequately represent the load-bearing capacity of the connection. The analytically determined forces on the screws may then be used to carry out further verifications on this connection method.

Numerical analysis on the lateral resistance and reinforcement of bolted glulam post and beam structures with local cracks

The lateral resistance of bolted glulam timber frame structural system is highly influenced by the mechanical performance of the moment-resisting connections, while local cracks are commonly observed in the bolted glulam connections with the restraint of steel fasteners to wood shrinkage. In this paper, a three-dimensional finite element model was established in business software ANSYS to investigate the influence of cracks on the cyclic behavior of moment-resisting bolted glulam connections and the strengthening effect of friction dampers installed in pre-cracked connections. The numerical model was validated by comparison with full-scale experimental results. Furthermore, a nonlinear numerical model was developed for the glulam timber post and beam structures, and comprehensive analysis was conducted to explore the effect of the number and location of pre-cracked connections and the application of friction dampers on the lateral performance of framed structures. It was found that with local cracks set in the moment-resisting connections, the lateral stiffness and capacity of the framed structures can be reduced by 27% and 30%, respectively. With the installation of friction dampers in pre-cracked connections, the lateral capacity and energy dissipation capacity of the reinforced frame can be up to 1.36 and 2.77 times that of initially perfect frame.

Experimental study on seismic behavior of high strength steel flange-plate connections with box columns

The flange-plate beam-to-column connections are a promising option for reinforced moment-resisting connections in ductile steel frames and have potential applicability in high strength steel frames. However, there have been few investigations on flange-plate connections with high strength steel box columns. In this study, experiments were conducted to evaluate the seismic behavior of high strength steel flange-plate connections with box columns. Seven specimens were designed and tested under anti-symmetrical cyclic loads, comprising three different combinations of Q355 or Q460 steel beams and Q460 or Q690 steel columns. While the expected beam failure mode was observed in five specimens, two specimens experienced ESW joints failure, and one specimen experienced CJP weld failure. These findings highlight the possible impact of welding quality defects in engineering applications. The test results about bearing capacity, rotation stiffness, deformation capacity, and energy dissipation were reported and analyzed. Under the similar design conditions, the use of higher strength steel members results in a decrease in the initial stiffness of the specimens, as well as changes in yielding modes, deformation proportion, and energy dissipation capacity. Six flange-plate connections met the deformation and bearing capacity requirements for special moment frames in AISC 341 with the ultimate story drift angle not less than 0.06 rad. The proposed criteria for determining the minimum size of flange plates was verified in this study, and design recommendations were made for flange-plate connections in high strength steel frames.

An Overview of Commonly Used Steel Beam-Column Connection in Indonesia for Low-Rise Building

The Indonesian seismic provision for steel structures was initiated in 2002. The use of steel has also been increasing as a choice of structural material since then. However, there are still many weaknesses in the seismic design of steel structures that have been carried out so far. A lot of beam-column connections in steel buildings in Indonesia use a haunch in a moment-resisting connection system. Haunched systems are not described in AISC 358 as permitted connections for earthquake-resistant buildings. Recently, Europe publishes European Prequalified Steel Joints (EqualJoints). There are four types of connections discussed, and one of them is the haunched type connections. The haunched connection meets the seismic requirements to be suitable for use as an earthquake-resistant connection in Europe. This can be used as a reference if we are going to design a haunched connection in Indonesia. However, special attention should be paid to the details. The bolt configuration, the thickness of the end plates, and the shape of the haunch are not like those commonly used in Indonesia, there must be improvements to be adjusted in EqualJoints. So that the performance of the connection against earthquakes becomes more guaranteed.

Glulam Beam-to-Column Connection with Coupled Steel Rods with Screwheads: Concept and Experimental Verifications

The bolted connections with slotted-in steel plates are basic beam-to-column connections of modern post-and-beam timber building structures. However, due to significantly pinched rotational behaviors, the moment resistance of such connections are usually ignored in design. In this study, the connection-level moment resistance is enabled for modern glulam frame structures with an innovative connection design. A pair of long steel rods with screwheads is designed to generate a force couple at the sides of the connection. The proposed connection could be considered as the key lateral force resisting component, indicating a significant reduction of lateral braces and shear walls. Specimens of the target connection were carefully designed and tested in the lab to obtain their mechanical properties and failure modes. Finite element models were established and calibrated according to the tested data. The moment-rotation curves of the new connection could be easily estimated through a fitted formula. Moreover, the suggestions to improve the proposed connection is also discussed based on the observed damage modes. Results show that the new connection could be treated as rigid moment-resisting connections while the ductility could be further improved.

Mechanical Behavior of Glued Laminated Bamboo Moment-Resisting Connections

Mechanical Behavior of Glued Laminated Bamboo Moment-Resisting Connections

A practical design of cold-formed steel bolted moment connection: numerical investigation with an improved bolt slip-bearing model

Cold-formed steel (CFS) is in the spotlight as a structural material for buildings and civil infrastructures because it is easy to produce and is cost effective. Recent studies have advanced the popularity and usability of CFS even more by showing its potential as a structural member suitable for special moment-resisting structures. Within the framework of those studies, CFS bolted moment-resisting connections allow the through-plate to protrude beyond the beam depth in both the upper and lower directions, like wings, which could hamper placing decks on the beams. This study proposes a modification to such through-plates, in which one protruded portion is eliminated and the depth of the other is extended instead in order to enhance the practicality in field applications. Finite element analysis is used to investigate and verify the proposed design candidates and finally, suggest an optimum design configuration. Since the bolted connection has a significant impact on the structural response of the CFS beam, an improved bolt modeling approach is suggested based on the bolt modeling approaches proposed by past researchers. The suggested bolt modeling approach is shown to provide better accuracy in simulating plastic deformations in the bolted connection area and the consequent failure behavior when compared to the existing approach. The numerical analysis results show that the through-plate with one wing-side cut should have the depth of the other wing-side such that the diagonal edge could make an angle larger than 35 degrees. To prevent the possibility of buckling in the changed through-plate, attaching the flange plate perpendicular to the diagonal edge is highly recommended. The findings from this study are expected to provide a guidance for the through-plate design in practical structure design. • A practical design for through-plate in CFS bolted connections is suggested. • Modeling approach for bolted connections based on measured torque is proposed. • In modeling of bolted connection, effect of rotational constraint is critical. • Significance of bolt slip-bearing mechanism included in bolt modeling is emphasized.

Cyclic performance of moment connections with reduced beam sections using different cut-flange profiles

Abstract Reduced beam section (RBS) behaviours with various cut-flange configurations were investigated numerically in this study. A three-dimensional finite element model material non-linearity was built and validated experimentally, and the impacts of the cut--flange profile on the moment-rotation behaviour and ductility response of moment-resisting connections were investigated in a parametric form. Five-moment connections with various forms of decreasing beam flange were thus modelled using ABAQUS software and compared in terms of cyclic behaviour. RBS with circular, rectangular, trapezoidal, triangular, and drilled holes cut-flange configurations were adopted, and the finite element analysis results showed that radius cut RBS have uniform stress contours, while a re-entrant corner in rectangular, trapezoidal, or triangular cut-flange profiles’ connections may result in stress concentration, resulting in a fracture of the flange. In addition, the numerical testing showed that the RBS connection with a circular cut-flange profile offers a lower rupture index than other connections. Thus, the RBS created using circular cut-flange profiles dissipates more energy than other connections.

Seismic Performance of Precast Concrete Frame Beam-Column Connections with High-Strength Bars.

As the construction industry is striding towards the industrialization of green buildings, a precast concrete frame beam-column joint with high-strength reinforcement was proposed. Simulate reversed cyclic loading was carried out on two precast connections and one cast-in-place connection to examine the seismic behavior of the proposed new precast connection. The main test variables between the two precast connections were the strength of the reinforcement at the bottom of the beam. The failure shape, hysteresis curve, skeleton curve, strength, deformation ability, stiffness degradation, and energy dissipation were monitored and compared with the cast-in-place connection. The findings of this paper showed that the precast joints had good strength reserve, and the seismic performance in the later stage of loading even exceeds the cast-in-place joints. It was also found that the plastic hinge zone of the beam could be moved away from the column surface via reinforcement method. Additionally, based on the experiment, a detailed nonlinear finite element analysis (FEA) method was developed to reproduce the test response of specific types of bending moment-resistant precast concrete beam-column connections under a reversed loading test, which provided a theoretical reference for further research of the connections.

Method for Designing Prequalified Connections Using Generative Design

Designing prequalified connections is a process of iterative calculation, in which certain dimensions are varied until the verifications and restrictions stipulated by the standard are met. This is a slow process that can be automated using various software and optimized using a new design method called generative design, which consists of establishing restrictions so that the script delivers multiple solutions that meet the objectives. This research was conducted based on the design science research (DSR) methodology and focused on developing a method to design moment-resisting steel connections, specifically end-plate connections, using generative design in a building information modeling (BIM) environment. From this, it was possible to obtain several end-plate connection design alternatives, and technical validation was carried out to verify the functionality of the program using a verification method proposed by a civil engineer.

Experimental and Numerical Study of an Innovative Infill Web-Strips Steel Plate Shear Wall with Rigid Beam-to-Column Connections

Steel plate shear walls (SPSWs) offer good energy dissipation capability when subjected to seismic forces as a robust lateral load resisting structure. This research investigated the cyclic behaviors of innovative infill web-strips (IWS-SPSW) and conventional unstiffened steel plate shear (USPSW) experimentally and numerically. As a result, two specimens of a 1:3 scale three-story single-bay IWS-SPSW and USPSW were fabricated and tested under cyclic lateral loading. Rigid moment-resistant connections were used for the steel plate shear wall beam-column connection. The steel shear walls with infill web strips showed high ductility and less shear load-bearing than the USPSW. The hysteresis results showed that the IWS-SPSW had high energy dissipation with no severe beam-columns damages. On the other hand, the USPSW displayed severe post-buckling, infill panel cracks, and first-floor column damages. Moreover, the IWS-SPSW shear strength did not fall in the test specimen beyond 2.5% average story drift, where the structure exhibited great seismic behavior. FE models were created and validated with experimental data. It has been proven that the infill web-strips can affect an SPSW system’s high performance and overall energy dissipation. From a parametric study, the material features of the infill web-strips, such as steel strength and thickness, can enhance the system’s impact even more.

Experiments on cyclic behaviour of cold-formed steel-rubberised concrete semi-rigid moment-resisting connections

This paper presents the results of full-scale physical tests on a recently developed cold-formed steel (CFS) semi-rigid moment-resisting connection infilled with rubberised concrete (RuC) for seismic application. The connection comprises side-plates attached to both sides of built-up tubular CFS beam and column sections through either screwed or welded connections. The tests were performed on both bare steel and CFS-RuC composite connections under cyclic loading for comparison purposes. The predominant modes of failure are beam local buckling and side plate plasticity in the bare steel connections and screw shear failure in the composite connections. The results show that the composite connection typically reaches 45% higher strength and 21% greater energy dissipation capacity than the bare steel connection both having 24 screw arrays. These indicate the beneficial effects of the infill RuC in prevention of the beam local buckling in connections with identical connection configuration. The energy dissipation capacity of the bare steel connection having 36 screw arrays, however, was 70% greater than that of the composite connection with 24 screw arrays. This reflects side plate plasticity being a more effective energy dissipation mechanism than the other identified mechanisms.

Experiments on cold-formed steel moment-resisting connections with bolting friction-slip mechanism

This paper presents an experimental investigation into the cyclic behaviour of cold-formed steel (CFS) moment-resisting (MR) beam-to-column connections utilising a friction-slip mechanism within a web-bolted connection arrangement. The bolting slip back and forth movements are accommodated through slotted holes to dissipate seismic energy within the CFS MR connections. Nine full-scale experiments were conducted on connections with and without slip for comparison purposes. The slip connections were designed to undergo slip prior to the initiation of local buckling in the CFS beam. This avoids premature local buckling, which could significantly degrade strength, particularly for connections with lower thickness beams. The slip connections, as a result, produce a greater energy dissipation capacity and ductility factor by up to 79% and 2.5 times, respectively, than that of the corresponding slip-resistant connections.

Moment-resisting self-drilling dowel connections between steel link beams and CLT for coupled walls

Coupled cross-laminated timber (CLT) walls can be created by connecting steel link beams between adjacent CLT wall panels and are an efficient alternative to conventional cantilevered CLT shear walls. Effective coupling in the coupled wall system requires the beam to wall connections to have adequate strength to ensure a ductile link beam response and adequate stiffness to yield the link beams at relatively low inter-storey drifts. This study evaluates beam to wall connections with a group of self-drilling dowels (SDDs) installed through an 8mm steel knife plate to connect 200UB18 steel link beams to 5-ply CLT walls. A simplified method for determining the connection strength is presented and used to capacity design the test specimens. The capacity design method was validated for the tested specimens because the damage was concentrated in the steel link beams and the connection’s peak strength was not exceeded. This study indicates that the SDD connections may be a feasible beam to wall connection solution in coupled CLT wall systems because the capacity protected connections had adequate strength and relatively high stiffness.

Mechanical performance of glulam beam-column moment-resisting connections with self-tapping screws as fasteners

The innovation and improvement of connection technology is an important topic in the field of timber structure. With the development of manufacture process, the self-tapping screws or threaded rods with sufficient lengths and optimized threads provide an alternative way to realize the strong and stiff timber connection. The self-tapping screw applied as a fastener can cut threads by itself on the internal surface of a pre-drilled hole in wood, and thus establish the mechanical interlocking through the tight fit between the self-tapping screw and the wood. In order to expand the application of self-tapping screws in timber construction and explore diverse techniques to achieve timber connections with a capacity to resist moment, this paper presents experimental investigations on the glulam beam-column moment-resisting connections using self-tapping screws as fasteners. A series of withdrawal tests are carried out on 240 specimens to research the withdrawal property of self-tapping screws in glulam. A total of 16 full-scale beam-column connections with 8 different geometric configurations are tested under cyclic loading to research the mechanical performance of the connections regarding moment resistance, rotation stiffness, deformability, hysteresis characteristics, stiffness degradation and energy dissipation capacity. The results indicate that this type of connection with self-tapping screws is characterized by a high moment resistance and rotation stiffness, but not very considerable deformability and energy dissipation capacity.

Development of composite cold-formed steel-rubberised concrete semi-rigid moment-resisting connections

This paper presents the development of a composite cold-formed steel (CFS)-rubberised concrete (RuC) semi-rigid moment-resisting connection suitable for framed building structures. The connection comprises built-up tubular cold-formed steel beam and column sections connected using side-plate screwed fasteners and infilled with rubberised concrete. A detailed finite element analysis validated against physical tests is employed to model both bare steel and composite beam-to-column connections subjected to lateral and gravity loadings. The governing design limit states are characterized as local buckling in bare steel beams, connection screw shear failure, and side plate plasticity. It is shown that the strength and ductility capacity of composite connections could be increased by up to 1.44 and 3.46 times, respectively, compared with those of the bare steel connections. The connection rigidity of both bare steel and composite connections can be classified as a semi-rigid joint.