Web Cleat Research Articles

Numerical Analysis for Behavior of Stainless-Steel Web Cleat Connections at Elevated Temperatures

Numerical Analysis for Behavior of Stainless-Steel Web Cleat Connections at Elevated Temperatures

Metoda procjene kolapsa čeličnog okvira temeljena na faktoru dinamičkog povećanja

To study the laws of evolution of dynamic increase factors (DIFs), relationship between the DIFs and progressive collapse resisting capacity of a structure with web cleat joints under the column removal scenario, a refined finite element model is established based on an existing quasi-static test. The laws of evolution of DIFs are studied for different loading type, beam height, and joint rotation stiffness. It was observed that the displacement-based dynamic increase factor (DIFu) increases with an increase in the load level in elastic and elastic-plastic stages, and it decreases with an increase in the load level in the plastic stage. With an increase in structural damage, DIFu reaches the maximum value when the frequency ratio is equal to 1 and decreases with a further increase in frequency and damping ratios. The load-based dynamic increase factor (DIFp) is negatively corelated to the “arch compression effect” of the beam. Finally, a method based on DIFu is proposed for judging the collapse of structures with web cleat joints. In addition, an improvement is provided for the design the web cleat joint. The improvement is proved to be reasonable and effective with the help of collapse evaluation method proposed in this study.

Resilience of prefabricated concrete frames using hybrid steel-concrete composite connections

The progressive collapse resistance of prefabricated concrete frames with hybrid steel-concrete composite connections (HSCC) is rarely studied. To fill the gap, five (one reinforced concrete (RC) and four prefabricated concrete) 1/2 scaled beam-column sub-assemblages were designed and tested. In four prefabricated concrete specimens, different HSCC types, top and seat with web angle (TSWA), end plate (EP), top and seat angle (TSA), and web cleat (WC), were employed. Experimental results demonstrated that the failure patterns of prefabricated concrete frames with HSCC are different from that of the RC frame counterpart. The failure of the prefabricated concrete frames is governed by the shear fracture or thread stripping of the bolts in the connections while that of the RC frame is governed by the fracture of beam longitudinal rebar. Due to brittle failure of the connections in prefabricated concrete frames, both ultimate bearing capacity and deformation capacity of prefabricated concrete frames are smaller than the corresponding RC frame. Among them, the prefabricated concrete frame with the EP connection achieves the greatest first peak load or compressive arch action capacity. However, no catenary action could be developed in this specimen.

Development of Rotation Capacity Model for Web Cleat Connections against Progressive Collapse: Bayesian Approach

Development of Rotation Capacity Model for Web Cleat Connections against Progressive Collapse: Bayesian Approach

Cyclic Response of Bolted and Hybrid Pultruded FRP Beam-Column Joints between I-Shaped Sections

This paper presents cyclic behaviour of bolted and hybrid–combined bolted and bonded fibre reinforced polymer (FRP) beam-to-column joints between I-shaped members using steel and FRP cleats. Five full-scale cyclic tests are carried out to study moment-rotation behaviour, cyclic response, and failure patterns. The test parameters include position of cleat (flange or combined web and flange), fastening method (bolting or hybrid–combining bolting and bonding) and cleat material (steel or FRP). First two tests had bolted and hybrid joints with steel flange and web double angles. Next two tests had the same joint detailing but with no web cleats. Last test used bolted joint only with FRP web and flange cleats. Three failure modes were observed: shear-out failure of the beam’s bolted zone, adhesive debonding with shear-out failure and delamination cracking. Cyclic performance of the joints was assessed by hysteresis moment-rotation curves and accumulated dissipated energy. Hybrid joints showed the best overall cyclic performance with accumulated dissipated energy about 75% higher than the bolted joints. Bolted joints with FRP cleats exhibited the worst cyclic performance. Flange cleated joints showed similar performance to web and flange cleated joints.

Effectiveness of CFS web cleat bolted connections between beam–to–column

This paper aims to study the experimental behavior of web cleat, bolted between beam–to–column in terms of strength, relative rotation, and failure mechanism of web cleat leg attached to the column web. The study was carried out to understand the effect of 230 mm depth (B) of web cleat primarily subjected to a shear load. Three different parameters were considered for the study namely (i) aspect ratio (L/B = 0.15–0.42) of web cleat leg attached to the column, (ii) thicknesses of web cleat (TC = 1.5 mm, 2.0 mm and 2.5 mm), and (iii) bolt configuration (Bn = 2 and 3 numbers). The aspect ratio (L/B) was taken as the ratio of the flat distance (between the folded line and bolt line) to the depth of the clip angle. A total of thirty-eight specimens of different configurations were tested under a four-point bending test. The test results indicate an increase in the ultimate strength with the reduction in aspect ratio. Similarly, the ultimate strength increased for the specimens with a three-bolt configuration when compared to the corresponding specimens with a two-bolt configuration. A majority of the tested specimens failed due to local buckling except few specimens which exhibited shearing of bolts and bearing of the beam under the loading points. A comparison of test results with the literature indicates that the test results are un-conservative for two–bolted specimens with slenderness ratio (λ) of the web cleat lesser than 0.6. The reliability studies were performed for the design of bolted web cleat configuration with limitation.

Numerical simulation for structural behaviour of stainless steel web cleat connections

A finite element model for predicting the moment-rotation curves of stainless steel web cleat connections is developed, and validated by test data. The effects of several parameters (i.e., number of bolts, gage distance of angles, thickness of angles, and types of stainless steel) on the moment-rotation curves of stainless steel web cleat connections are investigated using the validated finite element models. The stiffness and ultimate moment of stainless steel web cleat connections increase as the angle thickness or number of bolts increases, and they decreases as the gage distance of angles increases. S22053 stainless steel web cleat connections exhibit a higher stiffness and moment resistance than S30408 and S31608 stainless steel web cleat connections. Chen and Kishi's model can accurately predict the moment-rotation curves of stainless steel web cleat connections, but the initial stiffness and ultimate moment capacity calculated from Kishi and Chen are not ideal. An empirical formula for calculating the initial stiffness of web cleat connections is proposed. Compared with the test data for the initial stiffness, the average error of the proposed formula is only 14.67%, making it more accurate than existing models. The finite element analysis results indicate that current yield line mechanisms for the angle may not reflect the behaviour of the angle. A new yield line mechanism for the angle is proposed on the basis of stress distribution in the angle at the ultimate strength state. An analytical model for estimating the ultimate moment capacity of web cleat connections is derived. The proposed formula produces a more accurate prediction than the existing formulas, as the average error of the ultimate moment capacity between the estimated values and test data is only 6.00%. Good agreement between the proposed model and the moment-rotation curves of the test data is observed. Design recommendations for the structural behaviour of stainless steel web cleat connections are provided.

Moment-rotation behavior of semi-rigid web cleat connections

The behavior of beam-column semi-rigid connection plays an important role in the response of a steel moment resisting, stiffness and rotation capacity framed structure, especially under static loading conditions. In this study, the moment-rotation characteristics of semi-rigid bolted connections using web cleat connections with IPE standard profile is discussed, based on the experimental investigation. The study revealed that the moment resistance of beam-column semi-rigid connection is improved by increasing the height of the beam to the height of web cleat joint (H), and the increasing thickness of web and flange in web cleat joints. The aim was to provide necessary data to improve the Eurocode 3 and efficiently use residue IPE standard profiles, rather than send them back to the consumption cycle. While the resistance moment increased with an increase in H from Hmin to Hmax.

An Overview of Progressive Collapse Behavior of Steel Beam-to-Column Connections

Local failure of one or more components due to abnormal loading can induce the progressive collapse of a building structure. In this study, by the aid of available full-scale test results on double-span systems subjected to the middle column loss scenario, an extensive parametric study was performed to investigate the effects of different design parameters on progressive collapse performance of beam-to-column connections, i.e., beam span-to-depth ratio, catenary mechanism, and connection robustness. The selected full-scale double-span assemblies consisted of fully rigid (welded flange-welded web, SidePlate), semi-rigid (flush end-plate, extended end-plate), and flexible connections (top and seat angle, web cleat). The test results, including load-deformation responses, development of the catenary mechanism, and connection robustness, are presented in detail. The finding of this research further enables a comprehensive comparison between different types of steel beam-to-column connections since the effects of span-to-depth ratio and beam sections were filtered out.

Comparative experimental studies on the web cleat bolted CFS beam-to-column connection

Cold-formed steel (CFS) clip angles/web cleats are widely used as connectors between two CFS members. This study aims to determine the efficiency of a three bolted web cleat over a two-bolted web cleat joint between the beam-column predominantly subjected to a shear load. A total of 26 specimens were studied to investigate the three bolted web cleat configuration by considering two different parameters: (i) thickness of the web cleat (TC) and (ii) the aspect ratio (L/B) of the web cleat leg attached to the column. The experimental results show that the ultimate load increases with a decrease in the aspect ratio of the web cleat leg attached to the column. In addition, the experimental loads of three-bolted configuration were 13 to 95% higher than the corresponding two-bolted configuration. Two types of failure modes were observed: (i) local buckling and (ii) bearing failure of CFS beam under the loading points. The lateral deflection of the column, relative rotation of the connections, and vertical deflection under the loading points were measured and analysed. The nominal shear values calculated from available equations in the past studies are over-conservative when compared to the observed experimental shear values. Hence, a new design equation is suggested for the design of three-bolted web cleat configuration with some specified limits. Besides, reliability studies were performed for the existing and proposed equations for the design of web cleat with three-bolt configuration.

Structural behaviour of steel-timber composite (STC) beam-to-column connections with double angle web cleats subjected to hogging bending moment

This paper deals with an experimental study of steel-timber composite (STC) beam-to-column connections with double web angles, with the aim of developing an efficient composite flooring system that exhibits superior structural performance yet is simple and cost-effective from a construction perspective. The experimental program involved the testing of six cruciform subassemblies representing internal beam-to-column connections subjected to negative (hogging) bending moments. In four specimens, STC beams were connected to the flanges of a universal column by double web angles. Additionally, a specimen with bare steel beams and another specimen with steel-concrete composite (SCC) beams were fabricated and tested to provide benchmarks for comparing the structural behaviour of the STC with bare steel and SCC beam-to-column connections. It is shown that the STC connections exhibit semi-rigid behaviour with negative bending moment and rotation capacities larger than that of SCC connections. Lastly, an analytical model which is an extension of the existing component-based method is proposed for estimating the negative bending moment capacity of the STC connections with double web angles.

Semi-rigid partial-strength steel-timber composite (STC) connections with mechanically anchored steel rods

In steel composite constructions, replacing the concrete slabs with prefabricated timber slabs significantly reduces the embodied energy and carbon footprint and lowers the self-weight of the structure and the size of the columns and footings. Considering the advantages of the light-weight steel-timber composite (STC) floors, this paper presents the results of laboratory experiments conducted on six (STC) beam-to-column subassemblies with double angle web cleats and fin plate (nominally-pinned) connections. Preserving continuity of the slabs across the column increases hogging bending moment resistance and stiffness of the composite beam to column connections. Here, the connection between the timber slabs across the column was provided by threaded rods placed inside the timber slabs and mechanically anchored in the pockets of cementitious grout. The STC subassemblies were subjected to a monotonically increasing push-down load to simulate behaviour of the nominally-pinned beam-to-column connections. The results of laboratory tests revealed that mechanically anchored rods can be used to effectively transfer the tensile force developed in the timber slabs of the STC floors and accordingly enhance the stiffness and hogging bending moment capacity of the simple STC beam-to-column connections. The effect of the number, size, and strength grade of the steel rods on stiffness, strength and ductility of the STC connections were evaluated experimentally and component-based method was employed to develop a simple mechanical model for predicting the bending moment capacity of the STC connections with mechanically anchored rods.

Investigation of a steel connection to accommodate ductility demand of beams in fire

In fire conditions the provision of connection ductility is key to the prevention of brittle failure and progressive collapse of steel and steel-concrete composite framed structures. This paper describes the development and testing of a novel connection concept intended to provide appropriate ductility enhancement compared to that of conventional connection types. The connection consists of two connection pieces, each of which takes the form of a web cleat which includes a semi-cylindrical section. This section allows the beam-end to move towards or away from the column-face by deforming plastically. A simplified analytical model has been developed to simulate the mechanical behaviour of the proposed connection, and this model will eventually enable the incorporation of this new connection type into global frame analysis to be used in performance-based structural fire engineering design. The model has been tested against FEA simulations and against model-scale experiment results, indicating that it can predict the behaviour of the connection with satisfactory accuracy. Preliminary sub-frame analysis results indicate that the proposed connection behaves similarly to an idealized pinned connection under ambient-temperature conditions, but provide significantly larger ductility, and resistance to disproportionate collapse, compared to conventional connection types.

Structural behaviour of stainless steel beam-to-tubular column joints

This paper complements previous research conducted by the authors on stainless steel bolted joints and reports the first systematic study on the structural behaviour of stainless steel beam-to-tubular column joints with the use of Hollo-bolts. Six full scale specimens including two flush plate joints, two top and seat cleat connections, and two top, seat and web cleat connections of single-sided beam-to- hollow section column joints have been tested and the results are reported in detail. All specimens were in Grade EN 1.4301 austenitic stainless steel and were designed in such a way that a variety of failure modes could be obtained including plastification of the tubular column face, of the connecting angle cleats or the flush plates. For each specimen the moment-rotation response, the evolution of strains in critical locations of the connections and the separation between the column face and the connected beam was monitored and is reported herein. In parallel with the tests, advanced nonlinear FE models were developed. Following validation against the obtained experimental results, parametric studies were conducted to study the effect of key parameters such as, material grade, column face thickness, end plate/angle cleat thickness and bolt spacing on the stiffness, strength and ductility of the joints. Based on both the experimental and numerical results, it was verified that the connections displayed excellent ductility and attained loads much higher than the ones predicted by design standards for carbon steel joints.

Behaviour of stainless steel beam-to-column joints — Part 1: Experimental investigation

Research on stainless steel structures has primarily focused on the structural response of individual members, whilst the response of joints has received far less attention to date. This paper reports for the first time full-scale tests on stainless steel beam-to-column joints, subjected to static monotonic loads, whilst the companion paper reports numerical studies on similar connection typologies to the ones studied herein. The joint configurations tested include one flush and one extended end plate connection, two top and seated cleat connections, and two top, seated and web cleat connections of single-sided beam-to-column joints. All connected members and connecting parts including bolts, angle cleats and end plates are in Grade EN 1.4301 stainless steel. The full moment-rotation characteristics were recorded for each test and the experimentally derived stiffness and moment resistance for each joint was compared to the codified provisions of EN1993-1-8. It was verified that the connections displayed excellent ductility and attained loads much higher than the ones predicted by design standards for carbon steel joints.

Effect of boundary conditions on the behaviour of composite frames against progressive collapse

Boundary conditions, such as the horizontal and out-of-plane restraints, play an important role in structural resistance and deformation capacity of composite frames under column removal scenarios. Most studies only focused on interior frames with rigid horizontal and out-of-plane restraints, whereas limited data are available on the effects of weak restraints and out-of-plane rotations on the behaviour of composite frames against progressive collapse. In this study, a series of experimental tests were conducted on composite frames with different horizontal and out-of-plane restraints. Web cleat and flush end plate connections were used in the frames. Experimental results showed that when subject to in-plane loading, exterior composite frames could mobilise significant catenary action to mitigate progressive collapse and eventually column failure might occur under catenary action in bridging beams. For composite frames with out-of-plane rotation, the ultimate resistance was substantially reduced due to lateral torsional buckling of composite beams at large deformation stage. However, the flexural resistance of frames was less susceptible to boundary conditions compared to catenary action. Furthermore, bending moments at side columns were evaluated to gain insight into the behaviour of side columns under horizontal tension force at the catenary action stage. Moreover, component-based models were developed for composite frames and validated against test data. Design recommendations were provided in accordance with experimental and numerical results.

Experimental study about composite frames under an internal column-removal scenario

During the past decade, numerous research works have been conducted about building structures against progressive collapse. Among the conducted beam-column joint tests, normally it was assumed that the inflection point was located at the middle of the beam span. However, from the composite joint tests conducted by the authors, it was observed that this assumption may not be correct. In this paper, a series of experimental tests has been conducted to estimate the structural behaviour of composite frames under a middle column loss. The bending moment distribution among the middle and the side joints was investigated at the frame level. Two types of connections, namely web cleat and flush end plate connections were both studied. The experimental results show that the internal composite frames can form catenary action well. Also, it is found that the load-carrying capacities of the internal composite frames would be reached when beam-column joint failed. In addition, flexural action and catenary action can be formed more significantly if more reinforcing bars were used in the composite floor system. The bending moment distributions among middle and side joints are identified. In addition, according to UFC 4–023-03 published by DoD, all the horizontal tie forces should be carried by slab, since none of steel connections can reach the rotation angle of 0.2rad. According to this suggestion, more reinforcing bars were used in composite slab in the conducted experimental tests and the effectiveness of the enhanced tie forces was investigated in this study. Also, the rotational capacities of composite beam-column joints were obtained.

Distortional lateral torsional buckling for simply supported beams with web cleats

Critical moment expressions for steel beams based on elastic lateral torsional buckling as given in classical solutions and present standard provisions are based on assumed fully restrained support...

Dynamic analyses of bolted-angle steel joints against progressive collapse based on component-based model

Some design methods have been proposed to prevent progressive collapse of building structures. Alternate Path (AP) Method is the most effective and popular one among them. Based on component-based joint models, this paper takes AP Method to study the dynamic performance of two-dimensional (2D) bolted-angle steel joints under a sudden column removal scenario. The comparison between the quasi-static and dynamic responses of the component-based models simulated by finite element software and the experimental test results shows that the component-based models are reliable. After that, based on the validated component-based models, parametric study was conducted in order to study the dynamic responses of bolted-angle steel joints subjected to different levels of sudden gravity loads. These 2D steel joints employ two types of beam–column connections, including web cleat connections and top and seat with web angle connections. Dynamic increased factors (DIFs) are obtained by comparing the acquired dynamic responses with the corresponding nonlinear static responses of the bolted-angle steel joints. Finally, DIFs calculated in this study are compared with the regulations of Department of Defense (DoD) in United States and a simplified energy balance method. As a conclusion, it is found that the numerical results in this study are in good agreement with the energy balance method.

Robustness of simple joints in pultruded FRP frames

Structural robustness of simple beam-to-column joints in pultruded frames is assessed through tension pull tests. The tying capacity and failure modes are determined from static tests on two batches of specimens for six joints. Tying resistance is an important joint property for maintaining structural integrity in frames in case of accidental loads. No tests have been previously reported to investigate this key structural property for the design of Pultruded Fibre Reinforced Polymer (PFRP) structures. The tension pull tests consist of a PFRP Wide Flange (WF) section bolted to a stiff steel baseplate by a pair of PFRP web cleats, and at the other end the tensile load is applied. One batch of three specimens has a WF 254×254×9.53mm section with 100×9.53mm cleats of equal leg-angle material and the other has a WF 203×203×9.53mm with angles of size 75×9.53mm. Tension versus displacement curves are plotted to establish linear-elastic response, damage onset, non-linear response and ultimate tensile strength. Damage initiation is characterised by audible acoustic emissions. The load–displacement curve remains linear elastic up to 0.35 to 0.4 of the maximum (ultimate) tension force and damage happens at 0.6 of the ultimate value. Failure is from excessive delamination cracking emanating in the region of a cleat's fillet radius. A model to predict tying resistance is proposed, and successfully calibrated against experimental results. The most important finding of this study is that a pair of 9.53mm thick PFRP leg-angle web cleats should possess an adequate tying capacity for design against disproportionate collapse.