• Journal of Korean Society of Steel Construction
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• v.23 no.1
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• pp.83-97
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• 2011

In this study, the seismic details of a concrete-encased, U-shaped steel beam-to-RC column connection were developed. Three specimens of the beam-to-column connection were tested under cyclic loading to evaluate the seismic performance of the connection. The test parameters were the beam depth and the column section shape. The depths of the composite beams were 610 and 710 mm, including the slab depth. For the RC columns, a square section and a circular section were used. Special details using diagonal re-bars and exterior diaphragm plates were used to strengthen the connections with the rectangular and circular columns, respectively. The test results showed that the specimens exhibited good strength, deformation, and energy dissipation capacities. The deformation capacity exceeded 4% interstory drift angle, which is the requirement for the Special Moment Frame.

• Steel and Composite Structures
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• v.26 no.6
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• pp.793-808
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• 2018

In this study, the seismic performance of the connections between L-shaped columns composed of concrete-filled steel tubes (L-CFST columns) and H-beams used in high-rise steel frame structures was investigated. Seven full-scale specimens were tested under quasi-static cyclic loading. The variables studied in the tests included the joint type, the axial compression ratio, the presence of concrete, the width-to-thickness ratio and the internal extension length of the side plates. The hysteretic response, strength degradation, stiffness degradation, ductility, plastic rotation capacity, energy dissipation capacity and the strain distribution were evaluated at different load cycles. The test results indicated that both the corner and exterior joint specimens failed due to local buckling and crack within the beam flange adjacent to the end of the side plates. However, the failure modes of the interior joint specimens primarily included local buckling and crack at the end plates and curved corners of the beam flange. A design method was proposed for the flexural capacity of the end plate connection in the interior joint. Good agreement was observed between the theoretical and test results of both the yield and ultimate flexural capacity of the end plate connection.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1305-1330
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• 2015

The successful application of the component-based approach - widely used to model structural joints - requires knowledge of the mechanical properties of the constitutive joint components, including an appropriate assembly procedure to derive the joint properties. This paper presents a component-method model for a structural joint component that is located in the tension zone of blind-bolted connections to concrete-filled tubular steel profiles. The model relates to the response of blind-bolts with headed anchors under monotonic loading, and the blind-bolt is termed the "Extended Hollo-bolt". Experimental data is used to develop the model, with the data being collected in a manner such that constitutive models were characterised for the principal elements which contribute to the global deformability of the connector. The model, based on a system of spring elements, incorporates pre-load and deformation from various parts of the blind-bolt: (i) the internal bolt elongation; (ii) the connector's expanding sleeves element; and (iii) the connector's mechanical anchorage element. The characteristics of these elements are determined on the basis of piecewise functions, accounting for basic geometrical and mechanical properties such as the strength of the concrete applied to the tube, the connection clamping length, and the size and class of the blind-bolt's internal bolt. An assembly process is then detailed to establish the model for the elastic and inelastic behaviour of the component. Comparisons of model predictions with experimental data show that the proposed model can predict with sufficient accuracy the response of the component. The model furthers the development of a full and detailed design method for an original connection technology.

• Steel and Composite Structures
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• v.44 no.3
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• pp.437-450
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• 2022

When the vertical load-bearing members in high-rise structures fail locally, the beam-column joints play an important role in the redistribution of the internal forces. In this paper, a static laboratory test of three full-scale flush flange beam-reinforced connections with side and cover plates (CP-FBSP connection) with double half-span steel beams and single L-shaped columns composed of concrete-filled steel tubes (L-CFST columns) was conducted. The influence of the side plate width and cover plate thickness on the progressive collapse resistance of the substructure was thoroughly analyzed. The failure mode, vertical force-displacement curves, strain variation, reaction force of the pin support and development of internal force in the section with the assumed plastic hinge were discussed. Then, through the verified finite element model, the corresponding analyses of the thickness and length of the side plates, the connecting length between the steel beam flange and cover plate, and the vertical-force eccentricity were carried out. The results show that the failure of all the specimens occurred through the cracking of the beam flange or the cover plate, and the beam chord rotations measured by the test were all greater than 0.085 rad. Increasing the length, thickness and width of the side plates slightly reduced the progressive collapse resistance of the substructures. The vertical-force eccentricity along the beam length reduced the progressive collapse resistance of the substructure. An increase in the connecting length between the beam flange and cover plate can significantly improve the progressive collapse resistance of substructures.

• Steel and Composite Structures
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• v.46 no.3
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• pp.403-416
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• 2023

This paper summarised and re-examined the theoretical basis of the commonly used design rule developed by Cochrane in the 1920s to consider staggered bolt holes in tension members, i.e., the s²/4g rule. The rule was derived assuming that the term two times the bolt hole diameter (2d₀) in Cochrane's original equation could be neglected, and assuming a value of 0.5 for the fractional deduction of a staggered hole in assessing the net section area. Although the s²/4g rule generally provides good predictions of the staggered net section area, the above-mentioned assumptions used in developing the rule are doubtful, in particular for a connection with a small gauge-to-bolt-hole diameter (g/d₀) ratio. It was found that the omission of 2d₀ in Cochrane's original equation appreciably overestimates the net section area of a staggered bolted connection with a small g/d₀ ratio. However, the assumed value of 0.5 for the fractional deduction of a staggered hole underestimates the staggered net section area for small g/d₀ ratios. To improve the applicability of the above two assumptions, a modified design equation, which covers a full range of g/d₀ ratio, was proposed to accurately predict the staggered net section area and was validated by the existing test data from the literature and numerical data derived from this study. Finally, a reliability analysis of the test and numerical data was conducted, and the results showed that the reliability of the modified design equation for evaluating the net section resistance of staggered bolted connections can be achieved with the partial factor of 1.25.

• Steel and Composite Structures
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• v.52 no.1
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• pp.31-43
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• 2024

A very widely used analytical method (mathematical model), mentioned in Eurocode 3, to examine the connections' bending behavior is the component-based method that has certain weak points shown in the plastic behavior part of the moment-rotation curves. In the component method available in Eurocode 3, for simplicity, the effect of strain hardening is omitted, and the bending behavior of the connection is modeled with the help of a two-line diagram. To make the component method more efficient and reliable, this research proposed its advanced version, wherein the plastic part of the diagram was developed beyond the guidelines of the mentioned Regulation, implemented to connect the end plate, and verified with the moment-rotation curves found from the laboratory model and the finite element method in ABAQUS. The findings indicated that the advanced component method (the method developed in this research) could predict the plastic part of the moment-rotation curve as well as the conventional component-based method in Eurocode 3. The comparison between the laboratory model and the outputs of the conventional and advanced component methods, as well as the outputs of the finite elements approach using ABAQUS, revealed a different percentage in the ultimate moment for bolt-extended end-plate connections. Specifically, the difference percentages were -31.56%, 2.46%, and 9.84%, respectively. Another aim of this research was to determine the optimal dimensions of the end plate joint to reduce costs without letting the mechanical constraints related to the bending moment and the resulting initial stiffness, are not compromised as well as the safety and integrity of the connection. In this research, the thickness and dimensions of the end plate and the location and diameter of the bolts were the design variables, which were optimized using Particle Swarm Optimization (PSO), Snake Optimization (SO), and Teaching Learning-Based Optimization (TLBO) to minimization the connection cost of the end plate connection. According to the results, the TLBO method yielded better solutions than others, reducing the connection costs from 43.97 to 17.45€ (60.3%), which shows the method's proper efficiency.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.4 s.50
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• pp.67-76
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• 2006

In this paper the moment transfer efficiency of a web and the strain concentration at the RHS (Rectangular Hollow Section) column-to-steel beam connections was evaluated. Initially, non-linear finite element analysis of five bare steel beam models was conducted. The models were designed to have different detail at their beam-to-column connection, so that the flexural moment capacity was different respectively. Analysis results showed that the moment transfer efficiency of the analytical model with RHS-column was poor when comparing to model with WF(Wide Flnage)-column due to out-of-plane deformation of the RHS-column flange. The presence of scallop and thin plate of RHS column was also a reason of the decrease of moment transfer efficiency, which would result in a potential fracture of the steel beam-to-column connections. Analytical results were compared with the previous experimental results. The analytical and the previous experimental results showed that the strain concentration was inversely proportional to the moment transfer efficiency of a beam web and the deformation capacity of connection was poor as their moment transfer efficiency degrades. Further finite element analyses of composite beam with a floor slab revealed that the neutral axis moved toward the top flange and the moment transfer efficiency of a beam web decreased, which led to premature failure of the connection.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.4
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• pp.61-71
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• 2010

Five half-scale beam-to-column connections in a precast concrete frame were tested with cyclic loading that simulated earthquake-type motions. Five half -scale interior beam-column assemblies representing a portion of a frame subjected to simulated seismic loading were tested, including one monolithic specimen and four precast specimens. Variables included the detailing used at the joint to achieve a structural continuity of the beam reinforcement, and the type of special reinforcement in the connection (whether ECC or transverse reinforcement). The specimen design followed the strong-column-weak-beam concept. The beam reinforcement was purposely designed and detailed to develop plastic hinges at the beam and to impose large inelastic shear force demands into the joint. The joint performance was evaluated on the basis of connection strength, stiffness, energy dissipation, and drift capacity. From the test results, the plastic hinges at the beam controlled the specimen failure. In general, the performance of the beam-to-column connections was satisfactory. The joint strength was 1.15 times of that expected for monolithic reinforced concrete construction. The specimen behavior was ductile due to tensile deformability by ECC and the yielding steel plate, while the strength was nearly constant up to a drift of 3.5 percent.

• Steel and Composite Structures
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• v.37 no.3
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• pp.307-321
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• 2020

The slim-floor solution provides an efficient alternative to the classic slab-over-beam configuration due to architectural and structural benefits. Two deficiencies can be identified in the current state-of-art: (i) the technique is limited to nonseismic applications and (ii) the lack of information on moment-resisting slim-floor beam-to-column joints. In the seismic design of framed structures, continuous beam-to-column joints are required for plastic hinges to form at the ends of the beams. The present paper proposes a slim-floor technical solution capable of expanding the current application of slim-floor joints to seismic-resistant composite construction. The proposed solution relies on a moment-resisting connection with a thick end-plate and large-diameter bolts, which are used to fulfill the required strength and stiffness characteristics of continuous connections, while maintaining a reduced height of the configuration. Considering the proposed novel solution and the variety of parameters that could affect the behavior of the joint, experimental and numerical validations are compulsory. Consequently, the current paper presents the experimental and numerical investigation of two slim-floor beam-to-column joint assemblies. The results are discussed in terms of moment-rotation curves, available rotational capacity and failure modes. The study focuses on developing reliable slim-floor beam joints that are applicable to steel building frame structures located in seismic regions.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.3
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• pp.32-40
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• 2015

The torque shear high strength bolt is clamped normally at the break of pin-tail specified. However, the clamping forces on slip critical connections do not often meet the required tension, as it considerably fluctuates due to torque coefficient dependent on lubricant affected temperature. In this study, the clamping tests of torque shear bolts were conducted independently at indoor conditions and at construction site conditions. During last six years, temperature of candidated site conditions was recorded from $-11^{\circ}C$ to $34^{\circ}C$. The indoor temperature condition was ranged from $-10^{\circ}C$ to $50^{\circ}C$ at each $10^{\circ}C$ interval. As for site conditions, the clamping force was reached in the range from 159 to 210 kN and the torque value was from 405 to $556 N{\cdot}m$. The range of torque coefficient at indoor conditions was analyzed from 0.126 to 0.158 while tensions were indicated from 179 to 192 kN. The torque coefficient at site conditions was ranged from 0.118 to 0.152. Based on this test, the variable trends of torque coefficient, tension subjected temperature can be taken by statistic regressive analysis. The variable of torque coefficient under the indoor conditions is $0.13%/^{\circ}C$ while it reaches $2.73%/^{\circ}C$ at actual site conditions. When the indoor trends and site conditions is combined, the modified variable of torque coefficient can be expected as $0.2%/^{\circ}C$. and the modified variable of tension can be determined as $0.18%/^{\circ}C$.