• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.4
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• pp.33-46
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• 1999

In spite of 6.8 magnitude and the neighborhood of the epicenter, the steel moment frame survived after Northridge earthquake without collapse or casualties. However, following investigation revealed that there were severe damages at the column-weld interface of welded flange-bolted web (WFBW) steel moment connection, which was believed to be economic and safe from earthquakes based on experience and past tests. In this paper, this unexpected brittle fracture of the steel moment connection is explored using linear elastic fracture mechanics and post-Northridge tests. A method to predict the brittle fracture strength of the steel moment connection is proposed. Using this method, the failure mode of the WFBW connection and reduced beam section (RBS) connection are presented.

• Steel and Composite Structures
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• v.47 no.3
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• pp.375-382
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• 2023

The H-shaped steel beam is popular due to its ease of manufacturing and connection to the column. This profile, which is used as a shallow beam, needs the high weak-axis bending stiffness and torsional stiffness to meet the overall stability. Achieving the local beam flange stability, bearing capacity, bending stiffness, and torsional requirements need a great thickness and width of the beam flange, which causes, which will cause more uneconomical structural design. So, the box-section beam is the ideal alternative. However, the current design specifications do not have design rules for the bolt-and-welded connection of the box-section beam and box-section column. The paper proposes a novel bolt-and-welded connection of the box-section beams and box-section columns based on a high-rise structural design scheme. Three connection models, BASE, WBF, and RBS, are analyzed under cyclic loading in ABAQUS software. The failure modes, hysteresis response, bearing capacity, ductility, plastic rotation angle, energy dissipation, and stiffness degradation of all models are determined and compared. Compared with the other two models, the model WBF exhibited excellent seismic performance, ductility, and plastic rotation ability. Finally, model WBF was chosen as the connection scheme used in the project design.

• Steel and Composite Structures
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• v.47 no.2
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• pp.203-216
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• 2023

The composite beam connections often encountered fracture failure in the welded bottom flange joint, and a bottom flange bolted connection has been proposed to increase the deformation ability of the bottom flange joint. The seismic performance of the bottom flange bolted composite beam connection was suffered from both the composite action of concrete slab and the asymmetric load transfer mechanisms between top and bottom beam flange joints. Thus, this paper presents a comprehensive numerical study on the working mechanism of the bottom flange bolted composite beam connections. Three available modelling methods and a new modelling method on the flange-stud-slab interactions were compared. The efficient numerical modeling method was selected and then applied to the parametric study. The influence of the composite slab, the bottom flange bolts, the shear composite ratio and the web hole shape on the seismic performance of the bottom flange bolted composite beam connections were investigated. A hogging strength calculation method was then proposed based on numerical results.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.311-321
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• 2015

In this study, an experimental study to evaluate the seismic performance of beam-to-column connection for medium and low-rise building was conducted. Five connections using SHN490 steel were made with test variables such as flange welded or bolted, web welded or bolted. Specimen SHN-W-W is web welded and flange welded type. Specimen SHN-W-B is web welded and flange bolted type. Specimen SHN-B-W is web bolted and flange welded type. Specimen SHN-B-B is web bolted and flange bolted type. Specimen SHN-EP is a connection with the end plate to the beam ends. Cyclic loadings was applied at the tip of beam following KBC2009 load protocol. The load vs rotation curves for different connection are shown and final failure mode shapes are summarized. The connections are classified in terms of stiffness and strength as semi-rigid or rigid connection. Energy dissipation capacities for seismic performance evaluation were compared.

• Steel and Composite Structures
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• v.4 no.4
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• pp.303-315
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• 2004

Frame composed of concrete-filled steel tubular columns and I-shaped steel beam has been researched in order to development reasonable connection details. The present paper describes the results of an experimental program in four different connection details. The connection details considered include through-bolt between I-shaped steel beams and concrete-filled steel tubular columns and two details of welded connections. One of the welded connection details is stiffened by angles welded in the interior of the profile wall at the beam flange level. The specimens were tested in a cruciform loading arrangement with variable monotonic loading on the beams and constant compressive load on the column. For through-bolt details, the contribution of friction and bearing were investigated by embedding some of the bolts in the concrete. The results of the tests show that through-bolt connection details are very ductility and the bearing is not important to the behavior of these moment connections. The angles welded in the interior of the profile wall increase the strength and stiffness of the welded connection detail. In addition, the behavior curves of these connections are compared and some interesting conclusions are drawn. The results are summarized for the strength and stiffness of each connection.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.6
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• pp.21-28
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• 2012

Welded Unreinforced Flange-Welded Web (WUF-W) connection is one of Special Moment Frame (SMF) specified in ANSI/AISC-358. From the experimental test of WUF-W connection specimens conducted by the previous study, fracture occurred in the beam flange before achieving total inter-story drift angle of 0.04radian required for Special Moment Frames (SMF) system even though the specimens satisfied the design and detailing requirement specified in ANSI/AISC-358. These results are estimated as problem of the access hole geometry. In this study, a full-scale WUF-W connection specimen was made with a modified access hole geometry, and tested with the same test setting and loading as the previous test. From test results, the deformation capacity of the tested WUF-W connection specimen exceeded 4%, which is required for connections in SMF system. Comparing with the WUF-W specimens of the previous study, the strain demand of the beam flange in the tested specimen was decreased and energy dissipation capacity of the specimen was improved.

• Journal of Korean Society of Steel Construction
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• v.17 no.3 s.76
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• pp.325-335
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• 2005

This study tackles the development of an improved detail of partially restrained CFT square column-to-beam connection and the evaluation of its mechanical behavior under monotonic loading. The connection is designed to strengthen shearing capacity at the bottom of the connection due to the ultimate behavior of PR-CC by its detail of the bottom connection and simplify the fabrication process. The suggested connection is the welded bottom beam flange connection(M-2) and is compared with the existing PR-CC of bolted seat angle connection(M-1). Two specimens were fabricated in actual size and tested under monotonic loading. Based on the test results, the welded bottom beam flange connection exhibited about 85% of the stiffness of steel beam. It was similar to the bolted seat angle connection and behaved as PR-CC. The specimen of the supposed connection type failed at the shear connection of web but was similar to the bolted seat angle connection until the failure. It obtained sufficient stiffness and capacity through the reinforcingsteel and the capacity and deformational ability equivalent to the full-plastic moment through the anchor inside the steel tube at the web connection. So, it can be said that the suggested connection exhibits sufficient ductile behavior.

• Steel and Composite Structures
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• v.10 no.3
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• pp.261-279
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• 2010

Generally, a box tube, which is used for an existing square CFT structure, is made by welding four plates. The manufacturing efficiency of this steel tube is poor, and it also needs special welding technology to weld its internal diaphragm and the through diaphragm. Therefore, an interior-anchor-type square steel tube was developed using the method of cold-forming thin plates to prevent welding of the stress concentration position, and to maximize the section efficiency. And, considering of the flow of beam flange load, the efficiency of erection and the weldability of the diaphragm to thin walled steel column, the external diaphragm connection was selected as the suitable type for the welded built-up square CFT column to beam connection. And, an analytical study and tests were conducted to evaluate the structural performance of the suggested connection details and to verify the suggested equations for the connection details. Through this study, the composite effect of the internal anchor to concrete, the resistance and stress distribution of the connections before and after the existing column is welded to the beam, the effective location of welding in connection were analyzed.

• Journal of Korean Society of Steel Construction
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• v.28 no.5
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• pp.345-354
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• 2016

In the present study, hybrid moment connections of welding and bar reinforcement for composite beam-column connections were proposed. Concrete-filled octagonal tube and U-section were used for the column and beam, respectively. In the beam-column connection, the top flange and web of the beam U-section were connected to the column plate by welding. However, to reduce stress concentration at the weld joints, the bottom flange of the beam was not welded to the column plate. Instead, to transfer the tension force of the beam flange, reinforcing bars passing through the column plate were used. Four exterior connections with conventional welded and hybrid moment connections were tested under cyclic loading and their cyclic behaviors were investigated. The test results showed that the hybrid moment connections successfully transferred the beam moment to the column. The strength and ductility of the hybrid moment connections were comparable to the conventional welded moment connection with exterior diaphragm; however, the connection performance was significantly affected by the details of the hybrid moment connection.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.557-566
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• 2002

This paper summarized the results of a full-scale cyclic seismic testing on four reduced beam section (RBS) steel moment connections. Specifically, these tests addressed a bolted web versus a welded web connection and strong versus medium panel zone (PZ) strength as key test variables. Specimens with medium PZ strength were designed to promote balanced energy dissipation from both PZ and RBS regions, in order to reduce the requirement for expensive doubler plates. Both strong and medium PZ specimens with welded web connection were able to provide sufficient connection rotation capacity required of special moment-resisting frames. On the other hand, specimens with bolted web connection performed poorly due to premature brittle fracture of the beam flange at the weld access hole. Unlike the case of web-welded specimens, specimens with cheaper bolted web connection could not transfer the actual plastic moment of the original (or unreduced) beam section to the column. No fracture occurred within the beam groove welds of any connection in this testing program. If fracture within the beam flange groove weld is avoided by using quality welding procedure as in this study, the fracture issue tends to move into the beam flange base metal at the weld access hole. Supporting analytical study was also conducted in order to understand the observed base metal fracture from the engineering mechanics perspective.