• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.1 s.47
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• pp.25-32
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• 2006

In this study the seismic performance of welded steel moment connections to built-up box columns in the existing building built before 1994 Northridge earthquake was evaluated by cyclic tests. According to the test results, the pre-Northridge steel moment connections to the box columns also suffered from brittle fracture similar to that in the H-shaped column connections. However, the flange force transfer mechanism of the box column connections was substantially different from that of the H-shaped column connections, and the patterns of crack propagation may be changed due to the shape of the box column. Therefore, it is required to develop proper details for the box column connections instead of using the research results for H-shaped column connections in order to enhance the seismic performance the connections.

• Journal of Korean Society of Steel Construction
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• v.15 no.6 s.67
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• pp.701-709
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• 2003

The paper presented the seismic performance of T-stiffener moment connections for use in steel moment-resisting frames. The connections were strengthened by welding the vertical and horizontal clement of the T-stiffener to the beam flange and column f1ange. Finite clement analysis and experiments were conducted to determine the behavior of T-stiffener-reinforced connections. The results of the finite element analysis confirmed the effectiveness of the T-stiffener, whose horizontal element lengthened to mitigate local stress concentrations of the beam flange on the horizontal stiffener. Full-scale specimens were also tested cyclically to study hysteresis behavior. The main parameters used were the ratio of the T-stiffener to beam strength and the shape of the horizontal element. As the length of the horizontal element increased, the deformation capacity of the connections enhanced. Likewise, all specimens behaved according to the Ramberg-Osgood curve and showed stable hysteresis behavior.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.823-829
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• 2002

The composite frame system with reinforced concrete column and steel beam has some advantages in the structural efficiency by complementing the shortcomings between the two systems. The system, however has also a lot of problems in practical design and construction process due to the material dissimilarities. Considering these circumstances, this research is aimed at the development of the composite structural system which enables the steel beams to be connected to the R/C columns with higher structural safety and economy. Basically the proposed connection system is composed of four split tees, structural angles reinforced by stiffener, high strength steel rods, connecting plates and shear plates. The structural tests have been carried out to verify the moment transfer mechanism from beam flange to steel rods or connecting plates through the angle reinforced by siffener. The four prototype specimens have been tested until the flange of beam reached the plastic states. From the tests, no distinct material dissimilarities between concrete and steel have been detected and the stress transfer through wide flange beam - structural angle - high strength steel rod or connecting plate is very favorable.

• Journal of Korean Society of Steel Construction
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• v.27 no.6
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• pp.513-523
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• 2015

In steel moment frames constructed of H-shapes, strong-axis moment connections should be used for maximum structural efficiency if possible. And most of cyclic seismic testing, domestic and international, has been conducted for strong-axis moment connections and cyclic test data for weak-axis connections is quite limited. However, when perpendicular moment frames meet, weak-axis moment connections are also needed at the intersecting locations. Especially, both strong- and weak-axis moment connections have been frequently used in domestic practice. In this study, cyclic seismic performance of RBS (reduced beam section) weak-axis welded moment connections was experimentally investigated. Test specimens, designed according to the procedure proposed by Gilton and Uang (2002), performed well and developed an excellent plastic rotation capacity of 0.03 rad or higher, although a simplified sizing procedure for attaching the beam web to the shear plate in the form of C-shaped fillet weld was used. The test results of this study showed that the sharp corner of C-shaped fillet weld tends to be the origin of crack propagation due to stress concentration there and needs to be trimmed for the better weld shape. Different from strong-axis moment connections, due to the presence of weld access hole, a kind of CJP butt joint is formed between the beam flange and the horizontal continuity plate in weak-axis moment connections. When weld access hole is large, this butt joint can experience cyclic local buckling and subsequent low cycle fatigue fracture as observed in this testing program. Thus the size of web access hole at the butt joint should be minimized if possible. The recommended seismic detailing such as stickout, trimming, and thicker continuity plate for construction tolerance should be followed for design and fabrication of weak-axis welded moment connections.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.629-639
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• 1998

This paper summarizes the results of full-scale cyclic seismic performance tests on three column-tree type steel moment connections. Each test specimen consisted of a $H-600{\times}200$ beam and a $H-400{\times}400$ column of SS41 (SS400). Key parameter included was column PZ (panel zone) strength relative to beam strength. The seismic performance of specimen with stronger PZ tended to be inferior. Total plastic rotations available in the specimens ranged from 1.8 to 3.0 (% rad). The limited test results in this study seem to support the speculation that permitting PZ yielding shall be more beneficial to enhancing total plastic rotation capacity of the moment connection. Beam flange fracture across the heat affected zone and divot-type pullout of the column flange were observed in the tests. A conceptual mechanical model consistent with observed test results was also sought.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.431-439
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• 2014

Concrete filled tubular columns are widely used because the mutual reaction between the concrete and the tube improves strength and ductility of the columns. In an attempt to secure efficient use of members, built-up square columns featuring large width-thickness ratio and the use of thin steel plates are suggested in this study. In order to evaluate the structural characteristics and seismic performance of the column-to-beam connections of the new shape columns, cyclic load test of T-shaped column-to-beam connections was conducted with variables of diaphragms and concrete-filling. Moment-rotational angle relationship, dissipated energy and failure behavior were compared to evaluate stress transfer mechanism of the new shape built-up square column-to-beam connections associated with the variables.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.385-396
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• 2014

Traditionally, domestic steel design and construction practice has provided extra shear studs to moment frame beams even when they are designed as non-composite beams. In the 1994 Northridge earthquake, connection damage initiated from the beam bottom flange side was prevalent. The upward moving of the neutral axis due to the composite action between steel beam and floor deck was speculated to be one of the critical causes. In this study, full-scale seismic testing was conducted to investigate the side effects of the composite action in steel seismic moment frames. The specimen PN700-C, designed following the domestic connection and floor deck details, exhibited significant upward shift of the neutral axis under sagging (or positive) moment, thus producing high strain demand on the bottom flange, and showed a poor seismic performance because of brittle fracture of the beam bottom flange at 3% story drift. The specimen DB700-C, designed by using RBS connection and with the details of minimized floor composite action, exhibited superior seismic performance, without experiencing any fracture or concrete crushing, almost identical to the bare steel counterpart (specimen DB700-NC). The results of this study clearly indicate that the beams and connections in seismic steel moment frames should be constructed to minimize the composite action of a floor deck if possible.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.193-203
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• 2022

In this study, in order to compare the seismic performance of steel structure beam-column connection details and non-scallop connection details mainly used in Korea, a full-scale static cyclic loading test and FEM analysis were conducted through the same modeling as the experiment. For quantitative numerical comparison, the strain concentration ratio and moment transfer efficiency used in previous studies were cited. As the welding area of the beam web decreased, the deformation rate of the beam flange increased, and the plastic deformation capacity according to the rotation angle decreased or brittle fracture occurred. Comparing the analysis results with the experimental results, the possibility of brittle fracture tended to increase when the web welding ratio for the total cross-sectional area of H-shaped fell below 60%.

• Journal of Korean Society of Steel Construction
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• v.20 no.6
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• pp.829-838
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• 2008

In this study, cyclic tests of beam-column connections composed with members applicable to the domestic low-middle rise steel buildings were conducted to develop seismic connection details and its evaluation. Connection types and material properties of the steel were testing variables and the difference between the newly developed seismic rolled section (SHN490) and existing rolled section (SM490) was also investigated. Distributions of the yield strength and the ultimate strength of the SHN490 rolled section were relatively uniform comparing to those of the SM490 rolled section Brittle fracture in the weldments of the test specimens was not observed. Instead, fracture occurred at heat-affected zones or the stress-concentrated point near the weld access hole of the beam flanges. In the case of identical rolled-section specimens, the rotational capacity and dissipated energy of the WUF-W connection was larger than those of the WUF-B connection. In the case of identical connection types, the rotational capacity and dissipated energy of the SHN490 section connection was larger than those of the WUF-B section connection.

• Journal of Korean Society of Steel Construction
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• v.20 no.3
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• pp.445-454
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• 2008

Based on previous research on steel moment connections, experimental and analytical results showed that the deformation capacity was poor in specimens using RHS columns and with conventional weld access holes and strain concentration at the end of beam is influenced by the efficiency in transmitting the moment in the web of beam through the beam-to-column joint. This paper is focused on the retrofitting of pre-Kobe steel moment frame connections using a stiffened RBS and a welded horizontal stiffener. These retrofitting methods were considered only in beam bottom flange. A parametric study was performed using nonlinear finite element analysis to elucidate and improve the retrofit methods of connections.