Column Flange Research Articles

Experimental Investigation of Composite Moment Connections with External Stiffeners

This paper presents tensile behavior for Concrete-Filled Tubular (CFT) column to H-beam welded connections. These connections were reinforced externally with T-shaped stiffeners at the junction of column and beam. Tensile loading tests and analyses were carried out for the T-stiffener connections. The results demonstrated that the overall behavior and failure modes of all the specimens were governed mainly by the horizontal stiffeners rather than by the vertical stiffeners, while the vertical stiffener only played a role in transferring the load introduced from beam to column. In addition, a simple design method for the T-stiffeneris suggested, with consideration of the effects of the shear strength of the horizontal stiffener and yield line mechanism of the column flange. The prediction and test results are compared and they are in good agreement.

A Flexibility-Based Formulation for the Design of Continuity Plates in Steel Special Moment Frames

This paper introduces a rational approach for the design of continuity plates and associated welds in steel special moment frame (SMF) connections. The current AISC Seismic Provisions require welds attaching continuity plates to develop the full strength of the plate, resulting in the need to use complete-joint-penetration (CJP) groove welds. The combination of continuity plate thickness requirements, welding process and weld inspection often leads to costly detailing that may be overly conservative. The proposed design procedure, which is based on the relative flexibility between the column flange and continuity plate, aims to quantify the seismic force demand on continuity plates, thus allowing designers to efficiently size both the continuity plate thickness and the associated welded joints. In addition, the design procedure may allow the use of fillet welds or partial-joint-penetration groove welds as opposed to CJP welds, leading to a more economical design and fabrication. Formulation of the design procedure through analytical studies, including finite element analysis, is outlined.

Research on Initial Stiffness of Top-and-Seat Angle Connections in Semi-Rigid Steel Frames

Top-and-seat angle connection is a type of semi-rigid connection, usually used in steel frame. The initial stiffness of top-and-seat angle connection is an important index for steel frame design. The article studied the initial stiffness of the connection considering the influence of column flange. The deformation and mechanical characteristics of top-and-seat angle connection were analyzed using ANSYS. According to the results of FEM analysis, theoretical models of the connection and the initial stiffness formula of connection were proposed. For verifying the correction of the formula, 8 FEM models were built and initial stiffnesses were calculated correspondingly. The formula proposed by the article agreed well with the results of the FEM analysis. And it proves that, the initial stiffness formula of top-and-seat angle connection proposed herein can be used in the design.

Behaviour of pultruded beam-to-column joints using steel web cleats

Response of pultruded Fibre Reinforced Polymer (FRP) beam-to-column joints with steel bolted web cleats is studied through physical testing. Two joint configurations are considered with either three or two bolts per cleat leg, as per drawings in a pultruder's Design Manual. Moment–rotation curves, failure modes and potential performance gains from semi-rigid action are determined from two batches, each having six nominally identical joints. Results show that initial joint properties for stiffness and moment can possess, at 19 to 62%, an extremely high coefficient of variation. All joints failed by fracturing within the FRP column's flange outstands. Because this failure mode has not been reported previously there is a need to establish how its existence influences joint design. As joint properties for the three- and two-bolted configurations are not significantly different, the middle (third) bolt is found to be redundant. Damage is shown to initiate within the column flange outstands when the mid-span deflection of a 5.08m span beam, subjected to a uniformly distributed load, is span/500. This is half the serviceability vertical deflection limit recommended in the EUROCOMP Design Code and Handbook. The mean joint moment resistance for design is established to be 2.9kNm and this is 1.5 times the moment for damage onset.

Joint panel in steel moment connections, Part 1: Experimental tests results

This paper presents results of experimental tests performed to develop a deeper understanding in the effects of joint panel shear deformation on elastic plastic behavior of the beam-to-column connections. Fourteen full-scale beam-to-column sub-assemblies were experimentally tested under cyclic loading and results of careful global and detail observations are reported. Main parameters in this investigation were joint panel strength ratio, weld joint detail, material toughness and column flange width-to-thickness ratio. It is shown that in all specimens regardless of joint panel strength ratio and weld joint detail, first crack initiation was observed at root of the weld access hole. This occurred at earlier stage with higher progress for strong and balanced panel specimens compared to weak panels. The progress of this crack was governed by beam component rotation for all specimens, and specimens with higher material toughness could sustain higher crack opening before final failure. For each series of specimens with same failure mode of beam fracture, beam cumulative plastic rotation capacity was not strongly affected by joint panel strength ratio. Experimental test results revealed that the total cumulative plastic rotation capacity is increased by reduction of joint panel strength ratio. Even weak panel specimens with heavy flange column section, could show high amount of cumulative total plastic rotation capacity at a level comparable to other weak panel specimens.

Weak-Axis Behavior of Wide Flange Columns Subjected to Blast

Much of past research in the civilian area on the response of civil structures to explosive loading has focused on large detonations in the far field that result in relatively uniform pressure distribution over the structure and specific structural elements. A paucity of research has been conducted that investigates the effect of explosive loading in close proximity to key structural elements. The studies that have been conducted focused primarily on loading perpendicular to the strong axis of bending that result in global deformation, but no rupture or loss of material. Through experimental testing and finite-element simulation, the present study investigates the effect of blast loading on wide flange columns loaded perpendicular to the weak axis of bending. This loading scenario is critical for such columns because the near field shock wave can rupture the web, and in some cases, lead to material loss; both conditions can potentially jeopardize the axial load carrying capacity of the column as a result of increased demands on flanges and possible local buckling of the unrestrained flanges. Therefore, this critical scenario needs to be considered for developing blast resistant measures or assessing the remaining axial and bending capacity of the column. Finite-element simulation can be used for this purpose; the analyses conducted as part of this study replicate, with reasonable accuracy, the experimentally obtained localized deformation, ruptures, and loss of material as a result of blast load, although the finite-element simulation is less successful at replicating the global deformation of the column.

Flange Bending in Single Curvature

Local bending of beam and column flanges is a common design consideration in steel structures. In most cases, the flange bends in double curvature due to the restraining effect of the connecting element. When a restraining force is not present, the flange will deform in single curvature. Common cases of single-curvature bending occur at the bottom flange of monorail beams and at hanger rod connections. In this paper, the equivalent width method was explored in an effort to determine design procedures for elastic and plastic strength of flanges in single-curvature bending.This paper compares the available procedures for designing flanges bent in single curvature. New finite element models and yield line analyses are used to verify, expand and improve the existing design methods. Design recommendations are made for both elastic and ultimate strength approaches. Recommendations are also made for interaction of the local bending strength with longitudinal stresses in the flange. The effects of closely spaced loads and loads acting near the ends of members are also addressed.

WUF-W connection performance to box column subjected to uniaxial and biaxial loading

The prequalified connections presented in AISC are limited to the connections of the I beam to wide flange columns. It is necessary to investigate the seismic performance of the prequalified connections to the box column, which has a very low strength and stiffness panel zone in contrast with the wide flange column. In this study, the seismic behavior of the WUF-W (welded unreinforced flange) connection to the box column was investigated through full-scale cyclic loading tests. The experimental results revealed that this type of connection to the box column can satisfy the prequalified criteria of the special moment frame. Moreover, the main advantage of using box column is its high biaxial bending strength. Therefore, as part of the analytical study, the connection subjected to biaxial loading for a series of parameters was investigated. The analytical investigation showed that in order to achieve the desired performance under biaxial loading, the panel zone must provide the strong column/weak beam ratio of more than what is suggested by AISC. Furthermore, the analytical study revealed that for the box column under biaxial loading, the inner diaphragm may not be suitable because of the potential for the weld to fracture.

Experimental and numerical analysis of E-stubs in three dimensional joints: A new analytical formulation for the stiffness calculation

This paper focuses on the stiffness of the E-stub component that appears in three dimensional joints with additional plates welded to the column flanges. This component is not covered by the formulation of Eurocode 3. So in this work a new formulation for the calculation of the E-stub stiffness is presented. Numerical models have been calibrated on the basis of the results of six experimental tests with different geometries where column size and bolts distances have been taken into account. The comparison with the experimental results shows that the proposal finite elements models are able to accurately reproduce the behaviour of the E-stub. A parametric study is also undertaken and a new formulation for the calculation of the E-stub stiffness is proposed.

Resistance of flush endplate connections under tension and shear in fire

Abstract This paper presents an experimental and numerical study to the resistance of flush endplate connections in fire. Six transient fire tests were performed on two types of connections with flexible and stiff endplate. For each connection, three load combinations were tested and the test results were reported. The test shows that most connections failed within the range of 500 °C to 650 °C. Extreme bending deformation of the endplate and flexural deformation of the bolt were observed when the plate thickness was 8 mm. When the endplate thickness became 16 mm, deformations occurred to the column flange and the bolts as the endplate became thicker than the column flange. Connection fire resistances were found to decrease with increase of either tension or shear, but the connection deformations were similar regardless of the load combination within the range tested. The three-dimensional finite element simulations of the tests with flush endplate connections were conducted with general-purpose finite element program ABAQUS. The results obtained from analysis showed a good agreement with the experimental responses. Parametric study was performed to the connection failure mechanisms under an extensive range of load combinations of tension and shear in fire using the finite element model. Conclusions were drawn regarding the tension and shear interactive relationships for the two typical connections at different temperatures.

Buckling and Postbuckling Finite-Element Analysis of Pultruded FRP Profiles under Pure Compression

Results of nonlinear finite-element analyses of commercial pultruded fiber-reinforced plastic (PFRP) I-section profiles subjected to pure compression are presented. One narrow flange and four wide flange shapes are analyzed for 10 values of the column slenderness, involving 50 finite-element (FE) models. The imperfection sensitivity is investigated with reference to different imperfection shapes. For wide flange columns, if the imperfection amplitudes are identified with the limiting amplitudes reported by the pultruders, extremely low ultimate axial loads are obtained, associated with unrealistic failure mechanisms and strong interaction between local and global buckling modes. In contrast, reduced imperfection amplitudes reported in the literature lead to well documented failure mechanisms and to a small influence of the buckling mode interaction. As is known, the local buckling of wide flange shapes is triggered by the flange instability. Conversely, the local buckling of narrow flange shapes generally is triggered by the web instability. Because of this property, the paper shows that at equal cross section area, the narrow flange profiles may exhibit higher ultimate loads with respect to the wide flange profiles in a broad range of column slenderness.

Panel zone evaluation of direct connection to box column subjected to bidirectional loading

SUMMARYAs an effective factor for force‐controlled components, in special moment frames, the main advantage of using box column is high biaxial bending strength. Most research studies have been concentrated on the box column performance subjected to unidirectional loading. On the other hand, seismic provisions given so far in codes are limited to beam to wide flange column connections with planar webs. In the research work presented, the bidirectional loading configurations are adopted to better simulate the actual response of the box column subjected to a ground motion excitation. The connection used in the article is welded unreinforced flange–welded web, being the direct connection that was introduced in the American Institute of Steel Construction as one of the prequalified connection. Analytical results from finite element method indicate that when the structure is subjected to bidirectional loading, the level of shear and flexural strength capacity of the box column reduces. Because of the yielding of the panel zone and the inner diaphragm, the distribution of stress and strain in the finite element models reveals that the design criteria presented in most seismic codes seem not to place the plastic hinge out of the panel zone region and therefore need to be modified. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental analysis of column web under transverse loading

The case of a transverse load applied in the plane of profile is common in steel construction. Examples include the reaction at a simple support, the pressure of a roller on a beam of the raceway and the concentrated effort of compression provided by the compression flange in a column-beam joint. In this paper, the attention is focused on the study of the partially encased column web and flange in compression, by investigating the whole force displacement behavior of this component by means of an experimental program planned and carried out on eighteen specimens. Analytical formulations for predicting the resistance are analyzed. And the results obtained by the proposed formula are more aligned with the test results.

Panel zone modelling of Flanged Cruciform Columns: An analytical and numerical approach

Flanged cruciform sections are proper alternatives for columns of orthogonal moment-resisting frames because of their outstanding structural characteristics and their easy fabrication process, especially regarding continuity plates. However, providing all conventional details of I-shaped columns, such as panel zone doubler plates, is not applicable. In this paper, a new panel zone detail for Flanged Cruciform Columns is proposed as a practical solution to increase the shear strength and stiffness of the panel zone region and to supersede the common doubler plates. The proposed detail includes inclined plates welded to edges of the column flanges and to continuity plates and two new corrugated panel zones parallel to the main panel zone. According to the different load path and behaviour of the proposed detail, new behaviour models and design equations are provided. The results of detailed parametric finite element analyses showed that the inclined plates and Accordion Paths effectively contributed to panel zone shear strength and stiffness. Furthermore, the proposed behaviour models and the designed relationships are in good agreement to numerical results and can estimate the connection behaviour reasonably well.

Design and Analytical Evaluation of a New Self-Centering Connection with Bolted T-Stub Devices

A new posttensioned T-stub connection (PTTC) for earthquake resistant steel moment resisting frames (MRFs) is introduced. The proposed connection consists of high strength posttensioned (PT) strands and bolted T-stubs. The post-tensioning strands run through the column and are anchored against the flange of the exterior column. The T-stubs, providing energy dissipation, are bolted to the flange of beam and column and no field welding is required. The strands compress the T-stub against the column flange to develop the resisting moment to service loads and to provide a restoring force that returns the structure to its initial position following an earthquake. An analytical model based on fiber elements is developed in OpenSees to model PTTCs. The analytical model can predict the expected behavior of the new proposed connection under cyclic loading. PTTC provides similar characteristic behavior of the posttensioned connections. Both theoretical behavior and design methods are proposed, and the design methods are verified based on parametric studies and comparison to analytical results. The parametric studies prove the desired self-centering behavior of PTTC and show that this connection can reduce or eliminate the plastic rotation by its self-centering behavior as well as providing required strength and stiffness under large earthquake rotations.

Ductility Enhancement of Post‐Northridge Connections by Multilongitudinal Voids in the Beam Web

Since the earthquakes in Northridge and Kobe in 1994 and 1995, respectively, many investigations have been carried out towards improving the strength and ductility of steel beam to column pre- and post-Northridge connections. In order to achieve these objectives, recent researches are mainly focused on three principles: reducing the beam section to improve the beam ductility, adding different kinds of slit damper to beam and column flanges to absorb and dissipate the input earthquake energy in the connection and strengthening the connection area using additional elements such as rib plates, cover plates, and flange plates to keep the plastic hinges away from the column face. This paper presents a reduced beam section approach via the introduction of multilongitudinal voids (MLV) in the beam web for various beam depths varying from 450 mm to 912 mm. ANSYS finite element program was used to simulate the three different sizes of SAC sections: SAC3, SAC5, and SAC7. Results showed an improvement in the connection ductility since the input energy was dissipated uniformly along the beam length and the total rotation of the connection was over four percent radian.

이종강종을 사용한 고강도 CFT 합성부재의 구조성능

플랜지와 웨브에 서로 강도가 다른 이종강재를 사용한 CFT 합성구조의 거동특성을 파악하기 위하여, 플랜지는 건축용 800MPa급 강재인 HSA800, 웨브에는 일반강도 강재인 SM490 강재를 사용하여 실험연구를 수행하였다. 주요실험 변수는 강관의 강도 조합, 충전된 콘크리트의 강도, 콘크리트 충전효과이다. 이종강재간의 용접접합부는 낮은강도 강재에 적합한 용접부를 사용하여 접합부 성능을 검증하였다. 실험체의 거동특성을 평가하기 위해 편심압축 실험을 수행하였으며, 현행 설계기준들에 따른 예측결과와 비교하였다. 플랜지에 고강도 강재를 적용함에 따라 단면의 축강도 및 휨모멘트강도가 증가하였으며, 부재 강도를 충분히 발현한 이후 용접부에서 파괴가 일어났다. 실험결과 현행 설계기준을 적용하여 합성단면의 축력-모멘트 상관관계 및 유효휨강성을 안전측으로 예측 가능하였다. Structural tests were performed to investigate the structural performance of concrete-filled steel tube column using different strength steels in their flange and web with high-strength steel HSA800 and mild steel SM490, respectively. The test parameters included the strength of column flange and infill concrete, and effect of concrete infill. Connection between different grade steels were welded using the electrode appropriate for mild steel and verified its performance. To evaluate the behavior of test specimens, eccentric loading tests were performed and the results were compared with the prediction by current design codes. Axial load and moment carrying capacity of test specimens increased with the yield strength of compression flange and weld fracture occurred after the specimen shows full strength. The prediction result for axial load-bending moment relationship and effective flexural stiffness gave good agreement with the test result.

Shear strength formula of CFST column-beam pinned connections

Recently, as the height of building is getting higher, the applications of CFST column for high-rise buildings have been increased. In structural system of high-rise building, The RC core and exterior concrete-filled tubular (CFST) column-beam pinned connection is one of the structural systems that support lateral load. If this structural system is used, due to the minimal CFST column thickness compared to that of the CFST column width, the local moment occurred by the eccentric distance between the column flange surface from shear bolts joints degrades the shear strength of the CFST column-beam pinned connections. This study performed a finite element analysis to investigate the shear strength under eccentric moment of the CFST column-beam pinned connections. The column's width and thickness were used as variables for the analysis. To guarantee the reliability of the finite element analysis, an actual-size specimens were fabricated and tested. The yield line theory was used to formulate an shear strength formula for the CFT column-beam pinned connection. the shear strength formula was suggested through comparison on the results of FEM analysis, test and yield lime theory, the shear strength formula was suggested.

Numerical Investigations of Steel Beam-to-Column Connections with Reinforcing Plates

This study presents the results of nonlinear finite element analyses performed on improved steel beam-to-column connections with reinforcing plates. The aim is to protect the potentially vulnerable beam-to-column groove welded joint by relocating the plastic hinge away from the column interface. The numerical investigation is based on results from experimental tests carried out on a two-storey steel frame tested at the JRC ELSA Laboratory and involves the modeling of the 3-way beam-to-column joint. The results of the numerical analyses on reinforced joints show that failure indices decrease in the weld region and near the weld access hole compared to the unreinforced connection, but high values of the Triaxiality Index are registered in the weld at the column interface. In order to eliminate the high shear stress in the beam flange and to reduce the high triaxial stress condition at the beam flange-column flange interface, the beam flange was disconnected from the column flange.

Experimental investigation of inelastic buckling of built-up steel columns

This paper experimentally investigated the buckling capacity of built-up steel columns mainly, Cruciform Columns (CC) and Side-to-Side (SS) columns fabricated from two Universal Beam (UB) sections. A series of nine experimental tests comprised of three UB sections, three CC sections and three SS sections with different lengths were tested to failure to measure the ultimate axial capacity of each column section. The lengths used for each category of columns were 1.8, 2.0, and 2.2 m with slenderness ratios ranging from 39-105. The measured buckling loads of the tested specimens were compared with the predicted ultimate axial capacity using Eurocode 3, AISC LRFD, and BS 5959-1. It was observed that the failure modes of the specimens included flexural buckling, local buckling and flexural-torsional buckling. The results showed that the ultimate axial capacity of the tested cruciform and side-by-side columns were higher than the code predicted design values by up to 20%, with AISC LRFD design values being the least conservative and the Eurocode 3 design values being the most conservative. This study has concluded that cruciform column and side-to-side welded flange columns using universal beam sections are efficient built-up sections that have larger ultimate axial load capacity, larger stiffness with saving in the weight of steel used compared to its equivalent universal beam counterpart.