Column Flange Research Articles

Ductile fracture prediction for welded steel connections under monotonic loading based on micromechanical fracture criteria

Micromechanics-based fracture criteria for structural steels can be used to predict ductile fracture initiation with large-scale yielding and no initial flaws. High-fidelity finite-element analyses were carried out on ten welded connection specimens between the square steel tube column and H-beam flange under monotonic tensile loading. The calibrated micromechanics-based fracture criteria, including the Stress Modified Critical Strain (SMCS) model and the Void Growth Model (VGM), were used to predict fracture initiation for each specimen. The predicted results demonstrated high accuracy compared to test results. Sensitivity analyses of fracture toughness parameters in the SMCS model and VGM to the predicted fracture results were conducted. The results show that, when the fracture toughness parameters were increased or reduced by twenty percent, fluctuations in the predicted fracture results were within the acceptable range. Therefore, calibrated micromechanics-based fracture criteria can be used to predict ductile fracture initiation of connections under monotonic loading. Subsequently, the user subroutine VUMAT, from ABAQUS software edited by the authors, was employed. Using the SMCS model and VGM as fracture criteria, the post-fracture load–displacement curves of eighteen notched round bar specimens and two welded connection specimens (between the square steel tube column and H-beam flange) that fractured at different locations were traced by deleting the failure elements one by one. The predicted results agree well with the test results. Consequently, these calibrated micromechanics-based fracture criteria and associated simulating techniques can be used for collapse analysis of steel structures during extreme events.

Performance Study for T-Stub Considering the Bending Capacity of Bolt

The bending capacity of the beam end-plate or the column flange and the tensile property of the bolt could be expressed by an equivalent t-stub model. In this paper, ten groups of different sizes of T-stub are designed for monotonic loading test. The accurate element models are established for comparable study with the experimental result. The stress distribution and deformation characteristics of the T-stub and bolts are determined. A theoretic formula of tensile stiffness for T-stub is derived, it is presented that the calculation results are consistent with the tests.

Probabilistic demand and fragility assessment of welded column splices in steel moment frames

SummaryAn assessment of seismic demands and capacities of welded column splice (WCS) connections in steel moment frames is presented. For demand assessment, nonlinear dynamic analyses are conducted for two case‐study buildings, that is, a 4‐story and a 20‐story moment frame. Results from the nonlinear dynamic analyses are assessed through a probabilistic seismic demand analysis (PSDA) framework to characterize recurrence rates of longitudinal flange stress in these connections. The PSDA is applied in two contexts. First, in the context of WCS connections constructed prior to the M 6.7 1994 Northridge earthquake, the PSDA is combined with sophisticated finite element‐based fracture mechanics analysis to compute the mean annual frequencies of fracture in these connections. The pre‐Northridge WCS are especially critical because they feature partial joint penetration and brittle materials that compromise their resistance to fracture. The analysis indicates that the mean annual frequencies of fracture in these connections may be unacceptably high for both the 4‐story and the 20‐story frames. This warrants a serious and urgent consideration of retrofit strategies. These findings are attributed to the brittleness of the pre‐Northridge splices (as indicated by the fracture mechanics simulations), as well as the force‐controlled nature of these components, wherein low‐intensity ground motions contribute disproportionately to fracture risk, as evidenced by fracture risk disaggregation. Second, in the context of new construction, the PSDA provides meaningful stress magnitudes for design. Currently, WCS connections employ complete joint penetration welds with the intent to develop the smaller column flange in yielding. The PSDA conducted in this study suggests that this requirement may be too stringent because stress demands in the splices corresponding even to high return periods (e.g., 2475 years) are significantly lower (~40 ksi), as compared with the stress required to yield the column (~55 ksi). Limitations of the study are outlined. Copyright © 2015 John Wiley & Sons, Ltd.

Simulation Analysis on Hysteretic Performance of Cross-type Rigid Node for Steel Frame Based on Abaqus

In order to study the cross-type rigid steel frame node hysteretic behavior of components, the axial compression ratio, H type steel column web thickness, girder section and stiffener as design parameters, 8 steel frame cross-type rigid joints and a T-type rigid joint are designed. Based on simplified mechanical model and constitutive relations of material, using ABAQUS software the corresponding finite element model is established and the hysteretic performance analysis is carried out. Through comparison between given T-type node test results and analysis results, both are in good agreement, thus the rationality of the finite element model established in this paper is verified. Simulation analysis of cross-type node is developed in further, load -displacement hysteretic curve of nodes, skeleton curve, envelope figure and the stress nephogram are extracted and comparative analysis is conducted, influence regularity of four parameters on the seismic behavior of the joints is obtained. The corresponding design suggestion for the axial compression ratio and column web and flange thickness ratio is proposed, design limit value of axial compression ratio of column should be taken as 0.5 and limit value of column web and flange thickness ratio is taken as 0.75,and these can provide reference for actual engineering design.

Effect of column flange flexibility on WF-beam to rectangular CFT column connections

Researches in the United States discovered different tension and shear flow patterns between wide flange (WF) column connections and box column connections. On the other hand, researches in Japan started many research on flexibility of column flange and proposed connection flexural moment strength based on the out-of-plane deformation for hollow section box column connections. However, both force flow pattern research and out-of-plane influence study in WF beam to rectangular concrete filled tube (CFT) column connections are insufficient. While due to the different composition and geometry configuration, direct extension of previous results is not feasible. This paper discusses the out-of-plane deformation at column flange, force flow pattern and shear and moment transfer efficiency of WF-beam to rectangular CFT column connection. Results show that both Poisson effect and flexibility of column flange will lead to a change on force flow pattern in beam–column junction region and inefficient moment transferring ability through beam web, resulting in a high level of hydrostatic stress demand at beam flanges. Weld access hole, thickness of column flange and diaphragm and web connection details all have certain effect on column flange bending stiffness and the transfer efficiency of beam web. A flexural strength evaluating method for the rectangular CFT column connection based on the out-of-plane deformation is also presented.

Analytical frame approach for the rotational stiffness prediction of beam-to-column angle connections

The application of recent developed analytical methodologies, based on a plane representation of the T-stub analogy, to evaluate the rotational stiffness of top and seat angle connections with double web angle (TSDW) is dealt with in this paper. Effective width tables for stiffness calculations have been adapted for non-preloaded and preloaded joints. These analytical proposals, developed with the assessment of FE modelling and checked with the results of T-stub tests, have been introduced in a mechanical procedure following a non-aligned Eurocode model. The calculation of the rotational stiffness has been carried out with the aid of program DAC. This software implements these T-stub stiffness proposals linked with the effective width definitions relating to the angles and the column flange in bending. The results obtained with the proposed methodology are compared with experimental data on preloaded and non-preloaded joints showing the goodness of the frame approach to deal with angle connections. It also proves how the assembly of simple components to perform macro-components can contribute to simplify the evaluation of the joint response by means of the component method.

Experimental investigation on stiffened steel plate shear walls with two rectangular openings

One of the most important advantages of steel plate shear wall (SPSW) is to create openings with different sizes and arbitrary locations on the infill plate depending on their application. In this research, the effects of two openings on the structural behavior of SPSWs were studied experimentally. Experimental testing was performed on three one-third scaled single-story SPSW specimens with two rectangular openings under quasi-static cyclic loading. The differences between the three perforated experimental specimens were the interval between two openings and their closeness to the frame columns. The structural parameters of perforated specimens were compared to the similar specimen without any opening. The experimental results were utilized (a) to compare the ultimate shear strength, stiffness and energy absorption of specimens; (b) to evaluate the performance of central, lateral, top and bottom panels; (c) to investigate the effect of distance between the openings and the columns on the formation of plastic hinges on the column flanges; (d) to study the behavior of stiffeners around the openings. Test results showed that the ultimate shear strength, stiffness and energy absorption were the same in all three perforated specimens and the interval between the two openings had no effect on these values. Moreover, existence of openings will lead to reduction in values of structural parameters.

실물대 실험을 통한 H형강 기둥의 신형상 약축접합부 성능평가에 관한 연구

The bracket-type connection is often used for the weak axis steel connection of H-shape beam-to-column. However it leads to weakness of competitiveness in steel structure due to difficulty in production and installation of connection. Consequently, new shape weak-axis was developed. It has a simple shape with the less spot of welding points, and has advantage about showing the obvious power flow in connection points. In this study, monotonic and cyclic loading test in full-scale was performed to evaluate structural behavior and examine on-site application. Therefore, 12 specimens(9 specimens for monotonic loading test and 3 specimens for cyclic loading test) were built for the variables which are overlap length of beam-end and column flange. As the result, new shape of weak-axis connection appeared special Moment Frame(SMF) and had excellent structural performance and constructablility when the parameter is over 50mm.

Improved Link-to-Column Connections for Steel Eccentrically Braced Frames

AbstractLink-to-column connections in steel eccentrically braced frames must be capable of sustaining large cyclic forces and inelastic rotations. United States code provisions require that satisfactory performance of link-to-column connections be verified by testing under a prescribed loading protocol. However, there are few link-to-column connection details that have satisfied these testing criteria. This paper describes a pilot investigation of two promising link-to-column connection details, as follows: (1) the fillet welded connection, which uses fillet welds or a combination of fillet and groove welds between the link and the column flange; and (2) the supplemental web doubler connection, which reinforces the connection region using a pair of doubler plates in the first link web panel next to the column, parallel to but offset from the link web. These two details showed excellent performance in a series of eight tests. This paper describes these link-to-column connection details, summarizes the resu...

Hammer head beam solution for beam-to-column joints in seismic resistant building frames

This paper presents a research on an innovative stiffened extended end-plate joint, used to connect I-shaped beams to partially-encased composite wide flange columns. In the joint, T-shaped hammer heads cut from the same I-profiles than the beams are used, instead of using traditional haunches. At the joint level, the column web is strengthened by two lateral plates welded to the column flanges; these plates also reinforce the column flanges. This type of joint is proposed to use in the seismic resistance building frames, as a full-strength and a fully-rigid joint solution. Firstly, a test program carried out within a RFCS European project titled HSS-SERF “High Strength Steel in Seismic Resistant Building Frames”, 2009–2013, will be presented. Then, analytical developments based on the component approach and aimed at predicting the joint response will be described; their validity will be demonstrated through comparisons with the tests. Moreover, a new design concept for full strength joint accounting for the actual position of the plastic hinge and the possible individual over-strength factors for each component is proposed, respecting the requirements of EN1998-1-1.

Seismic performance of prefabricated steel beam-to-column connections

Three types of prefabricated steel beam-to-column connection different from common welded unreinforced flange-bolted web (WUF-B) connections are examined in this paper. Full-scale specimens with specific joint configurations were prepared, so that the effects of joint detail on the failure mode, ultimate capacity and ductility could be identified. They were tested under cyclic loading to further investigate their seismic performance. Experimental results showed that the measured moment capacities of these connections at the face of a column flange reached 120% to 140% of the beam's full plastic moment. The maximum plastic rotations of all connection types were greater than 0.025rad and the cumulative plastic rotations were 20 to 30 times the maximum plastic rotation. In this way, connection Types I and III were capable of accommodating a story drift angle of 0.04rad. These results demonstrated excellent joint strength, and showed potential opportunities for connection Types I and III to be used in special moment frames (SMFs) in AISC Seismic Provisions, and for connection Type II to be used in intermediate moment frames (IMFs). Finite-element analysis was performed and showed good agreement with the experimental results. It was found that rigid end-plate assumption is not appropriate for connection Type I, and higher likelihood of fracture was detected in the cover plates than in beam flanges for connection Types II and III.

Performance of partial strength connection connected by thick plate between column flanges

Traditional beam connections to the minor axis of a column have relatively low strength and stiffness. A modified detail, using a plate welded between the toes of the column flange - referred to as a toe plate connection - is examined in this paper. The results of an experimental investigation for both flush and extended end-plate connections connected to a 25 mm thick end-plate are presented. The tests are complemented by finite element modelling which compares very well with the test observations. The results show a significant increase in both moment resistance and initial stiffness for this connection detail compared with connections made directly to the column web. This offers the prospect of more optimal solutions taking advantage of partial strength frame design for the minor axis as well as major axis.

A phenomenological component-based model to simulate seismic behavior of bolted extended end-plate connections

In order to investigate seismic behavior of bolted extended end-plate connections, a phenomenological component-based model with several separated springs is presented where the constitutive relationships for individual components are determined using material and geometric properties. Analytical results using the developed model were compared with experimental data from full-scale moment connection tests including global load versus displacement and local response of beam hinge, panel zone and other components. The effectiveness of the model was demonstrated by these comparisons. The model is then leveraged to study the influence of design decisions such as weak columns and bolt pretension. The analytical results indicate that bolt pretension and related connection slip can significantly affect the seismic behavior of the end-plate and column flange and thus their inclusion in the proposed model is validated.

시공성을 고려한 H형강 기둥의 신형상 약축접합부 내진성능평가

H형강 기둥에 대한 신형상 약축접합부를 개발하여 단조가력실험을 통해 구조성능평가에 관한 연구를 수행하였으며, 선행연구결과를 바탕으로 본 연구는 시공성을 고려한 신형상 약축접합부의 내진성능을 평가하기 위해 반복가력실험을 실시하였다. 신형상 약축접합부는 접합개소 및 용접량이 적고 접합상세가 단순하며, 접합부에 작용하는 힘의 흐름이 명확하다는 장점이 있다. 이에 따라 H형강 기둥플랜지와 보 단부의 겹침길이를 실험변수로 한 신형상 약축접합부(WPL-WK-FC2, WPL-WK-FC3)와 건축강구조 표준접합상세지침에 근거한 표준 약축접합부(HH-WK-FC4) 총 3개의 실험체를 실물대 사이즈(Full-scale)로 제작하였다. 실험결과, 신형상 약축접합부는 0.04 rad 이상의 층간변위각에서 보 소성모멘트(<TEX>$M_P$</TEX>)의 80%이상을 유지하는 특수모멘트골조(SMF)의 내진성능을 확보하였으며, H형강 기둥플랜지와 보 단부의 겹침길이가 50 mm 이상이면 시공성 뿐만 아니라 구조적으로 우수한 것으로 나타났다. H-section steel column new shape weak-axis was developed and performed through monotonic loading test regarding basic structural performance evaluation. In this study cyclic loading test was followed up in order to evaluate seismic performance through the full-scale of new shape weak-axis connection for constructabilitiy. New shape weak-axis connection has a simple shape with the less spot of welding points, and it has advantage about showing the obvious flow of strength in connection points. Therefore, three specimens are built for the variables which are overlap length of beam-end and column flange. As the result, New shape of weak-axis connection is appeared special Moment Frame(SMF) and have excellent structural performance and constructablility when the parameter is over 50 mm.

A new steel panel zone model including axial force for thin to thick column flanges

During an earthquake, steel frame columns can be subjected to high axial forces combined with inelastic rotation demand resulting from story drift. Generally, the whole beam or component can be represented with one element. In elasto-plastic analysis, subdivision is necessary if the plastic deformation occurs within two ends of beams. If effects of the joint panel are necessarily considered in the analysis, the joint panel should be represented with an independent element. It is a special element to represent the shear deformation of the joint panel in the beam-column connection zone. Several analytical models for panel zone (PZ) behavior exist, in terms of shear force-shear distortion relationships. Among these models, the Krawinkler PZ model is the most popular one which is used in the AISC code. Some studies have pointed out that Krawinkler's model gives good results for the range of thin to medium column flanges thickness. This paper, introduces a new model to estimate the response of shear force-shear distortion for the PZ including column axial force. The model is applicable to both thin and thick column flange. To achieve an appropriate PZ mathematical model first, the effects of PZ strength and stiffness on connection response are parametrically studied using finite element models. More than one thousand and four-hundred beam-column connections are included in the parametric study, with varied parameters; then based on analytical results a simple mathematical model is presented. A comparison between the results of proposed method herein with FE analyses shows the average error especially in thick column flange is significantly reduced which demonstrates the accuracy, efficiency, and simplicity of the proposed model.

Stiffness modeling of bolted thick built-up T-stub connections including secondary prying effect

The results of experimental tests and finite element (FE) simulations are used to develop a stiffness model that predicts the behavior of bolted thick built-up T-stub connections including column flange deformation, and accounting for primary and secondary prying effect. The model incorporates the overall T-stub and column flange deformations of key component elements, and includes nonlinear material behavior of bolts and base material, and accounts for pretension of fasteners and contact interactions. The stiffness model consists of linear and nonlinear springs which model deformations from tension bolt elongation, slip-bearing, bending of T-stub flange, elongation of the T-stem, column flange deformation, and accounts for primary and secondary prying forces. The behavioral characteristics of the T-stub/column flange system are examined including strength, stiffness, deformation, and energy dissipation. A proposed strength model that predicts the capacity of the column flange for the failure mode of full plastification at the flange-to-web connection of the column (K-zone) followed by interior tension bolt fracture is developed. Furthermore, closed form expressions that are based on stiffness modeling techniques are developed to predict the energy dissipation capacity of the T-stub/column flange system with and without continuity plates. Comparison of the models predictions with experimental and FE data shows that the proposed models accurately predict the connection and the column flange load-deformation response. This study provides guidelines for engineers to account for the additional forces induced in the tension bolts and for the maximum rotational capacity demand in the connection which are required for seismic analysis and design.

Suggesting double-web I-shaped columns for omitting continuity plates in a box-shaped column

Generally the required strength and stiffness of an I-shaped beam to the box-shaped column connection is achieved if continuity plates are welded to the column flanges from all sides. However, welding the forth edge of a continuity plate to the column flange may not be easily done and is normally accompanied by remarkable difficulties. This study was aimed to propose an alternative for box columns with continuity plates to diminish such problems. For this purpose a double-web I-shaped column was proposed. In this case the strength and rotational stiffness of the connection was provided by nearing the column webs to each other. Finite element studies on about 120 beam-column connections showed that the optimum proportion of the distance between two column webs and the width of the column flange (parameter <TEX>${\beta}$</TEX>) was a function of the ratio of the beam flange width to the column flange width (parameter <TEX>${\alpha}$</TEX>). Hence, based on the finite element results, an equation was proposed to estimate the optimum value of parameter <TEX>${\beta}$</TEX> in terms of parameter <TEX>${\alpha}$</TEX> to achieve the highest connection performance. Results also showed that the strength and ductility of post-Northridge connections of such columns are in average 12.5 % and 54% respectively higher than those of box-shaped columns with ordinary continuity plates. Therefore, a double-web I-shaped column of optimum arrangement might be a proper replacement for a box column with continuity plates when beams are rigidly attached to it.

Experimental testing and simulation of bolted beam-column connections having thick extended endplates and multiple bolts per row

Retrofit of existing steel buildings often requires strengthening of the connection regions. One common connection, the bolted beam-column connection, is often strengthened in design using stiffened extended endplates, or with continuity plates welded between the column flanges. In a retrofit scenario, adding stiffeners to the endplate is difficult due to the concrete slab and metal deck, and excessive field welding of continuity plates may be uneconomical. Simplifying retrofit efforts, and for economy, connection strength may be improved by simply adding more bolts to the connection. Current code methods, broadly generalized to all connection configurations, are currently based on component experiments having only one bolt on either side of the column web. This study experimentally investigates strengthening of bolted beam-column connections, having no column web stiffeners, using more than one bolt on either side of the column web. Six full-scale bolted beam-column connections are tested, representing exterior beam-column connections (beams attached to only one column flange). Connections with both extended and flush endplates are considered. Two column sections (HE300A and HE300B) are tested along with HE300B beams creating both equal-column-beam, and weak-column strong-beam scenarios. Analytical simulations provide insight into local connection demands, and experimental results are compared with current code methods. The experiments indicate that closer inner-bolt spacing relative to the column web increases connection moment capacity but decreases rotation capacity (connection ductility) due to increased bolt prying forces from column flange distortions. The outer bolt of multiple-bolt-per-row configurations contributes very little to the connection resistance when column web stiffeners are not considered. With the exception of specimen T-3B which failed through bolt-thread shear after 0.02rad, all connections with multiple bolts per row still achieved rotations greater than 0.06rad. The Eurocode 3 component method and adapted Eurocode 3 procedures conservatively predicted the connection strength of each test specimen, including weak-column strong-beam assemblies, and accurately identified the initial connection limit states.

Test and simulation of full-scale self-centering beam-to-column connection

A new type of beam-to-column connection for steel moment frames, designated as a “self-centering connection,” is studied. In this connection, bolted top-and-seat angles, and post-tensioned (PT) high-strength steel strands running along the beam are used. The PT strands tie the beam flanges on the column flange to resist moment and provide self-centering force. After an earthquake, the connections have zero deformation, and can be restored to their original status by simply replacing the angles. Four full-scale connections were tested under cyclic loading. The strength, energy-dissipation capacity, hysteresis curve, as well as angles and PT strands behavior of the connections are investigated. A general FEM analysis program called ABAQUS 6.9 is adopted to model the four test specimens. The numerical and test results match very well. Both the test and analysis results suggest that: (1) the columns and beams remain elastic while the angles sustain plastic deformations for energy dissipation when the rotation of the beam related to the column equals 0.05 rad, (2) the energy dissipation capacity is enhanced when the thickness of the angle is increased, and (3) the number of PT strands has a significant influence on the behavior of the connections, whereas the distance between the strands is not as important to the performance of the connection.

A new analytical formulation for the E-stub strength calculation in three dimensional steel joints with additional plates welded to the weak axis

In steel design, engineers have to solve different problems related with the joints. In the case of three dimensional steel joints with additional plates welded to the weak axis, a new component appears. This component is formed by the additional plates and the column web in tension and the column flanges in flexion. This component is not covered by the formulation of the Eurocode 3. Its stiffness has been yet studied in a recente paper, but for a completed definition of the joint, the analysis of its strength is necessary. This paper focuses on the study of the strength of the E-stub. An analytical formulation for the calculation of the E-stub strength is presented, based on the experimental results of six E-stub specimens. Additionally, numerical models have been developed and calibrated, and the comparison with the experimental results shows that the proposal finite elements models are able to reproduce the strength behaviour of the E-stub accurately. Finally, a wide parametric study have been carried out in order to validate the analytical formulation in the most common configurations showing that such formulation predicts the strength of the E-stub with good accuracy.