Column Web Research Articles

Use of artificial damping factors to enhance numerical stability for irregular joints

The authors previously proposed a fast and easy assembly method for wide flange steel column-beam frames in which the column and beam steel web had skew cuts and the lower flange of the steel beam was partially removed to prevent the bottom flange of the steel beam from running into the flanges of the L-shaped guide angles (which were pre-installed on the column bracket) when they were erected. However, the joint experienced convergence difficulties at the irregular structural configuration of the skewed web connections when cyclic finite element analysis was performed. This study introduced artificial damping factors, implemented during nonlinear numerical computation, to balance the internal and external forces. The influence of the damping factors was explored to ameliorate the numerical instabilities by removing the aforementioned convergence difficulties. It was shown that a solution converged while the dissipated stabilization energy was sufficiently small, ensuring that the analysis results were not distorted by the use of damping factors in the range of 1.0 × 10−5 to 5.0 × 10−5. The best matches with monotonic runs and the convergence for steels with yield strength of 325 MPa were obtained by applying damping factors of 0.0002 and 0.0005.

Structural behaviour of stainless steel stub column under axial compression: a FE study

This paper presents a Finite Element (FE) study on Lean Duplex Stainless Steel stub column with built-up sections subjected to pure axial compression with column web spacing varied at different position across the column flanges. The thicknesses of the steel sections were from 2 to 7 mm to encompass a range of section slenderness. The aim is to study and compare the strength and deformation capacities as well as the failure modes of the built-up stub columns. The FE results have been compared with the un-factored design strengths predicted through EN1993-1-4 (2006) + A1 (2015) and ASCE8-02 standards, Continuous Strength Method (CSM) and Direct Strength Method (DSM). The results showed that the design rules generally under predict the bearing capacities of the specimens. It’s been observed that the CSM method offers improved mean resistance and reduced scatter for both classes of cross-sections (i.e. slender and stocky sections) compared to the EN1993-1-4 (2006) + A1 (2015) and ASCE 8-02 design rules which are known to be conservative for stocky cross-sections.

Implications of Structural Model on the Design of Steel Moment Resisting Frames

Background: Studies have shown that the flexibility of the connections has an important role in the distribution of forces and moments in the structure. This also applies for the displacements, deformations and the stability of the structure. Objective: The objective of the present study is to investigate the influence of the stiffness of column web-panel and connection on the ultimate response of Moment Resisting Frames (MRFs). Methods: A comprehensive parametric study was carried out. In particular, a set of one hundred and twenty planar frames was analyzed, considering three approaches for modelling the joints. Results: The results highlight that neglecting the influence of the connection and column web panel leads to significant over-estimation of the global instability factor αcr, which can lead to unconservative design and assessment of steel frames, especially for those cases subjected to severe horizontal forces as the seismic actions. Conclusion: Accounting for the joint deformability in MRFs is important even for the cases with connection stiffness (kb) larger than 25 times the beam stiffness where EN1993-1-8 allows neglecting the model of the connection stiffness. Indeed, the comparison of cases with kb ≥ 25 between the models with and without the connection deformability show that of αcr can decrease from 5% to 16%, depending on the refinement of the modelling assumptions. This decrease also lead to higher second order effects and thus to higher design forces but also the overall stiffness of the frame is overestimated.

Experimental investigation on shear behavior of steel beam-to-CFST column connections with irregular panel zone

This paper presents an experimental investigation on the seismic behavior of a novel steel-concrete composite beam-to-column connections reinforced by outer-annular-stiffener. This type of connection consists of beams with varying depths in opposite sides, and a concrete filled steel tubular (CFST) column. Four cruciform connection specimens with varying beam depth ratios (1, 0.75 and 0.5) were tested under monotonic and cyclic loading protocols to investigate shear capacity, hysteretic behavior, deformation capacity and failure modes within the irregular joint panel zone. From the test results, two types of failure modes were identified as global shear failure occurred in the panel zones 1 and 2 on the side of large depth beam when subjected to positive loading direction, and partial shear failure only in the panel zone 1 under the negative loading direction. The global shear failure was characterized by plastic deformation in the panel zones 1 and 2 prior to out-of-plane instability arose in the column flange near the outer-annular-stiffener. On the other hand, shear failure of panel zone under negative direction loading, the deformation of steel part was similar to that under the positive loading direction. While, the concrete panel zone located in the web of column only connecting with small depth beam, showed an arch mechanism. There was no fatigue fracture throughout the test, and all the specimens behaved in a ductile manner. All the tested specimens demonstrated good plastic deformation and energy dissipation capacity.

Strength of Thin-Walled Lipped Channel Section Columns with Shell-Shaped Curved Grooves

Thin-walled member is structurally superior to a construction member. However, by reason of complexity in structure the stress and the deformation to yield the cross section are complicated. Specially, in case thin-walled members, such as thin-walled channel section columns, which are subjected to compressive force, these members produce the local buckling, distortional buckling and overall buckling. A number of experimental and theoretical investigations subjected to axial compressive force are generated for thin-walled channel section columns with triangle-shaped folded groove by Hancock [1] and with complex edge stiffeners and web stiffeners by Wang [2]. In case thin-walled channel section column with folded groove which is subjected to axial compressive force, it is cleared that the buckling mode shapes are ordinarily generated for local buckling mode shape of plate-panel composing cross section of member in short member aspect ratio and overall buckling mode shape as column and distortional buckling mode shape interacting between local buckling and overall buckling similarly normal thin-walled member. It is cleared analytically and experimentally that buckling strength and critical strength of thin-walled channel section column with folded groove can increase sharply in comparison with that of normal thin-walled member composing only plate-panel. In this paper a new cross section of shell-shaped curved groove [3] was proposed instead of the thin-walled lipped channel section column with triangle- and rectangle-shaped folded grooves used ordinarily, and therefore the comparison and the examination of buckling strength and buckling behavior were generated in the case of preparing triangle-shaped folded and shell-shaped curved grooves to web and flange of thin-walled channel section column. And then in order to investigate the buckling behavior on the thin-walled channel section column with folded and curved grooves, exact buckling strength and the buckling mode shapes are generated by using the transfer matrix method. The analytical local distortional and overall elastic buckling loads of thin-walled channel section column with folded and curved grooves can be obtained simultaneously by use of the transfer matrix method. Furthermore, a technique to estimate the buckling mode shapes of these members is also shown.

Evaluation the behavior of pre-fabricated moment connection with a new geometry of pyramidal end block under monotonic and cyclic loadings

Researchers have been long studying new building implementation methods to improve the quality of construction, reduce the time of assembly, and increase productivity. One of these methods is the use of modular pre-fabricated structural forms that are composed of a beam, column, short column, pyramidal end block, and connection plates. In this study, a new geometry for the pyramidal end block was proposed that helps facilitate the assembly procedure. Since the proposed configuration affects the performance of this form of connection, its behavior was evaluated using finite element method. For this purpose, the connection was modeled in ABAQUS and then validated by comparing the outputs with experimental results. The research proceeded through analyzing 16 specimens under monotonic and cyclic loading. The results indicated that using the pyramidal end block not only makes the assembly process easier but also reduces the out-of-plane displacement of the short column webs and the vertical displacement of beam end. By choosing appropriate section properties for column and beam, the connection can bear a rotation up to 0.01 radians within its inelastic region and a total of 0.04 radians without any significant reduction in its bearing capacity.

Analysis of the Behaviour of Semi Rigid Steel End Plate Connections

The analysis of steel-framed building structures with full strength beam to column joints is quite standard nowadays. Buildings utilizing such framing systems are widely used in design practice. However, there is a growing recognition of significant benefits in designing joints as partial strength/semi-rigid. The design of joints within this partial strength/semi-rigid approach is becoming more and more popular. This requires the knowledge of the full nonlinear moment-rotation behaviour of the joint, which is also a design parameter. The rotational behaviour of steel semi rigid connections can be studied using the finite element method for the following three reasons: i) such models are inexpensive; ii) they allow the understanding of local effects, which are difficult to measure accurately physically, and iii) they can be used to generate extensive parametric studies. This paper presents a three-dimensional finite element model using ABAQUS software in order to identify the effect of different parameters on the behaviour of semi rigid steel beam to column end plate connections. Contact and sliding between different elements, bolt pretension and geometric and material non-linearity are included in this model. A parametric study is conducted using a model of two end-plate configurations: flush and extended end plates. The studied parameters were as follows: bolts type, end plate thickness and column web stiffener. Then, the model was calibrated and validated with experimental results taken from the literature and with the model proposed by Eurocode3. The procedure for determining the moment–rotation curve using finite element analysis is also given together with a brief explanation of how the design moment resistance and the initial rotational stiffness of the joint are obtained.

Analysis of the Behaviour of Semi Rigid Steel End Plate Connections

The analysis of steel-framed building structures with full strength beam to column joints is quite standard nowadays. Buildings utilizing such framing systems are widely used in design practice. However, there is a growing recognition of significant benefits in designing joints as partial strength/semi-rigid. The design of joints within this partial strength/semi-rigid approach is becoming more and more popular. This requires the knowledge of the full nonlinear moment-rotation behaviour of the joint, which is also a design parameter. The rotational behaviour of steel semi rigid connections can be studied using the finite element method for the following three reasons: i) such models are inexpensive; ii) they allow the understanding of local effects, which are difficult to measure accurately physically, and iii) they can be used to generate extensive parametric studies. This paper presents a three-dimensional finite element model using ABAQUS software in order to identify the effect of different parameters on the behaviour of semi rigid steel beam to column end plate connections. Contact and sliding between different elements, bolt pretension and geometric and material non-linearity are included in this model. A parametric study is conducted using a model of two end-plate configurations: flush and extended end plates. The studied parameters were as follows: bolts type, end plate thickness and column web stiffener. Then, the model was calibrated and validated with experimental results taken from the literature and with the model proposed by Eurocode3. The procedure for determining the moment–rotation curve using finite element analysis is also given together with a brief explanation of how the design moment resistance and the initial rotational stiffness of the joint are obtained.

Initial stiffness and strength characterization of minor axis T-stub under out-of-plane bending

No research has been performed yet that deals with the characterization of the minor axis of steel joints under out-of-plane bending. As a consequence, a complete description of all the components that become part of a 3D steel joint is not yet available either in scientific journals or current codes. Moreover, it is necessary to identify the behavior of each isolated component that is subjected to in and out of plane effects before studying the interaction among components and the interaction with the loads that act in both the major and minor axis of the joint.The aim of the research described in this paper is to define the behavior of the T-Stub under out of plane bending attached to the column minor axis. In the proposed kind of joint the minor beam is not attached to the column web but to additional plates welded to the column flanges.With the purpose of characterizing this component, two experimental tests have been performed that allow validating the finite element models. Then, a parametric study is performed by varying different characteristics of the joint to check their influence. Through the tests and models the additional plate in bending has appeared to be the most influential component, which is not characterized in the Eurocode 3.Finally, analytical expressions for the initial stiffness and strength of the additional plate of the T-Stub in minor axis under out of plane bending are presented.

Experimental performance of double built-up T moment connections under cyclic loading

Prequalification of the Double Split Tee (DST) connection has been conducted using hot-rolled shapes, whose availability is still limited in several countries. In addition, the range of available T web and flange thicknesses is narrow for these shapes. Thus, the use of built-up T-stubs on the DST connection seems to be a promising alternative, considering that they offer more freedom of sizing and allow a better use of the material. The experimental research reported here aimed to validate the use of built-up tees instead of hot rolled tees in DST moment connections. Four beam-to-column full-scale double built-up T (DBT) moment connections were subjected to cyclic loading following the prescribed loading history in AISC seismic provisions. The parameters varied among the specimens were the T flange thickness, the type of weld between the T flange and the stem (fillet weld or full penetration groove weld), and the column web thickness, in order to observe the most significant limit states of the connection, namely development of plastic hinges in beams, panel zone plastification, and T flange prying. The results indicate that the connection can sustain 4% drift without strength degradation, whether it is designed for T flange prying or beam hinging. In the case of the former, only limited permanent deformation of the flange is observed, while for the latter significant plastic deformation of the beam can be achieved with little or no damage of the T. The type of weld used has no significant effect on the connection performance.

10.35: Influence of joint stiffness on the behaviour of steel bearing frame under fire conditions

ABSTRACTThe reaction of the bearing steel frame to the direct fire exposure associated with the influence of monotonically increasing temperature of the constituent components is considered in this paper. For the comparative purposes, the frames with beam‐to‐column joints differing in rigidity are analysed in detail. Depending on whether there are stiffening ribs present, and the location of these ribs if present, the fire resistance of the considered structural component is determined by its failure mode. This may occur as the local instability in the column web or as the destruction of the column flange or beam flange. The internal arrangement of the joint is also one of the factors determining the redistribution of internal forces generated in the frame components when subjected to fire conditions. To show this, the dependencies specifying the relationships between temperature of the frame components and the bending moments and axial forces induced in these components during fire are presented, discussed and mutually compared. These relationships are arrived at after the detailed analysis of a numerical example, in which fire behaviour of three similar steel frames differing in the beam‐to‐column joint rigidity is considered. In the first analysed case the joint without ribbing is examined, while in the second case a joint with horizontal ribs and in the third case a joint with horizontal and diagonal ribs are analysed. The relationships listed above are accompanied by corresponding relationships specifying the dependencies between the steel temperature and the frame beam deflection. Additionally, the rigidity of the flexible supports, modelling the resistance of the columns to the horizontal displacement of the joints, is differentiated in the analysis. In conclusion, it has been shown that the analysed types of the considered frame exhibit substantial differences in the predicted structural response if the joints applied in them and subjected to fire differ in rigidity. Specification of these differences and their qualitative and quantitative description constitute the main objective of this work.

03.06: A study on the behaviour of steel beam‐column connections to deep wide flange columns for seismic applications

ABSTRACTThe use of deep column profiles in lateral force resisting systems is becoming increasingly commonplace for the purpose of providing sufficient stiffness to meet lateral drift limits. Existing research on the behaviour of connections to deep column profiles is limited, and consequently this study aims to explore potential issues with these configurations. A parametric analytical investigation was performed focusing on the behaviour of one‐sided reduced beam section connections to columns of variable depths. A total of forty assemblies were designed according to the 2010 AISC Specification. Four column sizes were considered, namely W14×426, W24×192, W27×194, and W30×191 (in metric designations, W360×634, W610×285, W690×289, and W760×284). Columns were subjected to five levels of axial load and were configured with either medium or weak panel zone strength. A common size beam was used for all configurations, namely a W36×150 (W920×223), so that the shear and bending moments transferred to the column were not a variable. Imperfections and second‐order geometric effects were considered as part of the parametric investigation which used geometry and material characteristics from a previous experimental study. The results of this study suggest that the use of doubler plates to strengthen column webs causes a larger twist of the column when the connection is loaded, leading to the recommendation of using heavier profiles instead of reinforcement plates when strength limit states govern. Finally, this study shows that the use of deeper columns does not have a negative impact on the behaviour of the connection as long as the axial loads in the column are relatively low. When column axial loads approach the stability limit of the member, the connection detail used does not perform as intended, as local buckling phenomena reduce the connection capacity before a plastic hinge can fully form in the connected beam.

FE parametric study of RWS/WUF-B moment connections with elliptically-based beam web openings under monotonic and cyclic loading

This paper provides numerical results investigating the behaviour of steel web-perforated beams with different shaped single openings located close to beam-to-column connections under monotonic and cyclic loading. In particular, the beams considered feature circular and patented elliptically-based perforations. Non-standard elliptically-based perforations have been proposed previously and are optimally designed to maximise resistance against Vierendeel moments and web-post buckling under static loads at the ultimate limit state. Comprehensive parametric nonlinear finite element analyses using the commercial FE package ANSYS were conducted. Initially, a FE model of the beam-to-column WUF-B moment connection was developed and calibrated against pertinent experimental results found in the literature. Next, parametric analyses were undertaken to assess the RWS/WUF-B connection regarding strength (moment), deformation (rotation) and column web shear panel zone deformation for different shapes of beam web perforations, hole sizes, and their locations. The study concludes that larger web openings are capable of moving the plastic hinge away from the column face and the CJP weld. Also, interstory drifts can be controlled with the wise use of the beam web opening size, shape, and distance from the face of the column, as suggested in the paper. Following, a step-by-step design process for RWS/WUF-B connection is presented.

Numerical approach to the evaluation of the transformation parameter β

The paper presents a finite element analysis of unstiffened welded connections, in double-sided configurations, in which the two beams do not meet at the same level. The results are used to propose a simple and reliable estimation of the transformation parameter β that accounts for the influence of the column web panel in shear.

Cyclic behavior of steel beam-concrete wall connections with embedded steel columns (I): Experimental study

This paper theoretically studies the cyclic behavior of hybrid connections between steel coupling beams and concrete shear walls with embedded steel columns. Finite element models of connections with long and short embedded steel columns are built in ABAQUS and validated against the test results in the companion paper. Parametric studies are carried out using the validated FE model to determine the key influencing factors on the load-bearing capacity of connections. A close-form solution of the load-bearing capacity of connections is proposed by considering the contributions from the compressive strength of concrete at the interface between the embedded beam and concrete, shear yielding of column web in the tensile region, and shear capacity of column web and concrete in joint zone. The results show that the bond slip between embedded steel members and concrete should be considered which can be simulated by defining contact boundary conditions. It is found that the load-bearing capacity of connections strongly depends on the section height, flange width and web thickness of the embedded column. The accuracy of the proposed calculation method is validated against test results and also verified against FE results (with differences within 10%). It is recommended that embedded steel columns should be placed along the entire height of shear walls to facilitate construction and enhance the ductility. The thickness and section height of embedded columns should be increased to enhance the load-bearing capacity of connections. The stirrups in the joint zone should be strengthened and embedded columns with very small section height should be avoided.

Cyclic behaviour characterization of web panel components in bolted end-plate steel joints

This paper addresses the characterization of the behaviour of the column web panel components in bolted end-plate steel joints subject to cyclic loading. Based on experimental test results, a calibrated parametric FE model of a double extended beam-to-column end-plate steel joint is implemented, that allows characterizing the behaviour of the joints both globally and in terms of the dissipative components. The numerical models have been developed using the ABAQUS FE package considering a detailed representation of the various joints components and taking into account the different sources of geometrical and material nonlinearities. Finally, based on the integration of the stress and displacement fields in predefined paths along the column web, a detailed extraction procedure for the cyclic force-deformation behaviour of the column web panel components is proposed, however extensible to other components. These relationships are needed for implementation in a components based approach that accounts for cyclic loading conditions.

Strength and stiffness of adhesively bonded GFRP beam-column moment resisting connections

For the first time, the feasibility of adhesively bonded connections in FRP frame structures is explored as an alternative to bolted connections. Eight full-scale GFRP beam-column connections are tested and their failure mode, strength and rotational stiffness are investigated. A single pultruded GFRP I-profile is used for the two members. In four of the specimens the beam and the column are connected by epoxy adhesive and GFRP seat angles, similar to the so-called “standard bolted connection”. In the remaining four specimens, the seat angles are supplemented by additional GFRP angles and stiffeners to strengthen the column flange and web. The beam-column assembly forms an inverted L-shape frame, with the column being fixed at the bottom and attached to the beam near the top. The beam, acting as a cantilever, is loaded by a point load near its free end, which subjects the connection to bending and shear. The current standard connection failed by debonding within the column flange while the improved/strengthened connection failed within the adhesive or at the adhesive-column flange interface. The test results reveal that both the standard and improved connection can have at least the same strength as the corresponding bolted connection, irrespective of whether GFRP or steel bolts are used to make the connection. Hence, the current restrictions against the use of adhesive beam-column connections in GFRP frame structures may be unjustified. In making this comparison, the observed failure load of each connection is normalized by the ultimate moment capacity of the GFRP profile in the beam-column assembly.

Mechanism of elasto-plastic behavior of composite beam connected to RHS column

Following to the experimental test of full-scale beam-to-RHS column sub-assemblies, it was observed that in the composite beam considerable reduction of rotation capacity occurs due to the increase of strain at the lower flange. In the case of bare beam-to-RHS column connection, it is already known that occurrence of out-of-plane deformation in the column web, results in the reduction of rotation capacity of beam. However, in the composite beam-to-RHS column connection due to slab axial force, web connection is in more severe stress condition. Further comprehensive understanding of effect of out-of-plane deformation of RHS column on the behavior of composite beam is needed. In this paper results of finite element analysis and limit analysis are presented to clarify the structural condition of web connection. The force flow pattern and ultimate flexural capacity are evaluated by considering main parameters affecting the deformation. Correspondence between FEA, limit analysis and experimental data is shown, mechanism of mechanical stress transfer and strain concentration is explained.

A new model for beam rigid connection to double I-shaped column's web

Due to the extensive use of built-up I-shaped columns in steel frames, especially in Iran, conducted studies have so far only considered the rigid connection between beams and the major axis of I-shaped profiles. Hence, box columns have become the most commonly used structural elements in two-way moment frames. However, less complicated, less time-consuming, and less costly, construction of double profiles in building sites, rather than that of box columns in fabrication companies, suggest the novel idea of a rigid connection to the minor axis of built-up I-shaped columns by haunch plates. Initially, data from a rigid beam to column flange connection were used to verify numerical analysis and result, owing to the unavailability of experimental data concerning rigid beam to web connections. Thereafter, seven numerical models of a one-sided sub-assembly of beam to column web connection with different arrangements of the haunch plates, and vertical and horizontal continuity plates were designed and assessed by means of finite element method using ABAQUS. After that, parameters such as restraint percentage, stiffness, strength, plastic hinge location, and also ductility under cyclic loads were calculated for each model. Results indicated that adding haunch plates along with horizontal and vertical continuity plates in the panel zone of double I-shaped columns can lead to significant increases in connection stiffness, as it restricts relative rotation of the tip of top and bottom connection plates. Consequently, models number HP6 and HP7, with respective stiffness values of 27.4 and 28.67, can be categorized as rigid connections by AISC.

A mathematical steel panel zone model for flanged cruciform columns

Cruciform sections are an appropriate option for columns of orthogonal moment resisting frames for equal bending strength and stiffness about two main axes and the implementation is easier for continuity plates. These columns consist of two I-shaped sections, so that one of them is cut out in middle and two generated T-shaped sections be welded into I-shaped profile. Furthermore, in steel moment frames, unbalance moment at the beamcolumn connection leads to shear deformation in panel zone. Most of the obtained relations for panel zone strength derived from experimental and analytical results are on I-shaped columns with almost thin flanges. In this paper, a parametric study has been carried out using Finite Element Method (FEM) with effective parameters at the panel zone behavior. These parameters consist of column flange thickness, column web thickness, and thickness of continuity plates. Additionally, a mathematical model has been suggested to determine strength of cruciform column panel zone and has been shown its accuracy and efficiency.