Web Buckling Research Articles

Experimental response of thin RC walls seismically strengthened with steel plates

In some Latin American countries, and especially in Colombia, the industrialized system of thin and slender walls has been chosen for the construction of residential buildings, thus reducing costs and increasing efficiency of construction processes. However, these walls differ considerably from traditional concrete wall system due to their reduced thickness, reinforcement detailing, and use of nonductile electro-welded reinforcement, which increases their seismic vulnerability, especially in tall buildings and in high seismic hazard zones. Strengthening proposals for walls with these specific characteristics of the industrialized system are scarce; therefore, it is necessary to evaluate alternatives that allow for improving their seismic performance. This article presents the experimental response of a thin wall that was brought to failure and subsequently repaired and strengthened with externally bonded steel plates to evaluate the effectiveness of the repair process and the strengthening. Additionally, the results of two thin walls externally strengthened with steel plates and bolts are presented, and their response is compared with that of the original walls. All the specimens were subjected to the same type of test under cyclical lateral load and constant axial load until failure. The behavior observed in the rehabilitated wall showed that it is possible to restore the stiffness of a wall that has previously been brought to a severe level of damage and increase its displacement capacity with the strengthening. In strengthened walls without previous damage, the displacement capacity was increased between 25 % and 43 %, reaching a roof drift of up to 2.0 % without a significant increase in resistance. A noticeable increase was obtained in the amount of dissipated energy (greater than 80 %), and the rupture of web reinforcement and buckling of longitudinal reinforcement of the boundaries were delayed for average drifts of 43 % and 32 % higher than in the original walls, respectively.

Local buckling behaviour of web perforated cold-formed steel lipped channel columns

To connect beams and bracings with storage rack uprights, closely spaced perforations are provided along the web, flanges, and rear flanges of uprights. These perforations can significantly lower the ultimate capacity of such compression members with the possible influence of its natural buckling modes. This capacity reduction can depend on various parameters such as (a) geometrical shape, proportioning of cross-section, and stiffeners; (b) perforation shape, size, spacing, and location; (b) slenderness of member, cross-section, and elements of cross-section; and (d) material properties. A thorough understanding of the influence of the above-mentioned factors is necessary for the accurate strength prediction of perforated Cold-formed steel (CFS) compression members. Even though the current design standards are updated for the accurate strength prediction of unperforated CFS compression members, they do not collectively account for the influence of all the aforementioned factors on the load-carrying capacity of the perforated CFS members, particularly for the local buckling capacity. Though the Direct Strength Method (DSM) of design is the most accepted method for accurate strength prediction of CFS members even for complex cross-sectional shapes, recent research on the strength evaluation of perforated CFS members using DSM has emphasized the need for refinement in DSM. The Modified Direct Strength Method (MDSM), which accounts for the simultaneous buckling of flanges and web, includes the cross-section aspect ratio and cross-section slenderness to predict more accurately the local buckling design strength. However, it was developed only for unperforated specimens. Hence, a systematic experimental and numerical investigation was done to understand the influence of the perforation in the local buckling behavior of the lipped channel section. In total, 14 specimens, including 2 unperforated and 12 web perforated CFS lipped channel stub columns were physically tested with fixed support conditions. The Finite Element Analysis using ABAQUS software was used to conduct an extensive parametric numerical study. The results were used to compare the strength curves of DSM and MDSM and the modification in the design curves has been proposed by considering the erosion in strength due to the presence of perforation.

Buckling mechanism and modified direct strength method of CFS built-up beams with multi-box cross section

A comprehensive study on the buckling mechanism of the Cold-Formed Steel (CFS) box beam composed of C- and U-shaped channels is conducted in order to improve the accuracy of the Direct Strength Method for calculating the bending capacity of CFS beams. Experimental tests involving four-point bending are carried out on six CFS box beams with varying screw spacing and stiffener numbers. In addition, numerical analyses are performed by finite element method. Based on the investigation of experiments and parameter analysis, an elastic constraint model for web buckling is proposed and the buckling coefficient are derived by the application of a generalized variational principle. The experiments reveal an interaction between local buckling in the upper flange under compression and the web. When the upper flange in compression buckles before the web, it leads to a reduction in the lateral constraint stiffness of the flange on the web, consequently, resulting in web buckling. An elastic constraint model for web buckling is proposed, incorporating the constraint effects of the upper flange's elastic support on the web. The critical buckling stress and buckling coefficient of the model are derived using the generalized variational principle. According to the experimental and numerical analysis results, the relative restraint stiffness of the flange on the web shows effects on the buckling coefficient. As the screw spacing and the length of the pure bending area decrease, as well as the number of stiffeners increases, the relative restraint stiffness increases. Subsequently, this leads to an increase in the buckling load and ultimate displacement of the CFS beam. Considering the interaction between the buckling of flange and web, the Direct Strength Method in AISI-2016 is modified for the CFS built-up box beam composed of C- and U-shaped channels. The applicability and correctness of the proposed modified Direct Strength Method is approved through the application of multi-box CFS beams composed of 2C-2 U and 3C–2 U channels. Compared with the Effective Width Method in current Chinese code and Direct Strength Method in AISI-2016, the proposed modified DSM exhibits the highest accuracy in predicting the bending capacity of the CFS box beam. It is shown that the proposed method can be effectively employed to calculate the flexural capacity of CFS beams with multi-box under local buckling control.

Cyclic behaviour of welded stainless steel beam-to-column connections: Experimental and numerical study

This paper presents an experimental and numerical programme on six welded stainless steel beam-to-column connections subjected to cyclic loading. The test specimens were designed in accordance with Eurocodes and comprised an I-section beam made from 316 L stainless steel welded to an I-section column made from 304 L stainless steel. Each specimen was subjected to a quasi-static cyclic loading protocol and the load-displacement curves are monitored and reported. The results are analysed in terms of failure characteristics, skeleton curve, strain distribution and energy dissipation. Typical failure modes are combined global flexural and torsional buckling and localised web and flange buckling of the beams. The slope of skeleton curve in the hardening region and the energy dissipation capacity appeared to reduce with the section size. Numerical models capable of successfully replicating the experimentally observed response were developed. The load-displacement behaviour and the failure pattern were compared to the experimental ones, showing a good validation. Overall, it has been demonstrated that good hysteretic performance has been achieved for the welded stainless steel beam-to-column connections.

Behaviour of concrete-filled circular steel tubular K-joints in wind turbine towers

The advantages of concrete-filled steel tubular lattice towers in stress efficiency, material consumption, and industrial construction are significant for the future development of ultra-long blades, ultra-high towers, and large-capacity units. The stress state of the joints is a key component of a wind tower structure. Therefore, experiments were conducted on four concrete-filled circular steel tubular (CFCST) K-joints in a lattice wind turbine tower, along with one hollow circular steel tubular (HCST) K-joint for comparison. The test results revealed that the CFCST K-joints failed due to local and overall buckling of the compression web, whereas no plastic deformation occurred on the chord. The stiffness of the CFCST K-joints significantly improved, and the stress concentration around the intersecting line was significantly reduced. Existing structural codes, both domestic and international, underestimate the bearing capacity of CFCST K-joints because the contribution of the core concrete cannot be accounted for. Finite element analyses indicate that the bearing capacity of the CFCST K-joints is dependent on the failure mode, primarily influenced by the thickness ratio τ and the angle θ. To prevent joint failure in the CFCST lattice wind turbine towers, specifically suggest τ ≤ 1 and θ ≤ 45°. Based on the bearing capacity calculation method proposed by CIDECT for HCST K-joints, design equations were obtained to predict the punching shear bearing capacity of CFCST K-joints using the least-squares method. The established formula exhibited high accuracy through regression verification.

Experimental study on flexural behavior and bending capacity prediction of Q550E steel beams within corroded shear span

An experimental study is carried out to investigate the degradation behavior of Q550E HPS steel beams with corroded shear span. At first, tensile tests of 15 pieces of steel are undertaken to obtain the degradation law of mechanical property parameters. Four steel beams with different corrosion damage levels in shear span are designed by electrochemical accelerated corrosion. The flexural loading tests of corroded steel beams are conducted, and the mechanical response of local corrosion to steel beams behavior is discussed. The necessity of lateral bracing is discussed theoretically. Considering the constitutive model affected by corrosion and the role of stiffeners, a predictive model of bending bearing capacity is proposed. The results show that the increasing corrosion damage will cause the failure position to move from mid-span to shear span, and the failure mode will shift from mid-span compressive flange buckling to bending-shear buckling, and finally appear web buckling. Corrosion damage level higher than 10% will lead to insufficient strain development. The proposed model can predict the flexural capacity and deflection well. Compared with the test results, the bearing capacity and deflection of corroded HPS beams are predicted by the nonlinear iterative method with high accuracy.

Evaluation on structural performance of hybrid composite post-tension plate girder through finite element analysis

ABSTRACT Plate girders are typically formed by the built-up of I-shaped plates. It is vulnerable and weak in resisting buckling. In this study, FE analysis models were developed to evaluate the flexural performance of a hybrid composite post-tension (HCPt) plate girder. The HCPt plate girder is made of double-web and in-fill concrete with pre-stressed tendon to prevent shear web buckling and improve flexural resistance. The sensitivity of design parameters to the performance of the girder was also investigated through a parametric study using four different configurations. The selected parameters are span length, steel grade, concrete grade, and level of pre-stressed force. The statistical analysis was performed using linear multiple regression model to predict the girder’s flexural load and displacement. The results showed that web shear buckling was eliminated for models with in-fill concrete and pre-stressed tendon and failed by bending. Failure of the girder with double web was demonstrated by the combination of bending and web shear buckling. The concrete in-fill prevents the web plate from buckling and the beams generally fail in bending with high ductility. The load capacity of the hybrid composite plate girders with pre-stressing improved by 76% and 44% compared to conventional single-web plate girders and double-web plate girders, respectively.

Strengthening of slender webs of steel plate girders using FRP composites

Web buckling of steel plate girders creates an undesirable failure mode as it can limit the ultimate load capacity of plate girders. This paper presents details of an experimental investigation aimed at strengthening slender end panels of steel plate girders using three different types of fibre-reinforced polymer (FRP) composite materials (glass-fibre-reinforced polymer (GFRP) pultruded section stiffeners and woven carbon-fibre-reinforced polymer (CFRP) and GFRP fabrics). The plate girders were fabricated using non-rigid end posts and were tested in three-point bending. The test results showed an increase of up to 54% in the ultimate strength of the FRP-strengthened end panels compared with the non-strengthened control panel, which was the result of increased out-of-plane stiffness of the web. A breakdown of the bond between the steel and the FRP fabric occurred in the end panels strengthened with CFRP and GFRP fabrics, while no bond breakdown of the pultruded sections was observed at the ultimate load. Analytical methods proposed by some of the design codes underestimated the critical buckling load and overestimated the ultimate load of the non-strengthened end panel.

Flexural performance of T-shape light-weight concrete filled steel tubular girder

This paper proposes an optimization study for both structure and materials to obtain an affordable, long-span, light-weight, and fast-constructing T-shape lightweight concrete-filled steel tubular (LWCFST) girder in order to be used in bridge construction. This research was performed on a hollow steel tube of Steel-52 (yield limit 360 MPa), which was filled with LWC. A set of parameters had been investigated to illustrate its effect on T-shape LWCFST girder stiffness, toughness, resilience, and ultimate carrying load capacity in order to obtain an equivalent stiffness to that of the typically used precast concrete girder. Based on design codes (EN 1994-1-1/Euro code 4 and ANSI/AISC 360-10) that permit the use of LWC as a filler material, the parameters considered were: the thickness of the steel tube, compressive strength of the filler concrete, and the bond condition between the steel tube and filler lightweight concrete. The yielding and ultimate bending capacity were determined based on the interpreted failure criteria of T-shape LWCFST girder, considering non-linear analysis for both material and loads using ANSYSWORKBENCH software. The results showed that T-shape LWCFST girder can be employed as a significant relative economic alternative to a typical precast girder in the bridge construction field, thanks to its high stiffness/weight ratio. The lightweight concrete inside was effectively employed to delay the local web buckling of the steel tube to increase its bending capacity. In addition, it reduced the total self-weight of the bridge’s superstructure by 20% compared with a typical precast concrete girder. The dominant failure of T-shape LWCFST girders was found in the upper concrete slab due to the compression stress, even though the tensile cracks in the filler concrete occurred after reaching tensile yield stress in the steel tube. Additionally, increasing the value of friction coefficient between steel tube and lightweight concrete up to 0.8 was found to significantly affect the girder stiffness and has a slight effect after, no matter how high it is.

Web Buckling of Steel and Composite I Girders Under Patch Load

A comparison is made between Steel I-girders and Composite I-girders under patch load conditions. The buckling phenomenon is observed using Finite Element Method (FEM), and the results are systematically compared with existing literature. The FEM results demonstrate good agreement at initial parameters. Composite materials emerge as a superior alternative to steel in plate girders. For composite web plates in I-girders subjected to patch loading, both the width of the applied load and the aspect ratio of the web plate are identified as pivotal factors influencing the buckling load. Key Words: Steel, Composite, I Girders, Finite Element Method, ANSYS

Stiffening of I-section MRF beams against degradation due to local buckling

Moment resisting frame (MRF) beams under cyclic loading are vulnerable to local flange and web buckling. The Seismic Provisions for Structural Steel Buildings (AISC341) prescribe width-to-thickness ratio limits, which are contingent on target rotations during predefined cyclic loadings. Some rolled I-sections available in the market cannot be employed in special MRFs since they fall short of satisfying the AISC341 flange slenderness limit. Moreover, local buckling leads to a decrease in both strength and stiffness in cyclically loaded MRF beams, ultimately increasing the risk of frame side-sway collapse. This paper introduces a stiffening method aimed at improving the behavior of I-section MRF beams. The proposed method involves placing a pair of stiffeners at the plastic hinge regions. A two-phase numerical study was conducted to assess the effectiveness of this approach. In the first phase, nine unstiffened beam cross-sections with varying flange and web slenderness were considered. The slenderness limits specified by AISC341 were evaluated based on cyclic analyses of these beams. In the second phase, a parametric study was conducted on the same cross-sections, with the flange width and the placement of the pair of stiffeners considered as variables. The results revealed a substantial improvement in behavior with the addition of a pair of stiffeners. Cross-sections that failed to meet the flange slenderness limit could be used in MRFs when stiffened. The optimal location for the stiffeners was found to be significantly influenced by the flange width. Design recommendations for the ideal stiffener placement are presented in this paper.

Flexural study on U-shaped steel–concrete composite beam cross joints with L-shaped connection longitudinal transition components

The paper focuses on the U-shaped steel–concrete composite bottom beam cross joints of U-shaped Steel-concrete Composite Open-web Sandwich Plate (USCOSP), presenting a new type of cross joints transmitting the internal force of steel web by L-shaped connection Longitudinal Transition Component (LLTC). LLTC consists of sleeves, L-shaped connection plates and threaded rebars installed on the steel web using sleeves and L-shaped connection plates. Compared with the conventional cross joints which transmit internal force of steel web by Welded Longitudinal Transition Rebar (WLTR), the LLTC cross joints transfer eccentric internal force within the steel web. Through simple-point loading experiments with simply-supported at four ends, the research experimentally investigated the flexural behavior of the WLTR cross joints and the LLTC cross joints. The five specimens were varied to differ in the type of longitudinal transition components, the diameter of WLTR, the number of threaded rebars of LLTC and the strength grades of threaded rebars of LLTC. Experimental results showed that the failure mode of U-shaped steel–concrete cross joint was the buckling of steel web, the buckling of top longitudinal rebar and crush on the concrete under compression near the central region. The LLTC cross joints experienced higher load capacity and better ductility than WLTR cross joints because of little steel web buckling. The ultimate load capacity calculated according to JGJ 138–2016 and the deflection in the elastic stage calculated according to the displacement method agree well with the experiment results.

A Horizontal Stiffener Detailing for Shear Links at the Link-to-Column Connection in Eccentrically Braced Frames

This study investigates the performance and viability of a horizontal stiffener detailing (HSD) to (1) be used at the link-to-column connection in a D-braced eccentrically braced frame layout where conventional link-to-column connections show poor performance, (2) minimize the overstrength factor of shear links caused by the hardening of link flanges, and (3) mitigate an undesirable failure mechanism previously observed in shear links fabricated using ASTM A992 steel. HSD and conventional stiffener detailing (CSD) were tested using W460×60 sections under two loading protocols, including one simulating near-collapse excitation. While the flanges of CSD shear links are greatly stiffened by vertical stiffeners, webs of HSD shear links exhibit inelastic buckling at large rotation angles. This allows the flanges to freely deform, thereby reducing the likelihood of brittle fracture at the flange connections, as well as undesirable link overstrength induced by the flange contribution. This study shows that the horizontal stiffener configuration developed a ductile failure mechanism resulting from gradually increasing local buckling in the web. The strength degradation of links with horizontal stiffener detailing was much more gradual due to the ever-increasing web buckling, unlike the sudden brittle fracture at the flange-to-column face of links with CSD. This research shows that the HSD is a viable and economic alternative for shear links, which has the potential to decrease welding in the shear link while exhibiting adequate seismic performance. HSD also maintains a low overstrength factor and utilizes a simplistic design approach. Finally, the bolted extended end-plate connection and its details at the link ends used in the test experiment provided a viable solution for replaceable links.

Effect of Web Perforations on the Web Buckling Resistance of 7075-T6 and AA-6086 High-Strength Aluminium Alloy C-Shaped Members under End-Two-Flange Loading Case

Recently, new types of C-shaped members made from AA-6086 and 7075-T6 high-strength aluminium alloy have become more popular due to their high yield strength and lower cost. These members are often manufactured with pre-punched web perforations to simplify the installation of services, but this can reduce their strength. Also, such aluminium C-shaped members that contain perforated webs are vulnerable to web buckling failure, as aluminium alloy has a lower elastic modulus compared to steel. However, this influence has not been investigated for high-strength aluminium alloy sections to date. An extensive numerical investigation was undertaken to examine the effect of web perforations on the web buckling resistance of high-strength aluminium alloy C-shaped members under an end-two-flange (ETF) loading case, and this study focused on two types of aluminium alloys, namely 7075-T6 and AA-6086. To achieve this, a nonlinear finite element (FE) model was developed and validated using the test data in the literature. The material properties used in the FE models were obtained from the relevant literature. A parametric investigation was carried out, consisting of a total of 1458 models. In this investigation, a number of variables were examined, including the web hole size, web hole location, bearing length, fillet radius and aluminium alloy grades. The results showed that increasing the a/h ratio from 0.1 to 0.5 resulted in a decrease of 9.7% and 9.3% in the web buckling resistance for the 7075-T6 aluminium and AA-6086 aluminium, respectively. When the length of the bearing plates (N) varied from 100 mm to 200 mm, the web buckling resistance experienced an average increase of 61.7% for the 7075-T6 aluminium and 54.1% for the AA-6086 aluminium. Also, the web buckling resistance increased by 6.2% for the 7075-T6 aluminium alloy, while the strength increased by 4.0% for the AA-6086 aluminium alloy when the x/h ratio increased from 0.1 to 0.5. The numerical data generated from the parametric study were used to assess the accuracy and suitability of the latest design recommendations, and it was found that the design rules presented in the previous literature cannot provide reliable and safe predictions for estimating the web buckling resistance of aluminium C-shaped members that contain perforated webs under an ETF loading case. Finally, new design formulas were proposed in the form of strength reduction factors. A reliability assessment was then undertaken, and the results of this analysis indicated that the proposed design formulas can accurately predict the web buckling resistance of such members with perforated webs.

Experimental research on curved continuous steel-concrete composite twin I-girder bridge

Due to the excellent economy and convenient erection, curved continuous steel–concrete composite twin I-girder (CTIG) bridges have been applied in mountainous bridges and unban overpasses. Rigorous investigation of the bending-torsion interaction is important for the curved continuous CTIG bridge design. A CTIG model bridge with a span arrangement of 17.46 m + 17.46 m and a curved radius of 200 m, was fabricated and tested under a symmetric static load. The mechanical behavior and failure modes of the model bridge were investigated. Results show that the non-uniform torsion and the web distortion effect are the characteristic mechanical behaviours of the curved CTIG bridge. The crossbeams resist the web distortion to ensure the transmission of the torsional moment. The constraint of the web distortion by the crossbeams results in the bottom flanges of the CTIG bridge being subjected to additional lateral bending moments. The ultimate strength of the CTIG bridge studied in this research is reached by a shear failure involving web buckling, formation of diagonal web yielding, and concrete deck crushing. This study contributes to a deeper understanding of the mechanical behavior of the curved continuous CTIG bridge and provides a valuable experimental basis for research regarding the design of bridges of this type.

Fire resistance of steel-concrete cellular composite beams having different end restraints

To determine the fire resistance of steel-concrete cellular composite beams having different end restraints, constant-load heating tests and numerical simulation analyses were conducted on end-hinged and rigidly-jointed circular-holed cellular composite beams to investigate the cross-sectional temperature field, displacement changes, and damage patterns of honeycomb composite beams during the entire fire process. The results showed that there was local buckling of the end web and lower flange of the beam, and lateral instability of the lower flange, in both types of beam-end constrained cellular composite beams after the fire. The definition of the fire endurance limit of the beam-end constrained cellular composite beam is the deflection at the mid-span reaching 1/20 of the beam span. Under ISO-834 standard heating conditions, the hinge and rigid connection restrained composite beams reached their fire resistance limit at 90 min and 75 min, respectively. Due to the existence of welds, the overall torsional performance of fixed confined cellular composite beams was better under fire. After a fire, the rigid connection restrained composite beams had more complex crack distributions on the concrete surface. During heating up, the opening edge temperature of the steel beam web was higher than that of inter hole web. The recovery ratio of deformation after a fire for the hinge and rigid connection restrained composite beams was 10.6% and 7.5%, respectively. The numerical simulation results were in good agreement with the experimental results, thus verifying the correctness and validity of the finite-element model.

In‐plane stability and shear deformation analysis of the H‐beam hollow arch

SummaryH‐shaped circular arc is a relatively novel type of open‐web steel arch, and currently, no reports have been published concerning its in‐plane stability. In this paper, the elastic and elastic–plastic in‐plane stability of the H‐shaped hollow circular arch is studied by theoretical deduction combined with numerical simulation. First, the overall shear rigidity of the H‐shaped circular arch is calculated, and the elastic buckling load formula of the arch is proposed and verified considering double shear deformation under full‐span radial and uniform loading. The overall elastic buckling load deduced in this paper is reasonable according to the finite element analysis. The results indicate that the influence of shear deformation on the overall elastic buckling load of the arch decreases with the increase of the span length. The arch‐bearing capacity is the largest when the rise‐span ratio is 0.25. Second, the restriction conditions necessary for avoiding local buckling of the chordal web before integral buckling of the H‐shaped steel hollow circular arch are analyzed. Finally, the elastic–plastic failure mechanism of the H‐shaped arch under full‐span radial and uniform loading is examined, and the formula for determining the ultimate bearing capacity that is achievable before failure under full‐span radial and uniform loading is proposed. ANSYS analysis shows that under the radial uniform loading, the chordal bars will yield near 1/4L and 3/4L, and ultimately, the structural failure of the lower chord occurs in the vicinity of 1/4L. The formulas presented in this paper agree well with the results obtained from the finite element analysis and can be used as a reference for engineering applications.

Influence of web distortion and onset of yield on doubly symmetric built-up I-girders subjected to high moment gradient

Recent studies have shown the AISC 360 Specification overpredicts the strength of certain built-up I-girders. The largest overpredictions occur for thin-unstiffened web members subjected to large moment gradient. The current study analytically investigates the combined effects of web distortion, web shear, web buckling and postbuckling, and onset of flexural yielding on built-up I girders. The findings show that AISC 360 overpredicts the member strengths due to: (1) unaccounted for web shear effects and (2) direct scaling of the uniform bending strength curve by the moment gradient factor. Based on these findings, potential paths toward AISC 360 Specification improvements are discussed.

Estimation of patch-loading resistance of steel girders with unequal trapezoidal web-corrugation folds using nonlinear FE models and artificial neural networks

Corrugated-web steel I-girders (CWGs) have better shear and torsional strengths, offering additional stability against out-of-plane web buckling and local crippling under patch loads than flat web girders. CWGs are lightweight and more cost-effective than flat web beams for applications in buildings and bridges. The existing design models for estimating patch-loading resistance in CWGs assume equal widths in web corrugation folds for a simply supported span. This study examined the parametric influence of unequal trapezoidal-web folds on the nonlinear behavior of CWGs under compressive patch loading. A total of 533 steel I-girders with simply supported (SS) and 478 cantilever spans (CS) were analyzed using a calibrated nonlinear finite element (FE) methodology. The generated datasets of CWGs consisting of governing parameters (i.e., girder geometry and material properties) were mapped to refined patch-loading resistance using artificial neural networks (ANNs) for both CS and SS-type spans. The proposed ANN formulation showed better prediction accuracy (mean absolute error of about 2–4% in this study) than the existing design models for estimating the patch-loading resistance of CWGs. For practical applications and conservative patch-loading resistance, prediction modification factors were also proposed for ANN formulation and existing design models within a targeted error margin.

Behaviour and design of double angle beam-column connection in fire conditions

The behaviour of composite floor systems in fire depends significantly on the performance of connections supporting the beam. This paper discusses the performance of double-angle shear connections under fire conditions investigated using numerical analyses and suggests changes to connection design and detailing for their improved fire performance. Finite element models are used to perform sequentially coupled, heat transfer and stress analyses of composite beams with end connections. The analysis technique is validated against several experimental studies. Two major triggers for connection failure in fire are identified: (i) excessive deformation following web buckling during the heating phase and (ii) contraction of the beam during the cooling phase. It is observed that the flexibility of angles used in the connection causes prying action and leads to a localized increase in the weld force demand, which increases the likelihood of a premature failure of the welded joint. The beams that have bottom flange coped at the ends are found to be more susceptible to web buckling during the heating phase. The web buckling can be prevented by using stiffened angles. The failure during the cooling phase can be prevented by using slotted holes.