Bolt Diameter Research Articles

Modified post-installed adhesive anchorage test: Investigation of in-place compressive strength of concrete and influential factors

This paper presents the Modified Post-installed Adhesive Anchorage test (MPAA) as a method for evaluating the in-place compressive strength of concrete. It considers various influential factors, including test surface characteristics, concrete strength, anchorage depth, bolt diameter, and rebar location. Additionally, a formula for calculating concrete compressive strength, applicable to various influencing factors, was suggested. The findings demonstrate the effectiveness of MPAA in assessing in-place compressive strength of concrete with a high degree of precision. Following pull-out test, the prevalent failure modes observed were vertebral failure and vertebral-bond composite failure. Moreover, diverse concrete strengths, anchorage depths, and rebar locations demonstrated differing impacts on failure modes, while test surface characteristics and bolt diameter exerted less noticeable effects. The pull-out force-displacement curve during pull-out displayed three discernible phases: the elastic phase, crack propagation phase, and descent phase. When conducting on-site assessments, it is advisable to situate test points on the side surfaces of the members. Furthermore, factors like cover thickness and rebar location should be thoroughly evaluated when positioning test points. This encompasses the prudent choice of anchorage depth and bolt diameter to improve test precision. The suggested formula for calculating compressive strength exhibited minimal error and is applicable in determining concrete compressive strength for a wide range of practical engineering contexts. This study not only establishes a theoretical underpinning and offers support for standard revisions but also furnishes valuable guidance for conducting on-site testing procedures.

High-strength preload indicator inner washer forward design method

The preload indicator bolt assembly is a fastener that achieves the desired preload effect by simply tightening the preload nut within a specified range without additional measuring tools. The inner washer is a critical component in this assembly, with its outer diameter and height serving as crucial design parameters. In this paper, an equivalent mechanical model is established for the preload indicator bolt assembly. Utilizing this model, an iterative search process is developed to determine the optimal outer diameter and height of the inner washer. The analytical relationship between the bolt preload force and nut displacement is compared and validated against finite element analysis and experimental results, yielding favorable agreement. Notably, the nut tightening angle can vary within the range of 187°–242°, while the preload force exhibits a minimal variation of only ±2% for type 10-0A bolt connection (Bolt diameter and bolt pitch are φ16 mm and 1.41 mm, respectively. The material of bolt, inner ring, and flat ring are GH4169, 40CrNiMoA, and 30CrMo, respectively). This feature significantly simplifies the installation process of the preload indicator bolt assembly in real-world applications, offering great convenience. The increment in tension force on preloaded bolts under external loads exhibits an almost identical trend for both connection methods. Under the same preload force and the same eccentric working load conditions, the thickness of the connected components follows the same trend as their contact area.

Experimental study on longitudinal embedding performance of bolted engineered bamboo connections

This paper summarizes the experimental results of longitudinal embedding tests of bolted engineered bamboo connections. Six groups of bolted engineered bamboo connection specimens were prepared and tested monotonically up to failure. Test variables were bolt diameter and type of engineered bamboo: laminated bamboo or bamboo scrimber. Connection stiffness and embedding strength of the specimens of bamboo scrimber were greater than those of the specimens of the laminated bamboo – reflecting the difference in material density. Embedding strength of the laminated bamboo was insensitive to bolt diameter whereas embedding strength of the bamboo scrimber decreased with an increase of the bolt diameter. It was shown that in order to accurately model bolt embedding into bamboo, a foundation model is required. Reduction factors for strength and modulus for such a model were calibrated using experimental results. A parametric study addressing friction and foundation model size is presented.

Study on the elastic stiffness calculation method of single-bolted steel-bamboo scrimber-steel shear connections

Bolted steel-bamboo scrimber-steel (SBSS) connections are commonly employed in composite bamboo structures, but their equivalent stiffness in the elastic phase is difficult to determine. This study develops a novel theoretical formula for estimating the equivalent stiffness in the elastic phase of single-bolted SBSS shear connections considering various failure modes. Specifically, the method focuses on calculating the contact stiffness between the bolt and the pre-drilled hole wall, as well as the shear load applied to the bolt end by the steel plate. The method uses the double-shear yield mode, which is included by European Yield Modes (EYM), and the beam on elastic foundation theory (BEFT), and considers the bamboo scrimber embedment stiffness, bolt diameter and steel plate strength class. The method is tested by conducting experiments on single-bolted SBSS connections with varying load and fiber direction (LFD) angles, bolt diameters, steel plate thicknesses and strength grades. The results show that the connection stiffness increases with bolt diameter and steel plate strength grade, decreases with LFD angle, and is not affected by steel plate thickness. The parameter μ, which is important in the theoretical equations, is also calibrated based on the experimental data. The proposed method is validated by comparing it with existing test results of single-bolted SBSS connections. This paper provides a simple and reliable model for predicting the equivalent stiffness in the elastic phase of bolted SBSS connections in bamboo scrimber structures and offers useful insights for their design.

Corrosion evolution and axial mechanical performance degradation of corroded M24 high-strength bolts

To investigate the axial static performance degradation of high-strength bolts subjected to long-term atmospheric corrosion in coastal environments, a neutral salt spray accelerated corrosion test was performed on M24 high-strength bolts over a period ranging from 0 to 330 days. Microscopic morphology observations and axial tensile tests were conducted after corrosion. A linear relationship between mass loss rate and corrosion period was established, and the evolution of pit depth and aspect ratio was proposed. Based on the tensile test, the failure modes of corroded high-strength bolts were categorized as bolt breakage and thread shear-out. The critical mass loss rate for the transition between these two modes was found to be 7.05% (corrosion period of 180 days). Equations characterizing the degradation of residual ultimate strength and relative stiffness as a function of mass loss rate were derived. Furthermore, based on average thickness loss and pit loss, a theoretical analysis on ultimate strength degradation was conducted, and its results were compared to the refined numerical simulations. Both methods were found to provide acceptable outcomes, and numerical results demonstrated more precise and conservative. With numerical method, parametric analysis was conducted, involving 5 groups and 222 models, leading to the formulation of a general ultimate bearing capacity assessment equation concerning bolt diameter and thread pitch.

Test on seismic behaviors of stainless steel bolted extended end-plate beam-column joints

This study conducted tests on the seismic behavior of austenitic stainless steel bolted extended end-plate beam-column joints, which have been few reported. Considering the influence of material type, end-plate thickness, bolt diameter, panel zone thickness, and loading scheme, 11 stainless steel joints and two carbon steel joints were designed and tested. Material properties, joint failure modes, moment-rotation curves, bolt load distributions, and joint component yield sequences were reported in detail. Experimental research showed that the beam-column joints in austenitic stainless steel experienced four failure modes, i.e. plastic hinge at the beam end, fracture failure of weld between the beam flange and end-plate, bolt rupture failure, and composite failure. All the tested joints had good seismic behavior, with rotation capacity greater than 0.03 rad. The influence of joint configurations on the seismic behavior were analyzed. The results indicated that the end-plate thickness, end-plate stiffener, and bolt diameter had a substantial impact on the joint seismic behavior, while the thickness of column web in panel zone, material properties, and loading scheme had a comparatively small effect. The initial rotational stiffness and moment resistance(yield moment) of joint obtained from the experiment were compared with the predictions of the EN1993-1-8, Design Guide 16, and JGJ 82-2011. Comparisons indicated that the EN1993-1-8 overestimated the initial rotational stiffness; Both the EN1993-1-8 and JGJ 82-2011 underestimated the moment resistance, while the predictions from the Design Guide 16 were significantly higher than the moment resistance and closer to the ultimate moment.

Study on the tensile performance degradation of bolt-ball joints after bolt-thread corrosion

Bolt-ball joints, which have been used in corrosive environments for a long time, are prone to corrosion problems, particularly in the contact area between the bolt and the ball, posing a threat to the overall structural safety. This paper established a refined finite element model of bolt-ball joints that considers the effects of bolt-thread corrosion and corrosion products using an integrated simulation method of 3D corrosion evolution and mechanical properties of steel building components. The reliability of the simulation method was verified through several tensile tests. Subsequently, the stress distribution and load-displacement curves of M20, M24, and M27 joints with varying degrees of corrosion were analyzed after tension. The results indicate that when the corrosion mass loss rate is less than 80%, the tensile failure mode of the joint is bolt rod yielding. However, when the mass loss rate of the thread reaches 80%, the failure mode is ball thread yielding. For joints with the same thread mass loss rate and section area, the bearing capacity degradation increases as the bolt diameter increases. Additionally, for joints with different cross-sectional areas of threads, the bearing capacity degradation rate is higher when the cross-sectional area of the thread is smaller. Finally, a degradation formula for the tensile bearing capacity, taking into account the corrosion mass loss rate and bolt diameter, was proposed through regression analysis. This formula serves as a technical reference for the safety evaluation of corroded bolt-ball joints and similar joints.

Seismic behaviors of CFT-column frame-four-corner bolted connected buckling-restrained steel plate shear walls using ALC/RAC panels

A Frame-Buckling Restrained Steel Plate Shear Walls (BRSPSWs) system has been designed, featuring a steel plate connected to frame elements, to withstand lateral loads like seismic or wind forces. This system incorporates recycled aggregate concrete (RAC) to create concrete-filled and concrete panels, promoting eco-friendly and sustainable construction materials. Two single-span, two-floor specimens were tested under cyclic quasi-static load. A four-corner bolted connection was used to connect the steel plate to the square concrete-filled steel tubes (CFTs) column and H-section beam, minimizing the potential deformation of the frame elements produced by the tension field of the steel plate after high-order bucking. The steel plate was sandwiched using either autoclaved lightweight concrete (ALC) or RAC panels. The study analyzed failure modes, load-displacement responses, and characteristic capacities. Test results inferred that BRSPSWs exhibited favorable cyclic behavior, with similar failure modes observed using both ALC and RAC panels. The buckling of steel plates was reduced, and the type of restrained panels had a negligible impact on buckling. Consequently, ALC panels can effectively replace RAC panels. Furthermore, bearing capacities and yield stiffness were primarily determined by the bolted connection forms. A finite element (FE) modeling was developed using ABAQUS software and validated against test results. This FE modeling method successfully simulated failure modes and load-displacement curves. Parametric analyses were conducted and revealed that bearing capacity and yield stiffness positively correlated with steel plate thickness, bolt diameter, and the number of bolts but negatively correlated with the axial compression ratio. In contrast, the panel thickness and span length had a minor impact due to shear deformation in the bolted connection. Based on the test results and parametric studies, an equation for the yield-bearing capacity of BRSPSWs was proposed and verified.

Bolted shear connectors in steel–concrete composite structures: Shear behavior

The use of bolted shear connectors is of great importance to the sustainable development of steel–concrete composite structures. In this paper, an experimental program consisting of four push-out specimens is performed to investigate the effects of bolt length and fabrication method of concrete slabs on the shear behavior of single-nut embedded bolted shear connectors in terms of failure mode and load-slip response. The concrete slabs are fabricated either as cast-in-situ monolithic slabs or precast slabs with reserved pockets which will be filled with grout in the final construction stage. The obtained results demonstrate that the fabrication method based on grouting, which is commonly utilized for strengthening and retrofitting works, does not affect the behavior of the bolted shear connection. Based on the experimental observations, a finite element (FE) model of the bolted shear connection is developed, after the obtained numerical results are verified against the test results obtained in this paper and those presented in other existing literature, a parametric study is carried out to further investigate the effects of the concrete strength, bolt strength, bolt diameter, bolt pretension load, and the length-to-diameter ratio of bolt on the performance of the bolted shear connection. Moreover, based on the obtained results, a design formula is proposed to obtain the ultimate shear resistance of the bolted shear connection, and the efficacy of the proposed design formula is proved through the comparison with the test results shown in the existing literature.

Finite element analysis for built-up steel beam with extended plate connected by bolts

Abstract Extended end-plate type connections are widely utilized in steel assemblies for easy production and assembly. The proper end-plate and bolt selection is paramount to confirming safety and economy in all connections and, consequently, steel buildings. This study presented an approach for refined parametric three-dimensional finite element analysis of bolted steel beam-to-beam extended end-plate connections. The model considers geometrical and material non-linearity to determine the impact of various factors on the connection’s performance. The proposed model was used to construct a parametric study. The study variables were bolt diameter and end-plate thickness, focusing on how thick and thin end plates affect connection conductivity. Numerical outcomes demonstrate that the connection's flexural strength and stiffness capability improved by increasing the end-plate thickness and bolt diameter. Finally, the analysis results were assessed, and the main conclusions were presented.

Study on the relationship between the maximum anchoring force and anchoring length of resin-anchored bolts of hard surrounding rocks based on the main slip interface

The critical anchoring length of the hard rock bolt anchoring system is relatively short, which is prone to problems such as the designed anchoring length being too short to achieve the expected anchoring force, or the excessive anchoring length, which causes waste of resin cartridges. Therefore, predicting the maximum anchoring force for a specific anchoring length is of substantial significance for the design of bolt support parameters design and surrounding stability control. Herein, laboratory experiments, theoretical analysis, and in-situ test are implemented to explore the relationship between the maximum anchoring force and the anchoring length for the bolt anchoring system. The achieved results reveal that the slip failure of the bolt-resin interface (B-R interface) is the main failure mode of the hard rock anchoring system. In the presence of the main slip interface condition (i.e., assuming that the anchoring system fails only at the B-R interface) and for specific values of bolt diameter and elastic modulus, the maximum anchoring force does not depend on the strength of the surrounding rock, but only the anchoring length. The proposed relational model based on the main slip interface of the maximum anchoring force and anchoring length can successfully break the strength limit or surrounding rock type to utilize more experimental data acted upon by various surrounding rock conditions. According to the relational model, the relational curve and function for the maximum anchoring force in terms of the anchoring length of the Φ20 mm rebar bolt are obtained. It is found that the obtained relational curves have high accuracy through in-situ verification and comparison with the curves proposed by other researchers. The research results could provide solid theoretical references for the maximum anchoring forces prediction and bolt support parameters design.

Data-Driven Prediction Model for High-Strength Bolts in Composite Beams

In recent years, the application of artificial intelligence-based methods to engineering problems has received consistent praise for their high predictive accuracy. This paper utilizes a BP neural network to predict the strength of steel–concrete composite beam shear connectors with high-strength friction-grip bolts (HSFGBs). These connectors are widely used in bridge and building construction due to their superior strength and stiffness compared to traditional beams. A validated finite element model was used to predict the strength of HSFGB shear connectors. A reliable database was created by analyzing 208 models with different characteristics for machine learning modeling. Previous studies have identified issues with result variation and overestimation or underestimation of shear connection strength. Among the machine learning methods evaluated, the backpropagation neural network model performed the best. It achieved a goodness of fit of over 93% in both the training and testing sets, with a low coefficient of variation of 6.50%. Concrete strength, bolt diameter, and bolt tensile strength were found to be important variables influencing the strength of shear connectors. Other variables showed a proportional or inverse relationship with compressive strength, except for concrete strength and bolt pretension. This study presents an accurate machine learning approach for predicting the strength of HSFGB shear connectors in steel–concrete composite beams. The study offers valuable insights into the effects of various variables on the performance of shear connection strength, providing support for structural design and analysis.

Investigation of Parameters Affecting Rotational Behavior of Cold-Formed Steel Connection

This study aims to understand the behavior of connection, which holds an important key to efficient designs of the cold-formed steel structure. The focus is on examining parameters that affect the rotational stiffness and behavior of the cold-formed steel connection made of single-lipped channel sections with a bolt and gusset plate system. The numerical study has been conducted using component-based finite element analysis, with the studied parameters including bolt diameters, number of bolts in the group, size of the bolt group, thickness of the cold-formed steel cross-section, and thickness of the connecting plate. The effect of the variables is evaluated and explained by comparison. The result of the study reveals that the rotational behavior of the connection depends on the details of the assembly. For the given base connection, the parameters that give the greatest effect on the rotation stiffness and the moment capacity are the number of bolts and the bolt diameters, whereas the parameter that provides the least effect is the bolt spacing. On the other hand, the bolt group size is the most influential parameter for the member connection. For both types of connections, the thickness of the cold-formed steel section and the thickness of the gusset plate have shown limited effect on stiffness and strength. Using different variables in assembling the connection can also lead to different failure types, either bolt failure or excessive bolt hole deformation, which leads to plate failure. Doi: 10.28991/CEJ-2023-09-11-08 Full Text: PDF

Study of the Mechanical Properties of Beam-Column Joints in a New Type of Aluminum Alloy Portal Frame

In the article, the semi-permanent aluminum alloy portal frame is used as the research background, beam-column joints are used as the research object, and experimental and numerical analyses are carried out. The influence of different bolt diameters and arch angles on the mechanical properties of beam-column joints under vertical load was analyzed using five sets of experiments. The experimental results show that the load–displacement curves of different bolt diameters in the elastic stage are basically consistent. After entering the plastic stage, the ultimate load first increases and then decreases, and the ultimate displacement is basically consistent. According to the experiment, there is no significant difference in the load–displacement curve when the arch angle increases from 90 degrees to 108 degrees. When the arch angle increases to 126 degrees, the stiffness and ultimate bearing capacity of the node under vertical load significantly increase. Then, a numerical analysis model was established to analyze the mechanical performance of beam-column joints under horizontal loads. The numerical analysis results indicate that under horizontal load, as the diameter of the bolt increases, the yield load, yield displacement, ultimate load, and ultimate displacement of the beam-column node exhibit no significant changes, and the change amplitude is minimal. When the beam-column node is subjected to horizontal loads, as the arch angle increases, the yield and ultimate displacement increase by 2.14 times and 2.78 times, respectively, and the yield and ultimate load decrease by 58% and 48%, respectively. Finally, a simplified design method for beam-column joints was proposed based on experiments and numerical analysis.

Shear behaviour of embedded nut-bolted connectors in precast steel-concrete composite beams: Experimental investigations and numerical analyses

Precast steel–concrete composite beam (PSCCB) has been applied extensively in bridge constructions owing to its excellent mechanical properties. Employing demountable embedded nut-bolted connectors (ENBCs) in PSCCBs has become a competitive solution to conveniently replace deteriorated components and to further extend their service life. However, investigations pertaining to shear behaviours of ENBCs in PSCCBs are limited. Hence, economical push-out tests are conducted for investigating the ENBC performance in PSCCBs. Experimental results show that increasing bolt diameters significantly improves the shear performance of ENBCs. Increasing the ring width enhances the initial shear stiffness slightly, minimally affects the ultimate shear capacity, and significantly reduces the slip capacity. Additionally, a finite element model is developed based on the present experimental results to capture the nonlinear response and damage processes of the ENBCs. Subsequently, a validated model is used for parametric studies. Results of numerical analyses show that larger bolt diameters and higher grades improve the shear behaviour of the ENBCs. In addition, steel beams and concrete with lower strengths increase the slip capacity. The pretension degree of the bolts significantly affects the initial shear stiffness of the composite beams. However, the embedded nut angle minimally affects the shear behaviour of the ENBCs. Additionally, the model provided in Eurocode 4 yields slightly conservative predictions for calculating the ultimate shear capacity of ENBCs, thus, a reliable predicted model was proposed for hexagonal-ENBC. Based on experimental analyses, the mechanism associated with the shear and internal stress variations of the ENBCs are revealed via the verified model.

Finite element analysis of concealed angle steel node in prefabricated frame beams and columns

Prefabricated construction is a structural form vigorously developed by the country and is the inevitable path for the sustainable development of the construction industry. In order to enhance the seismic performance of prefabricated concrete frame structures, concealed steel angle connections for prefabricated frame beams and columns are employed. Based on experimental research on the force performance of these connection nodes, a finite element model of the connection node is established using ABAQUS software to analyze the influence of design parameters on the force performance of the specimen. The analysis indicates that upgrading the concrete grade from C25 to C55 increases the positive bearing capacity by 12.3 %. The specimen’s energy dissipation capacity and stiffness are both improved. Increasing the thickness of the steel cover plate can enhance the specimen's bearing capacity, stiffness, and energy dissipation capacity. Increasing the angle steel thickness from 4 mm to 10 mm results in a 27.78 % increase in negative bearing capacity, consequently enhancing the specimen’s energy dissipation capacity. By increasing the bolt diameter from 16 mm to 24 mm, the positive bearing capacity increases by 8.2 %, and the negative bearing capacity increases by 10.9 %. The energy dissipation capacity and stiffness of the specimen also improve accordingly.

Shear properties of composite steel plate connectors for prefabricated steel–concrete composite beams

As a critical component of prefabricated steel–concrete composite beams, ideal connectors can ensure the mechanical properties of bridges and significantly improve the efficiency of assembly construction. CSPC connector (Composite steel plate connector) with excellent load-slip curve and assembly construction efficiency was designed to realize fast and simple assembly construction. CSPC connectors require prefabricated bridge deck with no holes and low installation accuracy requirements. The results of 6 push-out specimens and 12 finite element models show that the CSPC connector exhibits an excellent load-slip curve compared to the existing connectors, and its shear stiffness and ductility coefficient are 1.03 and 1.51 times that of the stud connector, respectively. The shear stiffness and shear capacity of CSPC connectors are 0.79 times and 0.96 times the original when the grouting material age is reduced from 28 days to 3 days due to the rapid construction demand. The weakening of shear capacity is not obvious. The shear capacity of the CSPC connector comes from the connection between high-strength bolts and composite steel plates. The pressure-bearing effect of grouting material is crucial in connecting composite steel plates. Meanwhile, the composite steel plate of CSPC connector should be designed with equal thickness, a height of 30 mm and a spacing of no more than 10 mm. The recommended ratio of high-strength bolt diameter to composite steel plate thickness is 1.25. Finally, fit the load-slip relationship of CSPC connector, and propose a shear capacity formula with a deviation of less than 12 % from the test results.

Experimental study on mechanical properties of bolted joints between Fe-SMA and steel plates

The new intelligent material Iron-based Shape Memory Alloy (Fe-SMA) brings novel solutions for the performance rehabilitation of existing steel structures. To fully utilize the potential of the Fe-SMA active prestressed reinforcement, the systematic study of reliable joint is significant. Therefore, the bolted joints between Fe-SMA and steel plates was experimentally studied in this paper, whose reliability and convenience in metal structures have been generally accepted. Firstly, a series of 15 mechanical performance tests of bolted joints between Fe-SMA and steel plates were carried out. The key influencing parameters of the bolted joints were obtained, and different failure modes were observed, which can provide experimental verification for further finite element modelling and theoretical study. Furthermore, the effects of end distance e, edge distance s, bolt diameter d, thickness of Fe-SMA plate t and bolt layout on the ultimate load-bearing capacity, initial stiffness and failure modes of the bolted joints between Fe-SMA and steel plates were discussed, and some specified design suggestions on bolted joints between Fe-SMA and steel plates were proposed. This paper mainly aims to provide the experimental basis and design recommendations for compilation of the relevant specifications, which is expected to advance the scientific application of Fe-SMA in the performance rehabilitation of steel structures.

Numerical Investigation of the Behavior of Unstiffened Semi-Rigid Top and Seat Angle Connections under Monotonic Loading

In steel structures, unstiffened top and seat angle connections (TSACs) show semi-rigid behavior and transfer both the vertical reaction and some end moment of the beam while also making some degree of rotation. The moment–rotation behavior of TSACs has been evaluated using experimental and numerical analyses under monotonic loading and generally compared in the linear elastic region. In this paper, three-dimensional (3-D) finite element models of the TSACs were developed based on experimental data available from the literature to accurately obtain the moment–rotation results along the curve. The numerical models were verified with the moment–rotation curves of TSACs and the deformed shapes of the angles in the connections. The experimental results show that the finite element model in this study is adequate to predict the moment–rotation behavior of TSACs. The effects of bolt material properties, bolt diameter, bolt pretension load, friction coefficient, and gage distance on the moment–rotation behavior of the connections were investigated using the verified numerical model. The parametric analyses show that almost the same moment–rotation behavior is obtained for the connections by increasing the bolt strength and pretension load and varying the friction coefficients. The ultimate moment capacity of the connections was increased with a decrease in the gage distance.

Compressive behavior of built-up H-section columns fabricated using H-SA700 steel: Experiment, numerical simulation and design method

This paper provides an experimental and numerical investigation into the compressive behavior of built-up H-section columns fabricated using H-SA700 steel. First of all, axial compression tests were performed on nine built-up specimens. Secondly, the 3D solid finite element (FE) models were constructed using ABAQUS, and their accuracy was verified by the experimental results. And then, the effects of slenderness ratio, web height-to-thickness ratio, flange width-to-thickness ratio, channel thickness, transverse bolt pitch, bolt diameter, and longitudinal bolt pitch on the compressive strength and buckling deformation of built-up members were analyzed. Finally, the applicability of the column curves from GB 50017–2017, EN 1993-1-1, and ANSI/AISC 360–16 for H-SA700 built-up columns were assessed, and the design curves were modified. The results indicated that slenderness ratio and channel thickness were the main parameters affecting the bearing capacity of built-up members. The design curves of current codes all underestimated the compressive strength of built-up columns around the weak axis under axial loading. In addition, modified column curves could provide a conservative design for built-up H-section columns.