Steel Frame Joints Research Articles

Effects of Cover-Plate Geometry on the Mechanical Behavior of Steel Frame Joints with Middle-Flange and Wide-Flange H-Beams

This study investigates the mechanical behavior of cover-plate reinforced connections in steel frames with I-section columns and middle- or wide-flange H-beams, addressing gaps in current design standards. Finite element analyses validated by experimental data were employed to explore the effects of cover-plate geometry—shape, length, and thickness—on seismic performance. Results demonstrate that cover plates improve load-bearing capacity and ductility by relocating plastic hinges outward from joint regions. Specifically, cover-plate connections increased ductility by 25%, yield moment by 15%, and initial rotational stiffness by 7% compared to non-reinforced connections. The shape of the top cover plate had minimal impact on mechanical behavior. The cover-plate length and thickness significantly influenced seismic ductility and load-bearing capacity. The cover-plate thickness should be at least 0.3 times the beam flange thickness (not less than 6 mm) while ensuring the combined thickness of the cover plate and beam flange does not exceed the column flange thickness. These recommendations address the conservatism of existing standards, balancing material efficiency and seismic performance. Optimal cover-plate lengths of 0.7 to 0.9 times the beam depth were also identified. These findings provide practical guidelines for designing resilient steel frame connections in seismic regions.

Experimental tests of welded knee joints of steel frames

The paper focuses on presenting the methodology of testing corner joints along with the presentation of obtained results. The objective of the conducted research was to experimentally determine the behaviour of welded knees with slender webs under similar loading condition that occur in the knee joints of portal steel frames. Laboratory tests were carried out on a specially prepared testing stand. During the laboratory work, load tests were performed on three identical knees. The testing stand was equipped with measurement equipment, including two data acquisition systems: the SAD 256 for displacement and force sensors, and the Pontos/Aramis – a digital image correlation system. The first knee test served as a verification of the testing stand and the adopted data collection method. After implementing certain changes to the stand, the remaining load tests on the knees were conducted. Based on the conducted studies and data analysis, moment-rotation M–ϕ characteristics of the joints were determined, along with parameters such as initial stiffness S, elastic bending resistance Mel and ultimate bending resistance Mu.

On the reliability of steel frame joints in earthquake zones exposed to low temperatures

The paper analyzes the existing construction solutions of steel frames with a box-section column and an I-beam crossbar in order to use them in earthquake zones, including areas with low temperatures. Such solutions will allow the structure to accept the seismic inertial forces, while maintaining its bearing capacity throughout the entire period of operation. In order to solve this problem, the study proposes to use steel frame joints, which can be used both for the entire frame of the building and on individual floors, thereby creating a “flexible story” effect. The authors studied articles, books and patents issued in Russia, the United States, Japan, China and Iran, analyzed the factors that reduce the reliability and performance characteristics of the joints. The main factor consists in a welded joint, which is used to attach the crossbars to the columns, transverse ribs in the column body, and to form the box section of the column from sheets, angles or channels. The reliability of the welded joint is reduced even more under conditions of seismic zones with low temperatures in Russia. However, units without welded joints require special cast parts or structures, thereby reducing their availability. In this regard, the task consists in developing new original construction solutions for joints that meet the requirements of reliability and availability.

A 2D-CNN-Based Two-Stage Structural Damage Localization and Quantification Technique Using Time Domain Vibration Data

The conventional approaches for detecting structural degradation are time-consuming, labor-intensive, and costly. The physical monitoring of the structure also poses risks to the health and safety of supervisors. Therefore, damage estimation of any structure using artificial intelligence (AI), more specifically deep learning (DL), is becoming more significant in civil infrastructure. In the presented research article, an efficient two-stage damage detection method is proposed for structural damage detection (SDD) from time domain vibration signals. The proposed method utilizes two-dimensional convolutional neural network (2D-CNN) architecture as a DL algorithm for damage detection. Here, a computer-aided damage detection method for steel beam and frame-type structures is developed using 2D-CNN algorithm in the Google Colab platform. The effectiveness of the proposed method is first verified, and it provides more than 90% accuracy for identifying the damage location and severity of a cantilever beam for single- and multi-damage scenarios from numerically simulated noisy displacement data. The algorithm is also experimentally validated through the raw acceleration data of damaged steel frame joints collected from the Qatar University Grandstand simulator (QUGS). The proposed 2D-CNN algorithm performs better than other DL algorithms by achieving 100% accuracy within 10 epochs for damage detection of steel frames using QUGS data. It demonstrates significant potential for detecting damage location and quantifying damages for single- and multi-damage scenarios using noise-free and noisy datasets. The primary contribution of this study resides in the implementation of two-stage damage detection algorithm utilizing 2D-CNN with time domain vibration response for multiclass damage identification and quantification.

Design-focused Interpretable Machine Learning Models for Compressive Capacity Prediction of Gusset Plate Connections

Gusset plates can experience large compressive loads when used to connect bracing systems to beam-column joints in steel frames and truss bridges. The strength of a gusset plate is therefore vital to allow the bracing members to reach their ultimate capacity without a brittle failure of the gusset plate connection. Due to the large complexity of the stress distribution mechanism, simplified approaches commonly adopted for design can lead to inaccurate and highly conservative results. The present study aims at developing a simple yet efficient gusset plate compressive strength prediction model that does neither rely on crude assumptions nor require complicated calculations. A meticulously compiled database consisting of 68 experimental and 184 numerical datasets was deployed to aid in developing a high-performance machine learning (ML) model selected amongst 10 machine learning techniques studied. The superiority of the CatBoost and XGBoost models was confirmed with an accuracy of 95% and 96%, respectively significantly outperforming current design practices and widely used empirical formulas. SHapley Additive exPlanations (SHAP) and Taylor diagram were used to explain the feature importance and model performance. The developed interpretable ML models can instill trust in a model that explains its decisions, as opposed to other black box approaches. It was found that CatBoost was the most efficient in predicting the compressive strength of gusset plates with lowest mean absolute error of 50.76 kN and Nash-Sutcliffe model efficiency coefficient of 0.984, compared to the most accurate predictions observed among the existing methods (modified Thornton method) with mean absolute error and Nash-Sutcliffe model efficiency coefficient of 227.22 kN and 0.872, respectively. Finally, a reliability analysis was performed according to the LRFD approach to identify the level of safety of predictions obtained by the CatBoost and XGBoost models. The CatBoost model exhibited remarkably low dispersion with a safety factor of 0.753 thereby providing an adequate level of safety for the design of gusset plates.

Study on seismic behavior of steel frame joint with external arc diaphragm

The application of External Diaphragm (ED) in steel frame system is able to reinforce the stiffness of joint and provide efficient protection for the critical part of joint. However, due to the limitation of the existing design codes, the inside space of building is affected frequently by the excessive size of the ED. To reduce the size effect of ED, a hysteretic experiment on four steel joint specimens is first carried out in this paper, the effects of the width ratio (the ratio of ED width to beam flange width) and connection type (Bolted web-Welded flange (BW) connection and Full Bolted (FB) connection) are investigated. Then, a numerical analysis is conducted to further explore the influence of the width ratio and the thickness ratio (the ratio of ED thickness to beam flange thickness). The results indicate that the specimen with BW connection exhibits larger stiffness and bearing capacity, but the specimen with FB connection has obvious ascendancy on the ultimate deformation capacity and ductility. Moreover, Changing the width ratio and thickness ratio are unable to cause significant variation on the seismic performance of steel joint if the thickness ratio is larger than 1.25. Therefore, the thickness of the ED is more critical than width to the seismic performance of steel joint. Meanwhile, in the circumstance of the thickness ratio is equal to 1, the width ratio of 0.1 is recommended for the minimum limited value in structure design.

Influence of semi‐rigid joints on the seismic performance of single‐storey steel frames

AbstractThe design of joints of steel frames is often simplified, assuming that they have a fully rigid or ideally pinned behaviour. This wrong assumption is sometimes acquiesced by national technical codes, which mainly focus on the behaviour of simple connections and neglect the role of the joints in terms of global structural behaviour, particularly under lateral loads. In this paper, a numerical study about the evaluation of the influence of partial‐strength/semi‐rigid joints on the seismic performance of one‐storey steel buildings is presented. For this purpose, a population of real steel buildings has been considered, for which column bases and/or beam‐to‐column joints were originally designed as infinitely resistant/rigid restraints, but that, after the application of the component method, were found to be characterized by a partial‐strength/semi‐rigid behaviour. Finite element models of the examined buildings were developed, assuming both the theoretical and the actual joint behaviour. Fragility curves were constructed through nonlinear dynamic analyses, so to evaluate the seismic vulnerability of the structures and assess whether they need joint reinforcement, or, otherwise, if they already ensure adequate seismic safety.

Cyclic loading test of earthquake-resilient steel frame joints with different connection forms

Three earthquake-resilient steel frame joints with different connection forms were investigated in this study. The three joints were first tested via cyclic loading tests. The test phenomena of the hinged joint were found to be similar to those of the bolted joint. Owing to the double-hinge connection, the instability of the energy dissipator occurred after its slippage. The cyclic performance of the bolted joint was the greatest among that of the three joints. Furthermore, the energy dissipation of the double-hinge joint was approximately identical with that of the hinged joint. The load–displacement relationships of the three joints were then deduced; a bilinear mechanical model was adopted for the joints. The theoretical results agreed with the test results. Thus, the monotonic load–displacement relationships can be used for evaluating the cyclic performance of the three joints. Ultimately, the test process was reproduced via finite element analysis, which was used to further analyze the difference of the three connection forms. The same amount of energy dissipation was observed for the energy dissipators. It was observed that the release of axial constraint has less effect on the cyclic performance of the joint.

Seismic Performance of Earthquake Resilient Steel Frame Joints with Replaceable Buckling-Restrained Flange Cover Plates

ABSTRACT This paper proposes replaceable buckling-restrained flange cover plates to improve the seismic performance and resilience of steel frame joints. Five full-scale specimens were designed and tested under cyclic loads to investigate the hysteretic performance. The investigated parameters were the core plate thickness (affecting strength ratio α and thickness-gap ratio β) and restraining plate configuration (affecting restraining length ratio λ and restraining plate disconnected position ratio ψ). Numerical models were established using ABAQUS and verified through comparisons with experimental data and phenomena. The results show that the proposed joint can achieve the expected target of buckling-restraint and damage control.

CROSS Safety Report: Connection fixity considerations for steel frame modelling

This month's CROSS Report concerns the modelling of steel frame joints when using computer programs.

Seismic performance of a double-hinge steel frame joint with replaceable T-shape energy dissipator

In this study, a double-hinge steel frame joint with a replaceable T-shape energy dissipator was studied by conducting a cyclic loading test. Four double-hinge joint and welded joint specimens were designed and tested. The energy dissipation and weight of the joint were subsequently investigated by performing FE analysis. The results indicated that the seismic performance of the double-hinge joint is better than that of the traditional welded joint. The working mechanism of the joint was demonstrated by performing tests, and the earthquake-resilient design was verified to be both accurate and reliable. The threshold value of the slenderness ratio for the weakening region of the energy dissipator can be conservatively set to 13. In case of the failure of the energy dissipator, the deformation of the remaining components was recoverable. Approximately 85% of energy was dissipated by the energy dissipators. The earthquake-resilient function was then validated. Finally, the test process was reproduced using FE analysis. The low weight of the double-hinge joint was determined via validated FE analysis, which will improve the application of this novel earthquake-resilient joint.

Novel joint for improving the collapse resistance of steel frame structures in column-loss scenarios

In this study, to improve the collapse resistance of steel frame structures, corrugated steel plates are welded between the inner side of the flange of the I-shaped beams and the column to form novel steel frame joints with corrugated plates (reinforced joints). Collapse resistance tests of the novel reinforced joints under welded and bolt-welded connections are conducted. After a finite element model is validated, the effects of the circular arc length, thickness, and central angle of the corrugated plates on the collapse resistance of the novel reinforced joints are analyzed, and design recommendations are proposed. Results show that the failure modes of the tested specimens are the fracture failure of the beam flange outside the reinforced area and the sequential fracture of the tension flange of the joint region and corrugated plate. Compared with the original specimens, the bearing capacities and ductility of the reinforced specimens are significantly improved. A partial or complete out-shift plastic zone can be realized in the novel reinforced joints. The novel reinforced joints can effectively improve the collapse resistance of steel frame structures under welded and bolt-welded connections without affecting their seismic behavior. The corrugated plate even provides an additional resistance reserve for steel frame structures.

Study on anti-progressive collapse performance of assembled steel frame joints with Z-type cantilever beam splices

A new type of joint with Z-type cantilever beam splices was proposed for assembled steel frame structures in this study. The basic specimen was designed based on the theory of bolt sliding energy dissipation, and three groups of specimens were obtained by changing key parameters. That is, there is no section weakening (Z-BASE), flange weakening of cantilever beam near column (Z-RBS), flange weakening of steel beam near splicing (Z-SRBS), and flange and web weakening of steel beam near splicing (Z-RBS-RWS). The effects of reducing beam section and beam web on the anti-progressive collapse performance of assembled steel frame joints with Z-type cantilever beam splices were studied. The test results were described in detail in general behavior, failure modes, deflection shapes, limit displacements, and resistance mechanisms. According to the test results, specimen Z-RBS had the best anti-progressive collapse performance, and its ultimate load and initial failure displacement were 116% and 114% higher than specimen Z-BASE, respectively. In addition, specimens Z-SRBS and Z-RBS-RWS also had better anti-progressive collapse performance than specimen Z-BASE. Moreover, the validity of the results was verified and study parameters were analyzed using ABAQUS. The assembled steel frame joints with Z-type cantilever beam splices had better anti-progressive collapse performance than ordinary cantilever beam assembled steel frame joints. And the bearing capacity and ductility of the structure were improved by increasing the distance from the cantilever beam splices to the failed middle column, a, and reducing the aperture of the bolt on the cantilever beam splices, b. However, reducing the number of bolts on the cantilever beam splices, c, exhibited the opposite influence. Based on the above comparisons, the proposed design details of assembled steel frame joints with Z-type cantilever beam splices are given.

Performance analysis of steel frame joints reinforced against progressive collapse by partially-penetrated butt-welded corrugated steel plates

To evaluate the progressive collapse resistance of reinforced steel frame joints for partially-penetrated butt-welded connections between corrugated steel plates and columns, experiments were conducted on two substructures, each comprising joints above the failed column and half-span beams on both sides. The experimental results were used to verify the established finite element models, before evaluating the effect on the collapse resistance of the welding form between the corrugated steel plates and columns. Furthermore, the seismic performance of steel frame joints reinforced with corrugated steel plates was analyzed. The results show that all specimens experienced a flexural phase with compressive arch action, a stretch-flexural phase, and a catenary phase. Corrugated steel plates can significantly improve the collapse resistance of steel frame joints and benefit the exertion of the catenary mechanism. The finite-element results agreed well with the experimental results. Sliding at the support is a predominant reason for the compressive arching effect and asymmetry of the final failure of the specimens. When the connections formed between corrugated steel plates and columns are partially or fully penetrated by butt welding, the progressive collapse resistance of the substructure is almost unchanged. Although there is no safety margin for joints with the former connection form, it far outweighs the latter for construction and can be widely used in practical projects. Corrugated steel plates can slightly improve the seismic performance of steel-frame joints.

Experimental study of the influence of the shear strength of panel zones on the mechanical properties of steel frame structures

The seismic behavior of the steel frame joints can directly affect the response of the structure under earthquake excitation. Steel frame structure systems with a scale ratio of 1:2 were tested under a constant axial force and a low-cycle horizontal reciprocating load. A parametric study was conducted to assess the interaction between the shear capacity of panel zones and the mechanical properties of the steel frame. As a result, although weakening the shear resistance of the panel zones also weakens the strength of the steel frame, the structure has better ductility and energy dissipation capacity. Therefore, a reasonable design of the panel zones is more conducive to improving the seismic performance of the structure. With the decrease in the aspect ratio of the panel zones, though the ultimate bearing capacity of the structure decreases and unfavorable column bending failure mode is observed, the ductility of the panel zones and the energy dissipation increase; reducing the thickness of the panel zones has little influence on ultimate bearing capacity of the frame, however, as the ductility increases, the energy dissipation capacity also increases. The experimental and numerical results for the skeleton curve, stiffness, yield load-bearing capacity, ultimate load-bearing capacity, and stress distribution are similar. The mechanisms of generation of plastic hinges and the final failure mode of steel frame are studied using finite element analysis methods.

Design and numerical analysis of steel frame joints with replaceable buckling-restrained links

This paper proposes a steel frame joint with a replaceable buckling-restrained link to prevent the buckling of joint plates and enhance the seismic performance. The calculation formulas of the yield load and initial stiffness are derived to determine a theoretical skeleton curve. A design method for the joints is proposed to determine the design parameters of the core plate area and length, ear and end plate thicknesses, and restraining plate thicknesses, based on the design conditions of the designed joint yield load and core plate strain limited values, plate deformation limited values, and restraining ratios, respectively. The derived formulas and design method are verified by analyzing the results of a cyclic loading test and 37 parametric numerical models calibrated with the test results. The results show that the theoretical skeleton curve is in good agreement with the test and numerical results, and the performances of the joints designed using the proposed method are close to the design conditions, implying the satisfactory performance of the design theory. The influences of the design parameters on the joint are well reflected by the parametric analysis

Dynamic Response Parameter Analysis of Steel Frame Joints under Blast Loading

A finite element model of steel frame joints is established using finite element analysis software ANSYS/LS-DYNA. The ideal triangular impact load is used to numerically analyze the dynamic response of steel frame welded joints under blast loading, the main factors affecting this response, and the failure modes of three types of joints, so as to provide reference for the antiexplosive design of steel frame joints. The results show that steel frame joints vibrate violently in the explosive blast direction. Due to the strain rate effect, the strength of steel increases, the material enters the plastic strengthening stage, and there is a certain residual displacement. In addition, displacement and stress caused by blast action in the joint area are large, and the flange shear failure of the beam and column is prone to occur in the joint. Increasing the flange width of the beam and the column cannot improve the antiexplosive performance of the joints, while increasing their thickness can. Furthermore, bolted and welded joints have the highest stiffness and best antiexplosion performance, followed by welded joints, while the antiexplosion performance of bolted joints was the worst.

Influence of composite slab on seismic performance of prefabricated steel frame joints

Influence of composite slab on seismic performance of prefabricated steel frame joints

Numerical study of the seismic performance of a double-hinge steel frame joint

As the strength of the rigid joints of steel frame structures affects their seismic performance, studies on improved steel joints have been conducted. In this study, a novel double-hinge steel frame joint that optimized the working mechanism of the traditional steel frame joint was developed. The design process of a double-hinge joint was proposed through theoretical analysis. Its reasonability was verified through a validated finite element analysis. Finally, the performance of the double-hinge joints in a steel frame structure was simulated to validate the feasibility of the joint in structures. The results indicate that compared with the single-hinge joint, the cover plate deformation and internal force decomposition of the novel double-hinge steel frame joint are more favorable for energy dissipation. When the slenderness ratio of the reducing area region for the cover plate is greater than 19, the hysteretic curve is plump, and the seismic performance is satisfactory. At the maximum loading displacement, the load and deformation patterns match well with the expected working mechanism. The reduction of the bearing capacity and the energy dissipation capacity is induced by the out-shift plastic hinge. The plastic deformation is concentrated on the T-shape cover plates. The earthquake-resilient function and the feasibility of the double-hinge joint are validated in overall structures.

Design and Mechanical Performance Analysis of a New Type of Column-Column-Beam Prefabricated Steel Frame Joint

Joints are the key factors that determine the construction difficulty and structural safety of prefabricated steel structures. However, the existing prefabricated joints of square steel tube and H-shaped steel beam frame have few reference forms, and there are still a series of problems in practical engineering applications, such as construction difficulties and poor applicability. Therefore, a new type of column-column-beam joint with variable beam height and its construction scheme are designed in this paper. The joint is bolted rather than welded in the process of field prefabricated. It can solve the problem of vertical and horizontal connection of steel frame structure through one joint at the same time, thus effectively saving construction cost and ensuring construction quality. In addition, the detailed modeling and comprehensive mechanical properties analysis of the joint scheme are carried out in this paper. The ultimate bearing capacity, stiffness characteristics, failure modes and hysteretic behavior of joint schemes under low cyclic loading are also evaluated.