Connections In Steel Structures Research Articles

Data-Driven Modeling of Cold-Formed Steel Bolted Angle Connections under Axial Tension using Artificial Neural Networks

Given that steel is one of the main structural materials in civil engineering, it is important to understand its mechanical properties and failure mechanisms. L-shaped laminated steel elements, known as angles, are commonly bolted to other metal elements to make connections in steel structures. When these elements are connected by only one of its legs and are subjected to axial tension, the failure of the angle can be caused by rupture of the section where the holes are located. In this case, there is influence of complex phenomena such as shear lag, therefore a reduction factor is applied to the resistance of the section. The general theme of this work is the use of Artificial Neural Networks (ANN) as an approach to the study of the load capacity of cold-formed steel bolted angles connected by one leg and under axial tension. Although this class of techniques do not provide a simple regression equation, they are powerful tools in Machine Learning (ML), having the ability to model any arbitrarily complex nonlinear problem. In this work, a dataset is built with samples from different numerical and experimental works, collecting steel angles’ geometric parameters, tensile strength of the material and ultimate capacity regarding net section failure. The data-driven models are trained with 80% of the data, tested with 20%, validated with 5-fold cross-validation and their hyperparameters are tuned with Bayesian Optimization. Feature generation, selection, and importance algorithms are implemented, hoping to achieve more accurate, less complex and more interpretable models. ML models’ predictions are compared with the ones given by the equations of Eurocode-3, Brazilian NBR 14762, American Iron and Steel Institute (AISI) and Australasian AS/NZS Standards. The comparison shows mostly superior results in the ANN models, proving the competitiveness and effectiveness of Machine Learning techniques and data-driven modeling.

Experimental and numerical investigation on cyclic behavior of beam‑to‑column connection with a lateral steel slit damper

The objective of this research is to propose an innovative slit damper that can be installed in beam-to-column connections of steel structures as a fuse and energy dissipation device. These devices can be used as an effective and inexpensive way to mitigate earthquake risks to structures, and they can also improve the seismic behavior of building structures. Specifically, structures equipped with these devices can withstand more drift while their main members remain in an elastic state, thereby reducing the cost of rebuilding structures after earthquakes. In this study, four specimens were experimentally tested. Three beam-to-column connections were equipped with the proposed damper, and the fourth one was used as a reference sample. This damper can be referred to as a lateral slit damper (LSD). The test results show that all samples have stable and complete hysteresis curves without pinching. So, the LSDs can improve the ductility of beam-to-column connections. The test results showed that the innovative system can enhance the strength and ductility of the T-stub connection around 73 % and 21 %, respectively. To validate the LSD experimental findings, finite element models were employed for calibration. A numerical study using ABAQUS examined the system's hysteretic behavior under cyclic loading, revealing excellent agreement between the numerical and experimental results. Finally, the proposed LSDs demonstrate exceptional ductility, strength, effective hysteretic curves, and post-earthquake reparability. These qualities position it as a promising and practical damper for mitigating seismic risks in engineering structures.

Optimization of gas metal arc welding parameters for dissimilar steel welds: A case study on duplex stainless steel 2205 and stainless steel 316L

The significance of welded connections in steel structures necessitates precise structural designs and processing adaptations to ensure robust mechanical strength and durability. Gas metal arc welding (GMAW) employing controlled curves presents advantages over conventional methods, offering enhanced weld bead properties, improved aesthetics, and reduced thermal inputs. This research investigates the impact of GMAW parameters using controlled curves on the microstructure and geometry of welds between dissimilar structural steels—duplex stainless steel 2205 and stainless steel 316L grade 50—commonly employed in construction. The aim is to optimize the GMAW welding process with controlled curves and surface tension transfer between these dissimilar steels. Through a 23-factorial experimental design encompassing feed speed (Va), arc focus (FC), and peak-to-base amplitude (APB), the study examines welding energy, geometry, deposition efficiency, microstructure, microhardness, tensile strength, and corrosion properties. Optimal welding energy fosters refined microstructures and uniform hardness, aiding in predicting weld throat area. Higher energy levels expand the heat-affected zone and coarse grains, while lower energies escalate variability. Predictive models facilitate fine-tuning welding energy and throat area for desirable properties and penetration while minimizing disruptions. This process optimization can be achieved by employing derived equations that limit welding energy and curve parameters, striking a desired balance between cost, structural integrity, and reliability.

Analytical and numerical investigation of the seismic behavior of tubular web reduced beam section connections

AbstractThe reduced beam section (RBS) connections in steel structures are widely used to achieve sufficient ductility and avoid creating brittle failures in moment‐resisting frames. Compared to other types of connections, conventional RBS connections have the potential to reduce moment capacity and induce larger lateral deformation in the structure. In order to resolve this problem, novel forms of RBS connections have been proposed in recent years, such as tubular web RBS connections, which have shown a desirable performance under various loading conditions in previous studies. Therefore, this study conducted an analytic and numerical investigation of this connection under seismic loading. In this regard, the first step is to introduce the analytic equations related to the structural properties and stability of the reduced beam with the tubular web. Using these equations, a comprehensive procedure for the design of the tubular web RBS connections is presented. After that, a numerical model of the tubular web RBS connections is created and then analyzed under cyclic loading using the finite element method in ABAQUS software. Based on the results of this simulation, the suggested connection meets the criteria of valid international standards and can be used in the special moment‐resisting frame. In order to assess the impact of using the proposed connection in moment‐resisting frames, the performance of two 2D moment‐resisting frames with this connection is studied. This study shows that the maximum percentage increase in relative displacement caused by using tubular web RBS connections is 1.68%, whereas this figure rises to 10.6% when conventional RBS connections are used. Therefore, the designers can use tubular web RBS connections instead of conventional RBS connections to increase the lateral stability of the structure and control its lateral deflection due to the seismic loadings without having to increase the dimensions of the frame elements.

Numerical Simulation of T Joints Constructed from Hollow Steel Sections

Welded structural hollow sections are becoming increasingly used in contemporary civil engineering buildings. More specific design techniques are needed for connections in steel structures with welded structural hollow sections than for traditional connections made with gusset plates. At the connecting site, stress and local deformations show very complex, non-linear behaviors. The application of non-linear numerical analyses to determine the ultimate bearing capacity of “T” connections was demonstrated in this study. A non-linear material model was used in the analysis. In order to validate the applicable steel modeling method, a comparative study between experimentally obtained results and analytically and numerically computed ultimate bearing capacities was carried out. The comparison showed good agreement between the numerical and experimental results and pointed out the highly conservative design of such joints was obtained using the analytical solution.

Stress biaxiality-based residual stress assessment in welded T-joints using the blind-hole method

The blind-hole method is widely used to measure the welding residual stress (WRS) in welded steel structural connections such as T-joints. To enhance the test accuracy, a rapid WRS evaluation method considering stress level and biaxial stress ratio was developed and validated. The proposed method was applied to measure the WRS distributions of T-joints in steel truss bridges, and a finite element model (FEM) simulating the WRS was verified by the test results. On this basis, the effects of welding parameters and geometric configuration of T-joints on WRS were analyzed by the validated FEM. The results show that the maximum error from ignoring the hole edge plasticity or stress biaxiality is about 20%, and the proposed method can effectively reduce the WRS measurement error caused by the above factors. The results of the experiment and FE analysis demonstrate that the WRSs in T-joint are in an obvious biaxial stress state, which further proves that it is necessary to consider stress biaxiality in calibration for the blind-hole method.

Comparative Study of Friction Stir, Stud and Seam Welding of Aluminium Alloys Using Different Grades

Friction stud welding is an innovative and efficient welding process used to create strong and reliable bonds between studs or fasteners and workpieces, particularly in applications where rapid and secure fastening is critical. This welding technique involves generating friction and heat between the stud and workpiece to forge a strong joint. The process consists of several key steps, including preparation, rotation, weld formation, and cooling. Friction stud welding offers numerous advantages, such as speed, consistency, minimal distortion, and the elimination of the need for additional filler materials. It is widely employed in various industries, including construction, automotive, and aerospace, for applications ranging from structural steel connections to automotive component assembly. However, successful friction stud welding necessitates careful selection of materials, welding parameters, and skilled operators to ensure durable and dependable welded joints. This abstract provides a concise overview of the friction stud welding process and its essential features.

FIRE DESIGN OF STEEL MEMBER BY COMPONENT‐BASED FINITE ELEMENT METHOD

AbstractThe Component‐Based Finite Element Method (CBFEM) is the quite commonly used method to analyse and design connections of steel structures. It is the combination of the analytical component method and the numerical Finite Element Method (FEM). In this paper, the CBFEM is applied to analyse steel beams and columns at elevated temperature. The main objective of this study is to verify the CBFEM for predicting the resistance of steel members at elevated temperatures.

Behaviour of bolted rigid joint with endplate under localised fire scenario

The bolted endplate rigid connections in steel structures are used due to their robustness in distributing forces between the connected members. Though numerous studies have been performed to investigate the response of endplate connections under conventional fires representing uniform temperatures throughout the members (ISO-834, ASTM E119, etc.), the response of the same in case of localised fire is still not explored fully. The present paper focuses on an investigation of the behaviour of a moment resisting frame (MRF) assembled with flush endplate connection with bolts as connecting medium under localised fire scenario using Finite Element (FE) technique. A series of cases with different magnitudes of applied loads was investigated. In all the cases, the frames were heated up to failure with the localised fire source underneath the beam midspan and the corresponding failure modes were investigated. Experiments were performed on the samples of material at high temperature to gather a firsthand information on material characteristics. The frames experienced member failure at the zone of maximum temperature in the beam (midspan) for load level up to 30% of its ultimate capacity, whereas for load level above this, the frame failed at the connecting bolts of grade 5.6, which were maintained at room temperature. Based on the numerical study, it was observed that the provisions of IS 800:2007 were conservative than EN 1993-1-8:2005 in evaluating the safety of bolts under localised fire scenarios. Finally, parametric studies with the variation in connection geometry and configurations were performed, and design suggestions were recommended.

Cyclic behavior of a web hourglass-shaped pin damper made of low-yield-strength steel: Experimental and numerical analyses

Web hourglass-shaped pins fabricated from low-yield-strength steel (LYSWHPs) can be utilized as energy dissipation (ED) components in the connections of steel structures to effectively enhance ED and reduce damage to the primary structural components under intense earthquakes. First, quasi-static tests were carried out on three LYSWHP specimens made of LY225 steel; when bolted to its supporting plate, each exhibited a stable, suitable hysteretic response, excellent ED capacity, high ductility factor of 5.01–9.55, and excellent plastic deformation. Axial force effects and large plastic strains significantly increased the strengths of the LYSWHPs, with the maximum overstrength factor reaching 2.36. A finite-element analysis model was established in ABAQUS and confirmed against the behaviors of the test specimens to perform parametric analyses on individual and group LYSWHP models. The results demonstrated that the shape of the LYSWHP significantly affects its load-carrying capacity, ED capacity, and failure mode; the shape factor and slenderness ratio of the ED segment should be within 0.375–0.75 and 2.75–4.25, respectively, to ensure the desired behavior. The number of LYSWHPs, supporting plate thickness, and LYSWHP shape significantly affect the hysteretic behavior of an LYSWHP group. When the supporting plate provides strong restraint, the ED capacity and ductility of each LYSWHP is fully developed, all cumulative damage is concentrated within the LYSWHPs while the supporting and loading plates remain elastic, and the group will exhibit ductile failure. The findings of this study provide reference for the practical application of LYSWHPs in building structures.

Strong column-weak beam relationship of 3D steel joints with tubular columns: Assessment, Validation and Design proposal

The study of moment connections in steel structures subjected to cyclic loads has been extensively studied, providing a great number of requirements, including the strong column-weak beam relationship, to guarantee a satisfactory cyclic performance. However, investigations on the cyclic performance of moment connections considering the bidirectional and axial load effects simultaneously with tubular columns are limited. This study aims to assess and validate the strong column-weak beam relationship of 3D steel moment connections using reduced order models. The simplified model (reduced order model) approach was employed to extend the range of beam and column elements sizes and reduce the experimental and computational costs. These models were calibrated from full-scale experimental studies. A great number of configurations with different beam and column sizes without loss of reliability and structural representativeness of the studied phenomenon were studied. A total of 13640 simplified models were developed. Results show a cyclic behavior controlled by the strong column-weak beam relationship to modify the joint's failure mechanism. The increasing of strong column-weak beam relationship and the biaxial effect caused degradation of the strength and stiffness as well as in dissipated energy. An optimal strong column-weak beam relationship was obtained for all joint configurations analyzed. Finally, a robust design procedure is proposed, ensuring the cyclic behavior of end-plate moment connection with built-up box column including biaxial effect and axial load. Therefore, the use of this type of moment connection can be used in special and intermediate moment frames designed according to Seismic provisions.

Component Based Finite Element Method for Steel Joints at Ambient and Elevated Temperatures

This paper introduces Component Based Finite Element Model (CBFEM) which is a numerical design model to analyze and design connections of steel structures with features demonstrated here on a portal frame eaves bolted connection. The connection in CBFEM procedure is analyzed by Finite Element Method FEM. The correct behavior of components is treated by introducing components that well represent its behavior in terms of initial stiffness, ultimate strength and deformation capacity, of bolts, welds etc. As for another FEM design procedures a special care is given to the validation and verification procedures which is demonstrated here in this contribution on example of portal frame eaves welded connection. In this paper, CBFEM is applied to analyze steel beams and columns also at elevated temperature. The main objective of this study is to verify the CBFEM for predicting the resistance of steel members and connections at elevated temperatures.

Component Based Finite Element Method for Steel Joints at Ambient and Elevated Temperatures

This paper introduces Component Based Finite Element Model (CBFEM) which is a numerical design model to analyze and design connections of steel structures with features demonstrated here on a portal frame eaves bolted connection. The connection in CBFEM procedure is analyzed by Finite Element Method FEM. The correct behavior of components is treated by introducing components that well represent its behavior in terms of initial stiffness, ultimate strength and deformation capacity, of bolts, welds etc. As for another FEM design procedures a special care is given to the validation and verification procedures which is demonstrated here in this contribution on example of portal frame eaves welded connection. In this paper, CBFEM is applied to analyze steel beams and columns also at elevated temperature. The main objective of this study is to verify the CBFEM for predicting the resistance of steel members and connections at elevated temperatures.

Mechanical properties of S355 butt welds at elevated temperatures

AbstractThe performance of welded connections in steel structures under fire depends on the mechanical properties of welds at elevated temperatures. Currently, EN 1993‐1‐2 [1] provides the following information for the design strength of welds: for butt welds, up to 700 °C, the design strength shall be taken as equal to the strength of the weaker part joined considering the reduction factors for material properties of the steel, while for butt welds above to 700 °C, and also for fillet welds, specific reduction factors for the design strength are proposed.This paper presents the preliminarily results of an experimental investigation of specimens of butt welds realised with GMAW process under elevated temperatures. Steady‐state tensile tests, at 20 °C, 300 °C and 600 °C, were conducted on tensile coupon specimens extracted from welded steel plates. Results from these experiments have been used to evaluate the stress‐strain response, yield strength, modulus of elasticity, ultimate strength, and ultimate strain, as a function of the temperature for butt welds. Reduction factors were predicted for these mechanical properties. Some differences were achieved, especially at 600 °C, between the calculated reduction factors and those proposed by the EN 1993‐1‐2 [1]. Finally, it was also observed that the temperature has an impact on the tension fracture surface in welds.

Study on load‐carrying capacity of MAG butt‐welded mixed connections with different steel strengths

AbstractMixed connections of normal‐strength steel and high‐strength steel can enable an optimum resource‐saving use of materials by adapting the material strength to the forces acting on them. But the design and calculation of butt‐welded mixed connections is not clearly regulated in the currently valid standards EN 1993‐1‐8 and EN 1993‐1‐12. In the research project Effective design concepts for mixed connections in steel structures an extensive experimental program with 180 mixed connections has been conducted to investigate the load‐carrying capacity and behaviour of these connections. The weld joint specimens were made with normal‐strength steel S355J2+N and different high‐strength steels S690QL, S700MC or S960QL. Varying parameters were also the filler metals, plate thicknesses, weld bevels and the heat input during welding. The influence of these parameters on the load‐carrying capacity and the deformation behaviour of mixed connections was investigated. Moreover, high‐resolution microhardness mappings (UCI) on the welded specimens were carried out to examine the formation of the soft zone in the heat‐affected zone of the high‐strength steels.

Investigations on the material behaviour of weld seams for the use in finite element analyses

AbstractThe design of complex structural steel connections by finite element analysis is common practice nowadays. However, for welded joints there are no normative regulations for the static finite‐element‐analysis. To analyse the specific material behaviour in the weld area and derive a geometry and material model for the finite element analysis, tensile tests on specimens with different weld geometries are made at the Technical University of Darmstadt. During the tests an optical measuring method, called Digital Image Correlation, is used. It records the deformations on the surface of the specimen and assigns the recorded analogue test load to the images. By this way, the load‐deformation‐behaviour in all areas of the weld can be determined. In addition to the tensile tests, microsection examinations are carried out. The applied colour etching makes the microstructure of the weld zones visible so they can be geometrically superimposed with the strain images of the tensile tests. In welded connections the stress state is very complex. Therefore, numerical investigation must be performed to derive the final stress‐strain‐curves of the weld area. These curves can then be implemented as a material model for the finite element analysis of welded connections.

Computer Vision-Based Autonomous Method for Quantitative Detection of Loose Bolts in Bolted Connections of Steel Structures

In this study, an autonomous computer vision-based method is presented to quantitatively detect loose bolts. The method integrates keypoint detection via YOLOv5 and PIPNet, distortion correction via perspective transformation, and rotation angles quantification via geometric imaging. Distortion correction is incorporated to address skewed angles and improve the accuracy of rotation angles. A representative experiment on bolted connection of steel structures is conducted to evaluate the presented approach. The effects of the focal distance, skewed angle, and lighting conditions on the detection and quantification performance are evaluated by varying the imaging conditions. The results demonstrate that the presented approach automatically detects all bolts and their corners, irrespective of the imaging conditions. No false detection occurs, and the quantification errors are lower than 1°. The proposed method can be deployed for automatic detection of loose bolts and quantification of rotation angles in bolted connections under different imaging conditions.

Analysis of Hollow Section “Y” Connections with the Application of Non-Linear Material Modeling

The use of welded structural hollow sections in civil engineering is relatively new. Design of connections in steel structures with welded structural hollow sections requires a more specified approach, compared to traditional connections achieved with gusset plates. Stress and local deformations at the connection area are non-linear and very complex. This paper presents the application of non-linear numerical analysis for the determination of the ultimate bearing capacity of “Y” connections. In the analysis, a non-linear material model was applied. In order to validate the applied method of steel modelling, comparative analysis of the analytically and numerically determined ultimate bearing capacity with the experimentally obtained results has been conducted.

A novel clevis-based beam-column model to investigate the hysteretic characteristics of steel moment connections: Experimental and numerical simulations

Following the 1994 Northridge and 1995 Hyogo-ken Nambu earthquakes, the potential for possible deterioration and failures in the connections of steel structures due to strong ground motions has been studied and explored. The most typical connection deteriorations have been fractures and deformation softening, as reported in earlier studies. The present study investigates the connection behavior uncertainties in fracture and deformation softening conditions. The connection behavior uncertainties were analyzed by applying a clevis-based mechanical connection under two loading protocols exhibiting far- and near-field earthquakes. In this connection, steel coupons on both sides of a middle pin were used to transfer the bending moment. Two notch patterns were formed on the steel coupons to create fracture conditions. Deformation softening cases were developed by reducing coupons’ cross-sections in various configurations. To compare the uncertainties, seven indicators were considered: (1) capping rotation, (2) fracture rotation, (3) yield bending strength, (4) capping bending strength, (5) residual bending strength, (6) negative post-yield stiffness, and (7) Park and Ang's damage index. The results of various tests, subsequent numerical studies, and nonlinear regression analyses show that some connection behavioral indicators have many uncertainties that should be seriously considered when analyzing structures with these types of connections. In addition to having varying dispersion, different indicators are also dependent on loading protocol characteristics.

Effective design concepts for welded mixed connections in steel structures

Effective design concepts for welded mixed connections in steel structures