Finite Element Parametric Study Research Articles

Axial compression behaviors of square steel tubes at low temperatures

This paper investigated the compression behaviors of square steel tube (SST) columns used in cold-region engineering structures. Twenty-eight SST columns were tested at low temperatures of 20, −30, −60, and − 80 °C. The studied parameters were low temperature (T) and slenderness ratio (λ) of SSTs. Under low-temperature compression, stub columns (λ = 5) failed in local buckling whilst slender columns (λ = 15 and 25) failed in global buckling. Low temperatures exhibited marginal effects on failure modes, and slightly improved (less than 12 %) the ultimate compressive resistance (Pu) of SSTs. Decreasing T and λ values increased the compressive resistance of SSTs. Finite element (FE) models were established to simulate compression behaviors of SSTs at low temperatures, with accuracy confirmed by 28 test results. The FE parametric studies indicated that decreasing the width-to-thickness ratio of SSTs generally improved their compression capacity and ductility. Moreover, different code prediction formulae in GB50017, AISC 360–16, and Eurocode 3 for SSTs were checked to predict the Pu. Finally, prediction equations were developed to predict the compression resistance of SSTs at low temperatures. The prediction equations provided reasonable estimations on Pu with an average discrepancy of 4 %.

Bending behaviour of surface corroded and perforated corroded steel tubes repaired by laser cladding additive manufacturing

In recent years, laser cladding (LC) technology has been increasingly applied and investigated for repairing damaged surface on metal structural components. However, there are limited experimental studies on the bending behaviour of the LC repaired steel components. And an effective repair method for the perforated corroded steel components is still lacking, therefore, this paper introduces a novel LC repair method for such steel tube. Four-point bending tests were conducted on four specimens, including one intact steel tube (IT), one surface corroded steel tube (SCT), one surface corroded steel tube repaired by LC (SRT), and one perforated corroded steel tube repaired by LC (PRT) to verify the effectiveness of the LC repair methods by evaluating their structural performance in terms of bending capacity, rotational stiffness, and ductility. The experimental results showed that the bending strength and rotational stiffness of the SRT and PRT can be fully restored and even slightly higher than those of the IT. The strain analysis indicated that the LC repair method can significantly reduce stress/strain concentration caused by surface corrosion and perforation corrosion. The experiments were replicated numerically by means of finite element (FE) analysis and parametric studies were performed to investigate the effect of different factors on the bending behaviour of the PRT and SRT. Furthermore, design formula for predicting the elastic bending capacity of the LC repaired steel tube was developed.

Modeling of innovative bolted shear connectors in demountable cold-formed steel-concrete composite beams: Validation of finite element model and parametric study

Composite cold-formed steel (CFS)-concrete structures have been widely used due to their benefits such as more ultimate strength, stiffness, and postponement of lateral buckling compared to bare CFS steel. Appropriate shear connectors should be used in order to establish composite performance between the CFS section and the concrete component. Traditional welded-stud connectors cannot be used due to the low thickness of the CFS members. Therefore, in this paper, a novel composite connection consisting of bolted-shear connectors embedded in grout is proposed and its performance is investigated by numerical models of push-out tests. A three-dimensional finite element model of the composite connection considering the non-linearities of the material and geometry, interfaces, and interactions between the components and materials are developed and verified against the results of the experimental study. After that, an extensive parametric study is carried out and the effects of different parameters, such as bolt strength and diameter, CFS section thickness, concrete compressive strength, and pretension load on the structural behavior of this type of composite connection are investigated and discussed in detail. It is concluded that the behaviour of the composite connection is significantly influenced by bolt strength and diameter, CFS section thickness and strength. The available design models provided in different provisions, including AISI, EC4 and AISC that predict the shear load capacity of connections with preload bolted shear connectors are reviewed and assessed. The results show that the ultimate shear load capacity values predicted by these provisions were found to be relatively less accurate. Finally, a new and more accurate design equation based on the results of this study is then proposed.

Numerical analysis of an innovative solar collector utilizing bistable composite laminates and macro fiber composite actuators

Innovative designs for solar collectors have attracted substantial academic and industrial interests owing to the high efficiency of solar panels in the recent past. This paper proposes the analysis and numerical design of a novel solar collector model composed of bistable laminates bonded with Macro Fiber Composite (MFC) actuators and solar cells. The bistable cross-ply laminate serves as the steering mechanism in this design by providing multiple stable shapes for the innovative solar collector design. Bistable morphing structures have received growing interest in aerospace structures and wind turbines due to their rapid shape-changing ability in response to changes in operating conditions, and this paper aims to integrate them more into the solar energy sector. The snap-through and snap-back motion of bistable laminates can be controlled by the voltage inputs of MFC actuators. The change of bistable laminate shape holds the solar cell in a position approximately at the latitude angle of the place to capture maximum solar energy. A systematic finite element parametric study has been performed to identify the optimum size and location of MFC actuators to achieve an energy-efficient snap-through and snap-back transition. As a result, a numerical design of a solar collector with six bistable elements has been proposed. In order to check the feasibility of the proposed designs, a numerical study has been performed to evaluate the total energy output and to optimize the solar panel tilt angle. ASHRAE’s solar irradiation model proposed in the literature has been used to identify the optimum solar panel tilt angle for maximum annual solar irradiation. This innovative solar collector model has demonstrated promising results, holds the potential for widespread application across various engineering domains, and paves the way for increased adoption of intelligent structures in everyday life.

SCFs for CHS-to-CHS T- and X-type moment-loaded end connections: Proposal for formulae

The research presented in this paper is part of a series of efforts to develop design recommendations for hollow structural section (HSS) connections situated at the end of a truss (or frame) under fatigue loading. Full-sized circular hollow section (CHS)-to-CHS regular and end connections (with open chord ends and chord-end cap plates) were tested under branch in-plane bending to measure strain concentrations at the critical locations. This experimental data was then used to verify a finite element (FE) modelling approach. An FE parametric study (totaling 1120 FE models, including 560 T-type connections and 560 X-type connections) was then carried out to investigate the effects of different chord end boundary conditions (i.e., varied chord end lengths, and open versus cap-plated chord ends). The effects of branch-to-chord width (β), chord slenderness (2γ) ratios and branch-to-chord thickness (τ) were also investigated. It was found that the stress concentration factors (SCFs) in end connections are sensitive to the boundary conditions (i.e., open chord end versus with chord-end cap plate) and all three non-dimensional parameters (β, 2γ and τ). Therefore, SCF correction factors based on e/b0, β, 2γ and τ, are derived for use with existing SCF formulae in CIDECT Design Guide 8.

Temperature change-induced linear and nonlinear axial responses of internal replacement pipe (IRP) systems for pipeline rehabilitation incorporating the effects of soil friction

The internal replacement pipe (IRP) is a developing trenchless system utilised for restoring buried steel and cast-iron legacy pipelines. It is crucial to ensure that this advanced system is appropriately designed to reinstate the functionality of damaged pipelines effectively and safely. The present paper investigates the structural response of IRP systems used in repairing pipelines with circumferential discontinuities subjected to seasonal temperature changes. Analytical and numerical approaches verified via experimental data and available closed-form solutions were implemented to analyse a total of 180 linear and nonlinear finite element (FE) simulations. A set of analytical expressions was developed to describe the loading and induced responses of the system. Based on an extensive FE parametric study, five modification factors were derived and applied to developed analytical expressions to characterise the structural response incorporating the effects of soil friction. Results showed that there is a major difference between the results of linear and nonlinear analyses highlighting the importance of including the material nonlinearities in the FE analysis. A significant difference was observed between the discontinuity openings with and without the consideration of soil friction implying that appropriate inclusion of soil friction in the FE model is crucial to get realistic system responses subjected to temperature change. Although the application of IRP holds immense promise as a trenchless solution for rehabilitating legacy pipelines, the lack of established design procedures and standards for these technologies has restricted their application in gas pipelines. Results obtained from numerical and analytical models developed in the present research will provide valuable insights for the design and development of safe and efficient IRP systems urgently needed in the pipeline industry.

Parametric Finite Element Study on FREEDAM Beam to Column Joints with Different Details of the Haunch Slotted Holes

Parametric Finite Element (FE) simulations were performed to investigate the ultimate flexural of different configurations of friction steel beam-to-column joints equipped with FREEDAM (free from damage) dampers. The main aim of this study was to compare the effectiveness of friction dampers featuring either single or multiple slotted holes, examining how these variations influence the behavior of the joint and the devices under seismic loads. In particular, the ultimate behavior of the connection (i.e., when the device reaches its maximum stroke) was investigated to characterize the involvement of the bolts in shear, the bearing of the plates, and the yielding of the supporting components. The analysis of bolt stress states revealed significant differences influenced by the number of bolts and slots. The FE models were calibrated against the experimental results obtained within the FREEDAM RFCS Project. These insights contribute to the design and performance evaluation of steel beam-to-column joints with FREEDAM connections, in particular the detailing of the haunch slots, laying the groundwork for future research and applications.

On the defect detection limits of flash thermography in reflection mode: A comprehensive parametric 3D FE study

Optical flash thermography is a promising non-destructive testing technique which offers a fast, full-field and non-contact inspection. This study provides a comprehensive study into the influence of different factors on the physical defect detection limits of hidden defects with flash thermography, which is a missing key piece in the present literature.Therefore, a large-scale parametric 3D finite element study is performed in order to explore the actual defect detection limits for a substantial range of inspection conditions:i.Defect parameters: type, size and depth.ii.Material parameters: anisotropic diffusivity and stacking sequence.iii.Excitation parameters: heating non-uniformity, excitation energy and temporal excitation profile.iv.Acquisition parameters: sampling frequency and measurement noise.The finite element model is carefully designed using the commercial Abaqus software in order to ensure both accuracy and computational efficiency, and its reliability in quantifying defect detectability is experimentally validated. Decisive defect detection thresholds are substantiated, through which the detection limits in several (fiber reinforced) materials are concisely visualized and critically compared for the raw thermographic sequence and well-known processing techniques for flash thermography.

A parametric finite element study of concrete cone failure in headed bars under tensile loading

A parametric finite element study of concrete cone failure in headed bars under tensile loading

Ultra-high strength concrete filled steel tube members: Classification, experimental database, and design

Current design codes do not endorse the use of ultra-high strength steel and concrete materials (Fy ≥ 690 MPa and f’c ≥ 120 MPa) for concrete filled steel tube (CFST) members. This paper makes efforts to address this gap using a four-step method. In the first step, the classification of CFST members based on material strengths and tube slenderness ratio is introduced. In the second step, an experimental database comprised of 805 ultra-high strength concrete filled steel tube (UCFST) specimens under various loading conditions is compiled, and the research gaps in the database are identified. In the third step, the possibility of extending Eurocode 4 and AISC 360–22 to UCFST members are evaluated using the experimental database. Finally, a research program including experimental tests, finite element (FE) parametric studies and new design equations for UCFST rectangular members is introduced.

Regression models for ultimate hogging moment prediction of composite cellular beams

ABSTRACT This work shows the accuracy and feasibility of polynomial regression models for the ultimate hogging moment prediction of composite cellular beams utilising different numbers of simulations. It discusses an attempt to reduce the number of samples in a finite element parametric study, which consists of using only the combination of extreme levels of each factor to develop the regression models. The parametric study has five parameters: cross-section dimensions, hogging moment distribution, unbraced length, opening diameter, and web-post width. The regression models are generated based on 32 (extreme values), 162 (extreme and intermediate values), and 360 numerical model results (all values). An ANOVA was performed on each regression model to assess the parameters’ order of relevance. According to ANOVA, the profile cross-section dimensions and hogging moment distribution were the most significant parameters on the beams’ ultimate moment for all regression models. As good precision was achieved, because of the insignificant differences within the regression models, it was observed that the combination of arbitrated extreme levels for the factors could significantly reduce the number of numerical simulations in a parametric study. Still, this approach could be used for any other type of structure to reduce the computational cost of future numerical investigations.

Finite Element Analysis and Parametric Study of Panel Zones in H-Shaped Steel Beam–Column Joints

This paper investigates the mechanical properties of a traditional welded rigid joint with a weakened panel zone under seismic load. The created finite element model is calibrated by the high-strength steel joint test, carried out by the team in the early stage, and the effectiveness of the finite element method was verified. The finite element software ABAQUS is used to investigate the influence of different joint web thicknesses on the mechanical properties of middle column joints under a low-cyclic-loading test. Supported by a validated numerical model, the ductility, energy dissipation, and other properties of different thicknesses of panel zone column webs are carefully analyzed. The results indicate that the thickness of the web plate in the panel zone significantly affects the location of the joint plastic hinge. The ultimate loading capacity of the joints increased significantly with an increase in the thickness of the webs in the panel zones. Compared with the joint with a weakened panel zone, the hysteresis curve of the strengthened joint is fuller; meanwhile, it cannot alleviate the stress concentration at the weld holes of the web. When the thickness of the joint domain web is too weak, excessive deformation in the joint domain will lead to a decrease in the bearing capacity of the joint, causing damage. The stiffness degradation coefficient of the web-thickened specimen was found to be dominated and controlled by the stiffness of the beam; however, with an increase in the thickness of the web, the stiffness degradation coefficient remained basically unchanged. Finally, a recommendation for weakened beam–column interior joints based on the steel frame panel zone is made, which will lay a foundation for the simulation and analysis of the seismic performance of this structure.

Cold-formed Steel-Concrete Composite Beams with Back-to-Back Channel Sections in Bending

Steel-concrete composite structures are very attractive because of their characteristics, which can be emphasised by using cold-formed steel instead of hot-rolled ones. This paper presents possible analytical approaches and a parametric finite element study of cold-formed steel-concrete composite beams in bending. Analysed beams are formed of back-to-back cold-formed steel channels and concrete slabs connected by demountable shear connectors. A solid concrete slab on a profiled metal sheet analysed. Also, the study investigates the influence of corrugated web between the back-to-back channels of different thicknesses. In the case of a corrugated web, the distance between the shear connectors is increased. Furthermore, different degrees of shear connection, shear connector quality, and their arrangements are considered. An analytical study is based on full and partial shear connection assumptions and non-linear bending resistance. It is shown that the steel channel thickness and degree of shear connection significantly influence the beam bending capacity as well as concrete slab configurations. Conversely, a discrete connection between steel elements has a minor effect. A comparison of the maximum obtained bending capacities in FE analyses is in good agreement with analytical approaches for full and partial shear connections. Doi: 10.28991/CEJ-2023-09-10-01 Full Text: PDF

Design of Cold-Formed High-Strength Steel Diamond Bird-Beak Tubular T-Joints and X-Joints

Numerical investigation and design of cold-formed high-strength steel (CFHSS) diamond bird-beak (DBB) T- and X-joints are presented in this paper. The 0.2% proof stress of braces and chords was 960 MPa. Tests of CFHSS DBB T- and X-joints undergoing compression loads were carried out by the authors. The test results were used to develop accurate finite element (FE) models in this study. A comprehensive FE parametric study was then performed using the verified FE models. The nominal strengths predicted from the literature and European code were compared to the joint failure strengths and ultimate capacities of 244 DBB T- and X-joints specimens, including 224 FE specimens investigated in this work. The failure of DBB T- and X-joints specimens at chord crown locations was identified as the dominant failure mode. It has been shown that the design provisions given in the literature and European code are unsuitable and uneconomical for the cold-formed S960 steel grade DBB T- and X-joints investigated in this study. Hence, accurate, less dispersed, and reliable design equations are proposed in this work, using two design approaches, to predict the joint failure strengths and ultimate capacities of the investigated DBB T- and X-joints.

Modelling and design of cold-formed S960 steel brace-rotated tubular T- and X-joints

This paper presents detailed numerical investigation and design of cold-formed S960 steel grade brace-rotated (BR) tubular T- and X-joints. The BR tubular joint is one of the novel bird-beak tubular joint configurations, where the rotation of brace member(s) enhances joint resistance and aesthetic appearance. The numerical investigation was performed through finite element (FE) analysis. The tests carried out by the authors were used to develop accurate FE models of BR T- and X-joints, which in turn precisely replicated the joint resistances, load vs deformation curves and failure modes of test specimens. With an aim to broaden the data size, a comprehensive FE parametric study was performed using the verified FE models. The nominal resistances predicted from the literature and European code were compared to the joint failure resistances of 211 BR T- and X-joints specimens, including 192 FE specimens investigated in this study. The BR T- and X-joint specimens were failed by two failure modes, namely chord face failure (F) mode and a combination of chord face and chord side wall failure mode, i.e. combined failure (F + S) mode. It has been shown that the existing design provisions are unsuitable for the design of cold-formed S960 steel grade BR T- and X-joints investigated in this study. Hence, using three design approaches, accurate, less dispersed, reliable and user-friendly design equations are proposed in this study to estimate the joint failure resistances of cold-formed S960 steel grade BR T- and X-joints.

Axial compression behavior of Q690E/Q960E high-strength steel tubes at low temperatures

This study reported the axial compression behavior of square Q690E/Q960E high-strength steel (HSS) tubes in cold regions. Sixteen HSS tubes with various wall thicknesses were tested at −80– 20 °C. Most of the tested HSS tubes failed in elastic local buckling. Low temperatures exhibited limited improvements (less than 8%) on their compressive resistances (Pu). Finite-element (FE) models considering low-temperature material properties were developed and used for further parametric studies. The FE parametric studies examined the influence of low temperatures and cross-sectional slenderness. Finally, this paper also checked the validity of different code equations on predicting Pu of HSS tubes at low temperatures.

Cyclic test and finite element analysis of a steel double K-braced frame with laterally-restrained plates for RC building retrofit

Damage was discovered in existing 24-story reinforced concrete (RC) buildings in New Taipei City under the 2015 Hualien earthquake with a magnitude of 6.3. A new scheme was proposed to retrofit the buildings by adding a steel concentrically double K-braced frame in a limited space, with diaphragm plates to laterally restrain each brace to increase its buckling strength. A cyclic test was first conducted on a full-scale steel braced frame specimen, composed of a steel boundary frame, two pairs of K-type-arranged plates for axially loaded braces, diaphragm plates for brace buckling restraint, and surrounding RC members. Secondly, a finite element (FE) analysis was conducted on the specimen for a correlation study and investigation of force transfer between the infilled braced frame and surrounding RC members. A finite element parametric study was then conducted on single braces with different numbers of restraint and plate thicknesses to investigate the cyclic behavior and buckling force. The AISC 360-16 (2016) provides a very conservative prediction of the brace bucking force, but the prediction based on Wolchuk (1963) reasonably matches well the test and FE analysis results. A cyclic backbone curve for a single brace modeling, considering in-plane lateral supports, was proposed in this work.

Design of cold-formed high strength steel CHS-to-RHS T- and X-joints at elevated temperatures

The static resistances of cold-formed S900 steel grade tubular T- and X-joints at elevated temperatures have been numerically investigated in this study. Circular hollow sections (CHS) were used as the braces, while square and rectangular hollow sections (SHS and RHS) were used as the chords for both T- and X-joints. In this study, both T- and X-joints were subjected to compression loads. The mechanical properties of cold-formed S900 steel grade hollow section members at elevated temperatures were used to perform the numerical investigation. The static resistances of CHS-to-RHS T- and X-joints were investigated at 400°C, 500°C, 600°C and 1000°C. The finite element (FE) models developed and validated by the authors for ambient temperature and post-fire investigations of cold-formed S900 steel grade CHS-to-RHS T- and X-joints were used in this study to perform numerical investigation at elevated temperatures. A comprehensive FE parametric study, including a total of 768 CHS-to-RHS T- and X-joints, was performed in this study using the validated FE models. Both CHS-to-RHS T- and X-joints were failed by chord face failure and a combination of chord face and chord side wall failure mode. The nominal resistances predicted from design rules given in European code and CIDECT, using mechanical properties at elevated temperatures, were compared with the resistances of CHS-to-RHS T- and X-joints at elevated temperatures. It is shown that the predictions from design rules given in European code and CIDECT are quite conservative but unreliable. As a result, economical and reliable design equations are proposed in this study for predicting the resistances of the investigated joints.

Numerical analysis and design of cold-formed high strength steel RHS X-joints at elevated temperatures

A numerical program is carried out in this study with an aim to investigate the static performance of cold-formed high strength steel (CFHSS) X-joints with square and rectangular hollow section (SHS and RHS) braces and chords at elevated temperatures. The numerical investigation was performed through the finite element (FE) method using mechanical properties at elevated temperatures. The FE models developed and validated by the authors for identical CFHSS X-joints at room temperature and post-fire conditions were used in this study to perform numerical investigation at elevated temperatures. The SHS and RHS X-joints were subjected to axial compression loads through brace members. The validated FE models were used to perform a comprehensive FE parametric study at 400°C, 500°C, 600°C and 1000°C that comprised in total 756 FE specimens. Using mechanical properties at elevated temperatures, nominal resistances were predicted from design rules given in European code and Comité International pour le Développement et l'Etude de la Construction Tubulaire (CIDECT) and compared with the residual strengths of the investigated X-joints. Overall, SHS and RHS X-joint specimens were failed by chord face failure, chord side wall failure and a combination of these two failure modes. Generally, predictions from design rules given in European code and CIDECT are quite conservative but scattered and unreliable. Therefore, economical and reliable design equations are proposed in this study for predicting the resistances of cold-formed steel RHS X-joints made of S900 steel grade at elevated temperatures.

Design of cold-formed high strength steel rectangular hollow section T-joints under post-fire conditions

A comprehensive numerical investigation looking into the static post-fire structural performance of cold-formed high strength steel (CFHSS) T-joints is presented in this paper. The braces and chords of T-joints were made of square and rectangular hollow section (SHS and RHS) members. The steel grade of SHS and RHS members was S960 with nominal 0.2% proof stress of 960 MPa. The static strengths of SHS and RHS T-joints were investigated corresponding to four post-fire temperatures, including 300°C, 550°C, 750°C and 900°C. Pandey and Young [1] carried out tests to investigate the post-fire residual strengths of cold-formed S960 steel grade SHS and RHS T-joints. The test results were used to develop an accurate finite element (FE) model. Using the validated FE model, a comprehensive FE parametric study was performed in this investigation. The validity ranges of critical geometric parameters were extended beyond the current limits mentioned in international codes and guides. The nominal resistances predicted from design equations given in EC3 [2] and CIDECT [3], using post-fire material properties, were compared with a total of 765 test and FE joint resistances, including 756 numerical data obtained in this study. Overall, SHS and RHS T-joint specimens were failed by chord face failure, chord side wall failure and a combination of these two failure modes. Generally, the current design rules in EC3 [2] and CIDECT [3] are quite conservative and largely dispersed. As a result, accurate, less dispersed and reliable design equations are proposed in this study.