Flange Plate Research Articles

Developing an innovative stiffened shear damper for concentrically braced frames

Although the concentrically braced frame (CBF) systems pertain high elastic stiffness and lateral strength, they reflect a low seismic energy absorption capacity. This is due to the buckling of CBF’s diagonal member under compressive loading. To overcome this, researchers have proposed the use of several types of dampers to improve the seismic behavior of the CBF systems. Among them, the metallic shear damper is the most popular due to its suitable performance characteristics. To overcome the low stiffness characteristics of shear dampers, strengthening the shear damper with X-stiffeners is proposed and the performance is evaluated numerically and parametrically in this paper. Results indicated that by adding the X-stiffeners, the ultimate strength and elastic stiffness of the shear dampers are enhanced, considerably. But, we found that the properties of the stiffeners do not impact the stiffness at rotation greater than 0.5%. The behavior of dampers is affected by some parameters such as the ratio of the strength of the web plate to the flange plate, and the ratio of the X-stiffener strength to the flange plate strength. Thus, to predict the behavior of the damper accounting for the parameters, modified equations are proposed. The results highlighted a good agreement between the proposed modifications and finite element modeling.

Utilizing Low Yield Point Steel to Improve the Behavior of the I-Shaped Shear Links as Dampers

Concentrically braced frame (CBF) systems are susceptible to buckling (which causes a decrease in energy absorption), although this system has considerable lateral stiffness and strength. To over this shortcoming, researchers have suggested the use of I-shaped steel dampers as a practical idea that prevents buckling and increases the energy absorption but reduces the stiffness of the system. To increase the stiffness of the damper, the thickness of the web or the thickness of the flange can be increased, but by increasing their thickness the shear capacity of the damper also increases. Nevertheless, with the increase in the capacity of the damper, the forces created in the elements outside the damper will also increase, which is usually not a suitable solution. Therefore, in this paper, the use of the low yield point for the web plate of an I-shaped damper is proposed to compensate for it. Accordingly, its behavior is investigated parametrically and numerically and also requires equations to design the system proposed. Results indicated that utilizing an LYP damper improves the behavior of the system in the case of energy absorption, stiffness, and strength. Comparing the LYP damper and the conventional I-shaped damper (made of A36 steel) reveals that both dampers pertain to stable hysteresis loops without any degradation, which confirms the capability of the I-shaped damper to dissipate seismic energy. Although the flange plate properties contribute to the load-bearing of the damper, the A36 damper is more affected by the flange plate than the LYP damper that is concluded for LYP dampers the flange plate contribution in the shear strength of the damper is ignorable at the beginning of imposed loading.

Robotic Manipulations of Cylinders and Ellipsoids by Ellipse Detection With Domain Randomization

A lot of objects commonly found in industrial and household environments are represented by cylindrical shapes (flange plates) and ellipsoids (oranges). The visual tops of cylindrical objects and the outlines of ellipsoids are approximately formed by elliptic shape primitives. Thus, a robot can manipulate these objects by ellipse detection. However, it poses a challenge for existing methods to detect ellipses that are largely interfered in cluttered environments. The supervised learning method provides a potential solution for ellipse detection in such environments, but manually labeling the ground truth for training the learning model costs much time, money and workload. In this work, we propose a novel approach to employing three-dimensional point-cloud models of cylindrical objects to construct synthetic images with ellipses based on domain randomization technology for training the supervised learning model. Using synthetic data generated in this manner, we build an end-to-end deep neural network with a detection backbone, rotating filters and the rotated region proposal net to do ellipse detection. To our knowledge, this is the first supervised learning model trained only on synthetic data for ellipse detection, enabling a robot to grasp cylindrical and ellipsoid objects. To demonstrate the capabilities of the proposed detector, the performance of the proposed method is superior to those of two state-of-the-art detectors on synthetic and public datasets. The proposed model for ellipse detection and data generation pipeline based on domain randomization in a simulation are evaluated by a series of robotic manipulations implemented in real application scenarios. The results illustrate a high success rate on real-world grasp attempts despite having only been trained on a synthetic dataset.

Shear flow capacity of stiffened flanges in steel box girders

The purpose of this paper is to model the shear flow capacity of stiffened flange in a steel box girder. The present study uses an energy-based variational approach to analyze the steel box girder. A new parameter is introduced that is strongly correlated to the shear lag response of stiffeners to flanges. This parameter is named as shear flow parameter. The shear flow parameter decreases with increasing stiffener area to flange area ratio. Along with increasing the stiffness of the flange, stiffeners also reduce the shear flow capacity of the flange plate. It is observed that the reduced shear flow capacity causes more shear lag in the flange, increasing the stress at the web-flange junction. As a result of a high percentage of longitudinal stiffeners, steel box girders have a small effective width ratio, high negative shear lag effect, and significant deflection. This approach is in close agreement with experimental results, finite element results and theoretical results.

Experimental and Numerical Study on an Innovative Trapezoidal-Shaped Damper to Improve the Behavior of CBF Braces

Among the existing passive energy dampers, I-shaped shear dampers had shown suitable performance in experimental and numerical studies. Although they improve the dissipating energy and ductility of concentrically braced frames (CBFs), they reduce the stiffness and ultimate strength of the system. Three approaches are generally used to overcome the problem, including (a) increasing the thinness of the shear plates, (b) increasing the number of shear plates, and (c) using more dampers in more bays. The mentioned approaches increase construction costs. Accordingly, to overcome this shortcoming, in this paper, an innovative shear damper with a trapezoidal shape is proposed and investigated experimentally and numerically. The results indicated that when using the same material for I-shaped shear dampers and the proposed damper, the proposed damper has greater ultimate strength, elastic stiffness, and dissipating energy capacity. Additionally, the flange plates are more effective in the behavior of the proposed damper than the I-shaped damper. Moreover, required equations were proposed to design the damper.

Experiment and design methodology of an IODR flange connection under bending load

A new type of inner and outer double-ringed (IODR) flange was introduced in this paper, which can make full use of the inside and outside space of circular tube and reduce the dimensions of connecting bolt and flange plate. Five groups of down-scaled IODR flanges with different flange plate dimensions were designed and tested under bending moment to study the failure mode and force-transferring mechanism. The finite element model was built to further investigate the influence of connection dimensions on the bending performance from different aspects, such as bearing capacity, location of rotation axis and bolt tension ratio. It reveals that the failure of IODR flanges occurred due to the necking of bolt. The bolt tension ratio has an insignificant change when the applied load is smaller than about 80% of bending capacity, then it tends to increase until approaching 1.0. A theoretical method for rotation axis position and bolt force was proposed considering flange geometry parameters and bolt arrangement. It was found that the obtained rotation axis positions are about 0.7r, which is smaller than 0.8r recommended in DL/T 5629–2021, meaning that the existing design method is unsafe. Based on the theoretical analyses, the design methods of flange plate, stiffener and bolt were proposed and a corresponding design process was also established.

The effect of flange plate thickness on bolted connections splicing square hollow sections

This paper focused on the flexural behaviour of unstiffened square flange plate connecting square hollow sections under pure bending. The purpose was to investigate the flexural response of the bolted connections with different flange plate thicknesses to determine their optimum range for a practical design that can be implemented in prefabricated steel structures. The study was undertaken by a validated finite element model. Flange plates with thicknesses of 10 mm, 12 mm, 14 mm, 18 mm, and 22 mm were investigated. It was determined that 10 mm and 12 mm flange plate connections should not be used as they behave poorly and are deemed inadequate choices. Thicknesses ranging from 18 mm to 22 mm are safe options for hollow steel sections under pure bending loading conditions. It was concluded that the optimum thickness for square flange plate connections is 22 mm.

Behaviour of cold-formed steel built-up beams under flexural loading

Cold-Formed Steel (CFS) built-up beams are most commonly used as structural elements such as columns, beams, and trusses. They are also used to avoid buckling and increase member flexibility by providing flanges and side plates/batten plates. This study describes the flexure behaviour of the CFS built-up beam. Six CFS built-up beams were tested to failure with a Universal Testing Machine (UTM). CFS built-up beams of thickness 2 mm were developed using channel sections put back to back and close to close, as well as a lip and flange plate. The overall deflection and strain against the incremental load were discussed and compared with the control beam without a lip and flange plate. A back-to-back CFS built-up beam with lip a section could withstand 32% greater load under flexure than a backto-back built-up beam without a lip. The Finite Element Analysis (FEA) was performed using the software ANSYS, and there was a high correlation between the experimental and analytical results.

Behaviour of cold-formed steel built-up beams under flexural loading

Cold-Formed Steel (CFS) built-up beams are most commonly used as structural elements such as columns, beams, and trusses. They are also used to avoid buckling and increase member flexibility by providing flanges and side plates/batten plates. This study describes the flexure behaviour of the CFS built-up beam. Six CFS built-up beams were tested to failure with a Universal Testing Machine (UTM). CFS built-up beams of thickness 2 mm were developed using channel sections put back to back and close to close, as well as a lip and flange plate. The overall deflection and strain against the incremental load were discussed and compared with the control beam without a lip and flange plate. A back-to-back CFS built-up beam with lip a section could withstand 32% greater load under flexure than a backto-back built-up beam without a lip. The Finite Element Analysis (FEA) was performed using the software ANSYS, and there was a high correlation between the experimental and analytical results.

Experimental and theoretical investigation of self-tapping bolt core tube flange column connection of prefabricated steel structure

This study proposes a column-column connection with self-tapping bolts, a core tube, flange plates, and high-strength bolts for a prefabricated steel structure, which can avoid on-site welding of traditional steel structure closed section columns and realize efficient assembly of vertical steel structure components. To determine the mechanical characteristics of the self-tapping bolt core tube flange column connection (SCFC) and the effect of the core tube and self-tapping bolts on SCFC, quasi-static tests were performed. According to the test results, altering the core tube thickness within a specific range had no discernible impact on the SCFC's seismic performance metrics, including hysteresis performance, skeleton curve, and stiffness degradation. The failure modes of test specimens were all steel fractures at the column foot, proving that SCFC can realize the seismic design goal of “strong joint, weak member.” The force mechanism of the SCFC and slip mechanism of the self-tapping bolt were explored. A finite element model (FEM) was established, and the results agreed well with the test results, confirming the accuracy of the FEM. Finite element parametric analyses were performed to further clarify the impact of the thickness of the core tube on the connection performance. Combined with the test and FEM results analyses, the bearing capacity calculation formulas of the SCFC were proposed based on the yield-line theory and verified by the results of the test and FEM. The design criteria for the SCFC were further proposed.

Operation State Evaluation of Miter Gate Based on On-Line Monitoring and Finite Element Analysis

As an essential part of the water conservancy hub, the miter gate undertakes the vital task of navigational operation and works in a complex basin with a high water level drop for a long time; therefore, it is necessary to ensure its safe operation. In this paper, taking the Gezhouba No. 2 ship lock miter gate as an example, the actual gate stress and crack signals are obtained using the online monitoring system. The stress distributions of the gate under different working conditions are studied using finite element simulation analysis. Combining simulation analysis with the collected signal analysis, the operation status of the actual gate under each working condition is evaluated. The results show that the stress analysis of the online monitoring is consistent with the finite element analysis results, which verifies the reasonableness of the sensor arrangement. The stress is more concentrated in the area of the gate shaft column, the middle door seam, and the rear flange plate during the operation of the miter gate, and the maximum stress appears on the central sector shaft column of the gate. The cracks of the miter gate mainly appeared in the lower layer of the gate body, and the cracks expand gradually during the long-term operation of the gate. The crack expansion speed corresponds to the miter gate’s stress magnitude.

Investigation on flexural behavior of novel GFRP grid web-concrete hybrid beam

A novel GFRP grid web-concrete hybrid beam was proposed to solve the problems of traditional concrete T-beam structures, such as heavyweight and easy cracking of the web. The GFRP grids arranged along the principal stress were partially embedded in concrete to achieve reliable connection and avoid the insufficient interlaminar shear strength between GFRP profiles. The flexural behavior of the novel hybrid beam was investigated through experimental and numerical studies. The experimental results indicated that the force form of the GFRP grid web was consistent with the proposed hypothesis, and the section bending moment was mainly borne by flange plates and longitudinal reinforcements. The flexural failure process of the hybrid beam can be divided into three stages: elastic stage, working stage with cracks, and failure stage. No relative slip or stripping was observed between the GFRP grid web and concrete throughout the loading process, indicating that the GFRP grid web could be reliably connected to flanges and vertical ribs to form composite action. The numerical analysis showed that the GFRP grids only contributed 7.30 % to the bending resistance of hybrid beam due to its weak longitudinal stiffness, compared to concrete and reinforcements. The staggered grid plates born the compressive and tensile stresses, while the part embedded in the lower flange plate in the mid-span area was in full-section tension with the maximum tensile stress of 85.7 MPa. The stress distribution of concrete flange plates basically conformed to the plane assumption, while the concrete stress near the support appeared reverse sign phenomenon, since local bending moment was generated in concrete flanges due to the weak longitudinal stiffness of GFRP grid web. Overall, the proposed novel hybrid beam with reduced self-weight retains good flexural strength, stiffness, and ductility characteristics of concrete beams compared to conventional concrete T beams.

Material properties and residual stresses of welded high strength steel and hybrid I-sections

High strength steel (HSS) I-sections are gaining increasing popularity compared with conventional strength steel counterparts, mainly due to its higher strength-to-weight ratio. Meanwhile, there has been growing interest in hybrid I-sections, which are made of different strength steels for flange and web plates, because of the increased need of maximising material utilization. This study investigates the welding effect on the material properties and residual stresses of welded HSS and hybrid I-sections. Tensile tests of coupons machined from both virgin plates and within the welded I-sections were carried out, followed by a metallographic analysis of welding position. It was found that the welding effect on the mechanical behaviour of steel materials varies, depending on the chemical composition and microstructure. Residual stress measurements for HSS and hybrid I-sections covering four web slenderness were conducted. The measurement results demonstrate that the effect of steel strength grade of constitutive plates on residual stress distribution of I-sections is negligible, and a new residual stress distribution model is proposed for welded HSS and hybrid I-sections examined in this study.

Longitudinal mechanical force mechanism and structural design of steel tube slab structures

A steel tube slab (STS) structure is a novel pipe-roof structure with significant promise as a supporting structure for underground stations. The structure is subjected to bending loading conditions during its service; therefore, research on the flexural strength of STS structures is essential. This study aimed to analyze the flexural behavior of STS structures through experimental and numerical investigation. The mechanism of forces in an STS structure was investigated using flexural tests, and the load–displacement curves, obtained during loading, were investigated in detail. Notably, the specimens exhibited highly ductile behaviors, and the structure was eventually damaged under integral bending. In addition, finite element (FE) models were established, and their accuracy was verified through tests. Detailed analyses in terms of the load–displacement curves, stress–strain development in steel tubes, flange plates and concrete, and damage modes were conducted, followed by studies on the various influencing parameters. Finally, formulae for calculating the elastic and ultimate capacity of STS structures were established. We found that the predicted results agreed well with the experimental and FE results.

Eurocode-compliant topology optimisation of steel moment splice connections

To address the meagre use of Topology Optimisation (TO) in the civil engineering industry, the case of bolted moment connections in steel construction has been investigated. Connections are essential in steel structures, contributing up to 25% of the global weight and concentrating the complexity in design and, therefore, the industry's added value. It has been found that compliance with code requirements and difficulties in employing advanced software packages in real, heterogeneous and complex connections are the two major deterrents to the widespread use of TO. Hence, a novel code-compliant methodology was proposed, applied to the cover flange plate under tension of a bolted beam splice moment connection and validated with non-linear Finite Element Analyses (NLFEA). It has been found that a 50% volume reduction is possible by employing linear elastic TO and establishing the non-exceedance of the steel ultimate stress as a criterion. NLFEA showed that if the original joint capacity is to be maintained, the maximum optimisation threshold reduces only 45% of the initial volume. Two critical conclusions are that linear elastic TO could not meet the safety needs and that the introduced validation stage with NLFEA is an essential step, highlighting the novelty and significance of the proposed method. Topologically optimised solutions showed a significant volume and cost reduction, meaningfully contributing to the steel construction decarbonisation goals and leading to joints with a more ductile behaviour.

A practical design of cold-formed steel bolted moment connection: numerical investigation with an improved bolt slip-bearing model

Cold-formed steel (CFS) is in the spotlight as a structural material for buildings and civil infrastructures because it is easy to produce and is cost effective. Recent studies have advanced the popularity and usability of CFS even more by showing its potential as a structural member suitable for special moment-resisting structures. Within the framework of those studies, CFS bolted moment-resisting connections allow the through-plate to protrude beyond the beam depth in both the upper and lower directions, like wings, which could hamper placing decks on the beams. This study proposes a modification to such through-plates, in which one protruded portion is eliminated and the depth of the other is extended instead in order to enhance the practicality in field applications. Finite element analysis is used to investigate and verify the proposed design candidates and finally, suggest an optimum design configuration. Since the bolted connection has a significant impact on the structural response of the CFS beam, an improved bolt modeling approach is suggested based on the bolt modeling approaches proposed by past researchers. The suggested bolt modeling approach is shown to provide better accuracy in simulating plastic deformations in the bolted connection area and the consequent failure behavior when compared to the existing approach. The numerical analysis results show that the through-plate with one wing-side cut should have the depth of the other wing-side such that the diagonal edge could make an angle larger than 35 degrees. To prevent the possibility of buckling in the changed through-plate, attaching the flange plate perpendicular to the diagonal edge is highly recommended. The findings from this study are expected to provide a guidance for the through-plate design in practical structure design. • A practical design for through-plate in CFS bolted connections is suggested. • Modeling approach for bolted connections based on measured torque is proposed. • In modeling of bolted connection, effect of rotational constraint is critical. • Significance of bolt slip-bearing mechanism included in bolt modeling is emphasized.

Fragility curves for steel moment frame with welded flange plate connection

The importance of evaluating the performance of structures against earthquakes is not hidden from anyone. It is important to have an overview of the resistance level of the structure to achieve a safe and economical design against the potential input forces. Therefore, a lot of research is always done in this area in different ways. This article contains the method and results of the study of seismic vulnerability for WFP connection which is widely used and pre-approved connection for steel moment frames that Has been introduced in the tenth section of the Iranian building code. The purpose is to draw the fragility curve using numerical methods. Due to the fact that this connection is pre-approved just for medium moment frames, it is necessary to check its reliability if want to use it in a special moment frame. The probability of structural damage caused by seismic force can be presented as a function of ground motion characteristics and various design parameters Using fragility curves. In this study, seven records of earthquake accelerograms were used for incremental nonlinear dynamic analysis (IDA) those most consistent with the site intended for this structure

Performance Improvement of Innovative Shear Damper Using Diagonal Stiffeners for Concentrically Braced Frame Systems

Although concentrically braced frame (CBF) systems enjoy high elastic stiffness and lateral strength, they show a low seismic energy absorption capacity. This dilemma is due to the buckling of CBFs’ diagonal members under compressive loading. To overcome the shortcoming, researchers have proposed the use of dampers to improve the behavior of CBF systems. Among the proposed dampers, the metallic shear damper is the most popular thanks to its suitable performance as well as its economic profit. The main shortcoming of the shear dampers is low stiffness. Therefore, in this article, an innovative approach is proposed to improve the behavior of the shear dampers. Subsequently, strengthening the shear damper with X-stiffeners is proposed, and its behavior is evaluated numerically and parametrically. Results indicate that by adding the X-stiffeners, the ultimate strength and elastic stiffness of the shear dampers are enhanced considerably. However, the properties of the stiffeners do not impact the stiffness in the nonlinear zone. Moreover, the behavior of the dampers is affected by parameters such as the ratio of the strength of the web plate to the flange plates, the ratio of the X-stiffeners to the flange plates, and the ρ factor. To consider the parameters to predict the behavior of the damper, required equations are proposed which demonstrate a good agreement with finite element results.

Component modelling of 3D laser cut joints with CHS columns and through-all members

3D laser cutting technology is a new automatised industrial process allowing the development of a range of novel applications in civil engineering. Its main advantage derives from the possibility to manufacture easily tridimensional cutting shapes with high precision (accuracy of about 10μm), minimising the hole size, optimising the welding quantity and costs. This technology is up to thirty times faster than traditional methods since all the operations are programmed and fully realised by the machine, avoiding any intervention of operators, eliminating human errors and increasing the quality level.3D-LCT allows joining hollow section profiles to through-all members with a straightforward production process. The main feature of joints with passing-through profiles is the higher flexural strength and stiffness compared to traditional connections without additional costs. Nevertheless, considering the recent development of these joints, currently, there are no codified rules, and their design usually implies the use of FEM. This work aims to take a step towards developing simple analytical tools for designing and modelling such connections through the component method, currently codified in EC3 part 1.8. Within this framework, the subject of the paper is the study of the behaviour of one of the main elementary components characterising the response of beam-to-column joints with CHS columns and I-beams, which is the “passing-through plate transversally welded to the column in tension/compression”. This component idealises the behaviour of the passing-through beam flange plates (in tension/compression) at the attachment with a CHS column. Its response is significant for the overall joint behaviour because it governs the deformability of the connection and may limit the joint’s resistance due to the CHS tube’s local failure. This paper presents the results of three monotonic tests of sub-assemblies of this joint component, showing the typical failure mode and the component behaviour. Subsequently, a FE model is built with ABAQUS software, carrying out parametric studies to individuate the main parameters influencing the behaviour of these joints. Finally, equations to predict the stiffness and strength are provided, showing the accuracy obtained.

Flexural performance of a novel pipe-roof structure and optimization of key parameters

Considering shortcomings of the current technology in controlling ground surface settlement and reducing the effect of excavation on the surrounding environment. This paper presents an experimental study on the flexural performance of composite structures of concrete-filled steel tubes, which are proposed as a new type of pipe-roof structure. It is also called as steel tube slab (STS) structure. The most important feature of this structure is that the adjacent steel tubes are connected using flange plates, bolts, and concrete in the transverse direction, forming the supporting system after pouring concrete. The main design parameters considered in this investigation are the connection type, spacing between the tubes, welding of the top flange, and thickness of the bottom flange. By conducting six flexural experiments, the failure process and crack development in the composite beams and their load–displacement curves are investigated. The results of laboratory tests show that the composite beams exhibit ductile failure. Increasing connections between the steel tubes has an obvious effect on the load-carrying capacity and flexural stiffness. The spacing between tubes can improve the flexural stiffness of STS beams, while having a limited effect on the longitudinal load-carrying capacity of the STS structure. Welding of the top flange and thickness of the bottom flange shows limited effect on the flexural performance of STS composite beams. Moreover, a series of numerical models is established to further identify the optimum tube thickness-to-flange-thickness ratio in terms of the flexural bearing capacity and stiffness. The numerical solutions suggest that the optimum ratio of the flange thickness to the tube thickness is between 1.0 and 1.25. Finally, a theoretical model for the flexural stiffness of the cross-section of this structure is also proposed, and the predicted results are found to be in excellent agreement with the test results. The research results can provide references for design and construction of STS method.