Plate Connections Research Articles

Structural Integrity of Welded Joints: An Investigation of the FPSO Module Stools

The main goal of the present work is the investigation of a construction and integration of topside modules for an FPSO in Brazil. Most of the topside module structure manufacturing was subcontracted to a third-party company in Europe. During assembling work undergoing at the construction site, several structural details nonconformities were reported by the EPC Group quality control team, e.g., misalignment of stiffeners at the diamond plate and stool connections, geometry irregularities, and unexpected thickness changes on the connection of diamond plates with the correspondent I beam flanges of the pancakes, unexpected bevel buttering to correct joint imperfections which presented several weld flaws in it. Topside structures are subjected to cyclic loading during operation, hence, subjected to fatigue loading. The latter is of concern since the structural integrity of the welded joints must be met for the entire life of the FPSO. The EPC Group required an independent appraisal of the welded joints and structural details nonconformities. They also requested an Engineering Critical Assessment (ECA) on critical joints to be carried out to determine if there might be any flaws compromising the structural integrity of the topsides. Finally, ECA recommended mitigation actions, which could contribute to new topside module integrations for FPSO in Brazil.

Seismic Performance of Brace Middle‐Connection in Steel Concentrically Braced Frames with X‐Bracing

AbstractThis paper presents the experimental investigation of two brace middle connections: 1) using a slotted tube knife‐plate connection (STKPC), and 2) a bolted sandwich plate connection (BSPC). The STKPC consists of a gusset plate slotted through the continuous brace and welded to discontinuous braces. The BSPC consists of two cover plates and four U‐shaped plates connecting the discontinuous braces using bolts. The two cover plates pass on either side of the continuous brace and are bolted to the U‐shaped plates. These connections are used to join the discontinuous braces in steel concentrically braced frames (CBFs) configured with X‐bracing. These connections were tested as part of a full‐scale CBF using quasi‐static testing. In both specimens, seismic energy dissipated through yielding and buckling of the braces. However, in the specimen with STKPC, axial deformation is concentrated in a single discontinuous brace, which led to local buckling at mid‐length and subsequent fracture. In contrast, the BSPC is able to better distribute axial deformation between the two discontinuous braces delaying local buckling. Moreover, the measured buckling capacity of braces when using the BSPC matches well the expected compressive resistance calculated using an effective length factor K = 0.45.

Experimental-numerical investigation and design of bolted-cover plate connections under bending for modular steel buildings

Experimental-numerical investigation and design of bolted-cover plate connections under bending for modular steel buildings

The efficiency of Chisala’s model in predicting the moment-rotation curve for double web angle, and welded flange plate connections

The efficiency of Chisala’s model in predicting the moment-rotation curve for double web angle, and welded flange plate connections

Seismic Performance Evaluation of Moment Resistance Connection by Load Velocity.

AbstractThe seismic performance of beam‐column connections is typically evaluated using a loading protocol specified by codes such as AISC. This protocol involves applying incremental and repeated loads at a specified speed to reach a target rotation angle, with a low load velocity of about 0.5 mm/s to 1.0 mm/s. However, testing at such a low load velocities may not fully account for brittleness breakdown due to factors such as a reduction in material toughness and a decrease in maximum deformation rate caused by stress concentration in vulnerable areas at high load velocities.Therefore, it is important to verify the seismic performance of connections, including their plastic deformation ability, under the influence of dynamic loads with high velocities, such as those experienced during an earthquake. We conducted a static and dynamic experiment on welded connections and extended end plate connections to analyze the effect of load velocity on connections behavior.Our results showed that increasing the load velocity reduced the strength of the connection, its plastic deformation capacity, and energy absorption capacity. These findings confirm that load velocity can significantly affect the seismic performance of connections and suggest that the current loading protocol may not fully capture the connection behavior under dynamic loads.

Performance of short links with flush and extended end plate connections using FEM analysis

AbstractEccentrically braced frames are commonly used as a seismic resistant system, due to the good balance of stiffness and ductility. Bolted links have been proposed in the past to allow replacing the damaged dissipative components following a strong earthquake. The goal of this research work is to investigate the influence of the connection type on the performance of bolted links using the Finite Element Analysis. Numerical models of links are first calibrated using past experimental tests. Modelling criteria adopted to replicate the experimental behaviour of the links highlighted in the tests are reported. The achieved results obtained regarding a flush end plate bolted link and an extended end plate bolted link with different lengths are then used as benchmark to assess the influence of the link length and type of connections adopted on the response of the links. The Finite Element Method is used to investigate alternative solutions to the tested ones. Finally, the investigated options are compared to determine the advantages and disadvantages of each solution.

Modelling of column base plate connections with plate stiffeners and non‐proportional loading

AbstractColumn base plate connections are used widely. Their design is currently codified by Eurocode 3, though with explicit consideration of only base plates without stiffeners and subjected to a proportional loading path. However, both new and existing steel structures might have stiffened base plates. Besides, there might be the need for analyzing the connection response for a non‐proportional loading path (e.g., increasing seismic loads and constant gravity loads). Therefore, the paper provides a contribution into the development of an analytical model for predicting the response of stiffened base plate connections subjected to a non‐proportional loading path. The paper deals with calculation of the connection rotational stiffness and moment resistance. The objective is pursued through finite element modelling and analysis. Then, the application of a proposed analytical model is shown and a comparison with the finite element analysis results is illustrated and discussed.

Strength Evaluation of Pipe‐Rack Connection Using Extended End Plate

AbstractPipe‐rack structure is generally designed as a steel structure, but size of each column and beam is small because vertical loads on the structure is relatively low. In addition, due to the surrounding environment, the end plate joint is mainly used as on‐site bolting rather than welding. In this paper, seismic performance evaluation of pipe‐rack structures was conducted for three types of extended type end plate connection using the panel zone reinforcement and end plate thickness as variables. Connection of the pipe‐rack structure which is commonly used is the type of panel zone yielding occurred before other members, and its ductility and energy dissipation capacity was calculated 24.2% and 19.5% higher than the type of reinforcing panel zone by plates. As a result of the test, it is judged that yielding of the panel zone in a steel structure such as a pipe‐rack structure can be beneficial in the seismic loads.

비확장 단부판 접합부의 헌치 형태에 따른 내력 평가

비확장 단부판 접합부의 헌치 형태에 따른 내력 평가

Study the muti-bolt fastening under different load positions in gear rack drilling rig.

During the operation of drilling rigs, bolts are subjected to significant loads, rendering bolt groups vulnerable to failure due to uneven load distribution. This study investigates the multi-bolt load distribution characteristics of eight-gear and four-gear symmetric transmission mechanisms in drilling rigs. The spring stiffness method is utilized to analyze multi-bolt load distribution. A finite element model of the bolted connection is developed by integrating the structural shape and transmission mechanism. The model's accuracy is validated through a rack strain test under various loads. Based on the finite element analysis results, this study proposes an evaluation method for bolted connections using relative deformation difference. The impacts of bolt pitch, end distance, preload, and thickness of the derrick connection plate under different load positions on the connection are examined. This paper presents a methodology and conclusions that can inform the design of bolted connections for heavy-duty drive systems.

An Experimental Study on Plate Splicing of Prefabricated Plate Foundation

Tower foundations are generally of a cast-in-place structure with the disadvantages of low industrialization level and long construction period. The development of prefabricated foundation for transmission line projects is efficient to improve the industrialization level of the construction of tower foundation. In this study, the schemes of post-pouring belt U-shaped steel connection, post-pouring belt lap connection, grouting sleeve connection, and post-tensioned bond prestressed reinforcement connection, which have been widely used on building structures, are newly proposed to apply on plate foundation. The schemes were compared on processing, transporting, on-site constructing and performance. The pseudo-static tests on cast-in-place plate strip, post-pouring belt U-shaped steel connection and post-pouring belt lap connection plate strip were carried out. The results revealed that all the test plate bands were damaged in the bending mode, same as that of ordinary concrete. When U-shaped steel is adopted, more than 90% of the cast-in-place bearing capacity can be reached. The initial stiffness of prefabricated plate strip and cast-in-place strip is basically the same. The load-bearing capacity of the component is relevant to the anchorage length of the U-shaped steel. Although increasing the concrete strength of post-cast belt can improve the ultimate bearing capacity and shorten the construction period, the deformation capacity is reduced. Compared to other connection methods, post-pouring belt U-shaped steel connections have the advantage of simple construction, higher bearing capacity and stability. In summary, the post-pouring belt U-shaped steel connection scheme is recommended.

Flexural performances of steel–concrete composite section of self-anchored suspension bridge: Experimental and theoretical research

This paper aims to clarify the flexural performance and the cracking load, the ultimate bearing capacity calculation theories of the steel–concrete composite section of the self-anchored suspension bridge. A refined local finite-element (FE) model of the steel–concrete composite section was built to evaluate the mechanical performance of key parts under three unfavourable load conditions. A test model of the steel–concrete composite section with a length × width × height of 7 m × 1.833 m × 1.2 m was fabricated according to the scale of 1: 3, and a four-point negative bending test was carried out. The test results show that the test model is in the elastic stage, and the residual displacement ratio is 0.7 % under the design load condition. Under the overload condition (2.3 times the design load), the experimental model is in the elastic–plastic stage, and the residual displacement ratio is 19 %. At the same time, the stress of each component still meets the requirements. Under the two conditions, the deformation angle of the composite section is small, and the stiffness transition is stable. The relative slip between the top steel plate and the concrete in the composite section is small (no more than 0.25 mm). The stress of the top steel plate and bottom steel plate of the composite section gradually decreases during the transfer from the steel stiffening beam to the concrete side. The bearing plate is the main bearer of the force transmission of the steel–concrete composite section, accounting for about 51.24 %, while the top steel plate, bottom steel plate and shear connectors share the remaining load. The steel–concrete composite section of the test model has reasonable force, smooth force transmission and good deformation coordination performance. In addition, the calculation methods of cracking load and ultimate bearing capacity of the prestressed steel–concrete composite section were proposed. The theoretically calculated value of the ultimate bearing capacity of the steel–concrete composite section is in good agreement with the FEA value, and the difference does not exceed 10 %.

Investigating the T-stub connection with different web-to-flange joint configurations

This article evaluates the impact of different web-to-flange joints in the T-stub connection. Mechanical properties of T-stub components were evaluated by experimental tests and by finite element simulations. Three different web-to-flange junctions are evaluated: laminated components, fillet welding and full penetration welding. Generally, laminated and fillet welded T-stub profiles have been considered in the past to study the behavior of the tension zone in the end plate connections. However, in structures predominately subjected to low and high cycle dynamic loads, and susceptible to a fatigue crack, is mandatory full penetration welds execution. This article evaluates the influence of full penetrated welding in the behavior of the full component, and not only in the mechanical capacity of the weld and the weld area. This article analyses how the increment of the free span between the bolt position and the web modifies the position of plastic hinges in the vicinity of the web, with the consequent reduction of strength and stiffness. A total of 72 experimental samples with 8 different geometries were tested to evaluate the different behavior of the web-to-flange joint configuration. A detailed finite element model of the T-stub component has been developed for each joint configuration. The model has been calibrated with experimental results, and it is able to accurately capture the full range behavior of the T-stub featuring any failure model. From the results of the experimental tests and their validation by finite element analysis, it can be concluded that the welded T-stub connection has a lower mechanical resistance, with no significant differences between fillet welding and full penetration welding. And the effect of the type of welding is only seen in ductility, and not in resistance or stiffness. On average, the typologies with full penetration welding have a maximum displacement 1.43 times higher than the fillet welded one.

Experimental and numerical investigation of seismic response of access floors based on shake-table tests using 2-story steel moment frame

In this study, a full-scale shake-table test was conducted utilizing a 2-story steel moment frame to evaluate the seismic performance of access floors (or raised floors). A total of four access floor specimens were fabricated that are typically used in offices and computer/server rooms. Based on test results, critical failure modes and nonlinear behavior of access floors were discussed in detail. Specimen utilizing a flexible 600 mm-high access floor (FH600-F) exhibited several cracks in its joint connection plates (or pedestal heads) before the specimen eventually collapsed under the 60% RRS intensity test (PFA = 0.65 g). Due to a partial pull-out of the pedestal heads from their supporting columns, a highly pinched hysteretic response was also observed. A simplified SDOF numerical model was presented that can effectively capture the complex pinching behavior of access floor specimens. Based on the calibrated numerical analysis, it was identified that the partial pull-out of pedestal heads caused about 60% strength loss during the reverse cyclic phase of the specimen, which was the main source of the high pinching. The specimen also exhibited severe stiffness-degradation, which may have resulted from the cracks that developed in a significant number of its joints. The initial stiffness of the specimen was reduced by about 30% before its eventual collapse. Extensive numerical analyses were also conducted to evaluate the effects of pinching and stiffness-degradation on the acceleration response of access floors based on the floor motions obtained from the time history analysis of four multi-story building models.

EVALUATING MESOSCALE STRAIN LIMIT FOR TRANSVERSE PLATE-TO-RHS X JOINTS

Recently, mesoscale strain limit has been introduced for finite element (FE) analysis and FE-based design of welded steel tubular joints. The strain limit criterion appears to be useful particularly for the joints made of high strength steels, considering their lower ductility and higher propensity to fracture failure when subjected to tensile strains. While the latest revised draft of ISO 14346 recommended the use of 5% principal strain as the strain limit for all kinds of tubular joints, a previous study by the authors has demonstrated that a limit lower than 5% principal strain may be required for welded plate connections. In this study, the load-deformation relationship and fracture failure of transverse plate-to-RHS X-joints are investigated to evaluate appropriate strain limit for such type of joints. Based on test and test-validated FE analysis with a high strength steel of grade 700 (i.e., nominal yield stress of 700 MPa), it is suggested that more conservative strain limit should be applied to transverse plate-to-RHS X-joints.

Triangular Position Multi-Bolt Layout Structure Optimization

Stress concentration often occurs around bolt holes in load-bearing joint structures of large complex equipment, ships, aerospace and other complex machinery fields, which is an important mechanical factor leading to the failure of joint structures. It is of great engineering significance to study the phenomenon of stress concentration on connected structures for the safety of large and complex equipment; meanwhile, the layout of bolts seriously affects the stress around holes. Many scholars have studied the layout optimization of multi-bolted structures through experiments and simulations, but few algorithms have been applied to the layout optimization of bolted structures. And most of the studied types of multi-bolt structures are symmetrical. Therefore, in this paper, the gray wolf algorithm is used to optimize the layout of nickel steel plate connectors with a bolt layout in triangular position, and the optimal objective function is found based on the hole circumferential stress of the nickel steel plate, maximum shear stress of the bolt and bending stress of the nickel steel plate. Comparing the optimal values obtained by the fruit fly optimization algorithm, particle swarm optimization algorithm, gray wolf optimization algorithm, multiverse optimization algorithm and wind driven optimization algorithm, the accuracy of selecting the gray wolf algorithm for optimization is verified. A multi-bolt connection structure model was established in ABAQUS, and the surface stress before and after optimization was compared to verify the correctness of the gray wolf algorithm applied to the structure layout optimization of the nickel steel flat bolt connection. The results show that under the force of 15 KN, compared with the original bolt structure layout, the optimized upper side nickel steel plate bore peripheral stress is reduced by 73.1 MPa, and the optimization rate is 24%; bolt stress is reduced by 47.7 MPa, and the optimization rate is 12.5%; when the load is less than 18 KN, the optimization effect of both the upper nickel steel plate and bolt group is more than 10%. When the load is greater than 18 KN, the optimization effect is reduced, and when the load is greater than 21 KN, the nickel steel plate has exceeded the yield limit. Due to the existence of fixed constraints, the optimization of the lower nickel steel plate is not obvious. The results of this study can provide data and theoretical support for the layout optimization of the nickel steel flat bolt connection structure, and help to improve reliability analysis and health monitoring in complex assembly fields such as large complex equipment and aerospace.

Mechanism and seismic performance of a novel precast concrete beam-to-very short shear link joint: Experimental and numerical simulation

This paper introduced a novel precast concrete beam-to-very short shear link (PCB-VSSL) joint with the separation from shear force and bearing moment. The mechanism and seismic performance of the PCB-VSSL joint were detailed investigated. In the present study, four specimens were investigated by cyclic loading tests, including a very short shear link-1 (VSSL-1), a novel joint with basic shear connectors (PCB-VSSL-1), and two improved joints (PCB-VSSL-2 and 3), and the influencing factors including the length of cross-bilinear-type (CBT) shear connector and lateral plate height in the CBT shear connector were analyzed by experimental and numerical simulation. The test results showed that the PCB-VSSLs had excellent bearing capacity and energy dissipation capacity, and maximum overstrength and inelastic rotation of VSSLs in the specimens PCB-VSSL-1, 2, and 3 were 1.85 and 0.15, respectively, which were the same as the specimen VSSL-1. The concrete cracks of the precast concrete beam could be minimized by enlarging the length and area of shear connectors. The results also indicated that the high-strength bolts would only transfer the bending moment from the VSSL to PCB-VSSL. The shear connectors only sustained the shear force, so the bending moment and the shear force of the novel PCB-VSSL could be effectively separated with the advantage of high bearing capacity, reasonable mechanics, ease of installation, and seismic resilience capacity. Furthermore, based on the finding of on failure mechanism of the PCB-VSSL joint, a simplified design methodology of the novel PCB-VSSL joint was proposed.

Simplified Calculation Model and Experimental Validation of the Force Transfer Ratio of Steel-Concrete Joint of Hybrid Box Girder.

The axial force transfer ratio of steel-concrete joints in hybrid box girder bridges is crucial for bridge design. However, the current standard oversimplifies the transfer ratio distribution coefficients, and both model tests and finite element analysis are time- and labor-intensive. This article proposes a simplified calculation model based on the deformation coordination theory to estimate the transfer ratio of the axial force between the bearing plate and shear connectors of the steel-concrete joint under compression bending conditions. Additionally, a large-scale model (1/5 scale) is established, and the mechanical properties of the steel-concrete joint section under compression-bending conditions are experimentally tested. A three-dimensional finite element model is developed and verified using the obtained test data. Results confirm the favorable mechanical properties and ample safety reserve of the SCJ, with all components remaining within the elastic stage under 1.6 times design conditions. By comparing the axial force transfer ratios obtained from the simplified calculation model and the finite element model, a small difference is observed, validating the reliability of the simplified calculation model. This paper provides a straightforward and efficient method for the design and evaluation of steel-concrete joints in hybrid box girder bridges.

Seismic behavior of welded high-performance steel beam-to-column joints with different reinforced configurations

Extensive experimental and analytical investigations have evaluated the hysteresis behavior of welded flange-bolted web beam-to-column joints made of high-strength steels subjected to simulated earthquakes. However, the seismic behavior of newly developed high-performance seismic structural steels, which exhibit a combination of high strength and high ductility at the joint level, has been less attentively scrutinized. In this study, four welded beam-to-column joints were designed with standard or reinforced configurations. The reinforced joints included tapered haunch and transition plate connections. Hysteresis tests were conducted on these joints under low-cycle reversal loading to evaluate their seismic performance. The results indicated that the failure modes of these joints were primarily influenced by the welded heat-affected zones. Last, numerical models were developed and validated. The analysis focused on assessing their ductility coefficient, load-bearing capacity, stiffness degradation, and energy dissipation. The reinforced connections proved to be more effective in improving the initial stiffness, load-carrying capacity, and energy dissipation of the joints compared to the standard joints with the same beam and column sections. The initial stiffness of tapered haunch and transition plate reinforced joints were found to be 29.9% and 12.7% higher than that of the standard joint without reinforced configuration. And the equivalent viscous damping coefficient of the standard joint was 23% lower than the transition plate reinforced joint. However, the reinforced joints exhibited a slight reduction in ductility coefficient compared to the standard joints, with decreases of 11% and 2% for the tapered haunch and transition plate reinforced joints, respectively.

Novel design method of screwed connections of cold-formed steel built-up plates

The ultimate capacity and failure modes of composite plates have been widely investigated, especially those assembled by using self-drilling screws. The cold-formed steel (CFS) built-up plate connected by self-drilling screws is the research object in this paper. The screw built-up plate (SBP) is taken from the built-up flanges of the CFS built-up double-limbs closed column. In conjunction with the author's previous experiment, a theoretical model for the critical buckling stress of the SBP is presented. The innovation lies in considering the influence of the shear slip effect in the theoretical model. The kinematic relations between single plates of the SBP are given according to the energy method, and the stress calculation equation of the SBP is proposed through theoretical derivation. In this equation, a thickness reduction coefficient of the SBP is proposed. Subsequently, the influence of key parameters on the proposed equation is studied by finite element analysis. It indicates that the proposed equation of the critical buckling stress in this paper can truly reflect the true loading of SBP through comparative analysis of multiple parameters. Additionally, the study in this paper lays the foundation for the calculation of the bearing capacity of the CFS double-limbs closed built-up columns.