Showing papers in "International Journal of Steel Structures in 2018"

Seismic Behavior Investigation of the Corrugated Steel Shear Walls Considering Variations of Corrugation Geometrical Characteristics

Abstract: The corrugated steel plate shear walls have recently been proposed to address the seismic issues associated with simple steel plate shear walls; however, stiffness, strength, and ductility of the corrugated shear walls are significantly affected by varying the corrugation geometry under seismic loading. The present study investigates steel shear walls’ models with corrugated or simple infill plates subjected to monotonic and cyclic loads. The performance of the corrugated steel plate is evaluated and then compared to that of the simple steel plates by evaluating the damping ratios and energy dissipation capability. The effect of corrugation profile angle, the existence of an opening, and the corrugation subpanel length are numerically investigated after validation of the finite element modeling methodology. The results demonstrate that incorporating corrugated plates would lead to better seismic damping ratios, specifically in the case of opening existence inside of the infill plate. Specifically, the corrugation angle of 30° decreases the ultimate strength, while increasing the initial stiffness and ductility. In addition, the subpanel length of 100 mm is found to be able to improve the overall performance of shear wall by providing each subpanel appropriate support for the adjacent subpanel, leading to a sufficient buckling resistance performance.

Assessment of the Progressive Collapse Resistance of Double-layer Grid Space Structures using implicit and explicit solvers

Abstract: A double-layer grid space structure is a conventional long span structure used where large column-free areas are required. Due to its’ large indeterminacy and the redundancy of its structural configuration, it is normally considered in design practice, that progressive collapse will not be triggered when the loss of an individual member occurs. However, research and several prior accidents have shown that progressive collapse could occur following the loss of some critical members when the structures are subject to abnormal loading such as heavy snow. To investigate the structural behavior of this type of structure, a 3D finite element model of a double-layer space structure grid was built by the authors, several collapse scenarios have been investigated using an implicit method which follows the alternative path method defined in GSA. In addition, case studies have been made using the explicit method which is to simulate the whole process of the structural collapse. In the analysis, different members failure or support collapses were studied. The response of the structure was investigated and the correspondent potential of progressive collapse was discussed in detail. Methods to mitigate the progressive collapse of this type of space structure have also been recommended.

A Novel Approach for Bolted T-Stub Connections

Abstract: This paper reports an investigation into new connection types and their behaviors determined using full-scale experiments. T-shaped connections were created using the IPE standard profile. The aim of this study was to analyze the influence of T connections based on the IPE standard profile, height of beam to height of T-stub joint (H) of T-stub joints, and lengths (X) of T-stub joints on the behavior of steel connections, in order to provide the necessary data for improving Eurocode 3 and enable efficient use of residue IPE standard profiles and back to the consumption cycle. While the moment resistance values increased with an increase in H from Hmin to Hmax in model groups with X of 126 mm, and the energy dissipation increased with an increase in H from Hmin to Hmax and also with an increase in the lengths (X) of T-stub joints from 54 to 126 mm.

Replaceable Fuses in Earthquake Resistant Steel Structures: A Review

Abstract: In earthquake-prone regions, steel structures are considered to be one of the best choices due to inherent material properties in terms of homogeneity and ductility. In the conventional seismic design of steel structures, prevalent specifications recommend that the column and joints should be strong enough such that the inelastic action or damage occurs in the beams in lateral load resisting frames. By following these design provisions, structural collapse can be prevented in the event of severe earthquakes to ensure occupant safety. However, repair and rehabilitation of damaged primary members is a challenging task and also time-consuming process, resulting in severe inconvenience to the occupants. To simplify the repair works in earthquake resistant steel structures after the event of severe earthquakes, recent research work is concentrated on designing structures to have localized inelastic damages at intended locations, which will dissipate the seismic energy and can be easily replaced after the event of a strong earthquake, so that normal life of the occupants can be restored immediately with lesser cost of repair. This paper presents a critical review of the state-of-the-art related to steel lateral load resisting systems comprising of replaceable fuses that help in the easy repair of steel structures following strong earthquakes.

Experimental Investigation of Aluminum Alloy and Steel Core Buckling Restrained Braces (BRBs)

Abstract: Buckling restrained braces (BRBs) display balanced hysteretic behavior under reversed cyclic tension and compression forces and dissipate a significant amount of seismic energy during credible earthquakes. This paper reports on an experimental investigation of newly developed BRBs with different core materials (steel and aluminum alloy) and end connection details. A total of four full-scale BRBs with two steel cores and outer tubes (BRB-SC4 and BRB-SC5) as well as two with aluminum alloy cores and aluminum outer tubes (BRB-AC1 and BRB-AC3) with specific end details were designed as per the AISC Seismic Provisions, manufactured and cyclically tested. These tests made it possible to compare the impact of the steel and aluminum alloy material characteristics on the hysteretic behavior and energy dissipation capacities. The proposed steel and aluminum alloy core BRBs with various end details achieved the desired behavior, while no global buckling occurred under large inelastic displacement cycles.

Nonlinear Buckling Analysis of H-Type Honeycombed Composite Column with Rectangular Concrete-Filled Steel Tube Flanges

Abstract: This paper was concerned with the nonlinear analysis on the overall stability of H-type honeycombed composite column with rectangular concrete-filled steel tube flanges (STHCC). The nonlinear analysis was performed using ABAQUS, a commercially available finite element (FE) program. Nonlinear buckling analysis was carried out by inducing the first buckling mode shape of the hinged column to the model as the initial imperfection with imperfection amplitude value of L/1000 and importing the simplified constitutive model of steel and nonlinear constitutive model of concrete considering hoop effect. Close agreement was shown between the experimental results of 17 concrete-filled steel tube (CFST) specimens and 4 I-beams with top flanges of rectangular concrete-filled steel tube (CFSFB) specimens conducted by former researchers and the predicted results, verifying the correctness of the method of FE analysis. Then, the FE models of 30 STHCC columns were established to investigate the influences of the concrete strength grade, the nominal slenderness ratio, the hoop coefficient and the flange width on the nonlinear stability capacity of SHTCC column. It was found that the hoop coefficient and the nominal slenderness ratio affected the nonlinear stability capacity more significantly. Based on the results of parameter analysis, a formula was proposed to predict the nonlinear stability capacity of STHCC column which laid the foundation of the application of STHCC column in practical engineering.

Analysis and Design of Elliptical Concrete-Filled Thin-Walled Steel Stub Columns Under Axial Compression

Abstract: To analyze the axial compressive performance of elliptical concrete-filled thin-walled steel tube (ECFTST) columns, finite element (FE) modeling was built up by ABAQUS software in this paper. The material nonlinearity and the complex interaction between steel tube wall and core concrete in an elliptical section were considered in this numerical analysis. Failure modes and interaction mechanism of ECFTST stub columns were also studied. Moreover, a modified equivalent circular diameter approach for ellipse feature was proposed to substitute for the constitutive relation of ECFTST columns. The prediction accuracy of this method was verified by the comparison of the FE and test results in terms of failure modes, axial compressive capacities and axial force-axial displacement relation curves. Further, the influence of diameter-to-thickness ratio, cross-section slenderness and scale effect etc. on the performance of ECFTST stub columns were estimated under axial compressive loading. The results of numerical analysis showed that the axial force-axial displacement curves of the ECFTST stub columns were obviously affected by the confinement factor. Lastly, based on the simple superposition approach and the unified theory approach, two simplified design methods were proposed to predict the axial compressive capacities of ECFTST columns.

Cyclic Experimental Behavior of CFST Column to Steel Beam Frames with Blind Bolted Connections

Abstract: This paper aims to investigate the seismic behavior of blind bolted end plate composite frames between square or circular concrete filled steel tubular (CFST) columns and steel beams. Two composite frames were tested under a constant axial load on the CFST columns and a lateral cyclic load on the frame. Each specimen composed of CFST columns and steel beams was selected to represent a plan frame in an assembly building. Failure pattern of the type of frames was analyzed to comprehend the structural response. The seismic resistance ability of the blind bolted CFST frames was also estimated in terms of hysteretic curves, ductility and energy dissipation etc. The effect of column section type and end plate type on the type of semi-rigid CFST frames was studied. The test results showed that at the same steel ratio of the column section, the bearing capacity and energy dissipation of square CFST frame were higher than those of circular CFST frame at ultimate state. Strain response of main members in each CFST frame was also estimated. The internal force analysis of the test CFST frames with semi-rigid connections was discussed and evaluated the effect of the bending moment distribution. It was concluded that the novel typed CFST frames exhibited excellent seismic performance and structural internal force redistribution. The experimental studies will be useful for design and application of the blind bolted CFST frames in fabricated steel structure building.

Investigation of Proposed Concrete Filled Steel Tube Connections under Reversed Cyclic Loading

Abstract: Concrete-filled steel tube (CFT) columns are used in the primary lateral resistance systems. The objective of this research is to analyse the behavior of the steel beam to CFT column connections. A three-dimensional numerical model for simulating the behavior of CFT connections was developed with the aid of the general purpose nonlinear finite element analysis package ABAQUS. In this paper, 90 CFT connection specimens include simple and moment connections that were tested under reversed cyclic loading. Shear capacity of joint, moment-drift response, energy absorption, and displacement ductility were studied in those models. The results have indicated that, the hysteresis curve of CFT columns was plump; no pinch phenomenon can be found; the damage and degradation degree of the strength and stiffness of specimens is lower; and high energy dissipation capacity can be achieved. Improvement in the behavior of CFT connection depends on the beam characteristics and column features.

Experimental and Theoretical Study on High Strength Steel Extended Endplate Connections After Fire

Abstract: In order to reveal more information and better understanding on the behavior and failure mechanisms of high strength steel (HSS) extended endplate connections at ambient temperature and after fire, an experimental and theoretical study has been conducted and presented in this paper. The provisions of Eurocode 3 are verified with the test results. Because strength of bolts decreases more rapidly than that of structural steels, failure modes of endplate connections may change after fire. Hence, a series of equations are proposed to predict failure modes of endplate connections after fire. Furthermore, FE simulations which can predicate the performance of HSS extended endplate connections with reasonable accuracy are adopted to study the behaviors of the connections after cooling down from various fire temperatures and to validate the accuracy of the proposed equations. Moreover, a parametric study is carried out to explore an optimization design method. It is found that the current provisions of EC3 can justifiably predict failure modes and plastic flexural resistances of HSS extended endplate connections both at ambient temperature and cooling down from 550 °C, but it is not the case for their initial rotational stiffness and rotation capacity. In order to avoid brittle failure mode of endplate connections after fire, appropriately increasing the diameter or grade of bolts in the design is suggested. What is more, the match of steel grade and thickness of column flange and endplate as well as beam should be considered in the optimization design of beam-column endplate connections.

Hysteretic Behavior of RHS Columns Under Random Cyclic Loading Considering Local Buckling

Abstract: In this paper, a hysteretic model of rectangular hollow section (RHS) columns that includes the deteriorating range caused by local buckling is proposed. The proposed model consists of the skeleton curve, the Bauschinger part that appears before reaching the maximum strength, the strength increasing part of the deteriorating range, and the unloading part. Of these, the skeleton curve, including the deterioration range caused by local buckling, which is considered to be equivalent to the load-deformation relationship under monotonic loading, is obtained through an analytical method. Bi-linear hysteretic models based on experimental results are applied to the Bauschinger part and the strength increasing part. The elastic stiffness is applied to the unloading part. The proposed model is verified by comparing with experimental results of RHS columns under monotonic and cyclic loading.

Seismic Performance Evaluation of Steel Diagrid Buildings

Abstract: In this study the seismic performances of axi-symmetric steel building structures with circular plan shape were evaluated based on the ATC-63 approach. For analysis models, thirty-three-story vertically convex, concave, and gourd-type axi-symmetric buildings were designed using diagrid structure system, and their seismic performances were compared with those of the cylinder type regular steel structure. Seismic fragility analyses were carried out using twenty-two pairs of earthquake records to obtain the probability of failure for a given earthquake intensity. The validity of the response modification factor used in the seismic design of the model structures was also investigated. Based on the analysis results it was concluded that the response modification factor of 3.0 used in the design of the model structures is acceptable for the ATC-63 methodology. It was also observed that the seismic safety margin for a specific level of earthquake decreases as the vertical irregularity of the structure increases.

Static Experiment on Mechanical Behavior of Innovative Flat Steel Plate-Concrete Composite Slabs

Abstract: A new type of composite slab is introduced in this paper, which is composed of normal flat steel plates and concrete slabs, connected and interacted by perfobond shear connectors (PBL shear connectors). Experiments on six specimens of this type of composite slab, loaded at two symmetric two-points, were described in this paper to get mechanical behaviors under bending moments. During the experiments, the crack patterns, failure modes, failure mechanism and ultimate bending capacity of specimens with composite slab were investigated, and the strains of concrete and flat steel plates were also measured and recorded in order to obtain the moment action. From the experimental results, it was found that composite interaction between the steel plate and the concrete fully developed, and such composite slab was verified to have good mechanical performance with high bending capacity, substantial flexural rigidity and good ductility. Plane section assumption was also verified and moreover, a design approach including calculation methods of bending capacity and flexural rigidity was established and proposed based on the experimental results, and the calculation methods were also verified and revised on the basis of comparisons of the calculated results and experimental results. Results from this paper provide references for the application of this new type composite slab.

Static and Fatigue Behavior of the Stud Shear Connector in Lightweight Concrete

Abstract: The lightweight concrete has been increasingly applied in the civil structures for the lightweight merit and the strength improvement. Concerning the composite bridges, the interlayer shear connector is actually quite important to achieve the composite action whereas the static and fatigue mechanism understanding of it in the lightweight concrete is not enough. Therefore, a series of static and cyclic push-out tests and analysis on the frequently used stud connector, together with the discussions on the existing results in literatures, have been executed. In this study, the stud shank diameter and height were 19 and 150 mm, respectively. The results showed that the lightweight concrete tended to lower down the stud static stiffness due to the lower modulus. Meanwhile, the stud in the lightweight concrete was found to be with a lower fatigue life. And some of the current civil codes cannot guarantee the corresponding safe fatigue life estimation, such as that based on the Japanese Standard Specification for Hybrid Structure may experience an overestimation.

Sensitivity of Seismic Response and Fragility to Parameter Uncertainty of Single-Layer Reticulated Domes

Abstract: Quantitatively modeling and propagating all sources of uncertainty stand at the core of seismic fragility assessment of structures. This paper investigates the effects of various sources of uncertainty on seismic responses and seismic fragility estimates of single-layer reticulated domes. Sensitivity analyses are performed to examine the sensitivity of typical seismic responses to uncertainties in structural modeling parameters, and the results suggest that the variability in structural damping, yielding strength, steel ultimate strain, dead load and snow load has significant effects on the seismic responses, and these five parameters should be taken as random variables in the seismic fragility assessment. Based on this, fragility estimates and fragility curves incorporating different levels of uncertainty are obtained on the basis of the results of incremental dynamic analyses on the corresponding set of 40 sample models generated by Latin Hypercube Sampling method. The comparisons of these fragility curves illustrate that, the inclusion of only ground motion uncertainty is inappropriate and inadequate, and the appropriate way is incorporating the variability in the five identified structural modeling parameters as well into the seismic fragility assessment of single-layer reticulated domes.

Blast Fragility and Sensitivity Analyses of Steel Moment Frames with Plan Irregularities

Abstract: Fragility functions are determined for braced steel moment frames (SMFs) with plans such as square-, T-, L-, U-, trapezoidal-, and semicircular-shaped, subjected to blast. The frames are designed for gravity and seismic loads, but not necessarily for the blast loads. The blast load is computed for a wide range of scenarios involving different parameters, viz. charge weight, standoff distance, and blast location relative to plan of the structure followed by nonlinear dynamic analysis of the frames. The members failing in rotation lead to partial collapse due to plastic mechanism formation. The probabilities of partial collapse of the SMFs, with and without bracing system, due to the blast loading are computed to plot fragility curves. The charge weight and standoff distance are taken as Gaussian random input variables. The extent of propagation of the uncertainties in the input parameters onto the response quantities and fragility of the SMFs is assessed by computing Sobol sensitivity indices. The probabilistic analysis is conducted using Monte Carlo simulations. The frames have least failure probability for blasts occurring in front of their corners or convex face. Further, the unbraced frames are observed to have higher fragility as compared to counterpart braced frames for far-off detonations.

Seismic Design of Coupled Shear Wall Building Linked by Hysteretic Dampers using Energy Based Seismic Design

Abstract: In coupled shear wall systems, the excessive shear forces are induced in the coupling beams. As a result, in such systems, the coupling beam and the joint of wall-coupling may yield first. The critical concern about the coupling beam is ductility demand. In order to have such ductility, the coupling beams are required to be properly detailed with significantly complicated reinforcement arrangement and insignificant strength degradation during ground motion. To solve these problems and to increase energy dissipating capacities, this study presents an investigation of the seismic behavior of coupled shear wall-frame system, in which energy dissipation devices are located at the middle portion of the linked beam. The proposed method, which is based on the energy equilibrium method, offers an important design method by the result of increasing energy dissipation capacity and reducing damage to the structure. The design procedure was prescribed and discussed in details. Nonlinear dynamic analysis indicates that, with a proper set of damping parameters, the wall’s dynamic responses can be well controlled. Thereafter, an optimized formula is proposed to calculate the distribution of the yield shear force coefficients of energy dissipation devices. Thereby, distributing equal damages through different heights of a building as well as considering the permissible damage at the wall’s base. Finally, numerical examples demonstrate the applicability of the proposed methods.

Experimental and Numerical Assessment of Reduced IPE Beam Sections Connections with Box-Stiffener

Abstract: Reduced Beam Section (RBS) is a new type of connection in steel moment resistant frames that was introduced after the Northridge earthquake of 1994. The application of RBS connections associated with reduced beam flange width can aid in accelerating web, flange, and lateral-torsional bucklings in the beam. To fix this problem, a new type of stiffener called the box-stiffener was presented in this study, which exactly encases the reduced portion of the beam. First, 4 laboratory tests were performed on RBS connections made of IPE140 and IPE270 sections in the two conditions of ‘with’ and ‘without’ a boxstiffener. Laboratory results showed that the stiffener considerably enhanced the connection ductility without a significant increase in the connection’s resistance. To examine other sizes of IPE sections, a verified Finite Element model was utilized. The results of the numerical models also confirmed the suitable performance of the box-stiffener.

Feasibility Study of Submerged Floating Tunnels Moored by an Inclined Tendon System

Abstract: Concepts of submerged floating tunnels (SFTs) for land connection have been continuously suggested and developed by several researchers and institutes. To maintain their predefined positions under various dynamic environmental loading conditions, the submerged floating tunnels should be effectively moored by reasonable mooring systems. With rational mooring systems, the design of SFTs should be confirmed to satisfy the structural safety, fatigue, and operability design criteria related to tunnel motion, internal forces, structural stresses, and the fatigue life of the main structural members. This paper presents a feasibility study of a submerged floating tunnel moored by an inclined tendon system. The basic structural concept was developed based on the concept of conventional cable-stayed bridges to minimize the seabed excavation, penetration, and anchoring work by applying tower-inclined tendon systems instead of conventional tendons with individual seabed anchors. To evaluate the structural performance of the new type of SFT, a hydrodynamic analysis was performed in the time domain using the commercial nonlinear finite element code ABAQUS–AQUA. For the main dynamic environmental loading condition, an irregular wave load was examined. A JONSWAP wave spectrum was used to generate a time-series wave-induced hydrodynamic load considering the specific significant wave height and peak period for predetermined wave conditions. By performing a time-domain hydrodynamic analysis on the submerged floating structure under irregular waves, the motional characteristics, structural stresses, and fatigue damage of the floating tunnel and mooring members were analyzed to evaluate the structural safety and fatigue performance. According to the analytical study, the suggested conceptual model for SFTs shows very good hydrodynamic structural performance. It can be concluded that the concept can be considered as a reasonable structural type of SFT.

Fatigue Behavior Investigation and Stress Analysis for Rib-to-Deck Welded Joints in Orthotropic Steel Decks

Abstract: The fatigue problems in orthotropic steel decks have raised widely concerns in recent years. This study focused on the root crack mechanism at rib-to-deck welded joints, based on the previous test results of sectional specimens and the matching FE analysis, the fatigue behaviors of structure detail were investigated by considering the effect of root gap shapes, weld penetrations, and plate thicknesses on crack initiation. Besides, various root crack depths were simulated in models to clarify the stress variations occurring during the propagation stage under cyclic loading. The results showed that the root gap shape and penetration rate have an impact on the root cracking direction and fatigue life at the initiation stage, but seem not directly related to the crack propagation mechanism; the higher penetration rate is advantageous for the prevention of root crack initiation. However, although the stiffness increased with the increase in plate thickness, the fatigue life of crack initiation might be reduced owing to the low fatigue strength of the thick deck plate, whereas the U-rib thickness has limited effect on the stress response of the root tip. Moreover, the significant difference between the 8 mm-crack model and other crack models is the high stress concentration around the crack tip. The stress conditions of root tip would be changed under loading cycles when a root crack propagated into half of deck plate thickness. Finally, the effect of structural dimensions on fatigue strength were also compared according to test results and FEA.

Two-stage Optimization Based on Force Method for Damage Identification of Planar and Space Trusses

Abstract: In this study, an efficient two-stage optimization procedure based on the force method is proposed to properly identify the sites and extents of multiple damages in the planar and space truss structures. In the first stage, the elements which have the higher probability of damages are selected by using the anti-optimization (AO) method and the weighed sum procedure. In the second stage, the genetic algorithm (GA) is performed to determine the actual damage sites and their extents based on the force method. The accuracy and effectiveness of the proposed method are proved through the planar and space truss structures. The results from the present study indicate that the combination of the first stage with the second one can provide a reliable tool to accurately and efficiently identify the multiple damages of truss structures.

Fatigue Resistance Improvement of Welded Joints by Bristle Roll-Brush Grinding

Abstract: In the periodic repainting of steel bridges, often the steel surface has to be prepared by using power tools to remove surface contaminants, such as deteriorated paint film and rust, and to increase the adhesive strengths of the paint films to be applied newly. Surface preparation by bristle roll-brush grinding, which is a type of power tool, may additionally introduce compressive residual stress and increase the fatigue resistance of welded joints owing to the impact of rotating bristle tips. In this study, fatigue tests were conducted for longitudinally out-of-plane gusset fillet welded joints and transversely butt-welded joints to evaluate the effect of bristle roll-brush grinding prior to repainting on the fatigue resistance of the welded joints. The test results showed that bristle roll-brush grinding introduced compressive residual stress and significantly increased fatigue limits by over 50%.

Performance Analysis of Steel Structures with A3 Irregularities

Abstract: Determination of the behaviour of structures during earthquakes is a very important engineering concern. Irregularities in the structure may lead to more damage imposed on it by weakening its defence mechanism during an earthquake. Some of these irregularities may be indentations or protrusions in the plan. Such irregular buildings may be encountered in practice because of various reasons. This study examined the state of irregularity by the A3 plan in the Turkish Building Earthquake Regulation of 2016. Four different A3-type irregularity cases were considered. The building with no irregularities in its plan was taken as the reference building. The five steel structures were compared by obtaining pushover curves for both the X and Y directions. Additionally, as a rapid assessment method, the Canada Seismic Screening Method was used in the study. Both in the rapid assessment method and from the pushover curves, it was determined that buildings without irregularities are safer. The study also allows a comparison among the earthquake performances of the structures using the rapid assessment method. It may be stated that there was an agreement between the two methods. This shows that the rapid assessment method may be used for steel structures. The importance of constructing structures that do not include irregularities is emphasized with the study. If one has to construct such structures, the defence mechanism of the structure should be strengthened by taking various measures.

Optimizing Structures with Semi-Rigid Connections Using the Principle of Virtual Work

Abstract: In this paper, the virtual work optimization method (VWOM) has been generalised to consider structures with semi-rigid connections. The VWOM is an automated method that minimizes the mass of a structure with a given geometry, multiple deflection criteria and load cases, while adhering to Design code requirements. In the optimization process, members are selected from a discrete database to meet all strength and stiffness criteria. Connections are modelled using rotational springs, allowing some moment transfer. The rotational stiffness of each connection can be varied form rigid to pinned. The example of a pitched roof frame is used to explain the method. Two case studies are considered: (i) a three-storey two-bay and (ii) a four-storey three-bay office building. The VWOM produced results up to 26.7% lighter than results in the literature. Furthermore, the structures were optimized for a range of rotational stiffness, where all connections in the structure were assumed to have the same rotational stiffness. Characteristic jumps in the optimized mass versus rotational stiffness were observed.

Post-fire Behavior of Welded Hollow Spherical Joints Subjected to Eccentric Loads

Abstract: Welded hollow spherical joints are widely used as a connection pattern in space lattice structures. Understanding the post-fire residual behavior of welded hollow spherical joints is crucial for fire damage assessment of the space lattice structures. However, the post-fire behavior of welded hollow spherical joints has not been explored in existing studies. In this paper, experimental and numerical studies were conducted to investigate the residual behavior of eccentrically loaded welded hollow spherical joints after fire exposure. Eccentric compressive tests were performed on five joint specimens after exposure to the ISO-834 standard fire (including both heating and cooling phases), and three highest fire temperatures, i.e., 600, 800, and 1000 °C, were considered. The temperature distributions in the specimens during the heating and cooling process and the related mechanical behavior of the specimens, such as load versus longitudinal displacement and rotation responses, load-bearing capacities, and strain distributions, were obtained and analyzed. Finite element analysis (FEA), including both heat transfer and mechanical analysis, were also developed using the ABAQUS software. Having validated the FE models against the experimental results, a design method was proposed on the basis of parametric studies to predict the residual load-bearing capacity of eccentrically loaded welded hollow spherical joints after fire exposure.

A Fiber Model Based on Secondary Development of ABAQUS for Elastic–Plastic Analysis

Abstract: With the aim to provide an efficient platform for the elastic–plastic analysis of steel structures, reinforced concrete (RC) structures and steel–concrete composite structures, a program iFiberLUT based on the fiber model was developed within the framework of ABAQUS. This program contains an ABAQUS Fiber Generator which can automatically divide the beam and column cross sections into fiber sections, and a material library which includes several concrete and steel uniaxial material models. The range of applications of iFiberLUT is introduced and its feasibility is verified through previously reported test data of individual structural members as well as planar steel frames, RC frames and composite frames subjected to various loadings. The simulation results indicate that the developed program is able to achieve high calculation accuracy and favorable convergence within a wide range of applications.

Parametric Study on Ultimate Strength of Four-bolted Connections with Cold-formed Carbon Steel

Abstract: The curling(out-of-plane deformation in the plate thickness direction) influence on the ultimate strength of cold-formed stainless steel bolted connection has been investigated and modified equations for predicting the ultimate strength considering strength reduction caused by curling through finite element analysis have been suggested by previous researchers. In this paper, single shear four-bolted connections fabricated with thin-walled carbon steel commonly utilized in the light-weight structural members of building were tested under static shear in order to investigate block shear fracture behavior and curling influence on the ultimate strength and fracture mode. Main variables of specimens are plate thickness and end distance parallel to the direction of loading. Curling in the perpendicular direction of applied force also occurred for bolted connections with a relatively long end distance and thin plate. The curling occurrence caused a sudden strength drop and reduced the ultimate strength of bolted connections. Current design specifications such as AISC, AIJ and AISI for block shear strength were summarized and it is known that design equations did not provide the accurate prediction of ultimate strength and fracture mode for thin-walled carbon steel bolted connections. Strength reduction by curling and the condition of curling occurrence were investigated through an additional parametric finite element analysis. As a result, revised strength equations for block shear fracture and bearing fracture were suggested considering fracture path and curling effect and their validity was also verified.

Effectiveness of Soil–Structure Interaction and Dynamic Characteristics on Cable-Stayed Bridges Subjected to Multiple Support Excitation

Abstract: The purpose of the study is to determine the effects of multiple support excitations (MSE) and soil–structure interaction (SSI) on the dynamic characteristics of cable-stayed bridges founded on pile foundation groups. In the design of these structures, it is important to consider the effects of spatial variability of earthquake ground motions. To do this, the time histories of the ground motions are generated based on the spatially varying ground motion components of incoherence, wave-passage, and site-response. The effects of SSI on the response of a bridge subjected to the MSE are numerically illustrated using a three-dimensional model of Quincy Bayview cable-stayed bridge in the USA. The soil around the pile is linearly elastic, homogeneous isotropic half space represented by dynamic impedance functions based on the Winkler model of soil reaction. Structural responses obtained from the dynamic analysis of the bridge system show the importance of the SSI and the MSE effects on the dynamic responses of cable-stayed bridges.

A Numerical Procedure Accounting for Fluid Drag Forces and Cable Extensibility for the Static Response of Mooring Cables

Abstract: An effective numerical method is proposed for the three-dimensional nonlinear analysis of mooring cables using catenary theory. In this method, the mooring line is divided into finite number of catenary elements. In addition to self-weight, each catenary element is subjected to drag force due to steady ocean currents. The proposed procedure is validated by comparing the results with those of the shooting optimization and the finite element methods. Finally, a parametric study is conducted to study the effect of extensibility on the static response of mooring cables. The effects of fluid drag forces and cable extensibility on mooring cable tension, equilibrium configurations, and stressed lengths are illustrated for two- and three-dimensional mooring cable problems. From the numerical results, the method is found to be numerically stable, and it provides a more rational static response for mooring cables.

In-Plane Stability of Concrete-Filled Steel Tubular Parabolic Truss Arches

Abstract: For determining the in-plane buckling resistance of a concrete-filled steel tubular (CFST) arch, the current technical code GB50923-2013 specifies the use of an equivalent beam-column method which ignores the effect of rise-to-span ratio This may induce a gap between the calculated result and actual stability capacity In this study, a FE model is used to predict the buckling behavior of CFST truss arches subjected to uniformly distributed loads The influence of rise-to-span ratio on the capacity of truss arches is investigated, and it is found that the stability capacity reduces as rise-to-span ratio declines Besides, the calculations of equivalent slenderness ratio for different truss sections are made to consider the effect of shear deformation Moreover, based on FE results, a new design equation is proposed to predict the in-plane strength of CFST parabolic truss arches under uniformly distributed loads