Longitudinal Stiffeners Research Articles

An analytical approach of nonlinear buckling behavior of longitudinally compressed carbon nanotube‐reinforced (CNTR) cylindrical shells with CNTR stiffeners in thermal environment

AbstractNonlinear buckling and postbuckling of longitudinally compressed carbon nanotube‐reinforced (CNTR) cylindrical shells stiffened by longitudinal or circumferential CNTR stiffeners in thermal environments surrounded by elastic medium are presented in the present study. Five linear distributions of CNT are considered for the shell‐stiffener structure system and they are modeled by innovation homogenization technique for CNTR stiffeners. Based on the classical Donnell thin shell theory with von Karman's nonlinearities and the Galerkin procedure, the governing equations can be built to analyze the critical buckling compression and postbuckling compression‐deflection and compression‐shortening behavior. The noticeable effects of volume fraction of CNTs, shell‐foundation interaction stiffnesses, uniformly distributed temperature, and geometric properties of stiffened cylindrical shells on the critical buckling compression and compression‐deflection and compression‐shortening postbuckling behaviors of stiffened CNTR cylindrical shells are obtained and remarked in numerical examinations.

Structural Performance of Thin-Walled Twisted Box-Section Structure

The light weight and high strength-to-mass ratio of thin-walled boxed sections have incited interest in their widespread use in the construction of domes. However, the installation of these sections in forming the dome geometry has induced initial twists and curving features, to which their mechanical response has rarely been explored. Therefore, the structural performance of a structure with thin-walled twisted box sections is numerically studied in this paper, employing ANSYS, the verification of which is carried out through a comparison with experimental results. Additional components examined include the longitudinal stiffening rib, diaphragm, and web. The effects of variations in the thicknesses of these member plates on the mechanical behaviors are investigated. In general, the ultimate capacity of the structure is improved by increasing the thickness of the longitudinal stiffening rib, diaphragm, and web, but the strengthening effect of the stiffener is limited by a certain thickness enhancement. The common failure mode of the initial model is found to be an overall elastic-plastic buckling. A reduction in the thickness of the stiffener or web creates a curving deformation zone in the lower arch at the ultimate capacity, whereas the diaphragm thickness has little effect on the failure mode of the model.

FATIGUE RELIABILITY ASSESSMENT OF WELDED JOINTS OF VERY FAST FERRY ACCOUNTING FOR VEHICLE LOADS

This work deals with the fatigue reliability assessment of a welded joint in a longitudinal stiffener of trapezoidal shape in a very fast ferry. Based on the analysis of wave and cargo induced loads the ship hull structure is evaluated. The local structure is represented by a longitudinal stiffener with a trapezoidal transverse section. The critical hot-spots and the stress distributions are defined by FEM. The fatigue damage assessment of considered hot spots is analysed accounting for the combination of wave induced and car-breaking transient loadings. The formulation for the assessment of the welded steel joint is based on the S-N approach and FORM/SORM techniques are applied to evaluate the reliability against fatigue failure accounting for corrosion deterioration. The structural system composed by several hot spots is evaluated as a series system based on second order reliability bounds.

REINFORCEMENT OF AGEING SHIP STRUCTURES

The objective of the present study is to investigate the possibility to recover the ultimate strength of a rectangular steel plate with a manhole shape opening subjected to a uniaxial compressive load and non-uniform corrosion degradation reinforced by additional stiffeners. Finite element analyses have been carried out to verify the possible design solutions. A total of four finite element models are generated, including 63 sub-structured models. The non-uniform corrosion has been generated by the Monte Carlo simulation. The reinforcement process covers three scenarios that include mounting of two longitudinal stiffeners, two longitudinal and two transverse stiffeners and the flange on the opening. The positioning of the stiffeners has also been studied. A total of 10 cases has been selected and tested for the numerical experiment. Three different assessments have been performed to evaluate the ultimate strength, weight and cost. Two additional studies on the effect of the plate thickness and slenderness have been also carried out.

Experimental Investigation on Concrete Filled Steel Tube Columns under Concentric and Eccentric Loading

Modern construction projects such as skyscrapers, bridge with a large span, residential structures, towers for transmission, warehouses and other industrial structures have all incorporated concrete-filled steel tube (CFST) columns. Fire resistance, excellent ductility and high bearing capacity are all the advantages of CFST columns. Among the different shapes of CFST columns, uses of rectangular and square CFST columns are becoming more favored in modern construction projects for their simple beam-to-column connections design. This study tested 10 concentrically loaded CFST columns and 8 eccentrically loaded CFST columns. One of the most effective techniques to delay local buckling and enhance the ultimate strength of the CFST columns is to use longitudinal inner stiffeners on these steel tubes. Cold-formed steel tube sections are vulnerable due to local buckling; however, a concrete core is able to restrict such early local buckling in the cold-formed steel tube. The test specimens consisted of unstiffened sections and longitudinal inner-stiffened sections. In total, the experimental program tested 18 CFST stub columns with both compact and slender sections, without longitudinal stiffener, with 2 longitudinal inner stiffeners and with 4 longitudinal stiffeners. The test strengths have been as compared with predictions based on the existing design code AISC 360-16 for calculating the ultimate capacities of the CFST stub columns subjected to both concentric and eccentric loading. The focus was mainly on the effect of vertical stiffener square concrete-filled steel tubes on the overall concentric and eccentric compression capacity. The results identified that the longitudinal inner stiffeners had a significant impact on the ultimate strength, deformability and mode of failure in the CFST stub columns. To prevent local buckling of such steel tube, a longitudinal inner stiffener could be applied. In addition, the compression capacity was increased by 12–13.5%.

Abstract 14303: Structural Remodeling in the Left Ventricular Myocardium Underlies Systolic Dysfunction in Myocardial Infarction

Introduction: Myocardial infarction (MI) leads to myofiber death and the formation of a fibrotic scar in the left ventricular free wall (LVFW) myocardium. Acute MI induces remodeling events in the LV consisting of alterations in the architecture and biomechanical properties of the LVFW, collectively leading to LV systolic dysfunction. We implemented a multi-modality pipeline bridging architectural remodeling, LVFW passive behavior adaptation, and ventricular dysfunction in MI. We hypothesize that biomechanical remodeling of the LV serves as an important predictor of clinical outcomes in MI. Methods: MI was induced in rats via the ligation of the LAD artery, and hearts were harvested at five time points: pre-MI, and 1-wk to 4-wk post-MI (n=6 for each time point). Echocardiography and terminal LV catheterization were performed. LVFW specimens were harvested and subjected to biaxial testing, followed by picrosirius red staining. Histological slides were analyzed to quantify fiber architecture. Results: Comparisons for 3-wk MI versus control groups are reported (animal-specific results for representative rats are shown in Fig. 1). Echocardiography imaging showed a decrease in EF (84±5 vs 73±10%; p=0.053) and a decrease in ESV (0.122±0.045 vs 0.31±0.195ml; p=0.013). LV catheterization revealed a decrease in SV (50±0.86 vs 10±0.38μL; p<0.001) and an increase in peak systolic pressure (36.62±0.87 vs 44.91±0.99 mmHg; p<0.001), indicating systolic dysfunction. Biaxial testing revealed longitudinal stiffening of the LVFW at 3-wk post-MI. Scarring and a shift in myofiber orientation towards the longitudinal direction corroborated changes in the LVFW mechanical behavior in the MI group. Conclusions: LV systolic dysfunction in MI is significantly influenced by disruption in myofiber architecture and fiber orientation remodeling in the LVFW. Assessment of LVFW remodeling events provides important incremental information over traditional organ-level indices.

Mechanical behavior assessment of FPSO mid-ship repaired stiffened corroded side panels under combined loading

Hull plating thickness reduction due to corrosion generates a significant decrease in the structure ultimate load capacity, which may compromise the vessel’s integrity. In offshore oil and gas production units demobilization to a shipyard is unfeasible, so reparation must be performed locally and efficiently. This article presents an experimental - numerical investigation to assess the performance of an alternative in situ repair methodology for FPSO mid-ship corroded side panels subjected to common types of loads. The repair technique consists in the inclusion, with a single-pass welding, of an intermediate light longitudinal steel stiffener on the plating exposed to considerable thickness reduction, to reestablish the load carrying capacity, thus extending its operational life. A set of nine mid-ship panels of a VLCC (very large crude carrier) converted into an FPSO (floating production storage and offloading) platform, on a scale of 1:3.5, are fabricated and subjected to uniaxial compression. The panels portray the corrosion free intact condition, two levels of thickness reduction (25% and two with 58%) and two repair light stiffener profile dimensions for each level of thickness loss. A finite element model (FEM) is developed and firstly employed to compare and validate the experimental results for uniaxial compression. The FEM is subsequently employed to evaluate other typical loading combinations encountered in hull structures, including lateral pressure, uniaxial compression and shear stresses. The results show that the inclusion of an intermediate light longitudinal steel stiffener may satisfactorily restore the plate and consequently the panel load carrying capacity, allowing additional hull plating thickness reduction.

Generalized Beam Theory deformation modes for steel–concrete composite bridge decks including shear connection flexibility

This paper proposes a procedure to calculate cross-section deformation modes for steel–concrete composite bridge cross-sections, including shear connection flexibility, within the framework of the Generalized Beam Theory (GBT). The proposed procedure is computationally efficient and makes it possible to (i) handle arbitrary (flat-walled) composite cross-sections, including complex configurations with several closed cells, (ii) consider the geometric offset between the steel and concrete mid-lines, which is essential in steel–concrete composite members, and (iii) automatically identify, separate, and hierarchize the deformation modes into physically meaningful sets, including a set of shear connection slip deformation modes. For illustrative purposes, the various deformation mode sets are determined for two representative cross-sections, namely a twin-girder and a box-girder with closed longitudinal stiffeners. These deformation modes are then employed to perform the structural analysis of simply supported decks, showing that very accurate results are obtained with a small number of deformation modes and that the modal decomposition of the solution provides in-depth insight regarding the bridge structural behavior.

Local buckling behaviour and capacities of Cold-Formed Steel Double-I-Box stub and short column sections

This paper presents an experimental and numerical investigation on the local buckling behaviour of a new built-up Cold-Formed Steel (CFS) homogeneous and hybrid Double-I-Box Column sections (DIBCs and HDIBCs) under axial compression. In total, 24 experimental tests are conducted, out of those 12 tests are on stub columns and the remaining 12 are on short columns. The parameters considered are hybrid ratio (Φh), section’s breadth to depth ratio (B/D) and column height (H). The columns considered in this study are having an overall slenderness (λ) less than 0.20, and the flange plate slenderness (λpf) less than 1.85. Test specimens failed in either of the following three failure modes: local buckling, yielding or by the interaction of both. In all the tested specimens, typical Bottom Zone Local Buckling (BZLB) similar to the shape of Elephant’s Foot is identified. The deformation shape is recognized by expansion (outward buckling) along the major axis and contraction (inward buckling) along the minor axis at the bottom 1/4th height of the columns in opposite faces, followed by the collapse. This kind of failure mode is a clear representation of Poisson’s ratio effect at the ends causing a restraint which then creates a local imperfection under load which leads to a localized failure at bottom zones in the stub and short columns of DIBCs and HDIBCs. BZLB phenomenon is enhanced because of the tubular cross-section geometry, boundary conditions plate element slenderness, overall slenderness of these built-up sections. The ultimate capacities of both the stub and short columns are governed by their strength limits and slenderness. Nonlinear Finite Element Analysis (FEA) is performed on experimental FE models using ABAQUS software and verified against the test results and validated with the actual structural behaviour. Further FEA is performed on 96 ideal parametric FE models considering different material properties and slenderness values. Effect of the intermediate longitudinal stiffener and the influence of edge constraints on axial strengths are also reported. The axial strengths obtained from the experimental tests and FE parametric studies are compared with the predicted results using the Effective Width Method (EWM) as suggested in the Eurocode specifications to access the feasibility of the current design rules, which is found to produce reasonable predictions albeit slightly conservative. It is found that for stub columns with λ<0.1, the experimental values are found to be 1.25 times higher than the predicted values. It is also observed that for columns having λ≥0.1<0.2 with λpf>1.2 there is a reduction in local buckling resistance of around 2.5% for each increase of λpf by 10%. Hence, it is concluded that the concentric axial compression capacities of DIBCs and HDIBCs subjected to local buckling can be computed as the arithmetic summation of effective strengths of individual channel sections calculated by using the EWM design equations, as recommended in this study. The attained results prove that these sections have a considerable local inelastic reserve strength as specified in North American standards.

Patch load resistance of longitudinally stiffened steel plate girders: A parametric study

AbstractIn this paper, an in‐depth nonlinear finite element analysis is carried out on longitudinally unstiffened and stiffened welded I‐steel plate girders subjected to patch loading. The most realistic load case is during the incremental launching of multi‐span steel and composite bridges over temporary or permanent supports. Bridge plate girders are usually reinforced by longitudinal and transverse stiffeners in order to prevent web panel buckling and to increase the bending and shear strength. The current European design standard EN 1993‐1‐5 also requires a stability control check for concentrated transverse forces (patch loading) since it can be a decisive design criterion. By using longitudinal stiffeners for flexural and shear resistance, the patch loading carrying capacity can be increased as well. Previous experimental studies showed that the EN1993‐1‐5 patch loading resistance model significantly underestimates the ultimate strength of longitudinally stiffened plate girders. The paper is primarily dealing with numerical research of the post‐buckling behavior and ultimate strength of longitudinally stiffened I‐steel plate girders reinforced by one longitudinal stiffener. The main objective of the present work is to investigate the influence of different geometrical parameters, including patch load length, web panel aspect ratio, and initial geometrical imperfections, on the ultimate strength of longitudinally stiffened plate girders. We showed in this study that for all the considered initial geometrical imperfections, the patch load resistance increases as the patch load length is increased. The lowest ultimate strength of longitudinally stiffened plate girders was determined for initial geometrical imperfections that resembled the deformed shape at collapse (collapse‐affine imperfections). The web panel aspect ratio also influenced the patch load resistance and lower ultimate strengths were returned for bigger web panel aspect ratios. Finally, further research recommendations are presented.

Design of stiffened plates subjected to axial compression and transverse load

AbstractStiffened plates (orthotropic plates) are used in many structures, for instance as plate girders and box girders in bridges, in ship hulls, and in bridge decks to minimize the dead load. Used as flanges or part of flanges in larger cross‐sections, stiffened plates develop membrane compression or tension, and in some cases in‐plane shear due to bending or axial actions on the cross‐section. The strength analysis of an orthotropic bridge deck has to take into account both buckling of the stiffened plate as a unit, local buckling of subpanels of the deck plate or the stiffeners, stiffener instability, and effects of transverse loading (e.g. dead load plus traffic load) on the stiffened plate.Adequate rules to determine the capacity of stiffened plates subjected to the combination of axial force and transverse load, as in bridge decks, are scarce or non‐existing in the present Eurocodes for design of stiffened plates and should be developed. An approach applying detailed FE‐analyses will often not be feasible in practical design due to an often weak correlation between the various loads, e.g. dead load, traffic load and loading in horizontal direction (wind), a large number of loading patterns for moving loads, different load combinations and loading levels in adjacent spans, as well as many different cross sections along the bridge.As a pre‐study of the mentioned load combination of axial force and transverse loading it have been simulated a stiffened plate (4 by 5 meter) motivated by the orthotropic deck of a bridge box girder for a suspension bridge. The axial stress was varied from 0 N/mm2 to 250 N/mm2 and combined with application of transverse loading until the stiffened plate collapsed in a flexural buckling mode. The capacity was determined following the provisions in Eurocodes prEN 1993‐1‐1, EN 1993‐1‐5, EN 1993‐1‐7 and the offshore standard DNV‐RP‐C201.It is evident that the modeled typical bridge deck, which is much wider than it is long and has large longitudinal stiffeners, behaves like a beam‐column between the supports. Even if the modeled stiffened plate is made almost quadratic, column‐like behavior prevails, and plate‐like behavior can be neglected.Capacity checks of a stiffened bridge deck, considering a strip of the deck comprising plate and one belonging stiffener, involve a highly mono‐symmetric cross‐section. Capacity should consider yielding both at the plate side and at the stiffener side. The DNV standard does this, and capacity determined from its equations agrees quite well with the FE‐simulations. The design provisions in the new prEN 1993‐1‐1 (Appendix C), which refer to its ordinary beam‐column formulas, must be modified to account for yielding at both sides of the stiffened deck to produce accurate results over the entire range of axial compression and transverse load. When modified, capacity predictions are on the safe side, yielding capacity approximately 70 % of the FE‐predictions.

Buckling problems of patch loaded plates with and without stiffeners – analytical approach

AbstractGeneralized analytical approach, with exact stress solutions, to buckling problems of in‐plane loaded plate with and without stiffeners has been presented through the case of locally distributed direct stresses. Several mathematical models have been chosen to represent high webs of steel girders under the patch load. Initially, the basic model has been built to simulate a girder used in the experimental research where the external load is equilibrated by support reactions. The second, more complex model included shear stresses along vertical stiffeners with a task to equilibrate the external loads, simulating a single web segment between the stiffeners of a long girder. The upgrade of the second model by adding a longitudinal stiffener resulted in the third model. Considering the complexity of stress distributions within the plate under such a demanding load, an analytical model for these problems has not been presented earlier. For the first time the influence of flexural stiffeners' rigidity on the plate buckling has been analysed with the exact solutions for in‐plane stress distributions, for simply supported plate. Results confirm the high quality of the analytical solution for the first and the second model and speak in favour of this approach and its potential for further upgrading in the case of the third model.

A proposal for the local stresses in retrofitted crane runway girders due to eccentric wheel loading

AbstractGenerally, the local stresses near the web‐flange connection represent one of the most decisive criteria for the fatigue design of steel crane runway girders, particularly because every crane wheel induces an individual stress cycle and fatigue failure can potentially occur at any position of the girder's length. This paper presents a crane runway girder made of steel that has been retrofitted in the past to reduce the local bending stresses in the web, because of the installation of a new, heavier crane. This was done by additional longitudinal stiffeners to form a boxed upper flange. The local vertical stresses in the girder's web are investigated numerically and experimentally and the influence of the subsequently attached reinforcement plates, forming a boxed upper flange, is studied. Traditionally, it is state of the art to neglect any local bending stresses in the web after retrofitting the upper flange area to get a local box section. The results presented in this paper indicate that the additional local bending stresses within the upper flange box section can be significant and should not be neglected for fatigue design. Therefore, a new design concept for the calculation of the local bending stresses in webs of retrofitted crane runway girders with new boxed upper flange is proposed.

Study on axial compression behavior of rectangular concrete filled steel tubular columns with Perfobond Leister Ribs

The built-in open-hole type stiffened rectangular steel tube concrete refers to a new combined structure formed by forming an open-hole steel plate in the longitudinal direction of the inner wall of the steel pipe and then filling the concrete. The PBL stiffener has the double functions of longitudinal stiffener and shear connector. In order to study the influence of stiffeners on the ultimate bearing capacity of rectangular CFST columns, the finite element model was established by ABAQUS and the parameters of the stiffeners were analyzed, including the aperture of the stiffeners, the spacing of the stiffeners and the width-thickness ratio. The results show that the finite element model established in this paper is in good agreement with the existing test data. The bearing capacity of rectangular CFST columns increases first and then decreases with the increase of the opening aperture of stiffeners, increases with the increase of the opening spacing, and increases with the decrease of the width to thickness ratio of stiffeners. The conclusions of this paper can provide some suggestions for the design of PBL stiffened rectangular CFST columns in practical engineering.

Deflection analysis of uniform cross-section hollow rectangular cantilever beam with transverse stiffeners under UDL and concentrated load

Offshore, bridges, steel structures, and heavy-duty equipment all use hollow cantilever beams. The great challenge for design engineers is to provide a better robust design of a cantilever beam that can withstand applied load with optimized design parameters. According to the literature review, strengthening a beam or plate can be accomplished by providing transversal and/or longitudinal stiffeners that can withstand post-buckling and lateral buckling moments. Thus, it is not sufficient for designers to provide only a better design of a part or component with the minimum weight and cost while ensuring optimum reliability and keeping the design secure in all loading conditions. The behavior of beam strength is influenced by various factors such as the number of stiffeners, their location, and their dimensional properties. In the present research, the slope and deflection equations of a uniform cross-sectional hollow rectangular cantilever beam with stiffeners subjected to concentrated and uniformly distributed load (UDL) and their combination are derived using Mohr’s Moment area method. Finite Element Analysis (FEA) was used to validate the results under known load and boundary conditions. The results demonstrate that the mathematical formulation can assist the design engineer in predicting the deflection of a cantilever beam under known loading and boundary conditions.

Long-term fatigue reliability enhancement of horizontal axis wind turbine blade

The enhancement of fatigue life of ultra-large horizontal axis wind turbine blade using longitudinal stiffening is the theme of this work. For this purpose, a tendon made of shape memory alloy is used along the longitudinal axis of blade, which is modelled in aeroelastic spinning finite element framework. The force developed in the tendon acts against the deformation where the material is modelled using Liang and Rogers constitutive relationship along with the principles of thermodynamics. The fatigue design follows the guidelines provided in internationally recognised codal provisions. The blade responses are simulated using aeroelastic loads obtained from blade element momentum theory. These dynamic responses are utilised to evaluate the longitudinal stress in the extreme fibre over the blade profile. Then, short-term and long-term damages are evaluated using rainflow matrix obtained from these stresses. Finally, the reliability of blade against fatigue failure is investigated. The numerical analysis presented in this study clearly demonstrates the performance of the longitudinal stiffening in combination with pitch angle on the fatigue life of the blade.

The direct strength method for combined bending and web crippling of second-generation trapezoidal steel sheeting

Second-generation trapezoidal sheeting, characterised by longitudinal stiffeners in webs and flanges, is loaded near a support by a concentrated force and a bending moment. Currently, design codes predict related failure by: (a) determining the ultimate bending moment via the effective width approach or the Direct Strength Method (DSM); (b) finding the web crippling load via a curve-fitted formula; and (c) using an interaction rule to take into account the load combination. However, the effective width approach is quite complex to use for many longitudinal stiffeners, and the accuracy of the design codes is subject to improvement. Moreover, nowadays the DSM provides a consistent and well-established method to predict ultimate loads for cold-formed steel structures. Therefore, in this paper the application of the DSM for combined bending and web crippling of second-generation sheeting is investigated. First, to create a set of numerical experiments, an internationally representative set of second-generation trapezoidal sheeting types is found, and these types are used to design numerical three-point bending experiments with relevant span lengths and load bearing plate widths. Then, finite element models are developed and verified, and used to predict the buckling, yield, and ultimate loads for the set of numerical experiments. Additionally, all simulations are also carried out for pure bending, and (Interior One Flange) IOF and (Interior Two Flange) ITF web crippling cases. With the resulting data, an explicit DSM approach is developed, fitted to the data of the three-point bending simulations, which predicts the ultimate load for combined actions directly. Hereafter, also an interaction DSM approach is studied, which first predicts the ultimate bending moment by the DSM (by fitting the pure bending simulations), then the web crippling load by the DSM (by fitting either the IOF or ITF simulations), and then uses a classic interaction rule for the load combination. The explicit and implicit DSM approaches perform equally well, with a Coefficient of Variation (CoV) equal to 0.13. As most commercially available sheeting has been incorporated, and the DSM approaches allow for sections with an arbitrarily number of stiffeners in the web (different from the current design codes), it is recommended to include the DSM in future code revisions. The interaction DSM approach resembles the current design rules most and may therefore be preferred; however, the explicit approach is more direct and certainly deserves consideration too.

Buckling of compressed plates with closed-section longitudinal stiffeners: Two new mathematical models for resistance prediction

Longitudinally stiffened plates appear in many structural engineering applications. One of the typical failure modes is induced by the buckling of the stiffeners, therefore enhancing our understanding of buckling behavior is of crucial importance. Recently, buckling resistance of longitudinally stiffened plates with trapezoid stiffeners has been investigated by numerous research projects. A large amount of capacity prediction data is available for stiffened plates with diverse geometries, obtained by advanced shell finite element analyses. In the research reported in this paper such data have been collected from two recent researches. Two mathematical models have been worked out for calculation of the load-bearing capacity, by curve fitting technique. The first developed method is similar to the Direct Strength Method: a single reduction factor is applied on the gross cross-section resistance in order to get the buckling resistance, and the reduction factor is calculated by one single Winter-type formula. The second method is based on the Effective Width Method, but for the middle part of the stiffened plate a further reduction factor is applied, which reduction factor is obtained from one single Ayrton-Perry-type formula. Though the two mathematical models show some differences in certain cases, they give very similar results, both leading to satisfactorily precise resistance values. The mathematical models have been applied to study buckling behavior, in order to understand how the plate geometry influences the resistance. The proposed mathematical models are potentially applicable in design calculations.

Tests of cold-formed steel built-up open section members under eccentric compressive load

An experimental study was performed on cold-formed steel built-up open section members under eccentric compressive load. The specimens with member lengths varied from 300 to 1500 mm were manufactured by composing two identical channels using self-tapping screws. The channels with longitudinal stiffeners were fabricated from the steel grades G500 and G550 zinc-coated sheets with nominal 0.2% proof stresses of 500 and 550 MPa, respectively. A total of thirty-three combined minor axis bending and compression tests were carried out under pin-ended supports to explore the buckling behaviour of the newly designed built-up section members. Six test series with a relatively wide range of axial load-to-moment ratio were included in this study to examine the interaction relationship of the built-up section beam-columns. The test loading capacities, full-history responses and failure modes were obtained for all the test specimens. Since the novel built-up open sections are not covered in the current cold-formed steel design standards, the comparisons of experimental loading capacities with nominal strengths predicted by the North American Specification, Australian/New Zealand Standard, European Code and American Specification were conducted to assess the appropriateness of the existing design rules. The applicability of axial load-moment interactive formulae specified in the aforementioned design standards with the nominal pure compressive resistance and nominal pure bending resistance determined by direct strength method was evaluated for the built-up section beam-columns. It is found that the axial load-moment interactive formulae generally underestimate the strengths of the cold-formed steel built-up open section beam-columns.

Design Criteria for Scantling of Longitudinal and Transverse Connections in the Torsion Box Under Fatigue Loading

Abstract Fatigue is one of the main failure modes in marine structures, and it is caused by the strong cyclic characteristics of the loads they support. This failure mode is amplified in areas of high stress concentration, such as at the intersection of primary and secondary elements. In this paper, a two-phase study is proposed that compares numerical and experimental results using a digital image correlation technique. The described procedure establishes selection, design, and scantling criteria and provides recommendations for the design of the transverse structure using specimens with different geometries. These geometries correspond to different designs for the transverse primary structure that use a longitudinal secondary stiffener with variable thickness and longitudinal spacing to transverse in a dynamic and quasi-static regime. The stress state for this regime is calculated based on the biaxiality indication concept, which uses the fatigue phenomenon (safety factor and sensitivity curves) and fracture mechanics (parameters of the Paris crack propagation law, correlation value, and law of variation of the stress intensity factor).