Vertical Stiffeners Research Articles

Fatigue life research of welded joints in railway girder

Progressive crack formation in welded joints of railway girders requires a reliable prediction of the fatigue life. It was found that the most common fatigue cracks are T-9 and T-10, which are formed in welded joints of vertical stiffeners to the beam web. The service life calculation of such joints, according to guideline, shows overestimated results. To reduce the error, the operational features of these joints were investigated under a moving loads. Stress-strain monitoring was carried out with the help of a small-sized automated tensometric complex «Tensor-MS». In total, 13 trussed and solid-web girders were investigated. As a result, it was found that the beam web near the welded ends of stiffeners subjected to bending deformations, but fatigue curves, obtained under tensile-compressive, are used to calculate the durability of such joints. To increase the reliability of fatigue calculation, laboratory tests were carried out for a high-cycle fatigue of welded specimens, simulating joints with T-9, T-10 cracks. The design and materials of laboratory specimens were assigned similarly to that of the main beams or the floor beams. Analysis of the actual stresses under the moving load revealed the necessary loading conditions for laboratory specimens. Totally, 42 laboratory samples were tested for bending. As a result of the tests, fatigue curves of welded joints were obtained. The results show a decrease in the joints durability by 20–50 % in comparison with the samples tested in tensile-compressive. In addition, as a result of the tests, the dependences of the fatigue cracks growth rate on the maximum cycle stresses were obtained.

Finite element study of the stiffening effects on torsional capacity of perforated stainless steel slender semi-elliptical hollow section members

A finite element study was carried out to investigate the effects of stiffened perforation on the torsional capacity of perforated slender lean duplex stainless steel semi-elliptical hollow section members. Four different stiffener arrangements viz. horizontal, vertical, square frame and ring, were considered for single circular perforation on flat element of the member. Effects of their geometric parameters i.e. width, thickness, anchorage length etc. on single circular perforated member torsional capacity were studied. Of the geometric parameters investigated, stiffener thickness was observed to provide considerable stiffening effect on the torsional capacity. For members with perforation on the curve element, horizontal and ring stiffeners were considered. Horizontal and vertical stiffener could only provide partial recovery, even at higher stiffener thickness. On the other hand, full recovery of torsional capacity was found to achieve with ring and square frame stiffeners with thickness higher than six times the member thickness.

An alternative detail for continuity plates in steel beam to box-column moment-connections

ABSTRACT In this study, the use of an internal vertical stiffener in built-up box-columns parallel to the beam web, which turns the column section into a boxed I-section in the connection region to eliminate the common continuity plates, is assessed through an experimental and numerical study. For this purpose, two full-scale exterior I-beam to box-column moment connections (one with common continuity plates and the other one with a vertical stiffener as an alternative detail) are tested under reversed cyclic loading. The test results in terms of hysteresis moment-rotation curves, strain in critical stations, and observations during the tests indicate that the connection with the vertical stiffener could survive story drifts of up to 4% without any strength loss and brittle failure such as weld fracture. For further investigation of the seismic performance of the proposed detail, Finite Element Modeling (FEM) of the test specimens is also conducted in the FE software ABAQUS and validated using the test results. The results of the numerical study also confirm the satisfactory behavior of the connections with the proposed detail.

Failure modes of end-plate connections with outer flange stiffeners: an experimental and numerical study

This paper presents the experimental and numerical results of six full-scale beam-to-column connections with bolted end plates in two groups. The effects of vertical and horizontal stiffeners on the static behaviour of the semi-rigid beam-to-column bolted connections were investigated. In addition, the aim of this research was to analyse the influence of end-plate connections that utilize the IPE profile with stiffeners welded on the behaviour of steel connections, to provide the necessary data for improving Eurocode 3, efficient use of residue IPE profiles and back to the consumption cycle. Furthermore, finite-element and experimental models of semi-rigid vertical and horizontal stiffened bolted connections were tested and compared. The main parameters observed are the evolution of the resistance, the stiffness, the rotation capacity, the ductility of a joint, failure mode and the energy dissipation.

Theoretical and numerical analysis and design of stiffened steel plate shear walls having unequal subpanels

SummaryFollowing the adequate seismic behavior, the steel plate shear walls have gained popularity among the designers worldwide, and many buildings have been designed employing such walls as their lateral load‐carrying system. Despite the fact that the steel shear walls using unstiffened thin plates outnumber the ones benefitting from stiffeners, it should be kept in mind that application of stiffeners prevents the buckling induced by lateral loads such earthquake or wind. On the other hand, the stiffeners enhance the stiffness and shear strength of the plate. Accordingly, this paper deals with an analytical and numerical investigation into the steel plates stiffened by unequaled vertical and horizontal stiffeners. The results obtained for the analyses led to the development of the analytical relations to compute the shear strength, stiffness, and displacement. To validate the proposed relations, analytical outputs were compared with those obtained from the numerical investigation indicating great accuracy of the proposed analytical relations. Moreover, in this paper, the design process of the stiffened steel plate shear walls has been presented based on the interaction between the plate and frame. The results indicate the addition of stiffeners to the steel plate, improves its shear strength by 6 to 15%.

A comparison of structural performance enhancement of horizontally and vertically stiffened tubular steel wind turbine towers

Stiffeners can be utilised to enhance the strength of thin-walled wind turbine towers in engineering practise, thus, structural performance of wind turbine towers by means of different stiffening schemes should be compared to explore the optimal structural enhancement method. In this paper two alternative stiffening methods, employing horizontal or vertical stiffeners, for steel tubular wind turbine towers have been studied. In particular, two groups of three wind turbine towers of 50m, 150m and 250m in height, stiffened by horizontal rings and vertical strips respectively, were analysed by using FEM software of ABAQUS. For each height level tower, the mass of the stiffening rings is equal to that of vertical stiffeners each other. The maximum von Mises stresses and horizontal sways of these towers with vertical stiffeners is compared with the corresponding ring-stiffened towers. A linear buckling analysis is conducted to study the buckling modes and critical buckling loads of the three height levels of tower. The buckling modes and eigenvalues of the 50m, 150m and 250m vertically stiffened towers were also compared with those of the horizontally stiffened towers. The numbers and central angles of the vertical stiffeners are considered as design variables to study the effect of vertical stiffeners on the structural performance of wind turbine towers. Following an extensive parametric study, these strengthening techniques were compared with each other and it is obtained that the use of vertical stiffeners is a more efficient approach to enhance the stability and strength of intermediate and high towers than the use of horizontal rings.

Stress Analysis of the Circular Pier Anti-collision Box Made of Sandwich Plate with Stiffening Rib

The pier anti-collision box made of steel-polyurethane sandwich plate with stiffening ribs can withstand greater impact force. In order to ascertain the influence of stiffening ribs to anti-collision box, the static equivalent method is adopted to numerically calculate the stress and impact depth of the anti-collision box in the conditions of no stiffening rib and the different forms and amount of stiffening ribs. The results show that it can reduce the stress and deformation of anti-collision box to set vertical or horizontal stiffening rib separately, and the effect of the former is much better than the latter, but the decrease degree of vertical stress is different from horizontal stress. The stiffening rib in the box should not be too many; especially horizontal rib and vertical rib should be considered mainly. The anti-collision box with horizontal rib and vertical rib is mainly to reduce collision deformation; however, it can reduce little than the box with only vertical rib in the aspect of stress.

Analytical study on local stress of the weld of vertical stiffener on orthotropic steel bridge

Analytical study on local stress of the weld of vertical stiffener on orthotropic steel bridge

Internal Force Transfer Mechanism and Bearing Capacity of Vertical Stiffener Joints in CFDST Structures

This paper firstly studied the internal force transfer mechanism of vertical stiffener joints in concrete-filled double steel tubular (CFDST) frame structures on the basis of finite element modeling (FEM). Analytical models of shear force and bending moment were established through the appropriate material constitutive equations and equilibrium theory. Then, the proposed models were used to predict and evaluate the shear and bending resistance of the vertical stiffener joint. Six joint specimens were tested to verify the rationality of the theoretical models, and the design suggestions for construction were subsequently discussed. The analysis indicated that the vertical stiffener together with the anchorage web played a dominated role in the internal force transfer mechanism. The computed bending resistance obtained by the tension model agreed well with the measured experimental data, and the shear resistance in the panel zone was sufficient to guarantee the ductile failure in the test. The vertical stiffener determined the plastic hinge so as to ensure the strong connection between the CFDST column and the steel beam. The ribbed anchorage web was an effective way of increasing the shear and bending resistance.

An experimental and numerical investigation of reduced beam section connections with horizontal and vertical web stiffeners

Following the 1994 Northridge earthquake, reduced beam section (RBS) was presented as a novel connection detail in the steel moment-resisting frames. Proposed detail aims to debilitate the beam at a limited interval from the connection so that less moment and force are assigned to the connection. Cutting of the beam flange, especially in the narrow sections such as IPE, leads to an increase in the potential for the web local buckling, beam lateral-torsional buckling, and reduction in the beam strength. The hysteresis curve of IPE profiles, particularly in medium and large sections, is highly declining after the buckling. In this paper, a simple method was presented to amend the efficiency of IPE beams with an arched cutting in the flange, using horizontal and vertical stiffeners of the beam web. The experimental results and those of finite element in IPE beams revealed that the simultaneous application of horizontal and vertical stiffeners of the beam web largely prevented the declining of the beam hysteresis curve and left a full effect on its behavior. Therefore, the use of these types of connections in seismic areas with high relative risks is recommended.

Capacity of short circular CFST columns with inner vertical plates welded intermittently

This paper deals with the strength and deformation characteristics of short circular Concrete-filled Steel Tube (CFST) stiffened columns. The intermittently welded vertical stiffener plates are used to strengthen the steel tubes. Plates are attached to the inner surface of the tube by welding it from outside through the predrilled holes in the tube. The stiffener plates improve the bonding between the steel tube and the concrete and also enhance the confinement in the concrete. The variables of the experimental study are spacing of the weld between the stiffener plate and the circular tube and number of vertical stiffener plates. The weld spacing of 10t, 15t, 25t, 35t and 50t, where t is the tube thickness and 3, 4 and 5 numbers of vertical stiffener plates are used in this study. The number of specimens cast and tested in this study is 29. The test results indicate that the strength and deformation of the circular CFST column are significantly influenced by the intermittently welded stiffener plates. The ultimate axial load-carrying capacity of the CFST columns is found to increase by 26% when the spacing of weld is reduced to 10t from 50t. A strength prediction model is developed for the CFST columns which are intermittently welded stiffeners. The prediction is found to be in good conformity with the corresponding test data.

Experimental cyclic behavior of connection to double-skin composite wall with truss connector

Double-skin composite walls have been increasingly applied in high-rise buildings. The behavior of connection to the wall under seismic action is essential to the performance of the whole structures. This paper investigated the experimental seismic behavior of four proposed connections to an innovative double-skin composite wall. The wall employs steel trusses as internal connectors. Large-scaled cyclic tests were performed on connections with different configurations. The seismic behavior was evaluated in terms of failure mode, hysteretic response, stiffness degradation, ductility, and energy dissipation ability. The test results found that all specimens exhibited stable and plentiful hysteretic performance without noticeable pinching effect. Reasonable stiffness degradation, good ductility and satisfying energy absorbing capacity were also observed. Strain distributions at key locations were analyzed to evaluate the strain development at beam, stiffener, and wall face. It is concluded that the connection with vertical stiffeners has good seismic behavior. The application of vertical plate or additional cover plate is also acceptable. In addition, the use of through plate should be careful as the welding quality is important to the behavior of connections.

The impact of local geometry on the fatigue life of a welded structural detail

ABSTRACTFatigue often limits the capacity of welded steel bridges, and thus often governs the amount of steel required. The fatigue life is, to a large extent, governed by stress concentrations and the magnitude is controlled by local as well as global geometry; by improving the local geometry the stress raising effects can be lowered and by increasing the global dimensions the nominal stress can be reduced. The fatigue assessment format presented in the Eurocode gives little or no room for the designer to control the local geometry of the structural detail, and is often left with increasing the overall dimensions in order to improve the fatigue life of the structure. This paper aims at investigating the possible impact on the fatigue life of welded steel structures by different weld geometries. In this paper a vertical stiffener will be studied by fracture mechanics. The study showed that significant improvements in fatigue life can be made by small changes to the weld geometry and the most pronounced effect was by changing the weld toe radius, and for the case studied at least one higher detail category could be assigned to the vertical stiffener.

Numerical simulation of distortion-induced fatigue crack growth using extended finite element method

Aiming to investigate the propagation behaviour of distortion-induced fatigue cracks in steel bridge web gaps, multi-scale numerical analysis models were built based on fracture mechanics theory and extended finite element method (XFEM), combining with the full-scale fatigue tests data. Propagation behaviours of representative fatigue cracks in vertical stiffener web gaps and horizontal gusset plate web gaps were analysed. Finite element models of welds connecting web, vertical stiffener and horizontal gusset plate were built, and the welding residual stresses of such details were analysed. Significant transverse welding residual tensile stresses exist at stiffener web weld toes for web gap details. Residual stress measurements were conducted, and the crack shape and the propagation direction path were basically the same with that in the numerical simulation, indicating that the numerical simulation results were relatively reliable. Furthermore, the welding residual stress fields were considered in the crack propagation analysis models. Representative fatigue cracks at web gaps are Mode I leading mixed-mode cracks of Modes I, II and III. Crack propagation considering welding residual stress has faster propagation rate and is more consistent with fatigue test results. The welding residual stress cannot be ignored for analysis and assessment of distortion-induced fatigue cracks in steel bridges.

Some aspects of vertical cylindrical shells’ calculation at the unsymmetrical load

The paper deals with the influence of the harmonica’s parameters of the unsymmetrical load, which is represented by trigonometric cosine-series. The analysis is based on the results of practical calculations of the silo capacities’ constructions by using the moment theory on the influence of the changeable wind load. The model of the silos construction is schematized in the form of orthotropic cylindrical shell of revolution with different thickness of the wall in meridional and circular directions, which allow approximately, considering the existence of vertical stiffeners.

Experimental study on the seismic behaviour of composite shear walls with stiffened steel plates and infilled concrete

A new type of composite shear wall, composed of dual steel plates, vertical stiffening steel plates to connect the dual plates and concrete infilled in the vertical channels formed by these steel plates, is proposed. Fifteen specimens were tested under horizontal cyclic loads, along with a constant vertical axial force, to investigate their seismic behaviour. Specimen failure mainly included three modes: severe local buckling at the corners of the flange plates and boundary channels, damage of the concrete occurring in the middle and bottom of the shear wall and local buckling waves originating at the middle of the specimen. All the specimens exhibited a good deformation capacity: the ultimate drift ratios of the specimens reached an average value of 4.55%, and the ductility has an average value of 4.0. The test results indicated that the thickness of the shear wall and the number of channels in the shear wall have a significant effect on the ductility of the specimens. However, changing the number of channels in the walls has a negligible effect on the shear strength of the wall. Formulas to predict the maximum shear strength and initial stiffness of the shear wall are proposed, and it is verified that they can provide a satisfactory prediction for most specimens, with an error within 10%.

Compression loading test for concrete-filled tubular columns with high-strength steel slender section

An experimental study was performed on thin-walled concrete-filled steel tubular (CFT) columns. In practical applications of CFT columns, the use of high-strength steel non-compact or slender section is expected to grow because thin plates are advantageous in steel production and economy. Thus, the present study focused on evaluation of the axial load-carrying capacity of rectangular CFT columns with high-strength steel (grade 800) slender section. The test parameters were the yield strength of steel, the width-to-thickness ratio of steel plates, and the use of stiffeners. Five specimens were tested under monotonic axial-compression loading. Although elastic local buckling occurred in the high-strength steel slender sections, unlike the expectation, the specimens exhibited significant post-buckling reserve strength, exceeding design code predictions. The specimens strengthened with vertical stiffeners showed enhanced performance, attaining the plastic capacity of the composite section. To investigate the characteristic behaviors such as steel local bucking and concrete confinement, nonlinear finite element analysis was performed on the specimens. The experimental and numerical results showed that the steel peak stress is affected by the lateral expansion of the crushed concrete, and the peak stress of the high-strength concrete is generally lower than the cylinder strength. On the basis of the results, a modified fiber analysis model and a simplified strength equation were proposed.

Design and optimization of fixture structure with stiffeners for large-scale battery stacks

To reduce the internal resistance of battery cells or electrolyte leakage, stacked type battery packs are typically assembled and are tightly compressed by fixture structures such as endplates. Endplates must have enough rigidity to uniformly compress a battery stack, especially for large-formatted battery stacks. The present study proposes a computational approach to analyze and predict the bending deformation of endplates of stacked type battery packs. Computational result agrees well with the actual measurement of bending deformation in a flow battery stack. Analyzing the stress distribution of endplates, nine stiffener models are considered to minimize the bending deformation by reinforcing the endplates. It is found that the endplate with three vertical stiffeners is the most effective design. Additionally, response surface method (RSM) is conducted to find the optimal value of design parameters for the stiffeners.

New Fused Steel-Coupling Beam with Optimized Shear Panel Damper

This paper summarizes the development of a new replaceable horizontally steel arc-cut damper (HACD) designed as a fuse element in steel-coupling beams for earthquake protection of reinforced concrete shear walls with openings. The HACD is fabricated from a steel arc-cut plate and restraining plates positioned by vertical steel stiffeners. The proposed damper is an in situ, weld-free energy dissipater device, which eliminates the on-site installation difficulties. The seismic induced energy is dissipated through shear yielding of the arc-cut plate when the device is subjected to inelastic cyclic deformation. The optimized shape of HACD with adequate ductility and dissipation energy capacity is obtained using finite-element analysis. The result of numerical analysis under pseudo-dynamic displacements indicates its suitable energy dissipation, stable hysteric response, and remarkable ductility through shear yielding of the arc-cut shear plate. The performance of the numerical approach is justified through the analysis of tested dissipative device available in the literature.

Shear behavior of steel I-girder with stiffened corrugated web, Part I: Experimental study

The shear stability of steel webs near the support section for long-span composite girders with corrugated steel webs is one of the main control factors for structural safety, which should be paid special attention to. Generally, concrete is poured on the inner side of corrugated steel webs to improve its shear stability, but encased concrete increases the weight of the girder, raises the difficulty of the construction process, and reduces the efficiency of the prestressing application. This paper proposes a new type of stiffened corrugated steel webs at the support area by adopting vertical or/and horizontal stiffeners instead of encased concrete. In order to explore the shear performance of proposed stiffened corrugated steel webs, experimental and numerical investigations were carried out in the present paper and the companion paper [1], respectively. Four steel I-girders with corrugated webs considering different stiffener arrangements were designed and tested under shear loading. The failure modes, shear strength and stiffness, strain distributions were obtained and analyzed in detail. The test results show that all specimens failed due to interactive shear buckling of corrugated steel web; shear buckling occurred between horizontal stiffeners and bottom flange for horizontal stiffened corrugated steel webs, but extended to the entire height for vertical stiffened corrugated steel webs, the stiffeners distorted associated with the deformation of corrugated steel web. Shear strength of corrugated steel webs can be improved by vertical and horizontal stiffeners. The vertical stiffeners do not affect the “accordion effect” of corrugated steel webs, but the horizontal stiffeners increase the axial stiffness of corrugated steel web in local area and resist bending moment together with top and bottom flanges. The shear strain of stiffened corrugated steel web still distributes uniformly along the height of the web. All the experimental results are then employed in the companion paper for the validation of finite element method and the evaluation of existing analytical models for predicting shear strength of un-stiffened and stiffened corrugated steel webs.