Rigidity Of Stiffeners Research Articles

Linear buckling behavior of longitudinally singly- and multi-stiffened steel plates under normal and shear stresses

In this paper, the linear buckling behavior of longitudinally singly- and multi-stiffened plates with simply-supported edges under normal and shear stresses is investigated. A comprehensive parametric analysis using a finite element model validated against results collected from the literature is performed and the results are presented. About 65,000 eigenvalue analyses are executed, in which (a) several values of the plate’s aspect ratio, (b) different number, position and rigidity of stiffeners, and (c) different load configurations are considered. New practical insights about the ideal rigidity and position of the stiffeners are given, including the assessment of the optimum positions of longitudinally multi-stiffened plates under different normal stress ratios, which is not covered by the literature so far. Additionally, the gain of increasing the number of stiffeners is also discussed for different load combinations.

Improved buckling analysis of stiffened laminated composite plates by spline finite strip method

Improved buckling analysis of stiffened laminated composite plates under axial compressive loads are conducted using spline finite strip method. The stiffened laminated composite plates are modeled as beam-plate structures, where the base plate and the stiffeners are formulated based on the respective first-order shear deformation theory and thin-walled composite beam theory. The eccentricity and torsional rigidity of stiffeners are taken into account, and the beam displacements are expressed by those of plate middle surface according to the compatibility condition between the base plate and stiffeners. The present model is capable of capturing both global and local buckling of stiffened laminated composite plates with stiffeners of any kind of cross-sections, and it is extended to analysis of transversely- and orthogonally-stiffened laminated plates through modification of spline interpolations. The validity of developed buckling analysis is verified by comparisons with the existing solutions and numerical finite element results, while parametric studies are conducted to demonstrate its effectiveness and capabilities in analyzing buckling behavior of stiffened laminated composite plates.

HSB 강재를 적용한 곡선거더 웨브의 수평보강재 휨강성

HSB 강재를 적용한 곡선거더 웨브의 수평보강재 휨강성

Experimental analysis of cold-formed steel columns with intermediate and edge stiffeners in fire

Abstract Although the use of longitudinal stiffeners in cold-formed steel members in compression is known to increase their ultimate strength at ambient temperatures, it is expected that the rigidity of such stiffeners and the strength of steel decreases when the cold-formed steel members are exposed to high temperatures. Therefore, this paper presents and discusses the results of an experimental investigation on the structural response of cold-formed steel columns with intermediate and edge stiffeners under fire conditions for assessing mainly their critical temperatures, critical times (fire resistance) and failure modes. The main variables studied included the: (a) cross-section shape, (b) boundary conditions, (c) edge stiffener configuration and (d) stiffness of the surrounding structure to the thermal elongation of such columns. Additionally, European fire design predictions (EN 1993-1-2:2005) were compared with the experimental results, in order to observe their accuracy. Finally, based on the findings of this research work it is obvious the advantage of using CFS sections with double edge fold stiffeners over the sections with single edge fold stiffeners. Moreover, built-up sections had lower critical temperatures than those for single sections, but with slightly higher fire resistance time. Furthermore, existing analytical methods have been shown to be incapable to predict sufficiently realistic the complex buckling behaviour of restrained CFS columns under fire conditions.

Experimental and Numerical Investigation of Steel Beam-to-CFST Column Frame-Thin Steel Plate Shear Walls with Cross Stiffness

Steel plate shear wall (SPSW) systems have been used increasingly in medium- and high-rise buildings in recent decades. Two major issues in the slender-web SPSW are the buckling of H-section steel column base and significant pinching in hysteretic curves. As a solution, SPSW using concrete-filled steel tubular (CFST) column and cross stiffeners was proposed in this paper. Cyclic tests of two specimens of 1/3 scaled steel beam-to-CFST column frame-thin SPSW with cross stiffeners or without stiffeners were conducted. Based on the verified finite element method, parametric investigations considering the effect of the flexural rigidity of CFST column, width-to-height aspect ratio, height-to-thickness ratio of infill steel plate and relative rigidity of cross stiffener were carried out. Findings show that SPSW using CFST column exhibited favorable ductility behavior with no sudden loss of lateral bearing capacity. Adding stiffeners to SPSWs relieves the pinching effect of hysteretic curves and reduces the maximum lateral displacement substantially. With stiffeners, the average yield load and the peak load of SPSWs were approximately 15% and 9% higher than that of the unstiffened specimens. Moreover, a flexural rigidity of CFST column of at least 2.5 and a stiffener rigidity of 30–50 were recommended to provide an economical and approving lateral bearing capacity.

Bend-buckling strength of steel plates with multiple longitudinal stiffeners

This paper presents an investigation of the optimum locations of multiple longitudinal web stiffeners (up to six) for steel plates under pure bending by using the gradient-based interior point optimization algorithm. Performing eigenvalue buckling analyses, buckling coefficients are calculated accounting for the lowest eigenvalues. The optimization algorithm is then employed to maximize the buckling coefficients until the optimum stiffener locations of the plates are attained. Based on this research, the optimum locations of multiple longitudinal stiffeners are suggested for plates under pure bending. Moreover, equations to determine minimum flexural rigidities of multiple longitudinal stiffeners for steel plates are also proposed. The results obtained from this study are compared with the AASHTO requirement and previous works. It is proved that the minimum flexural rigidities of stiffeners recommended by AASHTO and the previous work are conservative.

Contribution of longitudinal stiffener rigidity and position to bridge girder integrity

To increase the elastic critical load of a plate, such as I-shaped cross-welded section of bridge girders, slenderness is usually reduced by dividing the web into subpanels, by means of transversal stiffeners and a longitudinal stiffener to increase flexural and torsional stiffness. The optimal solution is defined when the stiffener maximizes the buckling coefficient, with a minimal cross-section area. For this purpose, seven forms of open and closed sections of longitudinal stiffeners, with differing second moment of area, are examined in terms of buckling coefficient by theoretical solution and numerical calculation, to compare their contribution in terms of weight per linear meter of beam. The optimum value of a conventional flat stiffener position, respect panel height and an useful practical law is given to correlate the best position with respect to variations in stress gradient, from pure bending to pure compression. This practical law facilities calculation regarding where to put a stiffener with respect to compressed edge in a web panel subjected to flexural-compressive loads, in order to maximize the benefit of its action and increase the stability of bridge girders.

Effect of stiffeners on steel plate shear wall systems

Stiffeners have widely been used in lateral load resisting systems to improve the buckling stability of shear panels in steel frames. However, due to major differences between plate girders and steel plate shear walls (SPSWs), use of plate girder equations often leads to uneconomical and, in some cases, incorrect design of stiffeners. Hence, this paper uses finite element analysis (FEA) to describe the effect of the rigidity and arrangement of stiffeners on the buckling behavior of plates. The procedures consider transverse and/or longitudinal stiffeners in various practical configurations. Subsequently, curves and formulas for the design of stiffeners are presented. In addition, the influence of stiffeners on the inward forces subjected to the boundary elements and the tension field angle is investigated as well. The results indicate that the effective application of stiffeners in SPSW systems not only improves the structural behavior, such as stiffness, overall strength and energy absorption, but also leads to a reduction of the forces that are exerted on the boundary elements.

Critical rigidity of stiffener for increasing shear stability of rectangular plate

In plate girder with slender web the big transverse forces lead to web buckling produced with shear. One of the ways to increase stability of web near supports is to install stiffeners. In work the task of finding of critical stresses of clamped rectangular plate with installed inclined stiffener is considering. Investigations were performed with the finite element method and were checked with the experiment. Recommendations were given on choice of optimal size of stiffener.DOI: http://dx.doi.org/10.5755/j01.mech.21.3.9045

Elastic buckling behavior of steel trapezoidal corrugated shear walls with vertical stiffeners

This paper investigates the elastic buckling behavior of steel trapezoidal corrugated shear walls (STCSWs) with vertical stiffeners. On the basis of an orthotropic plate model, by utilizing the theorem of minimum potential energy and the Ritz method, the buckling loads of stiffened STCSWs can be precisely calculated using MATLAB. Then, a value of transition rigidity of stiffener is suggested and, hence formulas of elastic buckling coefficients of stiffened STCSWs are proposed. Finally, the verification of proposed formulas using a FE model shows that the formulas are validated and applicable in estimating the elastic buckling loads of stiffened STCSWs.

Bending Resistance of a Slender Plate Girder with Longitudinal Stiffener

This paper presents an analysis regarding the bending resistance of a slender plate girder having a longitudinal stiffener in the compression zone of the web.The influence of the longitudinal stiffener rigidity on the bending resistance of a slender girder of Class 4 section is analyzed, starting from the hypothesis that the transversal stiffeners are infinitely rigid.

Stiffness requirements for transverse stiffeners of rectangular CFT compression panels

This paper presents a more rational calculation of the minimum stiffness required for transverse stiffeners of stiffened concrete filled tube (CFT) compression panels. As longitudinal stiffeners are essentially compression members, transverse stiffeners are required to control the effective length. Both the longitudinal stiffener and transverse stiffener subdivide the compression panel in a grid pattern so the relatively thin plate can carry the induced compressive load in the most efficient manner. However, the provisions for the required rigidity of transverse stiffeners in the literature are inconsistent in general and in particular; do not exist in the case of the concrete filled compression panels. Here, the parameters that govern the behavior of the transverse stiffeners are identified theoretically using the column buckling approximation. In order to calibrate and quantify the analytical equations developed, incremental nonlinear analyses were performed on a large number of finite-element models. The numerically collected data were then used to validate the equations developed.

Stiffness requirements for transverse stiffeners of compression panels

This paper presents a more accurate calculation of the minimum stiffness required for transverse stiffeners of compression panels. As longitudinal stiffeners are essentially compression members, transverse stiffeners are required to control the effective length. Both the longitudinal stiffener and transverse stiffener subdivide the compression panel in a grid pattern so the relatively thin plate can carry the induced compressive load in the most efficient manner. However, the provisions for the required rigidity of transverse stiffeners in the AASHTO specifications are inconsistent. Here, the parameters that govern the behavior of the transverse stiffeners are identified theoretically using the column buckling approximation. In order to calibrate and quantify the analytical equations developed, elastic buckling analyses were performed on more than 350 finite element models. The numerically collected data were reduced using a series of regression analyses for simple equations to determine the required rigidity for the transverse stiffeners. Incremental nonlinear analyses were performed to validate the reliability of the regression equations developed. Several design examples are also given to demonstrate the broad applicability of the proposed equations.

Hysteretic Model of Stiffened Shear Panel Dampers

A properly designed two-way stiffened (stiffened both in longitudinal and transverse directions) shear panel can sustain large deformation without pinching and consequent strength degradation. Hence it can be used as an effective passive energy dissipating damper (PEDD) in building and bridge structures to absorb seismic energy. In this Technical Note, a series of steel shear panels with 1, 2, or 3 two-way stiffeners has been analyzed under cyclic loading by the general-purpose finite element program ABAQUS, in which a modified two-surface model is incorporated to trace the material nonlinearity. Slenderness of web, Rw, is employed as a key parameter to investigate the hysteretic performance of stiffened shear panels. The sensitivities of the ratio of stiffener rigidity to optimum stiffener rigidity, γs∕γs*, the ratio of flange thickness to web thickness, tf∕tw, and aspect ratio, α, are also investigated. Finally, a simplified bilinear model for stiffened shear panels acting as a PEDD is presented in this Technical Note based on FEM results. The proposed model is expected to get use in the time-history analysis of engineering structures that employ the PEDD to mitigate seismic hazard.

Experimental behaviour of stiffened concrete-filled thin-walled hollow steel structural (HSS) stub columns

Test results on concrete-filled steel tubular stub columns with inner or outer welded longitudinal stiffeners under axial compression are presented in this paper. The research was mainly focused on square hollow section (SHS) columns; two rectangular hollow section (RHS) columns were also tested. A longitudinal stiffener was provided on each side of the stiffened SHS column, while only two stiffeners were welded to the longer sides of the stiffened RHS column. The main experimental parameters considered were the height-to-thickness ratio and stiffener rigidity. In addition, empty tubes with or without stiffeners, as well as unstiffened concrete-filled steel tubes were also tested for comparison. Requirements for stiffener rigidity are developed by modifying a formula presented in the literature. Existing theoretical model and design codes were used to predict the load versus axial strain relationships and load-carrying capacities of the adequately stiffened composite sections respectively; reasonable results were achieved.

Strength of Stiffened Flanges in Horizontally Curved Box Girders

Longitudinal stiffeners are often attached to increase the buckling strength of thin-walled box girder flanges. The minimum required rigidity for longitudinal stiffeners for curved box girder flanges is given by the AASHTO Guide specifications for horizontally curved steel girder highway bridges. However, this requirement is simply adopted from the current AASHTO specifications for straight stiffened flanges. The validity of this requirement has been questioned in a series of recent studies. The effect of important design parameters on the minimum required stiffener rigidity is investigated numerically in this study by examining the prebuckling stress distribution and elastic and inelastic buckling stresses of horizontally curved stiffened flanges. In order to characterize and quantify the analytically collected data, a series of parametric studies were performed. A new equation for the minimum required rigidity for the longitudinal stiffeners is derived from regression analyses. Through the evaluation of a few selected case studies and a design example, the validity and reliability of the proposed new equation is demonstrated.

Nonlinear FE analysis of longitudinally stiffened girder webs under patch loading

The ultimate load behavior of longitudinally stiffened girder webs under patch loading is studied here by means of a nonlinear finite element analysis. Large-deflection effects and initial shape imperfections are taken into account. The influence of the slenderness of the directly loaded web panel on the patch loading capacity is studied in depth, together with the size of the loaded flange. In addition, the influence of stiffener rigidity is also analyzed. This study was aimed at finding an optimum position of longitudinal stiffeners for patch loading. Currently, designers use the value recommended for bending, i.e. one-fifth of girder depth. The results presented here show that a stiffener located closer than one-tenth of the girder depth significantly increases the load carrying capacity of the plate girder due to a decrease in the slenderness ratio of the web panel between the loaded flange and the longitudinal stiffener.

単柱形式の薄肉鋼製橋脚柱の入力地震加速度の大きさと局部座屈損傷の程度との関係について

In this study, elasto-plastic and dynamic response analysis is carried out to investigate the influence of applied seismic acceleration and the flexural rigidity of longitudinal stiffeners onto damage to steel bridge piers having single thin-walled box columns and the relationships between the extent of the damage and the limit states, such as serviceability limit, repairable limit and ultimate limit of the bridge piers. Firstly, a method for estimating the proper flexural rigidity of longitudinal stiffeners is dealt with. Secondly, a parametric analysis is carried out by varying types of the seismic acceleration waves and the flexural rigidity of longitudinal stiffeners in order to investigate the definition of the limit states.

Postbuckling behavior of rectangular stiffened plates considering buckled pattern change

The postbuckling behavior of rectangular isotropic stiffened plates under inplane compressive load is investigated considering the phenomenon of buckled pattern change in the postbuckling load range. The finite deformation strains in the von Karman sense are incorporated in the geometrical nonlinear postbuckling analysis. The inplane and out-of-plane displacements are assumed as truncated Fourier series. The principle of minimum potential energy is applied. The total potential energy includes the strain energy due to bending and membrane action of plate, torsion of stiffeners, and the work done by external compressive force. The plates are assumed to be simply supported along the loaded sides and elastically restrained against rotation by longitudinal stiffeners along the unloaded sides. In numerical examples, the postbuckling load end-shortening curves and effective width curves are presented for the rectangular stiffened plates with various aspect ratios, torsional rigidities of stiffeners and inplane boundary conditions along unloaded sides.

Transverse-stiffener requirements for the post-buckling behaviour of a plate in shear

The optimum stiffener rigidity in a transversely-stiffened web under pure shear is sought in the post-critical range. An energy-based large-deflection scheme is employed to study the post-critical strength of the system up to the initiation of material yielding for the usual range of plate geometries and varying stiffener rigidities. Several criteria for “optimum” rib stiffness are assessed including stiffener deflection, the effective halving of the plate length and, finally, the strength of the plate itself. Tentative conclusions are reached on the basis of comparing optimal rib rigidities for the two instances of elastic and post-buckling regimes.