Position Of Stiffeners Research Articles

Experimental Research on the Low-Cycle Fatigue Crack Growth Rate for a Stiffened Plate of EH36 Steel for Use in Ship Structures

This paper presents a straightforward approach for determining the low-cycle fatigue (LCF) crack propagation rate in stiffened plate structures containing cracks. The method relies on both the crack tip opening displacement (CTOD) and the accumulative plastic strain, offering valuable insights for ship structure design and assessing LCF strength. Meanwhile, the LCF crack growth tests for the EH36 steel were conducted on stiffened plates with single-side cracks and central cracks under different loading conditions. The effects of stress amplitude, stress ratio, and stiffener position on the crack growth behavior were examined. Fitting and verifying analyses of the test data were employed to investigate the relationship between CTOD and the crack growth rate of EH36 steel under LCF conditions. The results showed that the proposed CTOD-based prediction method can accurately characterize the LCF crack growth behavior for stiffened plate of EH36 steel for use in ship structures.

Comparative Study of Strengthened Steel Structure Behavior Using Bracing and Shearwall

Multi-storey buildings are very susceptible to lateral forces, so reinforcement is needed to stiffen the building by adding a system of stiffeners to the building structure. In steel building structures, the system of stiffeners bracing and confessor shearwall can provide rigidity and strength by limiting the movement of the structure. In addition, the placement of stiffener systems in the right locations can also increase the rigidity of the building structure. This study aims to compare the effectiveness of structural behavior using a stiffener system based on the value of the fundamental period (T), the base shear force (V), the drift between stories (?x). In this research using a steel structure model that functions as an office building with a height of 10 levels, one variation of the model without stiffeners and four models with stiffeners, with two variations of the position of the stiffeners, namely in the middle and on the edge of the structure. The results of this study indicate that the addition of a stiffener system can increase the rigidity of the structure. The most effective structural model is found in the structural model with stiffeners shearwall the stiffener position in the middle which has a fundamental period value in the X and Y directions of 17.67% and 18.32% is better than the other models. For the base shear force values in the X and Y directions are 0.95% and 0.95% smaller than the other models. The deviation values between floor levels in the X and Y directions are 9.67% and 34.17% better than the other models. Meanwhile, the inefficient structural model is found in the structural model with stiffeners bracing on the edge which has a fundamental period value in the X and Y directions of 8.96% and 9.32% which is no better than the other models. For the base shear force values in the X and Y directions are 18.02% and 18.02% greater than the other models. The deviation values between floor levels in the X and Y directions are 1.69% and 13.15%, not better than the other models. So in this study it can be concluded that the stiffener system with a position in the middle is better than the position on the edge.

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.

Experimental investigation on flexural performance of T-joint concrete-filled steel tube with PBL

T-joint concrete filled-steel tube (CFST) members are widely used in many modern structures. The performance of T-joint CFST is studied as the brace is under axial compressive load and chord bends in this paper. A total of eight specimens were designed and manufactured, and FE models were built by ANSYS. The effect of different parameters, including the brace-chord width ratio, the brace-chord thickness ratio, the influence of the PBL, the thickness of the stiffener, the opening diameter and opening space of the PBL, the material strength, and the number and welding position of stiffeners, on the performance of T-joint CFST were investigated through experimental and numerical studies. A criterion for determining when the T-joint CFST with PBL reaches the ultimate bearing capacity is presented. The calculation method in this paper for ultimate moment capacity is derived based on the limit balance theory. The method considering the reinforcement of the brace on the upper flange of the chord, the confinement effect of the steel tube on concrete, and the plastic stress distribution of the steel tube is in better agreement with the test and FE analysis. The results show that the proposed method can well predict the ultimate moment capacity of T-joint CFST, while the method in DBJ is more conservative.

Local buckling behaviour of longitudinally stiffened stainless steel plate girders under combined bending and shear

This paper presents a comprehensive experimental and numerical investigation into the local buckling behaviour of longitudinally stiffened stainless steel plate girders under combined bending moment and shear force. Five plate girders configurated with longitudinal stiffeners with different geometrical proportions and vertical positions were fabricated from austenitic and duplex stainless steel plates. Initial geometric imperfections and material properties were measured, and all plate girders were tested to failure under a three-point loading configuration. The critical buckling strengths, ultimate capacities and failure modes were carefully analysed. Elaborate finite element (FE) models were developed and validated against the test results, and were then used to conduct parametric studies to generate further structural performance data over a wide range of cross-sectional properties, including various geometrical proportions and positions of longitudinal stiffeners, and loading combinations. The obtained test and FE results were utilised to assess the applicability of existing M–V interaction design methods in EN 1993-1-5 and that proposed by Jáger et al. for longitudinally stiffened plate girders. It was indicated that these two M–V interaction curves coupled with the design provisions in EN 1993-1-4 for determining the bending and shear endpoints, offer safe-sided predictions with a good level of consistency and accuracy, for longitudinally stiffened stainless steel plate girders under combined bending and shear. The reliability of these design approaches was further confirmed by statistical analysis.

Numerical and experimental buckling response of moderately thick and thick composite plates with various stiffener layouts

The buckling behavior of moderately thick and thick stiffened composite plates with different stiffener layouts is formulated based on the higher-order shear deformation theory. This investigation is performed under axial compression using the Finite Strip Method and experiment. The effects of dimensions, orientation, eccentricity, torsional stiffness, position and geometric configuration of stiffeners on the buckling load coefficient are achieved by employing the principle of minimum potential energy. Six grid-stiffened composite plate specimens with ortho-grid, angle-grid, and orthotropic-grid stiffeners are tested. The results of the presented method show good outcomes with those of experimental tests and the finite element ANSYS code.

Strengthening of Steel Beam by Inclined Stiffeners

AbstractThere are several ways how to increase the bending resistance of a beam. The simplest method is to increase the cross‐section size. But this method may not be the most efficient or feasible, especially in the case of an existing building in need of strengthening. In this paper, the method of strengthening a beam by welded inclined stiffeners is investigated. The beam is susceptible to lateral‐torsional buckling. A sensitivity study is prepared for the beam length and cross‐section size, boundary conditions, and the number and position of stiffeners. A validated numerical model using Component‐based Finite Element Method is used. The model combines shell elements for analyzed member and bar elements for related members. The joints are included in the model. Bolts and welds are simulated by special nonlinear elements with resistance based on codes. Validation and verification of the model is presented. It is based on the experiment performed at AdMaS center at Brno University of Technology of a beam with semi‐rigid joints loaded by three‐point bending. The model is verified by comparing critical buckling load and buckling resistances of columns and beams with clear boundary conditions. The results are also compared to those by another general finite element software, ANSYS and ABAQUS.

Optimum location of a single longitudinal stiffener with various cross-section shapes of steel plate girders under bending loading

This paper aims at investigating the optimum location of a single longitudinal stiffener having various cross-section types of steel plate girders subjected to bending loading. The optimum location is found using a gradient-based Interior-Point (IP) optimization algorithm. The optimization procedure involves a linear elastic buckling analysis with the finite element method, which is coupled with the aforementioned IP algorithm and used to calculate the buckling coefficient, which is maximized. Based on the optimization results, the effect of the various cross-section types of the stiffener and the web slenderness ratio on the optimum stiffener position is investigated. It is found that closed cross-sections of the stiffener and larger web slenderness ratios lead to higher critical buckling coefficients.

Simultaneous outline shape and size optimization for stiffeners in practical engineering structures

This article presents an engineering method to optimize the stiffener outline shape and cross-sectional sizes simultaneously for stiffened plate structures. A new optimization model for stiffened plate is established, and a hierarchical algorithm including external and internal optimization module is proposed to tackle the shape and size variables respectively. In external optimization, genetic algorithm (GA) is utilized to optimize binary-coded shape variables, and when calculating individual fitness values in GA, an internal optimization only involving size variables is carried out. For each individual, the stiffener outline shape is determined by a given shape variable vector and a reasonable finite element model could be automatically built with a parametric modeling method. The solution of internal optimization problem can be obtained by size optimization method, and an offset vector which updates during each cycle is created to modify the relative position of plate and stiffeners, ensuring the practicality of the optimal results in engineering. The presented approach is firstly verified through a typical example and then it is applied to the structural design of a micro-satellite. The results show that the method is effective in dealing with the simultaneous outline shape and size optimization problem of stiffeners, and the optimal results could be directly applied in practical engineering structures.

Local joint flexibility of tubular X-joints stiffened with external ring or external plates

In the present paper, the Local Joint Flexibility (LJF) of the ring-stiffened X-joints and plate-stiffened X-joints under compressive load is investigated. In the first phase, a finite element (FE) model was generated and verified with the results of available experimental tests and equations. In the next phase, a set number of 234 FE models were created to evaluate the role of the external ring size (βr and τr), the external plate size (βp and τp), and the connection geometry (γ, τ, and β) on the LJF factor (fLJF). In these FE models, the weld connecting the chord and brace members was generated. The results indicated that the fLJF of a plate stiffened joint can be down to 76% of the fLJF of the corresponding un-stiffened joint. Also, the effect of the ring size on the fLJF was more than the effect of the plate size on the fLJF, because of the stiffener position. Despite the notable effect of the ring and the plate on the fLJF, there is not any study or formula on tubular connections stiffened with ring or plate. Therefore, the FE results were used to propose two parametric formulas for determining the fLJF in X-joints with external ring or external plate under brace compressive load. Moreover, the derived formulas were checked based on the UK DoE acceptance criteria.

Free Vibration Behavior of Angle-Ply Laminated Composite Stiffened Plates

This paper reports for the first time the experimental investigation on the free vibration characteristics of angle-ply laminated composite stiffened plates along with the numerical investigation. The natural frequencies of these plates are computed experimentally using an FFT analyzer and numerically by employing the finite element method with combination of isoparametric nine nodded plate and three nodded beam elements. Angle-ply laminated stiffened plates are fabricated using woven glass fiber fabrics and epoxy by hand layup technique. The effects of various support conditions; number, orientation and types of stiffeners; aspect ratios of plates and different fiber orientations on the fundamental frequencies of the angle-ply laminated stiffened plates are investigated. These parameters significantly influence the natural frequencies. It is found that there is a very good agreement observed between the fundamental frequencies obtained from both experimental and numerical investigation. Mode shapes are also presented for angle-ply laminated square stiffened plates with three different support conditions to justify the trend of increasing/decreasing of the modal frequency with the addition of stiffeners. It is observed that the enhancement of the frequencies of the angle-ply plates due to addition of stiffeners is influenced significantly by the position of stiffeners and consequently mode shapes. As the research on the free vibration behavior of angle-ply stiffened plates with experimental analysis is very rare, this study can be considered as the benchmark for future research.

P‐6.4: Comprehensive optimum and adaptable design methodology for the Display Support Structure Based on ANSYS Simulation

The back cover is mainly used to strengthen the display product strength, increase rigidity, and prevent product deformation and distortion during assembly, use or transportation. This thesis studies the influence of different back cover thickness, backplane material and stiffener position, number of stiffeners, and stiffener structure on the strength of the backplane. Good display support structures are required that not only can offer better sustentation results, but also can reduce the negative effect with lesser back cover materials. By simulating and optimizing the design of the backplane, the strength of the product is increased and the unit price of the product is reduced.

Influence of stiffeners and pattern of shear screws on behaviour of cold formed profiled deck composite floor

The shear bond behaviour is the most complex phenomenon of composite slabs; this paper presents an experimental study on the shear bond behaviour of composite slabs subjected to monotonic loadings. Seven composite slab specimens having sheet thicknesses of 0.8 and 1.2 mm with two types of stiffeners in the flange (rectangular and V-type) and different position of shear screws (end; staggered) were prepared and tested. The structural response of test specimens was compared on the basis of load-displacement response, load-end slip plot, energy-absorbing capacity, failure type, ductility factor, and maximum strains developed in concrete and steel. The positions of shear screws and intermediate stiffeners in profiled deck sheet were found to considerably influence the shear bond strength of composite slabs. The test results showed that composite slabs with a staggered type of shear screws exhibited a higher energy-absorbing capacity, and the ductility factor results in a better shear bond behaviour. The wedge effect of stiffeners improved the ductility and stiffness of composite slabs.

A semi-analytical method for vibro-acoustic analysis of submerged ring-stiffened cylindrical shells coupled with arbitrary inner structures

A semi-analytical method is developed for vibration and acoustic analysis of a submerged ring-stiffened cylindrical shell coupled with arbitrary inner structures. The whole structure is firstly disassembled into the stiffened cylindrical shell and inner structures, which are respectively analyzed through analytical substructure method and numerical approach. For the analytical substructure method, the cylindrical shell is decomposed into several shell segments according to positions of stiffeners and external forces, including exciting forces and coupling forces. These shell segments are described by Flügge shell theory and the ribs are governed by the annular plate equations. The solutions for cylindrical shell segments and rings are expanded as wave functions and Bessel functions. For the inner structures with arbitrary irregular shapes, finite element method (FEM) is utilized to establish their motion equations. At each coupling node, an artificial spring is adopted to connect the shell and inner structures, so rigid and elastic coupling conditions can be easily simulated by setting different stiffenesses to these springs. For external fluid field, an axisymmetric boundary element method (BEM) is employed to calculate the acoustic pressure. Combining the displacement continuity and force balance conditions at the joints of adjacent shell segments and introducing the coupling forces derived from inner structures and the fluid loading, the vibro-acoustic equations of the coupled system are obtained. To verify the validity of the present approach, vibro-acoustic responses of the semi-analytical method are compared with the ones calculated through FEM/BEM. Furthermore, effects of the coupling stiffness between the shell and inner structures and external fluid loading on vibro-acoustic responses are also evaluated.

Donaldson Co Inc, USA

A semi-analytical method is developed for vibration and acoustic analysis of a submerged ring-stiffened cylindrical shell coupled with arbitrary inner structures. The whole structure is firstly disassembled into the stiffened cylindrical shell and inner structures, which are respectively analyzed through analytical substructure method and numerical approach. For the analytical substructure method, the cylindrical shell is decomposed into several shell segments according to positions of stiffeners and external forces, including exciting forces and coupling forces. These shell segments are described by Flügge shell theory and the ribs are governed by the annular plate equations. The solutions for cylindrical shell segments and rings are expanded as wave functions and Bessel functions. For the inner structures with arbitrary irregular shapes, finite element method (FEM) is utilized to establish their motion equations. At each coupling node, an artificial spring is adopted to connect the shell and inner structures, so rigid and elastic coupling conditions can be easily simulated by setting different stiffenesses to these springs. For external fluid field, an axisymmetric boundary element method (BEM) is employed to calculate the acoustic pressure. Combining the displacement continuity and force balance conditions at the joints of adjacent shell segments and introducing the coupling forces derived from inner structures and the fluid loading, the vibro-acoustic equations of the coupled system are obtained. To verify the validity of the present approach, vibro-acoustic responses of the semi-analytical method are compared with the ones calculated through FEM/BEM. Furthermore, effects of the coupling stiffness between the shell and inner structures and external fluid loading on vibro-acoustic responses are also evaluated.

Dynamic response of stiffened plate under internal blast: Experimental and numerical investigation

Stiffened plates are the basic units of ships, aircraft and other structures. The purpose of this paper is to investigate the dynamic response of stiffened plates under internal blast loading. A combined experimental and numerical investigation was carried out on the cabin structures with unstiffened, single-stiffened and double-stiffened plates. The characteristics of internal blast wave, the effects of stand-off distance and the stiffener position on the deflection and failure modes of stiffened plates were sequentially analyzed. It was interestingly found that the deflection first decreased and then increased with the increase of stand-off distance. Additionally, despite of the reinforcement on the deformation resistance, the stiffeners tended to reduce the damage tolerance of the target plates. This research provides the basic data and theoretical support for the blast resistance design of ships, aircraft and other structures.

The ultimate shear capacity of longitudinally stiffened steel-concrete composite plate girders

This paper presents the ultimate shear strength of longitudinally stiffened steel-concrete composite plate girders (LS-CPGs) under shear loading. The tension field action in the girder web, shear capacity of concrete slab, and the position of longitudinal stiffeners are considered in driving an analytical method to predict the ultimate shear strength of the girder. The accuracy of the proposed method is evaluated by finite-element (FE) models. A three-dimensional FE model has been generated, considering both the geometric and material nonlinearity of LS-CPGs. The results show that longitudinal stiffeners increase the ultimate shear strength of LS-CPG. The comparison between the analytical and corresponding FE results shows that the proposed analytical method can accurately predict the ultimate shear strength of LS-CPGs.

Validation of hysteretic behavior and prediction of energy dissipation potential of aluminium shear yielding devices

Metallic dampers are used to control the seismic vibration of civil structures through supplemental energy dissipation and damping thereby minimizing damages to the primary load-resisting elements. Shear yielding devices are one type of metallic dampers in which the hysteretic energy dissipation is achieved through the inelastic deformation of metallic plates under cyclic loading. This paper presents a numerical study to evaluate the hysteretic behavior of aluminum shear yielding devices (Al-SYDs) under cyclic loading. Finite element models of eighteen numbers of Al-SYDs have been developed in a computer software ABAQUS and are validated by comparing the predicted behavior with the past test results. A parametric study is conducted to investigate the influence of web aspect ratios, web slenderness ratios, grades of aluminum alloy, and position of vertical stiffeners on the hysteretic behavior, energy dissipation potential, and displacement ductility of Al-SYDs. The energy dissipation potential of these devices is found to be strongly dependent on the aspect ratio and slenderness ratio of web plates. A simplified expression has been proposed to estimate the hysteretic energy dissipation potential of Al-SYDs. Limiting values of panel aspect ratio and web slenderness ratio have been recommended for the design of Al-SYDs.

Optimal design of cold roll formed steel channel sections under bending considering both geometry and cold work effects

Optimal design of a structural member is a design process of selecting alternative forms to obtain its maximum strength while maintaining the same weight, leading to the most economical and efficient structure. Amongst steel structures, cold rolled steel ones can effectively gain this requirement as they are thin-walled structures that offer the high ratio of strength over weight. However, the design is very challenging as these members are prone to buckling and failure at low loads. In this paper, the buckling and ultimate strength of cold rolled channel sections was studied using numerical modelling. In order to improve the section strength, the development of various alternative cold rolled formed sections included additional bends such as intermediate stiffeners. The section strength was optimised through a practical approach which altered the stiffener's position and shape and searched for maximum buckling and ultimate strength under bending. In this approach, a nonlinear Finite Element model was first developed for an industrial channel beam subjected to four-point bending tests and this model was validated against experimental test data. The verified model was then used to conduct a parametric study in which the effects of a stiffener's properties on the section strength including its position, shape, size and material properties by the cold work at bends were investigated in detail. Several different cold rolled channel sections having intermediate stiffeners at web and flanges with and without the cold work effect on material properties at the stiffener's bends were considered for this investigation. In addition, a design method, the Direct Strength Method (DSM), was utilised to take into account the effects of a stiffener's properties on the section strength and results were compared with the Finite Element modelling results. It was found that some significant improvements were obtained for the section strength of the optimised sections in comparison to the original sections. An optimal shape for the channel section with maximum ultimate strength in distortional buckling could be obtained with both the stiffeners' position, shape, size and quantity, and the cold work effect. The cold work effect was found most significant in the cases of changing the width of the web stiffeners and the position of the flange stiffeners. It also revealed that, the currently available DSM beam design curve for distortional buckling provided good agreement in predicting buckling load and ultimate strength capacity for most of the considered sections with and without the cold work effect included; however, the DSM provided overestimate results compared to the Finite Element model results in the sections with web intermediate stiffeners, in particular, when the tip of web intermediate stiffener moved away from the web-flange junction in the horizontal direction.

Discussion of the role of geometry, proportion and construction techniques in the seismic behavior of 16th to 18th century bulbous discontinuous double shell domes in central Iran

Discontinuous double shell domes (DDDs) are a construction typology commonly used in Iranian architecture. They are very diverse in terms of geometry and construction techniques. The preservation of these domes, which often represent the most vulnerable parts of the buildings, requires adequate structural analysis. However, this is still an insufficiently researched topic. Geometric principles, such as proportion and symmetry, are the most important parameters affecting the structural behavior of these domes. The main goal of the present work is to numerically assess the influence of geometry and construction techniques on the seismic behavior of these domes. With that purpose, the paper presents the results of a detailed numerical study based on finite element modeling and nonlinear static (pushover) analysis. Four real case studies with distinct geometric characteristics, representative examples of historic Iranian architecture from the Safavid era (16th to 18th century), were selected for the numerical study. Results were systematically compared and they show that the proportions of the domes play an important role in the seismic behavior. The ratio between their height and diameter is a parameter that determines the ability of the system to transfer loads and to tolerate displacements, and also affects the failure mechanism. The position and dimensions of stiffeners contribute to ensure the monolithic behavior of the whole system. In the smaller domes, stiffeners control the crack pattern and evolution, but they are not much influential in the load capacity of the system. In larger domes, stiffeners were proven to be essential for the structural behavior under gravitational loads and for the seismic response of the system. The ratio of the dome-drum system height to the stiffeners height was found to be typically based on the golden ratio.