Plate-like Buckling Resistance of Longitudinally Stiffened Plates Subjected to Pure Compression

Plate buckling resistance calculation of orthotropic plates and the determination of the effective width is highly important in the design of bridges. The current effective width calculation method provided by the EN 1993-1-5 [1] is developed for I-sections subjected to bending. Previous research results proved that the application of the plate buckling curve can overestimate the buckling resistance in case of square box sections subjected to pure compression. It means, that the required safety level of the Eurocode is not fulfilled for buckling resistance of plates in compression. Several previous studies proved the unconservatism of the EN 1993-1-5 for this special case, where the plate has no support coming from the adjacent plates. The question arises, if the above mentioned calculation process also leads to unsafe resistances for other structural details, or this is the specialty of the analyzed worst case scenario. Longitudinally stiffened plates (bottom flange of steel box sections) subjected to pure compression could be also a worst case scenario, because they are not supported by adjacent plates and they are loaded by pure compression. Therefore, the current research focuses on the investigation of longitudinally stiffened orthotropic plates loaded by pure compression and investigates (1) the plate-like buckling resistance, (2) the applicability of the Winter curve and (3) determines the necessary partial safety factor according to the safety requirements of the Eurocode. In the present paper the results of an extensive numerical research program are introduced and the applicability of the Winter curve is evaluated based on the safety requirements of the Eurocode

Finite Element Model-based Design of Stiffened Welded Plated Structures Subjected to Combined Loading

Resistance calculation of steel bridges with orthotropic plates subjected to combined loading situation (bending moment, shear and transverse forces called as M-V-F interaction) can be challenging for designers due to the interactive stability behavior and combined buckling phenomena. The current EN 1993-1-5 standard provides a design method using analytical design equations checking the pure (bending, shear and patch loading) and interaction resistances separately. This design process is complex in the case of steel bridges, especially for box-section bridges having numerous longitudinal and transverse stiffeners. Finite Element Model (FEM) based design can provide suitable design tools for efficient and accurate resistance calculation of these structure types. However, within the modelling process there are numerous questions to be answered regarding material models and imperfections to ensure required accuracy and safe resistance. A new standard prEN 1993-1-14 is currently under development which will provide design rules to finite element model-based design of steel structures, having the aim to answer the main part of the above mentioned questions and standardize the design process. The current paper discusses and demonstrates the methodology of the FEM based design for welded plated structures. Benchmark example for a Hungarian steel box-section bridge subjected to combined loading situation is presented. Effect of different meshing, imperfection combinations and material models are presented and evaluated in the paper. Efficiency of the numerical model and the obtained resistance on the input parameters are evaluated and design example is given for the application of the FEM based design method

On the Fatigue Strength Improvement Factor for High Frequency Mechanical Impact Treatment Method

Nowadays, the most commonly applied post weld treatment method improving fatigue strength of welded structures is the High Frequency Mechanical Impact (HFMI) treatment method. However, the treatment process is already well-known and widely used, there are several unanswered questions about its impact on the mechanical properties and fatigue behavior of treated welded structures. For understanding the mechanical background of the fatigue properties of HFMI-treated, welded, normal and high strength steel structures, it is necessary to analyze fatigue test results from many different aspects. According to previous studies it can be observed that fatigue strength of HFMI-treated steel specimens increases with the yield strength of base material. However, the fatigue strength of as-welded details is independent of the steel grade; thus if yield strength increases, fatigue strength improvement factors (ratio between the fatigue strengths of as-welded and HFMI-treated specimens) of HFMI-treated steel specimens should increase as well. In this paper, the relationship between steel grade and fatigue strength improvement factors of HFMI-treated details is investigated by using previous experimental results. A large number of previous experimental results are revised by the authors; published test results were collected and re-evaluated. Using the analyzed measures, the effect of HFMI treatments was analyzed. Fatigue strength improvement factor related to HFMI is calculated for two different types of structural details (cruciform joints and longitudinal attachments). For both cruciform and longitudinal joints, it is observed that the improvement factor decreases with increasing yield strength

Equivalent Geometric Imperfections for Local Buckling of Slender Box-section Columns

Determining the plate or the local buckling resistance is highly important in designing steel buildings and bridges. The EN 1993-1-5Annex C provides a FEM-based design approach to calculate the buckling resistance based on numerical design calculations (geometrical and material nonlinear analysis - GMNIA). Within the GMNIA analysis-based stability design, the application of the imperfections has a special role. Thus, the applicability of the EN 1993-1-5 based buckling curve (Winter curve) has been questioned for pure compression, and previous investigations showed the buckling curve of EN 1993-1-5 Annex B is more appropriate for the design of slender box-section columns subjected to pure compression, the magnitude of the equivalent geometric imperfection to be applied in numerical models for local buckling is also questioned and investigated by the authors within the current paper. The aim of the current research program is to investigate the necessary equivalent geometric imperfections to be applied in FEM-based design calculations using GMNIA calculations. A numerical parametric study is executed to investigate the imperfection sensitivity of box-section columns having different local slenderness. The necessary imperfection magnitudes are determined to each analyzed geometry leading to the buckling resistance predicted by the standardized buckling curves. Based on the numerical parametric study, a proposal for the applicable equivalent geometric imperfection magnitude is developed, which conforms to the plate buckling curves of the EN 1993-1-5 and giving an improvement proposal to the local buckling imperfection magnitudes of the prEN 1993-1-14, which is currently under development

Numerical Simulation of Welding Process – Application in Buckling Analysis

Numerical simulations make the improvement of fabrication process and welding technology. Numerical simulations make the improvement of fabrication process and welding technology possible. Using finite element method the most important information about welded specimens can be determined such as deformed shape, residual stresses or even microstructural properties like phase proportions or hardness. The current study focuses on the modelling background of welding processes and the effects of different welding parameters on residual stresses and deformations. The paper focuses on heat sources, temperature dependent material properties and the development of a thermo-mechanical analysis. The virtually fabricated specimens are further analysed to investigate the stability behaviour