Parametric study on the collapse strength of rectangular plates with localized imperfections under in-plane compression

ABSTRACTSteel products which have various characteristic (e.g. high ductility, high yield stress, low yield stress and high weldability) are used as main structures by diversification of demanded application, and technology for steel manufacturing has developed. Because steel square tubular member is processed by cold‐forming and welding in the process of manufacturing, residual stress will exist in the products. Moreover, due to the cold‐forming process, geometrical initial imperfection, i.e., global and local, will exist. These initial imperfection are still remained even so the technology for steel manufacturing is developed. However, effect of the initial imperfection on elasto‐plastic behaviour of square hollow section columns under compressive axial force with bending moment is not clarified. In this paper, firstly, the effect of individual initial imperfection (e.g. initial global imperfection, initial local imperfection or residual stress) on elasto‐plastic performance is investigated independently; comparison between the experimental results are shown. It is shown that initial local imperfection has a significant impact on elasto‐plastic performance. Secondly, the effect of composite initial imperfections is investigated. The amplitude of the local imperfection is the most influential initial imperfection on the deformation capacity of the column, and the deformation capacity decreased with an increase of the amplitude of local imperfection. Validation of the numerical simulation were also performed and recommend values of imperfections are shown.

Buckling capacity of welded stainless steel flanges by finite element analysis

Design of cold-formed steel unequal angle compression members

The paper examines the sensitivity of buckling loads to the initial geometric imperfections in metallic cylindrical, toroidal, barrelled and torispherical shells subjected to uniform external pressure. The adopted approach is based on the FE analysis of a number of selected cases. The imperfection profiles include either localised (stripe, cos x cos, increasedradius flattening, etc.) or global (modulated eigenmode) distortion of shell's mid-surface. The lower bound methodology has been adopted for all localised shape deviations. Differences between buckling sensitivities to localised and global imperfections are given for the following cases: (i) for cylinders subjected to radial pressure, (ii) for toroids and torispheres subjected to static external pressure. It is shown here that the largest reduction of the buckling strength is not associated with one particular form of shape deviations. In bowed out shells the eigen-imperfections seem to be affecting the load carrying capacity to a lesser extent than ...

On the possibility of using damaged plasticity models in the assessment of structural response of gravity beams

Two-phase flow patterns in adiabatic refrigerant flow through capillary tubes

Geometric imperfections have an important influence on the buckling response of structural components. This paper describes an experimental technique for determining imperfections in long (5.7 m) structural members using a series of overlapping measurements. Measurements were performed on 31 austenitic stainless steel sections formed from three different production routes: hot-rolling, cold-rolling and press-braking. Spectral analysis was carried out on the imperfections to obtain information on the periodic nature of the profiles. Two series were used to model the profile firstly the orthogonal cosine and sine functions in a classic Fourier transform and secondly a half sine series. Results were compared to the relevant tolerance standards. Simple predictive tools for both local and global imperfections have been developed to enable representative geometric imperfections to be incorporated into numerical models and design methods.

Improved buckling reduction factors for existing steel columns accounting for different imperfections

The advantage of second-order nonlinear analysis lies on its capacity to model actual structural response instead of making assumption on the structural behavior such as the arbitrary assumption of effective length factor. Considering the construction process of a structure, it may become a sway frame from a non-sway frame when a story is added or, on the contrary, to convert to a non-sway frame from a sway frame when bracings or infill walls are constructed and this makes the first-order linear analysis extremely inconvenient to use. Further, the deformation and load distributions of the structures considering the construction sequence can be much different from those obtained by assuming all structural elements share loads simultaneously. This paper proposes an advanced simulation-based design using an improved second-order analysis for structures accounting for both local and global imperfections, sequential loads and construction process. The technique for such an analysis is described and the error for ignoring the effects of sequential loads and construction procedure is quantified. Both the elastic and the plastic second-order analyses are used for comparison.

Buckling strength of axially loaded cold formed built-up I-sections with and without stiffened web

Numerical investigation and design of aluminum alloy circular hollow section columns

Numerical investigation and design of perforated aluminium alloy SHS and RHS columns

Objective To evaluate the biomechanical characteristics of 4 fixation methods (single reconstruction plate, dual reconstruction plates, single cannulated screw and dual cannulated screws) in the treatment of pubic symphysis disruption. Methods Miniature spiral CT scans were performed on the complete pelvis in 5 healthy volunteers. The primary two-dimensional CT scan data at DICOM format were imported into software Mimics 15.0 for three-dimensional reconstruction of bilateral hips and sacrums. The finite element model of skeletal pelvis was obtained by grid partitioning and assignment using software Abqus 6.13. Models of pubic symphysis disruption were simulated by cutting off the unilateral sacroiliac ligament, sacral spine ligament, sacral tuberosity ligament, pubic ligament and pubic arch. Four implants(single reconstruction plate, dual reconstruction plates, single cannulated screw and dual cannulated screws) were simulated and emplaced onto the models according to standard surgical procedures. Compressive and rotational loads were implemented in all models for finite element analysis. The biomechanical properties were recorded and analyzed, including construct stiffness, micromotion of the pubic symphysis and von Misses stress. Results Under vertical load, the space of pubic symphysis disruption >25 mm. The vertical stiffness and rotational construct stiffness of the pelvis decreased significantly from 442.738±29.946 N/mm and 10.118±1.432 N·m/Deg in the normal group to 14.754±0.876 N/mm and 0.328±0.119 N·m/Deg, respectively. Dual reconstruction plates and dual cannulated screws displayed the best vertical tensile strength; their construct stiffness achieved 117.647±9.193 N/mm and 131.443±4.348 N/mm, respectively. Under anti-rotation load, dual cannulated screws displayed the best performance because they rebuilt 68.6% of the whole structural stiffness. For the local stability of the pubic symphysis, dual reconstruction plates showed a strong local anti-rotation capability and dual cannulated screws a good local anti-tensile capability. The displacement in the dual cannulated screws group was only -0.240±0.119 mm under vertical load while the angular displacement in the dual reconstruction plates group only 0.218°±0.182°. Single reconstruction plate endured the maximum von Misses stress which was obviously concentrated. Conclusion Dual cannulated screws may have biome-chanical advantages for treatment of pubic symphysis disruption. Key words: Pelvis; Finite element analysis; Biomechanical characteristics; Fractures fixation, internal; Comparative study

Three-dimensional (3D) outside diameter (OD) and wall thickness mapping of a casing joint include synchronized OD laser scanning and wall UT (ultrasonic testing) measurement at a resolution of every 1-inch along the length and every 1 or 2 degrees around the circumference. This full-length mapping data can then be used to construct a 3D finite element analysis (FEA) model that captures the geometric attributes, including OD, wall thickness, OD ovality, and wall eccentricity of a casing joint. Together with the actual nonlinear material plasticity model and the measured residual stress, the 3D FEA model can accurately predict the casing collapse strength. Also, the Klever-Tamano ultimate limit-state (KT ULS) collapse equation per API TR 5C3 [1] together with a calibrated moving-average scheme was used to calculate the joint's collapse strength. Results predicted by 3D FEA and KT ULS collapse models were then compared to the actual full-scale collapse test results. A 3D FEA model generally produces more accurate results than the KT collapse equation. In addition, both 3D FEA and KT collapse models predict slightly lower than actual collapse pressure, which therefore is on the conservative side. The accurate prediction of casing collapse strength can be beneficial to the end user in sorting and ranking the casing joints by collapse resistance, and therefore provides valuable information that can be used in the end user's risk assessment with the consideration of the worst-case discharge scenario. Furthermore, the end user may potentially select the joints with the highest predicted collapse strength for the bottom portion of the casing string where the highest collapse resistance is desired. In addition, the OD and wall mapping data together with the actual material tensile properties (yield strength, ultimate tensile strength, and strain hardening parameters) can be used in estimating the internal yield and ductile rupture pressures and other performance properties. This is outside the scope of this paper and can be pursued in future work. These predicted casing performance properties may then be used in sorting and ranking the joints based on a specific performance property of interest or combination of performance properties.

Sensitivity to local imperfections in inelastic thin-walled rectangular hollow section struts