A tube with a rectangular cut-out. Part 1: Subject to pure bending

2006 ◽  
Vol 220 (5) ◽  
pp. 625-643 ◽  
Author(s):  
B. J. Vartdal ◽  
S. T. S. Al-Hassani ◽  
S. J. Burley
Keyword(s):  
Fracture Behaviour ◽  
Deformation Behaviour ◽  
Plastic Hinge ◽  
Shell Structures ◽  
Pure Bending ◽  
Steel Tubes ◽  
Jacket Structures ◽  
Axial Dimension ◽  
Semi Empirical ◽  
And Control

The response to pure bending of tubes with rectangular cut-outs is considered. Experiments on 1000-mm long, 100-mm diameter, and 2.55-mm wall thickness DIN 2391 ST NBK supported steel tubes are described. Such a thickness-to-diameter ratio is typical of structural columns, rather than shell structures. Tubes containing cut-outs with an axial dimension of up to 30 mm and a circumferential size of up to 180° were tested. It was found that plastic hinge mechanisms dominated the response when the cut-out was on the compressive side, whereas fracture behaviour dominated the response when the cut-out was on the tensile side. Finite element and semi-empirical analyses were carried out to predict the global load-deformation behaviour of the tubes. All analyses gave reasonable predictions of the experimental results for the majority of the cut-out parameters investigated. The aim of this study is to investigate the feasibility of using cut-outs to initiate and control the toppling of offshore jacket structures.

A Tube with a Rectangular Cut-Out. Part 2: Subject to Axial Compression

2006 ◽  
Vol 220 (5) ◽  
pp. 645-652
Author(s):  
B. J. Vartdal ◽  
S. T. S. Al-Hassani ◽  
S. J. Burley
Keyword(s):  
Axial Compression ◽  
Deformation Behaviour ◽  
Diameter Ratio ◽  
Shell Structures ◽  
Steel Tubes ◽  
Reduced Cross Section ◽  
Simply Supported ◽  
Jacket Structures ◽  
Semi Empirical ◽  
And Control

Simply supported steel tubes with rectangular cut-outs of different sizes positioned at their mid-length were subject to axial compression to assess the effect of the cut-outs on the deformation behaviour. Experiments on 1000 mm long, 100 mm diameter, and 2.55 mm wall thickness DIN 2391 ST NBK supported steel tubes are described. The experimental tubes were relatively thick walled, with a thickness-to-diameter ratio typical of structural columns, rather than shell structures. The radial position of the cut-outs was such that the reduced cross-section was symmetric with respect to the direction of rotation of the pinned ends. Several permutations of the axial and circumferential dimensions of the cut-out were tested so that the effect of changing these dimensions could be assessed. Finite-element and semi-empirical analyses were carried out to predict the global load-deformation behaviour of the tubes. Both analyses gave good predictions of the experimental results for the majority of the cut-out parameters investigated. The motivation for the study was to investigate the feasibility of using cut-outs to initiate and control the toppling of offshore jacket structures.

Effect of Lu¨ders Bands on the Bending Capacity of Steel Tubes

2010 ◽  
Author(s):  
Julian F. Hallai ◽  
Stelios Kyriakides
Keyword(s):  
Limit State ◽  
Solution Procedure ◽  
Inhomogeneous Deformation ◽  
Pure Bending ◽  
Steel Tubes ◽  
Deformation Regime ◽  
Bending Capacity ◽  
The Moment ◽  
T Values ◽  
Structural Instabilities

In several offshore applications hot-finished pipe that often exhibits Lu¨ders bands is bent to strains of 2–3%. Lu¨ders banding is a material instability that leads to inhomogeneous plastic deformation in the range of 1–4%. It can precipitate structural instabilities and collapse of the pipe. Experiments and analysis are used to study the interaction of the prevalent structural instabilities under bending with Lu¨ders banding, with the objective of providing guidance to the designer. Pure bending experiments on tubes of various D/t values reveal that Lu¨ders bands result in the development of inhomogeneous deformation in the structure, in the form of coexistence of two curvature regimes. Under rotation controlled bending, the higher curvature zone(s) gradually spreads while the moment remains essentially unchanged. For relatively low D/t tubes with relatively smaller Lu¨ders strain, the whole tube eventually is deformed to the higher curvature, subsequently entering the usual hardening regime where it continues to deform uniformly until the expected limit state is reached. For higher D/t tubes and/or for materials with longer Lu¨ders strain, the structure collapses during the inhomogeneous deformation regime. This class of problems is analyzed using 3D finite elements and an elastic-plastic constitutive model with an up-down-up material response. It will be demonstrated that the solution procedure followed can simulate the experiments with consistency.

Response and Stability of Square Tubes Under Bending

1997 ◽  
Vol 64 (3) ◽  
pp. 649-657 ◽  
Author(s):  
S. P. Vaze ◽  
E. Corona
Keyword(s):  
Analytical Model ◽  
Cross Section ◽  
Thickness Ratio ◽  
Pure Bending ◽  
Steel Tubes ◽  
Elastic Plastic ◽  
Plastic Steel

This paper addresses the response and stability of elastic-plastic steel tubes with square cross section under pure bending. An analytical model with sufficiently nonlinear kinematics to capture the development of ripples in the compression flange was developed. the results indicate that collapse of such tubes is imperfection sensitive for tubes with “high” height-to-thickness ratio (h/t), but the sensitivity decreases as h/t decreases. Experimentally, the tubes collapse due to a limit moment instability which is followed by the formation of a kink on the compression flange of the tubes. The limit moment and the development of the kink are captured well by the analytical model.

Asymmetric Postbuckling Behavior of Hemispherical Shell Structure Under Axial Compression

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Shanshuai Wang ◽  
Shuhui Li ◽  
Ji He ◽  
Yixi Zhao
Keyword(s):  
Stainless Steel ◽  
Axial Compression ◽  
Shell Structure ◽  
Load Capacity ◽  
Plastic Hinge ◽  
Shell Structures ◽  
Postbuckling Behavior ◽  
Asymmetric Deformation ◽  
Deformation Stage ◽  
Hemispherical Shell

In real physical experiments, three typical deformation stages including elastic deformation stage, symmetric deformation stage, and asymmetric deformation stage appear step by step when the stainless steel hemispherical shell structure is under axial compression loading. During the asymmetric deformation stage, the rolling-plastic-hinge-radius which characterizes the size of the deformation area evolves along the circumferential direction with the compressive displacement. For the hemispherical shell structures with apparent asymmetric deformation stage, the double-buckling phenomenon of the structures in experiments can be clearly detected. The traditional theoretical analysis based on the assumption with circumferentially constant rolling-plastic-hinge-radius is not suitable to predict this phenomenon. For these hemispherical shell structures, load capacity and absorbed energy predicted by the traditional analysis are usually higher than experimental results in the asymmetric deformation stage. In this paper, a new description based on experimental observation for the evolution of rolling-plastic-hinge-radius has been proposed. Minimum energy principle was employed to obtain the postbuckling behavior. The energy evolution of different buckling stages during compression loading is investigated to evaluate the structure load capacity. Stainless steel hemispherical specimens with different sizes are tested under axial compression between two rigid plates to verify the theoretical modification. Good agreement is achieved between proposed model and experimental results. The theoretical model proposed in this paper can be used in prediction of postbuckling behavior for different deformation patterns in the asymmetric deformation stage. It also provides higher flexibility and efficiency for the postbuckling behavior prediction of hemispherical shell structures.

Systematic Modeling of Rotor-Driving Dynamics for Small Unmanned Aerial Vehicles

2018 ◽  
Vol 06 (02) ◽  
pp. 81-93
Author(s):  
Limin Wu ◽  
Yijie Ke ◽  
Ben M. Chen
Keyword(s):  
Unmanned Aerial Vehicles ◽  
Frequency Domain ◽  
Frequency Domain Analysis ◽  
Speed Controller ◽  
Aerial Vehicles ◽  
Dynamics And Control ◽  
Semi Empirical ◽  
And Control ◽  
Cifer Software ◽  
Systematic Modeling

This paper proposes a systematic modeling approach of rotor-driving dynamics for small unmanned aerial vehicles (UAVs) based on system identification and first principle-based methods. Both steady state response analyses and frequency-domain identifications are conducted for the rotor, and Comprehensive Identification from Frequency Responses (CIFER) software is mainly utilized for the frequency-domain analysis. Moreover, a novel semi-empirical model integrating the rotor and the electrical speed controller is presented and validated. The demonstrated results and model are promising in UAV dynamics and control applications.

Analysis and Control of Layer Deformation Induced by the Densely Arranged Large Diameter Underground Steel Tubes Jacking with NTR Method

2015 ◽  
Vol 744-746 ◽  
pp. 1010-1014
Author(s):  
Chun Fu Jin ◽  
Peng Niu ◽  
Yong Sheng Zhao ◽  
Xuan Wang
Keyword(s):  
Surface Deformation ◽  
Large Diameter ◽  
Influence Factors ◽  
Surface Subsidence ◽  
The Finite Element Method ◽  
Steel Tubes ◽  
Steel Pipes ◽  
Pipe Jacking ◽  
And Control ◽  
Layer Deformation

Combined with the finite element method (FEM) and the field data of Shenyang Metro NTR engineering for pipe jacking process, the variation of surface deformation and influence factors of NTR construction are systematically analyzed. The result is shown that the curves of the lateral surface subsidence produced by pipe jacking process are accord with the normal distribution curves put forward by Peck .When the top steel pipes are jacked , the surface subsidence develops rapidly and the rate of deformation is larger. In addition , grouting behind the wall and the sequence of the pipe jacking all have a greater impact on the deformation of the layer.

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