Compressive Strength of Tubular Members with Combined Pitting Corrosion and Crack Damage

Tubular members subject to combined pitting corrosion and crack damage were numerically studied to clarify the reduction of ultimate strength and failure behavior,based on numerical models validated against available experi-ments.The effects of length,location and inclined angle of a crack under combined damage were studied to disclose the mechanism of interaction between the crack and corrosion pits.The methods,named as linear superposition directly accumulating the effects of solo crack and solo pitting damage,as well as crack projection transferring an inclined crack to a transverse one,were discussed and verified in the view of assessing ultimate strength of tubular members with combined damage.It was shown that the former is practical but complex while the next always over-estimates the residual strength.Besides,the location and inclined angle of a crack have a subtle effect on the reduction of ultimate strength under combined damage,especially at higher level of pitting damage,due to the synergistic effect between corrosion pits and cracks.Such effect can lead to early occurrence of plasticity and local buckling by inducing stress interaction between crack tips and pits,and causing more significant strength reduction compared with a solo type of damage.A practical method was proposed to determine the loss ratio of cross-sectional area on the equivalent weakest section of a damaged member.Based on the loss ratio,a formula was presented to predict the ultimate strength of damaged members with combined damage,showing good applicability.

Moment-curvature relationship of FRP-concrete-steel doubleskin tubular members

Tests were conducted on 3 specimens to study the flexural behavior of fiber reinforced polymer(FRP)-concrete-steel double-skin tubular members(DSTMs).The strip method was used to calculate the section momentcurvature curves of the 3 specimens and 12 models.A theoretical formula is presented for the flexural strength of DSTMs.The test results show that the tension zone of the specimen FRP tubes was in hoop compression while the compression zone was in hoop tension.The load-carrying capacity did not decrease even when the mid-span deflection reached about 1/24 of the span length.The tests,simulation and theoretical analysis resulted in a simplified formula for the flexural strength of DSTMs and a tri-linear moment-curvature model was expressed as a function of the section bending stiffness for DSTMs.

Shear Failure of a Clamped Dented Tubular Beam Under Lateral Impact

The shear failure of a rigid-plastic dented clamped tubular beam under the lateral impact of a mass is investigated. Both the denting and the impact point are in the middle span of the beam. It is assumed that denting does not spread during the shear sliding. Numerical results show that the axial force and lateral deflection of the beam are very small at the moment of the occurence of shear failure, which means that the finite deformation effect can be neglected in the shear failure analysis. Also, some aspects of the initial impact energy are investigated.

考虑管状构件屈曲恰当建模的海洋导管架结构完整性评估——以Resalat导管架为例

In the present research,results of buckling analysis of 384 finite element models,verified using three different test results obtained from three separate experimental investigations,were used to study the effects of five parameters such as D/t,L/D,imperfection,mesh size and mesh size ratio.Moreover,proposed equations by offshore structural standards concerning global and local buckling capacity of tubular members including former API RP 2A WSD and recent API RP 2A LRFD,ISO 19902,and NORSOK N-004 have been compared to FE and experimental results.One of the most crucial parts in the estimation of the capacity curve of offshore jacket structures is the correct modeling of compressive members to properly investigate the interaction of global and local buckling which leads to the correct estimation of performance levels and ductility.Achievement of the proper compressive behavior of tubular members validated by experimental data is the main purpose of this paper.Modeling of compressive braces of offshore jacket platforms by 3D shell or solid elements can consider buckling modes and deformations due to local buckling.ABAQUS FE software is selected for FE modeling.The scope of action of each of elastic buckling,plastic buckling,and compressive yielding for various L/r ratios is described.Furthermore,the most affected part of each parameter on the buckling capacity curve is specified.The pushover results of the Resalat Jacket with proper versus improper modeling of compressive members have been compared as a case study.According to the results,applying improper mesh size for compressive members can under-predict the ductility by 33%and under-estimate the lateral loading capacity by up to 8%.Regarding elastic stiffness and post-buckling strength,the mesh size ratio is introduced as the most effective parameter.Besides,imperfection is significantly the most important parameter in terms of critical buckling load.