Numerical Analysis of Local Joint Flexibility of K-joints with External Plates Under Axial Loads in Offshore Tubular Structures

The Local Joint Flexibility(_(LJF))of steel K-joints reinforced with external plates under axial loads is investigated in this paper.For this aim,firstly,a finite element(FE)model was produced and verified with the results of several experimental tests.In the next step,a set of 150 FE models was generated to assess the effect of the brace angle(θ),the stiffener plate size(ηandλ),and the joint geometry(γ,τ,ξ,andβ)on the_(LJF)factor(f_(LJF)).The results showed that using the external plates can decrease 81%of the f_(LJF).Moreover,the reinforcing effect of the reinforcing plate on the f_(LJF)is more remarkable in the joints with smallerβ.Also,the effect of theγon the f_(LJF)ratio can be ignored.Despite the important effect of the f_(LJF)on the behavior of tubular joints,there is not available any study or equation on the f_(LJF)in any reinforced K-joints under axial load.Consequently,using the present FE results,a design parametric equation is proposed.The equation can reasonably predict the f_(LJF)in the reinforced K-joints under axial load.

Degree of bending of concrete-filled rectangular hollow section K-joints under balanced-axial loadings

It has been found that the fatigue life of tubular joints is not only determined by the hot spot stress,but also by the stress distribution through the tube thickness represented as the degree of bending(DoB).Consequently,the DoB value should be determined to improve the accuracy of fatigue assessment for both stress-life curve and fracture mechanics methods.Currently,no DoB parametric formula is available for concrete-filled rectangular hollow section(CFRHS)K-joints,despite their wide use in bridge engineering.Therefore,a robust finite element(FE)analysis was carried out to calculate the DoB of CFRHS K-joints under balanced-axial loading.The FE model was developed and verified against a test result to ensure accuracy.A comprehensive parametric study including 190 models,was conducted to establish the relationships between the DoBs and four specific variables.Based on the numerical results,design equations to predict DoBs for CFRHS K-joints were proposed through multiple regression analysis.A reduction of 37.17%was discovered in the DoB,resulting in a decrease of 66.85%in the fatigue life.Inclusively,the CFRHS K-joints with same hot spot stresses,may have completely different fatigue lives due to the different DoBs.

Fatigue crack in large-scale tubular joints for offshore structures

Tubular members have been used for constructing offshore structures. Large-scale fatigue tests of welded tubular K-joints under the balanced in-plane bending brace were carried out to investigate the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The experimental results were verified by numerical approaches and compared with the IIW, DnV RP-C203 and API RP 2A-WSD design curves. The test results based on the hot spot stress were in agreement with the design curves. The SCF factor for tubular K-joint was also obtained. The numerical parametric study of the K-joint (using the finite element program) was described and its results were compared with experimental results. The stress effects of various parameters including α, β, γ, τ and θ on the stress in the K-joint were investigated. The stress distribution for each parameter was introduced. The study showed that the maximum stress of the joint varied according to the variation of joint parameters.