Experimental and numerical analysis of fatigue behaviour for tubular K-joints

Yong-Bo Shao,Zhen-Bin Cao 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.19 No.6

In this paper, a full-scale K-joint specimen was tested to failure under cyclic combined axialand in-plane bending loads. In the fatigue test, the crack developments were monitored step by step usinga fracture parameter to be frequently used by many designers to predict the integrity and residual life oftubular joints, can be obtained from experimental test results of the crack growth rate. Furthermore, ascheme of automatic mesh generation for a cracked K-joint is introduced, and numerical analysis of stressintegral method is used to estimate the stress intensity factors along the crack front. The numerical stressintensity factor results have been validated through comparing them with the experimental results. Thecomparison shows that the proposed numerical model can produce reasonably accurate stress intensityinvestigated, and it has been found that semi-ellipse is suitable and accurate to be adopted in numericalanalysis for the stress intensity factor. Therefore, the proposed model in this paper is reliable to be usedfor estimating the stres intensity factor values of cracked tubular K-joints for design purposes.

Static strength of collar-plate reinforced tubular T-joints under axial loading

Yong-Bo Shao 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.2

To study the effect of collar-plate reinforcement on the static strength of tubular T-joints under axial loading, fundamental research work is carried out from both experimental test and finite element (FE) simulation. Through experimental tests on 7 collar-plate reinforced and 7 corresponding un-reinforced tubular T-joints under axial loading, the reinforcing efficiency is investigated. Thereafter, the static strengths of the above 14 models are analyzed by using FE method, and it is found that the numerical results agree reasonably well with the experimental data to prove the accuracy of the presented FE model. Additionally, a parametric study is conducted to analyze the effect of some geometrical parameters, i.e., the brace-to-chord diameter ratio <i>β</i>, the chord diameter-to-chord wall thickness ratio 2<i>γ</i>, collar-plate thickness to chord wall thickness ratio <i>τ</i>_c, and collar-plate length to brace diameter ratio <i>l_c</i>/<i>d</i>1, on the static strength of a tubular T-joint. The parametric study shows that the static strength can be greatly improved by increasing the collar-plate thickness to chord wall thickness ratio <i>τ</i>_c and the collar-plate length to brace diameter ratio <i>l_c</i>/<i>d</i>1. Based on the numerical results, parametric equations are obtained from curving fitting technique to estimate the static strength of a tubular T-joint with collar-plate reinforcement under axial loading, and the accuracy of these equations is also evaluated from error analysis.

Prediction on Static Strength for CHS Tubular K-joints at Elevated Temperature

Yong-Bo Shao,Shubin He,Dongping Yang 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.3

This study presents a design method for predicting the static strength of a Circular Hollow Section (CHS) tubular K-joint at elevated temperature. The presented method is obtained based on a parametric study by the authors (He et al., 2015a). In determining the static strength of a tubular K-joint at elevated temperature, a deforming rate criterion is proposed, and it is proved to be much safer and more reasonable for design purposes rather than the conventional definition on that static strength by using 3% of chord ovalisation for the K-joint at ambient temperature. In the presented design method, a strength reduction factor k is proposed, and the static strength of a CHS K-joint at elevated temperature can be obtained simply by multiplying the static strength at ambient temperature with k. The strength reduction factor k is a product of two factors, a revised reduction factor of elastic modulus (λ) and a revised chord stress ratio ( ). From the finite element results of overall 57 K-joint models, the accuracy of the presented design method is assessed to be reliable and accurate.

Experimental and Numerical Investigation on Stiffened Rectangular Hollow Flange Beam

Yong-Bo Shao,Hazem Samih Mohamed,Li Wang,Cheng Song Wu 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.5

Cold-formed thin-walled steel hollow fl ange beam (HFB) has been emerged and utilised structurally. It is composed of one or two closed fl anges with high torsional stiff ness and relatively fl exible web. Hence, the global stability of such beam has greatly been improved compared with conventional I-beams with fl at fl anges, due to their superior torsional stiff ness and stability. However, under concentrated loading, local fl ange deformation occurs easily at the load-action-region, because the tubular fl ange is hollow even if stiff eners are attached to the webs. Up-to-date, rather than fi lling the tubular fl ange with concrete, there is not any relevant literature or reports on how to improve the local buckling state of the hollow fl ange I-beams. Accordingly, in this paper, a stiff ened compression rectangular hollow fl ange beam (SCHFB) is presented, from which the web penetrates the bottom wall of the top tubular fl ange until it reaches its top wall. By doing so, several concentrated loads may be applied safely on the beams or the segmental lunching technique may successfully be used to erect the beam in its place. This paper examines experimentally this stiff ened beam and then extends to use the fi nite element modelling to replicate the actual behaviour of the beam. A numerical comparison between the SCHFB, conventional CHFB and I-beam shows that the ultimate bearing capacity and ductility are signifi cantly enhanced in the case of SCHFB compared with the other two beams. Additionally, the SCHFB has been found to own better local deformation performance than that of the CHFB. However, with the span increase, the vertical concave deformation, lateral deformations at top fl ange and vertical deformations of top fl ange plate of the tubes of the SCHFB and CHFB may approach each other. So, the SCHFB becomes the best choice for short-span beams under either concentrated or distributed loading.

Experimental and numerical analysis of fatigue behaviour for tubular K-joints

Shao, Yong-Bo,Cao, Zhen-Bin Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.19 No.6

In this paper, a full-scale K-joint specimen was tested to failure under cyclic combined axial and in-plane bending loads. In the fatigue test, the crack developments were monitored step by step using the alternating current potential drop (ACPD) technique. Using Paris' law, stress intensity factor, which is a fracture parameter to be frequently used by many designers to predict the integrity and residual life of tubular joints, can be obtained from experimental test results of the crack growth rate. Furthermore, a scheme of automatic mesh generation for a cracked K-joint is introduced, and numerical analysis of stress intensity factor for the K-joint specimen has then been carried out. In the finite element analysis, J-integral method is used to estimate the stress intensity factors along the crack front. The numerical stress intensity factor results have been validated through comparing them with the experimental results. The comparison shows that the proposed numerical model can produce reasonably accurate stress intensity factor values. The effects of different crack shapes on the stress intensity factors have also been investigated, and it has been found that semi-ellipse is suitable and accurate to be adopted in numerical analysis for the stress intensity factor. Therefore, the proposed model in this paper is reliable to be used for estimating the stress intensity factor values of cracked tubular K-joints for design purposes.

Poster Session : Purification and characterization of NADH oxidase from Thermococcus profundus

( Bo Lei Jia ),( Seong Cheol Park ),( Yong Gi Shao ),( Gang Won Cheong ) 한국생화학분자생물학회 (구 한국생화학회) 2006 생화학분자생물학회 춘계학술발표논문집 Vol.2006 No.-

Compressive performances of concrete filled Square CFRP-Steel Tubes (S-CFRP-CFST)

Qingli Wang,Yong-Bo Shao 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.16 No.5

Sixteen concrete filled square CFRP-steel tubular (S-CFRP-CFST) stub columns under axial compression were experimentally investigated. The experimental results showed that the failure mode of the specimens is strength loss of the materials, and the confined concrete has good plasticity due to confinement of the CFRP-steel composite tube. The steel tube and CFRP can work concurrently. The load versus longitudinal strain curves of the specimens can be divided into 3 stages, i.e., elastic stage, elasto-plastic stage and softening stage. Analysis based on finite element method showed that the longitudinal stress of the steel tube keeps almost constant along axial direction, and the transverse stress at the corner of the concrete is the maximum. The confinement effect of the outer tube to the concrete is mainly focused on the corner. The confinements along the side of the cross-section and the height of the specimen are both non-uniform. The adhesive strength has little effect both on the load versus longitudinal strain curves and on the confinement force versus longitudinal strain curves. With the increasing of the initial stress in the steel tube, the load carrying capacity, the stiffness and the peak value of the average confinement force are all reduced. Equation for calculating the load carrying capacity of the composite stub columns is presented, and the estimated results agree well with the experimental results.

Static behavior of steel tubular structures considering local joint flexibility

Yamin Wang,Yong-Bo Shao,Yifang Cao 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.24 No.4

As a thin-walled structure, local joint flexibility (LJF) in a tubular structure is prominent, and it may produce significant effect on the static performance for the overall structure. This study presents a simplified analytical model to analyze the static behavior for a steel tubular structure with LJF. The presented model simplifies a tubular structure into a frame model consisted of beam elements with considering the LJFs at the connections between any two elements. Theoretical equations of the simplified analytical model are deduced. Through comparison with 3-D finite element results of two typical planar tubular structures consisted of T- and Y-joints respectively, the presented method is proved to be accurate. Furthermore, the effect of LJF on the overall performance of the two tubular structures (including the deflection and the internal forces) is also investigated, and it is found from analyses of internal forces and deformation that a rigid connection assumption in a frame model by using beam elements in finite element analysis can provide unsafe and inaccurate estimation.

Stress analysis of a new steel-concrete composite I-girder

Yamin Wang,Yong-Bo Shao 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.1

A new I-girder consisted of top concrete-filled tubular flange and corrugated web has been proved to have high resistance to both global buckling of the entire girder and local buckling of the web. This study carries out theoretical analysis and experimental tests for this new I-girder to investigate the stress distribution in the flanges and in the corrugated web. Based on some reasonable assumptions, theoretical equations for calculating the normal stress in the flanges and the shear stress in the corrugated web are presented. To verify the accuracy of the presented equations, experimental tests on two specimens were carried out, and the experimental results of stress distribution were used to assess the theoretical prediction. Comparison between the two results indicates that the presented theoretical equations have enough accuracy for calculating the stress in the new Igirder, and thus they can be used reliably in the design stage.

Compressive strength of circular concrete filled steel tubular stubs strengthened with CFRP

Jialing Ou,Yong-Bo Shao 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.39 No.2

The compressive strength of circular concrete filled steel tubular (C-CFST) stubs strengthened with carbon fiber reinforced polymer (CFRP) is studied theoretically. According to previous experimental results, the failure process and mechanism of circular CFRP-concrete filled steel tubular (C-CFRP-CFST) stubs is analyzed, and the loading process is divided into 3 stages, i.e., elastic stage, elasto-plastic stage and failure stage. Based on continuum mechanics, the theoretical model of C-CFRP-CFST stubs under axial compression is established based on the assumptions that steel tube and concrete are both in three-dimensional stress state and CFRP is in uniaxial tensile stress state. Equations for calculating the yield strength and the ultimate strength of C-CFRP-CFST stubs are deduced. Theoretical predictions from the presented equations are compared with existing experimental results. There are a total of 49 tested specimens, including 15 ones for comparison of yield strength and 44 ones for comparison of ultimate strength. It is found that the predicted results of most specimens are within an error limit of 10%. Finally, simplified equations for calculating both yield strength and ultimate strength of C-CFRP-CFST stubs are proposed.