Fatigue Evaluation of Cable-stayed Bridge Steel Deck Based on Predicted Traffic Flow Growth

Zhongqiu Fu,Bohai Ji,Zhi Ye,Yixun Wang 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.4

Statistical analysis of the measured traffic flow over the Nanjing No. 3 Yangtze River Bridge from 2006 to 2010 was conducted. The predictions of traffic flow growth model were established. Random traffic flow was simulated by Monte-Carlo method to study dynamic impact effects under vehicle load. Considering the dynamic impact effects and wheel mark transverse distribution, the nominal stress, hot spot stress, and notch stress in the steel bridge deck details was calculated. The results of three evaluation method were compared. Suggestions of analysis models and fatigue evaluation were proposed. The study showed that the maximum magnification coefficient of the dynamic impact effects was close to the suggestion of BS5400. The simplified model could be used to analysis local stress ignoring the superimposed effects of longitudinal multi-vehicles. The evaluated service life under hot spot stress was comparatively longer. In terms of bridge safety and convenience, notch stress for the roof weld and U rib-to-diaphragm weld and hot spot stress for diaphragm arc gap were more suitable for fatigue evaluation. And the roof weld was most likely to crack.

The behavior of lightweight aggregate concrete filled steel tube columns under eccentric loading

Elzien Abdelgadir,Ji Bohai,Fu Zhongqiu,Hu Zhengqing 국제구조공학회 2011 Steel and Composite Structures, An International J Vol.11 No.6

This paper consists of two parts; the first part describes the laboratory work concerning the behavior of lightweight aggregate concrete filled steel tubes (LACFT). Based on eccentricity tests, fifty-four specimens with different slenderness ratios (L/D= 3, 7, and 14) were tested. The main parameters varied in the test are: load eccentricity; steel ratio; and slenderness ratio. The standard load-strain curves of LACFT columns under eccentric loading were summarized and significant parameters affecting LACFT column's bearing capacity, failure mechanism and failure mode such as confinement effect and bond strength were all studied and analyzed through the comparison with predicted strength of concrete filled steel tube columns (CFT) using the existing codes such as AISC-LRFD (1999), CHN DBJ 13-51-2003 (2003) and CHN CECS 28:90 (1990). The second part of this paper presents the results of parametric study and introduces a practical and accurate method for determination of the maximum compressive strength of confined concrete core ( fmax), In addition to, the study of the effect of aspect-ratio and length-width ratio on the yield stress of steel tubes ( fsy) under biaxial state of stress in CFT columns and the effect of these two factors on the ultimate load carrying capacity of axially loaded CFT/LACFT columns.

Fatigue Performance of Cracked Rib-Deck Welded Joint Retrofitted by ICR Technique

YuanZhou Zhiyuan,Ji Bohai,Fu Zhongqiu,Ge Hanbin 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.3

To evaluate the retrofit effect by ICR technique (a new technique developed in recent years), relative tests were carried out with two cracked rib-deck specimens. The fatigue performance, including crack propagation rate, remaining fatigue life, and stress variation was analyzed. An improvement was observed through the test results after the cracked specimen retrofitted. Crack propagation in the treated specimen was restrained by the closed surface and residual compressive stress, and the crack propagation rate was reduced significantly. Stress at the welded joint and the crack tip was redistributed after ICR treatment. An increasing has been found near the weld toe, and reduction is occurred at the crack tip, which matches FEM results. This stress variation might contribute to a delay in subsequent crack propagation.

Stress Concentration Factor-Based Hot-Spot Stress Prediction Model for the Web-Gap Weld of Main Girder in Steel Truss Bridge

Chuanxi Li,Bohai Ji,Zhongqiu Fu,Yue Yao 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.1

Fatigue cracking is one of the main diseases of steel bridges in operation stage. Scientific evaluation is of great significance to improve structural durability. However, obtaining the hot-spot stress (HSS) extrapolation point is challenging due to limited space around certain structural details in steel bridges. To overcome this limitation, a HSS prediction method incorporating the stress concentration factor (SCF) was proposed. Additionally, a structural mechanics model based on the mechanical characteristics of the web gap in the main girder of a steel truss bridge was established to calculate its nominal stress. Experimental and numerical simulations have been conducted to investigate the effects of various geometric parameters of the web gap on the SCFs. On this basis, a formula for predicting the SCF in web-gap weld was developed using multiple linear stepwise regression analysis. A fatigue evaluation framework considering the SCF for the web-gap weld were proposed. The result shows the web gap is affected by the joint actions of rotation and displacement, with the web gap of the end floor beam being more prone to fatigue damage. Moreover, the structural mechanics model considering the joint actions of rotation and displacement aligns better with the actual stress characteristics. The proposed SCF prediction formula for the web-gap weld demonstrates an error of less than 5% compared to the FE results. The fatigue damage obtained by the proposed HSS prediction method is consistent with the traditional extrapolation method, hence validating the feasibility and reliability of the proposed approach.

Fatigue Strength and Root-Deck Crack Propagation for U-Rib to Deck Welded Joint in Steel Box Girder

YuanZhou Zhiyuan,Ji Bohai,Li Di,Fu Zhongqiu 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.5

Fatigue tests and numerical analysis were carried out to evaluate the fatigue performance at the U-rib to deck welded joint in steel box girder. Twenty specimens were tested corresponding to diff erent penetration rates (80 and 100%) under fatigue bending load, and the fatigue strength was investigated based on hot spot stress (HSS) method. The detailed stress distribution at U-rib to deck welded joint was analyzed by the fi nite element method, as well as the stress intensity factor of weld root. The test results show that the specimens with fully penetration rate have longer crack propagation life due to the welding geometry, resulting in higher fatigue failure strength. The classifi cation of FAT-90 is reasonable for evaluating fatigue strength by HSS method. The penetration rate has eff ect on crack propagation angle near the surface, and the 1-mm stress below weld toe and root approves to be more suitable for fatigue stress assessment, because of its high sensitivity to weld geometry than HSS.

Behaviour of lightweight aggregate concrete-filled steel tube under horizontal cyclic load

Zhongqiu Fu,Bohai Ji,Dongyang Wu,Zhenpeng Yu 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.6

A horizontal cyclic test was carried out to study the seismic performance of lightweight aggregate concrete filled steel tube (LACFST). The constitutive and hysteretic model of core lightweight aggregate concrete (LAC) was proposed for finite element simulation. The stress and strain changes of the steel tube and concrete filled inside were measured in the experiment, and the failure mode, hysteresis curve, skeleton curve, and strain curve of the test specimens were obtained. The influence of axial compression ratio, diameter-thickness ratio and material strength were analysed based on finite element model. The results show that the hysteresis curve of LACFST indicated favourable ductility, energy dissipation, and seismic performance. The LACFST failed when the concrete in the bottom first crushed and the steel tube then bulged, thus axial force imposed by prestressing was proved to be feasible. The proposed constitutive model and hysteretic model of LAC under the constraint of its steel tube was reliable. The bearing capacity and ductility of the specimen increase significantly with increasing thickness of the steel tube. The bearing capacity of the member improves while the ductility and energy dissipation performance slightly decreased with the increasing strength of the steel and concrete.

Experimental Study on the Fatigue Performance of Roof and U-rib Welds of Orthotropic Steel Bridge Decks

Zhongqiu Fu,Bohai Ji,Chengyi Zhang,Di Li 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.1

The fatigue performance of a roof-U rib weld on orthotropic steel bridge decks was studied by fatigue experiments on 40 specimens, considering the influences of amplitude, penetration rate, loading position, and steel strength. Influences of different factors on the fatigue life of crack initiation and specimen failure were studied by analysis of crack propagation in the weld and changes in stress amplitude. In addition, nominal stress amplitudes and hot spot stress amplitudes of the welds were compared and the suggested values of fatigue strength were proposed according to the test results. The study shows that increase of penetration rate can decrease the crack propagation rate and extend failure fatigue life. A larger steel strength can increase the fatigue strength of crack initiation. Under the same loading conditions, the fatigue life of crack initiation is about half of the failure fatigue strength. A nominal stress of 70 MPa and a hot spot stress of 75 MPa are recommended for fatigue strength of roof-U rib welds under the manufacturing process investigated here.

Fatigue performance of rib-roof weld in steel bridge decks with corner braces

Zhongqiu Fu,Bohai Ji,Yixun Wang,Jie Xu 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.1

To study the effects of corner braces on fatigue performance of the U-rib and roof weld in steel bridge decks, the fatigue experiment was carried out to compare characteristics of the crack shape with and without corner braces. The improvement of fatigue life and stress variation after setting corner braces were also analysed. Different parameters of corner brace sizes, arrangements, and detail types were considered in the FEM models to obtain stress distribution and variation at the weld. Furthermore, enhancement of the fatigue performance by corner braces was evaluated. The results demonstrated that the corner brace could improve the fatigue life of the U-rib and roof weld, which exerted even no influence on the crack shape. Moreover, stress of the roof weld was decreased and the crack position was transferred from the root weld to U-rib and corner brace weld. It was suggested no weld scallop should be drilled on the corner brace. A transverse rib with lower height which was set between U-ribs was favourable for improvement of fatigue performance.

Effective Notch Stress Approach-Based Fatigue Evaluation of Rib-to-Deck Welds Including Pavement Surfacing Effects

Qiudong Wang,Bohai Ji,Zhongqiu Fu,Yue Yao 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.1

The eff ective notch stress-based fatigue evaluation approach considering the eff ect of pavement surfacing is developed and verifi ed in this research. Firstly, the sensitivity of stresses at fatigable welds to pavement surfacing was investigated. It turns out that rib-to-deck weld is most sensitive to pavement surfacing. Secondly, the infl uence of pavement surfacing on initial cracking position of rib-to-deck weld was analysed. Subsequently, the relationship between notch stress and temperature was developed based on the numerical results, so is the relationship between initial cracking position and temperature. Finally, the fatigue damages evaluated by eff ective notch stress approach and traditional approach were compared and analysed. The results show that the stress dispersal behaviour through pavement surfacing further improves the fatigue durability of rib-to-deck welds. The initial cracking position is related to the pavement temperature, rather than the transverse loading positions of vehicle loads. The eff ective notch stress concentration position varies with the pavement temperature. Such variation should be reasonably considered in fatigue damage evaluation process where eff ective notch stress approach is applied.

Study on Fatigue Performance of Arc Notch of Diaphragm in Steel Box Girder

Cheng Meng,YuanZhou Zhiyuan,Ji Bohai,Muye Yang 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.6

Steel box girders are easily subjected to fatigue cracking under the vehicle loading, and the crack initiating from arc notch of diaphragm is one of the typical fatigue details. The stress characteristics of diaphragm and U-rib in real bridge under the vehicle loading were analysed, as well as the deformation characteristics. Experimental work on fatigue crack propagation and bearing capacity was conducted. Simulations using the fi nite-element method were undertaken, and the crack propagation behaviours were studied. It is found that the out-of-plane deformation is the main cause of crack propagation at arc notch of diaphragm in real bridge. Fatigue testing data of 9 diaphragm-rib specimens carried out by the vibration fatigue test system and results of FEM simulations show that the rate and path of fatigue crack propagation changed signifi cantly during the fatigue crack propagation. The fatigue crack initiates as a tensile-shear mixed mode crack and turns to single tensile mode with the increase of crack length.