Thermo-mechanical behavior of prestressed concrete box girder at hydration age

Gang Zhang,Meichun Zhu,Shuanhai He,Wei Hou 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.5

Excessively elevated temperature can lead to cracks in prestressed concrete (PC) continuous bridge with box girder on the pier top at cement hydration age. This paper presents a case study for evaluating the behavior of PC box girder during the early hydration age using a two-stage computational model, in the form of computer program ANSYS, namely, 3-D temperature evaluation and determination of mechanical response in PC box girders. A numerical model considering time-dependent wind speed and ambient temperature in ANSYS for tracing the thermal and mechanical response of box girder is developed. The predicted results were compared to show good agreement with the measured data from the PC box girder of the Zhaoshi Bridge in China. Then, based on the validated numerical model three parameters were incorporated to analyze the evolution of the temperature and stress within box girder caused by cement hydration heat. The results of case study indicate that the wind speed can change the degradation history of temperature and stress and reduce peak value of them. The initial casting temperature of concrete is the most significant parameter which controls cracking of PC box girder on pier top at cement hydration age. Increasing the curing temperature is detrimental to prevent cracking.

Designing method for fire safety of steel box bridge girders

Xuyang Li,Gang Zhang,Venkatesh Kodur,Shuanhai He,Qiao Huang 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.38 No.6

This paper presents a designing method for enhancing fire resistance of steel box bridge girders (closed steel box bridge girder supporting a thin concrete slab) through taking into account such parameters namely; fire severity, type of longitudinal stiffeners (I, L, and T shaped), and number of longitudinal stiffeners. A validated 3-D finite element model, developed through the computer program ANSYS, is utilized to go over the fire response of a typical steel box bridge girder using the transient thermo-structural analysis method. Results from the numerical analysis show that fire severity and type of longitudinal stiffeners welded on bottom flange have significant influence on fire resistance of steel box bridge girders. T shaped longitudinal stiffeners applied on bottom flange can highly prevent collapse of steel box bridge girders towards the end of fire exposure. Increase of longitudinal stiffeners on bottom flange and web can slightly enhance fire resistance of steel box bridge girders. Rate of deflection-based criterion can be reliable to evaluate fire resistance of steel box bridge girders in most fire exposure cases. Thus, T shaped longitudinal stiffeners on bottom flange incorporated into bridge fire-resistance design can significantly enhance fire resistance of steel box bridge girders.

Seismic Fragility Analysis of V-Shaped Continuous Girder Bridges

Leping Ren,Gang Zhang,Yongfei Zhang,Shuanhai He 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.3

This paper presents an improved approach for evaluating seismic performance of V-shaped continuous girder bridges with different V-angles. A 3-D finite element model is established using the OpenSees for tracing the response of a typical three-span V-shaped continuous girder bridge. The analysis is performed in three steps: component fragility analysis, validated system fragility analysis and V-angle analysis. A series of nonlinear time history analysis(NLTHA), considering the uncertainty in bridge structural parameters and ground motions characteristics, is carried out to investigate the potential fragile position of a V-shapedcontinuous girder bridge. Subsequently, a new improved product of conditional marginal(PCM) method is validated successfully and utilized to form the system fragility curves. The application of the validated method is used to analyse the influence of V-angle on the bridge structural system fragility. The analysis result shows that variation of V-angle has significantinfluence on seismic fragility of V-shaped continuous girder bridges. The V-shaped continuous girder bridges with 80° V-angle has good seismic performance when PGA ≤ 0.8 g. Smaller V-angle can result in higher seismic fragility of V-shaped continuous girder bridges.

Fire Performance of Continuous Steel-Concrete Composite Bridge Girders

Gang Zhang,Chaojie Song,Xuyang Li,Shuanhai He,Qiao Huang 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.3

This paper presents a detailed investigation in to fire resistance along with failure mode in continuous steel-concrete composite twin I-shaped bridge girders under different localized fire through considering fire severity and fire exposure positions namely; mid-span zone in one of the two span, hogging moment zone and side-support zone. A 3-D finite element (FE) model, built utilizing the computer program ANSYS, is used to track structural fire performance in a typical two span of continuous composite twin I-shaped bridge girders (fabricated with twin I-shaped plates supporting a concrete slab) dependent on thermo-mechanical coupled analysis. The model validation is undertook through comparison of temperature and deflection response attained from a scaled composite single I-shaped girder tested exposed to ISO834 fire. The numerical analysis results show that the developed model can be favorably used to analyze the behavior and failure mode of continuous steel-concrete composite twin I-shaped bridge girders during entire range of fire exposure. Fire severity and fire exposure positions present critical influence in to the fire resistance of continuous composite bridge girders. Fire exposure prevention on hogging moment zone can significantly extend failure time of continuous girders, and further hold back progressive structural collapse. Web buckling based failure criterion can be applicable to calculate fire resistance of realistic continuous girders under simultaneous structural loading together with localized fire. Continuous composite bridge girders subjected to localized fire present highly significant local deformation response in the fire exposed bridge girder span.

Evaluating fire resistance of prestressed concrete bridge girders

Gang Zhang,Venkatesh Kodur,Wei Hou,Shuanhai He 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.6

This paper presents an approach for evaluating performance of prestressed concrete (PC) bridge girders exposed to fire. A finite element based numerical model for tracing the response of fire exposed T girders is developed in ANSYS. The analysis is carried out in three stages, namely, fire temperature calculation, cross sectional temperature evaluation, and then strength, deformation and effective prestress analysis on girders exposed to elevated temperatures. The applicability of the computer program in tracing the response of PC bridge girders from the initial preloading stage to failure stage, due to combined effects of fire and structure loading, is demonstrated through a case study, and validated by test data of a scaled PC box girder under ISO834 fire condition. Results from the case study show that fire severity has a significant influence on the fire resistance of PC T girders and hydrocarbon fire is most dangerous for the girder. The prestress loss caused by elevated temperature is about 10% under hydrocarbon fire till the girder failure, which can lead to the increase in deflection of the PC girder. The rate of deflection failure criterion is suggested to determine the failure of PC T girder under fire.

A numerical method for evaluating fire performance of prestressed concrete T bridge girders

Gang Zhang,Venkatesh Kodur,Chaojie Song,Wei Hou,Shuanhai He 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.25 No.6

This paper presents a numerical method for evaluating fire performance of prestressed concrete (PC) T shaped bridge girders under combined effect of structural loading and hydrocarbon fire exposure conditions. A numerical model, developed using the computer program ANSYS, is employed to investigate fire response of PC T shaped bridge girders by taking into consideration structural inherent parameters, namely; arrangement of prestressing strands with in the girder section, thickness of concrete cover over prestressing strands, effective degree of prestress and content of prestressing strands. Then, a sequential thermo-mechanical analysis is performed to predict cross sectional temperature followed by mechanical response of T shaped bridge girders. The validity of the numerical model is established by comparing temperatures, deflections and failure time generated from fire tests. Through numerical studies, it is shown that thickness of concrete cover and arrangement of prestressing strands in girder section have significant influence on the fire resistance of PC T shaped bridge girders. Increase in effective degree of prestress in strands with triangular shaped layout and content in prestressing strands can slow down the progression of deflections in PC T shaped bridge girder towards the final stages of fire exposure, to thereby preventing sudden collapse of the girder. Rate of deflection based failure criterion governs failure in PC T shaped bridge girders under most hydrocarbon fire exposure conditions. Structural inherent parameters incorporated into sectional configuration can significantly enhance fire resistance of PC bridge girders; thus mitigating fire induced collapse of these bridge girders.

Improved definition of dynamic load allowance factor for highway bridges

Yongjun Zhou,Zhongguo John Ma,Yu Zhao,Xiongwei Shi,Shuanhai He 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.3

The main objective of this paper is to study the dynamic load allowance (DLA) calculationmethods for bridges according to the dynamic response curve. A simply-supported concrete bridge with asmooth road surface was taken as an example. A half-vehicle model was employed to calculate the dynamicresponse of deflection and bending moment in the mid-span section under different vehicle speeds using thevehicle-bridge coupling method. Firstly, DLAs from the conventional methods and code provisions wereanalyzed and critically evaluated. Then, two improved computing approaches for DLA were proposed. Inthe first approach, the maximum dynamic response and its corresponding static response or itscorresponding minimum response were selected to calculate DLA. The second approach utilized weightedaverage method to take account of multi-local DLAs. Finally, the DLAs from two approaches werecompared with those from other methods. The results show that DLAs obtained from the proposedapproaches are greater than those from the conventional methods, which indicate that the currentconventional methods underestimate the dynamic response of the structure. The authors recommend that theweighted average method based on experiments be used to compute DLAs because it can reflect thevehicle’s whole impact on the bridge.

Improved definition of dynamic load allowance factor for highway bridges

Zhou, Yongjun,Ma, Zhongguo John,Zhao, Yu,Shi, Xiongwei,He, Shuanhai Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.3

The main objective of this paper is to study the dynamic load allowance (DLA) calculation methods for bridges according to the dynamic response curve. A simply-supported concrete bridge with a smooth road surface was taken as an example. A half-vehicle model was employed to calculate the dynamic response of deflection and bending moment in the mid-span section under different vehicle speeds using the vehicle-bridge coupling method. Firstly, DLAs from the conventional methods and code provisions were analyzed and critically evaluated. Then, two improved computing approaches for DLA were proposed. In the first approach, the maximum dynamic response and its corresponding static response or its corresponding minimum response were selected to calculate DLA. The second approach utilized weighted average method to take account of multi-local DLAs. Finally, the DLAs from two approaches were compared with those from other methods. The results show that DLAs obtained from the proposed approaches are greater than those from the conventional methods, which indicate that the current conventional methods underestimate the dynamic response of the structure. The authors recommend that the weighted average method based on experiments be used to compute DLAs because it can reflect the vehicle's whole impact on the bridge.