Study On Structure Performance For Multi-beam Concrete T-shaped Section Beam Girder Subjected To Fire

Fire is one of the most severe hazards to transportation infrastructure subjected duringtheir lifetime. In recent years with the rapid increase of traffic and the diversity oftransportation, fire hazard in bridges is frequent. When increasing transport vehicles filledwith stearinic acid and phenol and oil as well as gas is riding on the highway, a great threat tobridge caused by fire hazard has a tough issue as a result of traffic accidents and human factor.Bridge fires as one of accidental load can lead to significant economic and public losses,what’s more, permanent loss or collapse. The current research presenting an overview of firehazard in bridges is only stayed in the stage of single beam and local structure, which it ishard to be applied actually.Based on study on catastrophe mechanism and strengthening for concrete bridgestructure exposed to fire(Grant No.2011318812970) sponsored by Research Fund Ministry ofTransport of the People’s Republic of China, and Study on thermodynamics model and heatconduction mechanism for concrete bridge exposed to fire(Grant No. CHD2011TD010)sponsored by Research Fund for the Central Universities of China, fire temperature rise modelis established and fire scenarios is designed. Material properties and temperature rise curveare comprehensively putted into consideration, time-dependent formula of burning depth andcumulative burning damage depth for concrete is proposed. The deformation and stressdistribution of multi-beam concrete T-shaped section beam girder are studied under conditionof different fire mode. Fire-resistant performance of structure is revealed. Residual stiffnessand bearing capacity calculation formulae are suggested. Temperature calculation formulaincluding coating thickness and thermal conductivity is constructed on the basis of laminatealgorithm. All of these laid a foundation for fire designation and evaluation. The mainresearch contents are as follows:(1)The relationship between temperature gradient and temperature conductivity of spaceelements is studied. Based on variation of crystalliferous water in concrete, the latent heatfunction of crystalliferous water is studied with increasing temperature, then, thermalconduction matrix equation of elements in transient temperature field is obtained. Based on virtual layer method of heat conduction, calculation method of thermal stress for reinforcedconcrete solid is proposed, and the stress-strain matrix of structure internal force calculationfor reinforced concrete beam exposed to one-way fire is deduced, with extending time andincreasing temperature. also, sensitivity matrix of structure internal force is set up.(2)In the thermo-mechanical coupling analysis, calculation assumptions and mechanicalbehavior and failure criterion of multidimensional reinforced element is studied. Withmodified increment iteration method, total strain of element is gained, which includingthermal and plastic strain increment and total stress of iteration, in modified coordinatesystem.(3)The temperature rise curves such as ISO834and ASTM119and HC and HCM isstudied, fire hazard scene including deck fire and underbridge fire is set and classed in orderto put forward kinds of fire model, for example, deck span fire model, deck local fire model,underbridge span fire model, underbridge local fire model, combining deck and underbridgelocal fire model. all in all, the calculation condition of perfect fire scene is proposed.(4)Based on different fire temperature rise model, the time-dependent relationship amongsome parameters including ISO834model and HCM model and concrete burning depth isstudied, and time-dependent formula of burning depth during process of fire is fitted andproposed. Meanwhile, time-dependent formula of cumulative burning damage depth duringthe whole process of extending fire is put forward by step of the equivalent stiffness andstrength calculation method on the basis of reaearch on variation of cumulative burningdamage depth.(5)Based on high-temperature enthalpy conduction principle, thermo-mechanicalcoupling analysis method is applied to analyzed the variation law of space deformation andstress distribution and solid shear-lags for concrete T-shaped section beam girder undercondition of kinds of deck and underbridge fire model, are studied.①Temperature and stress distribution is studied for deck fire model, and time-dependentcurves of key point for every beam is obtained. During the whole process of extending fire,variation of transverse deflection under dead loads is calculated. At last, the time-dependentvariation of maximum and minimum shear-lags ratio for multi-beam concrete T-shapedsection beam bridges exposed to symmetrical underbridge fire is disclosed. ②Temperature and stress distribution is studied for underbridge fire model, andtime-dependent curves of key point for every beam is obtained. During the whole process ofextending fire, variation of transverse deflection under dead loads is calculated. At last, thetime-dependent variation of maximum and minimum shear-lags ratio for multi-beam concreteT-shaped section beam bridges exposed to symmetrical underbridge fire is disclosed.(6) Based on the burning depth and extending time of fire and temperature distribution ofconcrete, effective height calculation method of section is adopted to put forward thetime-dependent amendment formula of residual stiffness under condition of deck andunderbridge fire model, which the relative deviation estimated is located in acceptedinterval. Then, the residual bearing capacity calculation formula for concrete beam bridge isproposed under condition of each fire model. In addition, thermal conductivity and thicknessof the fire-resistant coat focused on is analyzed to expose time-dependent temperaturedistribution and temperature difference distribution for the concrete T-shaped section beam,and calculation formula of temperature for concrete solid structure is proposed.