Study On Solar Radiation Thermal Effects On Concrete Box Girders Strengthened With CFRP

In the past, lots of work about mechanism and performance of the reinforced concretestructures have been done by domestic and foreign researchers, includes experimentalresearch and theoretical analysis. Fruitful results have been achieved. The appearing of thewidely using of box girder bridge is relatively late, the engineering projects is rare, over time,the early construction of the box girder bridge will have to enter late service period, so theissue of the reinforcement must be on the agenda. Concrete is a poor conductor of heat, whenthe temperature of the external environment changes rapidly, the concrete structure will havea large temperature difference between inside and outside which would result in a thermalstress. Compare to concrete, CFRP has a different thermal parameters, so it will change theoriginal concrete box girder temperature field, besides, when the temperature changes, thestress and deformation performance of the CFRP-concrete composite structures will alsohave a change. Therefore, the solar radiation thermal effects on concrete box girdersreinforced with CFRP t is really necessary to study.Experimental research on the solar radiation thermal effects on concrete box girdersreinforced with CFRP had been conducted, three-piece experimental beams had been made,all of the beams are reinforced concrete box beams with the same geometry, length3.2m,horizontal section, height0.4m, width0.6m, roof and floor thickness are0.08m, webthickness0.06m. In every beam, temperature sensors and strain gauges are arranged atdifferent locations. Two of them are reinforced with CFRP in different ways, single-layerreinforcement for the underside and U-shaped reinforcement, as a reference, the other onewasn’t reinforced. Using insulation materials, three different shade of sunshine conditionswere simulated, each beam was tested for three days in each condition. The obtainedtemperature and stress data were analyzed preliminarily.Using ANSYS to simulate the research on the solar radiation thermal effects on concretebox girders strengthened with CFRP. Put the measured data as the initial condition, combinedwith knowledge of astronomy, meteorology and atmospheric to calculate boundary conditionwhich was applied to the finite element model in the form of an array, the temperature field atdifferent time was got. The temperature field was applied to the box beam model to calculatethe temperature stress directly. Then the measured data and finite element simulation datawere analyzed comparatively.After a comprehensive analysis of the measured data and simulated data, the conclusioneventually come: under the sunlight radiation, the highest temperature measuring points in theroof of the box beam appear at15:00~16:00pm, while the maximum temperature differencein the height direction appear at14:00~16:00pm. In the same box girder cross-section, with the height falls, the regular pattern of the temperature field is delayed noticeably, curves of thetemperature field cross twice a day, there is no temperature gradient at the crossing point, thetemperature field of the box girder is convergent. CFRP would change the solar radiationabsorption rate of box girder surface, compared to the beam which hasn’t been reinforced byCFRP, temperature on the top of the roof surface is higher, about4~5℃, the box girdervertical temperature difference become larger eventually. Different conditions of solarradiation have different impacts on the vertical temperature gradient of the concrete boxgirder strengthened with CFRP, when web surface is exposed to solar radiation, the verticaltemperature gradient changed greatly, especially when the web surface is pasted CFRP, thischange will be greater. When the temperatures of sunshine loads on the box girder whichhasn’t been strengthened with CFRP, main part of its roof suffer tensile stress, same to floor,the maximum tensile stress occurs in the bottom of the roof. After pasting the top surface withCFRP, the thermal stress withstood by the roof is compressive, tensile stress is greater thanthe box girder which hasn’t been strengthened with CFRP.