The Research On Temperature Field And Temperature Effect Of The Thin-wall Concrete-box Pier

At present, the thin-wall concrete-box piers are widely used in large spanprestressed concrete bridges especially across the steep valleys. But the crack ofthin-wall concrete piers was very common, and it had seriously affected the safetyand durability of structures. The lack of attention on the hydration heat and thermaleffects were important reasons for this cracking. According to the project “On theKey Cracking-control Technologies of Typical Concrete Bridge in Hunan HuaitongHighway”, this paper did a research on the thin-wall concrete-box pier of xiaochaxivillage bridge, three works involved are as followings:1.The testing of the hydration heat.The hydration heat of the thin-wall concrete-box piers was studied. And thispaper propose relevant measures to be taken to avoid the early temperature cracks onthe basis of these results of the test and theory analysis.An estimation model of finiteelement has been established according to the testing results, The resultsdemonstrated that the calculated results of hydration heat agreed well with themeasured values. The hydration heat didn’t cause the cracking of thin-wallconcrete-box piers. But the stress on the surface existing a certainly fluctuation, soeffective measurements shoule be taken to avoid the adverse effects on the staebiliyof the hydration heat temperature from outside temperature.2.The testing on temperature field and temperature effect.The highest temperature under solar radiation appeared at14:00, while thehighest and lowest temperature of concrete turned up around17:00and5:00,respectively, and it was stable on the inside surface of the concrete-box piers. Theresults of measure indicated that the grads of temperature between01:00and05:00are minor, which can be taken as the initial condition during the analysis of theinfluence of temperature field and temperature effect. An expression which isapplicable to the plus temperature gradients, is suggested on the basis of thecalculated results. Under the condition of typical climate, no craking phenomenawill happen, but rapidly drop in temperature should be paid sufficient attention.3.The thermal effects of temperature field.The influence of temperature field and temperature effect are analysedtheoretically, and it shows the credible degree of simulation result is high. Based onthe results, an expression which is applicable to the plus and minus temperature gradients in Hunan province, is suggested in this paper.The effect of temperature load on thin-wall concrete-box piers can be as largeor larger than the dead and the live load.The extern surface of concrete was intension while the inner surface was in compression under plus temperature gradients,and the extern surface was in compression while the inside surface was in tensionunder minus temperature gradients. The maximum thermal stress appeared one hourlater than plus temperature gradients.