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长线法生产预应力混凝土构件的台座,一般为普通混凝土平板式,下部做夯石垫层,宽约4～5米,长70～100米。由于其长度大,混凝土又处于露天环境,除了混凝土本身的凝结收缩外,还有温度变化引起的收缩。这二者会引起台座断面较大的拉应力。如以混凝土相对收缩值ε_1=1.5×10~(-4)计,则收缩应力达σ_1=Eε_1=3×10~5×1.5×10~(-4)=45公斤/厘米~2。在南方夏季气温38℃时,由于混凝土表面吸热,台座面温度可达65℃,而夜间温度可降至20℃,则日温差可达45℃。由于此温差,将在混凝土内产生σ_2=Eε_2=3×10~5×10_(-5)×45=135公斤/厘米~2的拉应
The pedestals for the production of prestressed concrete structures by the long-line method are generally plain concrete slabs, and the lower part is made of vermiculite cushions, which are about 4 to 5 meters wide and 70 to 100 meters long. Due to its large length, the concrete is in an open air environment. In addition to the condensation shrinkage of the concrete itself, there is a contraction due to temperature changes. Both of these will cause a large tensile stress on the pedestal section. If the concrete relative contraction value ε_1=1.5×10-4, the contraction stress reaches σ_1=Eε_1=3×10~5×1.5×10~(-4)=45 kg/cm~2. In the southern summer temperature of 38°C, due to the heat absorption of the concrete surface, the temperature of the seat surface can reach 65°C, while the temperature at night can drop to 20°C, and the temperature difference can reach 45°C. Due to this temperature difference, σ_2=Eε_2=3×10~5×10_(-5)×45=135 kg/cm~2 should be generated in concrete.