高温下钢筋混凝土梁热应力研究

Research on the Thermal Stress of Reinforced Concrete Beams Under High Temperature

为探究升温过程中混凝土与钢筋因膨胀变形差异产生的热应力,利用原位补偿法测出混凝土组成材料在30~300℃区间内的相关力学参数,基于Mori-Tanaka法推出混凝土线膨胀系数,导出理论热应力值.并且通过实测钢筋的约束应变得到钢筋混凝土梁在温度梯度下的热应力.试验结果表明:水泥砂浆和石灰石的线膨胀系数随着温度的升高整体呈上升趋势,而弹性模量、泊松比反之;超过100℃后,梁内混凝土受到钢筋施加的拉应力,且拉应力随温度的升高而增大;在300℃时,热应力达144 MPa.其导致的钢筋与混凝土黏结性能及相关材料力学性能的退化在设计中应予以重视.

In order to explore the thermal stress caused by the difference of expansion deformation between concrete and steel bars during the heating process, the in-situ compensation method was used to measure the related mechanical parameters of concrete components in the range from 30 ℃ to 300 ℃. Based on the Mori-Tanaka method, the linear expansion coefficient of concrete and the theoretical thermal stress value are derived. Then, the thermal stress of the reinforced concrete beam under temperature gradient is gained by measured constraint strain of the steel bar. The results show that the linear expansion coefficient of cement mortar and limestone increases with the increase of temperature, while the elastic modulus and Poisson’s ratio are on the contrary. When the temperature exceeds 100 ℃, the concrete in the beam is subjected to the tensile stress imposed by the steel bar, and the tensile stress increases with the increase of temperature. The thermal stress reaches 144 MPa at 300 ℃. Thus, the degradation of the bonding properties of reinforcement and concrete, and the mechanical properties of related materials should be taken seriously in the design.