Thick steel plates are widely used in high-rise buildings and large-span steel structures. However, the increase of steel plate thickness will induce variations of mechanical properties of steel plates, especially the thickness properties. The mechanical properties of structural steel Q345B with plate thickness from 60 to 150 mm were tested at low temperature through round bar tensile specimens which included two types, I. E. Transverse specimen that is perpendicular to the rolling direction and Z-direction (or through thickness) specimen. The indices of yield strength fy, ultimate tensile strength fu, percentage reduction of area φ and their variations with temperature and sampling locations were measured in the experiments} the corresponding indices for thorough thickness properties were also obtained, it is indicated that: (1) when temperature decreases, fy and fu of thick plate increase while Rvalue decreases; (2) from surface to center of the thick plate, φ values for transverse specimens decrease;(3) with the increase of plate thickness, φ values for Z-direction specimens decrease and are smaller than those of transverse specimens. Useful material property data of thick steel plate are provided for thick plate steel structures.%厚板钢材在高层建筑和大跨结构中得到了广泛应用,然而厚度的增加会引起钢板力学性能的变化,特别是厚度方向的性能.采用圆棒拉伸试样,对厚度为60～150 mm的建筑结构用厚板Q345B进行了低温力学性能试验,试样分为垂直轧制方向的横向试样和贯穿厚度方向的Z向试样.试验获得了4种厚度钢板的屈服强度fy、抗拉强度fo和断面收缩率Ψ等指标及其随温度和取样位置的变化关系,并测得4种厚度钢板Z向性能的相应指标.试验结果表明,随温度的降低,厚板的屈服强度和抗拉强度增大而断面收缩率减小；由钢板表面至中心,横向试样的断面收缩率呈下降趋势；随钢板厚度的增加,Z向试样的断面收缩率逐渐减小,且小于横向试样的断面收缩率.
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