为了完善平台巴西劈裂试验测定岩石抗拉强度的理论基础，基于二维弹性理论，建立对弦载荷下的平台巴西劈裂力学模型，采用应力场叠加法求得圆盘内的应力近似解析解。该应力理论解与有限元数值解一致，证明理论求解的合理性。在此基础上，对比研究了平台加载角对圆盘内应力大小及应力集中程度的影响，其结果表明：平台加载角越大，圆盘加载处的应力集中程度和压拉应力比都急剧降低，而圆盘内的拉应力值和拉伸区却只有一定程度减小；过大或过小的平台加载角都不利于平台巴西试样发生中心拉伸劈裂破坏，其最优平台加载角在20°~30°之间。最后，依据Griffith强度破坏准则，推得岩石抗拉强度的理论计算公式，其结果与已有抗拉强度经验公式及试验所得抗拉强度相符较好。

This study aims to improve the fundamental of theory of the flattened Brazilian disk test for determining the tensile strength of rocks. On the basis of the two-dimensional elasticity theory, a mechanical model is proposed with the chordally opposing distributed compressive loads. And the approximate analytical solution of stress components inside the Brazilian disk is obtained with the superposition method of stresses. The theoretical solutions are validated to be rational through comparing with the numerical results from the finite element method. By using the solutions, the effect of flattened loading angles on the value and the concentration degree of stress inside the disk is researched contrastively. The results show that the concentration degree of stress near loading point and the ratio of compressive stress to tensile stress inside the disk quickly decrease, but the tensile stress value and tensile region slightly reduce with the increasing of flattened loading angle. Further, it is found that both too large or too small loading angle is detrimental to the central tensile splitting failure of specimen in the standard Brazilian disk test, and the optimal flattened loading angles are between 20° and 30°. Finally, according to the Griffith strength failure criterion, the formula for tensile strength of rocks is theoretically derived. And the theoretical tensile strength values obtained in this paper are in good agreement with the existing experimental ones.