新型被动式真三轴试验装置

为探究混凝土在被动约束机制下的多轴本构关系，采用玻璃纤维增强复合材料（GFRP）筋和钢板作为组成侧向围压装置的主要部件，采用万能试验机作为竖向加载装置，形成新型被动式真三轴试验装置.该装置可在两垂直方向施加互相独立的随混凝土侧向膨胀线性增长的被动约束.通过单根GFRP筋及侧向围压装置的轴拉试验，验证采用同种GFRP筋的侧向围压装置的被动约束刚度的恒定性和可重复性，并确定不同GFRP筋直径对应的侧向刚度值.对12个100mm×100mm×100mm的混凝土立方体试块进行双向等约束的被动式真三轴试验.立方体试块的力学性能与FRP布约束混凝土标准圆柱的轴压结果类似，极限强度随约束刚度比的增长而增长.该装置可为混凝土提供有效的被动围压，替代FRP包裹圆柱的试验方法，为被动约束下混凝土的本构关系研究提供试验基础.
Abstract: A new true-triaxial test apparatus with passive confinement was developed to explore the multi-axial constitutive relationship of concrete under passive confinement mechanism. In the new test apparatus, the lateral confinement apparatus was mainly composed of glass fiber reinforced polymer (GFRP) bars and steel plates; the universal testing machine was employed to exert vertical load. The apparatus can apply independent passive confinement in two perpendicular directions. The passive confinement increases linearly with the increase of concrete lateral expansion. After the tensile testing on the single GFRP bar and the lateral confinement apparatus, the stability and repeatability of the lateral confinement apparatus with the same GFRP bars were verified, and the lateral stiffness value with respect to the GFRP bar of certain diameter was calibrated. The true-triaxial experiments were carried out on twelve concrete cubes of 100mm×100mm×100mm with bi-directional uniform passive confinement. The mechanical behavior of test cubes is similar with the concrete cylinders wrapped by FRP sheets. The ultimate strength increased with the increase of confinement stiffness ratio. Results demonstrate that the new test apparatus can provide effective passive confinement for concrete and replace the test method using FRP wrapped cylinder, as well as provide essential testing method for the study on constitutive relationship of concrete under passive confinement.