In the joints of seismic retrofitting structures, post-installed anchors are generally used. The concrete surfaces at the joints are roughened through a chipping process using a vibration drill in order to achieve the shear force stipulated in the Japanese guidelines for the seismic retrofitting of structures. However, there are no unified rules for concrete roughening in terms of shear force or the shape of the roughened surface. On the other hand, some previous studies focused on shear stress transfer mechanisms of cracked concrete surfaces. According to these research, we can estimate the shear stresses and normal stresses interacting on the entire cracked surfaces by integrating the contact stress over the area of the entire interface. Therefore, we conducted shear loading tests, and measurements of the roughened surface were taken. We then constructed a mechanical model based on the constitutive law that describes the shear stress transfer mechanisms of cracked concrete surface. Eight test specimens were prepared. We roughened the concrete surfaces of the eight specimens. For the test specimens, the existing member was modelled by a rectangular block with dimensions 580 mm × 400 mm × 200 mm. After roughening an area of 375 mm × 200 mm centered on the concrete surface, grouting mortar of dimensions 375 mm × 200 mm × 200 mm was cast on the surface. The test parameters considered here were the roughed concrete depth as well as the ratios between the roughened area and the surface area (0.10, 0.20, 0.30, 0.50, and 0.75). We took measurements of the roughened surface using laser displacement sensors. The measurement intervals were set to 0.04 mm in the x-direction and 0.5 mm in the y-direction. For the shear loading tests, we controlled the shear displacement and applied repeated cyclic loading. The constant normal stress was set to a constant value of 0.48 N/mm2. We constructed a mechanical model of the roughened concrete surface using the Bujadaham model (Bujadaham 1991). This model takes into account the stress transfer mechanisms of the cracked surface. The angle density function Ω(θ) in the Bujadaham model was set as Ω(θ) = 0.5cosθ However, it was not known whether or not we could use this defined angle density function for the roughened concrete surface. Therefore, we evaluated Ω(θ) using the three-dimensional data obtained from the shape measurements of the roughened surface. Additionally, we proposed Ω(θ) using the shape measurement results. The test and calculation results were in agreement. However, the contact stress in the Bujadaham model adopted an elasto-plastic model, we newly constructed the model between contact stress and contact displacement for the roughened concrete surface. In the proposed contact stress model, the stress softening behavior in the roughened concrete was considered. We constructed a mechanical model representing the roughened concrete surface and compared the experimental and analytical values. By using a constitutive equation that expresses the shear transfer mechanism of a cracked surface, and that takes into account the contact stress and friction on the local surface, the shear and vertical stresses of specimens with a roughened concrete area ratio of up to 0.3 can be evaluated. However, for specimens with a roughened concrete area ratio of 0.5 or 0.75, the shear and vertical stresses are underestimated. Thus, we were not able to express the specimens of shear failure modes using the proposed model. This problem will be a focus of future research.
既存コンクリート部材におけるコンクリート目荒らし面のせん断応力伝達と微小面の接触応力に基づく力学モデル
TAIJ_83_750_1151_1159
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