円錐台形のシアキーとあと施工アンカーを併用した耐震補強に用いる接合工法の開発

<p> To strengthen reinforced concrete structures against seismic events, design methods are being established to fit the interiors of existing structures with steel braces or shear walls as well as to retrofit existing structures with steel braces on the exteriors of existing frames for seismic protection. For example, indirect connections using post-installed anchors are frequently employed when steel-braced frames are used for seismic retrofits, with many post-installed anchors required for each existing structure. The connection with existing structures and reinforcement elements in seismic retrofitting of concrete construction must be effective for distributing stress. If the strength of the connection is not adequate and if the details are not properly designed, the structure as a whole is not likely to display effective seismic performance.</p><p> We proposed using shear connecters with a steel shear key of frustoconical shape and post-installed anchors as a new method of connecting existing concrete to extended concrete. A prior study on the strengthening method using steel angles and steel disks as shear keys reported that connections using steel shear keys improve shear strength. However, bearing failure often occurs in the concrete of a connection with steel shear keys, with drastic strength deterioration after the maximum carrying capacity of the reinforced structure and minimal ductility. We hypothesize that steel shear keys of frustoconical shape reduces the bearing failure of concrete. This shear connecter used together with a post-installed anchor is a “’funnel shape post-installed anchor’’.</p><p> In the present study, we first confirmed the mechanical behavior of the proposed shear connecter through structural tests under a cyclic shear force. The presence of the shear key, shape of the shear key (double or single funnel shape), and central angle of the frustoconical section (30° or 45°) were used as experimental parameters. It was found from the structural tests that a double-funnel-shaped post-installed anchor with a 45° shear key improves shear strength in comparison with other shear keys. Moreover, when the frustoconical-shaped shear key is used, an anchor bar is always required for spacing on the concrete joint surface. Second, three-dimensional nonlinear finite element model (FEM) analyses were conducted using ‘‘FINAL’’. The analytical values closely predict the experimental results of the ultimate strength of the test specimens, with the stress distribution and the deformation of the anchor bar, shear-key, and concrete further examined. From the FEM analysis, it is clear that the rotation of the shear key influences shear strength.</p><p> Finally, we proposed an evaluation method for shear strength of funnel shape post-installed anchors based on the stress transfer mechanism around the shear key, and the calculation accuracy of the proposed shear strength to the experiment value was shown.</p>