Anchoring

When the boundary element is strong enough and the horizontal rebars (distribution bars) get anchored inside the column’s core, a straight anchorage length can be used.

When the boundary column is weak and its length is not enough to allow for a straight anchorage, it is mandatory to anchor the horizontal rebars by forming a hook at their ends.

In this case, the disadvantage lies in the need for bending, albeit slightly, the horizontal rebars in certain areas. In this case, the ‘S’-shaped reinforcement must restraint the horizontal rebars at the point where they intersect with the vertical ones.

In this second case of a straight-line anchorage, the horizontal rebars do not have to be bent. This increases their cover thickness but since they mainly carry shear forces no serious problem arises. Moreover, the internal lever arm of the vertical rebars is diminished but only around 1cm so practically again, no problem appears.

No matter if the column is strong or weak, the horizontal rebars must end in a hook, which will be placed in the inside of the confined column. The anchorage can be achieved with a 90° hook placed inside the body of the boundary column.

When the column’s length is not large enough to provide an adequate straight anchorage length, hooks bend at 45° (135°) are being used. These are either completely prefabricated so as to have 45° bend in both edges, or they are assembled on site with horizontal rebars with ends bend in 45° and 90°. These shall be alternately placed along the wall height.

In continuous basement shear walls the difficulty in placing the reinforcement is located in the column area. This difficulty may be overcome by placing there straight horizontal distribution starter bars. These bars would have a relatively small length, they would be subsequently tie lapped with the larger intermediate distribution rebars and then, they would both be tied together to the vertical ones.

Usually, in the perimeter of the building, in the storeys above the ground, there is a seismic joint (30 to 100 mm), or a thermal insulation layer (30 to 50 mm), which are not required in the basement. However, their thickness can be used in the basement shear walls to secure the cover thickness and to enable the positioning of the distribution meshes outside the column reinforcement, as shown at the figure.