Week 8C: Concrete 101 pt.2

Before “grout filling” the wall HD (hold-down) hardware must be inserted at particular locations in order to provide resistance against stresses exerted on the building by earthquakes and wind. The hold-down literally holds the building to the foundation and in quake-prone SoCal the hardware required can sometimes be very large. At the lowest level of the project, we have HD25’s which are about 1.25” inches in diameter. The positioning of these HD’s is critical as one has to account for the correct spacing off the face of the building and the thickness of the column the HD will be bolted to.
The whole process is made even more difficult by the fact that the wall these HD’s are going into is 9’-0” tall and the HD’s must be positioned at the base and inside of the wall. In order to mark the HD locations careful measurements must be made to account for the precise locations and then the threaded rod which is one part of the HD’s is inserted into the cell. As you can see from the image, it has a 1/4 steel plate on the base which grips the concrete and prevents the rod from being ripped out of the cell.
Later, during the framing phase the rod is connected to a steel angle which bolts directly to a column. More on this later.