Slide 15 of 45
- Insufficient Depth of Embedment for Anchor Rods
- Hold-down rods anchored into the foundation should be embedded as required by the manufacturer or structural design.
- The rods should only be embedded into sound concrete or reinforced masonry.
- Unlike a typical anchor bolt, the hold-down rod must resist uplift forces.
- The depth that the rod is embedded in concrete is important
- The loads imposed on a hold-down rod are generally greater than those imposed on a typical shear wall anchor bolt.
- The figure shows a picture of a situation where normal foundation bolts were used instead of deeper hold-down anchor rods.
- These bolts are usually only 7” instead of the required 18”.
- Sill bolts only need to be 7” because they are only usually resisting shear forces, not uplift forces.
- Substitution of Hold-Down Anchor Type
- Wedge or expansion type anchors should not be substituted when chemical (adhesive) anchors are specified.
- For most retrofit work, should use chemical anchors.
- Obviously can’t set anchors into poured concrete.
- Chemical anchors are a threaded rod that is set in epoxy.
- For hold-downs, wedge anchors do not generally perform as well as adhesive anchors during the cyclic uplift loading caused by earthquakes.