Monday, December 20, 2010

Relocating Hold Down Anchors

Here is a common issue that can arise in the placement of hold down anchors.  In this picture, two cast in place anchors interfered with the installation of the hold down anchors.  The easiest fix from the Framer's perspective is to move the hold down to the nearest stud for a clean installation.  This presents several items that the Engineer needs to consider prior to approving this change. 
  • As you can see in the picture, the fasteners provided with the anchor are too long for one stud.  Hold down anchor manufacturers generally require an attachment to a minimum of two studs.  Additional studs may be required to meet the manufacturer's specifications.
  • If the hold down anchor is relocated away from the edge of the panel, does the shear wall diaphragm boundary element change? The tension load needs to be transferred into the stud pack with the hold down anchor.  I recommend requiring the specified edge nailing be used to fasten the sheathing to the new stud pack at the relocated hold down anchor.  
  • By relocating the hold down anchor, the length of the shear wall changes.  This may be critical in a high wind or seismic area.  The design of the shear wall should be verified based on the field changes.
Merry Christmas and Happy New Year. 

Monday, December 6, 2010

At First Glance

One of the things I quickly learned in the field is that not everything is what it appears to be.  Whether it is an epoxied anchor bolt that you can pull out by hand or a hurricane clip wedged between two pieces of wood with no nails, the closer you get to see and touch the structure the more confident you will be with your field observation.  The girder truss in the above picture looks to be properly supported.  A stud pack below the truss and hurricane clips on each side of the truss are standard fare in a region with a low wind design speed.   If I stood across the room and looked up at this condition, I would feel satisfied.  Walking further into the structure, however, I saw that the stud pack may not be adequate.   Have a look at the picture below.  

When observing the framing in apartment complexes or housing units, the framing quickly becomes redundant.  Continuing to walk through each room in each unit is still important to not miss the problem conditions that exist isolated to specific units.