1:5:10:365 EcoTip Blog

April 10, 2008

:101 Hold Down Bolts

Filed under: :101 Hold Down Bolts — Tags: , , , , , , — John Banta @ 4:01 am

Welcome to today’s 1:5:10:365 Tip for becoming a better steward for our home and planet.

1:5:10:101 Tip: The way a building is secured to the foundation has a great deal of influence on structural integrity. Square washers have more holding force than round, but must be installed properly to do their job.

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Additional Information

Suggested Review – :098, :099, :100

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The round washer on this sill plate has a holding force of 840 pounds

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This square washer increases the holding force to 1340 pounds.

The following excerpt is from my new book – Extreme Weather Hits Home:

 Increasing Structural Strength

 Cook states:

The Uniform Building Code (UBC) which is designed for new construction and is not intended for retrofit, specifies that only 5/8 inch bolts with plate washers may be used. They should be 6 ft. o.c. (on center) on single and two story homes. … The most significant increase in strength in this connection was achieved by installing large square plate washers on the bolts instead of round cut washers. [Round washers were acting like a wedge and causing the wooden sill plate to fracture.] … This one simple change resulted in a 60% increase in strength.

The sill anchor strength can be improved even more, he continues:

Harlen Metal Products also came up with a type of washer called a Mudsill Plate that is designed to increase the strength of the wood-to-bolt connection. This hardware is so effective that the earthquake resistance of a bolt can be more than doubled by installing one of these washers on the top and one on the bottom of the mudsill. The UBC recognizes a 1/2 inch bolt with a standard washer as being able to resist 840 pounds of shear. ICC report #1148 recognizes that installing one of these washers on top of the mudsill increases that resistance to 1340 pounds, a 59% increase in strength, while installing these washers on both the top and bottom of the mudsill increases the bolt strength to 2040 pounds, a 143% increase in strength. That’s pretty good for a fifty-cent piece of hardware (Cook).

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