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Re: Stepped Bond Beams

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The main reason to develop the vertical bars is for wind uplift. About the best you can do is count on a #4 with 7" embedment. That does not give the hook much cover. If the bar is bigger, the embedment requirements are greater. I have just made it a practice to top CMU walls with a 2 course bond beam, then I have plenty of room for development of the hook and vertical rebar whether I need it or not.

This is mostly an issue outside of California where partially grouted walls are more common. It is a no cost in California and just the cost of the extra grout where partial grouted walls are used. In most applications it is no extra cost.

It takes a pretty heavy roof to avoid a net uplift at the top of the wall.

Regards,
Harold Sprague





From: "Jordan Truesdell, PE" <seaint1(--nospam--at)truesdellengineering.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Re: Stepped Bond Beams
Date: Wed, 15 Feb 2006 14:28:35 -0500

Not to be difficult, but what would be the advantage to developing the vertical bars fully within the bond beam? Except for possible exception of the ends of fully-loaded shear walls, the maximum tensile stresses should occur near the center of the walls when resisting transverse wind loads. Is there something I'm not thinking of, or is this primarily a belt-and-suspenders, maximum strength everywhere wall design technique?

Jordan

Harold Sprague wrote:

As was suggested, the US Army Corps of engineers prefers to have a continuous bond beam at the top of a wall even if the top of the wall slopes. This requires cutting the course below the bond beam to accommodate the slope. I would suggest that the top bond beam be 2 courses tall. This would allow the development of the vertical rebar in the 16" deep bond beam as opposed to trying to develop the vertical rebar in an 8" bond beam. The vertical rebar should terminate with a hook in the top of the bond beam.

Use the normal high slump grout in the vertical cells, but (depending on the slope and the grout slump) you may have to use a low slump grout in the bond beam. As I usually preach, use the knock out type of bond beams.

Regards,
Harold Sprague



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