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Re: Hold Down Question - Using a bent (22-1/2 degree) A307 Rod[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Hold Down Question - Using a bent (22-1/2 degree) A307 Rod
- From: "Robert Kazanjy" <rkazanjy(--nospam--at)gmail.com>
- Date: Mon, 27 Aug 2007 21:09:20 -0700
Having done tests on bent hold down straps, I would be more concerned about the bend from a geometric point of view rather than a strength reduction due to bending. Bent (misplaced & then hammered over to fit the shea rwall location) PAHD's don't take substantial load until they straighten out & become tension elements.
An anchor bolt or rod for a hold down situation is stressed in tension (uplift) & isn't really very stiff unless its straight OR well restrained in the concrete.
A bent rod will want to straighten when tension is applied to it. Like a tree root in the lawn, when you pull up on it, if it is a surface root, it will "travel" sideways across the lawn. If it is a deep diving root you'll develop some substantial uplift loads.
Depending on how well (or poorly) the bent rod is restrained, it may or may not be able to develop tension loads until a fair amount of system slack has been generated.
The 22.5 deg bend is going to give you a horizontal force 40% of the uplift force or ~ 2.5 kips, the slab will probably be able provide this much lateral force on the anchor bolt without allowing it to loosen up.
Unless you're certain that the rod anchorage is stiff enough to get the Hardy panel to perform properly, I'd have the butchered shear wall repaired.
A client installed a Hardy Panel that I designed and that required a depth of 13-1/2" on a 7/8" dia. A307 threaded rod used as a hold-down when secured to the concrete with the Simpson SET Epoxy (based on the 2007 catalog). The framer hit horizontal steel at 6-1/2" down and wanted to find a way around the horizontal steel on the turned down edge of the slab on grade.
I re-ran the analysis considering the reaction of the header above the 24-inch wide x 10-foot high panels (Hardy HF1024 x 7/8". The job was done for another client who was the General Contractor that hired me. His name and company is listed on the package but it turned out that he did not get the job. The General Contractor who did get the job took the analysis I performed for this remodel and submitted it for permit. He received the permit and started work but never informed me that the job was back on and a new GC was chosen who used the work that my previous client hired and paid me to complete.
To make a long story short – the contractor installed the Hardy panels (2) based on the assumption that a 34-inch panel was to be removed between two sliding glass doors facing a golf course and that the panel removed was a shear wall. It turned out not to be a shear wall and the need for the Hardy Panels was not actually needed but was installed by the new GC. Fortunately, the owner was not only very understanding, but praised my work. The problem is that I needed an embedment of 13 inches to develop the tension necessary to resist overturning. This is not possible because of the horizontal steel.
One choice was to remove the Hardy Panels an reframe the area below the header with conventional wood and repair the shear walls that were cut out. This can be done and the advantage is that the MTT28B that was originally used at the 4x4 end post can be replaced with an epoxy anchor and I can obtain clearance by moving the MTT slightly to clear the horizontal steel. The GC would prefer to make the Hardy's work because the repair of the original wall would cost him in labor and materials.
I had two ideas (one offered by the owner). I can redrill the hole at a 22-1/2 degree angle and secure a bent A307 threaded rod for the full development depth I need for the Simpson SET Epoxy adhesive. I can also redrill the Hardy Panel post holes (according to Hardy) for a 1-1/8" dia.. threaded rod rather than the 7/8" dia. Threaded rod that was needed. If I use the 1-1/8" dia. Threaded rod I can reduced the embedment depth, but I still believe that it will need to be greater than 6-1/2 inches and does not solve the horizontal rod interference.
If I bend the 7/8" dia. A307 threaded rod once to clear the horizontal steel, I can use the epoxy to secure it and have it come up from the top of concrete plumb with the holes in the Hardy Panels. I know that if you bend a threaded rod more than once, you do reduce the strength of the steel, but it is not uncommon to order concealed anchors using 22-1/2 degree rods.
Can I get some opinions as to whether or not I would lose steel strength by bending the rod once for the angle I need to clear the horizontal steel. The turn down edge of the slab is 12-inches in width and the anchor is located at 1-3/4" maximum to center of anchor from the edge of the concrete slab on grade. The maximum capacity of the uplift on the Hardy is based on the strength of the 7/8" steel for a conventional hold down (A307) steel rod embedded into wet concrete. The actual uplift will be reduced by more than 1/3rd of the full capacity since the panel removed is not a shear wall and the original shear does not change, only the width of the panel which is less than the original shear wall width changes. The original shear wall is a 3/8" thick shear wall nailed w/ 8d common nails at 6:6:12 and was 4-feet in width. The original calculations on the wall minus resisting shear came up with the original uplift on the 4-foot wall at less than 3 kips. However, for the 24—inch Hardy, the required original calcs was closer to 8-kips and is now around 6-kips. At 22-1/2 degrees I can get the depth on the anchor for the Simpson SET but fear weakening the rod and not being able to gain capacity in the steel.
Any recommendations or opinions?
- Conventional Wood Framing
- From: Bill Allen
- Conventional Wood Framing
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