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- Subject: [SEAOC] Division 91 (Tilt-up) Anchor question
- From: "Dennis S. Wish" <wish(--nospam--at)cyberg8t.com>
- Date: Thu, 05 Dec 1996 18:48:56 -0800
If you have been doing Division 91 compliance I would appreciate your comments on the following items. If not, please disregard this long message and accept my apologies for sending it.
I was asked to inspect a reinforced brick building constructed in the late 1950's and located in the city of Los Angeles. The building is used as a warehouse and had suffered some damage to the brick lintels at large door openings. In addition to repairing the lintel damage, the owner asked that I inspect the building and suggest ways to make it safer.
After inspecting the structural elements of the building, I explained that the building was reinforced and was not considered a hazardous structure by the State of California and was not listed for any local compliance. I did, however, discover that the wood ledgers were subject to potential cross-grain tension failure as the joists and diaphragm connections where made by joist hanger and nailing to the top of the ledger.
After reviewing the original drawings I noted that there were details for appropriate tension ties that were, at some later date, deleted from the drawings (crossed out) and never installed.
I have designed the tension anchors using standard plated (6" square plates) tied back to blocking with a bent plate connection and to perpendicular joists via "V" strap connections. These are typical of those types of connections used in the L.A. RGA or Division 88 work.
To determine the diaphragm development length to the anchor, I used the current UBC horizontal diaphragm capacity based upon the original drawing material and nailing specifications (1/2" plywood CDX with 8d (6:12)) throughout.
Now for the questions. Please note that I moved away from Los Angeles about 3 1/2 years ago and have not done any Division 91 (Tilt-up) retrofit.
The following comments were made by the plan check engineer:
1. The use of 'V' straps is no longer allowed due to the eccentricity of the load. It was highly suggested that I install Simpson (or equal) HD2A anchors at each side of the joist and secure to the exterior wall plate. The intent is to create a concentric load to the joist or blocking.
Now I may have been away for too long, but there is a definite eccentricity on all holddown connections and this was considered when the connection to the wood member was determined. An HD2A connection to a 1 1/2" member (full capacity) is around 1,550 pounds. Why then must an additional anchor be installed on the opposite side of the rafter to force concentric loading to the joist?
2. A bent plate was not allowed. The bent plate is connected to the wall anchor and the plate is secured to blocking. The drag is made by connection of a continuous strap below the blocking for some bays back to develop the capacity.
The city would not allow more than 80 or 100 plf for the diaphragm connection. Considering that I can develop the capacity from both sides of the diaphragm I would only be allowed between 160 and 200 plf or a drag length of over 8 feet of blocking (4 joist bays) to develop the full capacity of the HD2A.
The city required that I determine the deflection of the bent plate before the connection would be allowed (in addition to developing the diaphragm capacity at a reduced rate).
3. The city determined that the work would not exclude the building from Handicap conformance! This is the most outrageous thing I have heard. Since when did the City of L.A. adopt a policy that would penalize the building owner from making his structure safer????? This was never the case with Division 88 RGA compliance. Does this mean that all full compliance Division 91 project require full Handicap compliance as well?
4. The increased cost for a double HD2A verses a bent plate or "V" Strap connection may cause the owner to back out of doing the work. This would be a mistake.
Can any provide me with a couple of details that I can work from for Tension anchorage connections that comply with Division 91 work? I would appreciate it if you would provide me a graphic in any format (DWG, DXF, GIF, JPG etc) that would help.
Thank you in advance for your consideration on this matter.
Dennis S. Wish PE
Dennis S. Wish PE
"Mother is the name for God
on the lips of all children"
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