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Re: concrete tilt-up wall anchors in L.A. county
- To: <seaoc(--nospam--at)seaoc.org>
- Subject: Re: concrete tilt-up wall anchors in L.A. county
- From: "Dennis S. Wish PE" <wish(--nospam--at)cyberg8t.com>
- Date: Fri, 31 Jan 1997 18:03:36 -0800
I recently designed a fix for a reinforced masonry building in L.A. that had a typical problem with cross-grained tension failure of the ledger connection. I had the contractor submit it to West Los Angeles and I can't believe the problems I had getting it permitted. To be fair, the plan checker was very nice and tried to be as helpful as he could, but his supervisor was unyielding in his approach to anchorage.
I treated the building as a compliance to Division 91 for tilt-up. The reason I did this was to obtain a certification for the owner of Division 91 compliance. This way the building could not be forced to upgrade to a more strict compliance should the city decide to create an ordinance to cover ledger connections for reinforced masonry.
The problems that I had included the following:
1. The City Interdepartmental memo issued in July of 1995 by Abe Habashi indicated a tension value for one Simpson HD2A at 855 lbs. L.A. City did not want to accept this design since they felt that there was no testing upon the eccentricity of the load applied at one side of the rafter. I did not see the concern since there is an inherent eccentricty in all HDA connections whether it's in a 1 1/2" member or a 5.5" member.
I finally convinced them to allow me to install one HDA and to use the value in the Departmental list.
2. The city would not allow me the actual diaphragm capacity for drag. The Division 91 code indicates that if the actual condition can be proven by original drawings or by testing, the actual value of the diaphragm can be used.
The city's position was that where joists are parallel to the wall and rafters are spaced at 24" apart, there is only one 10D or 8d nail at 12" on center (assuming that the inserted blocking is not nailed down from the top of the diaprhragm.
Therefore, they would only allow me 100 plf on the diaphragm which would have required a 8.5 foot drag for one HDA connection.
I tried to argue that the diaphragm capacity is not determined by a single line of shear, but that the system acts as a whole and at the very least a shear cone should be determined from the center of anchor back into the diaprhagm.
The city would not even allow me the connection of the blocking to the diaphragm as part of the diaphragm's capacity since no testing had been done beyond the last block.
I finally got them to comprimise that I could use 100 plf for the diaphragm and 50 lbs for each A35 installed from the block and screwed into the diaphragm. This gave me a drag length of 4 feet for each single HD2A connection.
I've discussed this with other's online as well as with engineers like Mike Krakower and Nels Roselund. Neither agree with the plan checker (supervisior), but I could not get past him.
To make matters worse, I started by designing for the use of 'Vee' straps and bent plate connections similar to those I used in Division 88 or RGA. These were immediatly thrown out as not sufficient or allowed in Division 91 design.
Boy, am I glad I no longer live in Los Angeles. I don't think I could stand going through these motions again - it certainly is not cost effective. In addition, the owner decided to leave the unsafe condition rather than spend the extra $4,000.00 that the construction would have cost due to the strict guidelines.
It seems to me that L.A. should not be publishing their ordinance until the there are answers regarding diaphram capacity for drag and at least having tested the HDA installation for one side of rafter. This is outrageous.
Dennis Wish PE