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Damaged Purlin and Cross-grain failure at ledger[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>, <Light_framing(--nospam--at)structuralist.net>
- Subject: Damaged Purlin and Cross-grain failure at ledger
- From: "Dennis Wish" <dennis.wish(--nospam--at)verizon.net>
- Date: Mon, 28 Jun 2004 19:33:10 -0700
I was called to inspect the repairs of a damaged purlin in a masonry building constructed between the early 60’s and late 70’s. The roof is panelized roof with 2x6 sub-purlins, 4x12 purlins spaced and GLB girders that have not been checked. The problem is that one of the Purlins split on the tension side (bottom) and was repaired by the manager of the building using 2x10’s sistered on to each side and lagged into the bottom half of the damaged 4x12. This is not a good connection as the purlin will tend to fail again with the line of failure parallel to grain.
Replacing the purlin is difficult due to a suspended T-bar ceiling, mechanical ducting and sprinklers. I thought I could fabricate a ¼-inch plate saddle that would place the bolts (A307 thru-bolts) in the top or compression side of the beam. I would have to slot the saddle to allow the line of bolts to occur between the 2x6 sub-purlins. The way the fix is now, I can see the sistered rafters starting to split and the bottom of the sub-purlins is almost at the neutral axis of the purlin.
The purlin is hung from a 4x8 or 4x10 ledger using top flange beam hangers. The ledger is secured to the face of the masonry walls and there are no ties to resist or prevent cross-grain tension failure. One of the pictures taken by a local testing company who does inspections shows some splitting at the face of the ledger. I am assuming the worst case – cross-grain failure. However, it may simply be cracking due to drying of the lumber over the years. Assuming the worst, I would have to suggest retrofitting the building and the potential for an imminent or highly possible failure at the ledger based on what I could see.
The owner of the building will not want to retrofit the entire building and there is no ordinance or city requirement to make him retrofit the entire perimeter of the building. Would it be unreasonable to suggest that we tie only those areas where splitting of the grain parallel to the face of the ledger is seen and leave the rest to another time? This is a city whose city council members have refused to enforce or set up a retrofit ordinance of their unreinforced masonry buildings located within 10 Km of the San Andreas Fault. We even suggested that they use specific triggers (change of occupancy, major remodel, new ownership, code violations etc.) to require retrofit but were voted down due to lack of money available to the building owners and their lack of ability to recollect the investment.
Thanks in advance for any advice you can give that would help me make up my mind as to what should be done.
Dennis S. Wish, PE
Structural Engineering Consultant
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