Rotted laminated beams 3

[RDK]

I have a potential client, a day care operation (read not a lot of $) who operate out of an old church.

The structure of the building consists of laminated wood beams in the shape of a triangle. The base of the triangle is the main floor beams, the sides form the ceiling. The ends of the triangle where the roof beams meet the floor beam has in several places rotted out. This was caused by the drains from the roof scuppers being on top of the beam ends. Needless to say this could be serious threat to the stability of the structure.

Not being very experienced in laminated beams I’m looking for some ideas. I may have to take this to a friend who knows a lot more about wood design than

My first thought was to put steel gusset plates or straps between the roof and the floor members to stabilize the connection. Would this work and how should I approach the design?

Is it possible to repair the laminated joint? I imagine that the laminated ends interlock to form the joint, most likely with shear connectors, would this be the case?

There are seven of these trusses in the building. They are about 15 m on the base and 10m high at the apex. The beams are 200 mm wide and about 800 mm deep. The trusses are spaced about 4 m o/c.



Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[dik]

I assume the structure is an 'A' frame type. I've refurbished arches that have rotted out by providing temporary support and 'nibbling' the rotted portion out using a drill/flex shaft with heavy duty wire brushes. These can be picked up at an autobody supply house. I've used a 'cobbled drill' bit that consisted of a shaft with a drill bit welded to it. The bit was an 1-1/4" dia and the shaft was 3'6 long and a 3/4" drill. This was used to drill from the interior, into the 'shoe' location and a chunk of 25M rebar was epoxied in place and then the base that had been 'nibbled' away was replaced with cementitious grout. Did some work on teeth about 30 years ago and used a similar model.

Problem with 'dry-rot' (generally brown rot; it goes for the cellulose and leaves the lignin) is that you can loose 50% of the strength and not be aware that any damage has occurred.

 

[jheidt2543]

Just a thought to consider. Contact the nearest laminated wood fabricator and see if they will come out to assess the damage and give a price for the fix. They are the most familiar and experianced with this product and may be able to provide a cost effective solution. Most companies will provide the cost estimate and sometimes the assement for the chance to do the repairs.

They may also have some non-distructive testing equipment to verify the condition of the A-frame members.

Good luck with a tough problem.

 

[boo1]

You might find the following guide glulam repair guide from AITC helpfull, for a free down load go the the following address:

https://www.aitc-glulam.org/shopcart/Pdf/aitctechnicalnote13.pdf

Cheers