Capacity of doubled wood lagging

[shorebob]

Does anyone know of a simple way to calc. the capacity of a double layer of 4x12 lagging in a soldier beam installation? This is a cost issue. Researching 'beam on elastic foundation' leads only to finite element, differential eqn. solutions. There must be a simpler way. Thanks.

 

[msquared48]

Unless the 4X12's are stitched together, making them composite, doubling the value for one when using two is the solution.

Not knowing the conditions here though, I would suggest that if you need double lagging, then your soldier pile are too far apart, and driving up the size of the soldier pile too.

Have you considered the reducing effects of any possible soil arching effect between the soldier pile, which would reduce the load to the lagging?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[shorebob]

Thanks for the confirmation. The issue here is an extreme soldier beam spacing in 2 bays to clear an U/G 108" existing sewer. The client wants as much clearance as possible so the driller doesn't nick it. Regarding arching, we typically use the 400 psf max. soil load per CalTrans, then add any applicable surcharge. Again, much thanks for the guidance.

 

[PEinc]

Bob, remember that 2 each 4 inch boards are only half as strong in bending as an 8 inch board. 1/6 x 12 x 8 x 8 > 2 x (1/6 x 12 x 4 x 4). It wouldn't be practical to nail or bolt the boards together to make them act as a solid 8 inch board (especially if you are using hardwood lagging. Instead of wood lagging in this wide bay, you might also try using a steel street plate down to the top of the pipe.

How are things in CA and NJ? Drop me a line.

http://www.PeirceEngineering.com