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[OM] Re: [OT] any structural engineers on the list

Subject: [OM] Re: [OT] any structural engineers on the list
From: "Piers Hemy" <piers@xxxxxxxx>
Date: Thu, 27 Mar 2008 17:07:40 -0000
Funnily enough, I looked in on a wooden-barn-construction weekend-course
last month, watched the tutor explain how to make a morticed lap joint to
make a 5 metre beam from two shorter pieces.  Woodwork on a major scale -
you should have seen the size of the chisels!

On that slim experience I hereby claim to be an expert!

I assume you mean the cross beam is mortice-and-tenon jointed into the wall
beam? http://en.wikipedia.org/wiki/Woodworking_joints may help.

The challenge is to maintain maximum strength in both pieces of wood, and
not make the joint so big that you take too much wood (and hence strength)
from the beams themselves.  It seems to me that the whole length of the wall
beam has to bear the weight of all the cross beams and the floor on top,
whereas each cross beam only has to bear its own weight and its share on the
floor.  For that reason you probably want the greater strength in the wall
beam.  Thus a relatively small tenon on the end of the wall beam will reduce
the strength of the wall beam significantly less than one which is half the
height of the wall beam.

--
Piers 
             

-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of swisspace
Sent: 27 March 2008 16:45
To: olympus@xxxxxxxxxx
Subject: [OM] [OT] any structural engineers on the list

I have been busy with the renovations and extension at the house but still
following the list, but have not bothered to see why my post about
E-3 raw in aperture and my theory on the tilted sensor issue post went
missing - anyway totally of topic but I know how the list enjoys such things
and is full of experts ;-)

They have now fitted the roof to our extension, it is a substantial
construction of thick wooden beams - I haven't measure them yet but I am
guessing 25cm (12") thick however what puzzles me is the puny joint they
have made (tenon if I remember correctly) see here

http://thattimeoflife.smugmug.com/gallery/613944#271142318 

it is maybe 5cm or two inches thick - I am not an expert and I am sure the
shear strength is enough but if I had done it I would have made the joint
50/50 here are some pictures from a wider angle

http://thattimeoflife.smugmug.com/gallery/613944#271142465
and even wider
http://thattimeoflife.smugmug.com/gallery/613944#271142622

and a view from above (excuse the distortion it was at 7mm end
http://thattimeoflife.smugmug.com/gallery/613944_WsNbX#271142813

the plywood boards they put on top were about an inch (25mm) thick and will
spread the load but somehow to me it seems either the beams are to thick or
the joints to thin

am I wrong


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