RSJ to short?

[paulljones]

Im currently having a single storey extension built by a local builder. He is at the stage where he is ready to fit 2x RSJ's (250mm x 150mm) that will span the width of the house (5.9m) at ceiling level to hold up the rear leaves of the house. This will allow us to knock out the wall underneath thus making the rear rooms and extension into one big room. We have had structural calcs done and from this have built 2x 600mm x 600mm pillars to support the RSJ's.

My problem is that the pre-cut steels that are waiting to be fitted and are sitting in my garden at the moment look to short on the length. Once they are sat on the padstones it will mean that just 225mm of RSJ will rest on each padstone, my builder assures me that this is 75mm above the minimum (150mm) but this doesn't seem enough to me. Considering the surface area of the pillar/padstone I think he could of had them cut at least another 300mm longer.

Can someone tell me what is standard practice in the building regs? and am I worrying too much?

 

[Hitachimad]

As much as 225mm, sounds alright to me. Unless your SE has specd a minimum i wouldnt be concerned.

Quite often have 100mm minimum bearing.

 

[paulljones]

Thanks for your reply.

What I can't figure out is if the bearing can be so small why does it need such a large column to sit on? It's driving me mad!

 

[noseall]

What I can't figure out is if the bearing can be so small why does it need such a large column to sit on? It's driving me mad!

the bearing point at which the steel joins the masonry can be relatively small because the crushing resistance of the masonry is equal or greater than the load imparted by the steel

after all, the masonry is not dealing with any impact, just load. it is not going to shear off.

now then, this load is transferred downwards ultimately to the softer ground.

spreading the load is important when loads are concentrated.

so, although the load has been collected by the pillar it then needs distributing by a larger footprint where it meets the softer earth - ie a larger concrete footing.

small steel meets larger pillar, larger pillar meets bigger footing and so on.

weight distribution.

 

[noseall]

p.s 'Shytalkz' will explain it better when he comes on line.

 

[Bowness72]

The masonry pillars may also be providing horizontal support by buttressing the adjoining wall to resist wind loads. 225mm is a good amount of bearing onto a padstone.

 

[The_Scotty]

225mm is plenty.

150mm is the norm.

Trust your builder

 

[Ossy]

The load will spread out down through the pillar at a 45 degree line from the end of the beam, so by the time it gets to the ground it'll be in the whole of the column/pier and distribute this to the ground at a nice low bearing pressure. 225mm bearing is pretty big - we normally assume a 100mm bearing when doing the calcs and with padstones there'd rarely (never?) be a time when 100mm is not enough.

You have absolutely nothing to worry about

 

[Shytalkz]

225mm is plenty.

150mm is the norm.

Actually, that's not strictly true, especially for longer span beam bearings such as this situation: the bearing length depends on the load, the size and depth of the padstone and the material strengths of the pier.

However, the OP's concern is that the beams won't bear the full length of the pier. They don't have to - it would be an extremely heavily loaded beam that required that. The piers seem enormous btw!