Sort of an engineering question

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My current project is a carport. It has been designed by an architect and the steel specified by an engineer. It's going to look fantastic when I actually finish it. The architect did it as a love job and the engineer has gone overseas for a while. So I'm hoping somebody here may be able to answer this question.Supporting one end of the carport, there is to be a 150mm beam sitting on a 100 x 100mm hollow post. The post will be welded to a base plate which is in turn bolted to the concrete driveway.Now the beam is only 75mm wide, so the junction of the beam and post will look a bit ugly.I'd rather go with a 75 x 75mm hollow post.The post will support the weight without any trouble. The only issue is that the structure may move/flex a bit more.So I'm wondering whether gussets or butresses (not sure of the correct term) where the post is welded to the base plate at the ground will help this or whether they will in some way cause a point that may fail?Scott
Reply:You should stay with the sizes specified by the engineer to be structurally sound.  He may have called for the 100 x 100 for buckling concerns due the height of the column.  You should be able to cut a flat plate to cap the top of the 100 x 100 and for the 75 mm wide beam flange to rest on.  Gussets at the base plate will do nothing to prevent buckling at the middle of the column.  You would need diagonal braces on 2 sides from the middle of the column up to the support beams, and this may still not be adequate for the wind loads assumed in the design calculations.Last edited by welder4956; 06-26-2006 at 10:59 PM.
Reply:Thanks. Deep down I suspected that would be the prudent thing to do. It's going to be the sturdiest carport in Sydney.Scott
Reply:Whilst its never a good thing to go against an engineers specs, speaking as a builder its a big post for a Carport Scott.Then again how high are they?What wall thickness ?What local wind load multipliers exist ?What is the shape of roof and what is roofing material?
Reply:It's hard to describe, Brett - definitley not a standard carport.The post will be 2400mm high. The 150UB 18 beam that sits on it spans 4 metres and is embedded in a brick wall at the other end.Sitting on top of the beam is the roof perimeter. It will be made out of 150mm PFC on edge. Bit of weight there. The other end of the roof perimeter is supported on a brick wall and on another post.Then there is a 100 x 100 SHS that runs 7 metres as part of a concealed gutter. More weight there.There there are the steel cross members for the roof sheeting. More weight.Hmmmm. Maybe the 100mm post isn't overkill.Bugger-all wind - completely sheltered from the westerlies and southerlies.
Reply:Any reason you can't use a thicker wall 75 x 75 SHS to equal the strength of the 100 x 100..?
Reply:That's what I thought. I just tracked him down. He said I could use a 75 x 75 post. He said it would flex more than the 100 x 100.He said that 100 x 100 was the correct size and that it was up to me. I hate it when they say that after planting the seeds of doubt.
Reply:Go for it Scott!   Go with the 75x75...me thinks it will sufficeIF it Catches...Let it Burn
Reply:When an engineer says: 'I would do such and such, but it's up you....', and then pauses and looks at you, it's a bit like your tax accountant saying in response to a slightly risky idea: 'I would do such and such, but it's up you....'I reckon I'll be going with the 100 x 100mm.
Reply:Sounds like one very solid carport Scott, Compared to a off the shelf kit carport. I built a double kit carport not so long ago and the posts were only two C150-15 purlin's boxed together with 1.6mm angle brackets fixing them to the concrete footings, the whole thing was screwed no welding or bolts but it was designed by an engineer and council approved. So I would not have a problem with using 75 x 75 x 4 SHS.Will you be doing all the fabrication yourself ?.How structurally sound is the brick wall ? Simonhttp://members.optusnet.com.au/~abba/index.html
Reply:Originally Posted by scott brunsdonThanks. Deep down I suspected that would be the prudent thing to do. It's going to be the sturdiest carport in Sydney.Scott
Reply:I think your choice to stay with the engineer's recomendations is correct.  One thing that puzzles me is why you want to reduce the size of the post when you are concerned about the appearance of a connection.  Why not INCREASE the size of the beam and resulting flange??  If appearance is so important you should err on the side of overbuilding.
Reply:Why not INCREASE the size of the beam and resulting flange??