Structure of Roof - Purlin supports

[Cashboy]

I am building a roof in steel on a house.

The distance of the columns are 4.5 metres centre to centre.

The tiles on the roof are the CPAC concrete type (4 kilos per tile)

The only support of the Purlins in the Architect drawings are the green verticle lines.

I am think that that would not be adequate.

I am thinking of adding steel horizontal supports (green) as diagram A or adding steel diagonal horizontal supports (green) as diagram B to get triangles for extra strength to carry the weight of the concrete tiles.

 

I was thinking B but the Thai builder is saying A.

 

Your opinions appreciated?

 

 

[kamalabob2]

What type of steel?  What size of steel?   C channel or Box steel?     2.3, 3.0. 3.2, 4.0?   Perhaps this is indicated on the approved house plans that the licensed engineer signed. 

[Cashboy]

Steel.

I am using 100mm x 50mm x 2.3mm (government stamped) box steel doubled where the drawing says  {2} even though the drawing was saying use C channel as I believed box would be stronger than 3.2mm C Section that was not obtainable at any steel shop I could find.

For the purlins I am using 100mm x 50mm x 2.3mm (government stamped) box steel.

Everything else is in 100mm x 50mm x 2.3mm (government stamped).

 

 

[Cashboy]

The roof is going to use about 2,600 tiles at 4 kilos each is over 10 tonnes.

I just worry that the steels can take the weight without flexing.

Steel work so far:

[Crossy]

I very much doubt that structure is going anywhere even with a dead load of 10 tons. It will move, steel is bendy like that, but I don't think you need to worry.

 

I do note that the steelwork is seemingly just welded on to the protruding re-bar in the columns, that gap should be filled with concrete to spread the load before the tiles go on.

 

I'd also rather they hadn't joined some of the beams, check those welds carefully, maybe add doubler-plates.

 

[Kwasaki]

It looks OK to me and good for roof work but put more diagonal steel bracing in if your not happy.  

[Cashboy]

2 hours ago, Crossy said:

I very much doubt that structure is going anywhere even with a dead load of 10 tons. It will move, steel is bendy like that, but I don't think you need to worry.

 

I do note that the steelwork is seemingly just welded on to the protruding re-bar in the columns, that gap should be filled with concrete to spread the load before the tiles go on.

 

I'd also rather they hadn't joined some of the beams, check those welds carefully, maybe add doubler-plates.

 

Thick square plates were welded to the 4 No 16mm raw bar sticking out of each column and then the steel box sections were welded to the square plates.

I shall make sure that they are all concreted.  I think from that photo they are concereting them then as some look dark, possibly wet.

 

 

1 hour ago, Kwasaki said:

It looks OK to me and good for roof work but put more diagonal steel bracing in if your not happy.  

So Drawing B.

I was thinking by putting the diagonals in the weight of the tiles will be pushed partly to the column and put less stress on the green beam from the purling onto the double horizontal beam?

Does that make sense?

[Kwasaki]

33 minutes ago, Cashboy said:

So Drawing B.

I was thinking by putting the diagonals in the weight of the tiles will be pushed partly to the column and put less stress on the green beam from the purling onto the double horizontal beam?

Does that make sense?

Yes !!  roof tiles are still a spread load, structural calculation have been made already the main point is to see the workmanship in construction is of good standard.

Putting extra steel if you feel it will give extra support and you do not mind the extra cost is not a problem.

[KMartinHandyman]

I am building a roof in steel on a house.
The distance of the columns are 4.5 metres centre to centre.
The tiles on the roof are the CPAC concrete type (4 kilos per tile)
The only support of the Purlins in the Architect drawings are the green verticle lines.
I am think that that would not be adequate.
I am thinking of adding steel horizontal supports (green) as diagram A or adding steel diagonal horizontal supports (green) as diagram B to get triangles for extra strength to carry the weight of the concrete tiles.
 
I was thinking B but the Thai builder is saying A.
 
Your opinions appreciated?
 
 

B

[Wirejerker]

As in A the horizontal can only transmit the force in the horizontal direction so it will do nothing but add extra weight in the truss

As in B the diag beam will carry some weight BUT it will transmit a horizontal force into the upper beam so the top half will be in tension and the bottom in compression. Not what the engineer designed it for. If you want the extra diagonal bead you will need to to put another one opposite to balance the forces so there is no additional forces put on /in that top beam. These extra beams also change the direction of forces and the size of the forces on the welded joints so you really are opening up a can of worms


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[carlyai]

My tiled roof is similar.
My purlins are double parallel beams with W steel welded between them. The same type of structure you will see on large construction buildings.
Evidently the main load will be pushed to the outside piers. I was so worried about the welding/strength of the construction, but the finished welds seemed to end up OK.
I'm not saying your roof construction is not right and I don't know the load bearing calcs. but double purlins looked stronger to me.
I'll try and find the pics.


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[Crossy]

 

You have signed off drawings, assuming you build to those drawings (including the roof covering as specified) you will be fine.

 

OK, yes I know TiT, but the professionals are actually pretty good.

[carlyai]

 
You have signed off drawings, assuming you build to those drawings (including the roof covering as specified) you will be fine.
 
OK, yes I know TiT, but the professionals are actually pretty good.

Yes you are right Crossy.
Once unexperts (like me) start commenting and others join in, it gets so confusing and worrying. Sorry for the confusion.

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[Crossy]

1 minute ago, carlyai said:

Once unexperts (like me) start commenting and others join in, it gets so confusing and worrying. Sorry for the confusion.

It never hurts to ask if something looks wrong.

 

[kamalabob2]

Quite a bit of excellent advise has been posted by Forum members for the OP. I have no clue where the OP or his house builder shopped for roof steel in Thailand, but rest assured that C section steel in the exact dimensions he listed  2" by 4" in 3.2mm  thick is readily available and in stock in Buriram Thailand. 23-24 kilo per meter top grade. This is not an exotic size or weight of steel when building a home in Thailand. It should not have to be a special order item. Special orders should take no more than 7 days at any direct buyer of Thai steel plants.  However, Indian or Chinese sourced steel that some shops sell might take longer to arrive. I recently bought 4 by 2 box steel in 3.2mm thickness in Buriram. 

[BEVUP]

I think you will be fine it's 2500 tiles spread over the area

I Had to have the same thing Carlyai said done on a previous place 10 mt x 20 mt

"C" channels welded back to back to support some 6000 tiles

 

[Crossy]

An off topic post intended to derail the thread has been removed.

[canuckamuck]

The best way to improve the strength is to add a ray instead of changing the angle. I doubt you could get them to do it though. I think you will be fine if you can avoid a heavy snowfall.

 

[Crossy]

Just now, canuckamuck said:

I think you will be fine if you can avoid a heavy snowfall.

I reckon what he's got will be fine even with the heavy snowfall

 

These things are heavily over-engineered anyway.

[Kwasaki]

1 hour ago, Crossy said:

 

These things are heavily over-engineered anyway.

 

Over the years that is my findings too, design strength is usually OTT.

OP should just see to the workmanship finish and make sure the drawings are followed during construction.

He can get someone independent to check if his in doubt.

[Cashboy]

As I already mentioned instead of using  2 Number 100mm x 50mm x 3.2mm  C section and welded together I used 2 Number 100mm x 50mm x 2.3mm Box section welded together because I was told this would be stronger.  This was more expensive because more steel.  I also used government certyified steel because there is some dodgy Chinese steel similarly.

 

I just got back to Thailand before they start to tile the roof.

 

Now my questions and concerns:

 

I totally agree with the remark that the space between the steel plate (supporting the steel beams) welded to the raw bar in the columns needs to be filled.

You stated concrete;  wouldn't Dry Packing it be better?  Dry packing is sharp sand and cement in ratio 3 to 1 with not too much water and letting it go hard for 3 days before putting any weight on it?

 

I am concerned about the welds that they use to join the 2 number 100mm x 50mm x 2.3mm box sections together.  This appears to be spot welded every 50 cm on the top side and every 1 metre on the bottom side.  I put some pictures for your information.

 

I also notice that the uprights holding the purlins are not welded all round onto the double horizontal beams.  I would think this was important?  Is it?  It cannot be because of the cost of the welding rods because we supplied all materials.  Is this poor lazy workmanship or is there a reason?  I just thought the more weld the better.

I also notice that a couple of the main column ridge supports is also lacks weld on the joins.  Picture for your information.

 

Comments appreciated.

 

 

 

 

 

 

 

[Kwasaki]

14 hours ago, Cashboy said:

wouldn't Dry Packing it be better?

A concrete mix is the same to point it correctly in with either would be OK for me.

 

14 hours ago, Cashboy said:

am concerned about the welds that they use to join the 2 number 100mm x 50mm x 2.3mm box sections together.

Looks OK to me, if your concerned get them bolted together every metre.

 

14 hours ago, Cashboy said:

I also notice that a couple of the main column ridge supports is also lacks weld on the joins.

The welds look good but pix are deceptive if your not happy get them to weld it to your satisfaction, more important to me would be the proper primer coating of the finished welds.

[Rimmer]

I thought I was looking at pictures of my roof when I built my house, VERY similar indeed.

I had a friend who is a British architect come and have a look at it, he said weight is not usually a problem but advised me to brace in between the spans as a problem can occur on the lee side of a large roof as it generates a lot of lift during high winds, he demonstrated the problem by standing there and flexing the roof. I think you have already done that looking at the pictures.

See attached picture for the extra anti flex supports he had me put in.

[Cashboy]

The roof is finished and the structure seems ok.

However I am not totally happy with the welding so will add more welds to the steel at the same time as I do the ceiling and will also paint on more "primer coating" while I still have easy access.

[janclaes47]

7 minutes ago, Cashboy said:

 

Is that just a visual effect or is that steel work more beside the column than it is on top?

[Cashboy]

On 6/9/2018 at 10:34 AM, janclaes47 said:

 

Is that just a visual effect or is that steel work more beside the column than it is on top?

That was the architect's fault.

When I designed the building (gave reasonably logical drawings to the Thai architect) the centre columns were in the centre for the purpose of supporting the centre roof beam in the middle.

However, the Thai architect screwed up and the builder of the skeleton roof clearly didn't think ahead.

The stairs were also a problem (steps became smaller) because of the Thai Architect pleased himself.

 

 

 

[MarcIssan]

Maybe you guys can help me regarding my roof structure.  I have a builder from Europe who is doing my house and mine won't be his first.  All is going well so far but now we are on the roof.  It is a hip roof design using nano blocks resting on a foundation (footing) 2 meters deep into the soil and the walls rising 3 meters above a 60 cm elevation off grade.

 

He is just now welding the 2" x 5" steel on the wall tops then the roof gets constructed onto that.

 

Above in my CAD drawing to represent the problem as I see it.  Each of these are 2x5 and he plans only to weld where the red circle shows.  He will have basically a spot weld at that tiny intersection of the two steel beams on each side.  I think he needs to well along the leading or trailing edge or both but he says it has not been a problem in the past. In other words the roof has not collapsed yet on any of his prior 7-8 builds.

 

If I ask for added (unnecessary) work he will likely bill me for the added time and materials however if I can present evidence his way is insufficient then he will have no basis for billing me.

 

I looked all over to find the weld strength of this type of weldment but I don't know what you might call this.  It is not a butt, lap, edge. fillet, or T joint so I'm hoping to hear from a trained welder or structural engineer.  

 

It is common sense to me  not to trust the 20,000+ lbs of this roof to a couple of spots but I seek solid evidence this is not sufficient...or maybe find out I have nothing to worry about.

 

Thanks

[Kwasaki]

3 minutes ago, MarcIssan said:

 

 

He is just now welding the 2" x 5" steel on the wall tops then the roof gets constructed onto that.

Above in my CAD drawing to represent the problem as I see it.  Each of these are 2x5 and he plans only to weld where the red circle shows. 

Could do with a better on site detail of this.

 

Nanoblocks OK it's all very well you pointing out this sole part of the roof construction but what about the complete and rest of roof truss structure.

[MarcIssan]

Ok here is more info

 

 

[Fruit Trader]

1 hour ago, MarcIssan said:

Ok here is more info

Quite a complex roof and will need some good tile work at the ridge intersections and valleys.