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What type of steel beam and steel columns do I need for the…

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What type of steel beam...
What type of steel beam and steel columns do I need for the following scenario.
Beam span 43'
Column height 14'
Static loadThe steel beam and columns will be used to add support under sagging wooden trusses built in the 1920's. The truss system consists of layers of full dimension 2x12's alternating between chords, diagonals and uprights.Over the years the roof has had numerous torch down roofing layers added and the ceiling inside with original lath and plaster had a layer of 5/8" sheetrock added over it. The weight of the additional roofing layers and sheetrock has caused all 5 trusses to sag down 5" from their original height.Our plan is to place the steel beams directly under the trusses and then lift all 5 trusses sequentially 0.5" at a time until all 5 trusses are up to the correct height.If this does not seem like a good plan of action I am open to a better solution.
Submitted: 7 months ago.Category: Structural Engineering
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12/29/2017
Structural Engineer: StructuralEng, Consultant replied 7 months ago
StructuralEng
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Category: Structural Engineering
Satisfied Customers: 7,753
Experience: Structural Engineer
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Structural Engineer: StructuralEng, Consultant replied 7 months ago
Is it your intention to put one steel beam under each truss? Directly under and parallel? Or one beam total under and perpendicular to the trusses?
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Customer reply replied 7 months ago
I intend to put one steel beam directly under each truss (inline)... Not one beam perpendicular under all trusses.Calculating the static and active load (snow) is the part I don't understand how to compute... Some additional info.
1. We are only adding support to one side of the roof... The other side of the roof is not as wide and is in good shape.
2. I can estimate the weight of the roof (sheeting, trusses, rafters, ceiling joists, drywall, light fixtures, etc) that is over the area we intend to reinforce.
3. The end of the trusses that terminate at an exterior wall sit on unreinforced brick pylasters that are formed into the brick walls of the building. The other end of the truss connects to a collector truss that runs perpendicular to the trusses we intend to support.... There is a wooden beam column directly under each connection where the trusses connect to the collector truss and they are in good condition.
3a. Because the pylasters are made from unreinforced brick I would like our column and beam system to support the entire weight that the current pylaster and wall system are supporting... We do intend to add bracing between each of our beams and columns to essentially form a cage that would support the entire roof system in the event of a catastrophic event such as an earthquake.If you need the static load and active (snow) load please help me understand how to calculate it and I will.
Customer reply replied 7 months ago
If I provide you with the entire weight of the area that the 6 trusses cover can you determine static load from that?
Structural Engineer: StructuralEng, Consultant replied 7 months ago
How about the spacing of the trusses, the floor construction above them, and the intended use of the space?
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Customer reply replied 7 months ago
The existing mono trusses are spaced 16' apart.
The trusses support the roof only as there is no floor above.We have mitigated the overloading conditions by removing all the old layers of torchdown roofing and removing all the lath and plaster ceiling and 5/8" sheetrock. The total weight removed from the roof and ceiling is 35,000 lbs. We will cover the roof with a membrane material adding very little weight back. We will not add sheetrock back to the ceiling leaving the area exposed. This is a commercial building and open ceilings are accepted and popular.My concerns are the following:
1. The overloading of the trusses has caused them to dip down in the center of the 43' span 5-6".... The steel beam's I intend to add under each of the 5 trusses is to raise each truss back to its original height and add permanent support.
2. The pylasters at the wall end of the trusses are made from unreinforced brick... This end should have a column added for this reason even if a steel beam was not added.Again I can calculate the total weight of the area supported by all 5 trusses. I don't know how to calculate the static load of each truss though. Please tell me if you can work with the total weight of the roof or if you need be to calc the static load of each truss. I would need a formula (and explanation) to calculate the static load of each truss.
Customer reply replied 7 months ago
Total static weight of the roof when new TPO membrane roof is added is 50,000 lbs.... With 5 trusses I estimate the static load for each at 10,000 lbs.Can you answer my original question based on this info?
Structural Engineer: StructuralEng, Consultant replied 7 months ago
What is the snow load? That will affect the answer, too
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Customer reply replied 7 months ago
25 psf is what the local jurisdiction uses... When I use a calculator that figures pitch, exposure and thermal factor it comes to 20 psf.
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