Acceptable practice for design of trusses

[UofAGrad]

Hello Eng-tips,

I was approached by a local Gym owner that would like to expand their operation. They own an ~100 years old adjacent building, the ceiling is too close to the floor for the equipment they would like to place in the gym and the walls are made of brick (opposed to brick veneer), I will know more about the scope after we meet this evening. The owner is in the feasibility phase, deciding whether to (1) demo and start over, (2) purchase a new building or (3) raise the roof ~4' placed on a new support structure built within the current footprint and raise the now brick veneer to the truss overhang. My scope at the moment will be option 3.

My question is, if we get to detailed engineering, what is an acceptable practice for design of the trusses? The span will be ~50', it appears wood trusses of this span can be found readily online. During detailed engineering would the truss design be provided by a 3rd party truss supplier given my design parameters? Leaving me to design the support structure and foundation. Would I be responsible for design of the roof truss as well as the support structures? Some combination of the two? Either is fine, I'm just curious what the standard practice may be. Any recommendations or guidance is appreciated.

Thanks in advance!

 

[dhengr]

UofAGrad:
I would typically buy the trusses from a normal truss supplier, be they wood or steel. But, there is a bigger problem with your proposed scheme. You have two fairly independent structures which act and are loaded quite differently and they must finally be connected at the new roof, extended wall juncture. The new inner structure has gravity loads, some uplift, etc. on it and moves independent of the existing wall structure. The existing wall is made up of old multi-wythe brick, and its condition must be evaluated now that its roof diaphragm (lateral support) has been eliminated, but it is acting as a cantilevered wall against lateral wind loads, etc. Then you are going to add 4-6’ of new wall height up to the new roof, with a potential hinge at the top of the old wall. That detailing and structural design area in your scheme is going to be critical.

 

[Guastavino]

My initial thought is that raising the roof 4' may be like the case where you spend 100,000 to save 50,000.

Area of country and AHJ requirements will be key. If building is ~100 years old and you are trying to do that big of a renovation, it may trigger seismic upgrades, etc. Goes back to my point of spend 100,000 to save 50,000.

Some jurisdictions are just happy the old building is getting upfitted and as long as you provide a reasonable load path you're good.

DHENGR is 100% right on the hinge point and separate structure tie-ins. Details will be key on that.

As to your questions about the roof trusses...in my area, the wood folks do them based on my working points. But I am engineer of record and am responsible for them too.

Lastly, the statement that about "Brick veneer" and ~100 year old building raises a red flag to me. Unless it's been retrofitted, I would very much doubt that's a veneer wall.

 

[spieng89]

Like others have stated utilizing the existing brick wall may be an issue. Personally, I would not use it to support the new roof structure and design an adjacent steel support structure. This would allow for easier detailing between roof trusses and steel support and allow for bracing of existing wall back toward steel framing

 

[charliealphabravo]

As far as how wood trusses are specified you want the TPI-1 chapter 2 which gives the default responsibilities for the various parties.