V Truss

[tribe]

During the mid 1980's Armco Metal Buildings produced pre-engineered buildings using a v-truss as roof purlins. I understand they have since gone out of business. I need to reinforce the existing roof purlins due to snow load impacts from an adjacent new building. Has anyone seen any published literature regarding methods of reinforcement, or span/load tables for the v-truss and associated roof decking. I have sent a email request to MBDA (Metal Building Dealers Association) asking for their assistance.

My current thoughts are to install new beams between the purlins to increase the roof and deck capacity by 4 times.

 

[ishvaaag]

Your solution may be simpler and cheaper, evaluate this.

Reinforcing it would be maybe even passably easy for tension and even compression (concreting atop, assuming stud-like shears and sehars at nodes can be met), but if you have web capacity problems, you better go for what you are thinking. Maybe you could weld or fasten plates to the web members, anyway, but surely mechanical services pass through the webs, no?

Also, since a roof problem, could it be possible to build your solution above the present roof? This may be the simpler.

 

[JAE]

Adding new, known quality, members between would be my preference. You most likely will have to do something to reduce the span of the roof deck anyway so adding the members between is simplest.

Also, I would be tempted to design your new members for all of the snow, ignoring the existing V trusses. Especially since I don't know the actual stiffness or strength of them. I know they currently take "X" amount of snow, but when adding new members, the newer may be stiffer, thus taking a greater share of the load than you would calculate using simple tributary area methods.

 

[dik]

Both ways work depending on what's present and what has to be done. It's often easy to weld bars to the top and bottom chords... usually encounter a 'mess' of electrical/mechanical clutter between joists. For snow accumulation problems, it's often better to add extra members; this increases the load capacity of both the roof purlins as well as the deck as noted.

As far as reinforcing web diagonals, often the diagonals are the same dia. size for the length of the truss and welding new bars is only required at a few end panels. Problem with some pre-eng things is that the design is generally so tight that they may change the diagonal web bars every 2 or 3 panels.

If the deck is deficient, then adding extra members between is possible. Increase is not likely 4 times due to the limitation on the deck shear, but you can likely double it or better (could be thinner material than 22GA, another one of the things I like about pre-eng stuff). If deck is only slightly deficient, I've (with the owner's blessing) left it alone because failure of this component is not likely life threatening.

Have been involved with many pre-eng type buildings and you might want to check on the quality of the deck. I've had a few 'rot' out and re-roofing is a major undertaking. Depending on the environment, the roof may only have a life of 20 or 25 years (like a garden shed, only longer).

I assume that both buildings are owned by the same person/company; if not, I usually let the other owner look after his own building at my client's cost. This way, you are not picking up the entire liability for the other owner's building. Also, almost any undertaking on a pre-eng building voids any warrantee it may have had including modifying the joists. I've often encountered where the original suppliers don't want to 'mess' with them, either. Also find that owners have modified existing pre-eng buildings by themselves including removal of an exterior haunched column.