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Field Assembly of Trusses

Field Assembly of Trusses

Field Assembly of Trusses

(OP)
I am looking at designing a 60'x120', 2 storey wood framed building. It would be preferable to use pre-engineered wood roof and floor trusses to span 60'. The building occupacy has many open space amenities including a gym space, etc... necessitating full clear spans.

Problem is ... this is to be constructed in a remote fly in community. They can have supplies delivered but not complete trusses, nor anything near 60' in length. I was wondering if anyone had experience with the field assembly of roof and floor trusses, if it is even recommended? If each truss member was cut and labelled before shipping to the site, once the ground floor was complete, they would have a large work area to commence site assembly of any trusses.

Any comments on whether this would be feasible? Is there a portable press that could be shipped to site to press the truss plates, or would it be recommended to switch to field plywood truss plates. Any comments appreciated.

RE: Field Assembly of Trusses

60' clearspan wood floor trusses? They would be about 6' deep with connector plates far to large for a portable press IMHO. Call up a wood truss company or maybe Mitek or Alpine connector plate companies and talk to them. This link (http://www.tpinst.org/links.html) will give you contact information to the major ones.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Field Assembly of Trusses

The connections would be a lot simpler with steel trusses, just have to consider fire requirements and mixing of materials.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

RE: Field Assembly of Trusses

In the past I've done a lot of northern stores in remote communities, but not 60' spans. Largest about 45' or thereabouts.

It can be done... analysis by graphical means and plywood gussets. Used hardened truss gusset nails (stainless steel or HDG roofing nails can be used, they have a large diametre shank). Contractors laid out the truss on site and used plywood 'stops' for alignment of the members, neatly cut the web and chord members and nailed the gussets in place. Hoisting was done by hand and/or a small crane. As the span increases, this becomes more problematic. Can they 'barge' the construction material in? might consider using steel as suggested.

Dik

RE: Field Assembly of Trusses

Dik, what depth were your 45' trusses and were they roofs (with or without snow?) or roofs and floor trusses?

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Field Assembly of Trusses

Roofs and with snow... I don't recall the depths, but they were likely 3:12 or 4:12 of that ilk...

Dik

RE: Field Assembly of Trusses

(OP)
Thank you for the info. There is some large equipment up in the area (loaders, truck mounted cranes, etc... ), taken up during winter on the ice roads. We could have the trusses trucked up on the ice road, however, they want construction complete before this winter. I will be contacting the local truss supplier at the beginning of the week. All your suggestions and info have provided me with some good background info.

Currently have 4 ft. depth for floor trusses. Will see if we can get more, once I have had a chance to speak with the truss company and have a better understanding of the constraints. There is a possibility of providing an intermediate beam line for the floor trusses, however, would only reduce the spans to 10'/50', not enough in my opinion to discount the much cleaner solution of spanning the entire 60 foot distance. Design roof slope is 4:12, but likely could be altered if necessary. Design snow load is about 45psf so not terribly high.

As mentioned, steel may also be an option, however, I believe working with wood would be better suited to the local labour.

RE: Field Assembly of Trusses

Should add, the truss detailing should provide as much 'heel' height as possible... increases longevity and reduces 'ice-damming'.

Dik

RE: Field Assembly of Trusses

Have you considered Modular Construction?

RE: Field Assembly of Trusses

(OP)
trussrepairguy,

I am starting to delve into Modular for other projects. Not an option here as I'm not aware of any modular unit that can be broken down sufficiently to fly into the site. We're looking at 2 stories, gymnasium (i.e. open span), etc...

RE: Field Assembly of Trusses

I have seen large trusses shop built in sections, and then the sections joined in the field.
Watch the floor joists. If you just design to the max allowed deflection at this span you will have floors that flex so much that people will not want to walk across them.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Field Assembly of Trusses

EdStainless is right, we have to be careful while designing against SLS state...

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-des...

RE: Field Assembly of Trusses

I have done it. Not easy - not cheap...

RE: Field Assembly of Trusses

60' span perfectly achieveable. We have made attic trusses to 75' span for our own office and trade counter building. We also manufacture trusses and timber mouldings. Portable presses are available but can be a little slow. Erect a gantry on sitre so the heavy press can be swung into position. We work with Mitek UK and have a sister company working with Gangnail.

I can get you photos of required of the type of set up you could use.

Fearghus Quinn
Structural Engineer
Quinn Building Supplies Ltd
Northern Ireland

RE: Field Assembly of Trusses

Obviously, the floor is the challenge. What is your floor live load?

RE: Field Assembly of Trusses

(OP)
Fearghus ... Thank you for your info. Good photos. The problem with a central beam or girder truss to reduce the span is that it would have to span approximately 120' over the gymnasium.

efsinc ... Floor live load would need to be 100psf for assembly type occupancy (public games rooms, hallways, lounges). Perhaps 50psf for a couple of small offices.

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