Wood truss connections 3

[WWTEng]

Single story building with cmu walls. Roof is gable wood trusses @ 24" oc. We show cont. (2) 2x8 plates at top of the wall anchored into a continuous bond beam. My question is about connection of the truss to this double 2x8 plate. I am assuming that this connection is to be designed and specified by the truss mnfr since the mnfr would know what up/down reactions to design for. Or is this connection typically specified by the EOR?

 

[hokie66]

As EOR, you should also know the reactions, and I think it should be your responsibility to design the connection. This may depend on where you are located in the world, as customs vary. As to up/down, don't forget horizontal, both parallel and perpendicular.

 

[IsaacStructural]

I agree with Hokie, Look to the manufacturer for a suggested detail if you can, but do the design/analysis yourself, shouldn't be too difficult.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[msquared48]

The truss manufacturer provides the design/reaction sheets and you design the connections.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[WWTEng]

Thanks all, makes sense. My question was because of the fact that you would typically get the truss shops after the drawings are already complete and may be even the foundations work has begun. But I guess those reacations (by mnfr) could be used as a check for EOR's calculated reactions.

 

[MiketheEngineer]

TPI (Truss Plate Institute) has very good direction on who is responsible for what!!

 

[BenAustralia]

In Australia, in housing/residential, the Truss manufacturer will often supply the specifications for the connection. I find that they, however, aren't very accurate and often specify something with less capacity than what I would specify. I'd contribute this mostly to that fact that the truss software operator isn't an Engineer and more just a software user.

 

[JAE]

The following is from a post back in 2005 that was a copy of an earlier post in another thread (NOTE ITEM 6):

The Idaho PE board issued a statement recently where they propose a more "proper" format for wood trusses (whether gluelam or pressed gangnail:

Basis of Design

1. Premanufactured roof trusses are an engineered system - that is, each truss has a specified location in the overall structural system.

2. The premanufactured roof truss system is both a vertical and lateral load system.

3. The lateral load forces must be developed by the EOR and given to the truss engineer to design (drag truss load, collectors, etc.).

4. All truss-to-truss connections are the responsibility of the truss engineer.

5. All drag load (horizontal truss transfers) connections between the truss and the structure are the responsibility of the EOR.

6. All truss-to-structure (walls or beams) connections are the responsibility of the EOR.

7. It is the responsibility of the truss engineer to develop the loading required to implement the requirements of snow load Appendix A.

8. It is the responsibility of the truss engineer to review all of the EOR’s design specifications, roof truss support, and drag details and to incorporate these requirements into the engineering design of the roof truss system.


Required Information from Truss Engineer:

The truss engineer should develop a truss layout plan for the truss system that clearly indicates the truss vertical support conditions, truss-to-truss connections, drag trusses and collectors, and any other field-installed reinforcement, including field-installed top chord reinforcement at eaves necessary to execute the truss system design. The truss roof framing plan should be sealed by the truss engineer and be included with the individual truss cut sheets. The truss engineer should also provide proper supervision of any truss company technicians.

 

[msquared48]

JAE:

This gets into previous discussions we have had regarding connections of East vs West coast practice (that was regarding steel detaining I believe). This is true for Idaho and the West coast, where Ipractice, but I wonder about the East coast.

Maybe some East coasters could chime in here...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[WWTEng]

A couple more questions about the same topic:

Since I wouldn't know the truss chord sizes, what is the proper type of Simpson anchor that I can specify in my design documents? I would like to use something like a Simpson H1 or H10-2, but they are for a specific chord size. What are some of the recommended connectors which would give me a decent load capacity and also flexibility in terms of chord size?

Gable end truss: For the end truss, sitting on the wall and transferring shear to the shear wall below, what is the common connection spec? Can I call out nail pattern to connect the truss bottom chord to the shear wall top plate or should this be done with Simpson connector or similar?

Thanks.

 

[charliealphabravo]

I have typically been fortunate enough to have the truss designs from the manufacturer prior to finalizing my plans. In that case the chord sizes, loads, and truss locations are known and the truss-to-structure connections can be specified on my plans.

When both the truss layout and the truss designs will follow later in the process, then as an alternative you might specify that truss-to-structure connections be selected by the manufacturer or delegated truss engineer, and then submitted for your review and approval. If the connections are shown on the layout then it is basically a shop drawing review. If they are specified on the engineered design drawings then you are doing a standard review of delegated engineering.

 

[RFreund]

If you have a design forces you can state these (i.e. uplift, shear x-fer from diaphragm) or list your desired connection then state "coordinate w/ chord size" or "or equal" then verify the connection when shop dwgs come in. I have seen a variety of these methods used. If you don't have a truss selected before 'bid' you should put something on there just so it doesn't come back as an extra.

EIT

http://www.HowToEngineer.com