Who is actually designing the trusses? 1

[FSS]

In sunny Florida we have a distinction for prefab wood trusses between a "truss system engineer" and a "truss design engineer." The former by definition designs a truss system and the latter designs individual trusses, but not a system. Working in the residential side of things, I receive and have to deal with truss documents that are signed and sealed by individuals labeling themselves as "truss design engineers." Have seen hundreds of projects come through and have never seen anyone call themselves a "system design engineer."

The trusses are typically designed by technicians (high school education as min. requirement) at the local truss plant and "sent off to engineering" to be approved and signed/sealed. Legally these engineers are not designing the "system" but only the individual trusses. This makes no sense to me. How can you design individual trusses but not the system, especially when mutiple trusses tie into each other? In my opinion taking a set of plans somewhere and getting trusses in return means someone had to do more than just engineer some individual components.

Seems like an unfair way to shift liability for truss designs to unsuspecting engineers or architects.

Is this common elsewhere? Other viewpoints would be appreciated.

 

[jheidt2543]

The truss is considered a component in the strutural system of the building. The Designer of Record (DOR) is responsible for the overall design of the building, of which the component is only a part. The DOR speicfies the loadings the component truss is to support and the truss designer certifies that the truss meets those specified loads, but is NOT responsible for the overall building design, only the component.

The same is true of other prefabricated structual components such as precast concrete roof plank and double tees, precast wall systems, glass curtainwall systems, etc.

The thing to remember is that if something should fail, everyone connected with the project gets involved, so liability isn't REALLY shifted. This "system" of design allows the major components of a building to be designed by speicalists in that particular field.

 

[Lutfi]

I agree with jheidt. In Florida DOR is called Engineer of Record. Please refer to Florida Administrative Code (Rules 61G15-30 and 61G15-31) at this link:

http://www.fbpe.org/pdfs/chapter61g15.pdf

The engineer signing and sealing the truss calculations should be in responsible charge of the design and calculations. Otherwise he would be violating the Florida rules and regulations.

I hope this clarifies the matter for you.

 

[oldrunner]

Back in April of this year and a previously, this subject was discussed extensively on the SEAINT listserver. I suggest you look at their arguments and comments made at that time.
Responsibility for completion of the design is by the engineer of record for the whole building. The truss engineers do not complete the bracing requirements. They indicate where the members in compression are to be braced and are suppose to provide you with the compressive force in that member (see 2304.4 of the IBC). The EOR then provides the size and connection to the resisting element to prevent the compressive members from buckling.

For a long time many engineers missed this as the UBC only referenced the TPI-1 code in Section 2321- Division 5. I always considered this a “gotcha” trap by attorney’s as most people don’t have the TPI-1 code where it passes the responsibility from the Truss engineer over to the Design Engineer for the completion of the bracing of the web members in compression and for bottom chords that don’t have sheathing and are in compression when the truss is subjected to uplift.

 

[bylar]

My experience is that the technician inputs the data into a computer program and the software does the design. The engineer working for the software company spot checks (at best) and seals the design generated by his company's softwre. The softwre is usually provided by the plate manufacture.