Detailing The Cambered Truss

[Jay0607]

Detailing The Cambered Truss

Hello everyone, for the truss in the above diagram, contract drawing calls for 1" camber. Usually, for the cambered elements, we provide the camber value in the part attribute and put a note in the shop drawings "Length of the member to be adjusted by shop to suit camber" and detail the beam in uncambered position.

But in this particular job, the clients want us to physically camber the truss. We attempted to detail this truss in the cambered position and encountered some issues.
Please note, the truss and connections are engineered by the client them-self and we are only doing the detailing.

1. Please suggest the usual detailing procedure to detail & produce the shop drawing for the cambered truss.

2. We have a pipe column (part 2147-TC1-5) on top of the truss and several other beams connecting to the top chord of the truss on the lateral side. Do we have to detail these members by assuming the truss is in a cambered position? or uncambered position?

3. Do we have to provide any special provision for truss connection and corresponding steel connection, such as vertical slotted hole connection, etc., as the cambered truss becomes into its normal (uncambered) position when the load is applied?

(Refer to the truss drawing below)

 

[sbisteel]

That is an awful connection for the erector, especially with camber. My guess is that the most ideal situation is to fabricate the cambered truss in a way that the end plates are perfectly vertical while the truss has 1" camber. This would mean the end chords would have a skewed cut to allow the end plate to be vertical, and 1" camber is probably too small to get that right.

Providing vertical slotted holes in the end connections should be a question for the EOR, I doubt it would fly but this is a strange mixture of an end plate and bearing seated connection.

The length of the pipe column is a question for the EOR, as that camber has some amount of DL baked into the equation. Does that include some loading from the column above? Is there a concrete slab supported by framing on that column? Concrete slab supported by the truss top chord? Sequence of construction? If it were me, I'd be detailing 1/8" and 1/4" shims to fit below the base plate of that column, same size and hole pattern as the base plate itself.

I wouldn't worry about anything framing into the top chord of the truss, as they'll follow the shape of the chord. Detail them normally, locating bolts & plates down from the top flange of that chord.

I'd also be hoping that the bolted connections of the diagonal braces are slip critical with oversized holes.

 

[Brad805]

What were the problems? Assuming they will roll the chords to the 1" camber it seems like you need to apply a camber in tekla to the top and bottom chords, draw radial centerlines using the same center point, and adjust the web centerlines to suit. I agree the end plates need to be vertical, and you will need to shorten the pipe column.

Did you ask the client how they would build this? If you have called out a 1" camber for a truss like this in the past what did they do?

 

[MotorCity]

Given the span, its borderline too short to camber....especially one inch. I'd expect a truss of this span to have 1/4"...maybe up to 1/2" camber, but thats pushing it. With the short span and the moment-like connections between the chords and web members, there's not much opportunity for the camber to come out when loaded. The better approach would be to increase the member sizes to result in less deflection.

 

[canwesteng]

The camber looks like a mistake by the EOR to me, but I guess you're stuck with it now.

 

[JLNJ]

Is the camber for the post load? If so, can you just fill under the post plate and not camber the truss?

On a side note, I'd like to see how they designed that big end connection. The eccentricity of a heavy load like this on a one-sided connection is a curiosity to me.

 

[human909]

I've never cambered a truss before but I would presume the 'correct' or at least ideal way of doing so would be to have:
-a shorter bottom cord:
-a longer top cord
-reduce/increased lengths struts as required

Which is enough of a nightmare for such a short truss, let alone one with what seem to be rigid strut connections. IMO the engineer needs a reality check. If they are desperate for a level finish then slope the floor suitably. Far easier.