Baseline Dimensioning

[Althalus]

I'm from the EPC sector for industrial structures. My company is mainly a mechanical fabrication shop.

We now make large prefab structures (like MCC buildings or LER buildings) ready to ship. But these are basically prefab industrial buildings the size of warehouses. We modularize them and send out shippable lego blocks.

One problem we're having between engineering and fabrication is that we're used to seeing different types of drawings.
1) We're used to standard structural drawings that are common throughout the industry. And we abide by AISC standards.
2) The shop is used to seeing mechanical drawing based on ASME standards.

They're asking us to use baseline dimensioning for the entire structure.

I don't really have a problem with this except for some management of drawings. But it got me to thinking, is there some reason we don't use baseline dimensioning at all? I've never seen it in over 20 years as an engineer. Why is that? Is there some weakness in the method that I'm not aware of?

 

[dauwerda]

My thoughts on this are as follows - don't know if they are correct or not.

Structural fabrication isn't generally held to super tight tolerances (compared to some mechanical assemblies).
So if you have a column cut at 20' and you have an attachment 19' up from the bottom, rather than measure up 19' from the bottom, it is easier to measure down 1' from the top to layout the attachment. In reality, we know the column wasn't cut to exactly 20', so laying out from both ends introduces more errors. In the structural world these errors are not enough to make fit-up an issue. Whereas with baseline measuring everything is being layed out from the same common point, which helps keep tolerances tighter.

 

[KootK]

I'd also think that a foundation plan drawing or thirty story building elevation would just get very cluttered if you were hitting every point of interest with a baseline dimension.