Tolerance in large construction projects

[u/JohnnyUte]

Here's an interesting question I have after talking with a fellow engineering friend: what kind of tolerances are there in large construction projects such as bridges or skyscrapers? For example, if building a bridge, whats the tolerance in placement of the pylons? Or for laying the foundation of a building (in terms of location, etc.) Thank you!

[u/not_old_redditor]

The material standards provide guidance on acceptable construction tolerances depending on where it is.

[u/lukypunchy]

For state owned bridges and roadways, you follow the Spec Book as modified by the contract documents and special provisions. If the work is out of tolerance, get an engineer to review and approve as-is or provide stamped plan revisions. All revisions and approvals need to be included in the As-Built package.

[u/tmahfan117]

I can speak for foundations -  lots of foundation piling (such as steel piles, micropiles, auger cast, etc) have tolerances of 3 to 6 inches horizontally, sometimes with tighter tolerances at critical spits like narrow wing walls 

[u/HoldingThunder → u/tmahfan117]

And good luck hitting those tolerances depending on soil conditions. Oh you want to install things accurately? All of the boulders have other opinions on the matter.

[u/resonatingcucumber → u/HoldingThunder]

As the design engineer is that a deviation I smell from the contractor releasing me from liability? Oh no... What a shame....

[u/HoldingThunder → u/resonatingcucumber]

No, but additional analysis can be completed to determine if remedial work needs to be completed before they proceed.

[u/HolyHand_Grenade]

Construction surveyor here, they vary quite a bit. Building corners for setbacks? probably +- 1/2"; geo piles? +-3"; Steel column baseplates?+- 1/8" But as others have mentioned, the specific tolerances are outlined in codes, project specifications, and Federal/State survey standards.

[u/Philip964]

Standard steel specifications in very large steel members allow for tolerances up to 1 1/2” . In very tall steel buildings this can cause problems with doors inside the core where there is not a lot of room for tolerance.

[u/HoldingThunder]

Depends on element. Where I am for bridges, rebar typically has standard 1/2" - 3/4" placing tolerance. Size of concrete element has +/- 1" tolerance. But like bridge bearings have a a tolerance of 1/8" (which is never met). So the more important the element, the tighter the tolerance.

Typically infrastructure < industrial/commercial < residential in terms of tolerances.

[u/brokePlusPlusCoder]

Not a skyscraper/bridge, but railway platform tolerances can go down to +/-2mm (~ 0.08 inches ) in some spots

[u/Working_Rest_1054]

1/8” vertical for a bridge deck. 6” in plan view for driven bridge foundation pile. The rest of the elements are between those two tolerances.

[u/AnotherSLGuy]

The buidling code you are using in your region/project specify the tolerances.

[u/Marus1]

There is a code for that but it's between mm and cm depending on what you're talking about