Service Load & Ultimate Load 2

[ashcac]

What is the difference between Service & Ultimate Load?

Thank you very much.

 

[WillisV]

42

 

[ashcac]

Can you please give me a definition for both the said load.
Thanks

 

[DETstru]

Sounds like you're new to structural engineering. Here's a good link explaining a lot of the basic concepts involved in structural engineering:

http://www.bgstructuralengineering.com/

To answer your question,
Service Loads represent the actual imparted loads on a structure.
Ultimate Loads take the service loads, and amplify (increased typically, but not always) them to represent the loads we design for.

For example, if I have a concrete floor that is 4" thick, it weighs 50 pounds per square foot (psf). This is called the "Dead Load." Let's also assume the use of this floor is a residential space, which requires a 40 psf "Live Load."

So... Our Service Loads are 50 psf Dead Load, and 40 psf Live Load.

In Load and Resistance Factor Design (LRFD), we amplify these loads to find our Ultimate Loads based on a number of "Load Combinations" outlined in the local building code (which generally reference ASCE 7-10 in the US).

The most common "Load Combination" is: 1.2 * Dead Load + 1.6 * Live Load
So, our Ultimate Load would be 1.2(50) + 1.6(40) = 124psf

Essentially, in LRFD, the Ultimate Load is the Service Load with a "Factor of Safety" included.*
*not an exact definition but I think it'll do for what you're asking.

 

[mike20793]

Based on the way you're asking service probably means unfactored and ultimate means factored.

 

[mike20793]

What's this for? Is this for design of some component where wind or seismic forces are given as service or ultimste?

 

[ashcac]

@DETstru: Thanks for the reply and for the link...i really appreciate it...