Design life of structures in US codes

[Tiato]

Hi all,

Normally when we design a structure in Eurocodes, design life is required as stated in BS EN 1990. Based on this design life we can determine the durability (concrete covers,..) requirement, environmental loads or corrosion protection requirements. When I study the US codes like ASCE, AISC, ACI or IBC, I could not find any guidance in term of design working life. It seems that the codes only use the concept of "Risk Category" to determine the wind or earthquake loads, I am not sure that durability requirement as well as corrosion protection requirement also based on "Risk Category"? Could anyone share your experience with US codes regarding the design life determination?
Thanks,

 

[CrabbyT]

As far as I know, there are very few explicitly codified service life requirements for structures in the USA. I think AASHTO bridges are required to be designed for a 75 year service life, and there might be some requirements for dams, roads, and sewers too.

Personally, I think things like settlement, creep, and corrosion should always be considered. Durability is a tricky subject to pin down because often times, rapid deterioration can occur due to neglect. About 10 years ago, I saw an entire neighborhood of new homes built 2 years prior. Nearly all the homes were uninhabitable because the developer took too long to sell, didn't take good measures to prevent moisture, and most of the homes became contaminated with mold.

I found this report from the ACI that might be of some interest to you though. There's a table on PDF page 33 that lists service life requirements for various codes. This report seems to do a good job of comparing codes on an international scale in terms of what different countries expect in terms of service requirements.

LITERATURE REVIEW OF CONCRETE DURABILITY & SERVICE LIFE REQUIREMENTS IN GLOBAL CODES AND STANDARDS

https://www.acifoundation.org/Porta...bilitySLGlobalCodesandStandards-10Aug2020.pdf

 

[GC_Hopi]

Agreed, there is very little that is explicit and this is by design. A lot of the material suppliers avoid labeling/research in service life. You have to look in code commentary to see talk of service life but as mentioned some code do have it.

OP: Is there a specific material or structure type you are interested in?

 

[STrctPono]

I think we need to be clear that we are discussing what the US would define as "service life." This is related to the structure's durability and how well it weathers under environmental conditions. "Design Life" is a very different thing and is related to the anticipated load demands that the structure might experience throughout its design life. The latter is covered by AISC, ACI, AASHTO, etc. but those codes are all very minimalistic when it comes to addressing "service life."

I don't design buildings so I can't speak for that industry but as far as bridges are concerned in the US, service life is not tied to AASHTO very tightly as AASHTO is rather loose with service life requirements and covers it only on a real basic level. SHRP2 is a committee that was established to try and reel this in more and has a document that discusses a more thorough approach to addressing service life. Link

However, service life is a bit more difficult to write into the code and expect people to be able to follow it like a recipe book. It's more qualitative than quantitative and is so affected by the environment that different locations can have very different approaches to addressing service life. That is why most State DOT's have their own preferred standard details that work for their environment. There are programs that have been created (Life 365) with the intention of trying to quantitatively tie service life down with a hard number when it comes to concrete design and the environment. These programs, however, are speculative at best.

 

[Tiato]

Thanks for responses everyone.

If they don specify any design life for a structure. So the wind load/ earthquake loads are the same for different design lives and only depend on the Risk Category of the structure? I mean if a building was categorized a Risk category of II, it will design with the same wind load/ earthquake load no matter what it is intended to design for 30, 50 or 100 years?
Normally, design life is one of the factors to determined durability requirements for the structures. For concrete structures, it could be affect the selection of concrete mixture, concrete cover, inspection and maintenance interval. Or for steel structure, design life will affect the selection of corrosion selection, such as what is painting spec, how thick is it, cathodic protection/sacrificial thickness, and again the inspection/maintenance interval.
So how these kind of things are selected or define in US codes? Or they apply the same scheme for all intended design life? And only depend on how bad the environment is?

 

[Tiato]

[ "Design Life" is a very different thing and is related to the anticipated load demands that the structure might experience throughout its design life. The latter is covered by AISC, ACI, AASHTO, etc. but those codes are all very minimalistic when it comes to addressing "service life."]

Yes. Design Life is defined as period of time on which the statistical derivation of transient loads/environmental loads is based, as stated in AASHTO. It's more about the conventional criteria to derive the loads acting on the structures. Could you share which section of AISC/ACI cover this?

 

[dik]

I didn't know they had a code designated design life... I usually stipulate in my notes that it is 50 years and for PEMBs it is 25 years.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Canuck65]

My response won't directly answer your question re US codes, but there is a CSA standard for Canada that talks about the design life of structures and components of structures. CSA S478-2019, Guideline on Durability in Buildings. It talks about Design Service Life and Durability among many other items. Various components of buildings have different design service lives, i.e. foundations have a much longer design life than roofing or windows, etc.... The guideline provides a framework, to be coupled with engineering judgement, etc....