guardrail & post deflection 1

[paullaup]

Often, as the structural engineer of record, we have to check other Engineers calculations. e.g. guardrail and posts. I usually adopt a deflection limit of L/180, for the cantilevered post, but I cannot find a definite deflection limit in any code for posts and guardrails.

Deflection limits were developed for various situations to limit aesthetical effects to finishes. (Cracking of plaster for example).
With guardrails, the idea is to stop someone falling over. So, am I being a “ball buster” by insisting on a deflection limit of L/180??? My feeling is that, by limiting the deflection of the posts/guardrails this will basically make the people using it feel safe.

Any thoughts???

 

[MotorCity]

paullaup,

I would contact OSHA. Aside from building codes, they are the primary governing body on issues concerning handrails, guardrails, etc. I know that they address loads that should be sustained but I'm not sure what their deflection requirements are (if any). They also may provide required dimensions such as maximum spacing of posts, opening sizes, etc.

Good Luck.

 

[paullaup]

OSHA !,.. I didn't think of them!,.. thanks

 

[griffengm]

paullaup,
I have not seen it but recently received a notice of a new set of standards for fences and railings from ASTM. Check them on the web.

Griffy

 

[epr]

Paullaup,
I suppose you are talking about guardrails at other than highway and road locations, but AASHTO is still a good guide for the design of the guardrail. I no longer do bridge designs etc., but have an older version of AASHTO's Policy on Design of Urban Highways and Arterial Streets, which states that the dynamic lateral deflection characteristics should be matched to the space available at the site. It further states that the maximum deflection may vary from 2 to 12 feet. This criteria is fine if you are talking about a catastrophic condition such as hi-speed impact along a roadway, but may not suit your conditions.

If you are talking about parking structures, etc., where low impacts may be more frequent, and replacement of the guardrail after impact is not proposed, I think you should set your own criteria incorporating a schedule of ranges of impact forces versus deflections.

 

[ERV]

I don't know and have never really come across deflection limits for guard rails and posts, however, the requirement is 50 lbs/lf commercial, 20 lbs/lf residential and single load of 200 lbs applied in any direction, at any section of the top rail.

Check out OSHA requirements:

http://www.osha.gov/pls/oshaweb/owa...able=STANDARDS&p_id=9715&p_text_version=FALSE

 

[GoodnPlenty]

Many gaurd rails are designed to span as catinary action eg. cable rails seen in parking garages and elswhere. Many gaurd rails only meet code by activating many posts (Catinary). We confirmed this with OSHA 20+ years past.

Remember the final result, safety of the person. So deflection would not be an issue unless or untill it presents a condition that is harmful.