Earthquake surcharge 1

[rlflower]

I am a civil engineer working on various residential projects thruout the greater Los Angeles area.

It has come to my attention that some jurisdictions - the City of Malibu, for example - are now requiring an earthquake surcharge for retaining walls in excess of 12 feet in height. It has been suggested that this surcharge be simulated by applying a horizontal line load surcharge to the wall at a rate of 21H^2 lb/horizontal foot of wall, where H is the height of the surface of the backfill above the base of the wall, and that this surcharge be applied at a height of 0.6H above the base of the wall.

I would like to know if certain juristictions - specifically, the City of Los Angeles - require this earthquake surcharge. If this is so, how do I get ahold of information on this subject?

Thank you for your help.

Richard L. Flower, P. E.

 

[whyun]

The City of Los Angeles retaining wall design requirements can be found in one of their Information Bulletins.

http://www.lacity.org/LADBS/faq/inf...IB-P-BC 2002-083 Retaining Walls-10-15-01.pdf

The requirements for additional lateral forces due to seismic effects is stated in the 2001 California Building Code Section 1611A.6. As I do not have the City of L.A. Building Code, I'm not sure if they adopted this California requirement.

When it is required by the jurisdiction, commonly the effect due to seismic loads is simulated by applying an inverted triangular distribution (opposite of active soil pressure). This inverted triangular load can be resolved into a line load at 2/3 H which is close to the City of Malibu requirements.

The magnitude of this soil pressure from seismic is commonly provided in the recommendation portion of the geotechnical report. If not, you may request this information.

 

[rlflower]

California Building Code Chapter 16A is for DSA/SS, OSHPD 1 & 4. This chapter therefore does not apply to the structures that I design. Chapter 16 (without the "A" designation) is the appropriate chapter. The earthquake surcharge appears in chapter 16A, but not in chapter 16.

To summerize, I am not required by code to apply the earthquake surcharge, however, my conciense may require that I seriously consider it.

Thank you for your help; I don't think I would have discovered this reference on my own.

 

[whyun]

I feel glad that I was of some help.

Yes, Chapter 16A is for school/hospital construction, therefore, most local jurisdictions probably adopted the portion of the CBC without the A designation.

I went to the City of Malibu site out of curiosity but was unable to find the earthquake surcharge requirements in your original post. Can this be found online?