Earthquake Restraint Bracing System

[300redbeard]

Modular Buildings supported by piers are not specifically called out in the IBC 2006 and ASCE 7-05. In southern California, San Diego, San Bernardino and Riverside counties all require Earthquake Restraint Bracing System (ERBS). I work on DOD base and have an issue with a contractor installing state approved ERBS.

International Building Code 2006: SECTION 1613 EARTHQUAKE LOADS
Every structure, and portion therof, including nonstructural components that are permanently attached to structures and their supports and attachments, shall be designed and constructed to resist the effects of earthquake motions in accordance with ASCE 7, excluding Chapter 14 and Appendix 11A. The seismic design category for a structure is permitted to be determined in accordance with section 1613 or ASCE 7.

I'm trying to find a code/provision, whatever, that specifically calls out modular building to require ERBS. FEMA 302? I need it to prove due diligence.

Also, what method should be used for base shear? Because it is on piers should it be designed as a multi-story (Moment?)? Or is it designing ERBS to overcome base shear?

Thanks

 

[JAE]

Whether it is a modular building, or a teepee, there should be, per the governing code, a lateral force resisting system in place to take the required wind and seismic forces.

So the question then is, what is the appropriate lateral seismic demand to which the modular building should be designed?

ASCE 7 outlines various typical lateral load resisting systems in their table 12.2-1 and this table provides various response modification coefficients to be used for each type in determining the seismic forces.

For a modular building, you would have to determine which lateral system in the table best represents the response of the modular building to a seismic event.

ASCE 7-05, section 12.2.1 states that [blue]"The basic lateral and vertical seismic force resisting system shall conform to one of the types indicated in Table 12.2-1..."[/blue]

And in the last paragraph of 12.2.1 it states [blue]"Seismic force resisting systems that are not contained in Table 12.2-1 are permitted if analytical and test data are submitted that establish the dynamic characteristics and demonstrate the lateral force resistance and energy dissipation capacity to be equivalent to the structural systems listed in Table 12.2-1 for equivalent response modification coefficient, R, system overstrength factor [Ω]_o, and deflection amplficiation factor, C_d values."[/blue]

 

[300redbeard]

Since the modular is supported by 18" piers, what method do you recommend for base shear analysis? In other words, should it be designed like a 2 story structure because of the piers or a 1 story and design for the restraint?

Thanks

 

[JAE]

Not sure I follow you - but is the building raised up above the ground level by the piers? So it is sort of like a house on stilts similar to what you see in flood-prone or ocean-side areas?

If so, then the piers would behave like cantilever columns and fall under section G of Table 12.2-1. The upper story would depend upon the make-up of the modular building.

So the piers plus modular would be designed like a two-story building in my view.

 

[300redbeard]

JAE,

That's exactly what I was asking for, and exactly what I thought.

Thanks for the reassurance.