ASCE Ra values for pile and slab foundation

[KevinNZ]

What R[sup]a[/sup] value is applied to,
a) Pile foundation where some lateral movement is tolerated and the this movement will dampen the EQ actions.
b) slab foundation where sliding and over turning has no mechanism to adsorb the seismic energy.

 

[HTURKAK]

Short answer,

a)R value for piles is 1.0 .Since response modification factor (R ) is already applied to superstructure, the design seismic effects are reduced values. ( pls. look to the attache doc. piles and foundation)

b)Small slidings and rocking will adsorb energy but at least the foundation should be designed assuming no mechanism to adsorb the seismic energy. The additional base shear from self-weight of the footing may be calculated using Section 15.4.2 V = 0.3*SDS*W*Ie Equation (15.4-5).




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[KevinNZ]

thanks HTURKAK

We are designing foundations for structures not like buildings. Basically a lumped/stiff mass supported ~1m about the ground. System response comes from the foundation.

 

[HTURKAK]

In this case , i will suggest you to look

Guidelines for seismic evaluation and design of petrochemical facilities (ASCE 2011)



Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM