Reinforcement detailing provision below the seismic base?
Reinforcement detailing provision below the seismic base?
(OP)
Say I'm doing a multi-story concrete building in low seismic region (0.1g) with double basement floors imbedded in a stiff soil/rock capable to transmit lateral seismic load on to basement walls constructed monolithically with floor slabs. The seismic base is at ground floor.
With all the stiffness gained by the retaining wall and stiff soil /rock surrounding the lateral resisting system do I still need to consider seismic reinforcement detail at column beam joint below basement 1 to allow for ductility?






RE: Reinforcement detailing provision below the seismic base?
RE: Reinforcement detailing provision below the seismic base?
Forgive my ignorance.... I practice in a region long been categorized as non-seismic, however the recent published code recommend 0.1g peak ground acceleration in some part of the region and I'm trying to refresh the little that I know about seismic actions.
Yes, I agree joints in ground floor and floors above require ductile detailing, but I can't visualize any ductile deflection below ground due to seismic action. I refer to the code and it recommends ductile reinforcing for members designed to resist forces induced by earthquake forces and doesn't state any different for structures below ground imbedded in stiff ground.
RE: Reinforcement detailing provision below the seismic base?
In general and particularly for these moderate earthquakes such reduction of structural response supports some lesser ductility requirement for the underground levels. But this is a matter of engineering judgement, and the view of the pertaining code or those reviewing its application may differ, in which case the safe path is to provide the ductilty to the same degree established for the whole superstructure.
RE: Reinforcement detailing provision below the seismic base?
Two overall questions come to mind.
1. At what level are the seismic loads imparted to the bldg
structure.
2. What is the response of the bldg structure to these loads.
Seismic base
a/ Base at bottom of second basement.
b/ Base somewhere between bottom of basement and grade. At best
this would be a WAG assuming sufficient contact and stiffeness
between soil and basement walls. Would also require design
of basement walls for this local seismic loads.
Bldg response
What really is driving all this uncertainty is that there is no marked difference in the bldg response structure from bottom of basement to top of structure.(from info as posted).
At a minimum, I would consider seismic reinforcing details all the way to bottom of 2nd basement. I would also attempt to bound the problem based on above assumptions and any others I may have missed.
Your saving grace is that this is a low seismic area.
RE: Reinforcement detailing provision below the seismic base?
thanks for your insight.
RE: Reinforcement detailing provision below the seismic base?
I quote again from chapter 10 of the same book some references recommended for soil structure interaction analyses:
"Numerous guidelines exist defining the required steps to perform SSI analysis for design or evaluation
purposes. All methods of analysis are treated. Selected guideline documents are:
ASCE Standard, Seismic Analysis of Safety-Related Nuclear Structures and Commentary [1998]
EPRI Guidelines for Soil–Structure Interaction Analysis [Tseng and Hadjian, 1991]
Earthquakes and Associated Topics in Relation to Nuclear Power Plant Siting"
Quite surely there are good references out there and I may have some others, I just remembered chapter 10 because I read it some months ago. If I find something suitable to your question I will post. For example, it is quite likely that for your level of demand, you could design one reinforced concrete building in Spain for bigger forces from assumed lesser ductility and then soften much the seismic detailing of your concrete structure. If you contrarily wanted to use some available ductility, the structural response might turn somewhat less but the seismic details more cumbersome to prepare.
RE: Reinforcement detailing provision below the seismic base?
So, the only proper way to proceed the best available soil structure interaction analysis.
By the way, one reference was lost above for SSI analyses:
"Seismic Design and Qualification for Nuclear Power Plants [IAEA, 1992]"