Deep and Shallow foundations
Deep and Shallow foundations
(OP)
Hi, what can be the main considerations or concerns if you have half of the building supported on piles and the other half supported on shallow footings? There is a big difference in the depth of the bedrock (mudstone bedrock from 1.5m to 20m below ground surface). The building is quite rigid (1-story box-type building with concrete walls and roof). Site is in active seismic area with liquefaction potential. Piles are approx. 15m-20m long. An expansion joint will be needed in the boundary of both systems. Some local engineers advice me to install piles for the entire building, even at locations where the bedrock is shallow. In any case, lateral resistance and displacement may have large differences throughout the building...





RE: Deep and Shallow foundations
RE: Deep and Shallow foundations
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Deep and Shallow foundations
RE: Deep and Shallow foundations
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Deep and Shallow foundations
I would concur anyhow that it is best, to treat the design as two separate designs: 1: building half on rock; 2: building half on soil, subject to different actions. Seismic action would be totally different in the two halves because of different site response, no amplification on rock, very likely amplification on soil, with unknown effects at the boundary. regulations usually ignore the unknown effects.
Let us know about the final decision, I'm interested in such peculiar cases.
www.mccoy.it
RE: Deep and Shallow foundations
RE: Deep and Shallow foundations
The Italian codes, drawing upon the European codes and probably the IUCB-ASCE codes (but I'm not sure here), say something about such an issue.
You may either:
1) use a single seismic action, the most severe one (simplest and not necessarily most conservative)
2) use a maximum relative displacement between two points, based on the soil maximum displacement in such points according to the different local site response (a formula is provided)
3) carry out two distinct analyses with two distinct sets of actions if the structure is divided into separate parts (that could be your case).
It is likely that the ASCE/SEI 7-10 have some specific reccomendations, I'm going to check the Eurocodes and these, since they are international codes they are pretty much authoritative and can be implemented if the national code has no specific reccomandations.
www.mccoy.it
RE: Deep and Shallow foundations