High shear at pier-bedrock contact
High shear at pier-bedrock contact
(OP)
We are using LPILE to analyze existing 48-inch diameter piers embedded in good limestone and supporting a pump station in a lake. A slide in the overburden soil is loading the piers laterally. The resulting shear diagram shows a high shear just below the top of the bedrock. The shear is much higher in magnitude than the value right above the bedrock and of opposite sign. I know the shear is there to develop a couple with the necessary moment. The structural engineers say they never consider this shear in design. Why?





RE: High shear at pier-bedrock contact
If it is the latter situation, then the situation is similar to a pole footing analysis, and the "shear" seen is raally lateral bearing couples between the limestone and bedrock on the 48" piles. Except in the 48" piles, shear really does not even enter into the picture in this scenario.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: High shear at pier-bedrock contact
The piers were installed with a temporary casing extending at least 5 feet into the bedrock and a permanent steel casing extending 3 feet below the temporary casing. The rock socket is 7 feet long below the permanent casing. I would expect, therefore, that the pier is loose in an oversized hole to the top of the rock socket. The lateral support from the rock develops abruptly, but the rock at the top of the socket is confined by 8 feet of overlying rock and 12 feet of overburden soil, so it can develop high lateral resistance there.
RE: High shear at pier-bedrock contact
What are you recommending as the lateral load to each pile?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: High shear at pier-bedrock contact
The concrete was specified to be 4000 psi. It is 35 years old, and I'm assuming it's at least 4500 psi now.
The pier is heaviliy reinforced with 28#11s and has several hundred kips of compressive load. The structural engineer tells me the ultimate shear capacity of the pier is about 400 kips. But he never considers the negative shear within the rock socket. My original question was: how is this justified, and it it common pratice?
RE: High shear at pier-bedrock contact
RE: High shear at pier-bedrock contact