ASCE 7 and IBC Foundation Tie Basis

[mrosecra]

ASCE 7-22 article 12.13.7.2 and 12.13.8.2 require foundation ties between pile caps without many alternatives when foundation ties can not be installed. Can anyone provide the research articles that formed the basis for this requirement in ASCE 7? The foundations I typically design do not allow foundation ties or floor slabs to be placed at the pile cap elevation because there are utilities or other structures that are not permitted to be integrated with the foundation system. No concrete is permitted between the pile caps. The foundations are typically on piles (approximately 10 to 15 piles per pile cap) due to the large compression or tension loads and not necessarily because the foundations are on soft soils. The requirements in ASCE 7-22 article 12.13.7.2 and 12.13.8.2 effectively force the columns to be supported on concrete piers that need to be 10' to 15' tall in order to allow foundation ties between the sunken pile caps to get below the utilities and equipment that can not be supported on the foundation system. If foundation ties are not required then the pile caps can be located at grade and there is no need to drop the pile caps 10' to 15' deep. It seems a much more robust and lower lateral movement of the column bases would be achieved by not providing foundation ties in these situations especially when the lateral movement of the pile caps due to the seismic loads would be relatively small (~0.2").

 

[JAE]

The ties are there to ensure that the supports for the columns don't move excessively sideways in a seismic event (due to liquefaction or other soil instability) causing the columns to do the splits, so to speak, and collapse the structure.

To me, the utilities need to accommodate the ties, not the other way around. Without the ties and a collapse, the utilities would be rendered useless.