PILE INTERCONNECTIONS

EXAMPLEA two-story masonry bearing wall structure has a pile foundation. Piles are located around the perimeter of the building. The foundation plan of the building is shown below. The following information is given:

Determine the following:

1. Interconnection requirements.2. Interconnection force between

pile caps 3 and 10.3. Required “tie” restraint between

pile caps 3 and 10.

1. Interconnection Requirements

The code requires that individual pile caps of every structure subject to seismic forces be interconnected with ties. The ties must be capable of resisting in tension and compression, a minimum horizontal tie force equal to 10 percent of the larger column vertical load. The column vertical load is to be considered the dead, reduced live, and seismic loads on the pile cap. An exception to Interconnection Requirements allows use of “equivalent restraint.”

2. Interconnection force between pile caps 3 and 10

Maximum loads on each pile cap under

E/W seismic forces are:

Pile cap 3 = 46 +16 + 0 = 62 kips

Pile cap 10 = 58 +16 + 0 = 74 kips

Minimum horizontal tie force is 10

percent of largest column vertical load:

P = 0.10 (74)= 7.40 kips

3. Required “tie” restraint between pile caps 3 and 10.

This is greater than 3'-0" pile cap width,

but pile cap and a tributary length of N/S grade

beam on either side of the pile cap may be

designed to resist “tie” forces using passive

pressure. This system is shown below, and if

this is properly designed, no grade beam

between pile caps 3 and 10 (or similar caps) is

required.

Commentary

Normally, buildings on pile foundations are required to have interconnecting ties between pile caps. This is particularly true in the case of high rise buildings and buildings with heavy vertical loads on individual pile caps. Ties are essential in tall buildings. Ties are also necessary when the site soil conditions are poor such that lateral movements, or geotechnical hazards, such as liquefaction, are possible. Also note that while pile interconnections has the wording “tension or compression,” the intent is that the ties must resist the required forces in both tension and compression.

In design of relatively lightweight one- and two-story buildings, the exception to the interconnecting tie requirement of pile interconnections may permit a more economical foundation design. However, when interconnecting ties are omitted, a geotechnical engineer should confirm the appropriateness of this decision.

PREPARED BY:PREPARED BY:

ANGCAYA, ERVIN JAYMANALO, IVY

BSCE 4-2