Page 92 - Riem-Vol6_nº3

1. Introduction
The choice of the kind of foundation is made after analysis which
considers the technical and economic conditions of the building,
the vicinity of the neighboring buildings, the nature and charac-
teristic of the soil, the magnitude of the actions and of the kinds of
foundations available in the market.
The foundations in piles are adopted when the soil in its superficial
layers is not able to stand actions from the superstructure, being
necessary, therefore, to consider strength in deep layers. When
using solution in deep foundation by piles, it is necessary the con-
struction of another structural element, the pile caps.
According to NBR 6118:2007[1], pile caps are important structural
elements which function is to transfer the actions of the superstruc-
ture to a group of piles. These structural elements, in spite of being
essential to the safety of the superstructure, usually does not allow
the visual inspection while working, thus, it is important the knowl-
edge of its real behavior in the Limit States of Service and Last .
Figure [1] illustrates this structural element.
When the superstructure is precast it is necessary that the column is
built-in on the pile. The length of the built-in of the column within the
pile, so that it is considered clamped, it is function of the internal forc-
es (bending, normal force and shear force) and the kind of superfi-
cial shape of the walls (rough or smooth) of the precast and column
concrete. The lengths of embed are definite by NBR 9062:2006[2].
There are some variations in the types of pile with precast (exter-
nal precast, partially embed precast and totally embed precast).
Figure [2] shows the variations of the blocks on piles for precast
columns. The technical mean uses more intensely the blocks with
external precast and partially embed.
The European code (EUROCODE 2) EN 1992-1-1 [3] presents
recommendations regarding the precast project for linking column-
foundation, considering the monolithic behavior of the set when us-
ing “shear key”. For the smooth conformation of the precast and the
column walls, it indicates that the friction coefficient between the col-
umn faces and the precast faces is higher than 0.3 and the embed
length higher or equal to 1.2 times the biggest column dimension.
As there is no consensus between the scientific means in relation
to the section of the pile cap where it forms the stanchion (or con-
necting rod), a numeric analysis was performed, aiming at observ-
ing the structural behavior of the pile caps. Thereunto, eighteen
two piles caps were analyzed, nine with rough interface and nine
with smooth interface.
The embed length of the column (ℓemb) and the thickness of
the bottom slab of the pile cap (hs) were assorted. Thus, the
embed lengths of the precast columns were equal to 80 cm,
60 cm and 50 cm. The thicknesses of the bottom slab were
equal to 30 cm, 20 cm and 10 cm. Bottom slab, it is not the
best term to express the dimension hs because there is not
such a slab in the bottom of the block. Although, it is consid-
ered that this term is the one which presents better under-
standing to the readers.
437 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
A. P. Martins | J. C. Pizolato Junior | V. L. Belini
Figure 1 – Pile cap with socket embedded
Figure 2 – Pile caps with external socket, partly embedded e fully embedded