Load bearing Piles vertical, horizontal and moment simultaneously follow TCVN 10304:2014 | Fundamentals for Structural Engineering
Pile foundations for civil buildings are usually designed according to the low pile cap foundation problem: all horizontal loads of the column foot internal forces are completely received by the soil by the horizontal pressure of the soil on the pile cap as presented in the Basics of pile cap design. Common cases that require calculation and checking of piles bearing horizontal loads are: single pile cap, bearing large horizontal loads (industrial buildings), high pile cap foundation…
This article presents a practical method for calculating piles when simultaneously bearing vertical loads, horizontal forces and bending moments according to the new pile foundation structure design standard TCVN 10304:2014.
Provisions of the Code
Appendix A of the standard specifically presents: Allows design consultants to use computer programs to describe the mutual mechanical effects between piles and foundations (seeing piles as beams on elastic foundations). In which, the soil surrounding the piles is considered as a linearly deformed elastic environment characterized by a foundation coefficient Cz that increases gradually with depth.
The calculated foundation coefficient of the soil on the pile body Cz is determined according to the formula (A.1) of the standard:
$$C_z=\frac{kZ}{\gamma_c} (kN/m^3)$$
k: proportional coefficient, in kN/m4, taken depending on the type of soil surrounding the pile according to table A.1 of the standard.
Z: depth of the pile section in the soil, where the foundation coefficient is determined, from the ground surface in the case of high pile foundation, or from the bottom of the foundation in the case of low pile foundation.
γc: working condition coefficient, for independent piles $\gamma_c=3$
Application Software
A software that can be applied to model the problem of elastic foundation around piles with foundation coefficient Cz varying with depth is the PILE software in the GEO5 package.
When modeling piles, the pile can be considered as a rigid bar in the soil at a depth of a distance from the base of the foundation:
$$l=l_o+\frac{2}{\alpha_{\varepsilon}}$$
$\alpha_{\varepsilon}$: deformation coefficient determined according to Appendix A of the standard
$I$: moment of inertia of the pile cross-section, in m4
$b_p$: conventional width of the pile, in m. For piles with a minimum pile diameter of 0.8m, take bp=d+1, for the remaining cases bp=1.5d+0.5, m
d: outer diameter of a circular pile or edge of a square pile or edge of a rectangular pile in a plane perpendicular to the direction of the horizontal load.
The analysis results of the PILE software are in the form of internal forces and deformations in the pile body, from which the pile material (reinforced concrete) is calculated and checked as with eccentric compression members.
For convenience in construction design practice, it is necessary to create a spreadsheet to determine the foundation coefficients according to the depth according to the changes of the soil layers in the calculated geological column.
