Soil-structure interaction (footings and pile caps)
Introduction
"Soil-structure interaction (footings and pile caps)" is a CYPECAD module that is used to consider the settlements of the foundations and their interaction with the rest of the structure, in terms of both forces and deformation, by defining elastic stiffness constants in foundation elements.
For footings, the stiffness is introduced as subgrade modulus. Similarly, for pile caps, the data that must be defined is the axial stiffness for each pile cap, which is determined by the ratio of its load to the settlement that is produced.
It should be noted that the usual process is to design the foundations previously, by considering the fixities at the base of the supports, and then considering the interaction between the soil and the structure.
Module description
"Soil-structure interaction (footings and pile caps)" allows users to consider the settlements of the foundations and their interaction with the rest of the structure. This interaction will result in variations in the forces and deformations of the structure, causing slight modifications, if any, in the result of the foundation design.
To assign the soil-structure interaction, the "Soil-structure interaction" option is selected from the "Foundations" menu and the program will then automatically detect the existing foundation type.
For foundations using footings, the assignment of the interaction is carried out by a subgrade modulus in the footing.
For pile caps, the axial stiffness of each pile must be defined, which is determined by the ratio of its load to the settlement that is produced.
For footings, the logical procedure is to design the foundations previously by considering the fixities as usual. Once the foundation is obtained, the subgrade modulus must be assigned to each footing in order to consider the soil-structure interaction.
It should be noted that the same value of the subgrade modulus does not have the same effect on two different sized footings and that, additionally, the interaction between the soil and the structure will cause settlements, rotations and, therefore, changes in the forces and deformations of the structural elements. As a result, after the second analysis and design of the foundation, with the consideration of the interaction, the program could display a warning to indicate that there is a difference between the size of the footings considered and the size of the footings obtained.
This message indicates that a new analysis and design of the foundations should be carried out, readjusting the subgrade modulus if necessary.
If the difference between the size of the considered footings and the size of the obtained footings is small enough, this warning will disappear.
As for pile caps, the equivalent to the size of the footings is the number of piles and the distance of each pile from the centre of gravity of the pile caps, which governs the axial and rotational stiffness as well as the surface and moment of inertia of the footing surface.
Characteristics that have been considered for the soil-structure interaction
To generate the report, users must select "Characteristics that have been considered for the soil-structure interaction" from the "Foundations" menu.
The program displays a report with the usual export and print options, in which users can consult the current data, and the data with which the last analysis was made.
The current data can also be listed by activating "Soil-structure interaction (footings and pile caps)" in the job data report.
Other features
In order to access further features offered by the program, there are several modules that can be found on the "CYPECAD modules" webpage.
