While tie beams are intended to prevent relative horizontal displacements between foundations, foundation beams are designed to work as an extension of the foundation itself, resisting shear, bending, and axial forces. These elements harmonize stresses, bearing pressures, and settlements between the foundations they connect, making them work in a collaborative manner.
When to use foundation beams?
As in most cases in structural engineering, there is no single answer to this question; instead, there are multiple solutions for the same problematic situation, with foundation beams being one of them. However, there are certain "standard" situations in which the use of foundation beams proves to be very convenient.
Due to site constraints or simply to reduce excavation volume, it is common to have eccentric foundations at the perimeter of a structure, such that the footing extends only toward the interior of the building. These cases pose a great challenge for an isolated foundation, as the high eccentricity of the pedestal causes a vertical load to generate large overturning moments. This situation could be solved by increasing the depth of the bearing level, increasing the foundation height, or even specifying a large mat foundation for the entire structure. However, a much better alternative can be a foundation beam.
This foundation arrangement is extremely common, often designated as a Strap Foundation; it consists of connecting an eccentric foundation with a centered one so that the eccentric foundation is supported by the centered one. This system is very efficient as it eliminates uplift and significantly decreases pressures on the eccentric foundation.
The same principle can be used to improve the structural performance of any foundation. Whenever a foundation exhibits excessive uplift or excessive bearing pressures, it can be joined to another foundation via a beam to make them work collaboratively.
Tie beams or foundation beams?
A well-trained eye could determine at a glance whether a beam is a foundation beam or a tie beam, as they will have differences in dimensions and reinforcement. However, in principle, the two types of beams are identical: a horizontal reinforced concrete element with a rectangular section, longitudinal reinforcement, and stirrups.
It is precisely the design that gives each type of beam its own characteristics. Tie beams are assumed to work only axially, so a square section makes sense, along with minimum longitudinal and shear reinforcement. On the other hand, foundation beams are assumed to work in shear and bending, so an elongated rectangular section makes more sense to increase inertia and, with it, bending resistance.
It is similar to what happens between columns and beams in a frame structure. Both reinforced concrete elements are topologically the same; in fact, in any structural analysis software, both would be modeled as "frame" elements indistinctly. However, due to the stresses they are subjected to, they naturally adopt one form or another.
Foundation beams in Foundaxis
In Foundaxis, you can model foundation beams manually and generate an arrangement as complex as you desire. Each foundation beam is defined independently, having its own section and insertion point relative to the foundations it connects.
Internally, a set of foundations joined together by a series of foundation beams is called a composition in Foundaxis. Compositions are analyzed using the Finite Element Method (FEM), in the same way as strip foundations and mat foundations, considering non-linear soil behavior through a series of non-linear springs.
Each composition is calculated using a continuous finite element mesh, respecting the characteristics of each element (e.g., height, bearing level depth). This ensures that the elements work collaboratively and that the load transfer is correctly modeled. Then, for the reinforcement design of each element in the composition, they are treated independently to respect each one's specific structure.
Discover how foundation beams design is integrated into the complete Foundaxis workflow:
Foundation Design Software: A Complete Guide for Structural Engineers 2026