Techniques to repair pier and beam foundations
Foundation is a group of structural elements that mainly transmit loads of the construction or features supported to it directly to the ground, distributing them so that the pressure is uniform. Generally, the resistance of the soil is lower than that of the pillars or walls it will support. Therefore, the contact area between the ground and the foundation will be proportionally more extensive than that of the supported elements.
- To distribute the weight of a structure to the ground.
- To be strong enough not to break due to ruptures.
- To resist the bending stresses produced by the ground, reinforcement is provided on its underside.
- Adapt to possible ground movements.
The choice of the type of foundation will depend on the mechanical particularities of the soil, such as its cohesion, angle of internal friction, the position of the water table, and the magnitude of the existing loads. There are two main types of foundations: direct and profound.
Direct foundations are placed in the superficial or shallow layers of the ground since they have the bearing capacity or are relatively light constructions of secondary importance. Generally, in this type of foundation, the load is distributed on a horizontally supported plane.
Wherever possible, shallow foundations are used, as they are the least expensive and most straightforward type of foundation to construct.
If the building is distributed in several areas of different heights, the proportional distribution of the basements and structural joints must be foreseen.
On the other hand, deep foundations rely on the shear stress between the ground and the foundation to support the applied loads or vertical friction between the foundation and the environment. Because of this, they must be deeper to provide a large area over which a large enough stress will be distributed to support the load.
Most older homes built before the 1900s have a pier-post style. This style used supporting beams every six to 10 feet using a concrete post or wood posts buried 1 to 4 feet in the ground. However, the pier and beam technique is flawed because the wood can rot, the beams can warp, termites can cause severe damage, and the rays can break.
Beams are the most versatile structural elements to reinforce since several techniques offer similar results, some more complex than others depending on the degree of importance of the work. Still, for this project, it was defined that the methods to be applied would be for small and medium-sized pieces for a maximum of two levels, where the design loads do not require complex reinforcement systems.
Based on this premise, the beams that present deficiency in their positive steel or bottom face can be reinforced by adding the required longitudinal steel in three ways.
- Case 1: using a spike that reaches above the hoop and allows the required steel to be added.
- Case 2: for more critical situations where there is a lack of reinforcing steel, the hoops’ areas can be resurfaced.
- Case 3: very used nowadays is using mechanical saws that form the necessary grooves to introduce the steel and then fill the space; this method works for both positive and negative steel. When the missing steel is shear, the hoops are installed by making grooves filled with high-strength cement.
When the deficiency of the beam is due to concrete strength, it is advisable to check and analyze if a decrease in the safety factor makes the shaft functional. Otherwise, in this particular case, it is better to demolish the beam and rebuild it since more complex and expensive techniques may work, but not the feasibility of reinforcement.
To repair the concrete beams, the techniques employed were based on incorporating the missing steel by making grooves in the shaft, using power saws, and filling the space with high-strength concrete. This technique applies to both reinforcing steel and shear steel.