Chemical or Mechanical Anchoring, how to choose?
Steel-concrete connections and their anchoring devices can be requested by tensile or compression forces, shear forces in both directions, bending moments in both directions and combined efforts (tensile or compression, shear and bending moment). At the dimensioning level, the existence of compression forces and bending moment is reflected in the distribution of efforts and in the compressed and tensioned areas of the connection, that is, they are not directly accounted for in the expressions for calculating the resistance forces.
Chemical or mechanical anchoring?
In order to choose the best anchorage, its operation must be understood.
Chemical anchorage works by adhering the steel to the support. The study of adhesion involves several parameters and is intended to determine the behavior of materials involved in the transmission of efforts that develop in the connections. This connection between different materials is of great importance for reinforced concrete, since its functioning depends on the joint work of materials with quite different characteristics, such as steel, a material with high ductility and high mechanical strength, and concrete, an extremely fragile material and with low tensile strength. The behavior of a connection depends mainly on the conditions of the interface of the materials involved, as well as on the type of interaction that takes place at these interfaces. The most important characteristic of a chemical anchor is the bond portion and the adhesive capacity between the bonding agents. The contact surface between them influences the adhesion capacity, as is the case of roughness, which improves the chemical interaction of the active compounds that act on adhesion. Since this is a friction connection, the applied force will always have a resultant of equal value, creating a less aggressive distribution of tensions in the support, allowing for a shorter distance to the edge and a smaller distance between anchors.
Bonding is carried out by filling the empty spaces between the bushing and the base material with synthetic resins. This bonding effect develops adhesion tensions aderênciab along the bushing, which will balance the applied force N.
Mechanical anchoring is a system that achieves the union of the metallic bushing to the rigid support through an expansion of the same or part of it by internal lateral stresses called expansion forces resulting from the tightening torque transmitted to the bushing. The absorbed loads then create a reaction pair system interconnected with the necessary forces to ensure the anchorage expansion, hence for an axial effort of 100 kg we will have an internal effort resulting from 300 kg of the 1:3 ratio. The resulting tension bulb creates a cone of about 45° on each side of the base of the same. Thus, this type of fixation is not typically a solution for high loads due to this internal interaction, which creates limitations on edge distances and distance between anchorages. Its great advantage is its easy application.
The force N applied to the bushing will be transmitted to the base material by friction. This is achieved by increasing the bushing section inside, causing a net force FR. This force has two components: Fexp (vertical) and R (horizontal). The horizontal component, R, will balance the force N.