When structural sealant assemblies first entered the building industry, only high modulus silicone products were available. This sealant has a specific formulation and technical requirements and provides a total "factor of safety" in structural applications. The design is based on the overall size of the glass, the width and depth of the joints and the calculated wind load. At that time, only high modulus sealants can meet the requirements of safety factor standards.
The term "factor of safety" is defined in structural assembly as the ratio of the ultimate strength (usually expressed as tensile strength) of the sealant to the most common design stress of 20psi. The ratio of 5:1 to 6:1 has proved to be sufficient since structural assembly was applied and has become the most common safety factor requirement.
The higher the safety factor is, the greater the error the system can bear due to the influence of various variables in structural assembly and the reliability of engineering materials. Today, that is considered too safe. After years of testing at the site and in the laboratory by different manufacturers, there is a tendency to use materials with a softer 2:1 coefficient. These medium - or low-modulus sealants provide good adhesion to most surfaces and allow greater movement between the glass and the structural frame. This ability is exactly what you want in a building during an earthquake.
In general, high modulus silicone sealants are applied to structural assembly. However, if unusual displacement conditions are considered, we recommend the use of low modulus silicone sealant. These sealants have a continuous elongation and compression ratio of ± 50%, which is about twice that of high modulus sealants. Before choosing a sealant for structural assembly, consult the manufacturer for recommendations on structural sealants. The practical safety factor for curtain wall structural components and fastener applications is 1.5:1. If this safety factor is used for a sealant designed for a stress of 20 psi, the ultimate strength of the sealant should be 30 psi.