Concrete Anchoring – Mechanical Anchors vs Chemical Anchors

One of the main criteria in a structural design between steel and concrete involves the choice of which type of anchoring system an engineer will choose. The system he chooses has to satisfy at least some, if not all the following; load transfer (static, cyclic, fatigue), ease and speed of installation, cost durability (including corrosion protection), aesthetics (including finish), fire resistance etc.

Structures are becoming more complex and demand new ways to anchor. Historically, a myriad of different types of mechanical anchors have been used which are still useful today. But since 1970’s, there has been an increase in the types and numbers of chemical anchors produced in the market. Chemical anchors have been developed to cater for use in both non-cracked and cracked concrete. In simple terms, cracked concrete refers to cross-sections of concrete that are subjected to tensile stresses whereas areas subjected to compression zones are generally non-cracked. Although not actually true, it would be safe to assume that most zones in a suspended slab are cracked.

Stronger adhesives have been developed and can be used to cater for more sophisticated anchor requirements. Below is a table showing general comparison of different anchor types and some of their suitability. A more rigorous method is to use software, like Mungo Design*, to assist the designer in the most appropriate and efficient choice of anchor to use in the design process.

REFERENCES

1. AEFAC Technical Note, “CRACKED VERSUS NON-CRACKED CONCRETE”, www.aefac.org.au

Typical Crack Zones

Cracked Concrete refers to concrete that may experience cracking passing through the plane of the anchor at some time after installation of the system. Cracked concrete does not refer to the state of the concrete at the time of installation and post-installed anchors are not currently designed for installation in existing racks.

Non-cracked concrete is concrete that has been demonstrated via stress analysis to remain crack-free in the vicinity of the anchor throughout the design life under all design load considerations.

Originally Published by Hobson Engineering

GABRIEL TERS B.Eng (Structural) UTS

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