Remodel and retrofit projects often require the design of new structural systems that are usually located within, or in close proximity of, existing buildings. Anchorage of the new structure into existing concrete members such as slabs and foundations is not only a viable option but could also be the most economical solution. These connections are critical components in the performance of any structure that should be carefully examined by the project structural engineer.
Design of anchoring to concrete has evolved through the years. The
American Concrete Institute (ACI 318 appendix D) provides the latest approach that has been adopted by the codes. It is based upon various failure modes under different loading conditions and includes provisions for anchors installed in cast-in-place concrete and anchors installed after the concrete hardens or in existing concrete. These types of anchors are generally called post-installed
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| Roseman University Research Lab Second Floor Addition - Joist and Girder Connections Utilizing Post-Installed Anchors to Existing Concrete Tilt-Up Walls |
anchors. However, design per ACI 318, appendix D is time consuming and could be confusing for post-installed anchors. It requires obtaining several values such as bond strength from the manufacturer. Consequently, our engineers use design software which combines the ACI method with those values that are specific for each manufacturer.
Some of the main factors affecting the design of anchorage into concrete are anchor size, concrete thickness and strength, bolt spacing and their effective embedment depth. For example, a group of larger bolts does not always mean a stronger connection, unless the bolt spacing and depth of concrete section are adequately increased.
Footings are normally designed based on their loading conditions and the allowable soil bearing pressure. However, footing design can also be governed by the requirements for bolt anchorage including concrete depth and/or width.
THOMAD Engineering has extensive experience in the design of post-installed anchors in existing concrete for a variety of projects over the past 10 years. From start, our engineers strive to not only maintain but also utilizes the existing concrete for anchorage and support of new structural members and avoid costly demolition and replacement. Our engineers know how to select the most efficient anchor bolt type, size and spacing that will provide the most economical solution for your project.
