Maximum angle drilled of rebar to concrete for deep embedment depth

Hi,

Anchor installation angle tolerance for adhesives is discussed within the ACI 355.4, “Qualification of Post-Installed Adhesive Anchors in Concrete,” provisions. Please reference Section 4.5.1.3. ACI 355.4 is referenced within each adhesive anchor’s Evaluation Service Report (ESR).

If an anchor is installed at an angle greater than six degrees from perpendicular to the concrete surface, there are some important items that need to be evaluated from an installation, capacity, and load application perspective:

• Applying a tension-only load on an anchor installed at an angle will have a tension and shear load applied to the anchor due to the angle. The engineer on the project should take the tension-only load and translate this to a tension and shear load based on the actual angle of the anchorage.
• An anchor installed at an angle will typically have a reduced embedment depth than what was originally specified. The effective embedment depth (hef) should be reduced to reflect the distance from the end of the anchor (or to the effective embedment mechanism for expansion anchors, screw anchors, and undercut anchors) normal to the concrete surface. This will result in reduced design concrete strength and bond strength capacity.
• In addition to embedment depth considerations, anchors installed at an angle may need to have reduced edge distance and spacing considered, using a similar approach as the embedment depth above.
• When installing the nut and washer for an anchor installed at an angle, the installation should be performed with an inclined washer. A standard flat washer may bend during application of the installation torque and may not allow proper installation of the anchor mechanism.
• Installing an anchor at an angle will apply additional bending moments in the steel reducing the overall steel capacity. The bending moments and reduction can be calculated similar to the design for stand-off connections noted in Hilti’s 2022 Anchor Product Technical Guide.

These are only items to consider for anchors installed at an angle. The final decision and design is at the discretion of the engineer on the project.

Regards,
Katelyn