Laboratory Tests, Analytical Modeling, and Design Model Development for Column-Foundation Connections with Headed Anchors

In collaboration with practicing structural engineers and experts in anchoring to concrete, the authors undertook a research project to explore the requirements for anchoring columns to reinforced concrete foundations. In early discussions it was realized that, while there were design procedures that were in use in different design offices, the design procedures differed from office to office and few of the methods had been verified by laboratory testing. Based on this knowledge, a series of laboratory tests was designed and carried out to develop benchmark data on the following types of column-foundation problems:- Interior footings supporting columns in direct tension and anchored by multiple anchor bolts, either with or without additional footing transverse reinforcement to increase strength and deformation capacity.- Interior footings supporting column in direct bending and anchored by multiple anchor bolts, either with or without additional footing transverse reinforcement to increase strength and deformation capacity. The laboratory tests were supplemented by nonlinear finite element studies using the software ATENA, both to calibrate the model material parameters and to extrapolate results from the laboratory tests to geometries that were not tested in the laboratory. Together, the laboratory and numerical studies were used to derive a design method to calculate the strength of connections in either direct tension, direct moment transfer, or combinations of the two, with or without additional transverse reinforcement intended to increase strength and deformation capacity. The authors subsequently worked with ACI Committee 318 Structural Concrete Building Code of the American Concrete Institute to develop design provisions that were approved and adopted in ACI 318-25 Building Code Requirements for Structural Concrete and Commentary.