Interim Report on Testing of Tension-only Steel Anchor Rods Embedded in Reinforced Concrete Slabs

When designing multi-story light-frame structures (i.e. wood or metal stud structures) over concrete podiums, lateral loads from the structure above the podium will produce large tensile forces in the overturning restraints. Tensile demands in excess of 100 kips are not unusual. Currently, capacities of tension anchors embedded in concrete, when derived from the American Concrete Institute (ACI) 318-11 Appendix D, can be much lower than historic values. Tests performed as part of an expanding research effort have focused on anchorage at both slab edges and center “field” locations. Experimental data shows that the capacity of embedded concrete anchorage can be significantly increased through the addition of basic anchorage reinforcement, as allowed by ACI 318 Appendix D. This project investigated the conditions associated with shallow anchorage reinforcement and its effect on behavior and capacity of embedded anchors subjected to direct tension. This interim report is aimed at providing useful findings to design professionals and building code officials for frequently specified anchorage details. Important recommendations are also made related to construction quality control and overall constructability. The goal of the final test report is to enhance the findings with useful design recommendations and data to support a successful proposal to change code provisions. This small, ambitious testing project was initiated by several practicing engineers in Northern California. The bulk of the report findings were made possible by significant technical and financial contributions from industry.

Read the article.