TENSILE CAPACITY OF SINGLE ANCHORS IN CONCRETE - EVALUATION OF EXISTING FORMULAS ON AN LRFD BASIS

This study concerns the prediction of tensile capacity as governed by concrete cone failure of single anchors placed in uncracked, unreinfor ced concrete and located far from a free edge and far from other ancho rs. A total of approximately 801 data points is available from tests o n such anchors. A total of 31 data points consisting of data on high-s trength anchors previously compiled by Klingner et al.,(1) Collins et. ,(2) and Cannon is accessible from tests on single anchors failing by fracture of anchor steel. Using common definitions and nomenclature fo r all variables and material properties, each data set is placed in a database using SI units and concrete cube strengths. The concrete cone failure data are then plotted against capacities predicted by three e xisting methods: 1) the 45 deg cone method of ACI 349-90, Appendix B; 2) a variable angle cone method (VAC); and 3) the concrete capacity me thod (CC method). Observed data are compared against these existing me thods in terms of average square error and load and resistance factor design (LRFD). Finally, using the principles of load and resistance fa ctor design (LRFD) and following the design procedure of ACI 349-90, A ppendix B, the probability of steel or concrete failure under known lo ads and the probability of concrete failure under unlimited loads are calculated. Based on those comparisons, each approach is evaluated wit h respect to accuracy and suitability for use in design. For single te nsion anchors with embedment depths less than 8 in., all three capacit y prediction methods fit most of the data relatively well. Hole ever, the CC method is more accurate and has a distinctly lower probability of failure when the embedment depth is greater than 8 in.