TENSILE CAPACITY OF ANCHORS WITH PARTIAL OR OVERLAPPING FAILURE SURFACES - 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 located close to a free edge and multiple anchor groups located far from a free edge and installed in uncracked, unreinforced concrete. A total of 160 data points is av ailable for single anchors close to a free edge, while 185 data points are available for multiple anchors. A total of 31 data points consist ing of data on high-strength anchors previously compiled by Klingner e t al., Collins et al., and Cannon is accessible from tests on single a nchors failing by fracture of the anchor steel. Using common definitio ns and nomenclature for all variables and material properties, each da ta set is placed in a data base using SI units and concrete cube stren gths. The concrete failure data are then compared with capacities pred icted by the three existing methods: the 45 deg cone method of ACI 349 -90 Appendix B; a variable angle cone (VAC) method; and the concrete c apacity (CC) method. Observed data are compared against these existing methods in terms of average square error and load and resistance fact or design (LRFD). Finally, using the principles of LRFD, and following the design procedure of ACI 349-90, the probability of steel failure or concrete cone failure under known loads and concrete cone failure u nder unlimited loads is calculated. Based on those comparisons, each a pproach is evaluated with respect to accuracy and suitability for use in design. For single anchors located near a free edge and for multipl e closely spaced anchors, the CC method fits most of the data better t han either the ACI 349-90 method or the VAC method, and gives lower an d more consistent probabilities of failure. This is especially evident at very shallow and very deep embedments.