Spring modelling approach for evaluation and design of tension loaded anchor groups in case of concrete cone failure

The behaviour of anchor groups under tension loading depends on a number of parameters such as anchor type, anchor configuration, concrete strength, base plate geometry and stiffness, vicinity of the concrete edge and load eccentricity. In order to calculate the resultant anchor forces and the group resistance, several assumptions are made in the current design methods, which simplify the calculations, but may also lead to over-conservative or even unconservative design solutions. This paper presents a spring model based approach for the realistic assessment and design of tension loaded anchor groups in case of concrete cone failure. The development is based on the evaluation of a comprehensive experimental study carried out on tension loaded anchor groups, reported in an earlier paper. The concept of the spring model is based on the assumption that within an anchor group, anchors resist the tension forces, while the compression forces are transferred directly by the base plate to the concrete. Nonlinear tension-only springs are used for modelling the anchor behaviour in order to account for the distribution of forces among the anchors of the group. While defining the characteristics of the nonlinear anchor springs, due consideration is given to the vicinity of the edge and the neighbouring anchors through a tributary area approach. All the postulates are justified through a detailed evaluation of the test results. The contact between the base plate and concrete is modelled using compression-only springs, while the base plate is modelled using finite shell or solid elements to consider realistically the base plate stiffness. Example calculations are presented on diverse anchor groups to demonstrate the procedure of the proposed spring modelling approach. The accuracy of the model is validated against a vast number of experimental results on diverse anchor groups. A number of open questions and possible topics for further extension of the model are discussed.