Design criteria for unified strut and tie models

Abstract

In the past two decades, the concept of strut and tie models (STM) has been used as one of the most popular and rational approaches for the design of non-flexural members of reinforced concrete structures. Design guidelines based mainly on technology from past decades are given in many national codes. The review of recent advancement in strut and tie modelling given in this paper enables a new set of design criteria and design tables for the strength of strut, node and bearing to be derived and presented. The design formulae proposed for strut and node in this paper are in the form of the product of two partial safety factors which take into account: (i) the orientation of the strut-tie; (ii) the brittle effects as the strength of concrete increases; (iii) the strain state of both concrete and steel; and (iv) the stress state of the node boundary. The design values proposed for plain concrete with a bearing plate ensure that the node does not crack under service conditions and that it possesses sufficient strength under ultimate load conditions. To enhance the worldwide use of such design tables, both the concrete cylinder strength and the concrete cube strength have been used to define the strength of the concrete.