Studio sperimentale sul taglio biassiale in travi a sezione quadrata.

In the scientific literature, there are limited studies about the effect of biaxial shear in reinforced concrete elements. However, this load condition is quite common in columns subjected to horizontal forces. Moreover, the design and evaluation methods reported in the codes do not consider any interaction between the shear strength in the two principal directions of inertia. The variable strut inclination truss analogy, useful in case of uniaxial load condition, must therefore be reconsidered in presence of biaxial shear. This paper presents the results of an experimental campaign on full size beam, with square section, subjected to inclined shear: 6 beams have been tested in order to understand how the shear resistant domain is influenced by the direction of load application. Out of the 6 specimens, each with a size of 300x300 mm, two have been tested under uniaxial shear, two with a load inclined 45° and two with an inclination of 22.5° to the horizontal. Each pair of beams presents a specimen without transverse reinforcement and one containing a low amount of stirrups, representative of the reinforcing condition of several existing columns, made before the introduction of the seismic design in the codes. All beams present a total length of 3 m and the same ratio of longitudinal reinforcement. Appropriate preliminary studies have been carried out in order to properly design the experimental tests. Moreover, particular attention has been given to the test set-up, which required suitable supports and load points for the application of the inclined load. Finally, an analytical model, modified according to Model Code and Eurocode 2 prescriptions, is presented.