Friction element for non-linear analysis of friction effect in externally prestressed beams

Abstract

Analysis of externally prestressed beams involves particular difficulty related to slip between the external tendon and deviator. Slip without friction is usually assumed to simplify the problem. A concise friction element located at the angle bisector between external tendon and deviator is constructed, to simulate the slip with or without friction between the tendon and deviator. The non-linear stress–strain relationships of concrete, steel and external tendon are considered; a trilinear model of the bending moment–axial force–curvature of the beam section is adopted, so that the behaviour of the externally prestressed beam up to ultimate state can be investigated. Calculations regarding a simply supported beam and continuous beam for various factors are conducted, including different friction coefficients, different areas of external tendon and steel bar, different eccentricities, symmetric or asymmetric load patterns. Results indicate that, for the simply supported beam and continuous beam under symmetric load, the friction effect on load-carrying capacity is negligible; the friction effect on maximum prestress increment and deflection may not be negligible; the friction effect on minimum prestress increment is obvious. For a continuous beam under asymmetric load, the friction effect on load-carrying capacity, maximum and minimum prestress increments and deflection cannot be neglected.