Shear Capacity of Bridge Pre-stressed Concrete Beams with Different Static Systems and using Vertical Prestressing

Strut and tie models have been increasingly used in recent years. Most of design procedures for concrete beams in shear are based on the truss analogy. The truss analogy proposes that the behavior of a cracked reinforced concrete beam is like a truss with parallel longitudinal chords. In prestressed concrete beams, prestressing force has two vertical and horizontal components along the beam length in which the amounts of these components depend on slope of cable in each section of the beam. In this research, internal vertical prestressing by means of suitable rods perpendicular to beam axis was used to create compressive stress in the beam web.Shear strength of bridge pre-stressed concrete beams with and without vertical prestressing is studied in this paper. First, several models of reinforced and prestressed concrete beams are selected and analyzed using the finite-element method according to continuous stress field theory. The analysis is performed using nonlinear behavior for materials. The concrete material is defined based on concrete damage plasticity by means of experimental stress-strain diagrams. The steel material is also defined according to perfect plasticity and stress-strain diagrams.In this regard the validity of modeling is evaluated based on some tests results. In the second part of the study two beam specimens are built and tested and their load-deformation curve and cracking pattern are studied. Using all numerical and experimental studies, the slope of shear cracks and shear reinforcement ratio are investigated and the effect of horizontal and vertical pre-stressing on the noted parameters is evaluated. Then the compression strut slopes derived from nonlinear analysis, the code relations are studied and compared.This paper focuses on a more realistic determination of the angle of orientation of the compression struts in prestressed concrete beams. The findings should be of interest to researchers as well as practicing engineers involved in analysis and design of prestressed concrete beams.