UNIT-2

TYPES OF FLEXURAL FAILURE  When prestressed concrete members to bending loads, different types of flexural failures are possible at critical sections, depending upon the principle controlling parameters, Such as the percentage of reinforcement in the section, degree of bond between tendons and concrete, compressive strength of concrete and the ultimate tensile strength of the tendons. In the post-cracking stage, the behavior of a prestressed concrete member is more akin to that of a reinforced concrete section may as well be used for prestressed concrete sections. The Various types of flexural failures encountered in prestressed concrete Members are examined in the light of recommendations of various codes of practise.

Fracture of steel in tension Failure of under-reinforced sections  Failure of over-reinforced sections  Other modes of failure

STRAIN COMPATIBILITY METHOD: The rigorous method of estimating the flexural strength of prestressed concrete section is based on the compatibility of strains and equilibrium of forces acting on the section at the stage of failure

ASSUMPTIONS The stress distribution in the compression zone of concrete can be defined by means of coefficients applied to the characteristic compressive strength and the average compressive stress and the position of the centre of compression can be assessed.   The distribution of concrete strain is linear (plane sections normal to axis remain plane after bending) The resistance of concrete in tension is neglected. The maximum compressive strain in concrete at failure reaches a particular value.

The stress distribution in the compression zone of concrete can be defined by means of coefficients applied to the characteristic compressive strength and the average compressive stress and the position of the centre of compression can be assessed.   The distribution of concrete strain is linear (plane sections normal to axis remain plane after bending) The resistance of concrete in tension is neglected. The maximum compressive strain in concrete at failure reaches a particular value.