Prestress analysis starts with the tendon force calculation, and based on the results the primary and secondary effects are determined.
Primary effects
are the internal forces i.e. moment, shear and axial generated at each section
due to the exerted tendon force.
Primary moment of
a section is the product of tendon force and its eccentricity from sectional
neutral axis.
Secondary effect
occurs when the bridge structure is firmly restrained and becomes statically
indeterminate.
Prestress
compresses the beam section and causes the beam to deflect. However, the
presence of extra supports hold the structure and prevent such deflection. As a
result, the secondary moment is generated.
Secondary effect
can be determined by using either equivalent load method or influence
coefficient method.
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