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This deflection multiplier is applied to all sustained loads on the members.
Hand Calculation
Below is a hand calculation and the corresponding Eriksson Beam file showing the procedure the program uses to calculation deflections, cambers, and shortening. Note that the hand calculation assumes that when the member cracks, a percentage of the total load is carried by the cracked section. This is similar to the procedure shown in the PCI Design Handbook and results in a conservative estimation of the deflection of a cracked section. Following this approach, the total moment being applied to the cracked section is shown below as shaded in red. It is important to note that the total moment applied to the cracked section as calculated by hand is larger than the total moment applied to the cracked section as calculated by Eriksson Beam, which calculates the this total moment on a point by point basis as shown above.
Because of this, any loading stage that cracks results in larger deflections in the hand calculations than in Eriksson Beam.
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Problem
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Hand Calculation
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Eriksson Beam File
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Prestressed Double T - Class C
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References
Martin, L.D., “A Rational Method for Estimation Camber and Deflection of Precast Prestressed Members,” PCI Journal, V. 22, No. 1, January-February 1977, pp. 100-108.
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