Hyperstatic loading

RAM Concept calculates the effects of the hyperstatic loading for all objects (elements, springs, support, design sections, design strip segment cross sections and punching checks) by using the following vector relationship:

F_h = F_b - F_p

where

F_h	=	the hyperstatic forces and moments
F_b	=	the balance loading forces and moments (tendon forces on real structure)
F_p	=	the "primary" forces and moments in the object (forces in object due to PT if the object was not restrained, but still contained tendons – if any)

For objects that do not contain tendons (walls, columns, springs, rigid supports, design sections without tendons and design strips without tendons), F_p is zero, so:

F_h = F_b

For slab elements the calculation of F_p for every element is not performed, as there is no clear definition of F_p for anything except a cross section. RAM Concept ’s slab analysis plots assume F_p = F_b ( F_h = 0), but these plotted values are not used in the slab design and checking. RAM Concept calculates design section and design strip cross section forces (without the assumption of F_p = F_b) as follows:

F_h = F_b - F_p

RAM Concept bases the calculation of F_p on the tendons at each cross section.

Note: Because of this issue, it is incorrect to use RAM Concept ’s slab analysis plots for cross-section design values in PT structures. (It is not recommend using slab analysis plots in RC slabs either, but that is because design strips and design sections provide much higher accuracy).

Note: For a more detailed discussion, refer to "Complete Secondary (Hyperstatic) Effects" by A. Bommer; PTI Journal, January 2004, Vol 2 No. 1).