member forces creaded by concrete shrinkage and creep
Dear Technical Support,
I have two questions about the member forces created by concrete shrinkage and creep:
(1) The member forces at Stage 12 (Closure) First Step (activate the closure segment with 4 days maturity) for shrinkage load case: primary and secondary
I get very large axial compression and small bending moment near the pier as shown in the following Excel sheet. The girder is not restricted for axial deformation and it can contract or expand freely, why I got the large axial force in the girder? How are the member forces (primary and secondary) calculated for shrinkage load case ?
For prestress, a clear definitions for primary and secondary load effects are given in text books. What are the definitions for the primary, secondary load effects on the structure for shrinkage and creep load cases?
In most cases, only the combined load effects are considered for these load cases. They are different from the load effects created by prestress, because the primary prestress loads are considered to be part of the resistance, and the secondary load effects are considered as a load.
(2) The member forces from Stage 12 (Closure) First Step (activate the closure segment with 4 days maturity) for Tendon Secondary load case
The following diagram is the moment for a part of the structure.
The secondary moment is normally in straight lines created by the reaction forces acting on the structure, which are created by the actual load.
The above diagram contradicts with the normal wisdom and I want to know how the secondary load effects due to prestress are calculated.
The structure has compression-only springs as falsework in the side spans for cast-in-place construction for the side spans, and they are deactivated in Stage 10. Do these springs have any impact for the secondary member forces due to prestress tendon forces?
Thank you very much for your help.
The current step force option can be activated by checking on the option below.
Staging Construction - Construction at two piers start at the same time.mcb