Release Stresses
Releases stresses are the stresses in the precast element at the time of transfer. Typically, these stresses are the combination of the prestressing producing tension in the top of the member while the self-weight of the member is producing tension in the bottom. When checking releases stresses, it is mandatory, per Section 24.5.3, to keep the compression under the allowable compression limit, but the tension stresses can exceed the tension limit if additional bonded mild reinforcement is provided.
The initial stress limits are used for the transfer stage and any stripping and handling page where the user sets the stress limits to the initial stress limits. For these given stages, the output will report the required area of tension steel that must be provided (if any). More information can be found on the analysis stages and stripping and handling below under More Information.
Stress Limit
Stress limits at release of prestress are found in Section 24.5.3. These limits are the default values used by the software but can be edited by the user. These limits are used at any stage where the user has selected to use the initial stress limits. Eriksson Beam uses the transfer length of the strand as the length of the end region listed in Section 24.5.3. This distance is not defined in ACI 318-14 but is instead based on standard practice in the precast industry.
Tension Steel
Tension limits in Section 24.5.3.2 shall be permitted to be exceeded if bonded mild reinforcement is included in the tension zone. The amount of reinforcement is equal to the total force in the tension block of the member. For this calculation, the yield stress of the reinforcement is limited to 60% of the yield but may not exceed 30 ksi. It is also assumed that the total tension force is equal to the area of the tension block times the average tension stress in the cross-section.
Code
ACI 318-14