References
ACI 318-14
Releases stresses are the stresses in the precast element at the time of transfer. Typically, these stresses are causes by the prestressing putting tension in the top while the self-weight of the member is putting tension in the bottom. When checking releases stresses it is mandatory, per ACI 318-14 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 reinforcement is provided.
The initial stress limits are used for the transfer stage and any stripping and handling page where the user set the stress limits to the initial stress limits. For these given stages, the output will report the required are of tension steel that must be provided. 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 members are given per ACI 318-14 section 24.5.3. These limits are the default values of the software but can be edited by the user. These limits are used at any stage using the initial stress limits. The stress limits given in 24.5.3 assign stress limits to both the end regions and all other regions. Eriksson Beam uses the strands transfer length as the length of the end region. This distance is not referenced in ACI 318-14 but instead comes from standard practice in the precast industry.
Tension Steel
Tension limits in ACI 318-14 section 24.5.3.2 shall be permitted to be exceeded if bonded 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 section.