Prestressing to ACI 318-19 in Detail
Features include input for pre- and post-tensioned tendons, a prestressing steel database, and comprehensive ACI checks. The application includes a database of prestressing steels, the ability to input and evaluate partially loaded areas, and all required ACI standard checks, including stress limitations and decompression checks.
Key terms
This article covers the basic definitions. More details can be found in the new chapter of the theoretical background dedicated to prestressing according to ACI.
- Prestressing load case type
For the ACI standard, a Load Case type, Prestressing, has been added, allowing input of prestressing reinforcement. This Load Case type is required for defining the cable.
- Pre-tensioned strands
The layer of pre-tensioned strands for walls and beams can be defined using the coordinates of two points referenced to the master point. To determine the cable prestressing intensity, the stress in the prestressing reinforcement just before release from the abutments, after short-term losses such as anchorage set, abutment deformation, and short-term relaxation, must be specified.
For long-term service combinations, an estimate of long-term losses due to shrinkage and relaxation must be provided as a percentage.
As outlined in the Theoretical Background, the loss due to immediate elastic concrete strain in pre-tensioned strands is calculated automatically and directly depends on the time-dependent factor for sustained load, ξ.
- Post-tensioned tendons
A post-tensioned tendon, with a customizable number of strands, can be defined using either two points like a prestressed cable or a polyline. The anchorage stress determines the prestressing intensity. Short-term losses are calculated automatically based on the tendon geometry and inputs from the prestressing procedure. For serviceability, long-term losses due to creep, shrinkage, and relaxation must be estimated as a percentage.
- Partially loaded area
For post-tensioned anchors, bearings, and point loads, the Partially Loaded Areas feature can be used to simulate increased concrete strength per ACI 318-19 (Chapters 22.8 and 25.9).
- Stress limitation in Serviceability for prestressed members
The application includes stress limitation checks for concrete in prestressed elements. Users start by selecting the prestressed flexural member class. For Classes U and T, serviceability stress limitations are verified per ACI 318-19 Section 24.5.4.1.
Reduction coefficients can be switched in Preferences.
