Code References
ACI 318-19
General Discussion
Analysis stages of precast in Commercial Projects are as follows:
Stage | Loads | Load Factors5 | Limit States3 | Cross-Section | Time (days) | Material Properties and Losses1 | Boundary Conditions2 | Comments/Details |
Production |
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Transfer/Release | P/S + SW | 1.0 | Transfer | Non-Comp. | 1-2 | User Defined | User Defined | Component still present in casting bed, includes calculation of Att4 |
Stripping | P/S + SW | User Defined | S&H | Non-Comp. | 1-2 | User Defined | Stripping | Pulling the member out of the casting bed (Deflection Stage 1 - Beam) |
Handling (in yard) | P/S + SW | User Defined | S&H | Non-Comp. | 1-2 | User Defined | Handling | Moving the member from the casting bed to the storage yard (Beam) |
Transportation | P/S + SW | User Defined | S&H | Non-Comp. | User Defined | User Defined | Transportation | Placing the member on the truck and driving to the construction site (Wall) |
Construction |
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Erection | P/S + SW | User Defined | S&H
| Non-Comp. | User Defined | User Defined | Erection | Lifting the member from the truck and setting it in place |
Post-Erection | P/S + SW | By Spec. | Final
| Non-Comp. | User Defined | Final | In-place | Member set in in-place position, may have construction loads |
NC Loads | P/S + SW + NC (excl. topping) | By Spec. | Final | Non-Comp. | User Defined | Final | In-place | Non-composite permanent loads added, excluding topping weight (Deflection Stage 2 - Beam), may have construction loads |
NC Topping | P/S + SW + All NC | By Spec. | Final | Non-Comp. | User Defined | Final | In-place | All non-composite permanent loads added (topping is placed) (Deflection Stage 3 - Beam), may have construction loads |
In-Place |
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Comp Loads | P/S + SW + NC + C DL | By Spec. | Final | Composite | 100,000 | Final | In-place | Composite permanent loads added (Deflection Stage 4 - Beam) |
Final | P/S + SW + NC + C DL + LL | By Spec. | Final | Composite | 100,000 | Final | In-place | Final conditions, all permanent and transient loads placed (Deflection Stage 5 – Beam) |
Notes
Material properties and prestress losses are combined here as they are highly interdependent. Prestress losses and material properties are typically simplified to either initial (Transfer/Release stage) or final (Final stage). Initial losses are used for all stages besides final. More information on losses can be found on the prestress losses page. The default setting shown in the table can be modified by the user.
Boundary conditions can and do change at various stages, and vertical members tend to have more complex boundary conditions. Some horizontal members such as spandrels can also have mildly complex boundary conditions. Boundary conditions, like material properties and prestress losses, are simplified by grouping them into broad categories. The default setting listed in the table can be changed by the user.
Limit states are limits imposed by specifications on stresses, flexure, shear, and other force effects.
Att is the required area of tension steel in horizontal prestressed members per Art. 24.5.3.2.1. The limits on stresses at the Transfer/Release stage are listed in Articles 24.5.3.1 and 24.5.3.2. If the allowable tension stresses are exceeded at any point in the member, the area of steel needed to resist the total tension force in the concrete is computed and listed as Att. Note that the ends of simply supported members are typically defined as the distance from the transfer point to the end of the member.
Even load factors that default to those defined in the governing specification (listed as ‘By Spec.’ in the table above) may be modified by the user.
References
None