Calculation of friction losses in tendons using CSI Programs
Frequently, users of CSI Software inquire about how prestress losses are calculated in structural models with prestressed tendons. This article aims to provide a comparison between the friction loss formula, specifically Expression 5.45 from the European Standard EC2, and the formula used in CSI programs.
Understanding that the tension in the prestressing cable is highest at the tensioning end and diminishes along the cable's length due to friction between the cable and its duct during tensioning, it's important to note that friction losses consist of two components: the length or wobble effect and the effect of curvature.
Below is the form where these values can be entered:
The force P0(x) on the cable at the distance x from the tensioning end can be expressed as follows:
SAP2000 VS EC2
| SAP2000 | EC2 |
|---|---|
.png) |
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where:
P0=tendon force at the jacking end
μ= curvature friction coefficient
α= cumulative angle (in radians) of changein the tendon - profile tangent between x and the jacking end
k'= Wobble Friction Coefficient
k= unintentional angular displacement for internal tendons
x= position along tendon from jacking end
The following demonstrates the equivalence between the two expressions. It is evident that when the Wobble Coefficient is entered into SAP2000, it should be the product of k by μ.
