pycba.prestress#

PyCBA - Post-tensioning equivalent-load preprocessor.

A preprocessor (not an analysis object): it turns a draped post-tensioning tendon into the equivalent (“balanced”) loads the tendon exerts on the concrete, returned as an ordinary PyCBA load matrix that you apply to a Beam / BeamAnalysis like any other loading.

The tendon is described span by span by a profile object whose geometry is given as eccentricities from the section centroid, positive below the centroid (so a sagging tendon balances gravity). The supported profiles mirror the standard library used by RAPT / PT Designer (12 profile types, 7 for spans and 5 for cantilevers) - see the PT Designer Theory Manual, Chapters 5 and 6 (https://secure.skghoshassociates.com/product/PT/download/TheoryManual.pdf).

Rather than tabulate twelve sign-sensitive closed forms, the equivalent loads are generated from first principles from the piecewise tendon profile e(x) (parabolic or straight segments):

  • a parabolic segment of constant curvature e'' contributes a uniform transverse load w = F·e'' over its length;

  • a slope change Δe' at an interior kink contributes a point load P = F·Δe' there (slope changes at a support are reacted directly and are not applied to the beam);

  • the tendon eccentricity at each end anchorage contributes a moment M = F·e there.

With the eccentricity-positive-below convention and PyCBA’s downward-positive loads, a tendon sagging a below the chord of a simply-supported span gives an upward w = -8 F a / L² and a midspan moment -F a; a constant eccentricity e gives a uniform -F e. Applying the returned matrix and analysing gives the balanced moment M_bal; the secondary (parasitic) moment is M₂ = M_bal − F·e.

Functions

equivalent_loads

Build the post-tensioning equivalent-load matrix for a draped tendon.

plot_tendon

Draw the tendon and its equivalent loads in three stacked, x-aligned panels.

Classes

CompoundParabola

Compound parabola (RAPT/PT-Designer Type 3): four parabolas - concave down over each support and concave up between - with points of contraflexure.

DoubleHarp

Double-point harped tendon (RAPT/PT-Designer Types 6, 7): straight segments with two bends.

Harp

Single-point harped tendon (RAPT/PT-Designer Types 4, 5; 10, 11 cantilever): straight segments with one bend.

Parabola

Parabolic tendon in a span (RAPT/PT-Designer Types 1, 2; 8, 9 on cantilevers).