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# Query on Flexural Shear Cracking of Postentioned Prestressed Beams

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## Query on Flexural Shear Cracking of Postentioned Prestressed Beams

(OP)
My query relates to the determination of V_0 = M_0 /(M*/V*) for continuous indeterminate post-tensioned prestressed beams in AS5100.5 Clause 8.2.7.2.  My understanding of the steps is:

The precompression moment, M_0, is determined using the total unfactored prestressed moment, i.e. primary prestressed moment plus secondary prestressed moment.

M* and V* determined from ULS applied moment and shear, excluding the effect of secondary prestressed effects.

Calculate V_uc using using 8.2.7.2(1) for flexure shear cracking capacity and 8.2.7.3(4) for web shear cracking capacity, and the lower of these two capacities is to be greater than V* (V* here includes the effect of secondary prestressing effect).

Are the above steps correct/appropriate ?

Replies continue below

### RE: Query on Flexural Shear Cracking of Postentioned Prestressed Beams

(OP)
Correction and modification to my earlier posting:

My query relates to the determination of V_0 = M_0 /(M*/V*) for continuous indeterminate post-tensioned prestressed beams in AS5100.5 Clause 8.2.7.2.  My understanding of the steps is:

I can think of two approach to calculate phi*Vuc for an indeterminate beam. Which of the two is more appropriate, or is there a different way of doing this ?

Approach 1
========
The precompression moment, M_0, is determined using the total unfactored prestressed moment, i.e. primary prestressed moment plus secondary prestressed moment.

M* and V* determined from ULS applied moment and shear, excluding the effect of secondary prestressed effects.

Calculate phi*V_uc using using 8.2.7.2(1) for flexure shear cracking capacity and 8.2.7.3(4) for web shear cracking capacity, and the lower of these two capacities is to be greater than V* (V* here includes the secondary prestressing effects).

Approach 2
========
Consider the secondary prestressed effects as effects from a load, and use the steps below:

The precompression moment, M_0, is determined using the  unfactored prestressed moment, (P/A +- Pey/I)

M* and V* determined from ULS applied moment and shear, including the effect of secondary prestressed effects.

Calculate phi*V_uc using using 8.2.7.2(1) for flexure shear cracking capacity and 8.2.7.3(4) for web shear cracking capacity, and the lower of these two capacities is to be greater than V* (V* here includes the secondary prestressing effects).

### RE: Query on Flexural Shear Cracking of Postentioned Prestressed Beams

The prestressing secondary effects are considered to be an external loading in AS3600 as they are in most codes, so Approach 2 above!

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