PCI Design Handbook

Precast and Prestressed Concrete 7th Edition

CHAPTER 5Design of Precast and Prestressed Concrete Components

5.2 Flexure 18.8.2 of ACI 318M-08:

Bending of Asymmetrical Sections sincos' YXX MMM sincos' XYY MMM

5.3 Shear Axial compression improves shear capacity

Under Axial tension, Vc = 0 ( 11.2.1.3)

Horizontal shear(Fh) composite sections

where Vnh is nominal horizontal shear strength

Total force in topping

Compression due to sagging

Tension due to hogging

nhu VV

Contd.

5.3 Shear Shear Friction 11.6 of ACI 318M-08

An existing or potential crack

Interface between dissimilar materials or

Interface between Concrete cast at different times

where is coeff. of friction

Contd.

Contd.

y

uvf

f

VA

5.4 Torsion

Low fixity compared to cast-in-situ members

Based on the Zia and McGee Proceedures

11.6.7 of ACI 318-05 : when d/b > 3

Cntd.

5.4 Torsion - Design1. Determine Vu and Tu at critical section

2. If Tu Tu(min) Neglect torsion

3. Ensure: and

(Avoid: potential compression failure due to over-reinforcing)

4. Calculate shear and torsion carried by concrete Tc and Vc

5. Stirrups for Tu - Tc & min. web reinforcement for ductility

6. Provide longitudinal reinforcement for diagonal tension due to torsion

Cntd.

u

n

TT (max)

un

VV (max)

5.5 Beams with Ledges (eg: L beams)

Shear strength of Ledge: Refer PCI handbook

Transverse (Cantilever) Bending of Ledge

Longitudinal Bending of Ledge

Attachment of Ledge to Web

Out-of-Plane Bending near Beam End

Pocketed Spandrels

Refer PCI Handbook (Important)

5.6 Bearing On Plain Concrete: when Vu (0.85 fc A1)

On RC: when Vu > Vn Additional hooks

Cntd.

5.6.3 Dapped-End-Bearing Failure modes