PCI Design Handbook
Precast and Prestressed Concrete –
7th Edition
Design of Precast and Prestressed Concrete Components
CHAPTER 5
5.2 Flexure
• § 18.8.2 of ACI 318M-08:
• Bending of Asymmetrical Sections
M X ' M X cos MY sin
MY ' MY cos M X sin
5.3 Shear
• Axial compression improves shear capacity
• Under Axial tension, Vc = 0 (§ 11.2.1.3)
• Horizontal shear(Fh) – composite sections
Vu Vnh
where Vnh is nominal horizontal shear strength
– Total force in topping
– Compression due to sagging
– Tension due to hogging
Contd.
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
Vu
Avf
f y
where μ is coeff. of friction
Contd.
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.
Cntd.
5.4 Torsion - Design
1. Determine Vu and Tu at critical section
2. If Tu ≤ Tu(min) Neglect torsion
Vu
T
u
3. Ensure: Tn (max)
and Vn (max)
(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
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)
Cntd.
5.6 Bearing
• On Plain Concrete: when Vu ≤ φ(0.85 f’c A1)
• On RC: when Vu > φVn
– Additional hooks
5.6.3 Dapped-End-Bearing
– Failure modes
•
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