High strength steel used in prestressed concrete can take how much maximum strain?
For a rectangular prestressed beam designed for operating stress conditions, what is the maximum prestressing force?
If a simply supported concrete beam, prestressed with a force of 2500 kN, is designed by load balancing concept for an effective span of 10 m and to carry a total load Of 40 kN/m, the central dip of the cable profile should be
Let the dip of the cable be h.
Upward pressure provided by the parabolic cable = 8Ph/L2
In order this upward pressure may fully balance the external loading.
8Ph/L2 = w
⇒ = 40 ⇒ h = 0.2 m
⇒ h = 200 mm
A prestressed concrete beam has a cross- section with the following properties:
A = 46,400 mm2, I = 75.8 x 107 mm4,
ybottom = 244 mm, ytop = 156 mm.
It is subjected to a prestressing force at an eccentricity ‘e’ so as to have a zero stress at the top fibre. The value of ‘e’ is given by
For zero stress at top fibre,
P/A = Pe/Z
in pre-stressed concrete
The purpose of reinforcement in pre-stressed concrete is
Prestress loss due to friction occurs
The coefficient of shrinkage for high grade concrete for pre-tensioned work is
If 'P' is the prestressing force applied at a maximum eccentricity 'g' at mid-span, figure, to balance the concentrated load 'W', the balancing load will be
Consider the following factors
1. initial prestress
2. losses in prestress
3. depth of cable from extreme compression fibre
Those which affect the ultimate moment capacity of a prestressed concrete beam would include