# Prestressed Concrete Structures Questions and Answers – Concept of Load Balancing

This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Concept of Load Balancing”.

a) Pe
b) 4Pe/L
c) Pe/L2
d) Pe/aL

Explanation:

a)
b)
c)
d)

Explanation:
Equivalent moment M=4Pe/L
Camber provided is WL2/48EI.

a) ML2/8EI
b) WL3/48EI
c) 5WL4/384EI
d) 12WL4/384EI

Explanation: Equivalent moment for cable provided for the given loading condition is W= 8Pe/L2
and Camber provided for the cable is 5WL4/384EI.

a) W=Pe/aL
b) W=Pe/4aL
c) W=Pe/16aL
d) W=Pe/24aL

Explanation: The moment profile for the given loading Equivalent moment is W=Pe/aL and
Camber provided is a(3-4a2)WL2/24EI.

5. A rectangular prestressed beam 150 mm wide and 300mm deep is used over a effective span of 10m and the cable with zero eccentricity at the supports, linearly varying to 50mm at the centre carries an effective prestressing force of 500kn(Z=225×104). Evaluate stress due to prestressing?
a) 22.2n/mm2
b) 42.2n/mm2
c) 32.2n/mm2
d) 52.2n/mm2

Explanation: b=150mm, d=300mm, l = 10m, e=50mm, p=500kn
Self weight of beam g = (0.15×0.3×24)=1.08kn/m,
Moment due to self weight = (0.125×1.08×102=13.5knm,
Stress due to self weight = (13.5×106/225×104) = 6n/mm2,
Stress due to prestressing = (P/A+Pe/A) = (500×103/45×103)+(500×103×50/225×104) = 22.22n/mm2.
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6. A rectangular beam of 300mm wide and 800mm deep supports two concentrated loads of 20kn each at a span of 9m. Calculate the prestressing force and suggest a suitable cable profile if the eccentricity is 50mm?
a) 600kn
b) 500kn
c) 200kn
d) 800kn

Explanation: Q = 20kn, e = 100mm, L = 9m, Z = 32×106mm3
Pe = QL/3 , P = (QL/3e) = (200×9000/3×100) = 600kn.

7. A beam of symmetrical I-section spanning 8m has a flange width of 250mm and flange thickness of 80mm, overall depth is 450mm, eccentricity of 150mm, g = 1.57kn/m, q = 2.50kn/m. Determine effective force?
a) 250
b) 217
c) 320
d) 200

Explanation: The bending moment at the centre of the span is Mg = (0.125×1.57×82) = 12.56knm
Mq = (0.125×2.50×82)=20knm, Total moment M = (Mg+Mq)=32.5knm
P = (M/e) = (32.5×103/150) = 217kn.

8. The shape of the bending moment diagram results from ___________
a) Tendon profile
c) Cable profile
d) Compression

Explanation: The cable profile in a prestressed member corresponds to the shape of the bending moment diagram resulting from the external loads, in a prestressed concrete member external type of loads are balanced by transverse component of suitable cable profile.

9. When the beam supports two concentrated loads, the cable follows which profile?
a) Straight
b) Bent
c) Curved
d) Trapezoidal

Explanation: If the beam supports two concentrated loads, the cable should follow a trapezoidal cable because of the concentrated loads the cable bends in a trapezoidal shape, the reactions are obtained by replacing the forces acting on concrete with tendons.

10. If the beam supports uniformly distributed load the tendon follows.
a) Straight
b) Ellipse profile
c) Random profile
d) Parabolic profile

Explanation: When the beam supports uniformly distributed load, the corresponding tendon should follow a parabolic profile, when a prestressed a concrete beam AB of span l it is subjected to an external load of w/m length the prestressing force p, the prestress is imparted to the beam with the help of parabolic tendon with the dip of h at the centre due to parabolic profile the beam is subjected to upward uniform force We is given as px = p = wel2/8h.

11. The concept of load balancing is useful in selecting the___________
a) Anchorage profile
b) Bending profile
c) Tendon profile
d) Jack profile

Explanation: The concept of loading balancing is useful in selecting the tendon profile, which can supply the most desirable system of forces in concrete, straight portion of cable profile does not produce any reactions at the end, while the curve and sharp angles of cable develop uniformly distributed and concentrated load respectively.

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