A simply supported rectangular prestressed concrete beam of span 9 m h...
Equating the moments
P = Prestressing force = 2000 kN
l = span of the beam = 9 m
w = load on the beam
e = eccentricity of the tendon = 0.18 m
w = 35.55 kN/m
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A simply supported rectangular prestressed concrete beam of span 9 m h...
Given data:
- Span of the beam = 9 m
- Prestressing force = 2000 kN
- Maximum dip of the tendon at mid-span = 0.18 m
Approach:
To find the maximum uniformly distributed load the beam can carry, we need to determine the maximum bending moment at mid-span. This can be done by considering the equilibrium of forces and moments.
Step 1: Find the cable profile:
- The cable profile is parabolic with zero eccentricity at the ends.
- Since the cable is symmetrical, the maximum dip occurs at the mid-span.
- The maximum dip of the tendon at mid-span is given as 0.18 m.
Step 2: Determine the force in the cable at mid-span:
- The force in the cable at mid-span can be calculated using the equation for a parabolic cable profile.
- The equation for a parabolic cable profile is given as:
y = (L/2)^2 / (8a)
where y = dip of the tendon at a distance x from one end of the beam,
L = span of the beam,
a = constant (to be determined)
- Substituting the given values, we have:
0.18 = (9/2)^2 / (8a)
Solving for a, we get a = 0.5625
- Now, substituting this value of a into the equation for the cable profile, we can determine the force in the cable at mid-span:
y = (9/2)^2 / (8*0.5625)
y = 0.5625 kN
Step 3: Determine the external load at mid-span:
- Since the beam is simply supported, the external load at mid-span will be half of the total load.
- The total load is the sum of the prestressing force and the external load.
- Therefore, the external load at mid-span is given as:
External load = (2000 + 2*y) kN
Step 4: Determine the maximum bending moment at mid-span:
- The maximum bending moment at mid-span occurs when the external load is maximum.
- The maximum bending moment can be calculated using the equation:
M = (wL^2) / 8
where M = maximum bending moment at mid-span,
w = uniformly distributed load (to be determined),
L = span of the beam
- Substituting the given values, we have:
(2000 + 2*y) = (w*9^2) / 8
Solving for w, we get w = 35.15625 kN/m
Answer:
The maximum uniformly distributed load the beam can carry is approximately 35-36 kN/m.