Question on calculating Bending Moment for Beam

In summary, it is not possible to calculate the bending moment of the bridge because the load data is not given.
  • #1
joeykeys
11
0
I would like to know ,
given with the 2 attachments below,

are there any ways to find the bending moment (as circled) of the bridge?

or it is not possible to calculate simply because the "load" data is not given?

Several attempts have been tried but the circled data can not be reached.

Thanks a dozen for the help!
 

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  • #2
These load values could be given as ultimate resistance values for the structure.
 
  • #3
radou said:
These load values could be given as ultimate resistance values for the structure.


However, this "ultimate" value is not currently provided so it is not possible to calculate the bending moment as shown..

is it?
 
  • #4
I think you need to provide further information about the context.

The first bridge is stated to be an arch. Arches have no bending moments, being pure compression structures.

The second bridge is stated to have a span of 98m and a (presumably) max bending moment of 134627 kN-m.

A simple RC beam with such a span would experience a max bending moment of 2*6*2400*10*98*98/8 = 345744 kN-m. This is nearly three times as much.

But the picture shows a prop at about 1/3 of the span. Such a prop would reduce the max moment and reposition it. The exact figure would depend upon the assumptions about continuity in the beam over the prop. If we assume the beam is fully continuous over the prop, can you calculate the approx moment? - it is possible to estimate if we can locate the prop along the 98 m overall span.
 
  • #5
Studiot said:
I think you need to provide further information about the context.

The first bridge is stated to be an arch. Arches have no bending moments, being pure compression structures.

The second bridge is stated to have a span of 98m and a (presumably) max bending moment of 134627 kN-m.

A simple RC beam with such a span would experience a max bending moment of 2*6*2400*10*98*98/8 = 345744 kN-m. This is nearly three times as much.

But the picture shows a prop at about 1/3 of the span. Such a prop would reduce the max moment and reposition it. The exact figure would depend upon the assumptions about continuity in the beam over the prop. If we assume the beam is fully continuous over the prop, can you calculate the approx moment? - it is possible to estimate if we can locate the prop along the 98 m overall span.
Could you tell me which formula have you used for calculating the bending moment?

say is it: (b*d* ? * ? * span^2 ) /8 = bending moment

what does 2400 and 10 stand for?

Thanks again for the clarifacation.
 
Last edited:
  • #6
reinforced concrete weighs about 2400 kg/cubic metre.
10 approximates the acceleration due to gravity to convert this to Newtons

the weight per metre run of beam is depth x width x1 x above density

the maximum moment in a simply supported beam is wL2/8

where L is the span length and w is the weight per metre run.

But you didn't answer my question so I can't help further
 

1. How do you calculate the bending moment for a beam?

The bending moment for a beam can be calculated by multiplying the force applied to the beam by the distance from that force to the point of interest on the beam. This can be represented by the equation M = F * d, where M is the bending moment, F is the applied force, and d is the distance.

2. What units are used for bending moment calculations?

Bending moment is typically measured in units of force multiplied by distance, such as newton-meters (Nm) or pound-feet (lb-ft). In some cases, kilonewton-meters (kNm) or kilopound-feet (klb-ft) may also be used.

3. How does the shape of a beam affect bending moment calculations?

The shape of a beam can significantly affect bending moment calculations. For example, a beam with a larger cross-sectional area will have a higher resistance to bending moments, while a beam with a smaller cross-sectional area will have a lower resistance. Additionally, the location and distribution of the applied force along the beam also play a role in the bending moment calculation.

4. Can bending moment be negative?

Yes, bending moment can be negative. A negative bending moment indicates that the beam is being bent in the opposite direction of a positive bending moment. This can occur when there is a force applied in the opposite direction of the bending moment or when the beam is experiencing a cantilevered load.

5. What factors can cause a beam to fail under bending moment?

Several factors can contribute to beam failure under bending moment, including excessive loading, improper beam design, poor material quality, and structural defects. It is important to carefully calculate and consider the bending moment for a beam to ensure it can withstand the expected forces and prevent failure.

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