We are designing an open web steel girder bridge of span 15m. The dimensions of the bridge are 15m x 2.6m x 3.8m. The bridge is a scaled down version of a Standard 30.5 m Indian Railways Bridge. The final objective of constructing this model bridge is to analyse the behaviour of the bridge and monitor its deflection, acceleration under loading. We would be using wireless strain gauge sensors and accelerometer sensors to record the deflection and acceleration respectively. However, the deflection which we are obtaining using point load of 5KN at 10 nodal points is 0.35 mm. This deflection is too less to be sensed by our sensor. Please suggest any way to obtain atleast 5 mm of deflection
Dear colleague,
there is nothing surprising in the fact that you got value modal displacement 0.35 mm.
It is caused with the fact, that the bending stiffness of the cross section is too large for the span of 15m.
You can go one of two ways.
1. Increase the length of the span. It is necessary to test the strength of the received section.
2. Reduce the size of the cross section. Again check section for strength.
3. InAdd your answercrease the load. And again check section for strength.
I wish you success,
Volkova Viktorija
Dear Maroju,
The loads in your model seem to be small. I'm not familiar with the Indian code. But according to AASHTO LRFD 2012 the live load on a bridge consists of (a three axle design truck loads or design tandem loads) combined with (design lane distributed load). The design truck axle's loads are 8, 32, and 32 Kips. The total load of these axles are 72 kips. These loads are multiplied by dynamic allowance factor, which is about 1.33 leading to design truck load of 96 kips (427 KN) before adding the lane load. The total loads in your model is only 50KN which is significantly small. I suggest that you check your design load again.
Regards
If you work with the same model, only remaining option is to increase the load. But you need to be aware of not taking the system to nonlinear range in an unwanted fashion for your project goals.
I am agree with Viktorija Volkova, but in exciting situation you can sense vibration with Ambient Sensors which are suitable for small vibration
Your aim for this experimental analysis is not clear. If some one is studying the scaled down model of a structure to verify the theoretical behaviour with experimental one then one needs to ensure the following:
1. Material property (using same material or different)
2. All Member sizes to be scaled down proportionately , which is not always feasible.
3. Loads to be scaled accordingly.
4. Pattern of load and its application needs to be taken care etc
In your case I am sure that no theoretical analysis was done to decide the member sizes or codes and standards are not followed or loads are not transformed properly.
So first decide your aim for such experiment, then if any help is needed you can contact me in this regard.
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