Lab1 Unsymmetrical Bending
The Hong Kong Polytechnic University
Department of Civil & Structural Engineering
BEng(Hons) in Civil Engineering
Structural Mechanics II
Laboratory Instruction Sheet: Unsymmetrical Bending
Objective:
To observe the two principal axes in a beam with unsymmetric cross sections; and make comparison between the theoretical and actual behavior in bending of two unsymmetrical section cantilevers:
1. An equal angle with one axis of symmetry.
2. A Z section completely unsymmetrical.
Apparatus:
Vertical cantilever system, dial gauges, standard weight, hanger, cantilever beams of L and Z section.
Procedure:
1. Mount up a beam section on the vertical cantilever system and measure the cross sectional dimensions.
2. Set the position of a geometrical axis of the beam section at zero degree.
3. Start the bending test on the cantilever beam with the angular position equals zero.
4. Add weights onto the hanger one by one. For L section, use loading 10N, 20N, 30N. For Z section, loading : 400g, 800g, 1200g. Record the dial gauge readings at each stage of load.
5. Repeat the bending test at different angular positions of the applied load with an increment of 22.5.
(Please properly show your calculations)
Training on critical thinking (20 marks out of 100):
1. If two dial gauges are not placed at a right angle to each other as shown in Figure (a), justify whether the objectives of the experiment are still achieved. (8 marks)
Ans. The objectives of the experiment can be still achieved, while it is necessary to do some substitution.
Therefore this method is still work when placed two dial gauges at an arbitrary angle as long as the exact angle had been measured.
However, the dial gauge may be not as sensitive as that of detecting the deflection of section of interest if the gauges are not placed at a right angle. As a consequence, the result could not be derived easily and directly and the corresponding error
Department of Civil & Structural Engineering
BEng(Hons) in Civil Engineering
Structural Mechanics II
Laboratory Instruction Sheet: Unsymmetrical Bending
Objective:
To observe the two principal axes in a beam with unsymmetric cross sections; and make comparison between the theoretical and actual behavior in bending of two unsymmetrical section cantilevers:
1. An equal angle with one axis of symmetry.
2. A Z section completely unsymmetrical.
Apparatus:
Vertical cantilever system, dial gauges, standard weight, hanger, cantilever beams of L and Z section.
Procedure:
1. Mount up a beam section on the vertical cantilever system and measure the cross sectional dimensions.
2. Set the position of a geometrical axis of the beam section at zero degree.
3. Start the bending test on the cantilever beam with the angular position equals zero.
4. Add weights onto the hanger one by one. For L section, use loading 10N, 20N, 30N. For Z section, loading : 400g, 800g, 1200g. Record the dial gauge readings at each stage of load.
5. Repeat the bending test at different angular positions of the applied load with an increment of 22.5.
(Please properly show your calculations)
Training on critical thinking (20 marks out of 100):
1. If two dial gauges are not placed at a right angle to each other as shown in Figure (a), justify whether the objectives of the experiment are still achieved. (8 marks)
Ans. The objectives of the experiment can be still achieved, while it is necessary to do some substitution.
Therefore this method is still work when placed two dial gauges at an arbitrary angle as long as the exact angle had been measured.
However, the dial gauge may be not as sensitive as that of detecting the deflection of section of interest if the gauges are not placed at a right angle. As a consequence, the result could not be derived easily and directly and the corresponding error