sf

Published on January 2017 | Categories: Documents | Downloads: 66 | Comments: 0 | Views: 333
of 3
Download PDF   Embed   Report

Comments

Content

Discussion:
1
2

When a load is applied to the beam, the beam will bend, this is due to
the internal forces that cause deflection in the beam.
Let the distance from the cut section to the fixed point support be r, we
know that the formula of torque is given by,

τ =F ×r

Where F = force or mg. As distance r increased under constant weight
mg(Force), the torque increased. Which means that when the load is
nearer to the cut section, the distance between the weight and fixed
point increase under constant weight, therefore the bending moment
will increase.
As the load is placed nearer to the cut section, the force distribution is
concentrated at the cut section, therefore the shear force will increase
when the load is placed nearer to cut section. To conclude this, the
distance between the load and the cut section is inversely proportional
to the bending moment and shear force.

Figure 1

3

If the horizontal load cell is located at 200mm from the top of the
beam , the magnitude of the load cell reading will become negative.
The load is applied to the beam and the force is facing downwards, and
there a two support supporting the beam, therefore the beam will bend
downwards and having tension on the lower part of beam and having
compression on the upper part of the beam.

Figure 2

4

Experiment 1
Referring to table 2a and table 2b, the percentage of error between
experimental value and theoretical value for bending moment and
shear force for case 1 is 17.1% and 5.8% respectively. While the
percentage of error between experimental value and theoretical value
for bending moment and shear force for case 2 is 3.6% and 7.7%
respectively.
Experiment 2
Referring to table 4a and table 4b, the overall percentage of error
between experimental value and theoretical value for bending moment
and shear force for two loads condition is 20.5% and 1.62%
respectively. While the overall percentage of error between
experimental value and theoretical value for bending moment and
shear force for three loads condition is 9.1% and 11.7%
The percentage of error should be as low as possible as beam is widely
use in our life, e.g. bridge and structure of building. The high
percentage of error could cause the allowable shear force and bending
moment to be calculated inaccurately and eventually caused the beam
to break into two. This could harm human as the broken beam could
cause the building to collapse or the bridge to break apart.

5

The possible factors that affect the accuracy of the experiment
including:
a

Hysteresis error
the difference between two load cell output readings for the
same applied load one reading obtained by increasing the load
from zero, the other by decreasing the load from the load cell’s
maximum rated capacity. the error caused by hysteresis
diminishes with small weight changes. The hysteresis error could
not be eliminated as it depends on the quality of the load cell.

b

Non-repeatability error

is the maximum difference between load cell output readings for
repeated loadings under identical loading conditions (that is,
either increasing the load from zero or decreasing the load from
the load cell’s maximum rated capacity). To overcome this error,
the value of load cell is taken twice; while increasing the load
and decreasing the load, and the average reading is used to
calculate for the experimental value.
c

Load factor
The load applied is not 100% 10N because every weight has
different dimension. To overcome this, a load of 10N
manufactured precisely by manufacturer is used instead of a
load of 1kg.

d

Over constraint of beam
Over constraint of beam limit the movement of the beam,
constraint will make the experimental value smaller than
expected.

e

Supports
The two support of the beam is not rigid enough. To overcome
this, the supports have to be stiffer in order to absorb the energy
better.

f

Position of Load Cell
There are two load cells attached to the beam, the vertical load
cell on the upper part and horizontal load cell on the lower part
of beam. This could cause error to the value taken from the load
cell. During the bending of the beam, the load cell that attached
to the beam also act as a part of the beam, the load cells resist
the bending and cause the value recorded is smaller than
expected. To overcome this, the experiment to find the shear
force and bending moment should be separated and the
horizontal load cell and vertical load cell should be both attach
at different beam and conduct the experiment separately.

Sponsor Documents

Or use your account on DocShare.tips

Hide

Forgot your password?

Or register your new account on DocShare.tips

Hide

Lost your password? Please enter your email address. You will receive a link to create a new password.

Back to log-in

Close