Examine and analyze forces taken in an experiment using a warren girder and comparing them with the theoretical forces calculated with mathematical methods of joints and the method of sections
The experiment
The pin Jointed Frame experiment allows you to detect the forces that are acting o themembers of the structure and determine if the structure could be classified as staticaldeterminate or indeterminate structure.We are using a Warren Girder structure controlled by an electronic load cell used to applyforces in the members of the structure,and the sensors, called strain gauges, willdetermine the load applied and the results are shown on the digital force apparatus usedduring the experiment. The sensors also, collect information in order to measure the forces in the members anddetermine the compression or the tensile forces in each member.Therefore, when the member stretches or compresses, the strain gauge stretches orcompresses the same amount.The digital strain results are given in micro strain (x10 ). Using te strain, the area wherethe force is applied and the elastic (Young’s) modulus of each member, we can convert thestrains into eachmember forces.
Experimental procedure
1. Make sure apparatus is set properly.
2. Annotate in the appropriate table 2, the number of each member.3. Annotate in the appropriate table 1, the diameter of each membermeasured using the micrometer gauge.4. Carefully apply a load of 100N (in the direction of loading) and zero theload cell. After a load of 500N is applied, carefully check that the frameis stable and secure. Return the load to zero and carefully zero the loadcell again (this may take a few tries as the indicator is very sensitive).Zero the digital dial gauge, which measures the deflection of one of the joints.5. Carefully apply loads in 100N increments and record the strain in eachmember in the appropriate table and the deflection of the joints.6. Return the load to zero. The experiment is now complete.
Analysis of Results
Subtract the zero readings from the measured strains in order todetermine the true strains. Record these values in Table 3.
Calculate the equivalent member forces at 450N and record the values inTable 4 (experimental force). You will need the information below:To get the elastic modulus you need to calculate the stress over the strain:
E=
!
/
”
where
E
represents the
elastic modulus (N/m
2
);
!
represents
stress inthe member (N/m
2
) and
!
represents
the true strain in the member. Note to obtain the cross sectional area of each member, se the measureddiameter The elastic modulus for steel E = 210 GN/m
2.See the attached calculations sheet for the complete calculations.
.
Select one compression member (strut) and one tension member(tie) and plot the graph of the strain and the loads and comment on your graph. Members choosen from Table 3 are member 2(T) and 7(C).
