EXPERIMENT: 2
THE EFFECT OF THE DEPTH ON THE STRENGTH OF RECTANGULAR BEAMS
In this chapter I have written about the experiments and the results on the effects of the depth on the strength of rectangular beams.
2.1 Purpose
To establish the effect of the depth on the failure load of
rectangular beams.
2.2 Hypothesis
I think the depth of rectangular beams will effect the
strength of beams. I think if the beam is deeper it will hold
more loads, because it is more layered.
2.3 Variables
Dependent Variable: Failure Load (N)
Independent Variable: Depth of the beam (mm)
Controlled Variables: Material, length, width, and shape.
2.4 Materials
45 wooden pieces, which are 16mm x 36mm x 550mm.
Nails
Data sheet
2.5 Making of the Test Specimens
For this part of the experiment, I decided to experiment
on five different types of beams. These five types of beams would
have five different depths, which are one wood deep, two wood
deep, three wood deep, four wood deep and five wood deep. For
example five wood deep specimen was made by nailing together five
pieces of wood. We used four nails for each specimen. There would
be there similar beams for each type of beam.. In this experiment
there were a total of 15 specimens. All of these specimens are
shown in Figure
2.1. After making the
specimens each specimen was assigned a label. For example
specimen 1-D-3 means , it is one wood deep, and it is the third
test of this type.
After labelling the specimens, you must measure the dimensions of each beam and record it on the data sheet. Table 2.1 shows the dimensions of the fifteen beams for the depth experiment. In the first column the table identifies each specimen. The second column shows the length of each specimen. As you can see, all the lengths are slightly different. The smallest beam was 525mm long and the longest specimen was 574mm long. The length doesn't really matter, since what matters is the clear span. We'll talk more about clear span in Section 2.6. The third column in Table 2.1 shows the width of each beam. The width is about the same in all of them because in this set of experiment the width was a controlled variable, so it was not changed. All the specimens should have a width of about 36mm. The fourth and the final column shows the depth of each beam. Each type of beam is about the same depth. As each type changes, the depth also changes because the specimen depth increases.
2.6 The Test Set-up
Figure 2.2 shows the planned test set-up. In Figure 2.2, the supports, specimen, and clear span are shown. The clear span is the distance between each support. Before you start experimenting, you must first prepare the specimen. Mark the centre of the specimen and the support points on the specimen. This will help with the correct placing of the specimen. Now place the beam onto the loading platform on the supports. Now place the loading block onto the centre of the specimen. After centering the specimen and the loading block, lower the loading head so that it's barely touching the specimen. The loading head can be lowered by the controls. It can be lowered faster by using a higher gear. The test set-up for depth experiment is same as the width experiment. More details were given in Experiment: 1. So, I will not repeat it here.
2.7 The Test Procedure
The Figure 1.5.(A) from Experiment: 1 shows the overall test set-up. Figure 1.5.(B) from Experiment: 1 shows the loading platform, the load control, and the load dial. The loading platform is where you set the specimen that needs to be tested. The load controls control the speed the loading head is decreasing at, and whether you want the loading head to rise, stop, or descend. The load dial shows how much load is being applied along the needle.
Now that everything is set-up you can start the experiment.
2.8 Behaviour of Specimens During Testing
As you experiment, you have to observe how the specimen reacts. You should notice that before experimenting, the specimens are all flat. When you begin to apply load on the specimen, the specimen will bend a little. Near the end of the experiment, you should have heard a lot of noises. Those noises are the cracking and breaking noises of the failing specimen. Figure 2.3.(A) shows the specimen at high loads. As you can see, the beam is bent and only cracking a little. When the beam failed, all the pieces broke. Those noises are the cracking and breaking noises of the failing specimen. Figure 2.3.(B) shows the failed specimen 4-D-1. This specimen didn't bend as much as in Those noises are the cracking and breaking noises of the failing specimen. Figure 2.4 (I'll get to Figure 2.4 later). Other specimens may have deflected more than this specimen, because of certain weaknesses such as knots, little cracks, and little bits of wood missing.
Figure 2.4.(A) shows specimen 4-D-3 at high loads. As you can see, the specimen is already really broken and chipped. Figure 2.4.(B) shows the specimen at failure. The Figure 2.4.(B) look almost alike to Figure 2.4.(A). That means Figure 2.4.(A) was near failure.
2.9 The Results
All the results for the depth experiment are shown on Table 2.2. The first column in this table identifies each specimen by its name. The second column shows the average depth of each type of beam. The third column shows the failure load for the first beam of each type. As you can see, the failure load increases by about 1000N to 2000N as each type changes. The fourth column shows the failure load for the second beam of each type. The fifth column shows the failure load for the third beam of each type. The results for each type of beam should be around the same failure loads for each test. However, some results are different may be because that certain specimen may have had some weaknesses, such as knots, and chips missing. The last column of the Table shows the average results for each type of beam. The average is found by adding the three failure load results of each type together, and dividing the total by three.
Graph 2.1 shows the average results using diamonds. The data seems to be going by the straight line, when it should be going by the parabolic line.
2.10 Conclusions
Looking at the final data, which are shown in Table 2.2 and in Graph 2.1, I would say that the depth does affect the failure load of rectangular beams. When the wood depth increases by a type of beam, the failure load increases by 1000N to 2000N.
2.11 Accept/Reject Hypothesis
I accept my hypothesis because the depth does
affect the strength of beams.