EXPERIMENT: 1

THE EFFECT OF THE WIDTH ON THE STRENGTH OF RECTANGULAR BEAMS

In this chapter I have written about the experiments and the results on the effects of the width on the strength of rectangular beams.

1.1 Purpose
To establish the effect of the width on the failure load of rectangular beams.

1.2 Hypothesis
I think the width of rectangular beams will effect the strength of beams. I think if the beam is wider then it is more sturdy because the beam will cover more area, and they are stronger.

1.3 Variables
Dependent Variable: Failure Load (N)
Independent Variable: Width of the beam (mm)
Controlled Variables: Material, length, depth, and shape.

1.4 Materials
45 wooden pieces, which are 16mm x 36mm x 550mm.
Nails
Data sheet

1.5 Making of the Test Specimens
For this experiment, I decided to use spruce wood to make the specimens. We bought eleven pieces of 16mm x 36mm x 2438mm long wood from a hardware store. I then had to cut the wood to make the specimen. The carpenter cut the wood so each piece would be 550mm long. There were joints in the wood, so we had to avoid the joints, because if they were in the specimen they would weaken the beam. After cutting the wood to length we had connect them together to make the specimens using nails.

I decided to experiment on five different types of beams. These five types of beams would have five different widths, which are one wood width, two wood width, three wood width, four wood width and five wood width. For example five wood width was made by nailing together five pieces of wood. We used four nails for each specimen. There would be three similar specimens for each type of beam. In this experiment there were 15 specimens. All of these specimens are shown in Figure 1.1. After making the specimens each specimen was assigned a label. For example specimen 1-W-3 means , it is one wood wide, 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 1.1 shows the dimensions of the fifteen beams for the width experiment. In the first column it identifies each specimen. The second column shows the length of each beam. As you can see, all the lengths are slightly different. The smallest beam was 550mm long and the largest was 572mm long. The length really doesn't matter, since what matters is the clear span. We'll talk more about the clear span in section 1.6. The third column in Table 1.1 shows the width of each beam. Each type of beam is about the same width. As each type changes, the width also changes because the specimen width increases. The fourth and final column shows the depth of each beam. The depth is about the same in all of them because in this set of experiment the depth was a controlled variable, so it was not changed. All the specimens should have a depth of about 36mm. Figure 1.2 shows me measuring the dimension of a beam.

1.6 The Test Set-up
Figure 1.3 and Figure 1.4 show the test set-up. Figure 1.3 shows the planned set up. In Figure 1.3, the supports, specimen, and clear span are shown. The clear span is the distance between each support. Figure 1.4 shows the actual set up. The actual set up consists of the supports, clear span, the specimen and the loading block.

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. Figure 1.5.(B) shows me changing the test load. I will talk more about Figure 1.5 in the next section.

1.7 The Test Procedure
The Figure 1.5.(A) shows the overall test set-up. Figure 1.5.(B) 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.

• Using the low gear begin to apply load to the beam at the rate of 0.1inch per minute. That means the loading head is slowly descending at 0.1inch every minute. Don't forget to write down any observations seen during the tests.
• Keep applying the load until the beam fails. Watch and monitor the load dial and the needle. The needle shows the amount of load that is being applied. When the beam [specimen] fails, the needle will decrease.
• Figure 1.5.(C) shows me monitoring the dial to see the failure load. Once the beam has failed, turn off the testing machine, and raise the loading head. Take the specimen out of the loading platform.
• Read the failure load from the dial and write the failure load on the data sheet. Figure 1.5.(D) shows me writing down the failure load the failed specimen.
• Write down any observations of the failed beam and prepare the testing machine for the next test.

1.8 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. Figure 1.6.(A) shows the beam before the testing began. In Figure 1.6.(A), the specimen is flat and is not bending. When you begin to apply load on the specimen, the specimen will bend a little as shown in Figure 1.6.(B). In Figure 1.6.(B), the specimen is at low loads, and is bending 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 1.6.(C) shows the specimen at high loads. As you can see, the beam is bent and only cracking a little. When the beam failed, there was a crack down the bottom middle. Figure 1.6.(D) shows the failed specimen. This specimen didn't bend as much as other. Other specimens may have deflected more than this specimen, because of certain weaknesses such as knots, little cracks, and little bits of wood missing.

1.9 The Results
All the results for the width experiment are shown on Table 1.2. The first column in this table identifies each specimen by its name. The second column shows the average width of each type of beam. The width should increase by about 16mm as each type of beam changes. The third column shows the failure load for the first beam of each type. As you can see, the failure load increases by about 3000N 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 1.1 shows the average results using diamonds. The straight is where the data should be. The diamonds are either on the line or a little off, so the results seem to be correct.

1.10 Conclusions
Looking at the final data, which are shown in Table 1.2 and in Graph 1.1, I would say that the width does affect the failure load of rectangular beams. When the width doubles, so does the failure load.

1.11 Accept/Reject Hypothesis
I accept my hypothesis because the width does affect the strength of beams.