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Surveying and Construction

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Introduction:

In this report we have discussed the structural analysis of wooden structural part in detail. We have followed all the requirements to check the various load carrying capacity of a particular wooden structure which is a straight Balsa wood stick. For both the cases we have performed the analysis like compression and tension of that part. On the basis of theoretical and practical methodology we have done this experiment in terms of survey of a structural wooden part. The methods we have applied for the practical part of this survey is the application of load in different condition with the help of Sash clamp. To measure the load application on the wooden part we used a load cell attached with the sash clamp for both the compression and tension testing. Along with the practical testing of this part we have also manually calculated the stress concentration on this part for better understanding of structural analysis in terms of buckling and fracture of this wooden structure.

Objective:

The objective of the survey or experiment is stated in this part of the report so that one can understand the basic requirements of this project report,

  1. To understand the various aspects of wooden structure and their usage.
  2. To become familiar with the various load carrying capacity of the balsa wooden stick type structure.
  3. To become familiar with the manual mathematical calculations of compression and tension of a beam type structure,
  4. To get the comparison between the practical result and the theoretical result for the same cases and making a comparative study.

Methodology:

For every report on an experiment or survey we need to be very careful about the methodologies we are following for the particular case study. The reason behind it is to show the reader about the procedures. For better understanding of this survey we have divided the methodology in two parts, these are Practical observation and result, theoretical observation and result.

On the first part of the procedure of this report we have done with the general calculations to finding out the entire process and the outcomes from the practical proceedings of this experiment. What we have as an output from the practical procedure we have attached in this report in tabular form. For that purpose, we have checked the compressive load testing with the help of sash clamp and attached load cell for measuring the critical load at which the failure is occurring.

  • On the second we have calculated the maximum load required for failure of the part for its different condition like compression and tension. Along with the compression and tension load testing we have also varied the length of the structure and the different conditions like pinned locking and fixed locking on the both ends. After consideration of all these parameters we have mathematically calculated the critical buckling load of the wooden structure made of balsa wood. The need of this manual calculation is to compare the result with the practical result we have beforehand.

Results:

Practical test result and discussion:

On the first part of the result we have discussed the practical test outcome for different condition we have found out,

Table: Compression test result (Practical)

Structure length (mm) End condition Failure load (N) Comments
500 Pinned- Pinned 1.5 Buckling
400 Pinned- Pinned 2.8 Buckling
300 Pinned- Pinned 4.4 Buckling
250 Pinned- Pinned 6.2 Buckling
200 Pinned- Pinned 9.0 Buckling
150 Pinned- Pinned 18.7 Buckling
100 Pinned- Pinned 27.2 Buckling
60 Pinned- Pinned 39.5 Buckling
500 Fixed-Fixed 2.6 Buckling
400 Fixed-Fixed 5.0 Buckling
300 Fixed-Fixed 7.5 Buckling
250 Fixed-Fixed 9.6 Buckling
200 Fixed-Fixed 15.4 Buckling
150 Fixed-Fixed 23.3 Buckling
100 Fixed-Fixed 111.2 Buckling
60 Fixed-Fixed 182.2 Buckling

 

Table: Tension test result (Practical)

Structure length (mm) End condition Failure load (N) Comments
N/A N/A 87.5 Fracture

 

For the first time we have measured the buckling load for a sample made of Balsa wood having a cross- section of 9 sq mm (L= 3mm, B= 3mm). But the varying nature of the bucking load is observed due to the change of its length. For a wide variety of length starting from 60mm to 500mm we have performed the same test for finding out the buckling load on this part and the result we have got from the attached load measuring instrument we have got the results in terms of failure load in Newton and illustrated them in a tabular form shown above. In the first case we have completed with a set of sticks for pinned end condition on the both side of the stick and on the second case we have done this same but the end conditions are changed into fixed end condition. The failure load on the fixed end condition of the wooden stick is higher compared to the pinned end condition. The reason behind it is, we are getting a complete structural support on the both end of the stick which is taken as a wooden beam for consideration. On the basis of the fixed end and pinned end condition and their corresponding failure load we have plotted two graphs to observe their behavior graphically.

After getting all of its compression test result we have also performed the tension test on which we have got the result as well. The wooden stick is taken for the tension test is a 2.25 sq mm (L= 1.5mm, B= 1.5mm) wooden stick as a beam. After applying a tension load instead of buckling we observe a fracture on it when the load application applied axially on this part. And for that sample we found the failure load is 87.5 Newton.

Manual Calculation and Discussion:

The manual calculation is based on the beam theory of mechanical strength analysis. Where we have calculated the compressive load testing and the results on the context of failure load of the wooden stick for both the cases like compression and tension we have done with the manual mathematical calculation. We have also considered all the lengths for different cases.

For compression,

By using the Euler’s buckling formula we get to know the critical buckling load can be found out by the formula we have in this report, it is,

E= Young’s Modulus of the material

I= Moment of inertial of the beam type structure

K= It is the effective length factor for different end condition

For 500 mm pinned end condition of beam we can find out,

Now the moment of inertia is.

For the first case we are having 500 mm structure with pinned end condition at this condition we have,

Accordingly, we have calculated the same for all the variety of lengths and along with it we have also calculated the critical buckling load and the critical stress for the fixed end conditions also by taking the value of K= 0.5

Table: Compression test result (Theoretical calculation)

Structure length (mm) End condition Failure load (N) Critical stress (N)
500 Pinned-Pinned 1.72 0.190
400 Pinned-Pinned 2.69 0.297
300 Pinned-Pinned 4.79 0.529
250 Pinned-Pinned 6.89 0.762
200 Pinned-Pinned 10.77 1.190
150 Pinned-Pinned 19.16 2.117
500 Fixed-Fixed 6.89 0.762
400 Fixed-Fixed 10.77 1.190
300 Fixed-Fixed 19.16 2.117
250 Fixed-Fixed 27.59 3.048
200 Fixed-Fixed 43.11 4.763
150 Fixed-Fixed 76.64 8.468

 

The above table shows the failure loads on the different cases like both pinned end condition and both fixed end condition. The loads are found as a failure loads for both condition of the beam. If we observe it carefully we can see the theoretical values are slightly higher than the practical value. The reason behind it is, on the practical test only a buckling condition is being taken into consideration for the failure mode but in the theoretical calculation the failure has a meaning of extreme buckling on the elastic region after which it will fracture on its plastic region.

Here is a table we have done for comparison between the practical and the theoretical value we have for this particular survey.

Table: Compression test result comparison (Practical and Theoretical)

Structure length (mm) End condition Failure load (N)
Theoretical
Failure load (N)
Practical
Stress (practical) Stress (theoretical)
500 Pinned-Pinned 1.72 1.5 0.167 0.190
400 Pinned-Pinned 2.69 2.8 0.311 0.297
300 Pinned-Pinned 4.79 4.4 0.489 0.529
250 Pinned-Pinned 6.89 6.2 0.689 0.762
200 Pinned-Pinned 10.77 9.0 1.000 1.190
150 Pinned-Pinned 19.16 18.7 2.078 2.117
500 Fixed-Fixed 6.89 2.6 0.289 0.762
400 Fixed-Fixed 10.77 5.0 0.556 1.190
300 Fixed-Fixed 19.16 7.5 0.833 2.117
250 Fixed-Fixed 27.59 9.6 1.067 3.048
200 Fixed-Fixed 43.11 15.4 1.711 4.763
150 Fixed-Fixed 76.64 23.3 2.589 8.468

 


Fig: Compression test result comparison for pinned end condition (Practical and Theoretical)

 


Fig: Compression test result comparison for fixed end condition (Practical and Theoretical)

For the tensional load application part of this experiment we have just calculated the stress concentration on the wooden stick tested as a beam. The tested failure load is 87.5 N and the young’s modulus for the part is taken as 3300 MPa and the cross-sectional area of the wooden stick is used in tensile test is 2.25 sq mm (L= 1.5mm, B= 1.5mm). Therefore, we can say the stress on the part at its tensile loading condition is about 38.88 N/mm2.

Discussion:

In this part of the report we have tried to make the all things clear for the reader. The first question may arise that, about taking the young’s modulus as 3300 MPa. The reason behind it is, the young’s modulus of Balsa wood varies in the range of 2600 MPa to 5500 MPa due to its general condition and moisture content in it and also the arrangement of fiber into the wood. So we just take a value approximately a midrange value of it for calculation. We have also got preferably good results in theoretical part, those can be observing in the comparison part.

The second question may arise about the need of this kind of findings. About this topic we can easily say there are so many important reasons are available for this kind of findings. Still we are not testing with a bulk amount of material but for a sample testing and to know the material property for any construction work this kind of observation and comparison is very important, so that we can be able to get the clear view on their load carrying capability.

Conclusion:

As a conclusion we can say, all the practical experiment has been done with proper perfection so that the error should be negligible. We can say that; the application of axial compressive load is varying in nature with the variation of length. For a same cross-sectional wooden stick there is extra loading needed if its length is less. If the length is large then we do not need higher amount of compressive load for getting buckling on it. According to the process we have observed all the necessary tests have been done with manual calculation in this report so that one can easily understand the findings of this survey.

Improvements:

These are the basic two things are to be taken into consideration for this kind of observation.

  1. The two end positions of the sash clam are of-centered or not that has to be check because at the time of compressive loading it is necessary to apply the load perfectly to its axis.
  2. If we need to check the exact result, then we should plot the exact results like buckling is it elastic zone after that we have to check the plastic zone then we should come to its failure zone then the finding might be much prominent.

Reference List

Briggs, D. (2006). “Forest Industry”, Microsoft Student 2007 [DVD]. Redmond, W A: Microsoft Corporation, 2006.

Wood Database. Ekki, from, http://www.wood-database.com/albizia/. (last accessed 29, Oct.2017).

BS 373: 1957. “Methods of Testing Small Clear Specimens of Timber”, British Standard Institution (BSI), London, UK. BSI 07-1999.

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Essays, BookMy. (November 2018). Surveying and Construction. Retrieved from https://www.samples.bookmyessay.com/surveying-and-construction/

Essays, Bookmy. (November 2018). Surveying and Construction. Retrieved from https://www.samples.bookmyessay.com/surveying-and-construction/

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