Contacting Mr Rawson

Hi Mr Rawson
The school email is down (at least for students) so im not able to contact you there, are you in school again now? If so would you like me to bring the equipment bask straight away as we said at the end of the school year, if so would friday morning or early afternoon be ok for you?
Thanks
Billy

Essay first draft - complete

I have just completed my first draft. This includes all the theory that I researched aswel as the experimental learnings.
Here are some graphs that are quite a good summary of the project as a whole, including lots of ideas developed throughout the essay:

I need to take some words out as I am slightly over the wordcount at the moment, and there are some final touches to make  such as modifying the appendix but all the significant work is complete.

experiment

I have now performed the experiment. here are some photos of the rig and procedure followed by the results yielded from the testing.

Easter holidays

Over the easter break I read through my theoretical research books, marking anything of interest that I may wish to refer to when writing the essay. I also wrote an outline for the project process, which incluses potential ideas to help me writing the essay up. I also ordered some books from the ICE (institute of civil engineers) that explain truss design and analysis theory in a simple manner, to help me enhance my understanding.
 Here is the word document I complied a summary of what is done, what is to do and any issues to clairify in, aswell as some potential essay ideas. This was useful to help me claer my mind up of what i want to get out of the experiment.

Copy of the document:

Subject	Physics
Topic	Investigation into lattice girders, how they work and what are their limitations?
Focus	Taking a warren truss as an example, use a combination of theory, calculation and experimentation to understand how the design features contribute to the strength and efficiency of the truss.
Title	Efficient load bearing structures
Research question	How does the configuration of a warren truss determine its ability to bear load?
Approach	An experimental approach to test the behaviour under loading of three warren truss configurations. Using force analysis calculations and the experimental observations to guide research into relevant failure mechanisms, to explain how the design features contribute to the strength and efficiency of the truss.

Investigation Plan:

Action	Progress
Preliminary research	Add book references + content
Preliminary experiment with single truss	Complete: ·         realised importance of fixing the truss at each end ·         need a rig to mount it including a loading mechanism. ·         Measurement of deflection was problematic
2nd experiment with three truss arrangements	Complete: ·         Rig was improvement ·         Common failure mechanism with all three trusses: buckling of top member in compression. ·         Need to investigate buckling failure mechanism. ·         Need more precise measuring equipment ·         Need to develop testing rig
Targeted research	·         Simple beam theory: bending moments, shear forces, youngs modulus, second moment of inertia, radius of gyration, buckling, effective length of columns ·         Deflection of trusses: work in progress
3rd experiment	·         Before exams! (mid june) ·         Repeat loading test on three trusses with nodes on the top chords restrained laterally. ·         Use a sonar device and logger pro software to measure deflection for greater precision.
Analyse results and evaluate correlation between theoretical calculated forces and experimental observation	·
First essay draft	·         First two weeks of june (deadline 17th june)
	·

Questions for Mr. Rawson:

1.       Can I use established equations without deriving them if I can reference them?

2.       Qualitative and quantative results from experimentation, are both acceptable?

Essay plan:

Introduction:

·         Significance: see them all around, used widely, from roofs to bridges

·         Invention and history of trusses – very brief

·         Context of research question:

·         Why it is worth investigating: engineering is about efficient use of materials. Trusses always look lighter weight compared with traditional beams and columns. Understanding how they work and their limitations could be important in a future world as resources become more scarce and engineering challenges become more demanding.

·         Scope/focus: using warren truss as an example of a commonly used configuration, simplifying the investigation to three simple versions of a warren truss. Taking a span to depth ratio of 10:1 (reference to be found).

·         Relevant physics principles: What is this?? E.g. structural frame analysis, bending moments, axial forces, calculations, principles of stress/strain, tension/compression, simple beam theory

·         Research question: see front page

·         Concluding statement: later!

Body:

·         Background Theory

o   Simple beam theory:

§  Loads

§  bending moments

§  Shear forces

§  Tension/compression

o   Compression and buckling

§  Effective length of columns

§  Youngs modulus

§  Second moment of inertia

§  Radius of gyration

§  Theoretical buckling load of a member(possibly)

o   Theory of trusses

§  Comparaison to simple beam

§  Analysis of axial forces

§  Deflection calculation

·         Calculations

o   Analysis of forces in the three trusses

o   Approximate deflection calculation for 4 section truss

·         Experimentation

o   Describe experiment (method, rig, material specs...)

o   Results

o   Analysis of results

o   Conclusions

§  Can I explain it

§  Errors

·         Conclusion:

o   Final argument/idea

o   Answer research question

o   Unresolved issues

o   New questions that have arisen

Sketchup design

This is the sketchup design I have made for the truss with a four triangled base.

Experimenting

I made three trusses from plastic to test and help me develop my ideas for my experiment. The three trusses were 1m by 10 cm, one with two triangular sections, one with four and one with eight. Using the warren truss, these are the only three fesable configurations  to experiment with since the number of triangular segments increases in exponents of two since  there must be a joint on the lower horizontal member at the mid point.

I made a rig on which we can fix the ends of the trusses in order to test them (see picture below). To test the trusses i suspenses slotted masses from the central joint and  measured the diflection. I expected all the force to convert into 2d stress in the individual members of the truss, but instead the truss started to buckle outwards (see pictures below). This is because normally 2d trusses are part of a lattice and take strength from the other lattice members in different planes. In order for my calculations to be valid, all the  forces must be within the 2d plane. To keep my trials coherent to the theory behind the tests i will have to ensure that only vertical motion is possible during the experimantation. this may involve making a 3d bridge or beam like shape or fixing the joints on vertical runners. The complications arrise when manipulating variables as it soon becomes difficult to see what i am manipulating or not.

                                         The rig:

                                         Deflection:

Theoretical experimantation

Over the weekend i designed some possible girders to test and using the information I found on resolving forces in griders theoretically, I proceded to draw up and calculate the forces involved in each individual member. This is one of the most significant steps I have undertaken so far as it has really given me a feel of what this project could hold. Over the next week I plan to use this experience to finalise my topic and research question, then I will have more concrete ideas on what to do next.