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.

Timeline

Here is my initial timeline. It shows what tasks i need to complete and the important deadlines. I hope it will help me to stick on track.

Progress so far

What I know so far:

• Girders are used because they are efficient ways of supporting loads over open spaces.
• The top member is in compression, the bottom member is in tension. Members act differently under forces when in compression or tension.
• Some lattice arrangements are stronger than others: the strongest girders spread the load  most efficiently (already seen in initial trial experiment).
• Assuming pin joints (strains and bending moments belong  to one member only) and assuming the materials are within their elastic limit, the forces in the members can be easily calculated.
• Deflection must be taken into account when designing trusses. Deflection is more likley to be influential on design than the actual failure limit. In real life girders and bridges, the acceptable deflection limit is between 1/1000 and 1/500 of the truss length.
• The strength of an individual member depends on its size, shape and material properties.

Questions to answer through research:

• Background knowledge required to design the trusses:
• can we use plastic (elastic vs plastic behaviour)
• how to calculate deflection in a lattice girder
• behaviour of members in compression
• behaviour of members in tension
• how to fix the beam at each end
• height depth ratio
• effect of having top and bottom beam as a continous member
• Continous member:
• easier to make
• easier to keep strength constant
• distortion of forces
• easier to controll variables
• Multiple members:
• closer to reality
• harder to construct
• connections add to error analysis
• harder to controll variables

To do:

• Drawup potental ideas and theoretically calculate the forces
• Refine/define research question
• Design the definitive experiment; size; shapes; material; rig
• Find equations for deflection
• Use EBSCO to find relevant articles

Things to consider for the experiment:
Variables:
Independant:

• angle between interior members and the straight tom and bottom members
• need to calculate uncertanties
• should test a large range of different angles,
• 5 different angles (=5 different bridges?)
• 6 or 7 different masses (large range without breaking the bridge)
• relationship between deflection and angle (linear?)

Dependant:

• Deflection (in mm)
• Could use a motion detecter and data logging software to measure deflection to a high accuracy

Controlled:

• each individual angle must be the same
• elasticity of the material
• pin joints
• length depth ratio

Not controlled:

•  mass of truss
• amount of material
• single member distortion forces

Other progerss to note:
I collected some library books that were sent from zurich during the week, they are definatley relevant to my topic and are quite specific, giving me precise information. The books are called:

• Advanced analysis and design of steel frames, G-Q Li and J-J Li
• Design of building trusses, J Ambrose
• Simplified truss design, M Melaragno
• Roof truss guide, P Eichenberger

Mr Rawson showed me how to use the EBSCO database during our meeting. This is an extremley usefull tool as it contains many relevant academic articles, including articles on trusses and girders. This will allow me to vary the research media I use.

Testing possibilities

During the week I went to a library in muttenz that is part of an architectural and design college and who have  books relevant to my topic. They are on order form zurich and should arrive within a week. there was only one book that I could not get as it is a reference book in the zurich library, this book sounded quite relevant though, if needs be I may have to go to the zurich library to take a look.

This weekend I bought some materials to start tinkering with and to decide what is possible to perform as an experiment. I decided on using plastic as a material as it is readily available and has a slight flex, meaning it would not require as much force to observe deflection and stresses. I found a solution to making pin joints by pushing nails through holes in the plastic members to secure them (see photo). This seems to work quite well.

 One potential variable to investigate would be the force required for a truss to deflect a specific amount (see photo below for a potential style of experimental rig). Plastic seemed to be well suited to this as the trusses deflected under some weight, yet this was still minimal (I tested the trusses with masses up to 400g), suggesting that for the actual experimant I will have to uses much heavier masses.

In one of my research books I read that in real life, the limit to acceptable flex is between 1/500 and 1/1000 of the trusses length. For the experiment this will not be possible though as the maximal deflection on a 1m long rig would be too small to read. On reflection I will still be able to learn about how the structure of a lattice girder affects it's strength even if I have to surpass the real life acceptability limit.

Today I tried three different types of structure, including a warren truss (which I intend to do my actual research on).

I plan to make a time plan and to design a virtual model of a warren truss on SketchUp this week, as well as continuing the research so that in within the next few weeks I can prepare myself for the actual experimentation.

The Next Step

Today the other 3 books I ordered arrived. The book "invention by design" has a whole chapter on how some of the big bridges of today were built and what influenced their design (including a 1880's lattice railway bridge in new york and several other lattice girder style bridges.

I plan to make a timeline in the near future so that I can keep track of where I am in the overall process of  the project. For this I will ask mrs Round about any intermediate deadlines before the final hand in date.
I hope this will help me keep track.

Tomorrow I am going to a library at the school of architecture and design in Muttenz to see if i can find any more relevant resources.

I also plan to have a google sketchup design of a potential testable structure soon so that I can plan what I will need to obtain in order to perform the experiment.

I wonder if trying to get information form different types of data sources (e.g. articles, reviews...) would help me gain a better understanding of lattice girder theory than just using books and the internet? Perhaps the most usefull part of my preparation could be to do more calculations of the forces acting on each member in a lattice girder to gain a greater understanding in the basics? I will try both of these in order to prepare myself for stating my hypothesis wich i will have to do in the not too distant future.

Google SketchUp

This week the first of my books arrived (The strains upon bridge girdersand roof trusses... by T. Cargill). This book is a scanned copy of quite an old book (1873) and some of the pages are damaged due to the wear of time. It does have some relevant sections on uniformly distributed weights, determining strains graphically, the strains upon the web of gidrers, and the lattice girder. I have started to read the relevant sections, and will use them to hepl me formulate my research question and hypothesis.

I also started working with google sketchup. I did the four beginners tutorials to learn the basics of the programm (http://sketchup.google.com/training/videos/new_to_gsu.html). the program is really interesting for this project as it will allow me to make a virtual 3D model of the bridge before i physically make it. Through the tutorials I made a chair using two different techniques.

More books

Today I put in an order for some books on my topic, some of which are quite general and some of which are very specific (written by university professeurs...). I am hoping that this will be usefull and will allow me to decide which specific aspects of girder bridge design I would like to test and help me formulate my hypothesis. I also plan to go to a toy shop soon and order some specific parts of meccano so that I may begin to get a feel of what will be possible with this construction medium.

The books I ordered are:

• The strains upon bridge girders and roof trusses: including the warren, lattice, trellis, boqstring and other forms of girders, the curved roof and simple compound trusses - T.Cargill
• Invention by design: how engineersget from thought to thing
• Structures: or why things don't fall down
• An introduction to the design of beams, girders, and columns in machines and structures with example

Meccano

I had an idea that meccano might be a good material to use for the structures being experimented on due to it's simplicity and its resemblance to steel members used in actual truss bridges. I had a breif play with some pieces and was able to make a simple truss shape quite quickly. if i were to use meccano though i will need a lot more so this will probably involve some research into ordering specific parts.

Meeting with Mr Rawson 18-1-11

Today I had a brief meeting with Mr Rawson. We discussed how far I was with the research and what was left to be done before I can start experimenting. Mr Rawson sugested downloading Google Sketchup so that I can make a 3D design of the truss bridge I plan to build to test before I actually start making the bridges I will test.

Initial research

Through the initial research of my extended essay I aim to gain enough knowledge to formulate a hypothesis on how changing one of the variables involved in constructing a lattice girder bridge will affect the bridges overall streingth.
I have found both online civil engineering lecture notes and civil engineering text books that have given me the basic knowledge of calculating the forces acting on steel members in lattice girders how the members act under tention and compression.
The main topics of my research have been:

• lattice girders
• tention and compression
• roof trusses
• steel bridge design

I took a trip to the university library of Basel to find aditional resources but was unable to find any as Basel University do not teach technical subjects. to resolve this problem i may have to travel to a library in Zurich or Muttenz.