Help with writting a Phd thesis

[george85]

There is a Phd competition at my faculty in Serbia - 3 people will get a free Phd course (the course lasts 3 years). The topics are already made by professors, mainly are crap related to some architectural bulshit (public space trough history, buidlings and it's design bla, bla). Only one of them is by my opinio the best among others:

"Lightweight three dimensional grid load bearing structures (space frames) and their relationship with architecture."

Can you just give me any indication, what can this be about? From architectural point of view, probably the most significant concept will be aestherical part. But as I stated before, I find this as a bullshit (and regret I finished architecture instead of civil engineering, I was just not well informed).
So the "potential" is a broad and vague term. I could say that the potentials of space frames in civil engineering and architectural are, that:
light, fully prefabricated, easy to assemble and erect, light and convinient for transport, can cover of huge spans and indoor spaces, material savers etc.

I know how to write a thesis (methodology, theoretical orientetion, research study, sources, materials, advantages and disadvantages of this system etc). And there are also a lot of thesis examples at our faculty library. Also I have downloaded the "How to write a Phd thesis" here from forum.

But what would be the main thing to focus on researching and doing the Phd thesis with this title in the following 3 years?
Any ideas?

Thank you.

[george85]

Any help please.
What would be the main thing to focus on researching and doing the Phd thesis with the title "Lightweight three dimensional grid load bearing structures (space frames) and their relationship with architecture." in the following 3 years?

[toa011]

I'm not and architect but a civil engineering, so I would suggest you take your Phd thesis from an architecture perspective. I don't think it is a good idea to try to take your thesis from a civil engineering perspective, your learning curve will be to great. I suggest to search the literature for what other architects have done on space grid structures, then go and and propose a light-weight three-dimensional grid structure for an existing and hypothetical structure with emphasis on the structures ability to bear load. For example you can select new materials that are becoming more popular in construction these days: fiber-reinforced polymers, come up with a space-grid structure and see you can handle the aesthetics and structural design/form.

[PanosP]

I would also add that owing to the fact that space frames comprise of handy-sized members, they offer the shape plasticity (see for example the Great Court at the British Museum) that can only be matched with that provided by concrete (in the form of ribbed concrete shells). Another hint would be the Eden Project in Cornwall or even the Water Cube in Beijing. On the other hand if you dont want to focus on the space enclosure aspects of such structural systems you can alternatively have a look on assembly issues of patented forms like the Mero joints and how these can be designed/dimensioned/improved etc or even construction detailing issues. Hope this helps

[george85]

Thank you for the answer both of you.

@toa: Wich application can use a carbon fibre polymers for members/joints? RSTAB, SAP?
Or even using a bamboo as a material for members? But are there also applications that can use a bamboo as a material.

@PanosP: I am now a little bit confused about the way space frames and thin concrete shell roofs are calculated. At the "Space structures" book there is a section about space frame calculations. And there says, that it can be done:
a) by calculating the space frame as a structure consisted of members - mesh
b) by calculating the space frame as continum - some kind of a thin concrete shell roof.

Now what is the difference between this b) method and the calculation of the thin concrete shell roofs?

I read somewhere that the problem at Space frame joints (the ones with less stiffness - for example the ones at two layer space grid) is in achiving this less stiffness of the joint - so that it can not bear a moment.
What kind of other investigation can be done related to this space frame design/dimensioning/improving

[PanosP]

@george85
Thin concrete shell roofs are nowadays mostly calculated by the use of finite elements methods and particularly shell elements. Most of the current software however will allow for the use of orthotropic element properties (ie different behaviour in different axes). In the case of unstiffened thin shell concrete roofs isotropic conditions may be assumed while for stiffened (ribbed) concrete shells orthotropic conditions should be accounted for.
In the past with less advanced or even lack of personal computers engineers would traditionally analyze such structures with the use of grillages which you can say they are the equivalent of the beam element space frame analysis. This method is still used for the assessment of such structures especially by more experienced engineers.
Nowadays, it is often quicker to model space frames with the use of shell elements. This is done by assigning the elements the equivalent stiffness of the space frame (upper and lower chords contribute towards the bending and axial stiffness while diagonals contribute towards the shear stiffness of the structure).
However, a word of caution, modelling space frames by shell elements will only assess you in the macroscopic behaviour of the structure (ie order of magnitude of deflections, overall buckling, initial sizing of the members etc.). In order to perform the final/detailed design I would think that you cannot avoid the use of a space frame model.
For concrete shell structures though, with the exception of high stress concentrations, you can get away without having to model it by the use of shell elements.
Hope this helps.

[marian33]

On your question on what would be the main thing to focus on researching and doing the Phd thesis, for me you should focus and check whether you know what a thesis statement is all about. If you will do that, you can effectively do your thesis.

[s0p9015]

Dear George,
Regarding question on the similarity between space grid and shells, I guess the analogy lies in the calculation of space frame members using the membrane solution for shells. Imagine that if your unit grid becomes infinitesimal, you are approching a continuum. At the end of the day, it's only a member with either in tension or compression and how you re-orient your selected materials in the most economical way to obtain the lightest and perhaps most economical way.

Also with all due respect, you should slightly change a bit of the way you look at the thesis. I am pretty sure that there are quite an interesting aspect of architecture that you may overlook. I am also a structural engineer not an architecture but I think aesthete is as equally important as engineering. The client seems to put more focus on architecture and sometimes make us a non-entity but that's OK as long as they pay me the bill.

The most important when you start doing a Ph.D research, you need to beleive in what you are doing. Otherwise, you might end up struggling on the way. If you try to change the topic, you might also end up with an argument with your supervisor(s) or some of the committee members and end up in troubles. Politics is alway there. If this happened, you could end up losing your valuable time and effort without getting your degree that you are aiming for.

Anyway, good luck with that. I'm pretty sure that you can make it.

[george85]

I am still not sure what am I going to do with this thesis.

I suggest to search the literature for what other architects have done on space grid structures, then go and and propose a light-weight three-dimensional grid structure for an existing and hypothetical structure with emphasis on the structures ability to bear load. For example you can select new materials that are becoming more popular in construction these days: fiber-reinforced polymers, come up with a space-grid structure and see you can handle the aesthetics and structural design/form.

I did not achieve to find the necessary info for creating a new material in structural analysis software (I am using RFEM and RSTAB - they are the same). I did found some info about fiber reinforced polymers, but I do not think that they can be implemented on my tube cross-sectioned space frame. I think those characteristics of carbon fiber I found are maybe for cloth shape not, tube (there Young's modulus is 450GPa !!!). Any help in finding the necessary characteristics for this material?