Is this steel project doable?

[hopeless]

Hello Science Buddies community. I've recently been assigned to select a science topic for the school science fair. i've been sort of interested that fire (from what i've heard) weakened the steel columns supporting the WTCs which may have increased its chances of collapsing. I've also heard that the steel columns of the buildings weren't encased in concrete (which, I guess, is believed to be more fire resistant). So, I'm planning on having thin, short steel columns (probably 1 inch in diameter and 2 ft high?) being exposed to fire to then be subjected to forces. Then do the same to steel columns encased concrete. I'd like to know if this project is even capable of being done by me. My budget is probably $120 max and I'm very intimidated by my physics teacher (don't understand her accent). Would a bunsen burner be efficient enough to heat steel enough like what happened at the world trade centers? Also is steel even available in those dimensions? And is it sold not in bulk? What are it's prices?
additional info about my capabilities:
i'm new in physics and so far we just learned about vectors.
i'm in precalculus but I am very slow in doing calculations.
i am a poor at time managing.

Thank you for your time.

[Craig_Bridge]

You should do a literature research into "Temper" or "Hardness" of steel to help understand one of the metal properties that help to give steel strength and to understand how one hardens and tempers steel and an understanding the role heat and temperature change plays in changing these properties.

You should also do a literature search into how beam cross section affects the strength of a beam.

Prestressed steel reinfoced concrete beams rely primarily on the concrete for strength. The rebar (steel) embedded in concrete is normally only used to prevent fractures in the concrete from causing catestrophic failures. You might want to think about how cylindrical shaped wooden beads strung on a taut string through their middle will resist bending.

I would recommend using significantly smaller pieces of steel in your experiments. A one inch diameter steel rod 2 feet long has a lot of strength and its thermal mass is much more than what a bunsen burner can heat up near enough to the softening point in any reasonable amount of time. You probably want to use something closer to #9 steel wire (about 1/8" diameter) if you are planning on using a bunsen burner to be able to heat bend it.

My understanding of how most fires affecting high rise steel structure catestrophically are cases where the heat softens the horizontal beams and they sag which then pulls in on the vertical members. Once the vertical pieces are no longer plumb, they soon become overloaded causing additional bending which leads to a catestrophic failure.

[barretttomlinson]

Hi,

You might investigate using a Meeker type burner rather than a Bunsen type burner. The Meeker burner has a wide top with a metal mesh on top, where the Bunsen has an open tube with less air gas mixing below the top of the burner - the result is the Meeker has a hotter flame.

It sounds like you have a good project idea! Best of luck with it!

Barrett Tomlinson

[hopeless]

AHHH. Man i'm really mad. I'm sorry for lashing out like this but I just spent about 8 hours (4 pm - now 12 am) writing a reply then screwing up by pressing a link on the page by accident, effectively erasing everything. I'm really sad. I was sooo close to finishing too! I even was going to copy and paste before I posted (since I know that there's a time out function)! I only needed a few more sentences...

Anyways, thank you both for replying.
I have to be less descriptive now since I slept at 3:00am yesterday and now I'm feeling tired and I have to submit my project topic (complete with reasons) by tomorrow at 7 pm. Haha, as mentioned, I have very poor time management skills.

I came across a lot of jargon in researching temper and hardness, as well as the cross beams. Gah all of my paraphrasing is gone so now i have to quote to show what i learned.
Temper

Typically steel is heat treated in a multi-step process. First it is heated to create a solid solution of iron and carbon in a process called austenizing. Austenizing is followed by quenching to produce a martensitic microstructure. The steel is then tempered by heating between the ranges of 150°C-260°C (300°F-500°F) and 370°C-650°C (700°F-1200°F). Tempering in the range of 260°C-370°C (500°F-700°F) is sometimes avoided to reduce temper brittling. The steel is held at that temperature until the carbon trapped in the martensite diffuses to produce a chemical composition with the potential to create either bainite or pearlite (a crystal structure formed from a mixture of ferrite and cementite). It should be noted that when producing a truly bainitic or pearlitic steel the steel must be once again taken up to the austenite region (austenizing) and cooled slowly to a controlled temperature before being fully quenched to a low temperature. In bainitic steels, upper bainite or lower bainite may form depending on the length and temperature of the tempering process. It is thermodynamically improbable that the martensite will be totally converted during tempering, so a mixture of martensite, bainite, ferrite and cementite is often formed

http://en.wikipedia.org/wiki/Martensite Martensite is not shown in the equilibrium phase diagram of the iron-carbon system because it is a metastable phase, the kinetic product of rapid cooling of steel containing sufficient carbon. Since chemical processes (the attainment of equilibrium) accelerate at higher temperature, martensite is easily destroyed by the application of heat. This process is called tempering. In some alloys, the effect is reduced by adding elements such as tungsten that interfere with cementite nucleation, but, more often than not, the phenomenon is exploited instead. Since quenching can be difficult to control, many steels are quenched to produce an overabundance of martensite, then tempered to gradually reduce its concentration until the right structure for the intended application is achieved. Too much martensite leaves steel brittle, too little leaves it soft.

Hardness

Hardness is a function of the Carbon content of the steel. Hardening of a steel requires a change in structure from the body-centered cubic structure found at room temperature to the face-centered cubic structure found in the Austenitic region. The steel is heated to Autenitic region. When suddenly quenched, the Martensite is formed. This is a very strong and brittle structure. When slowly quenched it would form Austenite and Pearlite which is a partly hard and partly soft structure. When the cooling rate is extremely slow then it would be mostly Pearlite which is extremely soft. Hardenability, which is a measure of the depth of full hardness achieved, is related to the type and amount of alloying elements. Different alloys, which have the same amount of Carbon content, will achieve the same amount of maximum hardness; however, the depth of full hardness will vary with the different alloys. The reason to alloy steels is not to increase their strength, but increase their hardenability — the ease with which full hardness can be achieved throughout the material.
Usually when hot steel is quenched, most of the cooling happens at the surface, as does the hardening. This propagates into the depth of the material. Alloying helps in the hardening and by determining the right alloy one can achieve the desired properties for the particular application.
Such alloying also helps in reducing the need for a rapid quench cooling — thereby eliminate distortions and potential cracking. In addition, thick sections can be hardened fully.

I didnt learn much about cross sections

the cross section of the beam affects its strength in a manner depending upon the moment of inertia and the depth of the cross section, both measured from the neutral axis. For any given cross section these quantities are constant, and hence do no enter into the diagrams presented in this book since each standard shape is represented by a separate diagram, or, in the case of spandrel or grillage beams, each shape is represented by a line on the diagram

Apparently for the WTCs

the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.

It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C.4 This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire

The perimeter tube design of the WTC was highly redundant. It survived the loss of several exterior columns due to aircraft impact, but the ensuing fire led to other steel failures. Many structural engineers believe that the weak points—the limiting factors on design allowables—were the angle clips that held the floor joists between the columns on the perimeter wall and the core structure (see Figure 5). With a 700 Pa floor design allowable, each floor should have been able to support approximately 1,300 t beyond its own weight. The total weight of each tower was about 500,000 t.

As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell.

Questions:
How will I know what category/phase of steel the steel wires will be (pearlmite, cementite, martensite)? Do they sell #9 steel wire at places like Lowe's or Home Depot?

How would I exert a controlled force on the steel, and how long should I wait after exposing it to heat? How do i measure the force? What is the maxium temperature of a bunsen burner?

If

Prestressed steel reinfoced concrete beams rely primarily on the concrete for strength. The rebar (steel) embedded in concrete is normally only used to prevent fractures in the concrete from causing catestrophic failures. You might want to think about how cylindrical shaped wooden beads strung on a taut string through their middle will resist bending.

then I guess my experiment will have no purpose? Also why would the beads bend if it is on a straight string (sorry if i misinterpreted that)?

also i found that concrete-encased steel columns are blast-resistant, energy-absorbing materials. does that mean they abosorb heat, or does this have nothing to do with heat?

What if you put that metal thing with mesh on top of a bunsen burner; would that give the same effect as a Meeker?

Also, this steel thing seems to be related more to chemistry (which in my class last year, we barely covered half the book).

Ugh, I had so much more questions but they're all gone. I'm sorry if I was not coherent or if I didn't provide enough details explaining my problems. I'm sorry but I'm very sleepy and extremely frustrated in not deciding to type my reply in word before posting.

I'm also beginning to think that since this project no longer has a purpose (Prestressed steel reinfoced concrete beams rely primarily on the concrete for strength. The rebar (steel) embedded in concrete is normally only used to prevent fractures).
if this project is not doable, I am sorry for wasting your time.

[Craig_Bridge]

How will I know what category/phase of steel the steel wires will be (pearlmite, cementite, martensite)? Do they sell #9 steel wire at places like Lowe's or Home Depot?

Without a lot of anaylsis equipment or knowing the manufacturer, you aren't going to know the category/phase of steel wire. I would hope that you can buy solid steel wire at Lowe's, Home Depot, and Ace Hardware. It doesn't have to be AWG#9, I just threw that gauge (diameter) as an indication of the approximate size of something that you could easily experiment with. Something that is stiff enough to take more than your fingers to bend it but not stiff enough that you need expensive equipment to apply enough pressure to bend it.

How would I exert a controlled force on the steel, and how long should I wait after exposing it to heat? How do i measure the force? What is the maxium temperature of a bunsen burner?

You will have to come up with something. Think about using some fire bricks to hold the ends of the piece under test. If you apply the force via gravity, then knowing the weight you use will tell you the force. If you let the piece cool, tempering will occur. I'd recommend applying the test force while heating the test article. After all, this what happens in real life situations like the WTC. This means that whatever you use for weight and attaching it will need to be heat resistant to about 2000 C. See http://www.engineeringtoolbox.com/flame ... d_422.html for flame temperatures of various gases. You will probably get something between 1950 C and 1970 C if you adjust the air mixture to get a bright blue natural gas flame.

then I guess my experiment will have no purpose?

Since it is similar to comparing apples and oranges (both fruits or in your case beams), I'd recommend doing something similar that avoids introducing as many variables as possible.

Also why would the beads bend if it is on a straight string (sorry if i misinterpreted that)?

I'm just trying to get you to think. If the string through the cylindrical beads is taut, then bending between the beads puts more tension on the string through them and they don't bend as far. If the string stetches or isn't as tight, the bead "beam" will bend with less force applied. Reinforced concrete beams are similar. The rebar behaves like the string and the concrete encasing it behaves like the beads.

does that mean they abosorb heat, or does this have nothing to do with heat?

I can't think of anything that can't be heated and cooled which means most things can absorb heat. When you heat ice, it melts into water. When you heat water, it evaporates and forms water vapor. These are called state changes. The properties of most materials is highly dependent on what state it is in.

What if you put that metal thing with mesh on top of a bunsen burner; would that give the same effect as a Meeker?

Sorry,I don't know what you are talking about. There are some metal flame spreader attachments that will spread out the flame of a bunsen burner and make it behave more like a Meeker. In any case, the whole idea is to heat up enough volume of the wire to soften it.

I'm also beginning to think that since this project no longer has a purpose (Prestressed steel reinfoced concrete beams rely primarily on the concrete for strength. The rebar (steel) embedded in concrete is normally only used to prevent fractures).
if this project is not doable, I am sorry for wasting your time.

Nobody designs a great science fair project in their first stab at it, NOBODY! The whole scientific inquiry process is usually an evolution and adjustment process. You come up with an initial idea of something you are interested in (you've done that part!). You ask some initial questions (you've done that part!). You do some background literature research to learn what others know about your area of interest (You've done the first round!). You then adjust and refine what you want to do (you're struggling with this a bit). Welcome to the scientific journey.

You should read up on the scientific method on this web site to get more insight into the process. You should think about how you can state a hypothesis to make it doable and interesting. At this stage of your project, we don't want to help you too much because we want it to be your project and your idea, one that interests YOU!

[ChrisG]

Hopeless,
I just wanted to add to Craig's advice to say that you should certainly not give up on this project because of the few unexpected surprises that have come along so far. You might adjust your scientific hypothesis and methods as you learn more about the problem, which is true of many good science fair projects. The structural integrity of steel under thermal stress is an important topic with many different potential applications. Hang in there!
Chris

[hopeless]

Sorry for replying so late. Thank you Mr. Bridge for answering my multiple questions as well as for your reasuring and uplifting guidance. I also thank you Mr. Chris G. for encouraging words.

Not Important Things:
Anyways, I haven't been up to much since my last post (poor time management, yet again ). I was able to, however, submit my topic with a bit of background info by the due date (turned it in about 5 minutes before the deadline). There's no need to read it since this is just a rough background we were supposed to send to our teacher, but I'll post it anyways (if anyone does read it, can you pleas point out where my information is wrong)?

After the World Trade Center collapsed, I started to think, "Why did a building made of steel, the strongest alloy, collapse?" I heard rumors that the steel of the twin towers melted, causing the collapse. Of course, I'll find out later why this is just not true. I have also found out that in the process of my research that the World Trade Center towers were designed as new high-rise towers (after WWII). This meant that these towers used more steel and shaped lightweight steel into tubes, curves, and angles to increase its load bearing capability. However, high rise designs reduce the number of concrete used significantly (compared pre WWII buildings such as the empire state building). Many people believe that since the steel columns supporting the towers weren't encased in concrete, the fire resistance was not as good as it could have been, causing the distortion and loss of strength, ultimately resulting in the building falling in just one to two hours. From this came my research question; is concrete encased steel more fire resistant than steel by itself?

First of all, I had to find out more on steel and what it was. Steel is heat treated in a multi-step process. The first phase of steel, austenite (created by heating iron and carbon), is quenched and in the process transforms into martensite. Martensite is strong but is very brittle which is why it is tempered (heated to diffuse out the carbon) to transform the alloy into having a different structure. Basically the concentration of martensite is reduced until it leaves the right structure (which depends on what the steel is to be used for). Too much martensite leaves steel too brittle, too little leaves it soft.

Now that I understand more about how steel is created, I'll need to find out more on its strength. Apparently, the tensile strength of steel can withstand 40,000 pounds of force per square inch, or PSI. Concrete on the other hand, can withstand between 3,000 to 10,000 PSI, depending on the mixture.

Structural steel doesn't melt until about 1510°C. Thus, this makes the rumor of the steel melting false. But structural steel does begins to distort and soften around 425°C and loses about half its strength at 650°C. However, Leslie Robertson, a structural engineer who had helped built the WTC towers, has said that steel and concrete at various temperatures showed that at the heat levels experienced by the towers, the two materials become similarly weak. Many people however think that the more mass there is, the more fire resistance there will be.

It is said that the failure of the steel in the World Trade Center towers was due to two factors. These were the loss of structural integrity due to the distortion of the steel from the non-uniform temperatures in the fire, and the loss of strength due to the temperatures of fire. If there was only one factor, the building would have stayed up much longer. Thus, I will test whether or not concrete encased steel will have more strength when exposed to heat than compared to steel alone. This experiment will be conducted on a much smaller scale than the world trade center of course. I am planning on using steel wires, a Bunsen burner, and weights (to act as forces on the heated steel). This topic is important because if it is found out that concrete encased steel is more fire resistant, then building architects should be advised to encase their steel columns supporting the buildings with steel to increase the chances of the survival of the people inside.

Ha, you can tell it was a rush job.

Questions:
So I guess my hypothesis can now be "If the concrete encased steel is believed to have more fire resistance than steel alone, then when the concrete covered steel wire is exposed to heat, it will take more force to bend it than when steel wire alone is exposed to heat and has a force exerted onto it." I don't know, just made that up, and it doesn't really sound right. Now that I made my hypothesis...hmm.

Wouldn't the concrete, regardless of whether or not it is exposed to heat, increase the strength of the steel wire anyways? And if the fire services believes there is a direct relation of fire resistance to mass of structure, wouldn't it be better to test steel that is the same length as the concrete encased steel wire but has a different diameter in which the mass would equal the concrete encased steel wire? Also, how would I cover the steel wire in concrete? Does the concrete need to be evenly spread? Also, if steel can withstand 40,000 PSI, and 20,000 PSI at half its strength, then why is a steel wire able to bend at smaller forces (I think it's because it's smaller but is there a more scientific explanation)? And how would I measure force per square distance (like Newton per square sm)? I think I'll be able to caculate the force part (thanks Mr. Bridge) but as to how would I calculate the force per area, I have no clue. Or do I only need to calculate for force in this experiment?

And back to heat; I believe we were supposed to go over heat in my chemistry class last year but the teacher barely covered half the book. Through this research, I learned that heat is different from temperature. If so how would I calculate the amount of heat the steel wires have? Would I still use a thermometer (are there thermometers in school that go up to 650°C)? Or do I just need force for data?

Oh wow, I went from a relatively content to as abysmal as I was at my last post. I think I have a lot more questions but since I'm so sleepy, I can't seem to remember them. I think I'm asking this board too much questions and if I am, please let me know. I am, however, truly grateful for the help I have received so far and will be for any new replies, suggestions, or criticism.

[Craig_Bridge]

Wouldn't the concrete, regardless of whether or not it is exposed to heat, increase the strength of the steel wire anyways?

You have quite a few differences to deal with. If you utilize a high grade concrete with appropriate dimensions encasing rebar, you will likely have a much stronger beam than just what the rebar alone would make. If you don't construct it well or use a poor grade concrete, you might end up with a beam that will hold less additional weight (The weight of concrete that is not helping with the load bearing will actually be a load on the rebar beam and you would be better off without it). At this point, you need to do some extensive literature searches into pre-stressed reinforced concrete beams. They are much more complicated than steel beams. Building high rise structures with concrete pose some additional problems because the concrete beams are heavier than equivalent strength steel beams. For an equivalent sized building, there will be a huge difference in weight which makes footings and other design issues more difficult.
Beam Shape I mentioned this earlier. You really need to do some more research to understand how the depth and width and thickness of a beam affect the length of a steel beam that will carry a dead and live load with a given deflection.
Heat and Thermodynamics vs Temperature Look up Heat. You should find that it is related to energy. In short, the amount of energy it takes to raise or lower the temperature of some mass some number of degrees of temperature. Thermodynamics is the study of heat transfer and energy states and other properties associated with temperature changes. Temperatures associated with fires are typically measured with thermocouples, an interesting research project simply on their own.
Exact wording of Hypothesis The precise wording of your hypothesis will determine what you have to measure