What was the flaw in the design of the Tacoma narrows bridge that cause it to collapse?
im studying for a science exam and this was a question that we needed to find the answer to on our own. I've looked all over the internet, but its not on wikipedia or answers or any of the first couple of pages of google. i just need to know what was wrong with the bridge that allowed the wind to break it.
How can a truss structure be stronger than a beam when in fact it has less material?
There are a lot of different ways to look at why this happens, but hands-down my favorite approach is to think about Buckling.When you apply load to a column and it’s really thin, it will deflect to the side instead of taking the load, which is called buckling:When you bend a beam, it puts a lot of compression and tension in the top and bottom of the beam. The further you can get material away from the center of the beam, the more of the bending force that material is going to be able to take:I-beams are good designs because they move a lot of material to where the compression and tension are the strongest, far away from the centerline:But, the downside of this is that the “flanges” of your I-beam can act like a thin column and buckle, which is called Lateral Torsional Buckling, and looks like this:Also, as you bend your beam, the top and bottom of the beam are trying to slide away from each other. You can see this in action by trying to use a stack of thin sheets of wood/plastic/etc like a single beam:This sliding (called shear flow) puts a lot of compression into the web that connects the two parts. If you’ve put the top and bottom of your beam far enough apart, then your web will act like a column and buckle too, which is known as web buckling.This video highlights it pretty well; keep an eye out for ripples that form in the web of the beam:Sometimes people will put in stiffeners to prevent this buckling; these stiffeners actually don’t wind up holding much load at all, and so the material is poorly utilized:So, we’ve seen that if you make the sections of an I-beam too thin or too far apart, they will start to buckle, just like a column.In general, pretty much any part of a beam can buckle if you make it thin enough. That means you often wind up having to add unnecessary material all over the place; this is why cables (which are in pure tension) are the smallest structural elements.Trusses circumvent this problem by lumping the material into smaller, unconnected elements. These shapes are less susceptible to buckling, and so you can make more efficient use of the material that you have.In the end, you wind up with a lighter but more complicated structure.I hope that makes sense!
Why is an I-beam shaped the way it is? How did an I-beam's eventual final design come to fulfill its primary function?
When a beam bends the top of the beam is in compression and the bottom is in tension. These forces are greatest at the very top and very bottom. So to make the stiffest beam with the least amount of material you would want the material to be only at the top and bottom sides. However you still need to connect them together or they would just be two separate plates and would not be stiff at all. So you put a web in the middle to connect them and make them work together. The resulting shape is the traditional "I-beam" or wide flange beam.This shape is used when the load is parallel with the flange. As you can see, the shape is not so good with lateral forces unless you turn it sideways. When the load will come from two directions, a square tube is used. In all these cases the idea is to remove material that is not carrying much load and concentrating the material where the load is highest. Increasing the depth of the beam increases the bending strength by the depth cubed, so we can gain a lot of stiffness this way. However, we start to get limited by things such as buckling when the sections start getting too thin. When folded sheet metal studs are used, this is done by placing a small bend (lip) at the end to add stiffness.You can experiment with these structural shapes with some cardboard or popsicle sticks and glue to get a physical understanding of how they work, or look in any structural engineering text book (Statics) for details on how to calculate.
How can I design a wooden truss?
Firstly you have to have some figures for the building , such as its width and length also what the roof covering is going to be so weight distribution can be calculated . From the width and length the span can be ascertained and the spacing of the trusses . There are tables that tell you what safe spans timber sizes can be used and what loading they will carry , recommended truss spacing based on loading and timber size used. You can also look at other buildings and see what was used in that circumstance , is it similar in size , design and weight loading . Generally trusses are over specified by about 30 % this can allow for weaknesses in timber , snow loading etc . Truss design can be simple to quite complex depending on the circumstances . Such things are best left to structural engineers or those with equivalent qualifications . Unless of course it's for a garden shed or similar .
Am I too heavy to go up in the attic? (300 lb) House built in 1976 - single story.?
I don't have a ladder. Just a little access hatch. I have to use a regular ladder to get up there. (Growing up, we had no chimney, so my mom told me that Santa Clause came through that little door. I have to think I'll look a little like that coming down.)
How would go about useing 3 2x6s instead of 1 6x6 for building a pole barn?
First you need to establish the level of treatment in the 2x6's. If they are not treated to a .25 or .40 level they will rot in the ground. The 6x6 will be treated to a .40 level as this is the most common application. Do not use anything less than .25 for ground contact. This can be determined by the tag that is attached to the end of the lumber. If you are satisfied that the lumber is sufficently treated, then just take the boards and lay them one at a time on top of each other and screw them together with exterior deck screws. You can make them stronger by applying exterior construction adhesive between each of the boards and drilling through all three of them and bolting them together with galvanized carraige bolts. If the building walls are to be 12 foot in height, you will need at least 16' post to give you enough height to put them 3' in the ground and still have some adjustment room for any differiences in grade. Cement the post with quikrete concrete mix or you can use pea gravel and tamp it tightly in the holes tightly
How can I make a rcc slab without any beam?
Yes it is possible to design slab without any beam. By using FLAT SLAB , it is a reinforced slab which built monolithically with the supporting column only. Load is directly transfers from slab to the supporting column. In the construction of flat slab we have to provide :1) Drop. 2) Column head or column capital.Drop is a part of the slab around the column, which have greater thickness than the rest of the slab.And in capital column or column head , the diameter of the supporting column is increased below the slab.Flat slab is design by two methods1) DIRECT DESIGN METHOD . 2) EQUIVALENT FRAME METHOD.You can design the flat slab according to IS CODE 456:2000.Advantages of FLAT SLAB1)Thus a plain ceiling is obtained, giving attractive appearance. 2) The plain ceiling diffuse the light better.3). Cheaper form work thus reduced the construction cost.Flat slab is constructed in case of large span and heavy load.
What is the lightest, most efficient holding truss or bridge design for a toothpick bridge?
From my experience, the easiest and most efficient will be the Warren truss, but a variation of it so that it is actually triangular in cross section - not exactly like you see in real bridges where the truss sides are actually vertical and require bracing in both top and bottom.This is a design I’ve used in Arch school and I was able to hold multiple (I think x12) full sized bricks with. A second identical structure wrapped in trace-paper was actually able to hold 19 bricks before being crashed. The Sketchup model below is not to scale, but you can extend it to meet your span and stick # requirements.It is actually made out of 3x main assemblies: the “sides” of the truss that are fully triangulated in themselves and act like sistered beams , and the bottom part that is the cross-bracing for the 2x sides.The exact angle of the 2x side assemblies is actually informed by the length of your sticks / toothpicks - remember that each connection point or “node” needs to be triangulated in 3D as I am trying to illustrate in the section below:Make sure you use properly mixed epoxy glue. It takes time to cure, but it is easily the best shear resisting bonding method. Second best is wood glue. CA (instant) glues are fast, but do not withstand shear and tension as good as your bridge will be demanding of them. A good glue will exceed the tensile and shear resistances of the wood it holds together - i.e. the bond should break after the wood itself breaks and not the other way around.Give your sticks/toothpicks some good overlap - at least in parallel members, otherwise the glue won’t have enough surface to adhere to.Triangulate all your connections, in 3D.For ultimate strength - and if it is inline with the rules of your “competition”, you can wrap the assembly with tissue or trace paper.This is how the last one I’ve build in my Architecture school did (span 36in):
For a school project, I need to build a cantilever that extends as far as possible over the side of the table into empty space. I only have access to 50 straws, tape, and scissors. Only one straw can be in contact with the table. How do I do this?
Better definition is needed. Can that single straw be in separate pieces? You need a piece that supports the fulcrum and a piece that supports the counterweight. Can you use the tape to secure the counterweight to the table? Probably not. If some of the straws are needed for counterweight, that impacts the length of the overhang.You should start with calculating how much counterweight you can use vs how many straws you can use for the structure. A triangle shaped truss with minimal width at the overhanging tip. Keep in mind that straws under tension can be cut into narrow lengthwise strips. Even the tape could be cut into tension strips.