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Situation: To design, build and test a truss in room A140. Problem: To design and test the strongest possible truss using the least amount of material. The truss must span a 220 mm gap. Investigation: 1)What is a kingpost ? King post is the middle supporting part which goes from the top to bottom. 2)What is a bottom cord ? The bottom cord is the bottom piece of a truss. 3)What are the top cords ? Top cords are the two pieces that come down at angle. 4)What is a lap joint ? Two popsicle sticks that overlap each other is called a lap joint. 5)What is a butt joint ? Two popsicle sticks that meet head to head is called a butt joint. 1)What is a truss ? A truss is a framework of beams or bars built to support a roof , a bridge etc. 2)What are gussets ? Gussets are metal plates thatare fixed over several beams meeting at an angle to make joints stronger. 3)What shapes do trusses come in ? Trusses have just about any shape because they are custom built. 4)What are advantages of using trusses ? Trusses are a lot cheaper than the alternative. They are incredibly strong. 5)What is a disadvantage of using trusses ? Trusses tae away all the attic space of a house. 6)How do trusses work ? Trusses transmits all of the weight to the exterior walls of houses. 7)How are trusses put together to build ? Trusses are stacked on top of walls by hand or by small metal plates , they are tied to the wall. 8)Why do builders like using trusses ? They like using trusses because they go up the roof fast and they can save time and money. 9)Why are trusses used very often these days ? They are used because they have a lot advantages. 10)What are trusses made of ? Trusses for houses are made out of wood because it is cheap, easy to work with and it is light. Sources of Information A: By what we have know already, we figured out the definition of truss and gussets. B: There are examples of trusses all around us, a range of different types of truss, notice the variety of shapes and the many are hidden from sight underneath cladding or bricking but there are also many good examples of truss structures left exposed. The range of trusses in use today is quite diverse, they vary enormously in shape and size. C: When we interviewed Andrea Lougheed , I got the definition of kingpost, bottom cord and top cord. I also interviewed Romao Desitva, I asked him: Q: What is the key to build stronger trusses ? A: Only make triangular trusses. Q: What about the joint ? A: Lap joints are much stronger than butt joints. D: Surfing on the interent helped us a lot in finding answers to the question above, we found out the advantages and disavantages of using trusses, the shapes of trusses , how they are put together to the building , what they are made out of and why are they common these days. E: Experimentation By building the prototypes of number two and five, I found out the weaknesses of each. Mainly I learned that my trusses were too short for the testing jig. Truss number two was too thin and it made it weak. The whole thing bent outwards from the top to the bottom. It could only stand 66 pounds of weight. The weak point was the right side of the top cords. Truss number five is really strong. It could hold 128 pounds of weight. It have the same weak point as number two, but it was similar in size. It was twice as strong as number two. It did not bend at all maintainly its firmness until if broke. Truss number five prototype number 2 was strong under compression that it did not even break at the weight of 329 lbs but the glue just came apart. What I learned from this is that gussets are really useful. By dubling the posicle sticks at the triangle frame makes the truss really strong. The strength per weight ration is 7542 grams. The truss that Geoffrey and I built in class was really well done. It could hold 329 pounds of weight. It is twice as strong as the prototype that we did. The weak point is the right top cord. We need to put gusset on it to make it stronger. Idea: -does not hold a lot of weight(66). -very light -Bends outwards from top to bottom instead of taking the force. -uses less materials(8 popsicles sticks). -Beautiful design. Design contains only triangles. -has a big area of weak point at the right top cord. -easy to build and save time . 2) -bends at the joints of the popsicle sticks. -can hold a lot of weight (329 pounds). -2 weak points. -a very strong structure. -it can hold very much (329 pounds of weight). -not easy to build. -take less time. -uses 12 possible sticks . 3) -break easily -use less popsickle sticks(7) -very easy to build with and save much time. -bends outward -very light -weak design -strong gusset -can't fit into the testing jig -save much time -unique design (does not have a kingpost) Choose: My partner and I have decided to choose truss number 5 for the real deal. Even though it takes more rime and is more complicated to build, it can hold a lot more weight than the other two trusses. The strength of this is high, the strength to weight ration is still very high. The weight of the other trusses are light, but due to their strength, the strength to weight ratio is low. There is no point in building a truss that is weak, so going with truss number 5 is the best thing for this technology learning problem. The main reason for this decision is that it holds 329 pounds of weight, which is the highest in the class so far. We used white glue, needle nose pliers and popsicle sticks. Construct: In order to build this truss, we went through 17 steps. Step 1: We cut a popsicle stick at 4.6 cm with a needle nose pliers. We ended up with 4.6 cm piece for the bottom cord and 6.7 cm piece for the kingpost. Step 2 : We used the 4.6 cm piece to joint two popsicle sticks for the bottom cord. We used glue to put them together. Step 3 : The kingpost was glued onto the 4.6 cm piece. Step 4 : We took a popsicle stick and cut it at 3.5 cm with a needle nose pliers. We took the 3.5 cm piece and glue it onto another popsicle stick to form a top cord. Step 5 : We did the same thing as procedure 4, but this time we cut it at 3.5 cm piece from the remaining popsicle stick piece left in procedure 4. Step 6 : We gled the end of the top cord (the end of the 3.5 ccm piece on the top of the kingpost and the other of the top cord under the bottom cord. Step 7: We did the same thing as procedure 6 for the other top cord. Step 8 : We used the remaining piece from procedure 5 and cut out a 3.3 cm piece from 7 with a needle nose plier for one of the four posts next to the kingpos(2 on each side). We glued it on to the top cord and the bottom cord. Step 9 : With another popsicle stick, we cut out a 3.3 cm piece with a needle nose plier to form a ost for the left side of the truss. We glued it on to the top cord and the bottom cord. Step 10 : We cut a 5.2cm piece from the remaining piece. In procedure nine for another post next to the kingpost. Then we glued it onto the top cord and the bottom cord. Step 11 : We used another popsicle stick and did the same thing as procedure 10 to make another post next to the kingpost. Step 12 : With the remaning piece from procedure 10 (2.7 cm ) and glue it onto the center of the bottom cord with white glue . Step 13 : We used the remaining piece from procedure 8 adb glued it onto the butt joint of the 2 top cords at the kingpost. Step 14 : With the remaining piece from procedure 11, we cut it up with a needle nose plier into 3 pieces(each one 2 cm long). We glued them onto the gaps on the top cords. Step 15 : We used two popsicle sticks and glued them on top of the top cords. Step 16 : We used the last 2 popsicle sticks and glued them on top of the bottom cords. Step 17 : We cut on two pieces of cardboard with a pair od scissors(1.5 cm by 4 cm) for gusset abd glued them onto each side of the top cord. This is the last step for building this truss . Evaluation: A:Quantified: When truss number five quantified in calss, it held 191 pounds or 86714 grams. My trusswas 20.4 grams heavy. It's strenght to weight ratio ws 4251 grams. B:Qualified: My truss tured out to be string and not very heavy. Its strengh to wiegh ratio was the highest in the class. The actual strenghts if this thruss are that the gusset are very strong, the truss is very strong under compression and it, can hold a lot of weight considering the size of this truss. The actual weakness of this truss are that it slants when it is fixed on to the testing jig (not standing straight up when the wood presses on it) , due to that it is very weak under bending and the bottom cord of the truss is not stronge enough. It bends and snaps apart under pressure. That is the weak point in this truss. One of the problems that our truss encountered was that it did not fit onto the slot of the truss. We just had to slant over truss to male it fit in. Our truss was hard to fit onto the testing jig without slipping because it had a pointed top. We just had to screw the screw down tight to keep it steady and not slip. Since the glue did not help keeping the bottom cord joints together that well , we had to make sure that the bottom corners fir into the slots really well so that the popsicle sticks do not break apart taht easily. To improve the design, we could have put gussets at the corners of the bottom cord to make to stay together a little better. We could have also make athe top a flat one that it would be easier to fit onto the testing jig. We could have also put them stick together better. Hersha's truss had a flat top instead of a pointed top which it is easier to fit onto the testing jig. Some people like Tony Y. used a lot of gessets(more than us) for his truss . That reduced the weak points og his truss to one or two. Ricky Ng strengthened the frame of his truss by putting several popsicle stick together . He used more popsicle sticks for the frame then for the inside. Geffery and I did not use as much popsicle sticks for the frame as them. From the TLP, we learned that the looks of the truss did not really matter. It's the strengh to weight rations that counts. We alos learned that it 's important to have a light truss that holds a lot of weight than to have a string truss with a heavy weight or a weak truss with a light weigh. We learned that ffrom testing out the trussed and be the top of the class just because our truss was lighter than Patrick's and the strenght of his truss was a little higher than ours. We ended up have a better strebght to wieht ratio than him. We also learned that the way we put the popsicle sticks really changes the strength og truss. Bibliography for Investigation(D): 1) Brian, Marshall. "Roof." How Stuff Works. Online. 2)"Trusses." Trusses. Online. |
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