spaghetti bridge report
MCD 4270: Project 1 Page 1 MCD 4270 –FASTER, LIGHTER, STRONGER PROJECT 1: SPAGHETTI TRUSS BRIDGE 1 INTRODUCTION Welcome to your first MCD 4270 design and build project as an engineer. Your task is to design, analyse and construct a truss bridge, made from dry spaghetti and hot glue, which will be known as the MCD 4270 bridge. Your spaghetti truss bridge is to be as lightweight yet as strong as possible; these are, however, opposing requirements. The bridges will be tested in the week 6 practical class. You will be required to provide design calculations to support your build and predict your bridge failure load. Your bridges will then be loaded to destruction to test their strength and the accuracy of your failure load prediction. In order to gain a deep understanding of the practical and theoretical aspects of Structural and Materials Engineering, you will also be required to carry out experiments (labs in week 1-3) to find the required material and geometrical properties of the spaghetti for your bridge design. This project will unify much of the theory of the first four weeks of the course that can sometimes seem to be unconnected. By building and testing and carrying out supporting design calculations, it is hoped some of the fundamentals of materials engineering and structural engineering design will become clearer to you. You will also practise teamwork skills, drawing on other people's abilities, experiences and perspectives, and contributing your own to support others. Your team’s assessment of your teamwork performance will be a contributing factor towards your individual project mark. You will be working in teams of four that will be allocated to you in your first practice class in week 1. Timetable clashes will be the ONLY reason to change teams and practical classes. In the first five weeks of semester you will come together in the weekly practicals to undertake tasks such as teamwork development, labs to derive spaghetti material properties, tensile testing and problem solving and work on your bridge design. You may choose to also spend time outside of classes as a team to refine your design. This brief is to be read in conjunction with the three labs scheduled in the first three weeks of semester, which cover the materials and geometrical testing of the spaghetti bridge itself. MCD 4270: Project 1 Page 2 2 MATERIALS AND EQUIPMENT Each team will be provided with a Monash College backpack containing all the materials and tools required for this project. On receiving the backpack, immediately fill in the ID tag with your team number and contact details. You will take this backpack away with you and return it in week 6. It is your responsibility not to lose the backpack and to bring it to every practical class in the first 6 weeks of semester. The pack and its contents must be returned at the end of the project. Some of the items in these kits are considered ‘consumables’ and do not need to be returned at the conclusion of the project. Most parts however will need to be returned in good working condition, and these will be checked off by the demonstrators. A cost may be incurred by the team for any lost or damaged components. Project marks will be withheld from the whole team until such time as your backpacks are returned. No substitution of any of the construction materials will be allowed during assessment tasks. Your Monash College Bridge backpack contains: Consumable Materials 2 x Woolworths Homebrand Spaghetti 500g packets 1 x Bostik HG3 Glue Stick packet (collect replacements when required) 1 x roll of masking tape 1 x permanent marker Equipment Provided (must be returned) 2 x Bostik HG3 Glue Guns 1 x Extension Lead 1 x 4-Outlet Power board with Switches 4 x Safety Glasses 2 x 300 mm Steel Ruler 1 x Digital Scale 1 x MDF Bridge Loading Plate (to load the bridge) PLEASE check you have all these items on receipt of your backpacks and come and collect missing items from the collection point at the front of the room. If you have more than the specified quantities above please return them for use by other teams. The following will be available during the laboratory sessions: Digital Vernier Calipers (to measure the spaghetti diameters). 600x900mm MDF boards (to form truss bridges and glue on). These boards are NOT to be removed from the room. If you wish to take away a half constructed bridge it is your responsibility to ensure its safe passage. A loading hanger container and washers (for lab 3) Guillotine for cutting of multiple strands of spaghetti at once MCD 4270: Project 1 Page 3 3 SAFETY & HOT GLUE GUN USE Good safety practices are of paramount importance in the Engineering profession, and applicable to you as students. Please exercise caution and common sense, particularly noting the following precautions: Safety glasses MUST be worn at all times when in the proximity of hot glue guns, whether you are actually using the guns yourself or not. Never point the guns directly at anyone when squeezing the trigger. Teams found not wearing their glasses will be warned once and if repeat offenders, they will be penalised in their lab marks. All gluing must be performed on the MDF boards provided. Laying the provided baking paper on top will allow easy release of the glue. Rest the gun on this board when not in use. Always use the stand on the gun to ensure that the tip does not contact anything when not in use and to ensure the gun does not clog up. Be careful using the glue guns, as they can cause burns. Immediately notify a member of staff if you burn yourself so first aid can be administered. Ensure that any excess hot glue is not left where others can inadvertently come into contact with it. Cover it with scraps of paper. Never leave hot glue guns unattended when they are on, or near flammable materials. Ensure guns are cool before packing them away in your backpacks. Packing away guns when still hot causes them to clog up. Never leave guns turned on when there is no glue in them and always have them resting on their stands so the glue flows into the nozzle. Never pull a half used glue stick out from the gun as this causes clogging. If you are found to have damaged a glue gun due to misuse and not following the above precautions you will be required to replace the gun or pay for a replacement. Maintain a clean and tidy work area. At the end of your session ensure all excess materials and offcuts are collected and disposed of appropriately and boards are returned to their supply location. You will not receive an assessment stamp on your lab work until you have done so. MCD 4270: Project 1 Page 4 4 PROJECT SPECIFICATIONS This section outlines the requirements for the bridge construction. 4.1 BRIDGE BUILDING Form A truss bridge is a structure made of connected members which form triangular units. Your bridge is to be of truss design and it must comprise two identical, planar, parallel trusses lying in the x-y plane. Refer Figure 1. These trusses must be determinate (see following section on ‘Where to Start’), to ensure that the structure can be analysed using techniques taught in the unit. Please note: the diagonal members in a truss are at their most efficient when angled between 40-50° from the horizontal. It is expected that you will trial various designs in order to select a truss form that optimizes the parameter Strength-to-Weight ratio (SW), while being relatively fast to build (refer Section 5.3). So start experimenting early. Materials and members Your truss bridge is to be made only from the spaghetti and hot glue provided. Glue may be applied at any location, but in the interests of minimizing weight and increasing structural efficiency, teams should attempt to minimise the amount of glue used. Members (between joints) may comprise single or multiple strands of spaghetti. A maximum of 3 bundled strands is allowed to make one member. Bridge measurements The bridge is to span 800mm between two tables as shown in Figure 1. It must only be supported by resting on the horizontal surfaces of the tables at each end. Thus fixing to the tables by any means is not allowed. It is recommended that no bridges be shorter than 825mm or longer than 850mm, to allow sufficient support from the tables. Load will be applied to the bridges using the loading plates found in your backpacks which must be positioned 50mm above the table supports, i.e. the centre height of your bridge is to be 50mm above the table tops. Your bridge is, however, allowed to protrude below the table supports. All bridges are to be 130mm wide in order to support the loading plate, and to have sufficient sideway stability. The shortest spaghetti member length, i.e. length between glue joints, must be greater than or equal to 100mm. Loading plates and loads Loading plates can be found in your backpacks. They are made from 150mm x150mm MDF board with soft foam adhered to one side. The foam side will be the one to come into contact with your spaghetti bridge, so as to provide a soft loading point and not accidently snap the spaghetti it comes into contact with. These plates must remain completely removable (i.e. cannot perform any structural function). MCD 4270: Project 1 Page 5 The loading plates will be placed centrally on the top of your bridges for testing. Trusses perform best when loaded only at their joints (and this is also one of the assumptions when analysing your truss), so a truss geometry should be chosen such that the loading plate sits centrally over typically four of the upper joints in your truss. Ensure these joints have glue or spaghetti protruding slightly higher than