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Team Burke der Miester's Final Design of RIPSAW.

Abstract

The purpose of this project is to design a safe bridge tester system that is able to measure the strength and endurance of bridges under pressure in pounds per square inch. Through the Engr215 Introduction to Design class at Humboldt state University, students from team Burke der Meister designed a bridge tester machine that will be integrated into the engineering section of the STEAM Program at Zane Middle school for projects and competitions.

Background

Zane Middle School introduced the STEAM program in the fall of 2013 that allowed students to include Science, Technology, Engineering, Art and Math into their already existing curriculum. The uniqueness of the STEAM program allows students to be exposed to design electives for real world situations. Zane Middle School came to the Humboldt State University Engineering Department in the spring of 2014 with the intent to improve their STEAM program. The objective of the engineering 215 group, Brücke der Meister, is to design a system able to test the strength and endurance of bridges under certain conditions for the client. The focus of the project is to construct a machine that measure the amount of pressure a bridge can withstand before breaking.

Problem statement and criteria

The Delphi Matrix results show that Project RAMROD was the most qualified solution based on the criteria. Project RAMROD proved to be the most effective solution based on the four most weighted criteria: safety, durability, functionality and educational value. Project RAMROD scored highest in safety due to the Plexiglas surrounding and safety key switch, this allows the machine to be operated under safe conditions by the instructor. The system scored high on durability and functionality because of its strong metal components as well as its simplistic design. The educational value of Project RAMROD was rated high because the resulting pressure from the bridge tester can be used in various ways to calculate force values throughout the STEAM program.

Table-1: Weighted Criteria
Criteria Weight Constraints
Safety 10 The bridge tester should include a safety switch to prevent injuries.
Functionality 10 The machine must be easily operated and work every time while providing consistent pressure readings.
Educational Value 9 Information gathered from measurements and calculations will be utilized by different aspects of the STEAM program appropriate for 6th to 8th grade education.
Durability 8 The machine must be constructed with materials to ensure proper use for 10 years and withstand long periods of inactivity.
Mobility 8 The machine will have wheels for easy transportation and must be able to fit through doors.
Cost 6 Each material for the project must not exceed 25 dollars in cost and must stay under the specified budget of 400 dollars.
Up-Cycle 5 50 percent of all materials used will be from recycled or reused products.
Aesthetics 4 The bridge tester needs to portray the purpose of design and have the appearance of a well-built professional project.
McElroy Compact Chain Sidewinder.

Description of final project

RIPSAW shown above demonstrates the integration of two the alternative solutions crank-it and project ramrod into the final design. The generation of mechanical pressure from the McElroy sidewinder shown to the right allows for pressures upwards of 600 psi to be applied to the model bridge decks. The sidewinder dimensions are 21.4”x 12.5”x 10.25” and allow for 18” of travel on the drive screw assembly. The sidewinder comprises of a load cell measurement system and integrated dry pressure gauge to display the desired pressure. The threaded drive screw assembly is controlled by the operator and can be moved up and down to a desired height. Once in position, the drive screw assembly is rotated by the knob clockwise to apply gradual pressure and counter-clockwise to relieve pressure. The McElroy sidewinder is bolted to a fabricated C-bracket frame and C-channel platform to ensure stability. The dimensions of the channel platform are 3’x 6”x ½” and is welded to two 12”x 12” x 1/4” iron plate to support the base of the model bridges. The c bracket runs 3” out from the back of the C-channel and up 17.7” and 14” across the top where the sidewinder is mounted. The sidewinder and frame assembly are bolted to moveable cart that comprise caster wheels with dimensions 24”x 18”x 42”. The dimensions of RIPSAW allow for the complete assembly to be easily stored and maneuvered for Zane Middle School teachers.

Cost

The bridge tester items, purchase size, quantity of items, team cost, individual retail cost and total cost of the final design bridge tester are summarized below in Table 1, Table 2, and Table 3.

Table-1: Bridge Tester Materials
Bridge Tester Item Purchase Size Quantity Team Cost Individual Retail Cost
McElroy Sidewinder (10.25inx12.5inx21.4in) 1 Donated $1,583.00
Iron Plate (12inx12in) 2 Donated $145.90
Cart with Wheels (24inx18inx42in) 1 Donated $106.99
Square Tubing (48inx1.5inx1.5) 4 Donated $34.24
Rectangle Tubing (72inx1.5inx0.75in) 1 Donated $20.94
C-Channel (25inx6inx2in) 1 Donated $20.50
Black Spray Paint 12 oz. 1 $8.49 $8.49
Red Spray Paint 12 oz. 1 $8.49 $8.49
Matte Clear Coat 12 oz. 2 $4.99 $4.99
Bolts (3/8inx3in) 2 $0.85 $0.85
Nuts (3/8in) 2 $0.23 $0.23
Washers (3/8in) 6 $0.23 $0.23
Total - - $30.50 $2190.99
Table-2: Bridge Material Cost
Bridge Materials Purchase Size Quantity Team Cost Individual Retail Cost
Fishing Line 1500 yard (50lbs) 1 Donated $117.99
Popsicle Sticks 1000 Pack 2 $5.99 $5.99
Popsicle Sticks 100 Pack 1 $3.49 $3.49
Dowels 8 Pack 5 $2.99 $2.99
Wood Glue 4 oz. 4 $2.49 $2.49
Fine Sand Block (4.8inx2.9inx1in) 1 $2.15 $2.15
Bass Wood (36inx3inx1/16in) 8 $1.79 $1.79
Total - - $56.85 $174.84
Total Design Hours for completion of RIPSAW.


Table-3: Maintenance Cost in Hours
Task Hours
Dust Equipment 0.5
Lube Wheels 0.5
Clear Coat Protection 1.0
New Black Spray paint coat 1.5
Total Task Hours 3.5

Testing Results

To test the final design created, each team member made several types of bridges. These bridges were made with the same equipment and materials that would be available to the students that will be making bridges to be tested. Different variations of bridges were constructed to test the flexibility of bridge design the machine could effectively test. RIPSAW was able to successfully test and break each of the bridge type while giving accurate information about how much pressure each one of them could take. All of these tests gave us a good inclination that the machine operated the way it is supposed to.

Table-4: Testing Results
Test Bridge Type Pressure (PSI)
1 Truss 270
2 Arch 250
3 Girder 400
4 Suspension 350
1 Truss 270
2 Arch 250
3 Girder 400
4 Suspension 350

How to build

File:tools_used.JPG
How to Replicate RIPSAW

Discussion and next steps

Several obstacles arose during the development process of our design that impacted the final design. Many changes to the design occurred to accommodate the various criteria and constraints.

The solution of “Project RamRod,” which scored the highest on the Delphi matrix, had a lot of components that were going to be donated. An integral part of the design is the pump that supplies pressure to the ram. This pump is powered by Alternating Current, which allows it to be plugged directly into the wall socket. This specific pump that was supposed to be donated was no longer available. This meant that we would have to buy a pump and this did not meet our cost constraint for the project.

Different alternatives to using the pump were considered, one of which would include an air compressor that that would serve the same purpose. While the air compressor would serve the same function as the pump, it created more obstacles to overcome. The air compressor that could be used was powered by direct current. This meant that in addition to replacing the parts from the compressor that needed it, e.g. the connecting hoses, more parts would have to be located and purchased in order to achieve the constraint of durability. A tickle charger would have to be applied to the power source, a battery, to increase the lifespan of the battery. Another solution researched was to purchase an inverter. An inverter converts Direct Current to Alternating Current. Once again this solution created problems with achieving the cost constraint.

While gathering materials for the project, Rick White, Gas Operations Manager with PG&E, had a piece of equipment that is no longer in operation and donated it to the project to be repurposed. This job specific piece of equipment would in fact take the place of several different components of the design. By using the McElroy Sidewinder, the need for a power supply source, pressure gauge, ram, and pump would no longer be necessary. All of the electrical components to the design would be obsolete. The acquisition of the mechanism would have the biggest impact on the specifications of the final design.



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References

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