Design Project #1 Replacement of Vehicle Bridge over Spring Creek Centre County, PA Introduction to Engineering Design EDSGN 100 Section 002 BridgeHawks Design Team 5 Alison Willingmyre Brandon Kong Carolina Biffe Ouniol Aklilu Warren Through Truss Bridge BridgeHawks Presented to: Prof. Berezniak Spring 2018
Statement of the Problem Severe flooding has caused a bridge located on a road of heavy traffic to collapse, causing many problems along with it. Access to medical care at the Mount Nittany Medical Center and local commerce depended on this bridge and must now be re-routed disrupting the daily flow of traffic. 2
Project Objective Quickly and effectively design a vehicle bridge to replace the original bridge that resided over Spring Creek in response to the flood emergency. 3
Required Design Criteria The replacement bridge must include: ✓ standard abutments ✓ one span ✓ medium strength concrete as deck material ✓ no cable anchorages ✓ designed for the load of two 225kN trucks, one in each traffic lane ✓ bridge deck elevation should be 20 meters cable anchorages ✓ bridge deck span should be 40 meters ✓ concept designs for a Warren and Howe through truss bridge should be completed. 4
The Technical Approach Phase 1: Economic Efficiency Based on the criteria in the previous slide, the cost should be determined using the EEBD 2016 software program. Each through truss bridge cost should be optimized while still ensuring that the replacement bridge can safely support the dead load and required live load. In other words, each bridge should have the lowest cost possible within the range of $150,000 to $250,000 while remaining safe. 5
The Technical Approach Phase 2: Structural Efficiency A standard prototype for each bridge will be created and load tested to failure. From this, the bridge exhibiting the best structural efficiency should be determined. The structural efficiency is the ability of a truss bridge to safely dissipate live loads. It is calculated by “Real life” load testing 6
The Results Phase 1: Economic Efficiency Howe Truss Warren Truss - - Quenched & tempered steel was determined to be the most efficient material Quenched & tempered was used in majority; had high strength to weight ratio allowing for thinner members (which caused the greatest cost reduction). in relation to cost. It was used throughout. - Carbon steel was exception in members 6,8, 13, and 15…has a limit of how slim it can be. - Solid bars were used where the tension was the largest. - Hollow tubes were used where compression was the largest. - Hollow tubes were used majority; their cost was less than a bar of equal - Tried to use hollow tubes often (65%) because they were the biggest factor to compressive and tensile strength. decrease cost. - - Thin tubes were used Thicker tubes were used for wherever possible. Less top chords otherwise tubes material = lower cost. were made as thin as possible without sacrificing safety to reduce cost. 7 7
The Results Phase 2: Structural Efficiency Warren Truss Howe Truss - Mass: 0.1781Ibs - Mass: 0.1825Ibs - Held: 66Ibs - Held: 66 Ibs - Efficiency: 371 - Efficiency: 362 Structural efficiency was the 3 rd Structural efficiency was the 3 rd highest, higher than class average of highest, higher than class average of 338. Warren Truss Bridge Prototype 294. Truss failed in breakage in bottom Failure after Load Testing Truss failed at the popsicle glued in the chord of prototype due to shear stress center of the bottom chord (location of at a glued joint between sticks. Howe Truss Bridge Prototype most tension based on simulation). Failure after Load Testing Reasons for failure: Reasons for failure: - Was only supported at two sticks instead of 3 at place where shear stress - More support to sustain high was high tension in middle. - Sticks were not properly glued at bottom chord and the shear stress could - Glue needing additional cure time. have been distributed unevenly Both constructed with 60 popsicle sticks (4x4.5x13.5 in) and held together with Both constructed with 60 popsicle sticks (4x4.5x13.5 in) and held together with Elmer’s glue and water mixture to help with glue absorption into wood Elmer’s glue and water mixture to help with glue absorption into wood 26 sticks were used for each truss; 8 sticks were used for floor beams and struts. 26 sticks were used for each truss; 8 sticks were used for floor beams and struts. 8 8
The Best Solution For the Howe Truss, Strengthening Middle Bottom cord through Adding more sticks to the bottom chord ● Adding more glue to strengthen the bonds between the fibers of the ● sticks. For the Warren Truss, Adding more sticks to places where the shear stress is high ● Also give more time for curing the bottom chord since lot of sticks were ● glued to construct it. We recommend the Warren Truss Bridge design. 9
Our Conclusions The objective of the project was to design a vehicle bridge that is cost and structurally efficient to replace the original bridge that resided over Spring Creek in response to the flood emergency. Our bridges were comparatively cost efficient and the structure designed sustained quite a load. For the Howe Truss, Cost: 212,698.18 Efficiency: 362 For the Warren Truss, Cost: 187,333.72 Efficiency: 371 This project was important because you learn that when you design a structure, you are not only thinking of how to make the structure strong, but also the cost to build the structure. 10
Our Recommendations To advance to the final bridge design, we should be able: Strengthen parts with high tension ● Tweak designs to lower cost ● We need a more detailed investigations on the bottom chord since they face the highest tension from all the bridge parts. Some course of action to take would be: Review your bridge for weak sticks ● Glue parts of your bridge if they are loose ● Allow more curing time ● 11
In Closing We would like to thank PennDot for giving the chance to show what we were capable of and sponsoring this project. Paula Scher once said “It’s through mistakes that you actually can grow. You have to get bad in order to get good.”
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