Successful Bridge Design Cameron Stacy

Introduction A bridge is a structure used to compensate for an obstacle such as a valley, river, or to assist traffic flow. Early bridge’s development used natural materials such as flat stones and tree trunks. Bridges have been seen in history from as long ago as 4,000 years crossing the Euphrates River. Romans can be considered the greatest bridge builders in ancient history. The Roman bridges were known for their water proof cement, massive arches, and the ability to make temporary structures to work on pier abutments under water called cofferdams. Many of the bridges throughout Europe follow the Roman design. Modern Bridge development began in the 17 th and 18 th Century. In the 18 th Century iron began to replace the timber, brick, and stone of ancient bridges. Iron aloud for longer spans that could cross great distances. This study will examine the weight supported by girder and suspension bridges.

What is a Girder Bridge? A girder bridge is perhaps the most common and most basic bridge. The two most common girders are I-beam girders and box girders. The typical span of a girder bridge is 10m to 200m. The girder bridge evenly distributes the weight of the traffic amongst its many supports.

What is a Suspension Bridge? The suspension bridge allows the largest span of all bridges to this day. The typical span of a suspension bridge is 70m to 1000+m. The cables on a suspension bridge needs stiffing to help distribute the weight amongst many cables. The two main cables then connect to huge concrete structures where the cables are secured into the ground and distribute weight into the earth.

Minneapolis Bridge Collapse In August of 2007 design flaws caused the Minnesota to collapse into the Mississippi river. When the bridge collapsed into the river 13 people were killed and almost 145 were injured. The design flaw found was that of the gusset plates were too thin to hold the weight of traffic. The Austin Public Works Department services the city’s bridges. There are hundreds of bridges in the greater Pittsburgh area. This fact that a city with only bridges could have one collapse compared to Pittsburgh’s hundreds prompted me to perform an experiment to designate the most efficient bridge design.

Purpose The purpose of this research is to determine the most efficient bridge design. This experiment will simulate constructions of bridges, from simple deck design to more complex suspension bridge designs. The experiment will take the designs of the computer to the laboratory, testing the affectedness of various designs.

Hypotheses Experimental Hypothesis: –There will be a significant difference between the weights supported by a deck depending on the design Null Hypothesis – There will be no difference in the weights supported by a deck depending on the design.

Materials 6” x 12” x ½” Styrofoam ¼” x ¼” Balsa wood strips 1/8” x 1/8” Balsa wood strips 4” x 4” x 24” Wood supports MAACO liquid nail adhesive Dental Floss Balsa wood knife Stop watch Ruler E-Hole screws Food scale Weights at.45kg increments Note book and pencil for data recording Computer for support design Calculator

Procedure Collect Materials necessary to complete testing. Research design of suspension and girder bridge. Take design from computer to libratory. Cut Styrofoam and balsa wood to appropriate sizes to match design. Adhere supports fabricated to Styrofoam bridge deck. Allow adhesive to cure as directed for 24 hours. Place bridge Mock-Ups on 4”x 4” wood supports. Place weights at.45 kg increments allowing 60 seconds between additions of weight. Add weight until the simulated bridge fails fully-cracking apart. Record weight necessary to break the bridge deck, recorded on data sheet in kg.

DATA TrialControl Flat With 2 1/4" Supports Small Upper Support Small Lower Support Large Upper Support Large Lower Support Small Upper With Floss Small Lower With Floss kg9.23 kg11.7 kg12.26 kg8.78 kg9.45 kg11.7 kg12.83 kg kg 9.00 kg11.36 kg12.15 kg8.55 kg9.23 kg11.81 kg13.05 kg kg9.45 kg11.93 kg12.15 kg8.78 kg9.45 kg11.59 kg12.6 kg kg9.23 kg11.81 kg12.38 kg9.00 kg9.56 kg11.7 kg12.83 kg kg8.78 kg11.7 kg12.26 kg8.66 kg9.45 kg11.81 kg12.83 kg

Results The smaller supports of the Styrofoam deck provided the most contestant support. Small lower supports were the most successful. Larger supports were not as successful as the smaller supports, both upper and lower. Adding floss to act as a suspension bridge enhanced the strength of all the bridge designs.

Analysis Failure of the large supports demonstrated weakness because of the added lengths of the girder system. Deck failure was common with the small supports, while the girder system failed in the larger support designs.

Sources of Error