Bunt/McLaughlin

The Sunshine Skyway Bridge

Neal Bunt and Ryan McLaughlin

Statics B36

Professor Stoakes

March 29, 2012

The University of Iowa

Bunt/McLaughlin 1

Executive Summary

Our names are Neal Bunt and Ryan McLaughlin, and we are freshman at the University

of Iowa. We would like to receive funding for a trip to visit the Sunshine Skyway in Tampa,

Florida in order to get a real life look at how the bridge operates. The Sunshine Skyway is a

bridge that interests us because it is unique and has numerous statics ideas built into it. We would

be able to study how some statics principles such as reaction forces work, and we could make

calculations that would give us insight on the world of engineering.

Introduction

Our names are Neal Bunt and Ryan McLaughlin. We are freshman at the University of

Iowa. We are currently enrolled in the class Engineering Fundamentals I: Statics. We are writing

this paper in order to gain financial support to visit the beautiful Sunshine Skyway in Tampa,

Florida. If given funding, we would like to get a first-hand view of how certain static principles

work in the real world by visiting this bridge. For example, by actually being on site we would

be able to study the effects of reaction, tension, and compression forces and gain a deeper

understanding of these important statics principles.

Background

The Sunshine Skyway was considered because of the demand for a way to cross Tampa

Bay (Ringwald, 2009). Originally, a suspension bridge or a tunnel was proposed to solve this

problem (Ringwald, 2009). Neither plan happened as quickly as desired because World War II

created a problem with funding (Ringwald, 2009). In 1950, after World War II ended, the

construction of the bridge began, and the 150-foot tall bridge was completed on Labor Day

weekend of 1954 (Ringwald, 2009).

This design did not last long, however. In only a quick few years the traffic on the bridge

increased so dramatically that they decided to build another bridge almost identical to the

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original Sunshine Skyway (Ringwald, 2009). It took four years to build a second one, and they

converted the first bridge to carry only northbound traffic while the southbound traffic would

ride on the new bridge (Ringwald, 2009).

This two bridge design worked well for nine years, but on the 9th of May in 1980, a boat

by the name of “Summit Venture” crashed into the southbound bridge because it could not see

through a heavy rain storm (Ringwald, 2009). It did not affect the northbound bridge, but it did

take thirty-five peoples’ lives (Ringwald, 2009).

An ultimate decision arose as to whether they should repair the southbound bridge or

demolish both and build a completely new structure (Ringwald, 2009). They decided on building

an entirely new structure, and the structure to be built is the one that stands today: the majestic,

cable-stayed Sunshine Skyway Bridge (Ringwald, 2009).

A cable-stayed bridge is one that has columns with cables attached to them, and the

cables stretch along the deck of the bridge to keep it up. Construction of the new (and current)

bridge began in 1984 and was completed in 1987 (Ringwald, 2009).

Technical Analysis

Many statics principles are incorporated into designing a bridge, and such principles

include applied loads, reaction forces, moments, tension, and compression. An applied load in

this case is a force that acts on the bridge such as a car, truck, or wind and requires a reaction

force to counterbalance it (Kraige, L.G., Meriam, J.L. 2012). Reaction forces are forces that

counteract applied loads (Kraige, L.G., Meriam, J.L. 2012). This is of obvious importance when

studying bridges because without analyzing which types of applied loads a bridge must take on,

designing one strong enough is impossible. These forces can be studied on bridges everywhere,

and their importance is paramount. Reaction forces are generally at the ends of the bridge, but

Bunt/McLaughlin 3

are also significant at the two columns of the Sunshine Skyway. The types of reaction forces at

these connections are determined by whether they are pinned or roller supports. Pinned

connections resist movement in both the horizontal and vertical directions, thus there are vertical

and horizontal reaction forces at pinned connections. Roller connections only resist vertical

movement, though, so there are only vertical reaction forces at roller connections. Reaction

forces are very important in the design process as they can be used to determine how heavy the

bridge can be, how much traffic it will hold, and they can even be used to determine how long

the bridge can be. The reaction forces must be large enough in magnitude to support the applied

loads to the bridge, otherwise it will topple over. Moments are another statics principle that may

be of less importance when studying bridges, but they can still be used in the equations of

equilibrium when considering bridges. The equations of equilibrium are shown below as Eq. 1

and Eq. 2.

∑ F = 0 (Eq. 1)

∑ M = 0 (Eq. 2)

These equations state that the sum of the forces equal 0 and the sum of the moments

equal 0, and although simplistic, these are the most important equations in Statics. A moment is a

force which tends to cause rotation about a point or axis (Kraige, L.G., Meriam, J.L. 2012).

Moments are very useful in the equations of equilibrium because the moment a force creates

about a point is the magnitude of the force multiplied by the perpendicular distance from that

force to the point. This becomes useful when relating the concept of axis rotation to structures. If

a moment attempts to cause rotation upon a fixed connection, like the columns of Sunshine

Skyway, the body itself will have a reactionary moment force to ensure its stationary position.

Bunt/McLaughlin 4

As previously stated, Sunshine Skyway is a cable-stayed bridge, which means there are

cables connected in a diagonal fashion to a tower on one end and a bridge on the other. The

tower has multiple cables on each side to help support a heavier load. The two towers of the

Sunshine Skyway are unique because they “attach cables to the center of its roadway as opposed

to the outer edges, allowing commuters an unobstructed view of the magnificent bay” (Nova

Online 2000). The Sunshine Skyway’s cables attach to the towers in a parallel pattern, linked to

different points on the vertical beam and roadway.

The function behind these cables is based on tension. The weight of cars on the bridge

and that of the bridge itself pulls on the cable, causing tension (or stretching) in the cable. Cable

tension always pulls away from the body that stretches it so it can return to its original length, so

there is a force in the cable pulling away from the roadway (upwards) and a force pulling away

from the tower (downwards). As a result of the downward force pulling on the tower, it is

compressed into the ground, but the upward (normal) force of the ground counterbalances this.

These forces are well described in Figure 1 shown below.

A primary advantage to cable-stayed bridges is its ability to counterbalance the horizontal

forces resulting from vertical force loads on the roadway. When a car is driving over the bridge,

Figure 1. Diagram of forces in a cable-stayed bridge (“Bridges,” Figure III).

Bunt/McLaughlin 5

not only does the tension pull downwards from the tower, but also in a horizontal direction.

There is an identical cable on the other side of the column, allowing it to pull in the opposite

direction and balancing out the horizontal forces. This places the column in horizontally static

(fixed) equilibrium. If a body is in equilibrium, “the resultant of all forces acting on it is zero,” so

this case refers to a zero net horizontal force, and the column doesn’t sway right or left (Kraige,

L.G., Meriam, J.L. 2012). The beam relies on the ground’s upward reaction force to qualify for

vertical static equilibrium.

Forces that reverberate throughout the bridge, the applied loads of a steady stream of

cars, the reaction forces of the ground and column, and force equilibrium all have a hand in the

functionality of this cable-stayed bridge. A trip to St. Petersburg, Florida, the home of Sunshine

Skyway, would provide the students with a better view of the structure, nice weather, and an in-

depth analysis of these statics concepts in a real life setting.

Itinerary and Cost Estimate

The trip is proposed to take to take place during the week before spring break from

Saturday to Wednesday of that week. Two charter buses will be used for transportation from the

Iowa Memorial Union to Crowne Plaza Hotel in Tampa, Florida.

The bus will depart at 9:00 PM on Saturday and the expected arrival time for Tampa is

10:30 PM (EST) on Sunday. At nine o’clock the next morning, everybody will load up in their

respective buses and head over to Tampa’s Museum of Science & Industry. A tour of the

attraction, featuring multiple interactive and educational exhibits, will begin at 9:30 AM and

conclude at noon.

The buses will depart at 1:15 PM and transport the students to the Tampa Bay History

Center by 1:45 PM. A tour of this museum will be conducted from two o’clock to four o’clock,

Bunt/McLaughlin 6

where the students will be exposed to the history of Tampa Bay’s most famous structures,

including the Sunshine Skyway, and other local historical content. The buses will depart for the

hotel at 4:15 PM and arrive there at 4:30 PM. The students will be allowed to explore the locale

until the dinner time.

After Tuesday’s complimentary hotel breakfast, the buses will leave at nine o’clock

towards the trip’s main attraction: the Bob Graham Sunshine Skyway Bridge. The buses won’t

be returning to the hotel afterward, so students should be sure to gather all their stuff onto the

bus. Two structural engineering professors from the University of Tampa will be giving a tour of

this bridge. We’ll drive across the bridge and pull over multiple times to talk about specific

aspects of the bridge, observe their functions, and stop at the far end to understand its force

interaction with the ground. After this four hour activity, people are free to eat wherever in

downtown St. Petersburg. The buses will leave for Iowa City at 3:00 PM and will arrive at the

Iowa Memorial Union at 3:00 PM on Wednesday.

The estimated costs of this trip (with the bulk of the expenses being covered by the

attending students because the hotel stays and meal plan are very costly) are shown below in

Table 1. The cost of the museum tours is a rough estimate along with paying the local professors

for their tour of the bridge. The total amount of funding required will be $12,304.50.

Table 1. This is a list of student-paid expenses.

Hotel Cost (2 nights) $209.88

Food (9 meals; $20.00/meal) $180.00

Table 2. This is a list of required funds (“Admission,” “Visit us,” “Bus types”).

Museum Tickets $3,624.50

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Tours $1,000.00

Charter Buses $7,680.00

Conclusion

With education being the main purpose in mind, we expect Statics students and even the

adults to learn a plethora of knowledge from the museums and bridge tour. We have strategically

scheduled the visit to Tampa Bay’s History Center to lay down the foundational knowledge to

truly grasp the pricelessness of the Sunshine Skyway. That way, during the tour of the bridge, the

students can understand the necessity of such an efficient structure and learn from the flaws of its

predecessors. A four hour, detailed tour of the bridge with the assistance of knowledgeable

structural engineering professors will guarantee a valuable insight into the applicable Static

principles the Sunshine Skyway withholds. We hope this firsthand impression, along with the

tragic history of the bridge, will further engrave its structural concepts into the students’ minds

so they may carry this precious, practical knowledge into future careers, courses, and projects. It

is with this well-intended goal that we politely ask you to fund this educational trip.

Bunt/McLaughlin 8

Reference List

“Admission.” (2012). Museum of Science and Industry. Admission. Retrieved March 26, 2012 from http://www.mosi.org/plan-your-visit/admission.aspx

“Bridges.” (2004). Making the Modern World. Bridges. Retrieved March 26, 2012 from http://www.makingthemodernworld.org.uk/learning_modules/maths/02.TU.03/?section=9

“Bus types.” (2012). Bus Rates: Charter & Group Travel Directory. Bus Types. Retrieved March 26, 2012 from http://www.busrates.com/buses/Bus-Types/

“Cable-stayed bridge.” (November 2000). Nova Online. Cable-Stayed Bridge. Retrieved March 26, 2012 from http://www.pbs.org/wgbh/nova/lostempires/china/meetcable.html

Kraige, L.G., Meriam, J.L. (2012). Engineering Mechanics: Statics (7th ed.). Hoboken, NJ: John Wiley & Sons, Inc.

Ringwald, Edward. (October 16, 2009). Interstate 275. The sunshine skyway bridge. Retrieved February 16, 2012 from http://interstate275florida.com/ssb.htm

“Visit us.” (2012). Tampa Bay History Center. Visit Us. Retrieved March 26, 2012 from http://www.tampabayhistorycenter.org/tickets.html