October 2001

"The oldest engineering work devised by man, the bridge is the only one universally employed by him in his pre-civilized state."

Joseph Gies, Bridges and Men

Bridges have fascinated people since the dawn of time when nature built many bridges in the form of trees fallen over rivers. As technology developed, people began to build artificial bridges where nature had not. Advances in bridge design, engineering, and construction have made possible many types of bridges using various types of material.

Today, bridges can be of the span, arch, or suspension type. Materials used throughout history include wood, masonry, cast iron, wrought iron, concrete, steel, reinforced concrete, alloy and silicon steel, pre-stressed concrete, carbon fiber, and aluminum.

One of the traditional competitions in the civil engineering community is the Popsicle Stick Bridge Contest. Individuals and teams from various schools build bridges with 30-inch spans using only popsicle sticks and white glue as building materials. Bridges are loaded until the bridge collapses. In the past, bridges weighing between 200 and 400 grams have carried loads ranging from a hundred pounds to over a ton!

Popsicle sticks are imperfect. Some may be bent, warped, or knotty; while others may be brittle, thin, or cracked. Visual inspection will weed out grossly deformed sticks, but students must deal with the slight imperfections present in all sticks. This is true in the real world where perfect materials are not available and careful thought must be given to the reliability of the construction materials. Engineers must attempt to quantify and account for deficiencies in both initial and post-construction material properties.

Popsicle sticks are limited to a standard size that falls short of the overall bridge dimensions. In order to span a distance of 30 inches, several sticks must somehow be connected together in a straight line. Again, this reflects real design problems where materials are finite in dimension and must be assembled in some manner to meet the engineer’s needs.

By being limited to only two allowable materials - wood popsicle sticks and white glue - students will need to use creativity, ingenuity, and resourcefulness in order to maximize the strengths and minimize the inherent shortcomings of each material.

The thrill of many bridge contests involves the testing of bridge models until catastrophic failure occurs. With sticks cracking, flying, and ultimately spilling all over the ground, team members can be satisfied that their bridge was pushed to its limit - incapable of bearing any more weight.

Bridges must also be designed to meet certain aesthetic criteria because they must function - not in a vacuum - but within a living, breathing environment.

In this contest, bridges will be loaded to failure. Failure will be defined as exceeding its ultimate load capacity. Bridges will be evaluated in three categories:

1. Best Estimated Load Capacity

2. Strongest, when loaded to failure

3. Most Aesthetically Pleasing, evaluating the overall "look"

Each bridge will be ranked against the others in each of the three categories for an overall score. All three categories have equal weight. For instance, the bridge that holds the most weight will receive the rank of 1, or score 1 point. The bridge that holds the second highest weight receives a rank of 2, or scores 2 points. In the event of a tie, both bridges will receive the same rank, and the following bridge will receive the next possible rank (i.e., if there is a 2-way tie for 3^rd place, the next bridge would receive 5^th place, or five points). The same ranking system will apply to the other two categories, and all points will be added together for an overall score. The bridge with the lowest overall score wins. In the event of a tie for the overall rank, a forth category, bridge weight, will be used as a tie-breaker, and the lighter bridge will win. An example of this system is illustrated in the table below:

Best Estimated Load Capacity is calculated using the following formula: BELC = |(Actual Load)-(Estimated Load)|/(Estimated Load) x 100.

Prizes will be awarded to the top three overall teams. The top 5 teams in each category will also receive a certificate.

Materials: 1) White Birch popsicle sticks manufactured by Solon Manufacturing. The sticks have the following dimensions:

4-1/2 inch long by 3/8 inch wide and  1/16 inch thick

2) Water soluble white Elmer’s glue. Yellow wood glue or glues containing resin additives or other cement binder is not allowed.

Definitions: A member is any portion of a wooden popsicle stick used in the construction of the bridge. A whole stick, half a stick, or even a segment of a toothpick-sized stick are all considered members.

Dimensions: No part of the bridge may exceed 10-inches above the end supports or 6-inches below the end supports.

The bridge must have a roadway that can accommodate a 4-inch high, 4-inch wide vehicle.

The total width of the bridge must be 5 inches or less.

The clear span (distance between supports) of the bridge must be 30-inches in length.

No part of the roadway may exceed 1-inch above the end supports.

Weight: The bridge must weigh 400 grams or less.

Roadway: The roadway must be constructed as if wheeled traffic were to cross over its span.

The roadway must be continuous along its width over the entire distance between the supports.

No gaps shall exist in the roadway except where natural warping has occurred after construction of the bridge.

The roadway is the portion of bridge to be loaded. If you have bridge structure over the roadway, at least a 3-inch square opening must be maintained above the loading area on the roadway to allow the bridge to be loaded.

The roadway must be constructed to accommodate a 4-inch high, 4-inch wide vehicle.

The roadway must not exceed a horizontal:vertical slope of 2:1 (approx. 26.5 degrees from the horizontal).

Construction: 50% Rule:

Not more than 50% of any plan surface of any member may be laminated. Each member consists of two plan surfaces (the two larger sides unless all sides are equal then all sides must comply with the 50% rule).

For example, when using a full-length stick, the sum of glued lengths (1) and (2) must be less than or equal to half of the stick’s total length (2-1/4 inch).

The length labeled (A) must be equal to or greater than half of the stick’s total length (2-1/4 inch)

Sections:

I-beams and box beams are not allowed.

T-sections are allowed only in the roadway and must be perpendicular to the length of the bridge.

A maximum of 6 sticks may be stacked at any joint. There must be at least a 1-inch clear gap between any two stacks. Stacks and gaps are illustrated below:

Supports: End supports will be provided by ASCE-YMF. No special supports may be used. The end supports will have the dimensions of 3/4- inch wide by 3/4-inch high by 5-inches long.

Mark where the end supports should come in contact with your bridge.

Loading: The bridge will be loaded on the roadway 10-inches from one of the ends. The loaded end will be determined on contest day.

The load will be applied on a 3-inch square plate placed 10-inches from one end of the bridge on the roadway. A 3x3-inch square will be drawn on your bridge at the contest.

Miscellaneous: The bridge must be self-supporting over its entire span.

The bridge must not exert any horizontal force on the supports other than friction. Therefore the bridge may only come into contact with the top surface of the end supports.

If dowels are used in construction, they must comply with the 50% rule.

First judging: During the first judging, a panel of technical judges will review the bridges for any rules violations. Any bridge with a rules violation will be disqualified.

Challenges: Challenges may be made following the first judging period. Only students with bridges that have not been disqualified may challenge any bridge that is felt to be in violation of the rules.

Any bridge that has been disqualified during the first judging period may be appealed.

Second judging: Any bridge that has been challenged, along with the bridge of the challenging team, will be examined again by the technical judges.

The technical judges will hear all appeals.

The decisions made by the technical judges during the second judging period are final. No challenges, appeals, or complaints will be heard after this time.

Can we notch the members?

Yes

Can we drill holes through the members or cut slots in them?

Yes, but consider..... Remember, if you use pins to connect your members, the pins are considered a member and must comply with the 50% rule. These "extra long" pins will be overlooked in the aesthetic portion of the contest and will not lower your aesthetic contest rating.

Can we shave the members to make them thinner?

Yes

Can we saturate the members in white glue?

Yes, but remember that the final weight must be 400 grams or less

Can we paint/color the bridges or add decorations to them?

No. The rules restrict the bridge to only popsicle sticks and white Elmer’s glue.

Can we glue the sticks together to form a corner or "L" section?

Yes. The rules have restrictions on T-, I-, and box beams but not L.

Does the 3 x 3 inch load area require clear access above it for the load to be applied?

Yes. The bridges are loaded from directly above the load area.

If some paper was accidentally glued to a member, will that count against us?

Not if it was truly accidental and wasn’t for aesthetic purposes.

Does the roadway have to meet the supports at grade?

No, you may build a bridge with the roadway above (or below) the supports but no part of the roadway can be more than 6-inches below the supports or 1-inch above the supports.

Can we glue "toothpick-sized" sticks along L and T shaped members to make the connections stronger (like a fillet weld)?

No, that’s a great idea but the toothpick-sized member violates the 50% rule. See illustration of toothpick-sized members below.

Always start with paper and pencil first. Sketch out your ideas. Draw your bridge in at least two views - looking at it from the side and looking at it from the end so you get a good idea of what you’re building.

Choose the design you are sure you can build. Are you confident your bridge will meet all the rules? Try using the West Point Bridge Designer at http://bridgecontest.usma.edu/

Think about how the load will transfer from the 3" x 3" loading area, through the structure and out to the supports at each end of the bridge. Not all parts of your bridge will have the same load running through them. What bridge members do you think will take the greatest load? Make those members stronger.

Which members do you think will be in compression? Which ones will be in tension? A single popsicle stick in tension can hold more weight than one in compression which will buckle and snap. Make sure your compression members are strong.

Your bridge members are only as strong as your connections, so pay special attention to the connections! How can you construct strong connections? Drilling or notching the end of bridge members is allowed.

If your bridge has similar patterns that are repeated throughout your design, construct modules so the pattern is accurately constructed each time. If your pattern is not dimensionally consistent or each side of your overall bridge is not symmetrical, some parts of your bridge will take more load than you originally planned.

Before you build your entire bridge you may want to test small parts of your bridge and compare one design to another to see which is stronger. You can even test your stick connections. How can you make a stronger stick connection?

If you design a truss, be sure it extends all the way to the ends where it will be supported. Don’t put a truss just in the center section.

If you use several rows of sticks to make up a structure, don’t leave any sticks out or the structure probably will fail at that point.

Lateral supports (members that are perpendicular to the direction of traffic on the bridge) are important, but the majority of the strength is needed in the main members spanning the 30-inch gap (members that are parallel to the direction of bridge traffic).

Your bridge is loaded on a 3-inch by 3-inch square on the roadway. Be sure to allow for the load to reach the rest of the bridge.

Be sure to make strong connections between the roadway and the main members spanning the 30-inch gap. You don’t want your roadway to fail before your main members are loaded up.

How does your bridge look? If this were a real bridge, do you think the public would find it pleasing to the eye? Can you make your bridge attractive and strong at the same time?

Construct a bridge on a surface that glue will not stick to! Try to work in an area you don’t mind getting messed up.

Are you at a loss for ideas? You can view photos and results from past contests on our website: http://sections.asce.org/seattle/AMF/popsicle/amf_psb.htm, but keep in mind that the rules were different each year. You will also find a copy of the latest contest rules and links to other helpful websites.

Plan ahead!!! Don’t wait until the night before the contest to finish the bridge! (Wet or damp glue doesn’t work very well.)

Tools to help you with your bridge construction:

• pencil
• paper
• wire cutters for cutting sticks
• Exacto knife
• clips, rubber bands, and weights to clamp pieces together when the glue is drying
• and finally, ........ PATIENCE !!! (Good bridges take time to build.)

TITLE: Popsicle Stick Bridge Building Contest

GOAL: Introduce popsicle stick bridge building contest to students.

OBJECTIVES:

• outline the PSBB contest
• engineering disciplines involved in design/construction of a bridge
• engineering as a career

MASTERY OF OBJECTIVES: question/answer session

MATERIALS:

PSBB contest pamphlet, overhead sheets, photographs, blueprints, chalkboard or white board, ASCE video tape, prototype bridges

TIME ALLOTMENT: 50 minute class period

AUDIENCE (SPECIFIC STUDENTS): science and/or mathematics class

OUTLINE:

I. Introduction to civil engineering field

A. speakers background (ASCE, specific work, education)

B. engineering in general

C. civil engineering (various disciplines - use stadium construction as example)

II. PSBB contest

A. background

1. photos from previous contest

2. video

B. judging

C. rules

1. overhead summary

2. samples of members not allowed (pass around class)

III. Engineering approach to contest

A. research

1. resource information provided to teacher

B. design concepts

1. rope demo (tension and compression, 2 students then 4 students)

C. design calculations/testing

D. drawings

1. multiple views

E. construction

1. tips for building bridge

ADDITIONAL SOURCES: engineering textbooks, internet, library

TITLE: Bridge design research

GOAL: Increase students understanding of bridge design

OBJECTIVES:

• show difference between bridges - suspension, span, arch
• identify bridges materials and connections used for design
• identify basic bridge terminology - truss, deck, arch, beam types, span
• presentation of local examples of bridge design

MASTERY OF OBJECTIVES: class presentation, question/answer, short report

MATERIALS: provided text handouts

TIME ALLOTTED: 50 minute class period

AUDIENCE (SPECIFIC STUDENTS): science and/or mathematics class

OUTLINE:

I. History of the bridge

A. materials

B. size

C. use

II. Bridge Types

A. suspension

B. span

C. arch

III. Bridge Components

A. terminology

B. member shapes

IV. Design Steps

A. concepts

1. local bridges

2. design texts

B. Rough Drawings

C. Dimensioning

1. member sizing

2. material

D. Preparation for Design Calculations

ADDITIONAL SOURCES: internet, library

TITLE: Mathematics in Bridge Design

GOAL: Incorporate mathematics skills into the design of the popsicle stick bridge

OBJECTIVES:

• mathematics used in bridge design
• review of mathematics concepts
• calculations required in specific design

MASTERY OF OBJECTIVES: design calculations (homework)

MATERIALS: handout, mathematics text

TIME ALLOTTED: 50 minute class period

AUDIENCE (SPECIFIC STUDENTS): science and/or mathematics class

OUTLINE:

I. Introduce mathematics involved with bridge design

A. truss configuration

B. force reactions

II. Review of Concepts

A. trigonometry

B. geometry

C. algebra

D. unit conversions

III. Example Calculations

IV. Application of Concepts to Specific Design

ADDITIONAL SOURCES: mathematics texts

West Point Bridge Designer (http://bridgecontest.usma.edu/)

TITLE: Physics in Bridge Design

GOAL: Incorporate physics skills into the design of the popsicle stick bridge

OBJECTIVES:

• physics used in bridge design
• review of physics concepts
• calculations required in specific design

MASTERY OF OBJECTIVES: design calculations (homework)

MATERIALS: handout, physics text

TIME ALLOTTED: 50 minute class period

AUDIENCE (SPECIFIC STUDENTS): science and/or mathematics class

OUTLINE:

I. Introduce physics involved with bridge design

A. materials strength

B. force reactions

C. beam strength

II. Review of Concepts

A. forces

B. strength

C. pressure loading

III. Example Calculations

IV. Application of Concepts to Specific Design

ADDITIONAL SOURCES: physics texts

West Point Bridge Designer (http://bridgecontest.usma.edu/)

TITLE: Construction of Popsicle Stick Bridge

GOAL: Outline steps required in construction of bridge

OBJECTIVES:

• outline steps in construction process
• construct bridge substructures
• assemble bridge components

MASTERY OF OBJECTIVES: bridge

MATERIALS: pencil, paper, wire cutters, exacto knife, clips, rubber bands, popsicle sticks, glue

TIME ALLOTTED: varies

AUDIENCE (SPECIFIC STUDENTS): mathematics and/or science students

OUTLINE:

I. Construction Steps

A. final drawings

B. assemble materials

II. Bridge Assembly

ADDITIONAL SOURCES:

TITLE: Popsicle Stick Bridge Presentation

GOAL: Construct display for popsicle stick bridge

OBJECTIVES:

• write description of bridge construction
• display including bridge specifications

MASTERY OF OBJECTIVES: display produced

MATERIALS: display board, bridge

TIME ALLOTTED:

AUDIENCE (SPECIFIC STUDENTS): students involved with bridge building

OUTLINE:

I. Bridge Construction Outline

A. how design was established

B. construction methods

II. Bridge Specifications

A. weight

B. estimated load capacity

ADDITIONAL SOURCES:

Return to YMF page.

Return to Popsicle Bridge Contest Page.