DIVISION ‘B’ & ‘C’

Inclined BRIDGE BUILDING 2016

Roy S. Highberg, P.E. … [email protected]

Inclined BRIDGE BUILDING 2016

UNDERSTANDING THE 2016 Inclined BRIDGE BUILDING EVENT MENTORING THE Inclined BRIDGE BUILDING EVENT for your students WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

Inclined BRIDGE BUILDING 2016

This is an Experimental Engineering event that places maximum emphasis on innovative design, efficient use of materials, and quality of construction – Coaches primary job is to help students understand the expectations of the event; ALL competitors should arrive at

competitions with TIER 1 bridges that can meet construction and competition requirements.

– Coaches primary job is to help students understand the experimental process; students should be encouraged to push the design envelope and learn what works through repeated structural failures, design revisions, and retests. – Student experimentation with different designs, material selection, and construction techniques will result in gains in efficiency, and thus improved results. – Experimental process. Student design, photographs, video and testing data records help document sequential bridge designs, failure modes and improved results.

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016

Scoring Tiers … Tier Tier Tier Tier

1 2 3 4

just means that bridges meet the written rules. SIMPLE is for bridges with COMPETITION violations is for bridges with CONSTRUCTION violations is for bridges that CAN’T BE TESTED.

Tier 1 bridges are ranked by score, and beat ALL Tier 2, 3 & 4 bridges. Tier 2 bridges are ranked by score, and beat ALLTier 3 & 4 bridges. Tier 3 bridges are Ranked by score, and beat ALL Tier 4 bridges.

NO MEDALS are earned by bridges in Tiers 2, 3 or 4. Bridges in Tiers 2, 3 & 4 only result in TEARS

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016 ACTIVITY_ Form groups of 2 to 4 coaches to read & understand the 2016 rules. Post written POST_IT NOTE statements on the whiteboard. On POST-IT notes, write statements describing a bridge that would (1) fail to meet a construction rules (para 3), and be a TIER 3 bridge (2) Be untestable, and be a TIER 4 bridge (3) Fail to meet a competition rule (para 5)and become a TIER 2 bridge Group discussion of the 2016 event rules based upon POST-IT NOTES Convert your previous “negative” statements to “positive” ones. Describe what a bridge would look like in order to ACCOMPLISH each construction and competition rule. For example, Build the bridge 37cm long to exceed the “B” clear span” of 35cm

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016 SIGNIFICANT 2016 RULES

Materials …

No manufactured composites, plies or laminates, bamboo or paper products No size limit on materials cross section

Construction …

Must be a single structure with NO separate or detachable pieces Must be long enough to cross a “clear span” of 35cm (B) or 45cm (C) No maximum or minimum bridge length or height, or minimum bridge width Bearing zone on one end is 5cm HIGHER than the other. (i.e. Inclined Bridge) Bridge structure in “Low” bearing zone has 2cm height limit Bridge structure in “high” bearing zone must be smaller than 2cm x 5cm Loading block will be positioned at the center of the “clear span”

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

PREVIOUS YEARS “BRIDGE BUILDING” RULES [ not 2016 ]

All prior years envisioned “balanced” bridges, mirrored on each side of loading centerline

Clear Span of 35cm (B) or 45cm (C)

CENTER OF SPAN Load Bucket Basic WARREN TRUSS with Verticals

PREVIOUS YEARS “ELEVATED BRIDGE ” RULES [ not 2016 ]

All prior years envisioned “balanced” bridges, mirrored on each side of loading centerline

CENTER OF SPAN Load Bucket Clear Span of 35cm (B) or 45cm (C)

Elevated WARREN TRUSS with Verticals

2016 [Inclined] BRIDGE BUILDING RULES “low” end of bridge has 2cm height restriction in entire BEARING ZONE

“high” end BEARING ZONE is 5cm higher than “low” end. Bridge must sit within 5cmx2cm touchdown zone

5cm height

2cm Height limit

CENTER OF SPAN Load Bucket Low End Bearing Zone

Clear Span of 35cm (B) or 45cm (C)

Basic WARREN TRUSS with Verticals

2cm long High End Bearing Zone

WHY WON’T THIS WORK IN 2016 ?

Vertical supports on “low” end won’t meet 2016 rules

2cm Height limit

Removing legs for High End is OK

CENTER OF SPAN Load Bucket Clear Span of 35cm (B) or 45cm (C)

Elevated WARREN TRUSS with Verticals

2016 Inclined BRIDGE BUILDING RULES Need structural members to add 5cm height & extend footing under 2cm restriction

LEVEL BRIDGE MODIFICATIONS to meet new rules Need structural members to shift loading block supports to center of clear span

Limit structural members to sit within 5cmx2cm touchdown zone

Low End Bearing Zone

5cm height

2cm Height limit

Clear Span of 35cm (B) or 45cm (C) CENTER OF SPAN Load Bucket Basic WARREN TRUSS with Verticals

2cm deep High End Bearing Zone

WHY WON’T THIS WORK IN 2016 ? bridge exceeds the 2cm height limit in “low” end BEARING ZONE

loading block supports are not level, and eye-bolt may introduce eccentric loading

High End of bridge meets specs, but load transfer onto 2cmx5cm touchdown zone may be a problem

Low End Bearing Zone

5cm height

2cm Height limit

CENTER OF SPAN Load Bucket

2cm long

Clear Span of 35cm (B) or 45cm (C) High End Bearing Basic WARREN TRUSS with Verticals Zone

2016 Inclined BRIDGE BUILDING RULES

Inclined BRIDGE MODIFICATIONS to meet new rules Added structural members extend footing under 2cm restriction

Add LEVEL structural members to shift loading block supports to center of clear span

Add LEVEL structural members to sit within 5cmx2cm touchdown zone

Low End Bearing Zone

5cm height

2cm Height limit

Clear Span of 35cm (B) or 45cm (C) CENTER OF SPAN Load Bucket Basic WARREN TRUSS with Verticals

2cm deep High End Bearing Zone

2016 Inclined BRIDGE BUILDING RULES DESIGN a LEVEL BRIDGE with unequal ends to meet new rules High end half of bridge uses standard truss

Low end of bridge uses shorter truss. Additional, longer structural members extend footing under 2cm restriction

Low End Bearing Zone

5cm height

2cm Height limit

Clear Span of 35cm (B) or 45cm (C)

CENTER OF SPAN Load Bucket Basic WARREN TRUSS with Verticals

2cm deep High End Bearing Zone

Inclined BRIDGE BUILDING 2016

• Knowledge base …

– General understanding of loads and forces on bridges and girders; and the relative strength of materials (balsa wood) subjected to tension, compression, shear, bending & buckling loads – Truss bridge and girder designs for efficient, LIGHTWEIGHT spanning structures; and how truss members are loaded (compression, tension); TRIANGLES for stiff and strong structures – Construction & gluing techniques; the importance of precise dimensions and balanced designs to resist vertical loads (gravity) – How to conduct Experimental Test Program, analyze failures, improve “weak” members, and achieve “Predictable “results

UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016 Jig for testing LOW BEARING ZONE height limits (photo to come)

Students place bridge structure on digital balance

Jig for testing Span [35cm B & 45cm C] And HIGH BEARING ZONE footprint restricton (photo to come)

Construction Specifications Check-in UNDERSTANDING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016

“UNDERSTANDING THE 2016 RULES” The COACH shares the responsibility if a BRIDGE DOESN’T MEET SPECS, but the students always pay the price Only those meeting the construction specifications will compete for medals. Common mistakes include … Bridge length too close to specs to “cross” the “clear span” Bridge exceeds the height limit where it touches the LOW BEARING ZONE Bridge exceeds the footprint limits (2cmx5cm) where it touches the test support in the HIGH BEARING ZONE Cannot accommodate the 5cmx5cm testing block and eyebolt @ centerline of span Pre-test extensions below the top of the test base Bridge structure touches vertical faces of the test support

… USING THE PREVIOUS YEAR’S SPECIFICATIONS …

EXPERIMENTAL Engineering as opposed to DESIGN Engineering The 2016 Scoring rules do not require holding a minimum load, and do not credit any “load supported” greater than 15 KG.

A bridge that will hold 20 KG has extra weight, and will lessen the structural efficiency score.

Learn from it and build another, LIGHTER one.

MENTORING THE Inclined BRIDGE BUILDING EVENT

MENTORING THE Inclined BRIDGE BUILDING EVENT

Truss Bridge Designs

Inclined BRIDGE BUILDING 2016 MENTORING THE Inclined BRIDGE BUILDING EVENT

Truss Bridge Designs

Inclined BRIDGE BUILDING 2016 MENTORING THE Inclined BRIDGE BUILDING EVENT

Truss Bridge Designs

Inclined BRIDGE BUILDING 2016 MENTORING THE Inclined BRIDGE BUILDING EVENT

Loads in members of a typical Truss Bridge

Inclined BRIDGE BUILDING 2016 MENTORING THE Inclined BRIDGE BUILDING EVENT

Girder Designs

Inclined BRIDGE BUILDING 2016 MENTORING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016

SOUND DESIGN FUNDAMENTALS

Gravity acts DOWN, VERTICALLY. Arrange the widest dimension of structural members vertically, too. “Triangles” are more rigid than rectangles ALL Trusses incorporate diagonal members. Yours should, too. Diagonal members should be incorporated in all three planes (L, W, H) “Truss Beams” or “Laminated Beams” are efficient for bending loads Place most of the material in these beams along top & bottom edges TENSION loads along the bottom and COMPRESSION along top MAXIMIZE glue joint surface area Arrange structural members face-to-face for strongest gluing Liberally use gussets for reinforcement of “butt” joints Never “hang” a load on a simple “butt” joint

MENTORING THE Inclined BRIDGE BUILDING EVENT

Always inspect glue joints !!! Some students weigh and mark each “stick” to ensure “balanced” Structure Use a sanding block Inspect each “stick” for flaws

QUALITY CONSTRUCTION NEATNESS REALLY DOES COUNT GLUE WEIGHS MORE THAN BALSA CUT, DON’T CRUSH BALSA

ONLY NEW EXACTO OR RAZOR BLADES ARE SHARP

A “THIN” GLUE JOINT IS STRONGER THAN A “FAT” ONE

THE WOOD REALLY IS STRONGER THAN THE GLUE (IN TENSION) DON’T LET “WOOD SHRINKAGE or EXPANSION” CREATE AN “OUT OF SPECIFICATION” BRIDGE (build it a tad longer, narrower, lower) THE BRIDGE WORKS IN 3-DIMENSIONS GRAVITY ALWAYS ACTS “DOWN” MAKE SURE THAT THE BRIDEG RESISTS LOADS IN THE SAME PLANE AS GRAVITY (i.e. not tilted sideways).

USE A “JIG” to assemble sides and ensure proper, balanced alignment

MENTORING THE Inclined BRIDGE BUILDING EVENT

STRENGTH OF MATERIALS AND JOINTS TYPE OF WOOD …

Balsa is the lightest wood available. Medal winning bridges are made from BALSA. Basswood has a high strength-to-weight ratio, but use it SPARINGLY, if at all. Spruce may also be available, but is MUCH TOO DENSE.

GLUE JOINTS …

Strong “sticks” but weak joints equals a weak bridge Strong glue joints maximize the surface area to be glued Gussets maximize the “shear bonding area” for glue joints Glue adds WEIGHT. Excess glue is excess weight … Trim it off Use “quick-set” glue to build and test designs. Use wood glue for your final structure(s) Thin CCA glue runs like water. Use a special TIP to control it DROP by DROP. DON’T USE GORILLA GLUE.

SIZE OF STRUCTURAL MEMBERS …

Make “Thicker” structural members by gluing thinner sticks together (laminating). Custom laminating can place the weight (wood) where the greatest stress is. Cut “sheet” stock to size. A “skin” provides a lot of “directional” strength

There are lots of good glues Its not so much which type of glue you use, its’ how you use it MENTORING THE Inclined BRIDGE BUILDING EVENT

The concept of gusset-reinforced joints

Inclined BRIDGE BUILDING 2016 MENTORING THE Inclined BRIDGE BUILDING EVENT

EXPERIMENTAL TESTING PROGRAM WHY ???

Students will load their own bridge during competitions. Bottled Sand, Loose Sand, Combination of bottles and loose sand, Hopper-loading Students need to be cautious, yet confident. Need to have done it before.

Testing EARLY will identify your team’s best builder Encourage students to build bridges at home. Testing to failure will identify design deficiencies Video recording & slow-mo replay can show failure mode Testing & analysis will identify the weak link in the design Always improve the weak link in the next design

Always test to destruction !!!! Otherwise you don’t know how overbuilt (AND OVERWEIGHT) a bridge design is.

MENTORING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016 EXPERIENTIAL LEARNING WORKS. BREAK STICKS/JOINTS BEFORE BREAKING BRIDGES BREAK BRIDGES BEFORE COMPETITIONS STRIVE TO BUILD FOR REPEATABLE RESULTS EVOLVE DESIGN TO ACHIEVE CLOSE TO 15-Kg held DOCUMENT YOUR TESTING AND DESIGN EVOLUTION [data table, photos, videos]

BUILDING & BREAKING IS JUST TOO MUCH FUN MENTORING THE Inclined BRIDGE BUILDING EVENT

Inclined BRIDGE BUILDING 2016 Suggested Materials for your Bridge Building Team TESTING SUPPORT

Test Base (see event sheet) 2- 5-ft poles to support test base btwn tables 2- 5cmx5cmx2cm loading blocks Eye bolt, chain & S-hook(s) 2- 5-gallon buckets 50 # of dry, white sand Digital bathroom scale (reading to 0,1 kg) Digital balance, 0 to 100g, (reading 0.01g) Bubble level

CONSTRUCTION TOOLS

Metric ruler, meter stick & caliper 2ftx3ft sheets of masonite, plywood, etc. for cutting & gluing surfaces Exacto knives (or balsa cutter) COACH CONTROL Fine sandpaper, sanding block Engineering triangles (for right-angles) Thin tip extensions for CCA glue bottles Saran wrap & wax paper for gluing surface

BRIDGE MATERIALS

Balsa sticks_ various dimensions_ square & rectangular x-section_ from 3/16 to 1/32in dimensions Balsa sheets_ from 3/16 to 1/32 thick, 2-ft long CCA glue (thin & gap-filling), Insta-cure, Un-cure Wood glue (yellow type)

MENTORING THE Inclined BRIDGE BUILDING EVENT

PROTECT THE INVESTMENT Do not “over-test” the same bridge. Bridges previously tested to loads nearing the breaking point may have been damaged. If you are getting consistent results, the smartest approach may be to build two identical bridges; one for testing to failure, and a second for the competition. Stress the “fragility” of the bridge to the student(s), the lighter it is, the more easily it can be damaged through mishandling. The student should do all handling, assembling, and loading, as it is his/her responsibility. Even event staff have been known cause damage by mistake. Plastic & cardboard boxes are great for storage & transport of bridges. Foam inserts will restrict movements and limit damage from loose tools and objects inside the box.

MENTORING THE Inclined BRIDGE BUILDING EVENT

EXAMPLE EVENT RESOURCE PAGE FROM NATIONAL SCIENCE OLYMPIAD WEBSITE (not 2016 rules)

MENTORING THE Inclined BRIDGE BUILDING EVENT

Truss Bridge Powerpoints

http://www.slideshare.net/sheikhjunaidyawar/tru sses-28955458 Truss Bridge Online Analysis

http://eng.umd.edu/html/HAMLET/resources/index.html http://mathonweb.com/truss.htm http://skyciv.com/free-truss-calculator/ http://pages.jh.edu/~virtlab/bridge/truss.htm http://pages.jh.edu/~virtlab/bridge/bridge.htm http://ivanmarkov.com/truss-simulator.html

Inclined BRIDGE BUILDING 2016 Basics for a TIER 1 Inclined Bridge (1) 2 cm more than the Clear Span between “footpads” (37cm B, 47cm C) (2) Clear space in bridge for vertical eyebolt/chain at center of span (3) Bubble-level supports for 5cmx5cmx2cm loading block at center of span (4) Restricted height at “low end” (max vertical of 2cm) (5) Restricted footprint at “high end” (max 2cm [bridge length] x 5cm) (6) Strong enough to hold mass of loading block, chain, empty bucket (7) Bottom of “footpads” are “bubble-level” (8) Balanced side-to-side (resists bridge falling over sideways) (9) Target failure load between 10-kg and 20-kg (if below or above these values, add or subtract mass from bridge structure by either adding or removing bracing, or adding or reducing size of critically-loaded members

WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

Inclined BRIDGE BUILDING 2016

Tips for a COMPETITIVE Bridge (medal-worthy at Regional Tournaments)

(1) If your bridge weighs more than 30g, IT IS TOO HEAVY (2) Choose structural members of different x-sections for heavily-loaded and lightly-loaded uses and locations (3) Diagonal cross-bracing can be quite thin, but is important. It keeps long, compressed members from BUCKLING. Diagonals are needed in all 3 axes. (4) Square & rectangular x-sections of the same area have the same weight, but the rectangular x-section is much stronger if oriented properly (5) Gravity acts VERTICALLY. Your stronger structural members should be aligned with the wider edge VERTICAL and the narrow edge HORIZONTAL (6) Larger strength members should always have rectangular, never square xsections. You can laminate multiple square members to make a rectangular one

(7)Precision, balanced assembly can allow a good design to EXCEL, whereas a more haphazard assembly of the same, good design may result in only 1/2 half the failure load (and scoring efficiency) WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

PREVIOUS TOURNAMENT RESULTS

2015 “C” NC State Tourney … Top 3 had efficiencies over 2,000 Top 3 had masses less than 7.5g

2015 “C” Charlotte Regional Tourney Varsity Medals … Top 6 weighed less than 18 grams 4 of top 6 weighed less than 12 grams Only 1 of top 6 held full 15 Kg. 2 more held more than 14 kg Remaining 3 held between 7 & 11 kg Top 6 had Structural Efficiencies from 1439 to 680 2015 “C” Hickory Regional Tourney … Top 2 had Structural Efficiencies greater than 1800

2015 “B” Charlotte Regional Tourney Varsity Medals … Top 7 weighed less than 15 grams 4 of top 6 weighed less than 9 grams None of top 7 held full 15 Kg. Top 7 all held between 9.57 & 12.33 kg Structural Efficiencies from 2,638 to 773 WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

Photos of structural failure testing of balsa components

WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

Photos of bridges from ELEVATED BRIDGE tournaments

WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

Photos of bridges from NCSO 2009 ELEVATED BRIDGE event

WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

Photos of bridges from NCSU 2010 ELEVATED BRIDGE event

WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?

Photos of bridges from NCSU BRIDGE events

WHAT DO BASIC and COMPETITIVE Inclined BRIDGES look like ?