Load Busters

Scenario 1: High-Tension Perimeter Outrigger Cables Dominant Force: Tension

Options considered: Braided high-carbon steel cables vs. Solid cast iron struts.

Selected Material:

Material Property Justification:

Scenario 2: Ground-Level Columns Supporting 50 Stories Dominant Force: Compression

Options considered: Steel-reinforced concrete columns vs. Hollow aluminum tubes.

Selected Material:

Material Property Justification:

Scenario 3: Joint Bolts Fastening Horizontal Floor Girders to Columns Dominant Force: Shear

Options considered: High-strength steel gusset rivets vs. Standard plastic bonding anchors.

Selected Material:

Material Property Justification:

Part 4: Skyscraper Failure Case Study

Incident Report: During a major windstorm, an unbraced 30-story commercial tower began violently swaying and corkscrew twisting. On the 12th floor, horizontal girder connection bolts sheared clean through, causing a corner vertical column to buckle outward under extreme compression.

1. What combination of lateral and vertical forces caused the joint shear and column buckling?

2. Propose one structural geometry modification (such as X-bracing) to prevent this tower failure:

Unit 1: Load Busters • Student Investigation Sheet Page 2 of 2

3. Quantitative Evaluation

• Enforce fair test controls during load testing.
• Compute structural efficiency (\(\frac{\text{Live}}{\text{Dead}}\)).
• Forensically diagnose failure & justify redesigns.

Required Lab Materials & Testing Apparatus Per Class of 28 (7 Teams of 4)

Prototyping: 350 balsa/basswood sticks (1/8" sq), wood glue or low-temp glue guns, cardstock gussets.

Drafting: Grid paper (1 cm / 0.25 in), metal rulers, drafting triangles, masking tape, hobby knives.

Testing Rig: 5-gal bucket, S-hook, loading block (5x5 cm with center eyebolt), sand or barbell weights.

Measurement: Digital scales (0.1 g precision), spring scales, safety goggles (ANSI Z87.1 for all).

Load Busters Engineering Curriculum • Sequence Overview • Document 1 of 2 Page 1 of 2

Pedagogical Facilitation, Safety & Evaluation

Managing Student Misconceptions, Destructive Rig Controls, and Performance Rubrics

Facilitator Playbook

Diagnostic Remediation: Common Student Misconceptions

× Misconception 1: "More glue equals a stronger joint."

Students slather globes of glue onto connections, believing mass guarantees hold. In reality, excess glue adds severe dead weight, creates brittle failure planes, and shrinks structural efficiency.

✓ Teacher Countermeasure: "Thin Fillet & Gusset Plate"

Demonstrate that wood-to-wood contact with a micro-thin glue film and cardstock gusset plate is 300% stronger and 80% lighter than globs. Reinforce dead weight penalty during efficiency scoring.

× Misconception 2: "Square bays provide adequate framing."

Students build rectangular boxes without diagonal members, assuming vertical sticks bear all vertical load. Under minimal lateral shear or uneven loading, rectangular bays instantly parallelogram and collapse.

✓ Teacher Countermeasure: "Triangle Rigidity Test"

Have students hold a 4-pin square vs. a 3-pin triangle. Point out that triangles cannot change angles without altering side lengths, forcing shear loads into pure tension and compression paths.

× Misconception 3: "A broken tower represents a failed project."

Middle schoolers often feel demoralized when their tower snaps. They conflate structural failure with academic failure, missing the essential purpose of destructive stress-testing.

✓ Teacher Countermeasure: "The Forensic Autopsy Mindset"

Frame testing day as a forensic autopsy. Emphasize that engineers purposely push prototypes to 100% capacity to isolate the single weakest link. High grades derive from failure diagnosis and redesign insight.

Controlled Destructive Testing: Standard Protocol & Safety

Standardized Loading Protocol (Fair Test Controls)

1. Pre-Test Tare: Record exact tower mass (\(M_{\text{dead}}\)) to 0.1 g on digital scale.
2. Centering Block: Place 5x5 cm wooden load block flat on tower top surface.
3. Level Suspension: Thread S-hook through eyebolt so load bucket hangs strictly plumb.
4. Incremental Addition: Add mass at a steady rate of 250 g every 5 seconds.
5. Failure Point: Cease immediately upon column buckling, joint rupture, or >15° tilt.

Mandatory Lab Safety Checklist

• Eye Protection: ANSI Z87.1 goggles worn by all students in testing blast radius.
• Containment Drop Box: Keep bucket over cushioned foam bin to absorb weight drop.
• No Hands Under Load: Use funnel tube or measuring scoop to pour mass safely.
• Clear Perimeter: Maintain 1-meter clear zone around testing rig during loading.

Assessment Weighting & Structural Efficiency Metric

Grading Architecture

Force Mechanics Lab (L1)20%

Blueprint & Tower Build (L2)30%

Testing Report & Autopsy (L3)30%

Redesign Defense Pitch (L3)20%

Structural Efficiency Ratio (SER) Benchmark Formula Key Evaluation Metric

\[ \text{SER} = \frac{\text{Live Load Supported (g)}}{\text{Dead Load of Tower (g)}} \]

A tower holding 12,000 g with a mass of 30 g achieves an efficiency score of 400. Scoring prioritizes high ratio over raw mass held, leveling the playing field against heavy, over-built structures.

Targeted Scaffolding (Striving Learners & ELL): Provide pre-printed 1:1 gusset templates and triangle jig guides. Use bilingual force terminology flashcards (tension/tensión, compression/compresión). Pair students strategically in 3-4 person specialist roles (Architect, Materials Manager, Quality Control Lead).

Engineering Extensions (Advanced Learners): Challenge advanced teams with dynamic lateral load testing using an oscillating box fan (simulating hurricane winds) or introduce cost-budget constraints ($100 virtual budget where sticks = $2/ea and gussets = $1/ea) to optimize cost-efficiency.

Load Busters Engineering Curriculum • Sequence Overview • Document 2 of 2 Page 2 of 2

Stations 3 & 4

Station 3: Shear Testbed (Parallel Sliding Stress)

Materials: Playing Card Decks • Foam Layers • Paper Fastener Pins

Procedure: Part A: Place a deck of 52 cards on a smooth table. Apply a horizontal palm force across the top card. Observe how internal friction allows parallel layers to slide past one another. Part B: Connect two cardstock strips with a single brass pin; pull opposite ways until pin cuts or card tears.

| | 3. Double-Pin + Gusset Cardstock | Opposite Pulling |

|

Shear Slip Diagram (Card Angle):

Key Analysis: How does high lateral wind against a skyscraper's facade produce shear stress on joint bolts connecting floors to columns?

Station 4: Torsion Testbed (Twisting & Rotational Torque)

Materials: Gridded Foam Beams • Rectangular Sponges • Protractors

Procedure: Secure the base end of the gridded foam beam flat against the table. Twist the top end clockwise by 45°, 90°, and 180°. Watch the square grid lines warp into diagonal diamonds. Measure the diagonal wrinkles and note where tension and compression coexist.

| | 90° Rotational Twist |

|

| | 180° Severe Torque |

|

|

Torsional Distortion Sketch (45° lines):

Key Analysis: Why does torsion create diagonal tension lines (at 45°) along the exterior walls of a skyscraper during an earthquake or vortex wind?

Engineering Synthesis: Preparing for Tower Prototyping

Synthesize your observations from all four stations. In the space below, explain which structural force you anticipate will be the most dangerous threat to your team's balsa tower during vertical load testing, and identify one design feature you will include to counteract it.

Load Busters Engineering Sequence • Force Mechanics Hands-On Lab Page 2 of 2

Ground Footprint 10 cm Story Height 10 cm Per Bay • Cross-Braced Top Load Deck 8 cm

Part 4: Quality Control & Pre-Test Inspection Checklist

Both team engineers must verify every criterion before the skyscraper prototype can be approved for destructive stress testing.

Vertical height ≥ 40.0 cm from base to roof

Base footprint fits within 10.0 × 10.0 cm square

Rooftop level allows flat 8×8 cm load plate seating

Dry Dead Load mass ≤ 60.0 grams

Joints cured 24 hrs (no wet or tacky glue)

All 4 exterior faces cross-braced against torsion

Lead Quality Inspector Approval Skyscraper qualifies for standardized fair testing

Inspector Signature:  

Tare Dead Weight:   g

Unit 1: Load Busters • Tower Prototype Blueprint Page 2 of 2

The Solution: 4-Faced X-Bracing

Install diagonal cross-braces across all four exterior walls and at horizontal floor levels:

• Creates rigid 3D space truss box structure
• Halves unsupported column length to prevent buckling
• Distributes downward live load evenly to all 4 columns

Every successful skyscraper tower uses X-bracing on all four sides to lock vertical geometry!

Workshop Action Plan: 50 Minutes

Sprint Timeline

00-05m

Blueprint Sign-off

Finalize 40 cm tower face layout on 1:1 drafting grid. Verify all triangles are closed.

Step 1

05-25m

2 Tower Faces

Pin sticks over wax paper on blueprint. Build 2 identical flat tower faces with thin glue films.

Step 2

25-42m

3D Box Assembly

Join the 2 faces with cross-struts and X-braces to form 4-sided tower. Seat 8×8 cm roof plate.

Step 3

42-50m

Tare Inspection

Weigh dead load on digital scale (≤ 60.0 g). Check ≥ 40 cm height. Place on curing rack for 24h.

Step 4

Safety Protocol: Wipe excess glue immediately • Safety glasses on when cutting sticks

[ Sketch fractured 40 cm tower frame & circle initial break point ]

Part 5: Engineering Redesign & Material Justification

Based on the exact failure point identified above, propose an engineering redesign that will increase live load capacity without exceeding the 60.0 g dead load limit.

1. Structural Modification (Story Height, Cross-Bracing, or Column Splicing):

2. Material Selection Justification (Why does your proposed material/composite solve the specific force that caused failure?):

3. Dead Load Impact: How will your redesign avoid adding unnecessary dead weight?

Lead Structural Engineer Certification I verify that testing was conducted under strict fair test conditions.

Lead Engineer Signature:  

Unit 1: Load Busters • Tower Destructive Lab Report Page 2 of 2

Structural efficiency measures how many times its own weight a skyscraper carries before failure.

Team Alpha: Heavy Tower

Dead Load: 58 g • Live Load: 2,320 g

Efficiency = 2,320 ÷ 58 = 40.0

Team Beta: Optimized Skyscraper

Dead Load: 34 g • Live Load: 2,720 g

Efficiency = 2,720 ÷ 34 = 80.0 (2× Winner!)

A lighter tower that carries the same load has double the structural efficiency.

The Redesign Defense: 3-Part Pitch

NGSS Redesign Step

Step 1

Isolate Failure

Name the exact mechanical force (tension, compression, shear, torsion) that exceeded material tolerance.

"Corner column buckled"

Step 2

Geometry Fix

Propose a structural geometric change (shorter story bays, extra cross-strut, corner gusset plate).

"Add mid-story X-brace"

Step 3

Material Defense

Justify material selection based on specific properties (lap splice wood columns vs card gussets for shear).

"Reinforce with card gusset"

Debrief Pitch: Every team presents their autopsy & redesign blueprint to the class!