Science · Grade 7 · Heat in the Environment · Term 4

Loads on Structures: Dead, Live, Dynamic

Identifying different types of loads (dead, live, dynamic) that act on structures.

• Ontario Curriculum Expectations
• MS-ETS1-2

About This Topic

Loads on structures fall into three categories: dead loads, the permanent weight of the structure itself such as concrete and steel; live loads, variable forces from occupants, furniture, vehicles, or snow accumulation; and dynamic loads, forces with motion like wind gusts, earthquakes, or traffic vibrations. In the Ontario Grade 7 science curriculum, students identify these loads and analyze their effects on everyday structures like bridges and roofs, addressing key questions on differences between dead and live loads, wind impacts on design, and snow load predictions.

This topic aligns with engineering design standards such as MS-ETS1-2 by building skills in evaluating how loads influence stability and safety. Canadian examples, including heavy snow on Ottawa roofs or wind on Toronto skyscrapers, make concepts relevant and show why engineers overdesign for worst-case scenarios. Students practice prediction and data analysis, essential for scientific thinking.

Active learning shines here because students can build and test simple models to see loads cause bending, buckling, or collapse firsthand. Collaborative experiments reveal patterns invisible in textbooks, while failures teach resilience in design.

Key Questions

1. Explain the difference between dead loads and live loads on a bridge.
2. Analyze how dynamic loads, like wind, affect building design.
3. Predict the impact of an unexpected heavy snow load on a roof structure.

Learning Objectives

• Classify given loads as dead, live, or dynamic based on their characteristics.
• Compare and contrast the effects of dead and live loads on a simple beam structure.
• Analyze how dynamic loads, such as wind or vibrations, influence the design requirements of a building.
• Predict the potential structural impact of an increased live load, like heavy snow, on a roof.

Before You Start

Properties of Materials

Why: Understanding how different materials like wood, steel, and concrete behave under stress is foundational to comprehending how loads affect structures.

Forces and Motion

Why: Students need a basic understanding of forces, including pushing and pulling, and the concept of motion to grasp how loads are applied and how dynamic loads differ.

Key Vocabulary

Dead Load	The permanent, fixed weight of a structure itself, including materials like concrete, steel, and the building's own components.
Live Load	Variable or temporary forces acting on a structure, such as people, furniture, vehicles, or snow accumulation.
Dynamic Load	Forces that involve motion or change over time, such as wind gusts, earthquake tremors, or vibrations from traffic.
Structural Integrity	The ability of a structure to withstand applied loads without failure, ensuring its safety and stability.

Watch Out for These Misconceptions

Common Misconception

Dead loads are always heavier than live loads.

What to Teach Instead

Dead loads are fixed but often lighter than maximum live loads like crowds or snow. Model testing lets students add variable weights to see live loads exceed dead ones, correcting overload assumptions through direct comparison and measurement.

Common Misconception

Dynamic loads act just like static live loads.

What to Teach Instead

Dynamic loads involve rapid changes and vibrations that amplify stress, unlike steady live loads. Hands-on fan tests on bridges show swaying and quicker failure, helping students observe motion effects and discuss energy transfer in groups.

Common Misconception

Structures in calm areas ignore dynamic loads.

What to Teach Instead

Even mild winds or footsteps create dynamics; ignoring them risks failure. Outdoor wind tests or shaker tables demonstrate this universally, with peer reviews refining predictions.

Active Learning Ideas

Stations Rotation: Load Testing Stations

Prepare four stations: dead load (fixed weights on beams), live load (adding/removing sandbags), dynamic load (fan blowing on models), and prediction sketches. Small groups rotate every 10 minutes, test structures, record deflections or failures, and discuss results.

45 min·Small Groups

Pairs Challenge: Pasta Bridge Loads

Pairs construct bridges from pasta and marshmallows, then apply dead loads with books, live loads by adding weights gradually, and dynamic loads with a fan or shaker. Measure span before collapse and redesign based on data.

50 min·Pairs

Whole Class Demo: Snow Load Roofs

Build cardboard roof models supported by walls. Class adds wet sand or snow-like weights to simulate accumulation, observing sagging. Predict safe limits beforehand and vote on strongest design.

30 min·Whole Class

Individual Prediction Sheets: Classroom Audit

Students list dead, live, and dynamic loads on school structures like desks or gym roofs, sketch forces, and predict failure points. Share and verify with group tests.

20 min·Individual

Real-World Connections

• Structural engineers in Vancouver must account for significant live loads from heavy snowfall on mountain resort roofs, designing them to prevent collapse.
• Bridge engineers designing the Confederation Bridge in Prince Edward Island must consider dead loads from the bridge materials, live loads from traffic, and dynamic loads from strong winds and ice movement.
• Architects designing skyscrapers in Toronto must analyze dynamic wind loads, using aerodynamic shapes and damping systems to ensure occupant safety and structural stability.

Assessment Ideas

Quick Check

Present students with images of different scenarios: a bridge with cars, a building during a windstorm, a house with a heavy snow layer, and the materials of a building itself. Ask students to label each scenario with the primary type of load (dead, live, or dynamic) acting upon it and briefly explain their reasoning.

Discussion Prompt

Pose the question: 'Why is it more critical for engineers to consider dynamic loads on a tall building than on a small, single-story shed?' Facilitate a class discussion focusing on the effects of motion, changing forces, and amplification of effects with height.

Exit Ticket

Ask students to write down one example of a dead load, one example of a live load, and one example of a dynamic load they might encounter on their way to school. For the live and dynamic loads, ask them to briefly describe how that load might affect a structure.

Frequently Asked Questions

What are examples of dead, live, and dynamic loads on structures?

Dead loads include the weight of beams, walls, and roofs themselves. Live loads cover people on a floor, cars on a bridge, or snow on a roof. Dynamic loads feature wind shaking a tower, earthquakes rattling foundations, or vehicles causing vibrations. Teaching with local Ontario examples like Toronto bridges under traffic helps students classify real cases accurately.

How do loads influence building design in Canada?

Canadian engineers design for heavy snow as live loads and high winds as dynamic loads, per national codes. Structures like the CN Tower use deep foundations for dead loads and flexible materials for dynamics. Students analyze these via diagrams, connecting curriculum to safety standards and predicting adaptations for regions like snowy Ontario winters.

How can active learning help students understand loads on structures?

Active learning engages students through building and testing models, such as spaghetti bridges under weights or fans, making invisible forces visible via collapses and measurements. Group rotations ensure collaboration, while prediction sheets build accountability. This approach corrects misconceptions faster than lectures, as failures provide memorable feedback and spark redesign discussions, aligning with inquiry-based Ontario science.

What key questions guide teaching loads on structures?

Focus on explaining dead versus live loads on bridges, analyzing dynamic wind effects on buildings, and predicting snow impacts on roofs. Use these to structure lessons with model tests and data logs. This targets curriculum expectations, develops prediction skills, and links to engineering design for Grade 7 mastery.