Lesson 9: Structural Loads – Permanent vs. Variable Forces

Why must engineers account for the weight of the building itself as a force?
How do temporary environmental factors, like snow or wind, change the requirements of a structure?
If a building is empty, is it under less "stress" than when it is full?

Load
Dead Load
Live Load
Variable Force
Constant Force
Structural Integrity
Magnitude
Foundation.

PS3: Energy (Forces and motion).

ETS1: Engineering Design (Developing models to analyze loads).

ETS 2: Links among engineering, technology, science, and society.

Students practice interpreting technical definitions from informational texts and categorizing data sets based on specific criteria (constant vs. variable).

Description:

Day 1: Defining the Weight of the World. The lesson introduces loads as the forces acting upon a structure. Students learn that dead loads are permanent, predictable weights like walls, floors, and fixed equipment. They contrast this with live loads, which are temporary or movable, such as people, furniture, or snow. Students perform a "Classroom Load Audit," identifying items and justifying their classification.

Day 2: Real-World Load Analysis. Using slides of iconic structures (e.g., The Mark Twain House, Golden Gate Bridge), students identify potential live and dead loads specific to those environments. They discuss how "Live Loads" can change in magnitude and position, such as traffic on a bridge or wind pressure on a skyscraper's walls.


Purpose: To understand that the weight of a structure (load) acts with gravity on the foundation and must be perfectly distributed to prevent buckling or snapping.


DOK Level: 2 (Basic Application) for identification; 3 (Strategic Thinking) for analyzing load distribution in complex structures.

Real-World Connections:

Calculating how many vehicles a bridge can safely hold (Live Load).

Understanding why roofs in snowy climates are designed differently than those in deserts (Environmental Live Loads).


Culturally Relevant Connections:

Analysis of the Great Mosque of Djenné, noting how its massive mud walls serve as a permanent dead load that requires annual communal maintenance.

Discussion of how religious structures like the Cologne Cathedral support massive bells and crowds of people as significant live loads.

Misconception: "Only heavy things count as a load."
Correction: Every part of a structure, including the lightest floorboard, contributes to the dead load.

Misconception: "Furniture is a dead load because it just sits there."
Correction: Furniture is a live load because it is movable and not a permanent part of the building's structure.

English Learners: Use a T-chart with pictures of "Fixed" vs. "Movable" items to build the load vocabulary.

Kinesthetic Learners: Have students stand still (representing a dead load) and then walk across a designated "bridge" area in the room (representing a live load) to visualize the change in magnitude and position.

Formative: Completion of the "Classroom Load Audit" table, including a reasoning column for each classification.

Summative: Students are given a photo of a new structure (e.g., a stadium) and must list five dead loads and five live loads it will likely encounter.

Source Texts: "0.5-Structural Forces Investigation," "0.5-Types of Stress on Structure".

Visuals: Slides 8-15 of "0.5-Types of Stress on Structure".

Speaker Suggestion: A local building inspector to talk about "Maximum Occupancy" limits as a way to manage live loads for safety.