Load-Bearing Strength
Load-bearing strength is how much weight a structure can hold before it breaks or bends.
A stack of dinner plates sits on a shelf. Each plate adds weight, and the shelf holds fine — up to a point. Add too many plates, and the shelf bends or snaps under the load. That breaking point is its load-bearing strength.
Explaining load-bearing strength by grade level
Think about an eggshell. It seems thin and weak. But when you press down on top of a curved eggshell, it holds a lot of weight. The curved shape pushes the force out to all sides. That spreading is what makes it strong.
Projects that explore load-bearing strength
How cables attach to towers changes a bridge's load-bearing strength. Both suspension and cable-stayed bridges use cables, but they connect them to the towers in different ways. When you build scale models and add weights until each bridge fails, the difference becomes clear. The cable-stayed design held nearly twice the weight. A suspension bridge collapsed right after a single cable snapped, showing how one weak point can destroy the whole structure's ability to hold weight.
A structure's load-bearing strength depends on its shape. Curved shapes like domes spread weight evenly. That is why they hold more weight before they break. In this experiment, four eggshell domes support far more books than most people guess. The curved shape pushes force outward and downward. This prevents the shells from collapsing.
The arrangement of layers inside a laminated beam changes how much weight it can hold. You design seven different five-layer patterns on paper, cut each layer on a scroll saw, and glue them together with wood glue. Each finished beam goes on a test platform, where a lever loads weight onto it until it breaks. The strongest beam resisted 149 kilograms before breaking; the weakest held only 83 kilograms. Small changes in how the layers were arranged produced large differences in strength.
The overall shape of a structure determines its load-bearing strength. Engineers choose from many bridge designs because each one handles force in a different way. You can test this by building three bridges with different structural designs and placing weights on each one. The amount each bridge bends tells you which design resists force best and holds the most weight before it breaks.
Proportions matter: making a dome wider without raising its height weakens the structure. To test this, you bend plywood strips of increasing length into arches that all stand 100 mm tall. As each strip gets longer, the span increases — representing a wider dome diameter. You hang a pail from the center of each arch and add sand in 100-gram increments until the arch collapses. The wider arches fail under less weight. Increasing the diameter while keeping the height fixed reduces how much the structure can hold before it breaks.