Adjust the beam properties to see how span length and material affect deflection and whether the bridge holds.
Truss Shape Analyzer
Click a truss type to see why triangles are the strongest shape in structural engineering.
What is Structural Engineering?
Structural engineers design buildings, bridges, towers, and other structures to safely carry loads. They must ensure structures do not break, bend too much, or sink into the ground — all while being cost-effective and buildable.
Types of Loads
Dead loads are the permanent weight of the structure itself — the beams, deck, and cables. Live loads are temporary forces: traffic, people, furniture. Dynamic loads include wind, earthquakes, and vibrations. Engineers must design for the worst realistic combination of all three.
Why Triangles?
Triangles are structurally rigid — you cannot change their shape without changing the length of a side. Rectangles, by contrast, can flex into parallelograms. Truss bridges use networks of triangles to distribute load efficiently along many members, each experiencing simple tension or compression rather than bending.
Beam Deflection
When a load is applied to a beam, it deflects (bends). The formula for maximum deflection of a simply-supported beam with a central point load is: δ = PL³ / (48EI), where P = load, L = span, E = modulus of elasticity (stiffness), and I = moment of inertia (cross-section shape). Doubling the span increases deflection by 8×!
Materials in Structures
Steel is strong in both tension and compression but heavy and expensive. Concrete is very strong in compression but weak in tension — reinforced concrete adds steel rebar to handle tensile forces. Wood is lightweight and renewable but variable in quality. Engineers select materials based on strength needs, cost, environment, and sustainability goals.
Check Your Understanding
1. The permanent weight of a bridge's steel beams and deck is called a:
Live load
Dynamic load
Dead load
Shear load
2. Why are triangles used in truss bridges?
They look attractive
They are rigid and cannot deform without changing side lengths
They are the cheapest shape to build
They weigh less than other shapes
3. If you double the span of a simply-supported beam (with the same load), deflection increases by: