Structural Stability and Strength Making it Work

Stability Stability is the ability of a structure to maintain, or regain, a balanced position when external forces act on it. A stable structure maintains it position and shape over an extended period of time An important factor in maintaining stability is an object’s centre of gravity Centre of Gravity: the point around which a structure’s mass is equally balanced in all directions; the point where the mass seems to be concentrated

Making Structures Strong The Beam

What’s a beam? A beam is any reasonably level structure that is designed to support a load A doorway consists of: a horizontal upper beam two vertical supports

Strengthening the Beam On its own, a beam might not be strong enough to support a large load Beams can be strengthened in many ways It can be as simple a choosing a stronger material, steel is stronger than wood, but also heavier Sometimes engineers use other ways to strengthen beams

I-Beams One way to strengthen a beam is to change its shape An I-beam is stronger than a normal beam

Corrugation Folding a beam also adds strength Placing triangular ridges, grooves, or folds in a structure is called corrugation Common in cardboard, and in plastic and metal for roofing

Rebar Concrete beams are often strengthened with steel rods called rebar Beams experience compression on top and tension on the bottom Concrete can handle a lot of compression, but not much tension Rebar solves that problem when it is added This is called reinforced concrete

Cantilevers Cantilevers are beams that are only supported at one end Tree branches and diving boards are simple examples of cantilevers

Supporting Cantilevers These supports are all built into the framework of a cantilever to strengthen it Tie: designed to resist tension Strut: designed to resist compression Gusset: flat, plate-like, often triangular, supports the connection to the support base

Making Structures Strong The Truss, Arch, and Dome

Making it stronger… and more interesting Sometimes designers want to use shapes other than beams to make structures stronger and more interesting looking They do this by using triangles (trusses) or curves (arches and domes)

The Truss A truss is a network or beams that form triangles A truss can be used as a bridge or a cantilever, and many other applications Most people are familiar with trusses used in roof construction for houses, construction cranes, hydro towers, and bridges Trusses can be bent and still retain their strength The triangles help the structure support more weight Trusses can be used for things that beams can’t

STOP!! Build a Truss

The Arch An arch is a curved structure often used to support loads They’re used in spaces where supporting beams are not practical It transfers compression force downwards Many early civilizations, like the Romans, used arches a lot. Some, built over 2000 years ago, are still standing

The Dome A dome is a structure that looks like the top half of a sphere or an egg Like an arch, a dome directs compression force downward Unlike an arch which directs force along only one plane, a dome directs it down many planes You could consider a dome to be a series of arches connected at a centre point

Geodesic Dome