STRUCTURES

1. STRENGTH AND STRUCTURES STRENGTH/FORCE: Is all that can deform a body or modify its state of movement or rest. STRUCTURE: is the group of elements of a body that are bound to support the effects of the strengths that act over it. The structure keeps the body from breaking or deforming in excess. Structures have to be resistant and stable.

The first structures were made of wood, then man also used stone. Nowadays we use concrete and iron

2. EFFORTS/STRESS If one or several strengths act over an element of a structure, the element will experiment an internal tension. This internal tension is called effort/stress.

2.1 Different kinds of EFFORTS/STRESS TRACTION/TENSILE COMPRESSION FLEXION/BENDING TORSION CUT/SHEAR

TRACTION/TENSILE THE ELEMENT OF A STRUCTURE STRETCHES

COMPRESSION THE ELEMENT OF A STRUCTURE CRUSHES

FLEXION/BENDING THE ELEMENT OF A STRUCTURE BENDS

TORSION THE ELEMENT OF A STRUCTURE TWISTS

CUT/SHEAR THE ELEMENT OF A STRUCTURE IS DIVIDED IN TWO PARTS

Efforts activities Which efforts are applied in the following examples? A B C D E F

A B C ImageStructureEffort ACableTraction BShock absorberCompression CRope guideTraction

D E ImageStructureEffort DColumnCompression EBridgeFlexion Which efforts are applied in the following examples?

ImageStructureEffort FNutTorsion GRivetShear FG Which efforts are applied in the following examples?

CHECK DIFFERENT TYPES OF EFFORTS Image Effort

CHECK DIFFERENT TYPES OF EFFORTS Image Effort 1traction 2flexion 3compression 4flexion 5compression 6traction

3. STRUCTURAL ELEMENTS These are the most common elements that can be found in a structure. Foundations Columns Girders Arches Traction bars (Cables)

Foundations are the base of any building and they are situated under the ground and made of concrete concrete

Girders are horizontal bars that receive flexion efforts Foundation Column Girder Forces Columns are vertical bars that receive compression efforts

Arch: A semicircular shape that joins the gap between two pillars. Traction bars: Cables or bars which support traction efforts.

As we know, a structure has to be resistant. A resistant structure keeps its shape when forces are applied. 4. RESISTANT STRUCTURES

The triangle is the only geometric shape that cannot be easily deformed by applying forces to any angle. 4.1 THE TRIANGLE

The use of triangular structures is very interesting because they are very resistant, light and easy to construct. crane pylon

Triangulation makes it possible to transform shapes into a combination of triangles and therefore makes them non-deformable.

Examples of triangulation are seen all around us especially in the construction industry (building and civil engineering).

Some examples are shown below. Look carefully how numerous triangles make each structure.

Add bars to these structures to form triangles and make them non-deformable.

The arch is another resistant structure that provides resistance to structures by distributing the effort that structure supports. 4.2 THE ARCH

5. STABLE STRUCTURES Structures have to be stable. A structure is stable if it keeps its position when forces are applied.

Stability is obtained by distributing the mass evenly. Mass centre evenly distributed Mass centre unevenly distributed

The mass centre is where all the weight is concentrated He has the mass centre evenly distributed

When the mass is not evenly distributed, you can stop the object from falling in different ways, such as increasing its hold to the ground. hold

6. TYPES OF ARTIFICIAL STRUCTURES Massive: a great concentration of material predominates

Vaulted : Arches, vaults and domes are important holding and supporting elements arches vaults domes

Sub-frame: made up of timber (wood), steel or concrete intersecting elements. The structural elements are: girders, pillars or columns, and foundations. Foundation Column Girder Forces

Triangulated: Made up by linking many triangles forming flat or spatial networks. crane oil rig pylon

Suspended: They are held by cables

REVISION ACTIVITIES 1Effort A door knob An arch A pen tip when you write A screwdriver when screwing The cable of a suspended bridge A lintel Scissors the cord of a blind Pedal axes Girders on a bridge

Effort A door knobTORSION An archCOMPRESSION A pen tip when you writeCOMPRESSION A screwdriver when screwingTORSION The cable of a suspended bridgeTRACTION A lintelFLEXION ScissorsSHEAR the cord of a blindTRACTOIN PedalsTORSION Girders on a bridgeFLEXION

2. Name the effort in each of the following objects A CB CD E

3. Which of the following structures will support efforts best? Why?

4. Which structure is more stable?

5. Which of the following shapes are non-deformable? What can we do to make the other shapes non- deformable?

working arm cables base weight mast 6. Indicate the efforts that the following parts of the crane are subjected to.

working arm cables base weight mast working armcablesbasemastweight FLEXIONTRACTIONCOMPRESSION TRACTION

7. Draw this bridge and indicate where the main efforts are.

Compresion Flexion