VOCABULARY+BRIDGES

1. **TENSILE STRESSES:** Any force that acts in order to lengthen, or pull apart the ends of, a structural element. When hanging from a rope, both the rope and your arms, will be under Tension.

2. **ELLIPTICAL ARCH:** The simplest is the semi-circular, but a shallow, flattened semi-circle becomes an ellipse, and many mediaeval stone bridges were built with an...

3. **STRESS:** The physical demands laid upon an object or material by the forces acting on it.

4. **TRUSS:** A framework of connected members, usually made from steel, which together bear the loads on a bridge

5. **WINDTUNELS:** A tunnel used by designers to test the effects of high winds on a planned structure. This may be part of a full-size structure, or a small-scale model of the whole structure

6. **SPAN:** The unsupported length of a bridge, between its towers or piers

7. **TENSION:** Any force that acts in order to lengthen, or pull apart the ends of, a structural element. When hanging from a rope, both the rope and your arms, will be under Tension.

8. **TIES:** A part of a framework that is carrying tensile forces, or keeping two elements of a structure together.

9. **COMPRESSION:** Any force that acts in order to shorten, or push together the ends of, a structural element. When pushing your hands together, your arms will be under compression. The towers of a suspension bridge, and the piers of an arch bridge, are under compression.

10. **BENDING MOMENT:** The internal force that prevents an object from bending freely under the action of the external forces. Sagging and hogging are visible signs of it.

11. **MIDPOINT:** The central point of a structure. This is often where the structure is at its weakest, and the load at its greatest.

12. **ANCHORAGES:** The points at which the main cables on a suspension bridge are 'anchored' to the ground at either end of the bridge.

13. **RESONANCE:** The build-up of oscillatory, or wave-like, motion in an object such as a plucked guitar string or the deck of a suspension bridge in a wind.

14. **VIADUCT:** A road or rail bridge of considerable length, usually carrying vehicles at an elevated height across a valley or round a mountain side, as opposed to simply across a specific obstacle.

15. **COMPOSITES:** Materials whose properties derive from the mixture of their component materials. Individual glass fibres held together by a plastic resin forms the easily moulded, yet strong, 'fibreglass' material used for canoes, car bodies etc.

16. **DECK:** The part of a bridge that carries the roadway. Usually horizontal, and often suspended from cables or resting on an arch.

17. **ESTUARIES:** The mouth of a river where it empties into the sea. Due to erosion, estuaries are often extremely wide

18. **BEAM:** A rigid horizontal element that is used to carry a load. A beam bridge often consists of a road deck reinforced with girders. 18. **BUTTRESS:** A structure, usually brick or stone, built against a wall for support or reinforcement to resist the sideways pressure of the weight of the building

19. **CORBELLED:** An arch constructed by successive layers of brick or stone projecting further towards each other from either side of the arch, until the gap is spanned

20. **MODELLING:** A simplification of the real-life object and situation that preserves their essential nature, and allows a solution using mathematics

21. **HOGGING:** The upwards bending in a beam, usually over its piers, that is the counterbalance to sagging in other sections of the beam

22. **CABLE STAY:** A bridge design in which the road deck is supported by a series of cables attached to the top of one or more towers.

23. **ABUTMENTS:** The side support at either end of an arch bridge, necessary to withstand the horizontal forces generated by the arch's shape

24. **CAISSONS:** A cofferdam is a temporary watertight enclosure constructed on the spot where a pier is to be built. A cofferdam usually consists of sheets of steel driven into the ground to create a walled chamber

25. **GIRDERS:** A beam, usually made from concrete or steel, that is designed to strengthen another structural element.

26. **SAGGING:** The tendency of a beam to bend downwards, when acted on by a load, including its own weight.

27. **VOUSSOIRS:** The trapezoidal stones that are often used to form a rounded arch.

28. **LOAD:** A force that is to be carried by a structure. Examples include the weight of traffic on a bridge and the wind on the side of a tent

29. **FOOTERS:** The stones at the base of a bridge structure that take the loads onto the foundations.

30. **PIERS:** The part of a bridge that supports the horizontal element, and carries the load to the ground, especially the intermediate support in a multi-arched bridge.

31. **KEYSTONE:** The central stone in an arch, and begins the distribution of the vertical 'load' forces down and around the arch

32. **ARAMID:** An artificially-made organic material that forms very long and stiff fibres

33. **AQUEDUCT:** a channel carrying water from its source (a lake or spring) to where it is needed

34. **STRUTS:** A part of a framework that is carrying compressive forces, or keeping two elements of a structure apart

35. **ARCH:** A span that consists of an upwardly curved beam. The forces from the centre are distributed outwards.