Construction and processing materials used in civil structures over time
Stone
- The earliest remaining bridges were made from stone/masonry materials.
- These date back to the Romans.
- They were successful due to the excellent structural design and massive weight.
- However they were often labour intensive and were expensive.
Timber
- Obviously one of the first materials used in bridges
- It holds excellent compression, tension and bending stress
- But it has very poor weather resistance and rots.
- Many of the older bridges don't exist today.
- Innovations such as the lamination of large cross sections of timber can increase its durability.
Iron
- Developments in the shaping of iron allowed it to be used in bridges
- Cast iron was used in the late 18th century.
- Yet cast iron was extremely brittle and poor in tension, making it a relatively bad material for bridges
- Developments in Wrought Iron made it the dominant material in the mid-19th century.
- Wrought iron was relatively difficult to make, and had some undesirable properties.
- Ultimately, Steel replaced Wrought Iron in 1890
- Steel was a much better material:
- It was malleable and ductile
- Production was simple
- Stronger in both tension and compression
- Steel was a much better material:
Recent developments
- Modern bridges utilise Steel reinforced Concrete within bridges.
- This allows for a material that is extremely easy to shape and yet strong in both tension and compression.
- Pre-tensioning and Post tensioning may be used to further reinforce the material
- Different cross sectional shapes such as I-Beams and Box Girders are being used to reduce the amount of material used while keeping the same strength.
- I-Beams have the best efficiency as it has the most material away from the neutral axis.
- Box girders can withstand unusual torsional loads
page revision: 0, last edited: 04 Jul 2011 02:26