This report aims to analyze and compare the construction methods and design of the Forth Bridge, Forth Road Bridge, and the Queensferry Crossing. Stephen Welsh requested this report on April 25, 2023.

2. Method

To gather statistical evidence about the construction, the report will include research and analysis of news articles and websites.

3. Findings

3.1

The Forth Bridge is an iconic cantilever railway bridge spanning the Firth of Forth located to the west of Edinburgh. It was built in 1882 and designed by John Fowler and Benjamin Baker. The cantilever design was unprecedented for its time and showcases Victorian engineering at its best. A cantilever bridge works by securing one side of a span, enabling the other end to carry a significant amount of weight. The bridge is 2,467 meters long and built from 53,000 tonnes of steel and 6.5 million rivets. The piers are constructed from 120,000 cubic yards of concrete enclosed within 2 feet of granite blocks, providing strong anchorage. During its construction, more than 4,000 workers were employed, resulting in 73 confirmed deaths and more presumed fatalities. In 2015, the Forth Bridge was inscribed as the sixth World Heritage Site in Scotland recognized by UNESCO.

3.2

The Forth Road Bridge, a long-span suspension bridge, opened in 1964. It was the world's largest aside from those in the United States. The bridge extends over 2.5 km. A suspension bridge uses massively tensioned cables to support the bridge's weight. The cables are attached to towers that carry the weight of both the cables and bridge. The two main cables that support the suspended deck are 590 mm thick, each made up of 11,618 high-strength wires that are 4.98 mm thick. The suspended deck comprises a steel stiffening truss with three longitudinal air gaps at roadway level for improved aerodynamic stability. Each main cable can support up to 13,800 tonnes of load. The decks are suspended from the main cables by 192 sets of four hanger ropes, varying in thickness between 44.5 and 52.4 mm. These hanger sets support between 176 to 244 tonnes of load, and they were replaced between 1998 and 2000.

3.3

The Queensferry Crossing, a cable-stayed bridge, utilizes cables that support the bridge deck and run to the supporting towers. It is 2.7 km long and is the world's longest three-tower cable-stayed bridge. In 2013, the south tower caisson was constructed with a world record 16,869 cubic meters of poured concrete handled continuously for 24 hours. Additionally, the bridge's cantilevers measured 322m in one direction and 322m in the other, totaling 644m, making them the world's longest cantilevers ever recorded during construction. It also has the highest towers of any other bridge in the UK.

4. Conclusion

All three bridges are remarkable feats of engineering. Having three distinguished landmarks in close proximity is a unique occurrence in the world. Each bridge represents different engineering practices from the Victorian-era Forth Bridge's steel and rivets to the record-breaking feats of the Queensferry Crossing's construction. It would be unfair to compare them against each other; instead, we should appreciate their individual contributions to technology and engineering.

7. References

1. The Balanced Cantilever Bridge, an Engineering Marvel

The balanced cantilever bridge is a stunning engineering feat that boasts unparalleled stability and strength. This bridge design involves two cantilevers that meet in the center, supported by a suspended span. The cantilevers essentially balance each other out, allowing for greater weight distribution and minimizing the risk of collapse.

One of the most notable examples of the balanced cantilever bridge design is the Quebec Bridge in Canada, which spans over 1,800 meters and can support the weight of huge freight trains.

2. Exploring the Functionality of Cantilever Bridges

A cantilever bridge is a type of bridge where the weight is supported by two beams or girders, which extend from opposite ends and meet at the middle. The strength of these beams allows the bridge to support heavy loads, making it an ideal choice for long spans that require maximum stability.

One of the most famous examples of a cantilever bridge is the Kingsgate Bridge in Durham, which spans nearly 100 meters and offers breathtaking views of the surrounding landscape. Cantilever bridges are also frequently used in highway and railway construction due to their durability and strength.

3. Understanding the Mechanics of Suspension Bridges

A suspension bridge is a type of bridge where the weight is supported by a series of cables, which are suspended from two towers or supports. These cables allow the bridge to span long distances while still supporting heavy loads, making them an ideal choice for extensive industrial and transportation projects.

One of the most well-known suspension bridges is the Golden Gate Bridge in San Francisco, which boasts a span of over 1,200 meters and has become an iconic symbol of America's engineering prowess. Suspension bridges are also frequently used in urban areas due to their aesthetic appeal.