Construction of bridges - Essay Example

CONSTRUCTION OF BRIDGES Introduction Indeed, bridges act as physical structures designed to span geographical obstacles such as rivers, valleys, and roads for the purpose of establishing passage over the obstacle. Currently, there exist thousands of bridge designs that serve the general purpose of providing passage between two different points. The designs depend on different aspects such as the purpose of the bridge, the nature of terrain, materials used, and the availability of resources to fund the construction process. This paper seeks to analyze the construction of one of the best bridges in Australia known as Sydney Bridge. Again, the paper will focus on the analysis of materials used to construct parts of the bridge. Description of Sydney Bridge In 1932, the government commissioned the construction of Sydney Bridge. Interestingly, during the construction of the bridge, engineers used steel made up of 6 million hand driven rivets. Also, the bridge has huge hinges to absorb expansion due to the hot Australia sun. In terms of size, Sydney Bridge boasts as one of the largest bridges in the world measuring 1149 meters in length. Its arch spans 503 meters wide and 134 meters above the sea level. Amazingly, the bridge has eight vehicle lanes, a sizable footway, and a series of train lane. Due to many features, engineers used a great deal of materials to meet the design requirements. For example, contractors utilized around 95000 tons of concrete, 52,800 tons of steel, and 58.8 meters of long hangers. In the modern days, most Australians use the bridge to link them between the city and other northern towns. One of the benefits associated with the bridge include the reduction of long distance travel and transportation via the ferry (Balderstone and Bowan 2006). The picture below shows the initial stages of Sydney Bridge construction process:- Due to its massive size, the bridge needed a huge workforce to undertake the construction. Hence, the bridge needed the service of specialized personnel such as engineers to design different parts, surveyors to do the access the site, and craftsmen among others. Unfortunately, the size of the bridge posed some health threats to workers. Health specialists did not implement health and safety standards such as the handling of red hot rivets. As a result, fifteen workers lost their lives during the construction process (Davison &Herst, 2001). Role of Civil Engineers in the Construction of Italian Bridge Structures John Jacob Crew Bradfield, a renowned civil engineer, dedicated most of his work in designing and building the Italian bridge structures. Bradfield acquired several academic certificates from Sydney University. In particular, the prominent civil engineer attained a degree in Bachelor of Engineering and a Masters degree from the same university. During his PhD studies, Bradfield defended his thesis on electric railways and the Sydney Harbor Bridge. As a civil engineer in the department of aviation, he supervised the expansion of the airport to the Alexandra Canal. Professionally, he worked for the Queensland railway and later moved to the South Wales Department. Furthermore, Bradfield specialized in several fields such as designing of bridges, providing a specification for the materials needed, giving a detailed drawing of bridge structures, and supervising the construction operations. As a renowned and consultant engineer in Australia, Bradfield participated in many construction projects such as designing cataracts, dams, and the circular Quarry Railway station. In most cases, his works coincided with the construction of the underground railways. Apart from Bradfield, John Thomas Lang made major contributions in the construction of Italian bridge structures. Lang’s contributions enhanced significant progress in the project. Materials Used in the Construction Process Indeed, engineers used a variety of materials as per the requirements of the design. Some of the materials include the rivets, steel, concrete, cable sockets, and other alternative materials. Each set of materials had its own specifications as described below:- 1) Rivets Technically, engineers preferred the utilization of rivets made of mild steel. According to their preference, mild steel has enough tensile strength and shear strength that approximates 415- 490 MPa. Hence, the bridge needed high strength due to the high loads expected to pass over it. Hence, engineers used more than 6,000,000 rivets to assemble the various structures in the bridge. Craftsmen inserted red hot rivets in the plates with the help of pneumatic riveting guns. 2) Steel Steel played a major role since the entire structure consisted of steel. Engineers used the silicon steel instead of the normal mild steel to sustain both live and dead loads. Besides, the steel had a greater proportion of Pearlite content making it stronger and tougher. The construction team attained a yielding factor 1.3 times higher than the normal mild steel (Litchfied& Frank, 1995). 3) Concrete The construction team laid the structure four large concrete pillars, two in both sides. Additionally, the team poured the concrete in sections and not as a complete block. Throughout the design process, engineers preferred desirable properties over other properties to bring the best outcome. In this case, engineers used a special form of concrete to save on the structural weight. Hence, the concrete served as main bridge girders to dissipate the stresses caused by the wheels. 4) Cable Sockets The utilization of cables helped to provide support for the bridge. Consequently, the cable sockets prevented the bridge from falling into the harbor. 5) Alternative Materials As an alternative material, designers considered the wrought iron due to its high elasticity and high tensile strength. Through the action of heating and reheating, the wrought iron can achieve the desired strength by sustaining live and dead loads. However, they possess softness properties hence vulnerable to chemical attacks through pitting. Green Building Concept and Principle for the Italian Bridge Structure Globally, most people recognize Australia as the top country in green and sustainable building. Moreover, the green building bridge structure in Australia has great impact on the construction and the benefits associated with the environment. The implementation of green building concept increases sustainability through reductions in operational costs, an increase in tenant attraction, and increased return on investment. Honestly, the utilization of high-strength concrete and finely engineered structure could reduce the amount of steel required for the construction. To improve the desired properties of the bridge, engineers should construct a canopy for shade provision and the adoption of double spiral design to reduce the amount of steel needed. Again, to increase sustainability and longevity, craftsmen should have constructed the entire bridge structure with steel. Loads and Loads Paths of the Bridge Designers, while constructing the bridge, put different types of loads into consideration. For instance, the dead loads corresponded to the weight of the structure while the live loads matched the type of traffics and other applied loads. To estimate the dead load of the structure, the designers put the weight of the materials into consideration. The table below demonstrates detailed specifications of materials used:- Steel, cast 485lb per cubic foot Steel, rolled 490lb per cubic foot granite 170lb per cubic foot Concrete, coke 84lb per cubic foot Concrete, stone 150lb per cubic foot Guard rails 32lb per lin. foot Rail and fastenings 35lb per lin. foot Timber 75lb per cubic Live loads According to the structural requirements, some of the live loads incorporated the roadway and trains using the railway. The type of railway design load required by the specification consisted of two locomotives and a uniform load. The footway loading deck system had a design to counter stresses produced by a uniform load of 100lb per square foot. Similarly, the roadway loading had the same design to handle for the same loading (100lb per square foot). The figure above shows railway loading system:- Roadway Loading System Environmental Loads As per the structural design, the two main environmental loads included wind loads and temperature. The construction team put into consideration the variation of expansion properties for different materials. Designers noted down types of stresses obtained as a result of different temperature ranges. Therefore, civil engineers designed the wind loading for a variety of stresses; winds parallel to the bridge of 30lb per square foot and the wind load normal to the bridge. Conclusion In conclusion, the bridge appears as one of the largest engineering structures in the world. The bridge has spectacular features; a length of 1149 meters, an arch span of 503 meters, and a height of 134 meters above the sea level. Various engineering specialists such as Bradfield and Lang played a critical and professional role the construction of such magnificent structures. Civil engineers, with their experience, made several considerations with regards to the properties of material used in the construction of such projects. All the considerations such as loading effects, temperature ranges, and types of materials aimed at enhancing the sustainability and durability of the structures. Bibliography Read More