Frankford Avenue Bridge (Pennsylvania) Essay Example | Topics and Well Written Essays - 3750 words

Frankford Avenue Bridge (Pennsylvania) - Essay Example Frankford Avenue Bridge was constructed in Poquessing Creek of Bristol Pike-Frankford Avenue, Route 13 between Cornwells Heights of Bucks County in the state of Pennsylvania and Philadelphia city in Philadelphia County (Beckman 200). The bridge was constructed in 1904 by JohnMcMenamy, Webster and Henry H as chief and assistant engineer respectively. The Bridge is current owned by Transportation Department of Pennsylvania. The bridge provides an early example of concrete bridges that were supported by steel with closed-spandrel arch that was single spanned. The exterior parts of the bridge resemble stonework with scored spandrel walls that demarcate voussoirs surrounding the arch ring. The parapet of the bridge is decorated by urn-shaped balusters that was common in the early 20th century Introduction There was a rapid evolution of bridge engineering in America during 19th century. During this period, patents were mostly given to contractors who had new designs with new construction m odes. By the year 1900, wooden timber was no longer used to construct bridges across rivers and streams. Wood was replaced by iron and steel as the latter constructed strong massive bridges that supported heavy locomotives. Wood was also sidelined because it could easily burn and be washed away when the river overflows. Steel bridges became more common in the late 19th century and they gave birth to a new era of designing and constructing bridges. Many Americans did not accept this new bridge design because of their industrial outlook. Steel bridges had no or minimal ornamentation and were vulnerable to rust. By late 19th century, France invented concrete, a new material that was accepted by many American engineers because of its comprehensive strength. In addition, concrete could be combined with steel to make bridges that were strong and fireproof (Beckman 215). By the year 1900, there were a small number of concrete-steel constructions of bridges in Midwestern US. Many eastern pa rts of the country had not explored the new technology but useful bridge making ideas and technology, begun in eastern US in late 19th century (Condit 39). In 1904, Philadelphia city and Bucks county begun the construction of a barrel arch bridge (7T-0") using steel and concrete. It had ornamented balustrade that was urn-shaped with a facade that resembled masonry. The bridge signified an important moment in bridge engineering history (Bromley 17). The construction of Frankford Avenue Bridge begun in 1895 and continued up to 1910.Steel-concrete bridges at this time were characterized by spandrel arches that were closed that later declined after 1910. Spandrel arches were meant to ensure that performs the intended function while at the same time reducing the amount of concrete used (Condit 42). Concrete and Steel Frankford Avenue Bridge was the first bridge in southeast US that utilized concrete and steel and was constructed along Pine Road over Penny pack Greek in Philadelphia (1983 -94).It was a two-span bridge with arches of 25’-5†. It also had a wire mesh which acted as a binding element. Bridge’s exterior resembled masonry. The most popular concrete reinforcing system in USA in the year 1904 was the system patented by Joseph Melan. It was used in construction concrete arch bridge in America. It included curved soffit steel I-beams which later developed other variations that included

Life's greatest miracle Term Paper Example | Topics and Well Written Essays - 750 words

Life's greatest miracle - Term Paper Example The producer of the program, Julia Cort notes that the urge to procreate is fundamental to all insects, birds, primates among others. DNA is a molecule responsible for carrying genetic material. It has been 4 billion years since the first discovery of this core molecule of life (Lifes Greatest Miracle). Bacteria replicate by cloning, that makes the parent and the clone identical with the exception of fornication mutants. Cloning as a type of reproduction is disadvantageous in that the species are prone to wipe out in case of a detrimental disease. Sexual reproduction on the other hand involves a male and female organism. Genes from each parent are vital for copulation to take place. The off spring from sexual reproduction is different from the parents and others. Sex results to difference. Variety is advantageous to a population because it translates to survival of a species. Sperm formation takes place in the testicles of a male organism with an approximation of 100,000,000 sperms per day (Lifes Greatest Miracle). Each sperm carries a unique genetic package. Miosis is the process that eggs and sperms undergo for them to exist (Lifes Greatest Miracle). The medical photographer explains the process with the aid of sex cells (egg and sperm). A pair of chromosomes in a sex cell replicate each forming two strands of chromosome attached at the centre. The chromosome then condenses to from an X shape. The partners coil around each other at specific points resulting to the transfer of genetic material. As mentioned earlier, sexual reproduction promotes diversity. Diversity increases the probability of organisms to survive. The narrator tells that majority of males start producing sperms during puberty while in females the creation of eggs onsets as a fetus. The eggs die off over the years. A teenage female outnumbers the adult female in terms of eggs in the ova ry. However, in comparison to a sperm, an egg is of quality rather