Bridges & Trestles
Functionality and Architecture Meet
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This double span bridge is located in Glen, NH. Wendell Kiesman photo - used with permission
Pratt Truss Bridge
Since its introduction in 1844, this bridge design became part of hundreds of bridges created up to Second World War. It was designed by the Thomas Willis Pratt (1812 – 1875) and his father Caleb Pratt, a pair of American engineers, just several years after William Howe patented his famous Howe truss design. This bridge design immediately became widely used during the period when many bridges moved from wood components toward all-steel construction designs. Its most compelling feature was the ability was to span great distances using simple construction methods. It was regularly used to span anchor points that are up to 250 feet (76 meters) apart. It was most commonly used in railroad bridge construction, although it was also a preferred choice for creating other types of bridges all around the world until early 20th century.
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What is a trestle Bridge?
With the increased use and development of railroads civil engineers had to deal with rough, unstable and often dangerous terrain and make sure that rails are adequately supported by trestle construction which was meant to be filled with solid material. When building railroad tracks across wide and deep valleys, trestles made of wooden timber were built to keep the track solid and safe high above the ground. Most trestles were meant to be temporary, allowing trains to transport materials necessary to create a solid fill beneath the tracks.
On the other hand, rather than temporary, trestles were used as permanent bridge support in sections of tracks where water flow or sudden flooding could cause solid fills to become unsafe. Despite the frail looks of trestle bridges, they remained a safe passage for freight trains around the still settling the United States while exploring and populating and developing western territories. In the United Kingdom, wooden trestles were used for a relatively short period of the main use of crossing deep valleys in mountainous areas and were soon replaced by stone, and concrete viaducts with only a few wooden trestles continued to be in use into the 20th century.
Frankenstein Trestle Crawford Notch about 1880. Spindly trestle supports indicate built on initial opening of the track through Crawford Notch by the P and O 1875.
Frankenstein was strengthened for heavier trains during the summer of 1905 as Maine Central RR began a bridge upgrade program from Portland to St. Johnsbury.
Stone Arch Bridges on the Mountain Division
Stone Arch Bridges were popular on Railroads and the Portland and Ogdensburg line from Portland, Maine to St. Johnsbury, Vermont was no exception.
Between milepost 7.34 Ink Horn, Maine and heading west to milepost 100.25 Carroll stream in Whitefield, NH there were 9 stone arch bridges constructed.
Finding the arch bridges on the line from North Conway to Crawford Notch starts at Artist Falls Brook (constructed in 1882 by the stone masons of the Portland and Ogdensburg RR) at Milepost 59.24 and ends in Crawford Notch at Milepost 81.82 Kedron Brook with 2 being constructed.
Here pictured is the stone arch bridge at Kedron Brook in Crawford Notch.
The stone was available from a near by quarry along the left side of the tracks heading west towards St. Johnsbury, VT.
Kedron Brook Arch was built by the stone masons of the Portland and Ogdensburg in 1875.
Stone bridges all have arches supporting them. Step 2: Plan Your Bridge. Step 3: Pour a Concrete Footing. Step 4: Build Your Wooden Support Frame. Step 5: Cut Your Stones. Step 6: Place Arch Support Stones. Step 7: Reinforce Arch with Concrete (Optional) Step 8: Build Side Walls.
You can find great information on construction of stone arch bridges at
**The picture at Kedron Brook was take with the permission of the management of the Conway Scenic Railroad. The line is the property of the State of NH and heavy fines are given for trespassing (no joke). Please enjoy the picture of Kedron Brook on this page nd do not attempt to find this on your own.
Kedron Brook Bridge - Crawford Notch, NH
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