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Howe truss
A Howe truss is a truss bridge consisting of chords, verticals, and diagonals whose vertical members are in tension and whose diagonal members are in compression. The Howe truss was invented by William Howe in 1840, and was widely used as a bridge in the mid to late 1800s.
The earliest bridges in North America were made of wood, which was abundant and cheaper than stone or masonry. Early wooden bridges were usually of the Towne lattice truss or Burr truss design. Some later bridges were McCallum trusses (a modification of the Burr truss). About 1840, iron rods were added to wooden bridges. The Pratt truss used wooden vertical members in compression with diagonal iron braces. The Howe truss used iron vertical rods in tension with wooden diagonal braces. Both trusses used counter-bracing, which was becoming essential with heavy railroad trains were using bridges.
In 1830, Stephen Harriman Long received a patent for an all-wood parallel-chord truss bridge. Long's bridge contained diagonal braces which were prestressed with wedges. The Long truss did not require a connection between the diagonal and the truss, and was able to remain in compression even when the wood shrank somewhat.
William Howe was a construction contractor in Massachusetts when he patented the Howe truss design in 1840. That same year, he established the Howe Bridge Works to build bridges using his design. The first Howe truss was a single-lane, 75-foot-long (23 m) bridge in Connecticut carrying a road. The second was a railroad bridge over the Connecticut River in Springfield, Massachusetts. This bridge, which drew extensive praise and attention, had seven spans and was 180 feet (55 m) in length. Both bridges were erected in 1840. One of Howe's workmen, Amasa Stone, purchased for $40,000 ($1,259,867 in 2024 dollars) in 1842 the rights to Howe's patented bridge design. With his financial backer, Azariah Boody, Stone formed the bridge-building firm of Boody, Stone & Co., which erected a large number of Howe truss bridges throughout New England. Howe made additional improvements to his bridge, and patented a second Howe truss design in 1846.
The Howe truss bridge consists of an upper and lower chord, each chord consisting of two parallel beams and each chord parallel to one another. The web consists of verticals, braces, and counter-braces. Vertical posts connect the upper and lower chords to one another, and create panels. A diagonal brace in each panel strengthens the bridge, and a diagonal counter-brace in each panel enhances this strength. Howe truss bridges may be all wood, a combination of wood and iron, or all iron. Whichever design is used, wooden timbers should have square ends without mortises and tenons. The design of an all-metal Howe truss follows that of the wooden truss.
The parallels in each chord are usually built up out of smaller beams, each small beam fastened to one another to create a continuous beam. In wooden Howe trusses, these slender beams are usually no more than 10 to 15 inches (250 to 380 mm) wide and 6 to 8 inches (150 to 200 mm) deep. In iron trusses, the upper chord beams are the same length as the panel. Upper chord beams are usually made of cast iron, while the lower chord beams are of wrought iron. A minimum of three small beams are used, each uniform in width and depth. Fishplates are usually used to splice beams together. (Lower chord beams may have eyes on each end, in which case they are fastened together with bolts, pins, or rivets.) In wooden trusses, cotters and iron bolts are used every 4 feet (1.2 m) to connect the beams of the upper chord to one another. In the lower chord of a wooden bridge, clamps are used to couple beams together.
Although generally of the same length, beams are positioned so that a splice (the point where the end of two beams meet) is near the point where two panels meet but not adjacent to the splice in an adjacent pair of beams.
The individual small beams which make up a parallel in a chord are separated along their long side by a space equal to the diameter of the vertical posts, usually about 1 inch (25 mm). This allows the vertical posts to pass through the parallel in the chord. Batten plates are placed diagonally between the members of a chord, and nailed in place to reduce bending and to act as a shim to provide ventilation between chord members.
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Howe truss
A Howe truss is a truss bridge consisting of chords, verticals, and diagonals whose vertical members are in tension and whose diagonal members are in compression. The Howe truss was invented by William Howe in 1840, and was widely used as a bridge in the mid to late 1800s.
The earliest bridges in North America were made of wood, which was abundant and cheaper than stone or masonry. Early wooden bridges were usually of the Towne lattice truss or Burr truss design. Some later bridges were McCallum trusses (a modification of the Burr truss). About 1840, iron rods were added to wooden bridges. The Pratt truss used wooden vertical members in compression with diagonal iron braces. The Howe truss used iron vertical rods in tension with wooden diagonal braces. Both trusses used counter-bracing, which was becoming essential with heavy railroad trains were using bridges.
In 1830, Stephen Harriman Long received a patent for an all-wood parallel-chord truss bridge. Long's bridge contained diagonal braces which were prestressed with wedges. The Long truss did not require a connection between the diagonal and the truss, and was able to remain in compression even when the wood shrank somewhat.
William Howe was a construction contractor in Massachusetts when he patented the Howe truss design in 1840. That same year, he established the Howe Bridge Works to build bridges using his design. The first Howe truss was a single-lane, 75-foot-long (23 m) bridge in Connecticut carrying a road. The second was a railroad bridge over the Connecticut River in Springfield, Massachusetts. This bridge, which drew extensive praise and attention, had seven spans and was 180 feet (55 m) in length. Both bridges were erected in 1840. One of Howe's workmen, Amasa Stone, purchased for $40,000 ($1,259,867 in 2024 dollars) in 1842 the rights to Howe's patented bridge design. With his financial backer, Azariah Boody, Stone formed the bridge-building firm of Boody, Stone & Co., which erected a large number of Howe truss bridges throughout New England. Howe made additional improvements to his bridge, and patented a second Howe truss design in 1846.
The Howe truss bridge consists of an upper and lower chord, each chord consisting of two parallel beams and each chord parallel to one another. The web consists of verticals, braces, and counter-braces. Vertical posts connect the upper and lower chords to one another, and create panels. A diagonal brace in each panel strengthens the bridge, and a diagonal counter-brace in each panel enhances this strength. Howe truss bridges may be all wood, a combination of wood and iron, or all iron. Whichever design is used, wooden timbers should have square ends without mortises and tenons. The design of an all-metal Howe truss follows that of the wooden truss.
The parallels in each chord are usually built up out of smaller beams, each small beam fastened to one another to create a continuous beam. In wooden Howe trusses, these slender beams are usually no more than 10 to 15 inches (250 to 380 mm) wide and 6 to 8 inches (150 to 200 mm) deep. In iron trusses, the upper chord beams are the same length as the panel. Upper chord beams are usually made of cast iron, while the lower chord beams are of wrought iron. A minimum of three small beams are used, each uniform in width and depth. Fishplates are usually used to splice beams together. (Lower chord beams may have eyes on each end, in which case they are fastened together with bolts, pins, or rivets.) In wooden trusses, cotters and iron bolts are used every 4 feet (1.2 m) to connect the beams of the upper chord to one another. In the lower chord of a wooden bridge, clamps are used to couple beams together.
Although generally of the same length, beams are positioned so that a splice (the point where the end of two beams meet) is near the point where two panels meet but not adjacent to the splice in an adjacent pair of beams.
The individual small beams which make up a parallel in a chord are separated along their long side by a space equal to the diameter of the vertical posts, usually about 1 inch (25 mm). This allows the vertical posts to pass through the parallel in the chord. Batten plates are placed diagonally between the members of a chord, and nailed in place to reduce bending and to act as a shim to provide ventilation between chord members.