Several attributes and accessories are associated with the overall functionality, aesthetics, and service of the bridge including deck type, steel finish, safety railing systems, camber, toe plates, and fencing.ĭeck type - The deck type selected is a function of the bridge use and has a direct impact on the dead load of the structure. Thermal Expansion (inches)= Bridge length (in inches) x 0.00065 Functionality Base plates with slotted holes on one end of the bridge allow for this thermal movement in the field. Note that the bridge bearing is typically 3 inches to 9 inches from the abutment backwall and thermal expansion of the bridge is accounted for with slide bearings and a gap derived from the formula below, which assumes 100 degree temperature differential. The most common method to specify the length of a pedestrian truss bridge is the distance between abutment backwalls. Environmental considerations such as wetlands, endangered species, and floating debris may also play a factor in determining the length. The Americans with Disability Act (ADA) allows for a maximum of 8.33 percent grade (1/12 slope) and 5.0 percent grade (1/20 slope) with and with out a pipe handrail, respectively. Bridges with a slight grade are good for surface water runoff. Typically, the most cost-effective structures are those with horizontal alignments constructed perpendicular to the stream because the result is the shortest bridge length. Length - The length of the bridge is a function of channel geometry (elevation differences), stream geomorphology, and horizontal and vertical alignments. To control lateral deflections and 'sway,' the horizontal center- to -center of truss dimension should preferably be no less than 1/20th of the bridge span, but should not - except in extreme cases - be less than 1/25th of the bridge span. In the event that this dimension is 'fixed,' it should be highlighted on the bid plans and also in the specification documents. Width - The most common method to specify the width of a pedestrian truss bridge is the clear width measurement between railing system elements. Reference the CE News article titled ' Articulated Concrete Block Design,' dated August 2010 for more information about scour countermeasures in those suspect locations.

A geotechnical investigation is recommended. A simple site investigation - paying close attention to abutment constraints, flood marks, the size of upstream logs, streambed strata, and drift locations - is advised. The layout and design of a prefabricated steel truss bridge begins with a site reconnaissance to determine the bridge width and length (also known as span) dimensions. This pedestrian through-truss has been custom designed for a skywalk application. A basic understanding of bridge components and layout, including design codes, bridge styles, and loading, is explained in general detail. This article provides an overall approach to siting and design considerations for prefabricated steel truss pedestrian bridges, but is not intended to be an all-inclusive, step-by-step tutorial on bridge design. These designs, combined with technology improvements and manufacturing efficiencies, will continue to support the ever-growing and ever-changing needs of society as they relate to pedestrian, bicycle, and equestrian traffic. Today, truss designs are longer, wider, stronger, and more durable. In the 1950s, deck/girder bridges were developed as a replacement for deteriorating timber bridges. The history of prefabricated steel truss bridges dates to the 1930s when modular systems were used to meet the needs of the British military in remote locations. The most common use of prefabricated pedestrian steel truss bridges is for trail applications in park and community environments, which is the main focus of this article. This growth is expected to create increased demand for pedestrian steel truss bridges for many purposes including, but not limited to, recreational and fitness activities and tourist attractions.

Its population is projected to increase to 392 million by 2050 - more than a 50-percent increase compared with 1990, according to the U.S. The United States remains one of the world's fastest growing industrialized nations.

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