Discuss this Article. They dilated my daughter's eyes 18 hours ago, and they're still dilated. Anyone that says the eyes are back to normal in 6 hours does not know what they're talking about. The job of an eye doctor is not let their patients go blind. Retinal issues are the number one cause of blindness in north america, and most limiting factor of seeing the retina is the size of the pupil.
A truss bridge is a bridge composed of connected elements (typically straight) which may be stressed from tension, compression, or sometimes both in response to loads. Truss bridges are one of the oldest types of modern bridges. The basic types of truss bridges are shown below.
All bridges have 4 main characteristics: form, span, material, and travel surface in relation to the structure. A truss bridge is one form that a bridge can take and there are at least 30 different kinds of truss bridges, including the Warren, Pratt, and Howe designs among others. Truss bridges can have any of the 3 span types including simple, continuous, or cantilever. They are often made of metal, specifically steel or iron, but can also be made of wood (such as covered bridges). The travel surface of a truss bridge may be called deck, pony, or through truss. A deck truss allows traffic to travel on top of the structure whereas a pony truss allows traffic to travel between two superstructures that do not connect at the top. Finally, a through truss is similar to pony truss, except the superstructures connect overhead. What makes a truss bridge historic?