![]() The George Washington Bridge is the world's busiest motor vehicle bridge, carrying a traffic volume of over 104 million vehicles in 2019, and is the world's only suspension bridge with 14 vehicular lanes as of 2012. It is named after George Washington, the first president of the United States. The George Washington Bridge is a double-decked suspension bridge spanning the Hudson River, connecting Fort Lee in Bergen County, New Jersey, with Upper Manhattan in New York City. June 2, 1959 64 years ago ( ) (lower level) September 21, 1927 95 years ago ( ) (bridge construction) Just impossible to make efficient.Port Authority of New York and New Jerseyġ4 ft (4.3 m) (upper level), 13.5 ft (4.1 m) (lower level) Įdward W. with at least a 16inx16in square solid cross section. I am having an issue with this now, designing trusses in ANSYS with an aspect ratio of 28:1, for my given deflection specification of 1/180th of the span maximum, I am finding I need a cross sectional area of steel to be around 250in^2, thats basically a large steel beam. ![]() Never try to build a truss with an aspect ratio of 20:1 or higher, unless you want unrealistic deflections. Anyone that knows the method of joints understands why increasing the height works. And there should be a way to calculate the efficiency of a truss based on the style of truss, and the aspect ratio.īut, again, I cannot find any solid evidence to point anyone to on how this works, other than that it is simple geometry. This is where the optimization gets a bit tricky. Taller trusses just hold more, yet the trade-off comes in the form of increased material requirements. I also found all of your information to be the case when I designed my first truss a few years ago. The title of this section should be “Aspect Ratio” becuase this is what it is called. I really cannot find anything in any of my statics or strengths textbooks, nor can I find any real information to prove this. Adding strength usually means adding weight.Ī truss has an optimal load distribution when it has an aspect ratio near 2:1 I believe. So that means the middle members will have to be made stronger the taller the bridge is. The amount a piece of wood can support in compression before buckling decreases with length. However, bridge builders have another problem when pieces become longer. Why is this a drawback? By increasing the height, the middle members have to become longer. By increasing the height, the load decreased on the top and bottom chords but remained the same on the middle “truss members”. A decrease in load means you can make it smaller. ![]() What does this mean to you?Īs you saw in the example bridges, by increasing the height of the bridge you decrease the load on the top (and bottom) chord. All I did is increase the height of the bridge by one inch. You can see in this second bridge that the middle section of the top chord is only holding 38% of the total load. The only difference is that this bridge is 4 inches tall, one inch taller than before. Now I will show you another bridge, with the same design. For instance, the very middle of the top chord of the bridge is supporting 50% of the total load. This means the numbers you see act as percentages. I have added two load points with a total load of 100. ![]() The bridge is 8 inches long and 3 inches tall. There is no cut and dry answer, as you should evaluate your bridge specifications and guidelines and conduct experiments to reach the best answer for you. All the time I am asked “How tall should I make my bridge?” This article will attempt to answer this question by illustrating a principle in model bridge building. ![]()
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