The First Bridges For thousands of years people have faced the same problem How can we get from one place to another when something blocks our way It might be a rushing river Or it might be a huge cavern or a deep ravine The answer to that question is to build a bridge Early bridges were simple The first bridge might have been a fallen tree laid across a river to create a walkway A fallen tree was a good solution for crossing a narrow body of water but it was not the safest or most reliable way It could wash away or shift or it could be scary to walk across its uneven surface Also what if people needed a bridge and there were no trees around A simple structure called a beam bridge provided a solution A fallen tree is a natural bridge However people soon realized they could build better stronger bridges to help them cross bodies of water 4
A beam bridge is a flat strong structure that stretches across a space There is a support at each end of the bridge to rest the bridge on and keep it in place To build a longer bridge the bridge designer adds more supports along the length of the bridge This is a beam bridge The roadway of the bridge is long and flat Supports hold the roadway above the water 6
Brain Builder The longest bridge in the United States is a beam bridge The Lake Pontchartrain Causeway is 24 miles 39 kilometers long It crosses Lake Pontchartrain in Louisiana It is the longest bridge in the world that runs completely over water To hold up the bridge engineers built 9,500 supports called pilings These pilings were driven deep into the lake’s bottom and hold up sections of the bridge Lake Pontchartrain Causeway New Orleans 7
