Small-Scale Bridge Building
时间：2018-12-01 作者：英语课 分类：VOA2003（下）-发展与科学
英语课
By Gary Garriott
Broadcast: September 8, 2003
This is Robert Covent with the VOA Special English Development Report.
Bridges are an important part of transportation systems. They make it possible to travel over rivers and between hills or mountains.
The most common kind of bridge is called a beam 1 bridge. It is made of wood that has been specially 2 treated. The treatment keeps the wood from 1)aging and breaking apart. Carpenters, people with woodworking skills, can build beam bridges.
Small beam bridges made from wood can be from three to fifteen meters long. The wood should be able to support about one-hundred kilograms for each square centimeter of area.
Beam bridges can also be made from 2)concrete. These can also be from three to fifteen meters long.
Carpenters can also build beam bridges made from concrete because wooden forms need to be built. The forms decide the shapes of the concrete beams 3. But in addition to 3)carpentry skills, people who build such bridges also must know how to mix 4)cement 4 with soil and water to form concrete.
It is important not to remove the forms until the concrete has dried. Concrete beam bridges can take more weight than wood beam bridges, up to two-hundred kilograms for each square centimeter.
A bridge going over a valley between two hills should be as long as the valley is wide. But a bridge crossing a river presents a more complex problem. The bridge must be high enough to be above the highest point water has reached during periods of flooding.
If it is not, the bridge and its supporting structures can reduce the water flow of the river. If this happens, flooding may take place 5)upstream from the bridge. Also, the water flowing under the bridge will travel faster. This may cause the soil holding the bridge in place to be washed away. Then the bridge may be damaged or destroyed.
Bridges need to be inspected often to be sure they are not damaged. From time to time, wooden bridges need chemical treatments painted on the beams. Concrete bridges also need to be repaired if pieces of concrete fall out or become weak.
You can get more information about building small bridges from the group Volunteers in Technical Assistance 5. VITA is on the Internet at vita.org.
注释:
1) aging [5eidViN] n.老化
2) concrete [5kCnkri:t] n.混凝土
3) carpentry [5kB:pintri] n.木工工作
4) cement [si5ment] n.水泥
5) upstream [5Qp5stri:m] adj.溯流而上的
1 beam
n.横梁；光束；vi.发光，发热
- The load on this beam is more than it will bear.横梁上的负荷比它能承受的要大得多。
- I could see the beam of his flashlight waving around in the dark.我可以看到他的手电筒光在黑暗中上下舞动。
2 specially
adv.特定地；特殊地；明确地
- They are specially packaged so that they stack easily.它们经过特别包装以便于堆放。
- The machine was designed specially for demolishing old buildings.这种机器是专为拆毁旧楼房而设计的。
3 beams
n.梁( beam的名词复数 )；束；1 光线；（电波的）波束v.发出光与热( beam的第三人称单数 )；面露喜色；播送；1 笑容满面，眉开眼笑 2 发射电波，播送 3 放出束状的光（或热）
- The beams are riddled with woodworm. 这些木梁被蛀虫蛀得都是洞。
- In front were five rooms with painted beams and carved pillars. 正面五间上房，皆是画梁雕栋。 来自《现代汉英综合大词典》
4 cement
n.水泥；胶结材料；vt.粘结；巩固
- We need 100 tons of cement at most for this project.这项工程满打满算有一百吨水泥就足够了。
- Let's cement the parts together.咱们来把这些部件粘接在一起吧。
5 assistance
n.援助，帮助
- She called and called but no one came to her assistance.她叫了又叫，但没有人来帮。
- He will get the great possible assistance.他将获得尽可能大的帮助。