胡佛大坝为什么是向水面拱形的？

俺扯过，这是个连河狸都明白的道理，可惜许多人还要吵的。

请看下图。

有人可能会说，我还能找到河狸的坝向外凸的，或者是直线型的。那种思维就是缺心眼的典型了。

这是胡佛大坝的外形。俺copy喂鸡百科上的照片。

它的两个有关的条目下的原文，俺copy如下。如果你不知道英文是什么，俺告诉你：Hoover Dam。

Even before Congress approved the Boulder Canyon Project, the Bureau of Reclamation was considering what kind of dam should be used. Officials eventually decided on a massive concrete arch-gravity dam, the design of which was overseen by the Bureau's chief design engineer John L. Savage. The monolithic dam would be thick at the bottom and thin near the top, and would present a convex face towards the water above the dam. The curving arch of the dam would transmit the water's force into the abutments, in this case the rock walls of the canyon. The wedge-shaped dam would be 660 ft (200 m) thick at the bottom, narrowing to 45 ft (14 m) at the top, leaving room for a highway connecting Nevada and Arizona.[23]

An arch-gravity dam or arched dam is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam. It combines the strengths of two common dam forms and is considered a compromise between the two. They are made of conventional concrete, Roller Compacted Concrete (RCC), or masonry. Arch-gravity dams are not reinforced except at the spillway. A typical example of the conventional concrete dam is the Hoover Dam. Changuinola Dam is an example of the RCC arch-gravity dam. A gravity dam requires a large volume of internal fill.[1] An arch-gravity dam can be thinner than the pure gravity dam and requires less internal fill.[2]

Arch-gravity dams are massive dams of concrete that resist the thrust of water by their weight using the force of gravity and the arch action.[3]

An arch-gravity dam incorporates the arch's curved design that is so effective in deflecting the water in narrow, rocky locations where the gorge's side are of hard rock and the water is forced into a narrow channel. Therefore, the span needed for the dam is narrow; the dam's curved design effectively holds back the water in the reservoir using a lesser amount of construction material.[4]

When properly situated on an appropriate site, the arch-gravity dam, combining the load resisting qualities of both a gravity dam and an arch dam, inspires the most public confidence because of its appearance of massive permanence.[5] However, curving a gravity dam may make it look stronger, but some of this effect may be psychological factors in operation in making a choice of dam style.[6]

这还有什么不清楚的吗？

连这样简单的问题，还要吵，还像自己发现了新大陆式的。

中国的教育是不是总把人教育成傻瓜啊？