推荐回答(3个)
1、赵州桥,是一座弧型单孔石拱桥,全长64.4米,拱顶宽9米,结构坚固,雄伟壮观。它的设计完全合乎科学原理,施工技术堪称巧妙绝伦。古人说它“制造奇特,人不知其所为”。从整体来看,是一座单拱桥。拱长达37.4米,在当时可算是世界上最长的石拱。桥洞不是普通半圆形,而像一张弓,桥面平坦宽阔,兼顾了水陆交通,方便了车船运行,这种形式被称为“坦拱”。这一石拱是由28道拱圈纵向并列砌成,每道拱圈可独立站稳,自成一体,既便于施工,又便于单独修补。这样大跨度的坦拱,对桥台水平推力很大,建造难度高。而桥台却是既浅又小的普通矩形,厚度仅1.529米,由五层排石垒成。其地基是承载力较小的亚黏土。在这样的地基上,用这样的小桥台,建这样大跨度的石拱桥,在世界上是罕见的。
赵州桥最大的科学贡献,则在于它的“敞肩拱”的创造。在大拱的两肩,砌了四个并列的小孔,既增大流水通道,节省石料,减轻桥身重量,又利于小拱对大拱的被动压力,增强了桥身的稳定性。这就有力地保证了安济桥在1400多年的历史中,经受住无数次洪水冲击,8次大地震摇撼,以及车辆重压,至今仍巍然挺立在河之上。
赵州桥至今仍是世界上现存最早、保存最完善的古代敞肩石拱桥。赵州桥结构所取的方式,表现出一种极近代化的进步的工程精神。 2、准备半个鸡蛋,把边沿弄的平一点,倒扣在桌面上,使凸面朝上。拿一根铁钉,钉尖朝下,在蛋壳10厘米处撒手,使钉尖正好击在蛋壳最凸起的位置上,蛋壳不会被击破。将蛋壳翻过来,凹面朝上,放在瓶口上,蛋壳会破。原因:力学上有一条极其有价值的原理,决定某一物质的牢度,除了构成物质的本身强度外,还有一个重要因素,那就是它的几何形状。什么样的几何形状最好呢?对于受外力来说,凸曲面形最好。乌龟壳,鸡蛋壳,蚌壳都是这样的几何形状。现代建筑学上的薄壳顶结构也是这样的形状。凸曲面能把外力沿曲面均匀地分散开来,在很大程度上避免了弯折现象。鸡蛋不容易捏碎,龟壳不容易压碎,就是这个道理.凸曲面的背面就是凹曲面,与凸曲面的情况正好相反,凹曲面便于力量的集中,因而容易破损
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