Design of Simple Structures

As any structure is designed to carry some external forces in the form of applied loads, local codes or ordinances which prescribe loads must be followed in assessing loading conditions. In all cases the code requirements are considered to be the minimum legal requirements.

因为任何结构都是被设计用来承受以荷载形式出现的外力，因此，必须遵循当地的法规或条例中关于荷载的规定来评定加载条件。在任何情况下，法规的要求都应该被认为是法定最低限度的要求。

Buildings

Structurally, buildings can be divided into three major groups：

(1) Shell or Surface Structures: These consist of a "skin" which is functional that is, which encloses a space and at the same time acts as a main load-carrying element.

(2) Framed Structures: These usually consist of planar systems which are combined into three-dimensional configurations. This type of steel-skeleton or beam-and-column construction can be used for residences, high-rise or low-rise apartment buildings, public buildings, and industrial buildings (workshops, warehouses, factories).

(3) Suspended Structures: These usually involve large clear spans which are achieved by the use of cables as main supporting elements. This type of structure was originated in 1896 by the Russian engineer Shookhov for special structures such as sport or exhibition arenas.

房屋建筑

在结构上，房屋建筑可划分为三个主要类别：

(1)壳体结构或表面结构：这类结构由一个起功能作用的“外壳”所组成－就是外壳包围一定空间，同时作为主要构件承受荷载。

(2)框架结构：这类结构通常是由平面体系所组成的三维结构。这种类型的钢骨架或梁与柱结构可用于住宅、高层或低层公寓建筑、公共建筑和工业建筑（车间、仓库、工厂）。

(3)悬吊结构：这类结构通常是对于大的净跨度，采用钢索作为主要支承构件。这种类型的结构最先由俄国工程师 Shookhov 在1896 年用于运动场或展览会场在这一类特殊结构。

Before starting to calculate loads and their "actions" or stresses and deflections the designer must select the material to be used and have a clear concept of the way in which the transfer of vertical and horizontal loads from the point of their application to the ground will take place. The soundness of this structural concept actually determines the success or the failure of a design, with respect to not only its safety, but also its economy. In any actual design situation the feasibility of various systems and the extent to which they reduce or increase the cost of other elements of the structure must be established first. The intelligent selection of the best concept can only be made after the criteria for a particular problem have been thoroughly investigated and defined.

在开始计算荷载和它们的“作用”或应力和挠度之前，设计者必须选定所使用的材料；并且，对竖向荷载和水平荷载从它们的作用点传递到地面的途径要有一个明确的概念。这个结构方面的概念是否完善，实际上决定着设计的成功与否，不仅与它的安全性有关，而且也和它的经济性有关。在任何实际设计情况下，必须首先确定各种体系的可行性和其他的结构构件所需费用的增减范围。只有对特定问题的技术标准进行了充分研究并予以确定之后，才能明智地选取最好的概念。

In any framing system a deck element is supported by regularly spaced beams, which in turn are supported by other beams or directly by columns or walls. Vertical loads thus carried by these elements are finally transmitted to columns and to their foundations. Horizontal loads, wind forces, or dynamic forces are usually transferred by rigid floor or roof diaphragms directly to frames, provided that the diaphragm capabilities of the deck and the adequacy of the assembly details make this possible.

在任何框架体系中，一个层面构件是由间距按一定规则排列的梁所支承，然后由其它梁或直接由柱或墙来支承。由这些构件所承受的竖向荷载最终传递到柱和柱的基础上。只要层面薄板的承载能力和装配细部适当，水平荷载－风力或动力通常是由刚性的楼板或层面薄板直接传递到框架。

Bridges

桥梁

Bridges can be classified in several ways. Often a bridge structure represents some combination of two or more types. First a classification according to the traffic load can be made under which there are highway, railway, or pedestrian bridges, with the understanding that very often any combination of these three is possible. According to the bridge axis there are straight and curved bridges. According to the position of the floor carrying the traffic there are deck bridges, with the floor on top of the main members, or through bridges, with the deck connected to the bottom chord of the main supporting members. Bracing is provided on the plane of the top chord above the traffic, but if the height is not sufficient, the space above is left open; such structures are called semithrough or pony truss bridges. Sometimes a combination in the form of double-deck bridges is used. According to the makeup of the web of the main load-carrying members we can recognize full web-girder or beam or box-girder bridges and open-web-truss bridges. If the system line of the bridge structure is straight and horizontal, the bridge is of the girder type; with a curved line it is an arch bridge. Further subdivisions within each of the above groups can be made. Older steel bridges were riveted while newer ones are welded and/or bolted. Finally, some bridges are movable either vertically or horizontally to allow traffic flow underneath if the available clearance is not sufficient.

桥梁可以采用几种不同的方式来分类。通常一座桥梁结构可以是两种或者多于两种类型的某些组合。首先可以根据交通荷载来分类，可以分为公路桥，铁路桥或人行桥，并且通常可能是这三种桥梁的任何组合。根据桥梁轴线又可将其分为直线桥和曲线桥。根据承载车辆的桥面位置又可将其分为桥面在主要构件顶部的上承式桥，或者桥面连接到主要构件下弦杆的下承式桥。在来往车辆以上的上弦杆的平面上用支撑，但是如果高度不够，则上部空间可敞开，这样的结构称为半下承式桥或矮桁架桥。有时还有组合成双层桥面形式的桥。根据主要承载构件腹板的构造，我们可以判断是全腹板大梁桥，或者是梁桥，或为箱梁桥，或为空腹式桁架桥。如果桥梁结构体系的外形为直线的和水平的，这种桥属于大梁桥；外形为曲线的桥是拱桥。上述桥梁还可以进一步再分类。旧式钢桥多为铆接，而新式钢桥则为焊接和/或螺栓连接。另外，有些桥梁如果有效净空不够，则采用竖向或水平方向开合的方式让船只在其下面通过。

Which type of bridge is to be used is a major design decision, and local conditions traffic, site, geological, geographical, and aesthetic--are to be considered. Available clearances, erection possibilities, and foundation construction are also major factors affecting decisions concerning the type and span length of a bridge.

采用何种类型的桥梁是主要的设计决策，应当考虑当地的情况－交通，桥址，地质，地理和美学等方面。桥梁的有效净空，架设的可能性和基础构造同样也是影响桥梁类型和跨度确定的主要因素。