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?yàn)槿魏谓Y(jié)構(gòu)都是被設(shè)計(jì)用來承受以荷載形式出現(xiàn)的外力，因此，必須遵循當(dāng)?shù)氐姆ㄒ?guī)或條例中關(guān)于荷載的規(guī)定來評(píng)定加載條件。在任何情況下，法規(guī)的要求都應(yīng)該被認(rèn)為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

在結(jié)構(gòu)上，房屋建筑可劃分為三個(gè)主要類別：

(1)殼體結(jié)構(gòu)或表面結(jié)構(gòu)：這類結(jié)構(gòu)由一個(gè)起功能作用的“外殼”所組成－就是外殼包圍一定空間，同時(shí)作為主要構(gòu)件承受荷載。

(2)框架結(jié)構(gòu)：這類結(jié)構(gòu)通常是由平面體系所組成的三維結(jié)構(gòu)。這種類型的鋼骨架或梁與柱結(jié)構(gòu)可用于住宅、高層或低層公寓建筑、公共建筑和工業(yè)建筑（車間、倉庫、工廠）。

(3)懸吊結(jié)構(gòu)：這類結(jié)構(gòu)通常是對(duì)于大的凈跨度，采用鋼索作為主要支承構(gòu)件。這種類型的結(jié)構(gòu)最先由俄國工程師 Shookhov 在1896 年用于運(yùn)動(dòng)場或展覽會(huì)場在這一類特殊結(jié)構(gòu)。

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.

在開始計(jì)算荷載和它們的“作用”或應(yīng)力和撓度之前，設(shè)計(jì)者必須選定所使用的材料；并且，對(duì)豎向荷載和水平荷載從它們的作用點(diǎn)傳遞到地面的途徑要有一個(gè)明確的概念。這個(gè)結(jié)構(gòu)方面的概念是否完善，實(shí)際上決定著設(shè)計(jì)的成功與否，不僅與它的安全性有關(guān)，而且也和它的經(jīng)濟(jì)性有關(guān)。在任何實(shí)際設(shè)計(jì)情況下，必須首先確定各種體系的可行性和其他的結(jié)構(gòu)構(gòu)件所需費(fèi)用的增減范圍。只有對(duì)特定問題的技術(shù)標(biāo)準(zhǔn)進(jìn)行了充分研究并予以確定之后，才能明智地選取最好的概念。

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.

在任何框架體系中，一個(gè)層面構(gòu)件是由間距按一定規(guī)則排列的梁所支承，然后由其它梁或直接由柱或墻來支承。由這些構(gòu)件所承受的豎向荷載最終傳遞到柱和柱的基礎(chǔ)上。只要層面薄板的承載能力和裝配細(xì)部適當(dāng)，水平荷載－風(fēng)力或動(dòng)力通常是由剛性的樓板或?qū)用姹“逯苯觽鬟f到框架。

Bridges

橋梁

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.

橋梁可以采用幾種不同的方式來分類。通常一座橋梁結(jié)構(gòu)可以是兩種或者多于兩種類型的某些組合。首先可以根據(jù)交通荷載來分類，可以分為公路橋，鐵路橋或人行橋，并且通?？赡苁沁@三種橋梁的任何組合。根據(jù)橋梁軸線又可將其分為直線橋和曲線橋。根據(jù)承載車輛的橋面位置又可將其分為橋面在主要構(gòu)件頂部的上承式橋，或者橋面連接到主要構(gòu)件下弦桿的下承式橋。在來往車輛以上的上弦桿的平面上用支撐，但是如果高度不夠，則上部空間可敞開，這樣的結(jié)構(gòu)稱為半下承式橋或矮桁架橋。有時(shí)還有組合成雙層橋面形式的橋。根據(jù)主要承載構(gòu)件腹板的構(gòu)造，我們可以判斷是全腹板大梁橋，或者是梁橋，或?yàn)橄淞簶?，或?yàn)榭崭故借旒軜?。如果橋梁結(jié)構(gòu)體系的外形為直線的和水平的，這種橋?qū)儆诖罅簶?/span>；外形為曲線的橋是拱橋。上述橋梁還可以進(jìn)一步再分類。舊式鋼橋多為鉚接，而新式鋼橋則為焊接和/或螺栓連接。另外，有些橋梁如果有效凈空不夠，則采用豎向或水平方向開合的方式讓船只在其下面通過。

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.

采用何種類型的橋梁是主要的設(shè)計(jì)決策，應(yīng)當(dāng)考慮當(dāng)?shù)氐那闆r－交通，橋址，地質(zhì)，地理和美學(xué)等方面。橋梁的有效凈空，架設(shè)的可能性和基礎(chǔ)構(gòu)造同樣也是影響橋梁類型和跨度確定的主要因素。