Where Rk----- is the characteristic strength of the material
γm-----is a coefficient depending on the probability of obtaining results less than Rk
The characteristic strength of a material is usually taken as the 95 per cent confidence limit of the material strength in a relevant test series. The reduction coefficient γm is a function of two coefficients.
γm1 which is intended to cover possible reductions in the strength of the materials in the structure as a whole, as compared to the characteristic value deduced from the control test specimen.
γm 2 which is intended to cover possible weakness of the structure arising from any cause other than the reduction in the strength of the materials allowed for by coefficientγm1, including manufacturing tolerances. 8.4通常情况下会采用特征荷载，特征荷载在结构的整个使用期内具有百分之五的被超越的可能性。然而，在很多情况下，统计资料并不可靠，特征荷载只能根据现行规范或其他规定中的名义值确定。RF是几个单独参数的函数。RF1考虑了外部特征荷载作用下不利荷载偏差的可能性，以及考虑了不正常或不可预见的荷载作用。RF2考虑了不同荷载共同作用时降低它们的特征荷载同时作用的可能性。RF3考虑了错误设计假定下荷载效应的修正。（例如，简化支撑条件的引入，或略了温度和其他难以评估的效应）。类似地，材料的设计强度是这样定义的。。。。。。。（公式）。。。。。。。。在这里，RK是材料的特征强度，γm是一个考虑了小雨γk的可能性的参数。8.5材
料的特征强度一般采用在相关的一连串试验中确定的具有95%保证率的材料强度。折减系数γm是两个参数的函数。
γm1考虑了与试验样品中推导出的规格值相比，包括材料强度总体上在结构中的减小。
γm2考虑了除了参数γm1考虑的材料强度的折减以外的任何因素引起的结构和衰弱，包括制作允许误差。
第九单元 Building codes, therefore, are concerned with such things as structural adequacy, the quality and strength of the materials used, sound workmanship, the correct installation of approved electrical wiring and equipment, the correct installation of approved gas-, coal-, or oil-heating equipment and their piping, the correct installation of approved sanitary plumbing fixtures and their piping, the fire resistance of the materials used, and the existence of fire exits.
因此，建筑规范涉及下列内容，比如，建筑结构的合理性、所用材料的质量和强度，良好的工艺过程、电线及电器设备正确的安装布置方法；天然气设备，煤及燃油加热设备及其管线的正确布置方法、卫生设施及其管线的正确布置方法、防火材料的选用，消防出口的设置。
Once a building has been approves and occupied, if the owner should thereafter want to make a basic alteration in the electrical, heating, or plumbing systems, or a basic change in the structure, the building department must approve the alterations beforehand and inspect the workmanship and materials after the alteration has been completed. If the
job is signed off by a licensed electrician or plumber, adequacy of workmanship and materials is usually assumed, although the buildings department always reserves the right to make a subsequent inspection and order any changes it thinks necessary。一旦建筑项目获得批准并开工，之后如果建筑商希望进行一些基本的改建工作，比如电器，采暖或管道系统，或者结构方面的一些基本变动，必须预先争得建筑部门的同意，并且检查工艺和材料是否也作相应的改动。尽管政府部门总是保留一些在必要时进行后期检查与责令整改的权利，但如果这项工作由合格的电工或者管道工签字保证，则施工工艺及所用材料将由他们来负责
Specification-type building codes were probably a necessity in a day, when speculative builders tried to get by using the cheapest materials they could buy, assembled in the most slipshod manner. But times changed, and new materials were developed. Since World War Ⅱ standards of a material or structure are outlined and the builder is free to select whatever materials or building techniques will meet these standards.在投机建造商尽量使用他们能买到的最廉价材料，以马虎的方式建造的时代，指定方式的建筑规范可能是必须的。但随着时代发展，新材料应运而生。从第一次世界大战后，现行的建筑规范发生了根本变化，结构或材料的性能标准被规定下来，建造商可以在这些标准内自由选择合适的材料及建造技术
For example, a specification-type code for a house sewer will simply specify that castiron pipe of a certain quality and size be used and that the pipe be installed in a specified manner. The plumbing contractor has no choice or say in the manner. In a performance-type building code, however, the code will specify that the piping not be affected by any corrosive or harmful substances in the sewage or in the soil in which the pipe is buried, that the pipe meet certain minimum strength requirements, and that pipe not be affected by any corrosive or harmful substances in the sewage or in the soil in which the pipe is buried, that the pipe meet certain minimum strength requirements, and that the pipe not be affected by temperature changes within a specified range. The plumbing contractor is free to use plastic pipe, castiron pipe, or gold pipe if he wants to, as long as he can show the local buildings officials that the pipe does in fact meet their standards.
例如，指定规范中对于房屋排污管，只是简单规定应采用特定质量和尺寸的铸铁管，并且管道应以指定方式布设，管道承建者对这种方式不能质疑或者有其他选择。然而，如今的现行建筑规范规定，管道铺设的地方，不能被土壤或污水中的物质腐蚀或破坏，管道必须具备所需的特定强度，在一定范围内的温度变化不应对管道造成影响。管道承建者可以选择使用塑料管道、铸铁管道，或者希望使用的其他金属管道，只要他能向当地建筑部门出示这些管道符合标准的证明即可。
第十单元 [3]Footings generally can be classified as wall and column footings. The horizontal outlines of the most common types are given in Fig.10-1. A wall footing is simply a strip of reinforced concrete, wider than the wall, which distributes its pressure. Single-column footings are usually square, sometimes rectangular, and represent the simplest and most economical type. There use under exterior columns meets with difficulties if property rights prevent the use of footings projecting beyond the exterior walls. In this case combined footings or strap footings are used which enable one to design a footing which will not project beyond the wall column. Combined footings under two or more columns are also used under closely spaced, heavily loaded interior columns where single footing, if they were provided, would completely or nearly merge. 基础通常被分为墙基和柱基。图10-1给出的是一些常用类型的平面形状。墙基呈简单的钢筋混凝土条状，比墙略宽，用来分布荷载。单柱基础通常呈方形，又是做成矩形的 ，是最简单经济的一种类型。如果所有权问题上不允许基础超出外墙，则可以通过在底部使用外柱来处理这种问题。碰到这种情况，我们还可以设计这种基础，比如联合基础或者条状基础，它们的投影不会超过墙柱。联合基础通常位于两根或者多根柱子的下方，或者间距很小，荷载很大的对独立基础内柱的下方，如果这样设置了，它们几乎会成为一个整体。 [4]Such individual or combined column footings are the most frequently used types of spread foundations on soils of reasonable bearing