Читать книгу Strength Of Beams, Floor And Roofs - Including Directions For Designing And Detailing Roof Trusses, With Criticism Of Various Forms Of Timber Construction - Frank E. Kidder - Страница 19

When we speak of the strength of a beam, we generally mean the load required to break it, and in which is included the weight of the beam itself. Now in the case of a wooden beam, its own weight, compared with the weight it will support, is usually so small that it need not generally be taken into account, but the weight of a wooden floor, meaning all of the material contained between its under and upper surface, is usually a considerable item, so that a distinction must be made between “safe strength” and “safe load.” In this chapter the term “safe strength” will be used to designate the maximum weight that the floor can support with safety, including the weight of all the materials used in its construction, and for forming the ceiling below.

The safe load of a floor is the maximum load which can be placed on top of the finished floor, or hung beneath the floor with safety, and is found by subtracting the weight of the material from the safe strength. Thus if the safe strength of a given floor is equal to 80 pounds per square foot of floor, and the materials used in the construction of the floor (and ceiling) weigh 20 pounds per square foot of floor, then the safe load will be 60 pounds per square foot. The load on a floor usually consists either of people, furniture, machinery or merchandise. The strength, or the safe load, of a floor is usually spoken of as so many pounds per square foot, as that is the only practicable unit of measurement.