LOADS IN STRUCTURES 85 



found that the normal pressure p amounts to 18.2 Ib. per 

 sq. ft. Proceeding in the same manner, it is found that for 

 horizontal pressures of 30 and 40 Ib., the normal pressures 

 are 27.3 and 36.4 Ib. per sq. ft., respectively. 



In Fig. 3, the normal force p has been resolved into its 

 two components, p%. and p v , the former acting in a horizontal 

 direction and the latter in a 

 vertical one. The force ph 

 tends to push the roof in a 

 direction parallel with the 

 wind, while the force p v tends 

 to depress the roof or, in some 

 cases, to press it sidewise. In 

 open sheds, where the wind is 

 liable to strike the inner, far FJ G. 3 



side of the shed roof, the effect of the force p v must be con- 

 sidered, as its tendency would be to lift the roof. 



DISPOSITION OF LOADS 



In warehouses where all floors are likely at any one time 

 to be fully loaded, the beams, girders, columns, and founda- 

 tions are always proportioned for the entire live and dead 

 loads. However, where the building exceeds four or five 

 stories in height and is used for any other purpose except 

 storage, as, for instance, a modern office building, it is cus- 

 tomary to assume that certain members, while proportioned 

 for the entire dead load, carry only a certain percentage of 

 the live load. 



In an office building, or similar structure, it is highly 

 improbable that all the floors or all parts of the same floor 

 will be fully loaded at the same time, and in view of this fact 

 it is considered good practice, while proportioning the floor- 

 beams for the full live load, to calculate only say 90% of the 

 live load on the girders and columns. It is customary to 

 proportion the columns supporting the roof and the top 

 floor for the full live load. The live loads on the columns, 

 in each successive tier, from the floor above is reduced 10% 

 until 50% of the live load is reached, when such reduced 

 loads are used for all the remaining floors to the basement. 



