76 



STEEL OFFICE BUILDINGS. 



CHAP. II. 



Schneider's specifications give the following empirical rule for calculating the. thickness of 

 walls in buildings several stories in height. 



"The minimum thickness of walls will be given by the formula 



t = L/4 + (Hi + H 2 + - + H n )/6 



where / = minimum thickness of wall in inches, L = unsupported length in feet, which shall be 

 assumed as not less than 24 ft. ; and Hi, H 2 , H 3 , etc. the heights of stories in feet beginning at the 

 top. Cellar walls are to be 4 in. thicker than the first story walls." 



The Chicago Building Ordinance (1911) contains the following: 



" (a) Brick, stone, and solid concrete walls, except as otherwise provided, shall be of the 

 thickness in inches indicated in the following table:" 



THICKNESS OF WALLS. 

 Chicago Building Ordinance (1911). 



WATERPROOFING. For methods of waterproofing walls, floors, etc., see methods of 

 waterproofing bridge floors in Chapter IV. 



CALCULATION OF WIND LOAD STRESSES. (i) The wind load on the sides of the 

 steel frame in a building in which the wind bracing is all in the outside walls of the building will 

 be carried to the ends of the building by means of bracing in the plane of each floor or by the floor 

 slabs where the floors are made of reinforced concrete, and the loads will then be transferred to 

 the foundations by means of bracing in the planes of the ends of the building. In calculating the 

 stresses in the bracing in the end panels it is usual to assume that the wind load carried by each 

 braced bent, consisting of two columns, together with the floor girders and wind bracing, is equal 

 to the total wind load divided by the number of braced panels in the plane. This was the method 

 used in calculating the stresses in the Singer Tower, New York. (2) As usually constructed the 

 interior columns have brackets and only part of the wind load will be transferred to the ends or 

 sides of the building, the remainder of the wind load will be transferred to the foundations by 

 portal action and flexure in the columns and beams. It is not possible to determine the proportion 

 of the wind load that will be taken by the main framework and by the ends of the building, as the 

 stresses in the framework are statically indeterminate. During erection and before the floors 

 have been put in place, or with types of floors which do not increase the rigidity of the building in 

 horizontal planes, the wind loads will all be taken by the framework normal to the side of the 

 building upon which the wind blows. This wind load is commonly taken as 30 Ib. per sq. ft. of 

 all framework exposed. When rigid floors have been put in place and the building is completed 

 the wind load will be taken by the end transverse frames and the intermediate transverse frames, 

 in proportion to the relative rigidity of the two frameworks. In a long narrow building with 

 efficient wind bracing in the intermediate framework, practically all the wind load will be taken 

 directly to the foundations by the transverse intermediate bents; while in the direction of the 

 length of the building, practically all the wind load will be carried by the bracing in the sides of 

 the building. For a building as long as wide with rigid floors and efficient transverse framework 



