HEAVY TIMBER MILL CONSTRUCTION BUILDINGS 



support a given uniformly distributed floor or roof load may 

 be found from the following formula: 



_3W i2L _ 

 4f 



To find the value of Wi, it will be necessary to know the 

 kind of occupancy or the live load which is likely to be placed 

 on the floor or roof, together with an allowance for the weight 

 of the floor material itself. If sudden jars, vibration, or im- 

 pact, is to be provided for, either a percentage may be added 

 to the ordinary live loads, or the allowable working unit 

 stresses may be decreased. The National Board of Fire Un- 

 derwriters recommend that at least 25 percent be added to the 

 stresses produced by live loads in structures carrying machin- 

 ery, such as cranes, conveyors, printing presses, etc., to provide 

 for effect of impact and vibrations. 



The load which is likely to come upon a roof is made up of 

 three parts; the dead load which consists of the weight of the 

 roofing material and of roof structure; the snow load which 

 may possibly come upon the roof, and a certain amount of load 

 due to the wind. These must all be taken into account in mak- 

 ing up the total. The element of wind load is not great on flat 

 roofs, but the snow load may be quite an appreciable quantity. 

 Table A gives average values for the snow load which may be 

 present on buildings in different parts of the country. 



The dead load may be found by estimating the quantity 

 of material necessary to form the roof construction, and adding 

 to it an amount to take care of the roof covering. Felt and 

 gravel roofing of a 5-ply quality will weigh about 6 pounds 

 per square foot of roof surface. Weights of timber and roof- 

 ing materials will be found in Table B. 



Live loads for various classes of occupancy may be esti- 

 mated from Table C in case the local building ordinance does 

 not specify a definite floor load for the class of building in 

 question. 



Table A. Snow Loads in Different Localities. 



Pounds 

 Location. per Sq. Ft. 



of Eoof . 



Southern and Pacific States 5 



Central States 30 



New England States 40 



Northwestern States 45 



Page fifty-three 



