56 LOADS IN STRUCTURES 



LOADS IN STRUCTURES 



The loads that a structure has to carry may be divided 

 into five classes namely, the dead load, the live load, the 

 accidental load, the snow load, and the wind load. 



The dead load is the weight of the materials of which the 

 structure is composed, as the weight of the beams, columns, 

 walls, floors, and the like. 



The live load is the weight of the various articles in the 

 building that are not part of the structure itself, such as 

 furniture, material stored, if the building is a storehouse, 

 the occupants of the building, light machinery, etc. 



The accidental load is one whose application is doubtful 

 or whose magnitude is great and its effect local. As exam- 

 ples of such loads may be classed the load that would be 

 generated if the ropes of an elevator broke and the safety 

 device was suddenly brought into action, and the load that 

 would be created on a stairway in a mill if there was a panic 

 among the employes, as during a fire. As an accidental 

 load may also be classed such loads as would be caused by 

 an especially heavy office safe or piece of machinery. Many 

 engineers no longer consider an accidental load. The load 

 that would come from an extra-large crowd, as on a stair- 

 way in a fire, they class as part of the live load. Such loads 

 as would occur from a large safe, they usually class as part 

 of the dead load, because the safe would be too heavy to be 

 moved. Therefore, only that part of the structure in the 

 vicinity of the safe need be strengthened. 



The snow and wind loads are, as the names imply, loads that 

 are caused respectively by snow and wind. 



DEAD LOADS 

 WEIGHT OF ROOF TRUSSES 



The dead load must be calculated for each member of a 

 structure by means of tables that give the weights of build- 

 ing materials, such as those on pages 59-61. However, it 



