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TYPES OF LOADS
Vertical loads fall into two categories called live loads and dead loads. When these two are combined they are referred to as the total load. Dead loads are the actual weights of all the permanent components of a structure such as wood framing, roofing, plywood sheathing, and insulation. On occasion, permanent equipment such as large air conditioners can be considered dead loads. These are loads that will be acting upon the structure throughout its life. Live loads on the other hand are transient items such as furniture, people, and snow. The anticipated weight of live loads to be used for building design are specified in the building code that is in force where the building will be constructed. Local building officials will also have site specific requirements for certain live loads such as for anticipated snow fall. The building use or occupancy can also affect the design load requirements.
Note: The loading examples included in this booklet may or may not represent the live load requirements of the building department having jurisdiction where your building will be constructed.
You should contact your building official to confirm the floor live load based on the type of occupancy and the roof live load based on the local history of snow fall. If the snow load is large, inquire whether a reduction is allowed for steep pitched roofs.
TERMINOLOGY OF LOADS
The structural design for gravity loads involves evaluating each member for performance under the anticipated live loads, dead loads, and a combined force of live load plus dead load often called the total load or "TL". The design process starts at the roof and continues down to the foundation. This is opposite the actual construction which starts at the bottom and works up. Loads are described in terms of pounds. An often used symbol for pounds is # or lbs. When designing large structures with large loads, engineers will often use the term kips symbolized by k. One kip is equal to 1000#. Kips simplify calculations by dropping the last three zeros. In residential design we deal with lower weights and use pounds for greater accuracy.
A.) PT LOAD
A Point Load is a concentrated load in pounds at a specific location.
This may be the location of bearing of a beam or a post.
B.) PSF
Pounds per square foot is used to describe loads on flat surfaces such as floors and roofs. Each square foot of the surface has the same load. To total the load on an area, multiply the Area times the PSF.
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