or more with live load of 100 lb/ft 2 or less can reduce loads by 0.08% /ft 2 of are supported by the member (with the exclusion of garages or public assembly space); limited to R and 60% where R = 23(1+D/L); storage loads exceeding 100 lb/ft 2 can’t be reduced, but the design loads on columns may be reduced by 20%. Many allowable stress design codes allow the load to be reduced when there is wind load or earthquake loads. Multiple combinations of loads MUST be considered and the structure design to carry that combination which is results in the highest design load values or stresses Effective modeling of the structures depends on correctly identifying the nature of the joints between members to obtain the actions (involves judgment) Joints must be analyzed for force or moment transmission to the supporting member Connections to the ground must provide for equilibrium to be satisfied Concentrated loads are modeled as point loads, while distributed loads need to be modeled from area loads to distributed (line) loads to even point loads; contributory areas are the areas of loading that an element supports Value of distributed load for a uniform width contributory area is w = area load x strip width
ARCH 631 3. Reading Notes F2011abn 3 Self weight must be considered in the dead load, but often isn’t know so an assumed or average weight can be included for preliminary design Examples illustrate that the loading strip widths are determined from the location of halfway to the next supporting element one side to halfway to the next supporting element on the other side (if there is one) and that openings have no load With closely spaced joists or decking, the supporting elements see a uniformly distributed load from the reactions of the joist or decking ends Trusses are usually not modeled with distributed load; they are modeled with loads only at the joints (or panel points); example shows the method of finding the contributory area for each panel point (half way both sides in each direction) and multiplying by the area load to get a concentrated force value; exterior panel points don’t have adjacent supporting elements (panel point) on one side Wind load is distributed load and can act horizontally; vertical members collect the load Building codes can influence the materials, size and shape of a building; example of combustibility type limiting height and square footage in Chart 1 of Note Set 3.1 from BOCA(Building Officials
You've reached the end of your free preview.
Want to read all 4 pages?
- Spring '19
- Dead and live loads, Structural load