1.6 Structural The building structure must be designed to or resist the loads that are applied to it over its design-life. The building structure will be subjected to loads that have been categorized as follows: Dead Loads (D): are permanent loads acting on the structure. These include the self-weight of structural and non-structural components. They are usually gravity loads. Live Loads (L): are non-permanent loads acting on the structure due to its use and occupancy. The magnitude and location of live loads changes frequently over the design life. Hence, they cannot be estimated with the same accuracy as dead loads. Wind Loads (W): are in the form of pressure or suction on the exterior surfaces of the building. They cause horizontal lateral loads (forces) on the structure, which can be critical for tall buildings. Wind loads also cause uplift of light roof systems. Snow Loads (S): are vertical gravity loads due to snow, which are subjected to variability due to seasons and drift. Roof Live Load (Lr): are live loads on the roof caused during the design life by planters, people, or by workers, equipment, and materials during maintenance. Values of structural loads are given in the publication ASCE/SEI 7-10: Minimum Design Loads for Buildings and Other Structures. The first phase of structural design consists of estimating the loads acting on the structure. This is done using the load values and combinations presented in ASCE/SEI 7-10 as explained in the following sub-sections. 1.6.1 Step I. Categorization of Buildings Categories I, II, III, and IV. See Table 1.5-1 below and in ASCE/SEI 7-10. 1.6.2 Dead Loads (D) Dead loads consist of the weight of all materials of construction incorporated into the building including but not limited to walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding and other similarly incorporated architectural and structural items, and fixed service equipment such as plumbing stacks and risers, electrical feeders, and heating, ventilating, and air conditioning systems.
Table 1.1 Member tributary areas and minimum design live loading. Beam Member Tributary area KLL L/Lo=0.25 + 15.0/(KLLAT)0.5 L/Lo min. bi-ei ei-hi AT = ½ x 25.0 x 12.5 x 2 = 312.5 ft2 2.0 0.85 0.5 di - ei ei - fi AT = ½ x 12.5 x 25.0 x 2 + 25.0 x 25.0 = 937.5 ft2 2.0 0.60 0.5 gi - hi hi - ii ai - bi bi - ci AT = ½ x (50+25) x 12.5 = 468.75 ft2 2.0 0.74 0.5 ai - di di - gi ci - fi fi - ii AT = ½ x 25.0 x 12.5 = 156.25 ft2 2.0 1.0 0.5 Step II. Estimate the distributed loads acting on the beams bi - ei and ei - hi b6 e6 b5 e5 h6 (0.85x50 x25)/1000=1.06k/ft. h5 b4 e4 b3 e3 b2 e2 bi ei h4 h3 h2 b1 e1 h1
Step III: Estimate the concentrated live loads acting on the columns of frame bi-ei-hi, which are produced by the live load distribution on the beams of the orthogonal frames di-ei-fi , ai-bi-ci , and gi-hi-ii d6 e6 28.125 k (0.60x50x25)/1000=0.75k/ft. f6 d5 e5 d4 e4 d3 e3 d2 e2 28.125 k 28.125 k 28.125 k Resultant 28.125 k f5 12.5’ f4 14.0625 k f3 f2 25’ 12.5’ 14.0625 k d1 e1 f1 12.5’ 14.0625 k 25’ 12.5’ 14.0625 k a6 b6 17.34 k a5 0.74x50 x12.5=0.46k/ft c6 c5 b5 17.34 k a4 4 17.34 k a3 c4 12.5’ 8.67 k c3 25’ 12.5’ 8. 67 k b3 a2 b2 a b1 17.34 k Resultant 17.34 k c2 c1 12.5’ 8.67 k x12.5=0.46k/ft 25’ 12.5’ 8.67 k Thus, the concentrated live loads acting on columns bi and hi are 17.34 kips The concentrated live loads acting on columns ei are 28.125 k