The effect of drifting or sliding snow on a roof should be considered as a matter of good design practice. 2.3. Structures kept just above freezing and others with cold, ventilated roofs in which the thermal resistance (R-value) between the ventilated space and the heated space exceeds 25° F × h × ft2/Btu (4.4 K × m2/W), Structures intentionally kept below freezing, Continuously heated greenhouses with a roof having a thermal resistance (R-value) less than 2.0 ° F × h × ft2/Btu. Our ground snow load values can be as high as 300 psf and the snow sticks around for more than 6 months at a time. The floor system of the classroom shown in Figure 2.2 consists of a 3-inch-thick reinforced concrete slab supported by steel beams. Flat roof snow loads of 30 psf (1.44 kN/m 2) or less and roof live loads of 30 psf (1.44 kN/m 2. Interior columns and exterior columns without cantilever slabs, Interior beams and edge beams without cantilever slabs, All other members, including panels in two-way slabs. To find the ground snow load, we use section 1303.1700 of the Minnesota Administrative Rules. This table says that roof snow loads equal .7 times the ground snow load. The weight assigned to all other levels is as follows: WTotal = 300,000 lb + (4)(600,000 lb) = 2700 k. Calculate the seismic response coefficient Cs. No reduction is permitted for floor live loads greater than 4.79 kN/m2(100 lb/ft2) or for floors of public assembly, such as stadiums, auditoriums, movie theaters, etc., as there is a greater possibility of such floors being overloaded or used as car garages. To meet the afore-stated requirements, structures are designed for the critical or the largest load that would act on them. To calculate Roof Snow Load per Residential Building Code: 0.7 x pg (ground snow load) = pf (roof snow load) Roof Snow Load Examples: Above line: 0.7 x 60 psf = 42 psf Below line: 0.7 x 50 psf = 35 psf psf (pounds per square The estimated value of V must satisfy the following condition: W = effective seismic weight of the building. According to ASCE 7-16, the design snow loads for flat roofs and sloped roofs can be obtained using the following equations: Table 2.10. Table 2.7. All beams are W12 × 44, spaced at 10 ft o.c. Fresh light and fluffy snow will weight much less than the dense, packed, or wet variety. They include the self-weight of structural members, such as walls, plasters, ceilings, floors, beams, columns, and roofs. MIXED MOISTURE: Light rains may help melt snow from the rooftops. The weight assigned to the roof level is as follows: Wroof = (32 psf)(75 ft)(100 ft) + (20%)(40psf)(75 ft)(100 ft) = 300,000 lb. 2.L is the dimension of the building normal to the wind direction, and B is the dimension parallel to the wind direction. Ground snow load = 30 psf Roof is fully exposed with asphalt shingles. Alaska Snow Loads. The critical load for a given structure is found by combining all the various possible loads that a structure may carry during its lifetime. R = response modification coefficient. Water accumulated on a flat or low-pitch roof during a rainstorm can create a major structural load. In our area the ground snow load is 25 psf and we typically design roofs for 25 or 30 (schools) psf of snow. Hydrostatic and earth pressures: These are loads on retaining structures due to pressures developed by the retained materials. Suggested design values of snow loads are provided in codes and design specifications. The Federal Emergency Management Agency (FEMA) states one foot of freshly fallen powdery snow weighs about three pounds per square foot. A four – story schol building. Currently enforced snow loads also vary widely at similar elevations in neighboring counties. Loadings: Roof = 100 psf Snow load = 30 psf Brick = 120 pcf Allowable stress: σ brick = 125 psi Find: Compressive stress at the base of the wall. It is computed using the following empirical formula: Ct = building period coefficient. Solution Determine the load for a 1-foot strip of wall. Dead loads are structural loads of a constant magnitude over time. Very wet and heavy snow can weigh seven times as much as dry snow. Retaining structures must be designed against overturning and sliding caused by hydrostatic and earth pressures to ensure the stability of their bases and walls. 1603.1.3 Roof Snow Load Data •Ground Snow Load, p g •Flat Roof Snow Load, p f ASCE 7, Equation 7.3-1 30 psf minimum (CT) •Snow Exposure Factor, C e •Snow Load Importance Factor, I s •Thermal Factor, C … Some building load impact factors are presented in Table 2.3. The tributary width for B1 is the distance from the centerline of the beam to half the distance to the next or adjacent beam, and the tributary area for the beam is the area bordered by the tributary width and the length of the beam, as shaded in the figure. Fig. The recommended weight values of some commonly used materials for structural members are presented in Table 2.1. R = 8 for special moment resisting steel frame (see Table 2.13). Kd = wind directionality factor. 2.4 The second-floor layout of an elementary school building is shown in Figure P2.1. They include the weight of structure and the loads that are permanently attached to the structure. Roof pressure coefficients, Cp, for use with qh, as specified in ASCE 7-16. SDs = design spectral acceleration. The weight assigned to the roof level is as follows: W roof = (32 psf)(75 ft)(100 ft) + (20%)(40psf)(75 ft)(100 ft) = 300,000 lb. snow-load-induced failure is reduced to an acceptably low level. Determine the dead load in lb/ft acting on a typical interior beam B1-B2 in the second floor. Table 2.2. The International Code Council requires that roofs with parapets include primary and secondary drains. Fig. 2.8. Lo = unreduced design live load per ft2 (or m2) from Table 2.2 (Table 4.3-1 in ASCE 7-16). ACCUMULATION: The snow from just one day does not tell the story, either. This is one if the unique challenges of structural engineering in Alaska. columns, etc.). The determination of the dead load due to structural members is an iterative process. Minimum uniform and concentrated floor live loads. A floor system consisting of wooden joists spaced 6 ft apart on the center and a tongue and groove wood boarding, as shown in Figure 2.8, supports a dead load (including the weight of the beam and boarding) of 20 psf and a live load of 30 psf. This factor is an equal unity for building on level ground and increases with elevation. Or the 25 Roof snow loads for the following counties (in pounds-per-square-foot ground snow load) will give you some idea of the wide range of specifications across the U.S. (Keep in mind that specific locations within these counties may have snow loads modified by local authorities. According to Figure 7.2-1 in ASCE 7-16, the ground snow load for Lancaster, PA is. Snow loads shall be determined by the building official. Examples of retaining walls include gravity walls, cantilever walls, counterfort walls, tanks, bulkheads, sheet piles, and others. The state's building code requires residential roofs withstand snow loads of at least 30 pounds per square foot. 40-58 for packed snow with ice; 58 for ice; For example, a roof with 3 feet of light snow has an estimated roof load of 60 pounds per square foot (3 ft depth X 20 lb/ft2/ft depth density = 60 lb/ft2). Figure 2.3 depicts a roof and these drainage systems. Fig. The publication is $20 Provisions on how to calculate the snow drift surcharge for structures can be found in Section 7.8 of ASCE 7-10. ), • Alameda County, CA: 0 psf AT = tributary area of member in ft2 (or m2). The values of R for several common systems are presented in Table 2.13. Snow, which is just frozen ice crystals, varies in weight by its volume and density. The design spectral acceleration parameters are SDS = 0.28, and SD1 = 0.11. 2.8. This information is found in the code book. Once the total seismic static lateral base shear force in a given direction for a structure has been computed, the next step is to determine the lateral seismic force that will be applied to each floor level using the following equation: Fx = lateral seismic force applied to level x. Wi and Wx = effective seismic weights at levels i and x. ℎi and ℎx = heights from the base of the structure to floors at levels i and x. KLL = AI/AT = live load element factor from Table 2.14 (see values tabulated in Table 4.7-1 in ASCE 7-16). They include the loads on a building created by the storage of furniture and equipment, occupancy (people), and impact. Therefore, it must be considered when designing a building. The southern portion of Minnesota, which includes the Twin Cities metro area, uses a ground snow load of 50 pounds per square foot. Some typical values of the ground snow loads from this standard are presented in Table 2.8. 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