04/26/2018

Determining Exposure Factors for Calculating Flat Roof Snow Loads on Structures per ASCE 7-10

In this post, I will provide a brief overview of determining exposure factors, Ce, for calculating flat roof snow loads on structures per ASCE 7-10, Table 7-2. The exposure factors are based on the terrain category of the location of the structure and the exposure of the roof.

 

Exposure Factors for Terrain Category B

 

Fully Exposed Roof, Ce – 0.9

Partially Exposed Roof, Ce – 1.0

Sheltered, Ce – 1.2

 

Exposure Factors for Terrain Category C

 

Fully Exposed Roof, Ce – 0.9

Partially Exposed Roof, Ce – 1.0

Sheltered, Ce – 1.1

 

Exposure Factors for Terrain Category D

 

Fully Exposed Roof, Ce – 0.8

Partially Exposed Roof, Ce – 0.9

Sheltered, Ce – 1.0

 

Exposure Factors for Terrain Category Above Treeline in Windswept Mountainous Areas

 

Fully Exposed Roof, Ce – 0.7

Partially Exposed Roof, Ce – 0.8

Sheltered, Ce – N/A

 

Exposure Factors for Terrain Category in Alaska, in Areas Where Trees do not Exist Within a 2-mile Radius of the Site

 

Fully Exposed Roof, Ce – 0.7

Partially Exposed Roof, Ce – 0.8

Sheltered, Ce – N/A

 

ASCE 7-10, Table 7-2

 

04/26/2018

Calculating Flat Roof Snow Loads on Structures per ASCE 7-10, Chapter 7

In this post, I will provide a brief overview of calculating flat roof snow loads that are specified in ASCE 7-10, Chapter 7. Before diving deeper, it’s a good idea to review the definitions of parameters used in the snow load formula. 

 

Parameter Definitions

 

Ce = Exposure Factor, ASCE 7-10 Table 7-2

Ct = Thermal Factor, ASCE 7-10 Table 7-3

Is = Importance Factor, ASCE 7-10 Table 1.5-2

pg = Ground Snow Load, ASCE 7-10 Figure 7-1 and Table 7-1

 

 

Flat Roof Snow Load Formula, ASCE 7-10, Equation 7.3-1

 

pf = 0.7CeCtIspg

 

Flat Roof Snow Load = 0.7 times the exposure factor times the thermal factor times the importance factor times the ground snow load

04/20/2018

Structural Deflection Limits per International Building Code 2015 (IBC 2015), Table 1604.3

In this post, I will provide a brief overview of the structural deflection limits of structural elements based on loading conditions specified in the International Building Code 2015 (IBC 2015), Table 1604.3.

 

Roof Members Deflection Limits

Members supporting plaster or stucco ceiling (Live Load) = L/360

Members supporting plaster or stucco ceiling (Snow or Wind load) = L/360

Members supporting plaster or stucco ceiling (Dead + Live Load) = L/240

 

Members supporting nonplaster ceiling (Live Load) = L/240

Members supporting nonplaster ceiling (Snow or Wind load) = L/240

Members supporting nonplaster ceiling (Dead + Live Load) = L/180

 

Members not supporting ceiling (Live Load) = L/180

Members not supporting ceiling (Snow or Wind load) = L/180

Members not supporting ceiling (Dead + Live Load) = L/120

 

Floor Members Deflection Limits

Floor members  (Live Load) = L/360

Floor members (Snow or Wind load) = N/A

Floor members (Dead + Live Load) = L/240

 

Exterior Walls Deflection Limits

Walls with plaster or stucco finishes (Live Load) = N/A

Walls with plaster or stucco finishes (Snow or Wind load) = L/360

Walls with plaster or stucco finishes (Dead + Live Load) = N/A

 

Walls with other brittle finishes (Live Load) = N/A

Walls with other brittle finishes (Snow or Wind load) = L/240

Walls with other brittle finishes (Dead + Live Load) = N/A

 

Walls with flexible finishes (Live Load) = N/A

Walls with flexible finishes  (Snow or Wind load) = L/120

Walls with flexible finishes  (Dead + Live Load) = N/A

 

Interior Partitions Deflection Limits

Partitions with plaster or stucco finishes (Live Load) = L/360

Partitions with plaster or stucco finishes (Snow or Wind load) = N/A

Partitions with plaster or stucco finishes (Dead + Live Load) = N/A

 

Partitions with other brittle finishes (Live Load) = L/240

Partitions with other brittle finishes (Snow or Wind load) = N/A

Partitions with other brittle finishes (Dead + Live Load) = N/A

 

Partitions with flexible finishes (Live Load) = L/120

Partitions with flexible finishes  (Snow or Wind load) = N/A

Partitions with flexible finishes  (Dead + Live Load) = N/A

 

Farm Buildings Deflection Limits

Farm Buildings (Live Load) = N/A

Farm Buildings (Snow or Wind load) = N/A

Farm Buildings (Dead + Live Load) = L/180

 

Greenhouses

Greenhouses (Live Load) = N/A

Greenhouses (Snow or Wind load) = N/A

Greenhouses (Dead + Live Load) = L/120

04/16/2018

Uniform Live Load Reduction Using ASCE 7-10, Section 4.7

In this post, I will provide a brief overview of how to reduce uniform live loads using ASCE 7-10, Section 4.7. This post does not cover the reduction of roof uniform live loads. .

 

Uniform Live Load Reduction Formula, ASCE Equation 4.7-1

 

 

Parameter Definitions

 

L = Reduced design live load per ft2 (m2) of area supported by the member

Lo = Unreduced design live load per ft2 (m2) of area supported by the member (ASCE 7-10, Table 4-1)

AT = Tributary area in ft2 (m2)

KLL = Live Load Element Factor (Table 4-2)

 

Limitations / Conditions for Reducing Live Loads

 

  1. Uniform live loads may only be reduced if the limitations listed in Sections 4.7.3 – 4.7.6 are satisfied
  2. Uniform load loads may only be reduced for members for which the product of the live load element factor and tributary area is at least 400 ft(KLL*AT ≥ 400)
  3. L  ≥ 0.5L for members supporting one floor
  4. L  ≥ 0.4L for members supporting two or more floors
04/16/2018

Live Load Element Factors Used in the Reduction of Uniform Live Loads per ASCE 7-10, Table 4-2

In this post, I will provide a brief overview of the live load element factors,KLL, used in the reduction of uniform live load specified in ASCE 7-10, Table 4-2.

 

Live Load Element Factors, KLL, by Element Type

 

Live load element factor for interior columns, KLL =  4

Live load element factor for exterior columns without cantilever slabs, KLL =  4

Live load element factor for edge columns with cantilever slabs, KLL = 3

Live load element factor for corner columns with cantilever slabs, KLL = 2

Live load element factor for edge beams without cantilever slabs, KLL = 2

Live load element factor for interior beams, KLL = 2

Live load element factor for edge beams with cantilever slabs, KLL = 1

Live load element factor for cantilever beams, KLL = 1

Live load element factor for one-way slabs , KLL = 1

Live load element factor for two-way slabs, KLL = 1

Live load element factor for members without provisions for continuous shear transfer normal to their span, KLL = 1

Live load element factor for all other members not identified, KLL = 1