A guide to ASCE 7-16 LRFD Load Combinations
In the United States, ASCE 7-16 is a key part of the building code. It focuses on the requirements for general structural design, as well as providing a means for determining loads (dead, live, soil, flood, snow, rain, ice, earthquake, wind) and their combinations.
Load and Resistance Factor Design (LRFD) involves seven basic load combination equations. This is different to Allowable Stress Design (ASD Load Combinations) which is another common philosophy with its own set of load combinations. For more information about the differences between ASD and LRFD, check this article.
This article will focus on how SkyCiv’s auto-generated load combinations feature meets the load combination equations as specified in ASCE 7-10 LRFD.
2.3.2 Basic Combinations
|Design Code Equation||Design Code Comment||SkyCiv Equation||SkyCiv Comment|
|1.2D + 1.6L + 0.5(Lrr or S or R)||Eq. 184.108.40.206||1.2G + 1.6QL + 0.5QS||The load type “Snow” is sub-categorized into “snow”, “roof live”, and “rain”. Selecting this load combination will automatically create 3 load combination equations due to the use of “or” in the equation specification.|
|1.2D + 1.6(Lrr or S or R) + (L or 0.5W)||Eq. 220.127.116.11||1.2G + 1.6QS + QL
1.2G + 1.6QS + 0.5QW
|Due to the presence of “or” in two places of this load combination, this generates 6 load equations. SkyCiv has separated this into two load combinations (for the L or 0.5W options) which generates 3 load equations each.|
|1.2D + 1.0W + L + 0.5(Lr or S or R)||Eq. 18.104.22.168||1.2G + QW + QL + 0.5QS||The load type “Snow” is sub-categorized into “snow”, “roof live”, and “rain”. Selecting this load combination will automatically create 3 load combination equations due to the use of “or” in the equation specification.|
|1.2D + 1.0E + L + 0.2S||Eq. 22.214.171.124||1.2G + QL + 0.2QS + E||–|
|0.9D + 1.0W||Eq. 126.96.36.199||0.9G + QW||–|
|0.9D + 1.0E||Eq. 188.8.131.52||0.9G + E||–|
Example: All Load Types Assigned
Whilst not practical, 7 load groups have been created and assigned to all 7 load types as seen below. This is done to check the equations that are formed from the load combinations
Try our SkyCiv Free Wind Tool for wind speed and wind pressure calculations on simple structures: