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Load Combination Example #1Given:^ A simply supported floor beam from the following sources:- (Source 1) floor loads (acting as a uniform load over the entire span):- (Source 2) a column located X distance from one end. (acts as a point load):- (Source 3) a part of the lateral force resisting system (acts as an axial load):
Service Level Load Magnitudes by SourceD^ L^ Lr
S^ W^
E
Source 1^ 1.150^ 1.
---^ ---^
---^ ---^ klf Source 2^ 8.000^ ---
4.800^ 20.^
---^ ---^ k Source 3^ ---^ ---
---^ ---^
15.000^ 25.000^ k
Wanted:^ Determine the loading diagram for the beam for each of the following load combinations.LRFD^
ASDEquation LRFD-2 Equation ASD-2Equation LRFD-4 Equation ASD-5Equation LRFD-5Note, that on a given project, you will use EITHER LRFD OR ASD… not both!Also the beam has to be strong enough to support ALL load combinations, not just the few we show here! Load Combination Example 1
A Beginner's Guide to ASCE 7-
Solution:LRFD-LC^
See the SCM for equation.Note that there are three permeatations for this equation… this means thereare three different load combinations to be consideredLRFD-LC2aD+F+T L+H^ Lr^ Comb.Ld Factor 1.2 1.6^ 0.5^ ValueSource 1 1.150 1.850^ 0.000^ 4.
klf Source 2^ 8.000^ 0.
4.800^ 12.000^ k Source 3^ 0.000^ 0.
0.000^ 0.000^ k LRFD-LC2bD+F+T^ L+H
S^ Comb. Ld Factor^ 1.2^ 1.
0.5^ Value Source 1^ 1.150^ 1.
0.000^ 4.340^ klf Source 2^ 8.000^ 0.
20.000^ 19.600^ k Source 3^ 0.000^ 0.
0.000^ 0.000^ k LRFD-LC2cD+F+T^ L+H
R^ Comb. Ld Factor^ 1.2^ 1.
0.5^ Value Source 1^ 1.150^ 1.
0.000^ 4.340^ klf Source 2^ 8.000^ 0.
0.000^ 9.600^ k Source 3^ 0.000^ 0.
0.000^ 0.000^ k In this case, it is probably obvious that LRFD-LC2b will be the controlling of this set of load combinations.There is no need to analyze for internal forces for LRFD-LC2a nor LRFD LC2c since they don't control.Also note that neither W nor E enters into this combination.
The values for this part ofthe table come from thegiven data for various loadsources.^
The combined values are the result ofmultiplying the data on each row by theload factors at the top of the table.For example, this value =1.28.00+1.60.00+0.5*4.80The other values are similarly computed.
Load Combination Example 1
A Beginner's Guide to ASCE 7-
Let's do this again, but with ASD combinations, recalling that LRFD and ASD are not directly comparable! (LRFD is at ultimate levels and ASD is at service levels)^ ASD-LC^
See the SCM for equation.Note that there is only one permeatation for this equation.ASD-LC2D L^ Comb.Ld Factor 1 1 ValueSource 1 1.150 1.850^ 3.000^ klfSource 2 8.000 0.000^ 8.000^ k Source 3 0.000 0.000^ 0.000^ k ASD-LC5 See the SCM for equation.Note that there are two permeatations for this equation.ASD-LC5aD W^ Comb.Ld Factor 1 1 ValueSource 1 1.150 0.000^ 1.150^ klfSource 2 8.000 0.000^ 8.000^ k Source 3 0.000 15.000^ 15.000^ k ASD-LC5cD E^ Comb.Ld Factor 1 0.7^ ValueSource 1 1.150 0.000^ 1.150^ klfSource 2 8.000 0.000^ 8.000^ k Source 3 0.000 25.000^ 17.500^ k
Summary^ This example demonstrates the application of the ASCE 7 load combinations. Each load combination represents the application ofa SINGLE permeatation of a load combination equation.Even though we did not do a thorough job of examining all the possible load combinations, this example will help you to understandhow to apply the various equations.Load Combination Example 1
A Beginner's Guide to ASCE 7-
