For designers like me who were trapped in the past (used to using the old codes), the introduction of new and smaller load factors might be quite hard to accept. In school, we were taught to use 1.4DL + 1.7LL in calculating the ultimate load involving basic dead and live loads. However in the latest NSCP which was released a few years ago, the new load factors are smaller - 1.2DL + 1.6LL.
Below is the table showing the comparison of the new and old codes:
Where:
D = dead load
E = earthquake load
F = load due to fluids
H = load due to lateral pressure of soil and water in soil
L = live load, except roof live load, including any permitted live load reduction
Lr = roof live load , including any permitted live load reduction
R = rain load on the undef1ected roof
T = self-straining force and effects arising from contraction or expansion resulting from temperature change, shrinkage, moisture change, creep in component materials, movement due to differential settlement, or combinations thereof .
W = load due to wind pressure
f1 = 1.0 for floors in places of public assembly, for live loads in excess of 4.8 kPa, and for garage live load.
= 0.5 for other live loads
Em = the maximum effect of horizontal and vertical forces as set forth in Section 208.6.1
Which one should we use? In practice, we could use any of these based on engineers discretion because presumably, both of them are safe to apply and there has been lots of studies, researches and experimentation done before structural scientists came up with the numbers. In schools, however, I am not sure if they are using the new code. If the professor says use the new code then use the new code otherwise you'll get the wrong answer because of using the load factors in the old code.
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