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Design results using DLF are rarely compared with results from time history dynamic analysis to evaluate the economic consequences of using one approach vs the other. How are the DLF "rule of thumb" values determined, and can they be justified? Having to beef up the structure and foundation can be costly, resulting in project delays. If such changes are truly needed, that's one thing. But if costly design changes are the result of an overconservative and unrealistic analysis approach, that's a problem.
Similarly, in seismic zones, design results using a static seismic load approach are not usually compared with results using time history dynamic analysis. However, unlike the use of DLF, at least the static seismic loads are usually based on codified values which have some justification. Although time history analysis would offer a more realistic distribution of seismic loads, an additional concern with the static seismic load approach are is the effects of pipe-structure interaction which can be significant.
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