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Dynamic seismic design

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Reading through the CBC 1998 and UBC 1994 prompted me to query the following (and comment) :
1.     What factor is used to multiply the custom spectrum ordinates in UBC figure 16.3,  to get the model spectral accelerations ?  I find that accelerations (and units) seem to become obscure in earthquake formulas.
2.    I understand that the dynamic base shear reactions are to be compared with the statically calculated reactions and brought in line. All member forces are then similarly factored up or down.
This suggest that all we are achieving with a dynamic analysis is distributing the effects of the earthquake realistically over the structure and using the static calculated shear force as a base value for design forces. The period used in the static method must therefore be very important. For combination of forces further reductions (1.4) are allowed.
The ductility of the steelwork is being heavily relied upon ? Are these adjustments implying that the theory is not reliable ?
Correct me if I am wrong and help some of us understand  earthquake design.