dynamic load in etab programm

[swelm]

when can take the effect of the dynamic load and the effect of the p- delta into consideration?


i hear that when the height of building more than 100 meter

is that right??


thanks

 

[hippo11]

It's kind of hard to say without know much about your specific project. Can you tell us more about what you are modeling in ETABS?

 

[zaes73]

hippo11 is right ! for a watertank upto 50 Ft. height its important to consider P-delta, where as for a 50 ft simple layout column beam structure you may get away without it, it depends on what you are designing !

and its not a matter of Etabs or any other software, its engineering judgement.

 

[hippo11]

why do so many people call it ETAB? It's ETABS.

 

[flyby911]

for columns it's not an option to use the P-delta effect if you're using american codes coz it's a necissity..if you didn't use p-delta analysis in the ETABS you'r gonna use it when designing columns and getting their buckling lenghths to get additional moments due to buckling

 

[flyby911]

i forgot to answer the first question..

when to take the effect of dynamic load...

when you have an acting significant dynamic load like earthquake or vibrating machines...sometimes you're gonna multiply the static loads by a dynamic amplification factor to count for the dynamic effect like in train loads other than making dynamic analysis

 

[zaes73]

flyby911 for my information can you specify the clause in ACI that suggests that P-delta effects are to be taken in consideration for every type of columns. ? by dynamic amplification factor you mean P.S. factors as in case of crane load you take 1.25 when designing the crane beam ?

"effect of dynamic loading"! are take in account always where applicable. Earthqauake and wind loads are Dynamic loads for multistorey building. its a different thing that you choose to solve the effects of these forces by performing a dynamic analysis or static analysis.

 

[swelm]

sorry about the missing information
my buidling is high rise building with hieght 80 meter
my question was is that nesscssary to take the effect of p-delta?
and is that nesssary to consider earthque as dynamic load and define response spectrum case?


thanks for all comment

 

[zaes73]

80m is surely a high rise building. Seismic and wind loading is a must, and for these loadings you need to perform dynamic analysis and generate atleast 8 Mode shapes of the building.

 

[flyby911]

zaes73

the equations that the ACI uses for deriving the extra moment generated from buckling are the P-Delta equations..if you use P-delta option in any analysis program you don't calculate the extra added buckling moments coz they're already taken into account in ETABS analysis

 

[hippo11]

flyby, i interpret the code differently...here's why...there are two kinds of P-delta:

1) P-delta from story drift (ETABS does do this when you click "P-delta" "Analysis Options", )

2) P-delta from member curvature (ETABS does NOT do this when you click "P-delta" under "Analysis Options", according to the ETABS literature)

And if you look at the beginning of the ACI chapter on columns (Chp 10?)it says that you don't have to do moment magnification on your columns ONLY IF your analysis takes into account BOTH story drift AND member curvature...but ETABS only does story drift p-delta...

Therefore I don't think the "P-delta" option in ETABS gets you out of the moment magnification stuff...and for that matter, any computer analysis program--you better make sure it does BOTH types of P-delta before you say you don't have to do the magnification stuff.

Do you agree?...