Why does the longitudnal reinforcement output from response spectrum more than equivalent static ?

[curiousinvite]

Why does the longitudinal reinforcement output from response spectrum more than equivalent static ?
if i scaled response spectrum value so that seismic base shear is equal in both method , what causes such huge difference in reinforcement output?
Output for response spectrum

Output for equivalent lateral force

 

[Agent666]

Why does the longitudinal reinforcement output from response spectrum more than equivalent static ?

Because the modal response spectrum results in a larger member actions in your case.

The equivalent static distribution of loads is typically based on the fundamental first mode response with a nod to higher modes by adding an additional percentage of the load to the uppermost level (typically this is 0.08 times the base shear in my own local code, and the remaining 92% of the base shear is distributed amongst all levels including the uppermost level, but check your local code to review how the loads are distributed).

If you have a structure where higher modes of vibration contribute to the response, then of course it is possible that the contribution from these higher modes results in a higher design action than the fundamental first mode response as the effects are additive.

https://engineervsheep.com

 

[curiousinvite]

Which code do you follow? can you put it for reference

 

[Agent666]

NZS1170.5 if it matters.

https://engineervsheep.com

 

[curiousinvite]

thank you

 

[HTURKAK]

curiousinvite (Civil/Environmental),

I will suggest you to compare the storey shears for RSA and EFL cases although the base shear is the same for both analysis.
Notice that, the OT moment also differs..