Seismic Load on Underground Structures? 1

[jackyyau]

For an underground multi-story basement structure, will the seismic load be citical to the design of the structure? If so, how the lateral quake loads be modelled?

 

[Qshake]

This really depends on the soil mass. You could experience layered displacement similar to interstory drift which would force your structure to displace with differing magnitudes vertically.

It is also possible that the soil mass will not move and therefore develop a certain amount of passive pressure on the side opposite inertia force.

You'll need to investigate some similar applications in soil-structure interaction.

 

[jackyyau]

Thanks Qshake. It seems that there is no simple way to model the lateral load of the soil mass on the perimeter walls of the basement structure dur to earthquake. In addition, it seems that the taking off of dead load and imposed load due to earthquake varies place from place depending its design code.

Can you point me to some of the reference materials. Thanks.

 

[ARIFSIDDIQUI]

There is now such specific provision for underground structure in general it is found that earthquake forces are not critical for the underground structure provided the plan layout of the building is symmetrical and also fitting in to the aspect ratio criterion .

however for analysis u can assume some racking for example around 5-7mm for the structure about all the axis and check the forces.

irrespective of the analysis resulta the detailing must be done following the ductility provisions which is very important.





ARIF ALI SIDDIQUI
STRUCTURAL DESIGN ENGINEER
IMCC 8 JANTAR MANTAR MARG
NEW DELHI INDIA

 

[ludvik]

First of all i should say that i am a bridge man and not a building man, but for soil pressures on bridge abutments and retaining walls under seismic conditions we have a simple technique.

We generally use Mononobe Okabe method, which is basically a modification of the simple coulomb method for active and passive pressures. You can find the proceedure in any geotechnical reference. My personal favorite is Foundation Analysis and Design by Bowles.