How to Analyse Railing Beam to Diaphragm Walls of Underground Station
How to Analyse Railing Beam to Diaphragm Walls of Underground Station
(OP)
How to Analyse Railing Beam to Diaphragm Walls of Underground Box Station
In Hong Kong, a 25m wide by 25m deep railway box station with 3 slabs (roof, concourse and base slabs) is to be constructed underneath a busy urban carriageway. The cross section:
__Ground Level (0.0 mPD)
_________\/___________carriageway
roof
|==============| (-7.0 mPD)
| |
| |diaphragm wall
| concourse |
|]============[| (-14.0 mPD)
| |
| |
| base |
|]============[| (-25.0 mPD)
| |
| | (-40.0 mPD or socket in rock)
The station is to be constructed by top-down construction method as follows:
1. construct and complete the two side diaphragm walls (reserve couplers for slab-wall connetion).
2. excavate soil down to the roof slab level and cast slab, with openings reserved for removal of soil during construction and escalators, vent shafts during operation stage.
3. excavate down to concourse slab level (install props as necessay during excavating downward) and cast the slab.
4.excavate down to base slab level (install props as necessay during excavating downward) and cast the slab.
5. pull the TBMs through the base slab.
Some structural considerations (only the station, not include the adjacent buildings) are to be taken during the design of the station:
1. the slabs are under axial loads and bending
2. the diaphragm walls are subjected to lateral soil and water pressure and are to be deflected inward and therefore the slabs are acting as props.
3. the diaphragm walls are constructed panel by panel (limitation of current construction technology!), i.e. the walls are not longitudinally continuous (although there are shear keys between panels). Each panel is limited to 2.8m long, 1.2m thick and about 40m deep.
Therefore all the lateral pressures on the walls are to be transfered to the slabs and resisted by their internal axial forces.
However, the roof and concourse slabs have many big openings (upto 18m long by 8m wide), therefore railing beams have to be designed to transfer the lateral pressure in opening zones to adjacent solid slab zones.
By simple hand calculations, the bending moment of the railing beam due to the lateral pressures is much much larger than that of SAP2000 3-D frame-shell model.
The SAP2000 model shows that the lateral pressures are taken by the bending of walls and base slab instead of the bending of the railing beam. But structurally, the railing beam takes these pressures.
The question are:
How to model the railing railing beams in SAP2000 both in 3-D frame-shell model and 2-D frame model?
What are the joint releases of the frame elements?
Thanks.
In Hong Kong, a 25m wide by 25m deep railway box station with 3 slabs (roof, concourse and base slabs) is to be constructed underneath a busy urban carriageway. The cross section:
__Ground Level (0.0 mPD)
_________\/___________carriageway
roof
|==============| (-7.0 mPD)
| |
| |diaphragm wall
| concourse |
|]============[| (-14.0 mPD)
| |
| |
| base |
|]============[| (-25.0 mPD)
| |
| | (-40.0 mPD or socket in rock)
The station is to be constructed by top-down construction method as follows:
1. construct and complete the two side diaphragm walls (reserve couplers for slab-wall connetion).
2. excavate soil down to the roof slab level and cast slab, with openings reserved for removal of soil during construction and escalators, vent shafts during operation stage.
3. excavate down to concourse slab level (install props as necessay during excavating downward) and cast the slab.
4.excavate down to base slab level (install props as necessay during excavating downward) and cast the slab.
5. pull the TBMs through the base slab.
Some structural considerations (only the station, not include the adjacent buildings) are to be taken during the design of the station:
1. the slabs are under axial loads and bending
2. the diaphragm walls are subjected to lateral soil and water pressure and are to be deflected inward and therefore the slabs are acting as props.
3. the diaphragm walls are constructed panel by panel (limitation of current construction technology!), i.e. the walls are not longitudinally continuous (although there are shear keys between panels). Each panel is limited to 2.8m long, 1.2m thick and about 40m deep.
Therefore all the lateral pressures on the walls are to be transfered to the slabs and resisted by their internal axial forces.
However, the roof and concourse slabs have many big openings (upto 18m long by 8m wide), therefore railing beams have to be designed to transfer the lateral pressure in opening zones to adjacent solid slab zones.
By simple hand calculations, the bending moment of the railing beam due to the lateral pressures is much much larger than that of SAP2000 3-D frame-shell model.
The SAP2000 model shows that the lateral pressures are taken by the bending of walls and base slab instead of the bending of the railing beam. But structurally, the railing beam takes these pressures.
The question are:
How to model the railing railing beams in SAP2000 both in 3-D frame-shell model and 2-D frame model?
What are the joint releases of the frame elements?
Thanks.
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