high rise basement- superstructure

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Top down contruction method

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Project Land & Rajuk rules on utilization factor:The project land is 205.46Lx121.13W, measuring 24886.10 sft. (34.564 Katta)OrientationNW-NE206'3"NW-SW121'SW-SE204'8"NE-SE121'3"A digital Map of the land has been attached is given below:

The constructed floor space has been taken as 20000 sft leaving the set back area as required by RAJUK rules. Podium height is limited to 12m maximum height which at 4 meter can accommodate only 3 floors. Podium floors can utilize only 75% of the plot area. Each floor in tower block is allowed to use only 50% of the plot area. Hence the 46 tower blocks have each been allotted a space of 14800 sft. The constructed floor space has been taken as 19000 sft leaving the set back area as required by RAJUK rules. Podium height is limited to 12m maximum height which at 4 meter can accommodate only 3 floors. Podium floors can utilize only 75% of the plot area. Each floor in tower block is allowed to use only 50% of the plot area. Hence the 46 tower blocks have each been allotted a space of 12800 sft. Structural Design Major load factors for design basis shall be wind velocity and earthquake.Bangladesh National Design Code (BNBC) previously classified Dhaka under seismic Zone 2 (moderate) which has presently been upgraded to Zone 3 (major) which falls under SDC category D.The design maximum wind load is specified as Wind load 210 KM/hrImpact & limits of drift due to wind on top most floors and lateral forces on structure shall be considered with reference to high rise buildings in various other countries.

1. Live loads for office buildings are assumed at:Live load in office area : 4 kN/sq mLive load in passage area : 4 kN/sq mLive load in urinals : 2 kN/sq mFloor finish load : 1.5 kN/ sq mWall thickness : 150 mm thick wallStair case loading : 4 kN/sq m

2. Codes used for analysis are R.C.C. design: IS 456: 2000 [5]Steel design: IS 800: 1984 [8]Composite design: AISC LRFD 99 [9]3. Conceptual structural design has been based on Geophysical & soil test data as follows: The strata from EGL-33.3meter upward to 3.75m comprises of Gray spotted brown to gray very stiff to stiff clay. The strata from EGL-45.4m upward to 12m comprises of non plastic, SILT with sand, trace mica. The strata from EGL-51.3m upward 6m comp[rises of Brown and very dense sand, trace mica. up to 6m (from EGL- 51.3m) The strata from EGL-39m upward comprises of very light brown to dark gray.

4. Design code BNBC for earthquake and wind:Major load factors for design basis shall be wind velocity and earthquake. Bangladesh National Design Code (BNBC) previously classified Dhaka under seismic Zone 2 (moderate) which has presently been upgraded to Zone 3 (major) which falls under SDC category D. The design maximum wind load is specified as Wind load 210 KM/hr Impact & limits of drift due to wind on top most floors and lateral forces on structure shall be considered with reference to high rise buildings in various other countries. Design code BNBC for earthquake and wind:

Pile foundation

Basement DesignBy top down method1. High rise superstructure & Sub basement are to be built simultaneously2. The height of sub basement floors shall not be more than 10% of the total height above GFL3. Perimeter foundation walls are constructed using the diaphragm or secant wall method4. Building columns are installed on load bearing element or drilled shafts and brought upto grade level5. Ground floor slab is cast and a hole is left to excavate down to 1st basement floor6. 1st basement floor slab is cast from perimeter wall to all spans through network of load bearing walls and access holes to excavate upto next basement floor7. Then 1st floor slab is cast and subsequently 2nd basement slab is cast.8. Each sub-basement floor once completed act as lateral bracing for the perimeter wall system9. Above grade construction can proceed while the sub-base construction is on going since the buildings structural support is already in place.10. Equipment used for excavation is Casagrande C90/HT55 with high torque

12-GFL

13-1st basement

12-2nd basement

Core11-3rd basement

10-4th basement

9-5th Basement

9-6th Basement

Top down construction1. Formation of permanent retaining walls to the perimeter of basement area2. Form internal foundation and column support by using plunge method3. Create the uppermost floor slab with temporary base4. Excavate downwards tru openings on slab or service shafts

5. Remove temp. base, excavate until the depth of next floor level.6. Cast the next floor level, repeat the process.7. Can use non-suspended slab for the basement slab

Typical sequence of construction1. Install perimeter secant piles 2. Install bearing piles and plunge columns 3. Cast ground floor slab 4. Excavate and cast upper basement floor slab 5. Extend column and cast 1st floor slab 6. Excavate and cast middle basement slab7. Extend columns and cast second floor slab 8. Excavate and cast lower basement slab9. Extend columns and cast upper floor slabs10.

Questions:1. Construction procedure of RAMP in the basement floors2. Can perimeter wall be done on steel sheet piles3. Shall all the piles (30 diax450 nos) for foundation should be done together with perimeter piles4. Basement Columns shall be RCC or Steel or composite5. How the RCC slabs and beams shall be connected with the Basement columns6. How the basement column loads shall be transferred to the Raft foundation at lowest basement7. What will be per square meter cost for 4th, 5th and 6th basement floors and a proportionate comparison in top down method.8. How to remove excavated Earth to disposal area9. How to remove ground water to disposal area10. How to handle ground water percolation.

Typical illustrations

1) Architectural detailsTo study the behavior of high rise building under highseismic forces as here taken Zone IV as per IS 1893 : 2002where building is situated, a typical office building plan isselected with area covering 24 m x 42 m.X30 storey

Design of the building in ETABS version 9.7.1.[2]The basic parameters considered for the designSlab depth : 125 mm thick; Wall thickness : 150 mm thick wall; Lift shaft : 300 mm thick shear wallLive load in office area : 4 kN/sq m; Live load in passage area : 4 kN/sq m; Live load in urinals : 2 kN/sq mFloor finish load : 1.5 kN/ sq m; Stair case loading : 4 kN/sq m; Earthquake parameters considered is Zone : IVSoil type : Hard soilImportance factor : 1Time period : Program CalculatedSeismic zone factor : 0.24 for zone IVEarthquake load in X and Z direction.Rigid frame diaphragmCodes used for analysisR.C.C. design: IS 456: 2000 [5]Steel design: IS 800: 1984 [8]Composite design: AISC LRFD 99 [9]