1. INTRODUCTION:

The structure is a “Multi-storied building” consisting of Two Basement Floors + Stilts Floor + Thirteen upper floors.

The 2 basements are used for two-wheeler parking and one stilt floor for four-wheeler parking and all other floors are Residence area.

The Structure is designed as a Reinforced concrete framed structure supported on raft slab placed at approximately 6.5m below existing ground level. Dense Disintegrated Rock is available at this depth. The sidewalls and the raft slab of the basement floor are considered and designed as reinforced concrete members.

2. MATERIALS USED:

Following materials are generally used in the design of the various components of the structure.

1. M40 grade concrete for reinforced concrete Columns of the structure.
2. M30 grade concrete for all other reinforced concrete part of the structure.
3. Fe415 grade reinforcement steel for 8mm, 10mm and 12mm bars.
4. Fe500 grade reinforcement steel for 16mm and above diameter bars.
5. Concrete Solid Block masonry are used for constructions.

3. CODES FOLLOWED:

Following codes and specifications have been used in the design of the members of the structure.

1. IS 456 : 2000 Code of practice for Plain and Reinforced concrete
2. SP: 16 Design Aids for Reinforced concrete
3. IS 875 : 1987 Design Loads for building and structures
4. IS 1893 : 2002 Criteria for Earthquake Resistant design of structures
5. IS 13920: 1993 Ductile Detailing of Reinforced Concrete structures subjected to Seismic Forces.
6. SP: 34 Handbook on Concrete Reinforcement & Detailing

4. DESIGN DATA:

1. No. Of floors =2 Bases + Stilts + 13 Upper floors
2. Height of floors =3.05 + 3.5 + (1 x 3)+ (13 x3)
3. SBC of soil @ 6.5m =500 kN/m² (50T/m²)
4. Water Table =7.7m below G.L.
5. Density of Concrete =25 kN/m³
6. D.L. due to partitions

(Light Partition as per IS 875) =1.50 kN/m²

1. D.L. due to flooring

(0.060 X 24) =1.50 kN/m²

1. D.L. of 200 thk walls i /c plastering

(0.20 X 24 + 2 X .015 X 21) =5.43 kN/m²

1. D.L. of 100 thk walls i /c plastering

(0.100 X 24 + 2 X .015 X 21) =3.03 kN/m²

1. D.L. due to False Ceiling =0.50 kN/m²
2. Live Load in residence area =2.00 kN/m²
3. Live Load in Stairs =3.00 kN/m²
4. Live Load in Parking Area =5.00kN/m²
5. Live Load in Lift Machine Room =5.00kN/m²
6. Basic wind speed =50 m/sec
7. Design wind pressure =1.75 kN/m²

0.6 X (1.0×1.08×1.0×50)²

1. Seismic Zone =III
2. Design mix =M40 for Columns
3. Design mix =M30 for other members

5. ANALYSIS OF STRUCTURE:

The structure is analysed as a Space frame structure in STAAD Pro 2006. Columns, Raft slab, Basement walls, Lift lobby slabs, and Staircases are designed as reinforced concrete members.

6. DESIGN CONCEPT

Limit State concept of design will be used as per IS: 456-2000 & SP – 16. The detailing of reinforcement shall be done satisfying the requirements of IS: 456-2000, SP-16, IS: 13920, IS: 4326-1993 and SP-34.

The Slabs and beams are checked for deflection as per IS 456:2000.

Cover for Reinforcement is considered as per Table 16A of NBC, for a Fire resistance of 2 hrs.

7. LOAD CASES:

7.1. Primary Load:

1. Dead Load (DL)
2. Live Load (LL)
3. Earthquake Load (EL)
4. Wind (WL)

7.2. Load Combinations:

The following combinations of Loads as per IS 1893 is considered in the STAAD Analysis

1. DL + LL
2. 1.5(DL +LL)
3. 1.2(DL + LL ± WL)
4. 1.2(DL +LL ± EL)
5. 1.5(DL ± EL)
6. 0.9DL ± 1.5EL

8. SEISMIC ZONE:

The Proposed Residence at Velachery, Chennai falls in Zone III as per the IS Code. Seismic Coefficient Method for seismic analysis of R.C.C. Frames as recommended by IS: 1893 shall be used.

Seismic Zone =III

Zone Factor ‘Z’ =0.16

Response Reduction Factor ’R’ (for SMRF) =5.00

Importance Factor ‘I’ =1.00

Foundation Factor ‘β’ =1.00

Type of Structure =1.00

9. WIND LOAD:

Assumption considered as per IS 875:1987

Basic Wind Speed ‘V_b’ = 50m/s

Risk Co-efficient ‘k₁’ =1.00

Terrain, Height and

Structure size factor ‘k₂’ =1.08

Topography factor ‘k₃’ =1.00

The Design Wind Speed ‘V_z’ =V_b x k₁ x k₂ x k₃

=54 m/s

Design Wind Pressure ‘p_z’ =0.6 x V_z²

=1749.6N/m²≈1.75kN/m²

10. COVER FOR REINFORCEMENT:

Cover for Reinforcement is considered as per Table 16A of NBC, for a Fire resistance of 2 hrs.

1. Raft Slab = 50mm
2. Raft Beam = 30mm
3. RC Wall = 30mm
4. Columns = 40mm
5. Beams = 30mm
6. Slabs = 25mm

11. RETAINING WALL:

R.C.C. retaining wall of thickness 300 mm is considered as a continuous vertical wall with R.C.C columns at approximately every 9m intervals and intermediate slab supports at each of the basement floor.

The R.C.C wall is designed as a 2 span continuous slab subjected to lateral pressure due to ground water and Surcharge load due to vehicle movement apart from the earth pressure. The Retaining Wall is cast from the Raft Slab to the bottom of the 2nd Basement roof Slab, and then the roof is cast. Similarly the wall is continued for the rest of the floors in the same manner casting the floor slab before proceeding with further rising of the wall. Filling of the sides of the wall will be done after completion of Lower ground floor slab.

In STAAD the Retaining Wall is taken as a Plate element.

Height of wall =6.5m

Density of the Earth =16 kN/m³

Angle of Repose of soil =35°

Surcharge Load =15 kN/m²

Height of Water above raft bottom =6m

Height of the Earth =6m

12. FOUNDATION SYSTEM;

The topsoil as observed in the Geo Technical report up to a depth of 4 m is expansive type of clay except in borehole 1. This soil cannot be used for back filling also. Except in bore hole 1, at all other 6 boreholes dense Disintegrated rock is available at the Raft level. Only in Borehole 1 location Hard rock is available at a depth of 5.5m below ground level.Safe Bearing Capacity of Disintegrated Rock is taken as 50 T/Sq.m at (-) 6.5m depth from ground level as per the Geo Technical Report. It is proposed to have Independent footings to resist floor loads along with raft to resist uplift pressure due to ground water of height 6m. But due to insufficient interval between columns, raft with 1m depth is recommended.Waterproofing of 80mm thk. and leveling coarse of PCC 1:3:6 of 100mm thick below the raft shall be also provided.

The support condition for columns in STAAD model is considered as fixed support. The independent footings are designed, for the axial loads and moments due to floor loads considering the effect of raft slab partly. The raft slab is designed for an uplift pressure due to ground water as a flat slab with inverted drop panels at column locations.

13. PARKING AREA FLOOR SLABS:

The floor slabs are designed as a conventional slab with beams for floor loads as mentioned above.

The load considered on the floor slab is 12.56 kN/m².

Self Weight of slab(0.18×25) = 4.5kN/m²

Load due to Floor Finish (65mm thk.) = 1.56 kN/m ²

Load due to partition = 1.5 kN/m ²

Live load = 5.00 kN/m²

Total load taken =12.56 kN/m²

14. CONSTRUCTION JOINTS:

Construction Joints to be decided as per the contractors requirements. However it is suggested to provide the Construction Joints at l/3 distance from the column support.

15. PREPARATION OF DRAWINGS:

AUTOCAD 2000 will be utilized to prepare structural working drawings.

16. CEMENT:

It is advisable to use 43 grade cement for all R.C.C structural works for durability reasons.

17. RENTFORCEMENT STEEL:

Reinforcement steel of grade Fe 415 for 8mm, 10mm & 12mm and &

Fe 500 for 16mm & above can be of TMT bars manufactured by Tata steel (TISCO), Vizag steel (RINL), SISCOL, SUJANA or SAIL purchased directly from the manufacturer.

_____________________________________________________________