alternative floor systems of a 20 storied concrete v2.0

ALTERNATIVE FLOOR SYSTEMS OF A 20 STORIED CONCRETE BUILDING

FLOOR SYSTEM 01

• One-way slab, supported by (i) Monolithic concrete beams(ii) Steel beams

• One-way slab with cold-formed steel decking and reinforcement• One-way joist floor (also known as ribbed slab)• Two-way slab supported by edge beams• Flat slabs /plate

(i) With column capitals or drop panels or both, but without beams(ii)without beams and with no drop panels or column capitals

• Two-way joist floors, with or without beams on the column lines

One-way slab (Steel or RC Beams) One-way slab with cold-formed steel decking

One-way Joist floor Two-way slab (With Edge Beam)

FLOOR SYSTEM 02

Flat Slab with Capital & Drop Two-way joist floors

FLOOR SYSTEM 03

RC JOIST

STEEL OPEN WEB JOIST

BENEFITS

• Efficient framing system • Economical and lightweight • Exceptionally high strength-to-weight ratio. • Minimize floor-to-floor heights

Since steel joists are lighter than wooden / RC materials, the size of the supporting structural elements as well as the size of the building's foundation can be reduced for cost efficiency.

COMPOSITE STEEL JOIST

DEFINITION

• Joist top chord and overlying concrete slab will actas an integral unit once the concrete has cured.

• Welded shear studs to ensure adequate transfer of shear

• Simplified erection, faster connections, and minimal crane lifts occur.

COMPOSITE STEEL JOIST

BENEFITS

• A more efficient and stiffer composite design makes it possible to support a given load with a shallower joist

• Weight savings from the joist design reduces building costs

• Simplified erection, faster connections, and minimal crane lifts occur.

COMPARATIVE ANALYSIS

BEAM SUPPORTED AND JOIST SUPPORTED SLAB.

CODE & MATERIALCODE AND STANDARD

• Steel Joist Institute (SJI) 2010• Bangladesh National Building Code - 1993 (BNBC)• American Institute of Steel Construction

MATERIAL PROPERTIES

Concrete : fc’ = 4,000 psi.Reinforcement : fy =72,500 psi.Steel Joist : fy = 50,000psi.

Fire Safety & Floor Vibration have not been considered in Joist supported slab.

FLOOR PLAN – BEAM SUPPORTED

Weight: 1138 kip / floor i.e 267 lb / sft

FLOOR PLAN – JOIST SUPPORTED

Weight: 878 kip / floor i.e 206 lb / sft

MEMBER DIMENSIONS

BEAM Supported slab (A) JOIST Supported slab (B)

Slab: 6inch Slab: 3.5inchBeam: 15x24inch Beam: 12X21 inch & 15x24inchColumn:36x36inch (GF-6th) 30x30inch (7th-12th) 24x24inch (13th-Roof)

Column:33x33inch (GF-6th) 27x27inch (7th-12th) 20x20inch (13th-Roof)

Pile Length: 120ft (Cap: 100T) Pile Length: 105ft (Cap: 90T)- Joist : 14K6 (7.7lb/ft)

LOADSDEAD• Self weight & SDEAD load of 60psf.• Live Load : 60psf• Wind Load : BNBC 93, (210kph, Exposure A)• Seismic : BNBC 93 (Zone: 2, I : 1, R:8)

LOAD COMBINATION

RCC structure : BNBC 93 Joist (LRFD) : 1.4 DL (ASCE 2.3.2-1) 1.2 DL + 1.6 LL (ASCE 2.3.2-2)

OUTPUT 01BEAM Supported slab JOIST Supported slab

3.28 inch 3.14 inch

BEAM Supported slab JOIST Supported slab

28639 kip 23440 kip

TOP DEFLECTION

TOTAL BASE REACTION (Full Dead & Live Load)

BEAM Supported slab JOIST Supported slab

267lb/sft 206lb/sft

WEIGHT / sft (Dead Load Alone)

OUTPUT 02-A

Member Type

(A) RC Beam Supported Slab

(B) Joist Supported Slab % Saving

in BQuantity Unit Amount, TK

Quantity Unit Amount, TK

i) Concrete 483 cum 5859297 412 cum 5000564 14.66ii) Shutter 970 sqm 22219 867 sqm 19859 10.62iii) Rebar 116706 kg 11305321 106553 kg 10321758 8.70

SAVINGS IN COLUMN

OUTPUT 02-B

Member Type


(B) Joist Supported Slab

% Saving in B

Quantity Unit Amount,

TKQuantity Unit Amount,

TK


SAVINGS IN BEAM

OUTPUT 02-C

Member Type



% Saving in B

Quantity Unit Amount,


TK


SAVING IN SLAB

OUTPUT 02-D

Member Type



% Saving in BQuantity Unit Amount,


TK

i) Concrete 1613.39 cum 18679772 1473.02 cum 17054631 8.70ii) Boring 5700.00 rm 6891300 5278.20 rm 6381344 7.40iii) Rebar 145181 kg 14063693 130662.98 kg 12657323 10.00

SAVING IN FOUNDATION

OUTPUT 02-E

Member Type



% Saving in BQuantity Unit Amount,


TK

i) Joist 0.00 Ton 0 77.00 Ton 6970000 (100)ii) Metal Deck 0.00 Ton 0 45.00 Ton 5400000 (100)

ADDITIONAL COST IN RC JOIST

OUTPUT 02 SUMMARY (A-E)

COST SAVING IN CONCRET & REINFORCEMENT

• 9% saving in Joist slab for column / wall.• 9% saving in Joist slab for beam & foundation.• 55-60% saving in Joist supported slab. (Without considering joist cost)• 25% saving in Joist supported slab (Considering joist cost)

Overall 12~13% cost saving in Joist Supported Slab

OUTPUT 03-AJOIST CALCULATION - 01

DESIGN DATA:JOIST ID : 14K6 (7.7lb/ft)Design Code : SJI 2010Design Type : LRFDMaterial criteria : 50ksi

OUTPUT 03-BJOIST CALCULATION - 02

LoadDL-Dead Load : 3.5” slab = 44psf

SDEAD = 60psfLL-Live load : 60 psfFactored Load : 1.2DL+1.6LL = 124.8 + 96 ~ 220.8psfFactored Load / ft of Joist : 220.8*3.62 lb/ft = 800lb/ft + 7.7lb/ft = 807.7lb/ft. Allowable Load : 825 lb/ft >807.7lb/ft

SAFE

OUTPUT 04JOIST ALLOWABLE LOAD TABLE

ESTIMATE 01SOURCE: PWD 2014

ABSTRACT OF COST (CONSIDERING RC BEAM SUPPORTED SLAB)

A. CIVIL WORKS: Tk. 118972404

Tk. 118972404

Add @ 5% contingency Tk. 5948620

Total Tk. 124921024

Say Tk. 124,921,100

Rate / sft 1,470

Floor area: 4250 sft (20 Storied Bldg)


ABSTRACT OF COST (CONSIDERING OPEN WEB JOIST SUPPORTED SLAB)

A. CIVIL WORKS: Tk. 10520996Tk. 105209960

Add @ 5% contingency Tk. 5260498Total Tk. 110470458

Say Tk. 110,470,500.00

Rate / sft 1,300

Floor area: 4250 sft (20 Storied Bldg)


SLAB TYPE Cost /sft

RC BEAM SUPPORTED SLAB Tk1470

STEEL JOIST SUPPORTED SLAB Tk1300

SLAB TYPE Weight / floor

RC BEAM SUPPORTED SLAB 1138 kip (267lb/sft)

STEEL JOIST SUPPORTED SLAB 878 kip (206lb/sft)

CONCLUSION1. Saving in cost has observed in steel joist supported slab

for about 15% in column / wall, 8% in beam & foundation, near about 55-60% in slab.

2. Additional cost shall imply for steel joist, decking sheet etc for Joist supported slab.

It is worth to note that Fire issue and Vibration analysis has not been

considered in Joist supported slab. This consideration might lead to additional cost .

alternative floor systems of a 20 storied concrete v2.0

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