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 floorTwo-way slab (With Edge Beam)FLOOR SYSTEM 02

Flat Slab with Capital & DropTwo-way joist floorsFLOOR SYSTEM 03

RC JOIST

OPEN WEB JOIST-01BENEFITS Reduced construction time (save on rent and move in sooner). Floor is easily accessible to accommodate wiring plumbing / AC Service. All services such as plumbing and electrical are easily accessible after construction enabling alternations to be carried out.

OPEN WEB JOIST-02BENEFITS Efficient framing system Economical and lightweight Exceptionally high strength-to-weight ratio. Minimize floor-to-floor heightsSince 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.

STEEL OPEN WEB JOIST - 01COMPONENTS

STEEL OPEN WEB JOIST - 02COMPONENTS

COMPOSITE STEEL JOIST - 01DEFINITION

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 -02BENEFITS

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 ANALYSISBEAM 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 PROPERTIESConcrete: 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 SUPPORTEDWeight: 1138 kip / floor i.e 267 lb / sft

FLOOR PLAN JOIST SUPPORTEDWeight: 878 kip / floor i.e 206 lb / sft

MEMBER DIMENSIONS

BEAM Supported slab (A)JOIST Supported slab (B)Slab: 6inchSlab: 3.5inchBeam: 15x24inchBeam: 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 COMBINATIONRCC structure: BNBC 93 Joist (LRFD): 1.4 DL (ASCE 2.3.2-1) 1.2 DL + 1.6 LL (ASCE 2.3.2-2)

CONCRETE & JOIST JOINT

OUTPUT 01

TOP DEFLECTIONTOTAL BASE REACTION (Full Dead & Live Load)WEIGHT / sft (Dead Load Alone)

BEAM Supported slabJOIST Supported slab3.28 inch3.14 inch

BEAM Supported slabJOIST Supported slab28639 kip23440 kip

BEAM Supported slabJOIST Supported slab267lb/sft206lb/sft

OUTPUT 02-ASAVINGS IN COLUMN

Member Type(A) RC Beam Supported Slab(B) Joist Supported Slab% Saving in BQuantity UnitAmount, TKQuantity UnitAmount, TKi) Concrete483cum5859297412cum500056414.66ii) Shutter970sqm22219867sqm1985910.62iii) Rebar116706kg11305321106553kg103217588.70

OUTPUT 02-BSAVINGS IN BEAM

Member Type(A) RC Beam Supported Slab(B) Joist Supported Slab% Saving in B

Quantity UnitAmount, TKQuantity UnitAmount, TKi) Concrete441cum5307032403cum48466168.68ii) Shutter484sqm12065426sqm1061812.00iii) Rebar132194kg12805600120693kg116915138.70

OUTPUT 02-CSAVING IN SLAB

Member Type(A) RC Beam Supported Slab(B) Joist Supported Slab% Saving in B

Quantity UnitAmount, TKQuantity UnitAmount, TKi) Concrete1370cum16850049584cum718179157.38ii) Shutter1266sqm308020sqm0100.00iii) Rebar161403kg1563506164924kg628918259.78

OUTPUT 02-DSAVING IN FOUNDATION

Member Type(A) RC Beam Supported Slab(B) Joist Supported Slab% Saving in B

Quantity UnitAmount, TKQuantity UnitAmount, TKi) Concrete1613.39cum186797721473.02cum170546318.70ii) Boring5700.00rm68913005278.20rm63813447.40iii) Rebar145181kg14063693130662.98kg1265732310.00

OUTPUT 02-EADDITIONAL COST IN RC JOIST

Member Type(A) RC Beam Supported Slab(B) Joist Supported Slab% Saving in B

Quantity UnitAmount, TKQuantity UnitAmount, TKi) Joist0.00Ton077.00Ton6970000(100)ii) Metal Deck0.00Ton045.00Ton5400000(100)

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-A

JOIST CALCULATION - 01DESIGN DATA:JOIST ID:14K6 (7.7lb/ft)Design Code:SJI 2010Design Type:LRFDMaterial criteria:50ksi

OUTPUT 03-B

JOIST CALCULATION - 02LoadDL-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 04

JOIST ALLOWABLE LOAD TABLE

ESTIMATE 01

SOURCE: PWD 2014Floor area: 4250 sft (20 Storied Bldg)

ABSTRACT OF COST (CONSIDERING RC BEAM SUPPORTED SLAB)A. CIVIL WORKS:Tk.118972404Tk.118972404Add @ 5% contingency Tk.5948620Total Tk.124921024Say Tk. 124,921,100Rate / sft 1,470

ESTIMATE 02

SOURCE: PWD 2014Floor area: 4250 sft (20 Storied Bldg)

ABSTRACT OF COST (CONSIDERING OPEN WEB JOIST SUPPORTED SLAB)A. CIVIL WORKS:Tk.10520996Tk.105209960Add @ 5% contingency Tk.5260498Total Tk.110470458Say Tk. 110,470,500.00 Rate / sft 1,300

ESTIMATE 03

SOURCE: PWD 2014

SLAB TYPECost /sftRC BEAM SUPPORTED SLABTk1470STEEL JOIST SUPPORTED SLABTk1300

SLAB TYPEWeight / floor RC BEAM SUPPORTED SLAB1138 kip (267lb/sft)STEEL JOIST SUPPORTED SLAB878 kip (206lb/sft)

CONCLUSION

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.

*