ANSI/SDI-C1.0 Standard for Composite Floor Steel Deck 3

Deck and Concrete as a Composite Slab:

1. General: The “SDI Method” (refer to SDI Composite Deck Design Handbook) shall be

limited to galvanized or topside uncoated steel decks with embossments. The embossment patterns shall be typical of the manufactured steel deck with the depth of the embossment not less than 90% of the tested embossment depth. (Refer to Attachment C4 for further limitations).

The composite slab shall be designed as a reinforced concrete slab with the steel deck acting as the positive reinforcement. The deck must be suitable to develop composite interaction. Justification of this requires full scale testing as per ASTM E2322, or calculations based upon testing.

a. Allowable Strength Design  (ASD) shall be permitted as an alternate design method. (See SDI Composite Deck Design Handbook.)

b. Standard reinforced concrete design procedures shall be used to determine ultimate load capacity. The allowable superimposed load shall then be determined by deducting the weight of the slab and the deck. Attachment C4, Strength and Serviceability Determination of Composite Deck Slab shall be used for strength determination.

Commentary:

 High concentrated loads, diaphragm loads, etc. require additional analysis. Horizontal load capacities can be determined by referring to the SDI Diaphragm Design Manual. Concentrated loads can be analyzed by the methods shown in the SDI Composite Deck Design Handbook. Most published live load tables are based on simple span analysis of the composite system; that is, the slab is assumed to crack over each support.

2. Load Determination: Using standard reinforced concrete design procedures, the allowable superimposed load shall be found by using appropriate load and resistance design factors (LRFD) and applicable reduction factors based on the presence, absence, or spacing of shear studs on beams perpendicular to the deck. (Refer to Attachment C4 and C5)

Commentary: 

By using the reference analysis techniques or test results, the deck manufacturer determines the live loads that can be applied to the composite deck slab combination. The results are usually published as uniform load tables. For most applications, the deck thickness and profile is selected so that shoring is not  required; the live load capacity of the composite system is usually more than adequate for the superimposed live loads. In calculating the section properties of the deck, the AISI provisions may require that compression zones in the deck be reduced to an “effective width,” but as tensile reinforcement, the total area of the cross section may be used. Coatings other than those tested may be investigated, and if there is evidence that their performance is better than that of the tested product, additional testing may not be required.

3. Concrete: Concrete design shall be in accordance with the ACI Building Code Requirements for Reinforced Concrete. Minimum compressive strength (f’c) shall be a minimum of 3 ksi (20 MPa) or as required for fire ratings or durability. Admixtures containing chloride salts shall not be used. Commentary: Load tables are generally calculated by using a concrete strength of 3 ksi (20 MPa). Composite slab capacities are not greatly affected by variations in concrete compressive strength; but, if the strength falls below 3 ksi (20 MPa) it would be advisable to check shear stud strengths. Fire rating requirements may dictate the minimum concrete strength. The use of admixtures containing chloride salts is not allowed because the salts will corrode the steel deck.

a. Minimum Cover: The minimum concrete thickness above the top of the steel deck shall be 2 inches (50 mm). When additional (negative bending) reinforcement is placed in the slab, the minimum cover of concrete above the reinforcing shall be in accordance with the ACI Building Code Requirements for Reinforced Concrete.

4. Deflection: Deflection of the composite slab shall not exceed 1/360 of the clear span under the superimposed live load. Commentary: Live load deflections are seldom a design factor. The deflection of the slab/deck combination can be predicted by using the average of the cracked and uncracked moments of inertia as determined by the transformed section method of nalysis. Refer to Attachment C5 of this specification or the SDI Composite Deck Design Handbook.

5. Suspended Loads: All suspended loads must be included in the analysis and calculations for strength and deflection.

Commentary: 

The designer must take into account the sequence of loading. Suspended loads may include ceilings, light fixtures, ducts or other utilities. The designer must be informed of any loads applied after the composite slab has been installed. Care should be used during the placement of loads on all types of hanger tabs or other hanging devices for the support of ceilings so that an approximate uniform loading is maintained. The individual manufacturer should be consulted for allowable loading on single hanger tabs. Improper use of hanger tabs or other hanging devices could result in the overstressing of tabs and/or the overloading of the composite deck slab.

6. Reinforcement:

a. Temperature and shrinkage reinforcement, consisting of welded wire fabric or reinforcing bars, shall have a minimum area of 0.00075 times the area of the concrete above the deck (per foot or meter of width), but shall not be less than the area provided by 6x6-W1.4 x W1.4 welded wire fabric. Fibers shall be permitted as a suitable alternative to the welded wire fabric specified for temperature and shrinkage reinforcement. Cold-drawn steel fibers meeting the criteria of ASTM A820, at a minimum addition rate of 25 lb/cu yd (14.8 kg/cu meter), or macro synthetic fibers “Coarse fibers” (per ASTM Subcommittee CO9.42), made from virgin polyolefin, shall have an equivalent diameter between 0.4 mm (0.016 in.) and 1.25 mm (0.05 in.), having a minimum aspect ratio (length/equivalent diameter) of 50, at a minimum

addition rate of 4 lb./cu yd (2.4 kg/m3) are suitable to be used as minimum temperature and shrinkage reinforcement.

Commentary: 

Neither welded wire fabric or fibers will prevent cracking; however, they have been shown to do a good job of crack control. The welded wire fabric must be placed near the top of the slab [3/4 to 1 inch cover (20 to 25 mm)] at supports and draped toward the center of the deck span. If a welded wire fabric is used with a steel area given by the above formula, it will not be sufficient as the total negative reinforcement. If the minimum quantity of steel fibers, or macro synthetic fibers, are used for shrinkage and temperature reinforcement, they will not be sufficient as a total negative reinforcement.

b. Negative: When negative moment exists, the deck shall be designed to act only as a permanent form.

Commentary: Composite steel deck does not function as compression reinforcing steel in areas of negative moment. If the designer wants a continuous slab, then negative bending reinforcing should be designed using conventional reinforced concrete design techniques in compliance with the ACI Building Code Requirements for Reinforced Concrete. The welded wire fabric, chosen for temperature reinforcing, may not supply enough area for continuity. The deck is not considered to be compression reinforcement. Typically negative reinforcement is required at all cantilevered slabs, or if a continuous slab is desired.

c. Distribution: When localized loads exceed the published uniform composite deck load tables, the designer shall proportion distribution reinforcement using conventional concrete design methods.

Commentary: 

Distribution steel may be required in addition to the welded wire fabric or steel fibers. Concentrated loads, either during construction or in-service, are the most common example of this requirement. Concentrated loads may be analyzed by the methods in the latest SDI Composite Deck Design Handbook.

7. Cantilever Loads: When cantilevered slabs are encountered, the deck acts only as a permanent form; top reinforcing steel shall be proportioned by the designer. For construction loads, the deck shall be designed for the more severe of (a) deck plus slab weight plus 20 psf (1 kPa) construction load on both cantilever and adjacent span, or (b) deck plus slab weight on both cantilever and adjacent span plus a 150 pound (665N) concentrated load per foot of width at end of cantilever. The load factors for bending, shear, and interior bearing shall be as required by ASCE 7. Resistance factors for bending, shear, and

interior bearing shall be in accordance with the North American Specification for the Design of Cold Formed Structural Members. The maximum cantilever deflection as a form, under deck plus slab weight, shall be a/90 where “a” is the cantilever length, and shall not exceed 3/4 inches (19 mm). Side laps shall be attached at the end of the cantilever and a maximum spacing of 12 inches (300 mm) o.c. from the cantilever end. Each corrugation shall be fastened at both the perimeter support and the first interior support. The deck shall be completely attached to the supports and at the side laps before any load is applied to the cantilever. Concrete shall not be placed on the cantilever until after placement on the adjacent span.

8. Diaphragm Shear Capacity: Diaphragms with concrete shall be designed in accordance with

the SDI Diaphragm Design Manual, or from tests conducted by an independent professional

engineer.

Commentary: 

Calculations of diaphragm strength and stiffness should be made using the SDI

Diaphragm Design Manual. If testing is used as the means for determining the diaphragm

strength and stiffness, then it should follow the AISI TS 7-02 test protocol.