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38 V1.0 • Composite and Non-Composite Design Guide

1.12 Composite Deck-Slab Tables

General

The composite deck-slab load tables are intended to provide

a designer with easy to use design aids for common compos-

ite deck-slab conditions. The tables provide uniform load in

both allowable and factored superimposed loads. Factored

diaphragm shears are provided for composite deck-slab sys-

tems for lateral design. Diaphragms may be attached with

a variety of attachments to supports including traditional arc

spot welds, power actuated fasteners (PAF), and self-drilling

screws. Factored shear tables for diaphragms with steel

reinforcing and headed shear stud anchors are provided for

high shear diaphragms. All of these tables are supported with

complete composite deck-slab properties including bending

moment, vertical shear, and section properties to aid in the

design of conditions exceeding the scope of the tables.

Superimposed Uniform Load Tables

Uniform superimposed load is the load which the composite

deck-slab can carry in addition to its self-weight. Both allow-

able and factored superimposed loads are provided. The

superimposed load tables assume that the minimum tempera-

ture and shrinkage reinforcement is not adequate to develop

negative bending resistance at supports, therefore all spans

are treated as simple spans.

Most floor systems are designed using allowable stress design

(ASD). The allowable superimposed load tables present the

maximum uniform load based on the allowable bending

strength, allowable vertical shear, and a deflection limit of

L/360. ASD assumes that the superimposed load is primarily

live load and is conservative for dead loads.

Load and Resistance Factor Design (LRFD) is recommended

for conditions in which the majority of the superimposed load

is dead load, and the maximum superimposed load is the

limiting design criteria. The factored superimposed loads in

the tables do not include a deflection check. The designer will

have to check the service load deflection to ensure that the

deflection meets the projects deflection serviceability require-

ments when using an LRFD approach.

Composite Deck-Slab Properties

For conditions exceeding the scope of the uniform load tables,

composite deck-slab properties are provided in the tables.

The properties can be utilized as part of the solution for con-

centrated loads, deflection limits, or spans not included in the

superimposed load tables. The properties include both allow-

able and factored moments, and vertical shear for determining

the capacity of the composite deck-slab system. Cracked,

uncracked, and the average of cracked and uncracked

moment of inertia are provided to assist in determining the

deflection of the deck-slab system.

Factored Diaphragm Shear

The IAPMO ER-329 report presents composite steel deck-

slab diaphragm shears using a load and resistance factor

basis. The diaphragm shears presented are factored shears.

Composite steel deck-slab systems have traditionally been

designed using allowable stress design (ASD), in part because

manufactures have presented allowable shears. These shears

were based on research and engineering studies dating back

to before LRFD was commonly used for steel design. The

factored shears presented in the IAPMO ER-329 report work

seamlessly with the design of the lateral force resting system

for steel and concrete buildings designed using the LRFD

approach. The designer does not have to convert the lateral

forces to ASD when selecting a factored diaphragm from the

shear tables.

Factored shears are provided for a variety of fastener types

to supports. This range of fasteners reflects a full range of

building types that composite deck-slab systems are used in.

Wide Flange Multi-Story Steel Construction: Arc spot

welds are the traditional method for attaching composite

deck to structural steel support members. This method

provides good shear performance and is applicable to

a wide variety of support steel, from heavy wide flange

beams to light weight open web steel joists. Welded steel

headed stud anchors are commonly used for composite

beam design. They are also a good choice to transfer large

diaphragm forces into the composite deck-slab system.

This system is ideal for high shear diaphragms on wide

flange beams and requires the use of welded wire fabric or

reinforcing bars in the slab.

Open Web Steel Joist Mezzanine and Floor Systems:

Composite steel deck-slab systems can be attached with

arc spot welds, however, power actuated fasteners (PAF)

are an ideal cost effective method of attachment to light

structural angles used for open web steel joist framing.

PAF selection is dependent on the support steel thickness.

(See figure 1.13.12)

Cold-Formed Steel Mezzanine and Floor Systems:

Self-drilling screws are the best choice for attaching com-

posite steel deck to cold-formed steel framing. Common

examples of this application include: cold-formed steel

framed multi-story mini-storage buildings, mezzanines,

and conventional cold-formed steel stud, and joist framed

buildings.

Composite Deck-Slab with Cellular Deck

Cellular composite deck panels can be conservatively

designed using the non-cellular deck-slab tables. The super-

imposed loads, vertical shear, and moment of inertia can be

conservatively used for the design, based on the gage of the

beam section of the cellular profile. This ignores the contribu-

tion of the steel used for the bottom pan of the cellular deck.

Maximum unshored spans for cellular deck-slab system are

listed with the cellular deck section properties.

Allowable Stress Design

Historically, most composite steel deck-slab systems dia-

phragm shear tables have been presented using an allowable

stress design basis. To compare composite steel deck-slabs

designed using ASD basis, it is recommended that the ASD

shear demand be converted back to an LRFD basis. This can

be accomplished by dividing the required allowable shear by

0.7 ASD seismic factor, for seismic controlled designs, or 0.6

ASD wind factor for wind controlled designs.