# Composite Steel Beam Design

Composite steel beam design is based on steel design, sharing many features, assumptions, parameters, and limits, but is specific to beams with a slab on top.

## Creating Composite Beam Groups

Composite Beam design requires member elements to be in a steel design group. Once the steel design group is created, the option to design as composite beam is an available design group parameter in the

tab. Because of the way composite shape properties are calculated, you should only group together members that have the same model-shape and length.## Composite Beam Topics:

- Composite Beam Construction Self-Weight Loads
- Composite Beam Deflection Assumptions
- Composite_Beam_Bracing
- Composite Beam Parameters
- Composite Slab Parameters
- Composite Deck Parameters
- Composite Beam Report
- Composite Beam Check Reports

## Composite Beam Construction Self-Weight Loads

In the design of unshored composite beams, there are typically two situations that must be considered. The first is the strength of the steel beam alone, acting under construction loads that include the wet concrete slab weight. The second is the full composite beam acting under design loads typical of all steel members.

Of course, if you choose a shored construction procedure, then construction loads do not apply and no steel-only check is performed.

VisualAnalysis will automatically estimate self-weight
construction loads for **unshored** construction. It uses only the
self-weight of the steel and concrete slab as a simple steel-only check.
Currently there is no way to specify specific construction loads or load cases
for additional steel-only checks. If you have high construction loads, you will
need to check the beam manually for these conditions.

## Composite Beam Deflections

When designing composite beams there are typically two distinct deflections that are of concern. The first is construction deflection of the steel beam alone, and the second is the deflection of the composite section after construction under service loads.

*VisualAnalysis *makes no provision for limiting or calculating
deflections of the first kind. It is assumed that the deflection values can be
readily obtained using construction loads for analysis. Furthermore, the beam is
generally cambered to handle this deflection. As with stress calculations,
construction deflections play no part if the beam is constructed using a shored
procedure.

*VisualAnalysis *does allow you to limit the service load deflections of
the fully composite beam. It also estimates these deflections by scaling the
reported deflections by the ratio of the steel moment of inertia to the
composite moment of inertia. This check is performed for all serviceability load
cases.

## Composite Beam Bracing

Bracing for composite beams is assumed to be continuous for the top flange (metal deck or formwork) and the full member length for the bottom flange. Bracing differing from these defaults cannot be specified. If you want a different bottom bracing, you could split the member in the Model View to effectively create shorter elements. See Bracing in VisualAnalysis for a complete description of bracing member elements for design checks.

## Composite Beam Parameters

### Composite Design Shapes

For composite beam design a reduced shape list is available. For AISC shapes this list is: W, M, S, HP, C, MC, and TS or HSS (square and rectangular). If you are using other database shapes or parametric shapes you will be restricted to those that use the same basic 'property sets' as the AISC shapes listed here.

Composite shapes are generally modeled for analysis using just the steel section. You may
choose to model the slab with plate elements in your model, but these elements
are not affected by, nor do they directly affect the design software, which will
look only at the member element and its forces. There is no built-in way to
model composite beams directly in *VisualAnalysis* by defining slab
properties along with the steel members.

**Specification:** You can choose between ASD and LRFD provisions.

See Steel Design other input design parameters.

## Composite Beam Slab Parameters

Some of the following parameters have default values that you may define in preferences to speed up your design work. These are 'per machine' default settings that only apply to new design groups you create.

**Concrete**

**Shored:** This option allows you to specify whether shored or
unshored construction will be used. With unshored the construction load cases
are enabled so that *VisualAnalysis* can correctly include the effect of
construction loads on the beam (see see construction load section above). With shored
construction, no construction loads are necessary as the member is fully
supported until it can act as a composite unit.

**Strength f'c:** Specify the concrete strength, f'c.

**Thickness:** Specify the slab thickness.

**Weight:** Choose the proper concrete weight to be used for the slab.

**Beam Spacing:** Enter the centerline to centerline distance between
adjacent beams.

**Is Spandrel:** If yes, you are required to enter the overhang. Enter the
distance from the centerline of the beam to the edge of the slab for the
overhang distance.

**Effective Width:** The effective width of a slab is determined using the beam spacing, slab thickness, distance to a slab edge, and
the span length. The effective width the design software calculated and
used in the design checks is listed in the design report under "Slab and Deck
Parameters".

## Composite Beam Deck and Studs

### Metal Deck

**Deck Type:** There are three choices for slab construction: no
metal deck (solid slab), perpendicular metal deck and parallel metal deck. These
are shown in the following sketches.

**Rib Height/Rib Width:** Deck dimensions for rib height and width
must conform to the limits prescribed in AISC. These limits are automatically
checked in the inspector. Refer to the diagram above when specifying the rib
height and width.

The size and orientation of the deck will determine the effective thickness of the concrete slab, and may also reduce the effectiveness of shear studs. AISC has placed certain restrictions on deck dimensions and the inspector will prevent entry of numbers that are out of the allowable range.

### Shear Studs

**Stud Type:** Shear studs may be headed studs or channels.

**Stud Length:** If you choose a headed stud, the length is
interpreted as the height of the stud. For channel studs, the length field is
interpreted as the horizontal width. There is a minimum of 0.5" cover
recommended. If you have selected a metal deck, then the stud must also
extend 1.5" above the deck.

**Nr:** The N_{r} parameter is only used for perpendicular
metal decks and represents the number of studs per rib. The number must be
between one and three (more studs may be placed in the rib, but only three are
allowed for calculation purposes). Placing more studs in a rib may reduce the
effective capacity of each stud. All of the appropriate stud capacity reductions
are used to calculate the member strength.

## Composite Beam Report

In the parameters section of the composite beam report there is more information included than simply what was entered in the parameters dialog. Specifically there is a section about stud capacities and another with composite beam properties. Both of these involve additional calculations using the parameters you defined. These sections contain more information if the design group has a valid design shape.

In reporting shear stud requirements, the report contains minimum and maximum stud spacing requirements and the number of studs required between points of maximum and zero moment areas. VisualAnalysis does not produce a detailed stud arrangement schedule, but rather provides enough information for you to layout the studs.

If partial composite action is permitted, information
will be shown regarding stud requirements for the minimum partial composite
action that provides the required moment capacity.* VisualAnalysis*
does not perform calculations for any level composite action between the full
and minimum values reported.

## Composite Beam Check Reports

**The checks for composite beams are fewer than for general steel design. Axial
forces, weak axis shear and bending, and weak axis deflection checks are not
made.** Forces, stresses, or deflections from these are simply ignored in the
software.

There are two types of strong bending checks performed for unshored construction: a Steel Flexure Check (Construction) and a Composite Flexure Check. The first is identical to the strong flexure check appearing in steel reports. The composite check uses a plastic distribution of composite forces. With shored construction only the composite check is performed and construction stresses are assumed negligible. The composite check unity value is equal to the moment demand divided by the fully composite moment capacity. Partial composite action is not reflected in the unity check.

Composite deflections are approximated using the non-composite deflection
reported from *VisualAnalysis*, and scaling them based on the composite
moment of inertia for the beam. The scaled deflections are then checked against
your specified deflection limits. There is no provision in the software to
specify a pre-camber or to ignore deflections from certain loads, other than how
you choose your serviceability load cases.