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Composite Steel Beam |
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Composite Steel Beam |
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This module provides analysis and design of AISC steel sections acting compositely with a concrete slab that is continuously connected to the compression flange of the beam with suitable shear connectors.
Factors provided for in the module include:
| • | The concrete slab can be either full depth or cast over formed steel decking, with rib orientation perpendicular or parallel to the beam. |
| • | Stud capacity can be calculated by the module using standard AISC procedure. |
| • | Normal or lightweight concrete may be used for both strength and deflection calculations. |
| • | Both shored and unshored construction techniques can be analyzed by the module. |
| • | ASD or LRFD analysis methods can be chosen. |
| • | Flexible specification of shear studs is available. |
| • | Very flexible loading specification, including the ability to specify loads applied before curing, loads removed after curing, and loads applied after curing. |
| • | Single and multiple span composite beams can be designed. |
| • | Extensive load combination capability. |
The module can use any section from the internal AISC databases, and provides automatic member selection incorporating user-specified criteria.
General Data Tab
This tab gathers all input except for the beam section size and loads.
To the left you can select AISC 360-05 ASD or LRFD methods. Note that these methods are somewhat different from prior AISC codes, and the user should be familiar with them, of course.
To the right is the complete ability to specify the slab, its effective width, stud information and optional metal deck specification.
For Qn you can enter the value directly or click the 
button to display the stud capacity calculation dialog:
When you click the checkbox for Slab on Metal Deck, the associated input fields appear to allow the selection of a manufactured deck product, or the manual specification of the required deck properties.
Click the 
button to display the metal deck selection window as shown below, or simply enter the deck cross section profile in the dimension input fields:
Partial Composite Action
This area provides three ways to have the module calculate stud requirements.
Full Composite tells the module to use the number of studs necessary to provide full Vh shear resistance for the slab to beam
Specify % Composite allows you to enter a % of maximum composite action. The module will then determine the number of studs needed for that Vh' and complete the bending capacity calculations.
Calc Min Studs tells the module to calculate the minimum number of studs (greater than 25% composite per code) that will adequately supply the allowable moment for the actual moment.
Beam Span Data Tab
This is basically the same tab used for a normal steel beam except that there is no ability to specify unbraced compression flange lengths. For regions of positive moment, the top flange is considered to be continuously braced by its composite connection to the concrete slab. For regions of negative moment, the bottom flange is also considered to be continuously braced.
Span Loads Tab
This tab is basically the same as the normal load entry for other beam design modules except for two differences:
1- There are two checkboxes that allow you to select whether you want the module to automatically calculate and apply the beam self weight and slab self weight.
2- There are three additional checkboxes that allow you to indicate when the specified load is applied. 75% curing has historically been considered the point at which the concrete slab has cured enough to work compositely with the steel beam.
Load Combinations Tab
No differences from other materials.
Results Tabs: This set of tabs provides detailed results for the current calculation. The vertical tabs on the left edge of the screen allow you to select the three major areas available for review: Calculations, Sketch, and Diagram.
The Calculations tab offers the following results options:
Summary Results tab presents the maximum/governing values from all of the results presented on the Max. Combinations tab. The module looks for the maximum bending stress ratio and presents the components that are calculated to create that ratio.
For the bending stress item the module reports the Construction bending ratio which considers all loads specified to be applied to the beam before curing. The resulting moment is compared to the capacity of the steel section acting alone (non-compositely).
For the item reported as After Curing, the module takes the moments calculated before curing and subtracts moments due to loads removed after curing and then adds in the moments created from loads applied only after curing. That moment is then compared to the full composite section moment capacity for the percentage of shear connection you have specified.
Given in the results is the load combination that creates the governing values along with the span location and span id.
For maximum deflection, the module calculates a deflection of the non-composite steel section resisting all of the loads applied before curing , then deducts the deflection due to the loads that are removed after curing, and then superimposes the deflection based on a composite section resisting the loads applied after curing.
Note! The screen shown below which gives information for Construction loads is only for unshored beams. For shored beams the Construction portion of moments is not applicable, so it is not shown.
Max Combinations tab presents in more concise detail the bending and shear values for all load combinations. Here is the summary of unshored result values:
Ma-Const is the moment due to loads applied before curing.
Mn-Stl/Omega is the allowable moment on steel section alone according to ASD design.
Ma-NonConst includes the moments generated by loads applied before and after curing less the loads removed after curing.
Mn-Tr/Omega is the allowable moment for the composite steel/slab section for the percentage of shear connection you specify calculated according to ASD.
When LRFD is used, the allowable nomenclature will change to the Mn value times Phi (instead of divided by Omega).
Here is the screen for shored cases:
Studs tab presents the shear connector density for certain span sections. When point loads are present, this chart may list more detailed spacing requirements because of the shear change between applied point loads.
M-V-D Summary presents moment, shear, and deflection results. Four screen captures of this tab are shown below. Depending upon the ASD or LRFD selection and whether the beam is shored or unshored, these lists will present different values and headings.
ASD/Service Stress Combinations - SHORED:
ASD/Service Stress Combinations - UNSHORED:
LRFD/Strength Stress Combinations - SHORED:
LRFD/Strength Stress Combinations - UNSHORED:
Service Deflections - SHORED:
Service Deflections - UNSHORED:
Reactions tab has two versions, one for shored and one for unshored construction. The only differences are the load combinations and the explanations of load applications listed.
"Dbc" stands for Dead load applied before curing. "Dac" stands for Dead load applied after curing. "Dra" stands for Dead load removed after curing.
Properties tab shows the calculations for transformed section properties calculated in increments of 1% shear connection, from 100% down to the code minimum 25%. "I Lower Bound" and "I Constant Stiffness" are terms described in AISC 360-05.
The Sketch tab provides two ways to view a graphic representation of the beam currently being designed:
Span & Loads tab:
Cross Section tab:
The Diagram tab offers the ability to view shear, moment, and deflection diagrams for selected load combinations:
