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Concrete Beam

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In this section, for each input tab we will review only the items that are unique to the CONCRETE material type.

 

General

The concrete beam module handles single- and multiple-span beams using ONE cross section shape. That shape can have up to six groups of reinforcing per span, and the reinforcing can vary on a span-by-span basis.

 

This tab collects all the required rebar, concrete strength and elastic modulus entries, shear stirrup data, strength reduction factors and deflection criteria to check.

 

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NOTE: It is important to know how this module operates with regard to beam stiffness along the span, and how this affects multi-span beams. This module divides each span into a series of segments. The effective moment of inertia for each segment (for each load combination) is calculated using the actual unfactored moment on that segment. Thus the module creates a very accurate variable stiffness model of the beam based on actual moments.  For multiple-span beams, this will affect the relative stiffness of each beam span. Thus the moment distribution across multiple spans will be properly performed. This will affect factored load moments and shears and service load level deflections and reactions.

 

Beam Span Data

This tab has some pieces of input that are constant for all spans and some that can vary on a span-by-span basis.

 

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The cross section shape and dimensions are the same for all spans.

 

When you click on a span (for multi-span beams), the span length and rebar layout will update to display the arrangement that is specific to that span.

 

On the bottom of this tab you can specify up to 6 bar sets (quantity, size, vertical location and start/stop endpoints). Each bar set is referenced on the sketch with a color shown as a dot to the left of the set description.

 

The column titled "Dist of bar center....from...." is how you set the vertical position of the bar sets in the beam. When you look at the top one, you can read it as "The top bar set is 3 inches from the bottom of the beam". Note that the module will know whether the bars are in tension or compression and will handle the calculations properly.

 

The item labeled Bar Position This Span defines the starting and ending location of the bar ends with respect to the left end of each respective span. The data in the screen capture below shows that bar set #1 and #2 run from the left end (0.0 ft) to 24.0 ft from the left end of Span 1.  Using these starting and ending locations you can fine tune the bar layout and end cutoffs.

 

Note: The module will report an error message if any beam segments are found to be completely unreinforced.  Therefore, it is imperative that the rebar be defined in such a way as to prevent completely unreinforced segments.  This includes the short segments at the extreme ends of a beam, where rebar is typically terminated.  Remember that this module is an analysis tool, not a detailing tool, so don't be tempted to define rebar as starting or ending short of the physical end of the beam. The button labeled "FL" adjacent to each rebar definition has been provided as a convenient way to indicate to the program that the selected rebar runs the Full Length of the span.

 

Important:  Bars are assumed to be fully-effective at the locations where they are defined.  This can be seen from the capacity diagram.  So in situations where development must be considered, the user must understand this behavior and should define bar locations accordingly.

 

Span Loads

No differences from other materials.

 

All Span Loads

No differences from other materials.

 

Load Combinations

No differences from other materials.

 

Results Tabs

This set of tabs provides detailed results for the current calculation. The tabs in the upper right-hand corner of the screen allow you to select the four major areas available for review: Calculations, 2D Sketch, Diagram and 3D Rendering.

 

The Calculations tab offers the following results options:

 

Summary Results provides details for shear, moment and deflection for the governing load combinations. Shear results are not shown here...they are summarized on a separate tab that gives the required stirrup layout.

 

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Max. Combinations provides detailed results for each beam segment for each load combination.

 

These results are a consolidation to the highly detailed incremental results on the M-V-D Summary tab.

 

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M-V-D Summary - LRFD Shears & Moments shows highly detailed moment and shear results for each beam and for each load combination. For multi-span beams using Automatic Unbalanced Live Load Placement there may be thousands of lines of results.

 

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M-V-D Summary - Deflections shows highly detailed deflection results for all load combinations. When each load combination is expanded by clicking the [+] icon, you will see the deflections along the entire beam. You will also see the effective moment of inertia used in that region. (Remember that the effective moment of inertia is calculated based on service-level moments at many locations along the length of each span.)

 

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M-V-D Summary - Cross Section Values shows the moment capacities and moment of inertia for all of the identified cross sections. The  module has examined all of the spans you defined and looked for identical reinforcing layouts. It has eliminated the duplicates, and for simplicity, it only lists the unique reinforced cross sections here.

 

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M-V-D Summary - Design Shear shows the shear stirrup requirements along the span(s) as required by the governing load combinations that generate the highest shear at each section.

 

The column labeled Comment indicates the ACI code condition that governs the requirement for shear reinforcing at each design location.

 

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Support Reactions shows reactions for each support for each load condition.

 

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The 2D Sketch tab provides a graphic representation of the beam currently being designed:

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The Diagram tab offers the ability to view shear, moment, and deflection diagrams for selected load combinations, as well as a moment envelope:

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The 3D Rendering tab offers a 3D view of the beam, with controls to display options:

Concrete Beam 3D rendering

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