Voided Slab Example

CONSPAN Version 4.0.0

Voided Slab Example 1.0

VOIDED SLAB DESIGN EXAMPLE

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Concrete Properties Strength @ time of release: Strength @ 28 days: Unit weight:

4000 psi 5000 psi 150 pcf

Strand Properties: 7 Strand type: /16” diameter - low relaxation strands Ultimate strength: 270 ksi Modulus of Elasticity: 28,500 ksi

Rebar Properties: Grade 60

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Start of Voided Slab Tutorial Open CONSPAN Program: Double Click on CONSPAN icon on Desktop

OR Click on Start All Programs LEAP Software CONSPAN – AASHTO Standard & LRFD

Before getting started on the example problem, click on the About icon at the top of the screen.

Verify that the CONSPAN program is version 4.0.0, if not; this must be addressed before moving forward with the example problem.

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Screen 1: Project Screen

Input the following in the appropriate fields: Project Name: Voided Slab Example User Job Number: leave blank State: VA Date: the program will input the date - If the example program is revised at a later date, the revised date may be entered. (the program does not auto update) State Job Number: leave blank (may input state project # in this field for actual project) By: designer’s initials

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Screen 1: Project Screen (continued)

Design Code: LRFD (program default) Units: U.S. Units (program default) - NOTE: o If SI Units (Metric) is selected, successive screens will display metric units. Span Type: Simple Span (program default) State Specification: None (program default) - Only other alternative is Florida, therefore select none at this time.

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Screen 2: Geometry Screen

Input the following in the appropriate fields: Overall Width – 42 (ft ) Skew Angle Start – 0 (deg) End – 0 (deg) Curb Data Left – 1.6667 (ft) Right – 1.6667 (ft) Topping Data Suppl. Thickness (not the sacrificial thickness) – 0 (in) Deck Thickness (effective) – 0 (in) NOTE: A sacrificial topping surface thickness is input later on the Loads Screen. Haunch Thickness – 0 (in) Haunch Width – 0 (in)

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Screen 2: Geometry Screen (continued) Lane Data Number and Width: These values are generated by the program using default lane width of 12 feet. (3.6 meter for metric) Simply verify lane with and the number of design lanes that are computed. Span Data Precast length – 42.5 (ft) Release Span – 42.5 (ft) (same as precast length) Bearing to Bearing – 41.5 (ft) View Beam Section Library:

Click On

OR

Select Libraries Beam Sections…

For this example – using Prestressed Voided Slab Span (3’-0” x 21”) - Highlight pcs21a and click on Modify tab to view the section properties.

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Hollow Core Slab Section screen should appear after clicking on Modify tab.

The pcs21a voided slab section is already defined. This screen simply provides the geometry details and section properties of the selected pcs21a voided slab. The Template and Edit tabs can also be used to define the properties of the slab section.

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Click on Template tab to view the location and number of strands allowed in the section.

To modify the strands, highlight those to be modified and change the height and/or number of strands at that location. Location and number of strands can also be deleted or added using the corresponding tabs. Once you are satisfied, click on Modify tab. If changes are made to the number of strands and/or location, click OK tab. NOTE: For this example, do not revise the stand arrangement, simply click Cancel tab.

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Click on Edit tab to view the slab section.

Place pointer on the tabs to the left to view the different commands on this screen.

Example: Return and update (click this, if revisions are made and are to be saved) NOTE: For this example, do not revise the voided slab section, simply click on the red X in the upper right hand corner of the Section Drawing Editor screen.

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After closing the Template screen (shown on pg. 9) and the Section Drawing Editor screen (shown on pg. 10), the Hollow Core Slab Section screen is still open.

If changes were made in the Template screen, the Section Drawing Editor screen and/or the Hollow Core Slab Section screen and wish to be saved, click on the OK tab. NOTE: For this example, no revisions are to be made, simply click Cancel tab.

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After closing the Hollow Core Slab Section screen (shown on pg. 11), the Beam Section Library screen is still open.

If changes were made to the voided slab section that was selected and wish to be saved, click on the Save tab.

Click OK to save the changes made to the voided slab section. NOTE: For this example, no revisions are to be made, simply click Close tab.

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Screen 2: Geometry Screen (continued)

Beam/Type Location Under Beam Type, select Rectangular Beam w/ Circular Voids Under Beam ID, select pcs21a Distance From Last Beam, ft - program reads this distance from left to right - Method 1 to input beam sections: o Beam No. 1 distance from last beam => 1.5 ft (this is distance from left edge of slab to center of beam 1), input and click Add tab o Beam No. 2 distance from last beam => 3 ft (this is distance from center of beam 1 to center of beam 2), input and click Add tab o Continue the same process until all 14 beams are entered. o Test the program by highlighting the 14th beam and click Add button

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o Program does not allow this since it exceeds width previously defined -

Method 2 to input beam sections: o Click on Generate… tab in lower right hand corner

o Input number of beams Quantity: 14 o Input distance from left end of slab to center line of first beam D: 1.5 ft o Click OK o Geometry screen should look the same as shown in screen shot on page 13.

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View Sketch of Transverse Section:

Click On

OR

Select Show Image…

This provides a visual representation of the voided slab deck section that you have just defined. PROGRAM NOTE: - To exit this page without exiting the program, click on the gray X in the upper right hand corner (NOT the red X) - Program does not auto-save. Now is a good time to save this example problem. (It would be a good idea to save the program after information has been input into each screen)

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Screen 3: Materials Screen

Input the following in the appropriate fields: Concrete Girder Release Unit Weight – 150 pcf (program default) Strength – 4 ksi K1 – 1 (program default) Elasticity – computed by program Girder Final Unit Weight – 150 pcf (program default) Strength – 5 ksi K1 – 1 (program default) Elasticity – computed by program Deck Unit Weight – 150 pcf (program default) Strength – 4 ksi K1 – 1 (program default) Elasticity – computed by program Tendon Rebar Elasticity – 29000 ksi (program default) fy – 60 ksi (program default) 9/8/2006

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PROGRAM NOTE: - The F1 key is the help function key - The program will provide online help whenever this key is selected - Example of program help function (F1 key): o What is K1? o While on the Materials screen, press F1 key

o Click on Material Screen Terms

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o Provides description of K1 variable, and where this factor can be found in the AASHTO LRFD Specifications. o When finished with the Help screen, click on the red X in upper right corner of the CONSPAN v4.0.0. Online Help screen.

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View Prestressing Tendon Properties:

Click On

OR

Select Libraries Prestressing Tendon…

For this example – using 7/16” diameter low relaxation strands - Highlight the view the Tendon ID labeled 7/16”-207K-LL to view the strand properties - The prestressing stand properties can be modified and saved similar to what was described under the Beam Section properties part of the handout NOTE: For this example, no changes to the strand are to be made, simply click Close tab.

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Screen 3: Materials Screen (continued)

Transformation of Steel Transform All Prestressing Tendons - Do not check this box for the example problem. - If selected, the program will transform all strands into an equivalent area of concrete and use it to calculate the section properties. Transform Rebars - Do not check this box for the example problem. - If selected, the program will transform the designated rebar area into an equivalent area of concrete and use it to calculate the section properties. Prestressing Tendon - Under Tendon ID, highlight 7/16-207K-LL Pattern - Check Straight for this exampleproblem. Debonded Length Increment, in - Program inputs default value as shown on screen shot, but since we are not considering debonded the stands this value does not affect the design - N/A Maximum Auto-Debonding Percentage - N/A (for similar reasons as stated above)

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Screen 4: Loads Screen

Before Dead Loads values are input by hand, first open the Wizard Screen Wizard - Click on Wizard tab on the right edge of screen

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Input Load Values: Left Barrier Weight = 0.4455 klf Future Wearing Surface = 0.015 ksf Sacrificial Wearing Surface = 4.5 in o Thickness of overlay input here as discussed on pg. 6 of handout Right Barrier Weight = 0.4455 klf Stay-in-Place Deck Forms = 0.060 klf (Construction Tolerance) To see how the loads were calculated, refer to MATHCAD program o File Name: Voided Slab Design Example.mcd – pg 4 o For simplicity, MATHCAD values are shown below Dead Load: W c := 0.150 ⋅ kcf

Unit weight of concrete

Sg := 3.0 ⋅ ft

Girder spacing

W const := 20 ⋅ psf

Construction tolerance

yd wtjersey := 0.110 ⋅ ft

3

Volume for F-shaped barrier (S & B Manual Vol. V - Part 5: PSS-3F)

Weight of railing:

wrail := wtjersey ⋅ W c

Future wearing surface:

wfws := 0.015 ⋅ ksf

Sacrificial wearing surface:

td := 2.0 ⋅ in

Stay-in-Place deck forms:

wconst := W const ⋅ Sg

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wrail = 0.4455klf

wconst = 0.060klf

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Once the loads have been input into the Load Wizard, Click OK.

The Loads Screen should now look similar to the screen below:

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PROGRAM NOTE: - It is important that the correct load information is entered into the wizard. - Once OK is clicked on the Load Wizard screen, the program calculates and distributes the loads to all the beams as seen on the previous page. - At this time, the loads that were input into the wizard are no longer shown. o Click on Wizard tab to verify that the input loads are no longer shown. o For this example, no changes to be made, click Cancel.

-

-

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If the computed load values are to be changed after running the wizard, they can be changed manually on the Loads Screen or the desired loads can be deleted from the Loads Screen and the wizard can be run again. If all of the loads shown on the Loads Screen are not deleted and the wizard is run again, then certain loads may be placed more than once onto the transverse section. Therefore, it is important to check that none of the loads on the Loads Screen have been duplicated if the wizard is run more than once.

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View Live Load Library:

Click On

OR

Select Libraries Live Load…

For this example – designing for Design Lane, Design Tandem and Design Truck Live Loads - Highlight the Deign Lane type with Design Lane ID (since using English unit for this example) and click Modify… tab

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-


The loads used for the design calculations can be viewed for the Design Lane Live Loads case. There are no changes are to made to this load case, click Cancel. The same process can be used to view the remaining Live Load cases shown in this library.

NOTE: For this example, no changes are to be made to the live load cases, simply click Close tab.

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Screen 4: Loads Screen (continued)

Diaphragm - There are no diaphragms for this example. Therefore, leave these fields blank. Design Live Load Include LL Deflection o According to the LRFD design code, if the user invokes the optional live load deflection criteria specified in LRFD Art. 2.5.2.6.2, the deflection should be taken as the larger of (a) the resulting deflection from the design truck alone, or (b) the resulting deflection from 25% of the design truck taken together with the design lane load. If this is selected, the above two conditions are checked and the deflection under the governing load is printed in the camber and deflections section of the printout. o Check box for this example. Include Pedestrian Load o No pedestrian load for this example. o If there is a pedestrian load, check the box and input the load (plf) in the indicated box to the right. Available & Selected - These tabs are for the types of vehicular Live Loading to be included in the voided slab design. - For this example, include: o Design Lane o Design Tandem (Program default includes these) o Design Truck Make sure that these LL cases under Selected do not show (=> not incl.)

}

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Screen 4: Loads Screen (continued) Available & Selected (continued) - Examples on how to include and/or remove Live Loading cases: o Include Design Lane load case: Highlight Design Lane under Available Click Under Selected, Design Lane should not show (- not incl.) o Remove Double Truck load case: Highlight Double Truck under Available Click Under Selected, Double Truck should show (- not incl.) o The screen should look similar to the one below

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Screen 5: Analysis Screen

Click on Analysis Factors… tab

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Analysis Factors – Distribution Tab - Distribute Dead Load o Check, Based on Tributary Fraction o Composite loads are currently distributed using this method and until told otherwise, this method will continue to be used. - Dead Load o Program provides a computed distribution for DL equally to all beams - Dynamic Load Factor o Truck = 0.33 (program default) o Lane = 0 (program default) - Live Load – Girder o Program provides a computed distribution for LL shear and moment for 1 lane and 2+ lanes o These computed values can be verified by hand or by viewing the MATHCAD program 9/8/2006

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Analysis Factors – Load Factors Tab - Program defaults to the values listed above. - User can verify these values with AASHTO LRFD Specs. - For this example, these values will not be adjusted. - NOTE: o Strength II Limit State is not included since this deals with a permit vehicle under analysis, which is not under consideration in this example.

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Analysis Factors – Modifier Tab - Program defaults to the values listed above. - For more information on these factors, see AASHTO LRFD Spec., 1.3.2. - For this example, these values will not be adjusted. NOTE: -

If changes have been made under Analysis Factors screen, it is important to click OK before exiting the screen or the changes will not be saved.

Click on Project Parameters… tab

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Project Parameters – Limiting Stress Tab - Program defaults to the values listed above. - User can verify these values with AASHTO LRFD Specs. - Click Edit Factors… tab to view the calculated values.

-

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For this example, these values will not be adjusted. Therefore, click Cancel.

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Project Parameters – Restraining Moments Tab - Program defaults to Full Continuity - Not applicable for simple span design of voided slab. Therefore, click the next tab labeled Multipliers.

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Project Parameters – Multipliers Tab - Program defaults to the values listed above. - Deflection Multipliers o As specified in the PCI Design Handbook (Fifth Edition), long-term deflections for a prestressed beam are obtained by multiplying short-term deflections with specified factors. CONSPAN follows this same approach. o Can refer to the PCI Design Handbook (Fifth Edition) for a list of such factors for different loads. - Length Multipliers o Bonded: Transfer Program default is 1.0. o Bonded: Development In the LRFD mode, as well as in the Standard Specifications mode, this factor has been set to 1.6. o Debonded: N/A - No changes are to be made. Therefore, click the next tab labeled Resistance Factor/Losses.

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Project Parameters – Resistance Factor/Losses Tab - Program defaults to the values listed above. - Resistance Factor o The default resistance values shown are as specified in LRFD Art. 5.5.4.2 and LFD Art 9.14. o More information can be found by using the Help Function (press F1) - Prestress Losses o There are two methods to calculate the prestress losses: The AASHTO method is as specified in LRFD article 5.9.5. (using 5.9.5.3. Approximate Estimate of Time Dependent Losses). The Manual method allows the user to specify the loss percentages at release and final. - Compute Losses using o Select the approximate method to compute losses according to the provisions of LRFD Art. 5.9.5.3 Approximate Estimate of Time Dependent Losses. - No changes are to be made. Therefore, click the next tab labeled Moment and Shear Provisions.

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Project Parameters – Moment and Shear Provisions Tab - Program defaults to the values listed above. - Program default set to: o Moment Method AASHTO o Horizontal Shear Method Include Beam and Slab Contribution in Vu - For more information on the Moment and Shear Provisions tab, use the program Help Function. (press F1 key) - No changes are to be made. Since no changes were made under the Project Parameters screen for this example problem, click Cancel.

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Screen 5: Analysis Screen (continued) Click on Run Analysis… tab

User screen should look similar to screen shot below.

Toolbar at top of screen allows user to view certain desired output:

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Screen 6: Beam Screen

For this example, the strand arrangement will be designed for an interior slab section. Place the pointer on Beam 2 and single click. This should highlight Beam 2 in red (should look like the screen above). Before a strand pattern is designed for an interior beam, click on the Edit… tab on the left hand side of the Beam Screen.

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Design Parameters – Effective Width Tab - Verify that the effective width calculated by program is accurate. - Effective width for this example should be 36 in. If so, click Cancel (no need to change). Notice that there are other tabs included under the Design Parameters which have already been addressed: Design Parameters – Limiting Stress Tab - Under Project Parameters – Limiting Stress (see pg. 33 of handout) Design Parameters – Prestressing Tendon Tab - On Materials Screen (see pg. 20 of handout) Design Parameters – Prestress Losses Tab - Under Project Parameters - Resistance Factor/Losses Tab (see pg. 36 of handout) Design Parameters – Transform Steel Tab - On Materials Screen (see pg. 20 of handout)

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Screen 6: Beam Screen (continued) Now, design a strand pattern for interior Beam 2 Single click on Strand Pattern… tab.

Unless the user knows what strand pattern to analyze, single click on the Auto Design tab and the program will provide a strand arrangement.

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The program will automatically provide a screen titled Design Status. This screen provides the stresses computed by the program at release and final conditions as well as the moments at both strength and service limit states. If a stress failure has occurred, the program will highlight that value in red. At this point, click the Close tab.

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The program indicates that 14 straight strands are adequate for Beam 2 design. PROGRAM NOTE: - If Reset Pattern is selected, the strand pattern currently shown on the screen will be erased. - If a strand pattern is input by hand and Auto Design is selected, it will ERASE the previous strand pattern and provide a new strand pattern. o Example on how to avoid this: Select Beam 2 and select Auto Design to see what strand pattern the program provides, click OK. Next, select Beam 3 and input a strand pattern to analyze, click Design Status to view if it passes. If satisfied, click OK. This should prevent the accidental overriding of the previous input. At this time, click OK for this example problem.

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The beam screen should now look similar to the screen below.

At the bottom of the screen the location of the 14 tendons previously designed for Beam 2 are shown in the transverse beam sections at mid-span and at the end of the beam. Above the transverse section sketches, the location of the tendons as well as the precast and bearing to bearing beam lengths is provided in the longitudinal beam sketch.

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How to input strands by hand (For future reference, NOT for this example):

Type: Straight or Draped NOTE: On Materials screen straight strands were selected. Therefore, straight is the only option for this example. End: The distance provided is from the bottom of slab. NOTE: Strand location previously defined (Tendon Icon) # of Strands (max available) Input number of stands at defined location. NOTE: Maximum number of strands previously defined (Tendon Icon) Add After the strands are defined, click Add tab. Modify Highlight row of existing stands to be modified. Make changes to location and/or number of strands and click Modify tab. Delete Highlight row of stands to be removed and click Delete tab Copy to… Option to copy strand pattern to any of the other beams or all beams If Copy to… is selected and a strand pattern is not to be copied, click Cancel tab to exit.

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View Rebar Library:

Click On

OR

Selection Libraries Rebar…

For this example – using #3 bars designated as US#4(M13) - The rebar properties can be viewed from this screen and modified and saved similar to what was described under the Beam Section properties part of the handout. NOTE: For this example, no changes to the reinforcement are to be made, simply click Close tab.

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Screen 6: Beam Screen (continued) Now that a strand pattern design has been performed for interior Beam 2, design the shear reinforcement for the same interior beam. Single click on Rebar Pattern… tab.

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First, refer to the Auto Design on left hand side of screen.

Auto Design Stirrup Increment: in - Enter 6.0 (Program default is 6.0) Size: - Select US#4(M13) (Program default is US#3(M10)) Legs: - Enter 2 (Program default is 2) Unless the user knows what shear reinforcement pattern to analyze, single click on the Auto Design… tab and the program will shear reinforcement required for the example problem based on the information defined above. (similar to the deign of the Strand Pattern) Click Auto-Design… tab

The message above appears whether or not shear reinforcement has been previously defined. Since shear reinforcement has not been defined for Beam 2, click OK.

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The program provides the following stirrup spacing for Beam 2. Notice at the top of the Rebar Pattern screen, there is a Neg. Moment Continuity Steel tab. Click on this tab.

Program recognizes that this does not apply to our simple span example. Click OK to exit. Click OK at the bottom of Rebar Pattern screen.

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Screen 6: Beam Screen (continued)

The shear reinforcement designed by the program is placed on the sketch of the longitudinal section of the beam.

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How to input shear reinforcement by hand (For future reference, NOT for this example):

Number of Legs: Defined number of stirrup legs to be placed. Once this is defined, the screen should appear similar the one below.

Stirrup Size: Select stirrup size from the pull-down menu. NOTE: Stirrup sizes previously defined (Stirrup Icon) Stirrup Area (in^2): Program will input this value. NOTE: Stirrup area previously defined (Stirrup Icon) Stirrup Spacing (in): Enter desired spacing. Start: Enter the starting location of the defined stirrup size and spacing. End: Enter the ending location of the defined stirrup size and spacing. Once these fielded have been entered, click Insert… Continue the same process until shear reinforcement is defined for the entire precast beam length.

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Stirrups Insert… Copy… Delete… Copy to…

}


(These commands are similar to the ones discussed on the Strand Pattern screen)

Graphs… - Click on Graphs… tab

-

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Program provides a diagram of the area or steel required curve (in green). When reinforcement has been defined, either by the user or the program, the diagram will show an area of steel provided curve (in red). This provides a graphic check for the user whether enough steel has been provided or not. To exit this screen, click on the red X in the upper right hand corner.

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Stirrups Symmetrical Design - If stirrups have been defined for the first half of the beam, this command can be used if same reinforcement is to be mirrored about the center of the beam. - Click on Make Symmetrical tab.

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If symmetrical stirrup design is desired, click Yes.

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View Results: Program provides a number of different ways to view design results: 1. Results on Analysis screen (described on pg. 38 of handout) 2. Results on Beams Screen, Design Status tab (described on pg. 42 of handout) 3. After defining stand pattern for Beam 2 on this example, on Beam Screen click Results tab on left side of screen

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Destination -

-

To view the output after the initial run, make sure it is set to Screen because there are approximately 30+ pages of output for each beam in this example problem. This should prevent wasting paper by accidentally sending it to the printer. Can also set it to File and save it as a .txt document. This allows the user to view the results in the future without opening the CONSPAN program again. For this example, set it to Screen.

Project Geometry Loads -

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Provides information as seen on Geometry Screen (located at top of output screen). For this example, do not check. Provides information as seen on Loads Screen (located at top of output screen). For this example, do not check.

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Library -

Provides vehicular live loads selected for design on Loads Screen (located at bottom of output screen). For this example, do not check.

-

Make sure Beam 2 is selected since this is the beam to be analyzed.

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If only certain design calculations are to be viewed, simply check the corresponding box or boxes and select Print/View. For this example, check All.

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Check the corresponding live load box or boxes to be viewed and select Print/View. Does not apply to this example.

Beam Specific Design

Rating

Click Print/View at bottom of screen

Scroll through the design output to view the desired results. To exit this screen, click on red X in upper right hand corner.

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4. View results by either of the following:

Click On

OR

Select Show Results…

To exit this screen, click on grey X (NOT red X) in upper right hand corner.

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5. View graphic results by either of the following:

Click On

OR

Select Show Diagrams…

To exit this screen, click on red X in upper right hand corner.

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Voided Slab Example

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