Prestress with Substructure Tutorial...2018/03/14 · Define substructure design settings by double...

AASHTOWare BrDR 6.8.2

Prestress with Substructure Tutorial Two Simple Span Prestressed I Beam with a Multi-Column Pier on Drilled Shafts Example

PS13 - Two Simple Span Prestressed I Beam with a Multi-Column Pier on Drilled Shafts Example

Last Modified: 3/14/2018 1

This example details the data input of a prestressed concrete I beam bridge and performing an analysis. This

example is a bridge from the Mississippi DOT inventory. The bridge is comprised 8 total spans. However, only

spans 3 and 4 are entered.

Topics Covered

• Comments and Assumptions

• General Data Entry

• Superstructure Definitions

• Bridge Alternatives

• Pier Data Entry

• Analysis and Results

Comments and Assumptions

• Due to rounding on the design plans, the BrR span lengths are slightly off from the design drawings.

Lengths are within 1/16”.

• Fence Load = 0.015 k/ft

• Due to the varying overhang, use 2/3 point for constant overhangs in the program.

o Span 3 Left Overhang = 2.7816’

o Span 3 Right Overhang = 3.6133’

o Span 4 Left Overhang = 3.0566’

o Span 4 Right Overhang = 3.6133’

• Traffic data and design speed for LRFR analysis

o Assumed ADTT = 469 per NBI

• Barriers are equally distributed to all beams.

• Assume 5000 psi for the 28-day compressive concrete strength of the Type III PS Beam for the 60-foot

span.

• The plans show a discrepancy for strand type for the 135 ft beam details. The section indicates ½” diameter

270 K-LR strands, but the table and notes show 0.6” diameter 270 K-LR strands. Therefore, 0.6” diameter

270 K-LR strands will be used in the model.

• SIP form weight = 20 psf. The presence of SIP forms was verified using Google Maps.

o Span 3, Exterior Beams = 0.016 k/ft

o Span 3, Interior Beams = 0.032 k/ft

o Span 4, Exterior Beams = 0.056 k/ft

o Span 3, Interior Beams = 0.113 k/ft

• 0.25” Integral Wearing Surface

• HL93 will be the vehicle used for ratings

• District, County and Owner information is not populated

• For the Span 3 exterior beams and Span 4 – G6, a LRFD effective width = Overhang + S/2 is used, even

though the overhang is greater than S/2 (C4.6.2.6.1).

• Piers 3 and 5 are not entered into the program due to the fact that the adjacent spans are not entered for this

example.

• Due to the limitations of the program, Pier 4 cannot be analyzed with the current version. The issue results

due to the fact of splayed framing plans and the overhangs varying from the back span to the ahead span.

• Soil density = 0.120 ksf.

• Finished ground line elevation = 376.5 ft.

• The column unbraced length is the average of all the columns.



General Data Entry

From the Bridge Explorer create a new bridge and enter the following description data:

Close the window by clicking Ok. This saves the data to memory and closes the window.

To enter the materials to be used by members of the bridge, click on the to expand the tree for Materials. The tree

with the expanded Materials branch is shown below:



To add a new concrete material, click on Concrete in the tree and select File/New from the menu (or right mouse

click on Concrete and select New). Click ‘Copy from Library’, select ‘Class A (US) and click OK.

The window will be populated. Change to name to ‘Class AA” and click OK to close.

To add the 6 ksi and 5 ksi prestressed concrete material, double click the Concrete folder again. Repeat the process

of copying in the Class A (US) concrete from the library. This time, however, update f’c and enter the f’ci as shown

below. Other data affected by the changes will update automatically.



Enter the 5 ksi concrete in a similar manner:

f’ci can be found on the drawings



Add reinforcement material and prestress strand material using the same techniques. The windows will look like

those shown below:



To enter a prestress beam shape to be used in this bridge expand the tree labeled Beam Shapes as shown below:



Click on I Beams in the tree and select File/New from the menu (or double click on I Beams in the tree). The

window shown below will open.

Select the Top Flange Type as Wide and click on the copy from Library button. Select BT-72 (AASHTO-PCI Bulb-

Tee BT-72) and click Ok. The beam properties are copied to the I Beam window as shown below.



We will now edit the Strand Grid to simplify the process when we defined strand locations. Delete the existing grid

and enter the following data.

Enter the AASHTO Type IV beam using the same techniques.



To enter the appurtenances to be used within the bridge, expand the tree branch labeled Appurtenances. To define a

parapet double click on Parapet in the tree and input the parapet dimensions as shown below. Click OK to save the

data to memory and close the window.



Create a second barrier without the additional load which accounts for the fence.

Define substructure design settings by double clicking LRFD Substructure Design Settings and click Copy from

Library. Select Final Design Setting (US) and click OK.



The default impact factors, standard LRFD and LFD factors will be used so we will skip to Structure Definition.

Bridge Alternatives will be added after we enter the Structure Definition.

Superstructure Definitions

Double click on SUPERSTRUCTURE DEFINITIONS (or click on SUPERSTRUCTURE DEFINITIONS and

select File/New from the menu or right mouse click on SUPERSTRUCTURE DEFINITIONS and select New from

the popup menu) to create a new structure definition. The following dialog will open.



Select Girder System and the Structure Definition window will open. Enter the appropriate data as shown below:

Click on Ok to save the data to memory and close the window.



The partially expanded Bridge Workspace tree is shown below:



Click Load Case Description to define the dead load cases. The completed Load Case Description window is shown

below.

Double-click on Framing Plan Detail to describe the framing plan. Enter the appropriate data as shown below.



Switch to the Diaphragms tab to enter diaphragm spacing. Enter the information for each Girder Bay shown below.

NOTE THAT THIS SHOULD BE DONE AFTER THE STRUCTURE REFERENCE LINE IS SET IN THE

TYPCIAL SECTION WINDOW.

Girder Bay 2

Girder Bay 3

Girder Bay 4



Girder Bay 5

Girder Bay 6

Girder Bay 7

Select OK to close the window.

Next define the structure typical section by double-clicking on Structure Typical Section in the Bridge Workspace

tree. Input the data describing the typical section as shown below.

Basic deck geometry:



The Deck (cont’d) tab is used to enter information about the deck concrete and thickness. The material to be used

for the deck concrete is selected from the list of bridge materials described above.

Parapets:

Add two parapets as shown below.



Lane Positions:

Select the Lane Position tab and use the Compute… button to compute the lane positions. A dialog showing the

results of the computation opens. Click Apply to apply the computed values. The Lane Position tab is populated as

shown below.

Now define a Stress Limit. A Stress Limit defines the allowable concrete stresses for a given concrete material.

Double click on the Stress Limits tree item to open the window. Select the “Class F6” concrete material. Default

values for the allowable stresses will be computed based on this concrete and the AASHTO Specifications. A

default value for the final allowable slab compression is not computed since the deck concrete is typically different

from the concrete used in the beam. Click OK to save this information to memory and close the window.



Double click on the Prestress Properties tree item to open a window in which to define the prestress properties for

this structure definition. Define the Prestress Property as shown below. We are using the AASHTO Approximate

method to compute losses so the “General P/S Data” tab is the only tab that we have to visit. Click Ok to save to

memory and close the window.

Now define the vertical shear reinforcement by double clicking on Vertical (under Shear Reinforcement Definitions

in the tree). Define the reinforcement as shown below. Click OK to save to memory and close the window.


Last Modified: 3/14/2018

A partially expanded Bridge Workspace is shown below.

Describing a member:

The member window shows the data that was generated when the structure definition was created. No changes are

required at this time. The first Member Alternative that we create will automatically be assigned as the Existing and

Current Member alternative for this Member.



Defining a Member Alternative:

Double-click MEMBER ALTERNATIVES in the tree to create a new alternative. The New Member Alternative

dialog shown below will open. Select Prestressed (Pretensioned) Concrete for the Material Type and PS Precast I for

the Girder Type.

Click OK to close the dialog and create a new member alternative.

The Member Alternative Description window will open. Enter the appropriate data as shown below. The Schedule-

based Girder property input method is the only input method available for a prestressed concrete beam.



For this example, change the Loss & Stress Calculations to “Use transformed section properties”.

Double click Member Loads and enter the uniform load to account for the SIP forms.



Next describe the beam by double clicking on Beam Details in the tree. The Beam Details windows with the

appropriate data are shown below. Click OK once finished with the Slab Interface tab.



Expand the tree under Strand Layout and open the Span 1 window. Place the cursor in the schematic view on the

right side of the screen. The toolbar buttons in this window will become active. Select the Zoom button to shrink the

schematic of the beam shape so that the entire beam is visible.

Select the Description Type as Strands in rows and the Strand Configuration Type as Harped. The Mid span radio

button will now become active. You can now define the strands that are present at the middle of the span by

selecting strands in the right-hand schematic. Select the strands in the bottom flange of the schematic so that the

CG of the strands is 4. 23 inches.



Now select the Left end radio button to enter the following harped strand locations at the left end of the precast beam.

Place the cursor in the schematic view on the right side of the screen. You can now define the strands that are present

at the left end of the span by selecting strands in the right-hand schematic. Select the top 8 strands in the schematic so

that the CG of the strands is 20.37 inches. Close the window by clicking OK. This saves the data to memory and

closes the window.

The user will return to the Deck Profile window after the information for Beams 2 – 8 is entered.

No reinforcement is described.



The haunch profile is defined by double clicking on Haunch Profile in the tree. The window is shown below.

The Shear Reinforcement Ranges are entered as described below. The vertical shear reinforcement is defined as

extending into the deck on this tab. This indicates composite action between the beam and the deck. Data does not

have to be entered on the Horizontal tab to indicate composite action since we have defined that by extending the

vertical bars into deck.



SIP

The description of an exterior beam (except for the deck profile) for this structure definition is complete. Using the

techniques used for Beam 1, enter the data for the remaining beams for Span 3.

Shear reinforcement ranges:

G2-G7

G8

Stress Harp

Beam Span Uniform Beam Girder Prestress Left Right Limit Point Haunch

No. Length Load Shape Material Properties End End Range Location Y1

--- ft k/ft --- --- --- in in ft ft in

G2 132.0632 0.032 BT-72 Class F6 0.6" (7W-270) LR 16 16 134.7299 53.8645 1.25

G3 132.0632 0.032 BT-72 Class F6 0.6" (7W-270) LR 16 16 134.7299 53.8645 1.25

G4 132.0632 0.032 BT-72 Class F6 0.6" (7W-270) LR 16 16 134.7299 53.8645 1.25

G5 132.0632 0.032 BT-72 Class F6 0.6" (7W-270) LR 16 16 134.7299 53.8645 1.25

G6 132.0632 0.032 BT-72 Class F6 0.6" (7W-270) LR 16 16 134.7299 53.8645 1.25

G7 132.0632 0.032 BT-72 Class F6 0.6" (7W-270) LR 16 16 134.7299 53.8645 1.25

G8 131.2993 0.016 BT-72 Class F6 0.6" (7W-270) LR 16 16 133.9660 53.4830 1.25

Beam Projection



The user can now input the deck profile windows for each beam. Double click ‘Deck Profile’ for G1.

Click the ‘Compute from Typical Section’ button.

Enter the structural thickness and click OK.

The following warning message will appear.



This warning appears because the assumed constant overhang for the analysis is slightly larger than the limits per

AASHTO C4.6.2.6.1 (0.5 * Beam Spacing). For this example, the user will enter the Std effective flange widths into

the LRFD effective flange widths.

The Deck Profile windows for the remaining beams are shown below.

G2

G3



G4

G5

G6

G7



G8 (Note that the same warning message will appear as it did for G1. Enter the Std values for LRFD values)

Once the input for Span 3 is complete, the user can create Span 4 in a similar manner. The required superstructure

input screens and member input data are shown below.



Member Input Data:

Remember to wait to compute effective flange width until all member alternatives have been created.

SIP Stress

Beam Span Uniform Beam Girder Prestress Left Right Limit Haunch

No. Length Load Shape Material Properties n End End Range Y1

--- ft k/ft --- --- --- --- in in ft in

G1 50.51026 0.056 AASHTO TYPE IV Class F5 1/2" (7W-270) LR 7 16.875 9 52.6665 1.00






Beam Projection



The Deck Profile windows for the beams are shown below.

G1

G2

G3



G4

G5

G6 (Note that the same warning message will appear as it did for Span 3, G1 & G8. Enter the Std values for LRFD values)

The Superstructure Definitions are now complete. Bridge Alternatives can now be created.



Bridge Alternatives

Double click the BRIDGE ALTERNATIVES folder and enter in the information shown below:

In the Substructures tab, define substructure locations as shown below and click OK.



Double click the SUPERSTRUCTURES folder and enter the name “Span 3”. Move to the Substructures tab and

assign substructures at each support. Click new to Click OK to close.

Double click the SUPERSTRUCTURE ALTERNATIVES folder. Enter the name “Span 3” and select “Span 3”

from the dropdown box. Click OK to close.



Follow the same process for creating alternative for Span 4.



See the completed Bridge Alternative below. User can now enter Stiffness Analysis information and create the pier.

For this example, we will assume 50 percent of the total span length is applied to Bent 4 and 25% each to the other

units. Click OK.



Pier Data Entry

Double click ‘Bent 4’ and enter the information shown below. Click OK.

Double click the ‘Pier Alternatives’ folder. Select ‘Frame Pier’ and click Next.



Enter the information shown below and click Finish.

The following window will appear. There is no input needed for this window. Click OK.



Double click ‘Geometry’. Edit the blue dimensions as shown below. Click OK.

Double click “Cap” and enter the information below. Click OK.



Double click “Components” in the ‘Cap’ subfolder and enter the information below. Select ‘Straight Cantilever’ for

both the left and right side and click OK.

Double click ‘Geometry’ in the ‘Cap’ subfolder. Edit the blue dimensions as shown below. Click OK.



Double click ‘Reinforcement’ in the ‘Cap’ subfolder. Enter the information shown below in both the ‘Flexural’ and

‘Shear’ tabs. Click OK.



Expand the ‘COLUMNS’ and ‘Column1’ folder. Double click ‘Components’ in the ‘Column1’ subfolder. Enter the

information shown below. Click OK.

Double click ‘Geometry’ in the ‘Column1’ subfolder. Edit the blue dimensions. Click OK.

Double click the ‘Reinforcement Definitions’ folder and click the ‘Generate Pattern’ button.



Enter the following information and click Apply.

The Column Reinforcement window will populate. Click OK.



Double click ‘Reinforcement’ in the ‘Column1’ subfolder. Enter the information shown below in both the Flexural

and Shear tabs. Click OK.

Double click the ‘FOUNDATION ALTERNATIVES’ folder. Select ‘Single Drilled Shaft’ and click Next.



Enter the information shown below. Click Finish.

Double click ‘Geometry’ in the ‘C1 Shaft’ subfolder. Edit the blue dimensions. Click OK.



Double click ‘Reinforcement Definitions’ in the ‘C1 Shaft’ subfolder. Click the ‘Generate Pattern…’ button. Enter

the following data and click Apply.

The window will populate. Click OK.



Double click ‘Reinforcement’ in the ‘C1 Shaft’ subfolder. Enter the information shown below in both the Flexural

and Shear tabs. Click OK.

The input for Column 1 is complete. Use the same process to enter Columns 2 and 3. The input windows for each

are shown below.

Column 2



C2 Shaft



Column 3



C3 Shaft



All the data entry for the pier columns is now complete.



Analysis and Results

Typically, the user can open the Superstructure Loads and Substructure Loads window and have the program

automatically compute the loads to be applied to the substructure unit. However, Bent 4 in this particular example

cannot be analyzed with the current version of the program. The issue results due to the fact of splayed framing

plans and the overhangs varying from the back span to the ahead span.

The superstructure can still be analyzed. To perform LRFR or LFD rating, select the View Analysis Settings

button on the toolbar to open the window shown below. Choose the desired rating method and vehicles. A window

for LRFR and HL-93 vehicles is shown below as an example. Click OK.



The user can either highlight the entire structure, an individual Superstructure, or an individual member alternative.

Once the desired superstructure or member alternative is selected, click the Analyze button on the toolbar to

perform the rating. When the rating is finished you can review the results by clicking the View Analysis

Report button on the toolbar. LRFR and LFD results for Span 3, G1 are shown below.

Prestress with Substructure Tutorial...2018/03/14 · Define substructure design settings by double...

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