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Modeling Touch Shoring
BridgeSight Inc. P.O. Box 19172
South Lake Tahoe, CA 96151 877-441-0346
www.BridgeSight.com
BridgeLink Professional
Touch Shoring
Title PGSuper Tutorial – Modeling Touch Shoring Publication No. BS02282011-2
Abstract This document provides a discussion and step-by-step procedure for modeling precast-prestressed girder bridge structures constructed with touch shoring.
Disclaimer The information contained in this publication is believed to be accurate; however, it is being provided for informational purposes only. Publication of this document by BridgeSight Inc. should not be construed as BridgeSight Inc. engaging in or rendering engineering, legal or other professional services. Use of the information contained in this publication should not be considered by the user as a substitute for the advice of a registered professional engineer, attorney or other professional. If such advice is required, it should be sought through the services of a registered professional engineer, licensed attorney or other professional.
Notes
Author Staff – BridgeSight Software Sponsor BridgeSight Inc P.O. Box 19172 South Lake Tahoe, CA 96151
Specification AASHTO LRFD Bridge Design Specifications BridgeLink Professional 2.0 - PGSuper 3.0
Original Publication Date 3/13/2011 Date of Latest Revision 9/9/2017 Version 2.0
Notice of Copyright
Copyright © 2017 BridgeSight Inc. All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopied, recorded, or otherwise), without prior written permission from BridgeSight Inc.
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Introduction This tutorial demonstrates how to model a touch shoring construction scenario with PGSuper. Touch shoring supports precast girders during deck placement to reduce the final stresses in the composite deck and girder system. In this construction scenario, temporary shoring towers are erected before the girders are placed. After the girders are placed, the shoring is adjusted to touch the bottom of each girder without introducing any significant force into the system. Subsequent loads placed on the non-composite girder, such as the deck slab, will be partially supported by the shoring effectively reducing the girder’s span length. At temporary shoring locations, the additional dead load creates negative moment. This reduces the positive bending moment stresses in the bare girder from the subsequent loads applied to the completed structure.
The shoring is removed after the deck slab reaches a specified compressive strength. Any force carried by the temporary shoring tower is then carried by the full span girder, which is now a composite section. This method can reduce total stresses compared to when touch shoring is not utilized.
Scenario Our example is a fictitious design-build construction scenario where the builder has realized a large cost savings by eliminating a bridge from a project. However, six girders for the removed bridge have already been fabricated, and the cost savings would be even greater if these girders can be used in a different bridge.
The six girders are AASHTO Type V with 32 straight and 8 harped strands. They were constructed for a 130 ft span structure (127.33 ft between bearings). The design concrete strengths are f’ ci = 5.9 ksi and f’ c = 6.6 ksi. The bridge where the builder would like to use these girders is also 130 ft long, but slightly wider. The girders would be spaced at 8 ft and the deck would have 4 ft overhangs. The girders were originally designed for a closer spacing and thus might not have adequate capacity.
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Our job is to assess the girders and determine if they can be utilized in a different bridge. The purpose of this tutorial is to describe modeling technique, so we will limit the engineering evaluation to flexural requirements. Of course, a full evaluation must be performed if this were an actual bridge project.
Creating the PGSuper Project Create a PGSuper Project to evaluate the bridge. The fastest way to start a project with AASHTO girders is to use the AASHTO Standard Girder templates published by the Washington State Department of Transportation (WSDOT).
Configure PGSuper for AASHTO Girders This project uses AASHTO girders so begin by configuring PGSuper for AASHTO standard girders.
1. Start BridgeLink 2. Select File > Configure BridgeLink… to activate the configuration wizard 3. The second step in the configuration wizard is the PGSuper configuration. Select
the WSDOT configuration server and the AASHTO Standard Girders from PCI BDM configuration
4. Press [Next>] and proceed to through the wizard. Default configurations for the other BridgeLink applications are acceptable
5. Press [Finish] to end the configuration wizard.
Create a New PGSuper Project1. Select File > New 2. Under PGSuper Project Templates, select I3. Press [OK] to create a new project
Describing the BridgeThe bridge in this example can be defined by changing just a parameters.
1. Select Edit > Bridge
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Create a New PGSuper Project
Under PGSuper Project Templates, select I-Beams and then the Type V to create a new project
Describing the Bridge The bridge in this example can be defined by changing just a few of the default
Bridge
Beams and then the Type V template.
of the default
2. On the General Tab input the girder spacing (8 ft)
3. On the Layout tab elength (1+30)
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On the General Tab input the girder spacing (8 ft)
tab enter the station of Abutment 2 to define the overall
2 to define the overall bridge
4. On the Deck Geometry and Materials ta(24ft)
5. The default value for the remaining parameters are sufficient for this Press [OK].
6. In a normal situation, the next step would be to use PGSuper’s bridge model view and girder view to This is covered in other tutorials, so we will skip model validatation and define the girder properties.
Describing the GirdersAll of the girders used in the bridge are the same. parameters to the remaining girders.
1. Select Edit > Girder
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On the Deck Geometry and Materials tab, enter the left and right deck offset
The default value for the remaining parameters are sufficient for this
In a normal situation, the next step would be to use PGSuper’s bridge model view and girder view to confirm that the bridge’s geometry has been input correctly. This is covered in other tutorials, so we will skip model validatation and define the girder properties.
the Girders All of the girders used in the bridge are the same. Define Girder A and tparameters to the remaining girders.
Girder then edit Span 1, Girder A
enter the left and right deck offset
The default value for the remaining parameters are sufficient for this tutorial.
In a normal situation, the next step would be to use PGSuper’s bridge model view that the bridge’s geometry has been input correctly.
This is covered in other tutorials, so we will skip model validatation and define
efine Girder A and then copy the
2. Enter the concrete strength
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Enter the concrete strength
3. Enter the strand configuration
4. The remaining parameters are not of significanceall girders in this span
Press [OK]
Evaluate the Girders for Evaluate a typical interior girder accomplished by creating
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Enter the strand configuration
The remaining parameters are not of significance for this tutorial. Check the rders in this span box to copy these parameters to all other girders in Span 1.
Evaluate the Girders for Conventional ConstructionEvaluate a typical interior girder for a conventional construction sequence. This
a Spec Check Report for Girder B.
Check the Copy to e parameters to all other girders in Span 1.
Conventional Construction construction sequence. This is
1. Select View > Reports 2. Select Span 1 and Girder B. Press [OK]
3. Reviewing the analysis results, we see that the girder does not satisfy the level stress criteria.
NOTE: There are other specifitutorial we are only interested in flexure.
With a conventional construction are not within acceptable service level stress limits. construction as a means of reducing the
Shored ConstructionLet’s see if the final service level stresses can be reduced through the use of shored construction. Shoring towers cannot be explicitly modeled in be simulated with user defined loadare of interest:
• Event 4 : Cast Deck into their final position
• Event 5 : Final without Live Load strength and is composite with the girders. railing system, are applied.
We model the addition of equal to the shoring tower reactions in
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Reports > Spec Check Report Select Span 1 and Girder B. Press [OK]
eviewing the analysis results, we see that the girder does not satisfy the stress criteria.
NOTE: There are other specification checks that do not pass. For purposes of this tutorial we are only interested in flexure.
conventional construction sequence, these girders have adequate strength but not within acceptable service level stress limits. We will investigate
construction as a means of reducing the service level stresses.
Shored Construction he final service level stresses can be reduced through the use of shored
horing towers cannot be explicitly modeled in PGSuper;user defined loads applied during key construction events
Event 4 : Cast Deck - During this event, the non-composite girders into their final position and carry the deck slab load as simple span membersEvent 5 : Final without Live Load - The deck slab has reached its required strength and is composite with the girders. Superimposed dead loads, such as the railing system, are applied.
touch shoring towers by applying upward userequal to the shoring tower reactions in Event 4. Shoring tower removal is
eviewing the analysis results, we see that the girder does not satisfy the service
cation checks that do not pass. For purposes of this
sequence, these girders have adequate strength but We will investigate shored
he final service level stresses can be reduced through the use of shored PGSuper; however they can
during key construction events. Two events
composite girders are erected le span members.
he deck slab has reached its required Superimposed dead loads, such as the
ing upward user-defined loads horing tower removal is then simulated
by applying downward user defined loads loads in Event 5.
Assume the shoring towers located
Slab Loading Start by using PGSuper to by the shoring towers.
Create a Details Report for Girder
1. Select View > Reports 2. Select Span 1, Girder
From the Details Report, the
Compute the Shoring Tower ReactionWhen the shoring towers engage the bottom flange of the girder and the deck is cast, the girder acts as a three span continuous beam.
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user defined loads that are equal and opposite of the reaction
shoring towers located at the 1/3 and 2/3 points in the span.
to compute the deck slab dead load that will be carried, in part,
Create a Details Report for Girder B, with just the Loading Details chapter.
eports > Details Report Select Span 1, Girder B, and deselect all chapters except for Loading Details
From the Details Report, the total slab load is 0.970 k/ft
Compute the Shoring Tower Reaction When the shoring towers engage the bottom flange of the girder and the deck is cast, the girder acts as a three span continuous beam.
that are equal and opposite of the reaction
at the 1/3 and 2/3 points in the span.
compute the deck slab dead load that will be carried, in part,
just the Loading Details chapter.
, and deselect all chapters except for Loading Details
When the shoring towers engage the bottom flange of the girder and the deck is cast, the
A BRA=0.4wl
l
The total span length, between bearings, is 127.33ft.
The shoring tower reaction at B and C is
Modeling the Shoring TowerThe effect of the towers is modeled with two upward Event 4 so the loading activity is assign
User defined load for s1. Select Loads > Add Point Load2. Define the first shoring tower reaction load. Note that positive loads are in the
direction of gravityof the span length.
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B C D
l l
w
RB=1.1wl RC=1.1wlRD=0.4wl
, between bearings, is 127.33ft.
� � 127.33�3 � 42.44�
ower reaction at B and C is 1.1�� � 1.1 �0.970 ���� �42.44
Modeling the Shoring Tower is modeled with two upward point loads. The deck is cast in
so the loading activity is assigned to this event.
for shoring tower reaction Add Point Load shoring tower reaction load. Note that positive loads are in the
direction of gravity. Enter a load of -45.3 kips. The load is located at the 1/3 point
D
� 44�� � 45.3���
deck is cast in
shoring tower reaction load. Note that positive loads are in the kips. The load is located at the 1/3 point
3. Repeat this process to define the shoring tower reaction load at the 2/3 point of the span.
User defined load for Shoring The shoring towers are removed agirder. Removal is modeled with two dupward loads applied in Event 4
The user defined loads can are listed in the Loads window. Select
Evaluate the Girders using Shored ConstructionWe will review the moment diagram to verify that the user defined loads that simulate the shoring towers have the desired effect.
1. Select View > Graphs > Analysis Results2. Select Girder B 3. Select Interval 10: Cast Deck4. Select Moment 5. Hold the CTRL key and sel6. Select Incremental results
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Repeat this process to define the shoring tower reaction load at the 2/3 point of
oad for Shoring tower removal The shoring towers are removed after the deck cures and becomes composite with the
emoval is modeled with two downward loads that are equal and opposite ofEvent 4. These loads are applied in Event 5.
The user defined loads can are listed in the Loads window. Select Edit > Loads
Evaluate the Girders using Shored ConstructionWe will review the moment diagram to verify that the user defined loads that simulate the shoring towers have the desired effect.
View > Graphs > Analysis Results
Select Interval 10: Cast Deck
Hold the CTRL key and select “Slab”, “Haunch”, “User DC”, and “DC” loadsSelect Incremental results
Repeat this process to define the shoring tower reaction load at the 2/3 point of
fter the deck cures and becomes composite with the and opposite of the
Edit > Loads.
Evaluate the Girders using Shored Construction We will review the moment diagram to verify that the user defined loads that simulate the
ect “Slab”, “Haunch”, “User DC”, and “DC” loads
The incremental DC moment diagram mimics that of a three span continuous span. The DC moment is considerablywithout the shoring towers.
Create a specification check report
Upon review of the service level stress checks, we see that the use of touch shoring has reduced the final service levelchecks do not pass, this is ok since we are focusing on reducing flexural stresses in this tutorial).
Further evaluation of exterior girders should be performed to ensure that they are also adequate.
Conclusion These girders can be used level stresses within acceptable limitsfeatures available in PGSuper scenarios quick and easy.
Customizing PGSuperPGSuper Professional has an advanced software architecture that allows third parties to extend and enhance its capabilities. At BridgeSight Software, we can add new analysis capabilities to meet your needs. For details, contact us at
BridgeSight Inc P.O. Box 19172
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The incremental DC moment diagram mimics that of a three span continuous span. The ly less than the simple span “Slab” + “Haunch” moment
towers.
Create a specification check report for Girder B using the same steps as described
Upon review of the service level stress checks, we see that the use of touch shoring has reduced the final service level stresses to acceptable levels (NOTE: Other specification checks do not pass, this is ok since we are focusing on reducing flexural stresses in this
Further evaluation of exterior girders should be performed to ensure that they are also
hese girders can be used in the new bridge structure. However, to keep the final service level stresses within acceptable limits, touch shoring must be utilized. The advanced features available in PGSuper Professional make modeling these complex constructi
Customizing PGSuper Professional has an advanced software architecture that allows third parties to
extend and enhance its capabilities. At BridgeSight Software, we can add new analysis your needs. For details, contact us at
The incremental DC moment diagram mimics that of a three span continuous span. The less than the simple span “Slab” + “Haunch” moment
using the same steps as described above.
Upon review of the service level stress checks, we see that the use of touch shoring has : Other specification
checks do not pass, this is ok since we are focusing on reducing flexural stresses in this
Further evaluation of exterior girders should be performed to ensure that they are also
o keep the final service The advanced
make modeling these complex construction
has an advanced software architecture that allows third parties to extend and enhance its capabilities. At BridgeSight Software, we can add new analysis
