Shop Drawings - Research Project 5197 Implementation
Release Strength Reduction
Revisions
(5/12/2009 - Original)
9/11/2009 - TBPE optional design sealing requirements
10/1/2010 - utilizing the .65 release factor in design instead of
fabrication
Design Engineers, Shop Plan Reviewers, and Fabricators:
Findings from TxDOT Research Project 5197 “Allowable Design Release
Stresses for Prestressed Concrete Beams” were originally implemented
in May 2009. The research allowed us to reduce the release strength
in prestressed concrete beams using a 0.65 compressive release
factor instead of the historical 0.60 factor. The primary reason for
this research was to reduce prestressed beam predisposition to
ASR/DEF damage by lowering design release strengths. This, in turn,
reduced the Portland cement content in the concrete mixes while
maintaining production efficiency.
In the year since implementation,
average design release strengths have decreased, and fabricators
utilized the release strength reduction optional design. However, in
September 2009, the Texas Board of Professional Engineers provided
an advisory ruling requiring that all optional design details be
signed and sealed by a registered professional engineer. This ruling
added cost to most fabricators' operations and hindered continued
implementation.
TxDOT's prestressed beam design programs are now
capable of incorporating the new release factor. In order to
implement the research more completely and consistently, TxDOT is
implementing the following changes:
- Bridge design engineers will use the .65 design release factor in
the design of all prestressed concrete beams on projects designed
after October 1, 2010, in place of the existing .60 factor.
- On all beam designs that incorporate the .65 design release factor,
designers will add a note to all beam design sheets (IBNS, IBND,
UBND, etc.), lower right hand corner above the title block, stating:
“All beams designed using a compressive design release strength
factor = 0.65. Release strengths shown may NOT be further reduced
using 5197 criteria in optional designs.” Place a bold rectangular
border around this note.
- Designers will target 5,500 psi as their design release strength
maximum. Under extreme circumstances where the span length or beam
spacing can not be reduced for reasons of practicality, design
release strength shall not exceed 6,000 psi.
- For projects that have plan sets completed, fabricators should
continue to submit optional designs utilizing the May 2009
implementation notice for all release strengths greater than 4,350
psi. (See “Interim Optional Design Release Strength Reduction
Methods” below.)
- Fabricators will not utilize 5197 criteria in optional designs to
reduce release strengths when the above note is present on contract
plan beam design sheets. Exercise caution when contemplating a
reduction on all projects let after September 2010, even if the note
is not present. Contact the designer to verify the release strength
factor used in these designs before submitting shop plans with
release strength reducing optional designs.
- Fabricators may obtain copies of the PSTRS14 Version 5.1 (and later)
program to aid in performing conventional optional designs using the
0.65 release strength factor to reduce release strengths on eligible
projects in lieu of utilizing the previously approved 5197 reduction
factor.
- For shop plans submitted for projects designed prior to October 2010
and using the 0.60 release factor, shop plan reviewers may reject
shop plans that do not employ either of the 5197 release strength
reduction options (7.7% straight reduction option, or the
conventional optional design using the .65 compressive release
factor) when contract plan release strengths exceed 5,500 psi.
For additional information concerning prestressed beam design
programs and the usage of the new design release factor, or for
other related questions or comments, please email
BRG-ShopPlanHelp@txdot.gov.
See the
Superstructure Design Information page for additional ASR
discussion. Under "General Recommendations," scroll down to "Prestressed
Concrete Design."
Interim Optional Design Release Strength Reduction Methods
For contract plans containing prestressed concrete beam designs
utilizing the old .60 release factor (i.e., designed before
10/1/2010, and do not have the .65 factor usage note on the beam
design sheets), fabricators “may” (mandatory usage if design release
strengths are greater than 5500 psi) employ one of two available
methods for reducing release strengths. Both methods utilize
versions of the current optional design submittal process. Note:
confirm the actual design release factor used by contacting the
designer before using either of the following reduction methods.
Method 1
“Modified” Optional Designs
(straight 7.7% release strength reduction)
- Contract plan required release strengths may be reduced by
multiplying them by the ratio of .60/.65 (= 7.7% reduction),
provided that the fabricator also increases the required final
strength by 500 psi over what is called for in the contract plans
for that beam.
- If the application of the reduction factor would drop the required
release strength to below 4000 psi, the release strength defaults to
4000 psi. 4000 psi is the minimum release strength.
- A sealed Prstrs14 analysis run is not required as supporting proof.
However, all affected shop plan details sheets must be sealed,
signed and dated by an engineer licensed in Texas. (accompanied by
the registered firm name and number)
Shop Plan Handling
Fabricator:
- Send the complete set of shop plans to the reviewer as identified by
the District. For any “modified” optional designs, also do the
following:
- Flag the release and final concrete strengths and add this note:
“The release strength shown in this submittal includes up to a 7.7%
reduction of the contract plan value, and the contract plan final
strength has been increased by 500 psi, per agreement with TxDOT in
accordance with Research Project 5197 findings.” Clearly note both
the beam index sheet(s) and the fabrication details sheet(s).
- Seal, sign, and date all affected shop plan details sheets. (index
and fabrication detail sheets)
- Note at the top of the email body that this submittal contains
“modified” optional design(s) based on Research Project 5197
findings, and to contact Jeff Cotham at 512-416-2187 or
BRG-5197Issues@txdot.gov if there are any questions as to the basis
for the concrete strength revisions, or for shop plan handling
guidance.
- “CC” BRG-5197Issues@txdot.gov on these types of submittals for the
purpose of documenting 5197 implementation.
- Include any “modified” optional designs in the “No. “O.D.s”:” value
indicated in the email body.
Reviewer:
Example Release Strength Reduction/Final Strength Increase:
Contract
plan requirement for a beam~ Release = 6100psi, 28 day = 8200psi.
Modified” Optional Design~ Release = .6/.65 x 6100 = 5631psi, 28
day = 8200 + 500 = 8700psi.
Method 2
“Conventional” Optional Designs
(re-designing the beams using Prstrs14 Version 5.1 or later , or
PGSuper, and utilizing the new .65 release factor
- After the release of Prstrs14 Version 5.1, and in lieu of Method 1,
fabricators may submit conventional optional designs using Prstrs14
Version 5.1 (or later version) or a TxDOT approved version of
PGSuper and a .65 release factor, on all contract plan designs where
required release strengths are greater than 4000 psi.
- 4000 psi is the minimum release strength.
- All optional designs must be sealed by a registered professional
engineer.
- All shop plan sheets affected by the optional design(s) must
likewise be sealed, signed, and dated. (index and fabrication detail
sheets)
- Optionally include the Prstrs14 input file with the shop plan
submittal to speed the processing of the submittal.
Shop Plan Handling
Fabricator:
- Submit in accordance with typical optional design methods per the
Guide to Electronic Shop Drawing Submittal.
- For all optional designs, flag the release and final concrete
strengths and add this note: “This optional design includes the use
of a .65 release factor per agreement with TxDOT in accordance with
Research Project 5197 findings.” Clearly note both the beam index
sheet(s) and the fabrication details sheet(s).
- Seal, sign, and date all affected shop plan details sheets. (index
and fabrication detail sheets)
- Note at the top of the email body that this submittal contains
optional design(s) based on Research Project 5197 findings, and to
contact Jeff Cotham at 512-416-2187 or
BRG-5197Issues@txdot.gov, if
there are any questions as to the basis for the release factor used,
or for shop plan handling guidance.
- "CC”
BRG-5197Issues@txdot.gov on these types of submittals for the
purpose of documenting 5197 implementation.
Reviewer:
- Review the optional design(s) in accordance with the 5197
implementation instructions in this document.
- Use Prstrs14 Version 5.1 (or later version), or a TxDOT approved
version of PGSuper to verify the concrete strengths noted in the
optional designs.
- Process in accordance with the
Guide to Electronic Shop Drawing
Submittal.
Comments:
- In some cases, a conventional optional design (Method 2) using a .65
release factor will provide a release strength that is less than
that provided by the Method 1 7.7% reduction, and there is no
associated final strength increase provision when using Method 2.
- The entire set of
5197 research reports are available for review. Of
the four reports, 5197-4 is the most germane to this implementation.
More Information
Shop Plan Drawings
125 East 11th Street . Austin, Texas 78701 
