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RESEARCH PROBLEM STATEMENT:
The design protocols used to determine rigid airfield pavement thickness include an assumption that there is stress (load) transfer at the joint equal to 25%. It is also understood that for most of the calendar year the load transfer efficiency is much higher. However, depending upon the season, there may be conditions when the efficiency is lower than the assumed value.
Random field studies have been accomplished at select airports but there has been no intent to use those studies to evaluate the sensitivity of the load transfer efficiency with respect to the variables that directly influence the quantitative value. It is known that some of the variables that influence load transfer efficiency includes subbase support, joint design (plain, tied and dowelled), construction quality, ambient environment and, at some airports, using aircraft.
Understanding the impact of sensitivity of the variables could significantly influence the choice of boundary conditions used for the thickness design of airfield pavements. If the variables that influence load transfer efficiency are documented, it is possible that the selection of the joint transfer efficiency could be introduced into the design protocol at the macro scale.
Several questions need to be answered if the science of load transfer is to be understood.
- What is the genesis of the assumption that a partial transfer of the load at a joint reduces the flexural stress by 25%? What were the variables examined that resulted in the adoption of that value? For the variables examined, is the 25% conservative? What variables used in the development of the current assumption are valid and applicable to pavement design as it exists today?
- How sensitive are the pavement thickness design protocols being used to the assumed load transfer variables? Do the minimum design conditions dictate the thickness requirement? Is it feasible to dictate the use of a “short duration” period of low load transfer for the design?
- Under what conditions is there a difference in load transfer efficiency for a dowelled, tied and a plain contraction joint? On a contraction joint does the depth of saw cut impact the value of the load transfer efficiency?
- Is there an ambient environment regime where load transfer efficiency is nearly constant? Is there an ambient environment when load transfer efficiency has a minimum value? Can ambient environment be a design variable? If so, what are the conditions that must be satisfied before a reasonable value for load transfer can be assigned?
- What are the variables that affect the quantitative value of load transfer efficiency and are those variables equally significant? If not equally significant, what variables can be ignored for the purpose of assigning a value for load transfer?
- Is there a simple technique that can be employed to determine when aircraft gear configuration will significantly influence the quantitative value of load transfer efficiency? Is there sensitivity in the thickness computation that is a result of the interaction between gear configuration, slab curling, slab warping, slab size and load transfer for a given set of variables?
- What metric is best used to define and model joint load transfer when data are collected using a Falling Weight Deflectometer (FWD)? When using the FWD is it necessary to correct for slab bending? What dynamic loading is required to evaluate load transfer efficiency?
The questions must be answered before any conclusion can be made about the magnitude of the value used for load transfer efficiency in design protocols. Field studies of “typical” pavement systems must be accomplished to begin to arrive at answers for the questions.
OBJECTIVES:
- Define those variables that influence the quantitative value of the load transfer efficiency used in concrete pavement design protocols. Accomplish a sensitivity analysis and determine which of the variables directly influence the value and which would be considered as not significant.
- Determine which variables identified in Objective 1 can be measured in the field. Field measurements are to be made using FWD technology and / or other common industry accepted protocols and equipment. Small scale laboratory evaluations for some of the variables may be better options than field measurement. In those cases, define how the laboratory investigation is applicable to field performance of joints.
- Identify those existing airport pavements that have the physical parameters that represent those variables previously identified. Define how the quantitative value of each variable can be determined or measured for the pavements that are accessible for testing. Develop a test plan for each pavement section, coordinate the test plan with the respective airport(s) and obtain approval of the airport to accomplish the test plan.
- Accomplish the first measurement and evaluate the results of the field investigation. Determine if the data represents the case study and if it is applicable to this study. Make test plan corrections as required and accomplish a consecutive series of testing.
- Accomplish analysis of the field data acquired, develop conclusions and make recommendations for implementation of findings as they apply to the design protocol used for airfield pavement thickness determination.
PRODUCTS:
The final product will be an Innovative Pavement Research Foundation (IPRF) report that provides a summary of the results of the investigation. The report will define the variables that influence the quantitative value of load transfer efficiency, which variables can be controlled through the design and construction process and make a recommendation for the use of load transfer as a part of the thickness design protocol for airfield concrete pavement. At the conclusion of the research there should be a document(s) that the engineer, airport owner or constructor can read and gain an understanding of the problem and how to implement design solutions.
An electronic database of the field measurements shall be provided as a deliverable product separate from the written report. The database shall be in a format that can be utilized through the use of conventional database analysis software packages.
The final report will be provided to the IPRF in the form of two originals, in a camera-ready format, including any artwork, graphics or photos. An electronic version of the final report in a format compatible with off-the-shelf desktop computer publication software will also be provided. The investigator will not be responsible for the reproduction and printing of the final document(s), but will assist with minor editing requirements generated by the printing and reproduction process.
RESEARCH TASKS:
The investigator is expected to develop sub-tasks, that when completed, will result in completion of the project within the time and budget available. It is not necessary that the proposal reflect the exact budget or the planned time provided in the advertisement. However, any deviation from the designated resources must be justified and clearly explained as a part of the proposal. The following are the minimum tasks that are considered necessary to complete the project.
Task 1 – Literature Review and Information Gathering.
A. Review existing literature. Provide a summary of any previous research that is applicable to the objectives of this research.
B. Review existing databases and any analysis or interpretation of the database as it may be applied to the objectives of this research. Data is available from instrumented pavement sections at Denver International Airport and full scale test sections that were loaded to failure at the FAA National Airport Pavement Test Facility.
Task 2 - Identify the Variables that Influence the Quantitative Value of Load Transfer Efficiency. The variables, as a minimum, should include ambient environment, subbase support properties, subgrade type, joint type and presence of supplementary load transfer devices. The ambient environment will be sub-divided into northern tier, mid-continent, coastal and arid. Perform a desktop sensitivity analysis of the variables that are identified and determine which of the variables influence the pavement thickness design.
Task 3 - Identify Airports. Locate airfield pavement sections that can be used to measure the variables that are identified in Task 2, e.g., joint opening between winter and summer and impact on load transfer. Coordinate with the airport owner for access to the pavement sections that are to be used to measure the variables. Pavement sections should be selected from taxiways and / or aprons where access is achieved with minimal impact on airport operations. The pavements used for the evaluation shall be those constructed after 1985 that are more than 11-inches in thickness. There will be a minimum of 12 pavement sections used in the study. Develop a test plan for each pavement section (airport) included in the study.
Task 4 – Document a Research Plan and Schedule. Integrate the findings for Tasks 1 through 3 and develop an overview plan that includes visiting the airports identified in Task 3. Define the techniques to be used for measuring the variables and the screening procedures for determining when outliers in the database occur. The anticipated means, methods and actual tests to be employed in the measurement of influence of the variable will be straightforward and direct, i.e., no long term monitoring of installed gages or devices.
Task 5 –Discuss the Concept for the Research. At an on-board meeting with the Technical Panel discuss the findings and recommended protocol that is the result of findings from Tasks 1 through 4. The intent of the protocol is to use field measurement and or laboratory small scale testing to answer those questions that are the subject of this research.
An on-board review will be accomplished. The investigator will not proceed to Task 6 without the written approval of the IPRF. An on-board review must be scheduled at least 30 days prior to the actual meeting. The PI will submit the products produced from Task 1, 2, 3 and 4 for technical panel review 30 days prior to the meeting. The location of the meeting will be coordinated with the IPRF. The PI is responsible for documenting the comments of IPRF Technical Panel members and the disposition of their comments.
Task 6 –Perform Visits to Airports. Visit the airports identified in Task 5 and implement the individual test plans. Accomplish small scale laboratory investigations if any were described. Develop a hypothesis about the influence of the identified variables on the load transfer efficiency based upon the initial measurements. Make corrections to the research plan(s) based upon the observations. Plan a second series of follow up airport visits and measurements.
The Principal Investigator (PI) will submit the results of Task 6 to the IPRF as a report as to the initial findings. The report will include the summary of observations of the study and the lessons learned. The report should include the recommendations for the correction of the research plan, and/or modifications of test protocols, as deemed appropriate. The work on Task 7 will not begin without approval from the IPRF.
An on-board review will be accomplished. The review will be a meeting between the PI and the IPRF Technical Panel. The initial findings report will be provided to the technical panel at least 30 days prior to the meeting. The investigator is expected to present to the technical panel discussion items that will result in policy decisions for critical elements that impact the future of the research. Additional research may be needed to respond to questions that are developed as a result of the on-board review. The Technical Panel will determine, based upon the results presented if the primary research will go forward. The location of the meeting will be coordinated with the IPRF. The PI is responsible for documenting the comments of IPRF technical panel members and the disposition of each comment.
Task 7 – Accomplish a Second Series of Airport Visits. The research team will visit and make measurements at the same airports that were a part of the first visits. Evaluate the data and determine if the measured properties are representative with respect to the first series of measurements. Explain any outliers and / or significant deviation between the two different measurements. Develop recommendations with respect to using load transfer efficiency in future design protocols.
Task 8 – Prepare Draft Final Report. Include in the report the results of Tasks 1 through 7, all artwork, graphical presentations, format, etc. The document shall be in a form that for all intent is complete with the exception of final comments made by the Technical Panel.
An on-board review will be accomplished. The draft final report will be submitted to the IPRF Technical Panel for review. The Technical Panel will have 30-days to perform a desk top review and comment on the report. The report will include a summary of the results of testing and recommendations for future research. The principal investigator is responsible for documenting the comments of the IPRF Technical Panel and the disposition of comments.
Task 9 – Final Report. Make corrections to the document and submit the documents to the IPRF. Assist the IPRF with publication related editing.
PRODUCTS SUMMARY:
- A summary of the literature search, initial review of existing databases, identification of airports and a research plan with time schedule. Submit 6 copies.
- On-board reviews will be accomplished approximately 30-days after submittal of reports. Each report will be report will include the previous submittal. The interim report(s) (6 copies of each) will include a summary of all research completed to date.
- Advanced final report (6 copies) for review.
- A final report (an IPRF Report) that includes recommendations based on the research with all artwork, graphics, tables, pictures, documentation, etc. ready for reproduction and distribution. The report will be submitted as two original documents and one on electronic media. An electronic database that includes the results of field testing will be submitted as a separate deliverable.
SPECIAL REQUIREMENTS:
- The Principal Investigator (PI) will have a working knowledge of airfield concrete pavement design and evaluation. The PI will define, as a part of the proposal, the technique that will be employed to define when the research results describe a reasonable answer after reasonable resources have been expended.
- During the research team visits to airfields, the research team is responsible for coordinating their own arrangements for access to the pavements that are the subject of this study.
- The PI will be responsible for the preparation of quarterly reports that describe the progress of the research effort. Reports are due in the offices of the IPRF on the last day of the fiscal year quarter. The reports will be limited to two pages in a format specified by the IPRF. The first page will be a WORD document describing the progress of the work. The second page will provide a summary of the estimated costs versus the costs incurred to the report date.
SPECIAL CONSIDERATIONS:
After the Technical Panel completes the evaluation of proposals, each of the proposals will be rank ordered. The organization, group, or individual that is ranked as the first and second choice for the recommendation to award may be asked to participate in a telephone interview. The Principal Investigator, and one other person, representing the entity ranked first and second choice by the Technical Panel may be asked to participate in the interview to discuss the project details, goals, and objectives. The interview, if required, will occur within a 45-day window subsequent to the proposal submittal deadline.
IPRF PROCEDURAL GUIDANCE:
Persons preparing proposals are urged to review the following documents to be sure that there is a full understanding of IPRF procedures and requirements. Proposals must be prepared in the format specified in the instruction documents. The proposal will be submitted as one (1) original and 7 copies.
The
documents required to aide in the preparation of the proposal
include:
PDF files require Acrobat Reader to view.
FUNDS
AVAILABLE: $550,000
CONTRACT
TIME: Not to exceed 39 Months
PROJECT
DIRECTOR: Mr. Jim Lafrenz, P.E., (785) 742-6900, (jlafrenz@pavement.com)
ESTIMATED
NOTICE TO PROCEED DATE:June 2, 2008
PROPOSAL
DUE DATE: April 11, 2008 not later than 4:00 P.M. (Central Time)
DELIVERY
INSTRUCTIONS:
Proposals will be delivered to:
Innovative Pavement Research Foundation
Cooperative Programs Office, Attn: Jim Lafrenz
201 Shawnee Street
Hiawatha, KS 66434
Fax: (785) 742-6908
