Form ProjStat (Rev. 5/2013)

(RTI)

Research Project Statement 18-60
FY 2018 Annual Program
Title: / Strut-and-Tie Modeling and Design of Drilled Shaft Footings
The Problem: / Drilled shaft foundations are commonly used to support bridge structures. When a group of drilled shafts are used to support a bridge column, a deep footing is required to distribute the loads from the column to the shafts. These footings behave as D-regions, in which plane sections not do not remain plane after deformation. As such, their behavior is better represented by strut-and-tie models (STM) than by sectional analysis. AASHTO LRFD Bridge Design Specifications encourage using STM to design drilled shaft footings and other deep members. Furthermore, they place an increased emphasis on design by STM in their 8th edition to be published in mid-2017. The STM design provisions in the AASHTO LRFD Bridge Design Specifications were originally developed and validated for planar two-dimensional (2D) elements, such as bent caps. The application of these provisions to three-dimensional (3D) elements like shaft footings presents some difficulties related to the definition of the distribution of forces in the model and the strength limits for concrete. For example, current provisions do not account for the increase of strength in the concrete struts and nodes due to confinement effects resulting from the 3D loading conditions. There are also ambiguities in the reinforcement details required by the STM method for drilled shaft footings, such as the required embedment length of column and shaft reinforcing bars in the footing. Research is needed to extend STM provisions to 3D members.
Technical
Objectives: / This research will develop and validate STM procedures and detailing recommendations for drilled shaft footings. The researchers will conduct the following tasks:
  1. Laboratory testing of large-scale drilled shaft footing specimens subjected to 3D loading conditions. Several tests will be conducted to evaluate the effects of different geometries, loading conditions and reinforcing details.
  2. Finite element modeling of drilled shaft footings to complement the experimental study. The numerical models will be validated with test results and will be used to investigate the flow of forces in the footing.
  3. Development of improved STM procedures for 3D members based on the experimental and analytical results.

Desired
Deliverables: /
  1. Technical memorandum for each task completed.
  2. Monthly progress reports.
  3. Value of Research (VoR) that includes both qualitative and economic benefits.
  4. Research report documenting the results of the experimental testing and analytical modeling..
  5. Project Summary Report.
  6. Guidelines for strut-and-tie modeling and design of drilled shaft footings, including a set of examples.

Proposal
Requirements: /
  1. Utilize the deliverable based templates (see the appendices provided or in the University Handbook)
  2. Proposals will be considered non-responsive and will not be accepted for technical evaluation if they are not received by the deadline or do not meet the requirements stated in RTI’s University Handbook.
  3. Proposals should be submitted in PDF format, 1 PDF file per proposal. File name should include project name and university abbreviation.

Pre-Proposal Meeting Information: / Monday, March 27, 2017 1:00 – 3:00PM
Austin Riverside Campus
118 E. Riverside Dr.
RTI Conference Room, 1st Floor
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Notifying RTI of Intent to Propose: / In order to be notified if additional project information is distributed by TxDOT, you must contact RTI, at (512) 416-4730 or by April 3, 2017, if you plan to propose.
Proposal
Deadline: / Proposals are due to RTI by 4:00 p.m. Central Time, May 11, 2017. Email submissions should be sent to .

Project Statement 18-60