Link to Report: Coming Soon
Background :
Limited techniques are available to accelerate construction of bridge substructures. Previous research was conducted by the research team on innovative hollow-core FRP-concrete-steel (HC-FCS) bridge columns consisting of an ultra-high performance concrete (UHPC) or self-consolidating concrete (SCC) core sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The results of these previous projects indicated the proposed column design had significant potential, but lingering questions remained about the possibility of eliminating the FRP outer shell and relying on UHPC to provide required confinement of the steel tube and durability of the overall column. The proposed project will build on the results of the previously funded projects on HC-FCS columns sponsored by the Oklahoma Department of Transportation (ODOT) and ABC-UTC to extend to UHPC-steel (HC-US) columns and to examine unanswered questions relative to column composition, UHPC thickness, and column-footing connection. The project will consist of experimental testing of four approximately half-scale column and footing specimens with variation in steel wall thickness and column to footing connection type. Results from the proposed research will provide an improved basis for comparison with completed finite element modeling and for subsequent design guidelines, thereby increasing the likelihood of implementation. The final report will include a section with guidance for design and construction of the proposed HC-US columns. These guidelines will include equations to determine steel thickness, UHPC thickness, footing and girder embedment depths, and nominal flexural and shear strengths of HC-US columns.
Objectives :
The overarching goal of this research study is to implement hollow-core UHPC-steel (HC-US) columns for accelerated bridge construction. The objectives necessary to achieve that goal include:
- Experimentally evaluate the strength of HC-US column designs and compare to previous project results for hollow-core FRP-concrete-steel (HC-FCS) columns.
- Experimentally evaluate the capacity of a UHPC socketed connection for an HC-US column.
- Modify design procedures for HC-FCS columns to be applicable to HC-US columns.
Scope :
Task 1 – Design and Construct Half-Scale HC-US Columns
Four (4) half-scale HC-US columns will be designed and constructed having different steel thickness, UHPC wall thicknesses, and monolithic vs socketed connection. The initial column design parameters will be based on the results of previous testing by the research team (Volz et al. 2024). Figure 1 shows the dimensions of the column specimen that will be used in this project. Baseline dimensions will be modified to include one increased steel wall thickness and one reduced UHPC wall thickness. The steel tubes will be fabricated from ASTM A500, Grade B or Grade C structural steel. Three of these columns will be connected monolithically to the footing and one will be precast consisting of only the steel tube and UHPC outer wall with a portion of the steel tube exposed to connect with the UHPC socket.
Figure 1. Half-Scale Column Specimen General Dimensions
Task 2 – Construct UHPC Socketed Connection
A socket will be cast into one of the footings for the HC-US columns constructed in Task 1 using a corrugated steel tube similar to that shown in Figure 2. Dimensions of the socket and procedures used for casting the socket will be determined using results of previous testing at OU and recommendations from the literature. The primary consideration will be diameter of the socket relative to the steel tube diameter and resulting UHPC thickness. The precast column constructed in Task 1 will then be connected to the footing using UHPC to fill the socket around the protruding steel tube.
Figure 3. Concrete Socket Made with Corrugated Steel Tube
Task 3 – Test Half-Scale HC-US Columns Under Cyclic Lateral Load and Constant Axial Load
The half-scale HC-US column specimens will be tested under cyclic lateral loading and a constant axial compressive load, as shown in Figure 3. The cyclic loading will be applied in a displacement-controlled manner using a push-pull hydraulic actuator connected to the column loading stub. The loading protocol is based on FEMA Publication FEMA P-2082-1 (2020), which recommends increasing each subsequent displacement amplitude by 40%. The protocol includes two cycles for each specified increment of displacement.
Figure 3. Half-Scale Column Specimen Testing Setup
The axial compressive load will represent 5% to 10% of the nominal axial capacity of the RC control column tested in the previous project (Volz et al. 2024) determined based on the AASHTO LRFD Bridge Design Specifications (2020), which will simulate the dead load acting on a column in an actual bridge structure. The axial load will be applied through a series of tensioned, unbonded, prestressing strands running through a duct located along the central axis of each column and anchored within the loading stub and footing (Prakash, 2010).
Instrumentation for each test will consist of load cells to record the lateral force, wire pots to measure the lateral displacements, and strain gages to measure strain in the steel tubes.
Task 4 – Develop Design Procedures and Recommendations for HC-US Columns
The results of Tasks 1 through 3 combined with the results from previous research will form the basis for modifying the design procedures and recommendations previously developed for HC-FCS columns. These guidelines will include equations to determine steel thickness, UHPC thickness, footing and girder embedment depths, and nominal flexural and shear strengths of HC-US columns.
Task 5 – Document Progress, Results, Recommendations, and Design Guidelines of the Study Through Quarterly Progress Reports and a Final Report
This task involves documenting, reporting, disseminating, and promoting the results of the research and will include quarterly progress reports and a final report. The quarterly progress reports will document the progress of the research. The final report will provide in-depth details and results of the research, as well as guidelines to determine steel and UHPC wall thicknesses, footing and girder embedment depths, and nominal flexural and shear strengths of HC-US columns. A section of the final report will be structured as a step-by-step guide for design and construction of the proposed columns.
Research Team :
Principal Investigator: Royce W. Floyd, Ph.D., P.E., S.E.
Co-Principal Investigator: Jeffery S. Volz, Ph.D., P.E., S.E.