Link to Report : Comming Soon.
Background :
The continuity of steel girders in a multi-span bridge system is achieved by splicing girders at locations where moment demand is lower (between 1/3 or 1/4 of span length). For a conventional construction sequence of a continuous steel bridge system, the deck is cast in place after the launching of the steel girders. An alternative to this conventional construction is the simple for dead load and continuous for live load (SDCL) system. In the SDCL steel bridge system, girders are placed over supports (abutments and intermediate piers). The girders are connected to the adjacent girders using a concrete diaphragm so that the girders behave simply supported under dead loads and become continuous under superimposed dead and live loads after hardening the concrete diaphragm. SDCL steel bridge system can be constructed using conventional methods where the deck is cast-in-place; however, the system’s merits can be embraced by using precast deck panels or a modular approach for accelerated bridge construction (ABC) applications.
Most in-service steel bridges develop corrosion problems due to leakage at joints, increasing uncertainty regarding their structural performance. Also, during the periodic inspection of steel bridges, special emphasis is given to connection elements (such as splices), which increase the cost and time of these inspections. For SDCL systems, the connection between the girders and the intermediate pier (the diaphragm) encases and protects the end of the steel girders, thus resulting in improved service life. Furthermore, using an SDCL steel bridge system eliminates the field splices and the deployment of additional cranes and shoring. This results in a reduced impact on intersecting traffic.
Objectives :
The objective of this project is to provide a new SDCL connection made primarily of UHPC, reducing complexities associated with rebar detailing and construction of SDCL connections made of normal-strength cast-in-place concrete alone. A connection detail using NSC consists of a girder-end detail with an endplate and steel blocks at the end of the bottom flange, as well as additional longitudinal reinforcement in the deck. The deck reinforcement should be hooked in ABC applications to develop inside the diaphragm. Furthermore, the NSC diaphragm is required to be reinforced with steel bars. The steel blocks at the end of the bottom flange are placed to create continuity and transfer the compression forces in the flange. The steel block of girders from adjacent spans must touch each other or be welded together to prevent crushing in the concrete diaphragm.
Scope :
Task 1 – Literature Review and Synthesis.
The research team will conduct a comprehensive literature review with a focus on the uses of SDCL using NSC. The review will cover traditional detailing of connections, testing methodologies, finite element modeling, and performance predictions using simplified expressions.
Task 2 – Large-Scale Testing.
The configuration and specimen for this study are modeled after previous experiments on the SDCL steel bridge system utilizing cast-in-place normal strength concrete (NSC) for the diaphragm, led by Dr. Azizinamini at the University of Nebraska–Lincoln. Unlike the previous work, the specimen will be tested in an inverted configuration, with loading applied at mid-span to replicate gravity-type loading. The specimen features a 7.5-in. thick concrete deck and employs W40X215 rolled I-girders positioned 2.5 in. above the NSC surface to prevent NSC crushing at the pier location. The required gap between adjacent girders is 5 in., significantly less than the 8-in. gap employed in the SDCL connections using NSC diaphragms. The longitudinal reinforcement in the deck is identical to those of the SDCL connection with NSC, featuring #5 bars at 12 in. on center in the top layer and #4 bars at 12 in. on center in the bottom layer, without additional longitudinal continuity reinforcement.
The cyclic test serves as a proof-of-concept to evaluate whether the proposed UHPC detail meets the required design criteria against cyclic loading expected throughout the bridge’s lifespan. Over its 100-year expected lifespan, bridge structures are anticipated to withstand more than 180 million cycles of axle loads from vehicular traffic. Replicating such extensive load repetitions in a laboratory setting is not practical. Therefore, increasing the load magnitude is imperative to reduce the number of required cycles. The methodology for increasing the load magnitude will be adopted here and detailed elsewhere. The cyclic testing in this study will employ a similar methodology, applying a cyclic load of 104 kips over 2 million cycles to evaluate the performance of the UHPC connection against repeated vehicular loads throughout its design life. Following the cyclic testing phase, the specimen will undergo ultimate flexural testing to determine the ultimate capacity of the connection and identify the governing failure modes.
Task 3 – Finite Element Modeling.
Finite element modeling and analysis will be performed using commercially available finite element software to simulate the structural behavior of the tested specimens. The analysis will incorporate both the experimental data obtained in this research and the reference testing conducted by Floyd et al. to ensure a comprehensive evaluation. Additionally, to establish a comparative baseline, reference connections utilizing normal-strength concrete (NSC) will be modeled under similar conditions. This approach will facilitate an in-depth assessment of the performance differences between the newly developed connections and traditional NSC connections, providing testing-based recommendations into their structural efficiency and performance.
Task 4 – Final Report.
A final report will be presented that will thoroughly outline the results and the testing and analysis of the previous tasks. Quarterly reports will also be submitted, meeting the timeline presented in the Gant chart.
Research Team :
Principal Investigator : Fray F. Pozo-Lora, Ph.D.
Co-Principal Investigator : Atorod Azizinamini, Ph.D., P.E.