The focus of this NEESR payload project is to accurately model and control plastic hinging locations in concrete bridge structures through an investigation of actual hinging behavior in large-scale testing of bridge systems subjected to multiple excitations that includes the effects of joint and foundation flexibility.
Models that are created to represent the hinging behavior in reinforced concrete systems, and the resulting understanding of this behavior under different loading conditions, have traditionally been limited by the ability to validate the model with experimental data - either from pre-existing bridge structures with inadequate access to internal reinforcement, or from component tests that are unable to simulate realistic boundary conditions.
The validation of these detailed models is now possible with the data that will be collected during the NEESR investigation of the seismic performance of four-span large-scale bridge systems, which includes the soil-foundation-structure interaction effects at the footings and abutments at the NEES site at the University of Nevada, Reno (NSF Award #0420347).
The proposed research will be conducted in two parts:
This study will use the NEESR-0420347 setup to validate the use of shape memory alloy (SMA) recentering devices in multi-span bridges. Shape memory alloys are a class of unique alloys that have the ability to undergo large displacements, and revert back to their original undeformed configuration (see figure 1) via a martensitic transformation.
Previous work by the PI has focused on the optimization of the properties of the alloys such that they can be used in seismic applications. The results of previous component testing and analytical work will be validated by designing, developing, and testing innovative SMA devices on the four-span bridge built at the University of Nevada, Reno Laboratory.
Two sets of devices will be developed and tested (at the locations shown in Figure 2) including:
Large-scale validation, as provided by this study, is the first step towards the acceptance of a new class of materials for seismic retrofit of bridges. The experimental tests will be coupled with analytical studies using OPENSEES to determine the optimal properties of the devices. Results from the analytical models will be used in development of bridge fragility curves to illustrate the viability of these SMA recentering devices in typical bridges.
The objective for the proposed payload project is to use distributed fiber optic sensors for structural health monitoring of the full scale bridges that are currently being tested at the University of Nevada, Reno shake table facility.
The proposed payload project will be conducted in conjunction with the current NEESR project, under the direction of Professor Saiidi, titled "Seismic Performance of Bridge Systems with Conventional and Innovative Design."
The NEESR project makes use of the large-scale shake table systems at the NSF NEES site to develop detailed understanding of bridge seismic performance of multi-span bridge models. The testing program encompasses single and two-column bents as well as full-scale bridges.
The objective for the proposed payload project is to use two different types of distributed fiber optic sensor systems for real-time health monitoring during seismic activities and for post seismic evaluation of beam column joints, abutments, and slab spans. The sensor response will be analyzed to examine the various design issues related to bridges supported on drop cap bents.
The proposed distributed sensory system will be effective in development of deterministic tools for assessment of damage and verification of analysis schemes and design parameters. The serially multiplexed fiber Bragg grating sensors will be used for measurement of dynamic response and real time detection of damage. Fiber optic long gauge distributed sensors will be used for post seismic damage assessment and safety following of an earthquake.
The bridge models currently being tested at the University of Nevada, Reno include conventional reinforced concrete columns, concrete-filled fiber reinforced composite tubes as well as innovative damage-reducing materials that are being used in the locations where plastic hinges develop. The post hazard evaluation aspect of the distributed sensor system will be an important aspect of the project providing a deterministic tool for assessing the health and safety of bridges following seismic events.`
The NEES@University of Nevada, Reno equipment site is funded in part by the Geoge E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Program of the National Earthquake Hazards Reduction Program (NEHRP) of the National Science Foundation (NSF) under Award Number CMMI-0927178.