Ground Penetrating Radar Data Processing for Concrete Bridge Deck Evaluation
Presented By: Sepehr Pashoutani
Affiliation: University of Nebraska - Lincoln
Description: This work presents a procedure of Ground Penetrating Radar (GPR) data processing for concrete bridge deck evaluation. GPR signals are analyzed in the depth range from concrete surface to top reinforcement mat. Although most GPR analysis methods focus on attenuation of signals from rebar reflection only, the proposed algorithms analyze three types of parameters from GPR scans: direct wave amplitude, wave velocity in concrete cover depth, and normalized GPR signal amplitude from rebar reflections. These parameters provide information of bridge deck deterioration conditions at different depths. First, the signal reflection amplitude of the direct wave is analyzed over the entire bridge. Second, the wave velocity in cover concrete is obtained through migration of rebar reflections. Third, signal attenuation in concrete is calculated from the rebar reflection and further corrected by two way travel time. In addition, the true zero time for GPR signal analysis is validated by numerical simulation and experimental data. In the end, this algorithm is demonstrated on field testing data, and the final results are presented in the forms of direct wave amplitude, wave velocity, and attenuation maps and quantitative comparison is performed on the results between the three parameters.
Large-Scale Testing of a Lightly Reinforced Concrete Wall and Proposed FRP Retrofit Approach
Presented By: Anahid Behrouzi
Affiliation: California Polytechnic State University - San Luis
Description: The L.A. Ordinance 183893 and C.A. Senate Bill 1953 have motivated building owners to begin addressing deficiencies in over 3,000 pre-1980s non-ductile concrete buildings in the state, many of which employ structural walls. Thus, engineers are faced with designing economical, non-invasive, and effective retrofits to improve wall ductility. The objective of the wall test discussed in this presentation is to investigate the seismic behavior of a characteristic pre-1980s slender reinforced concrete shear wall that is lightly reinforced and has no confinement in the wall ends, expected to have a non-ductile failure due to concrete crushing or buckling in the compression zone. Understanding the failure was important as this wall design would be utilized to test a retrofit involving confinement of the boundary element
region with fiber reinforced polymer (FRP) sheets and splay-anchors. The observed damage of the baseline wall included few, wide flexural cracks at the base of the wall and the locations of horizontal reinforcement. Concrete crushing occurred in the compression zone region at wall base and the crack plane at the first level of horizontal reinforcement. With increasing drift demand, base rotation/rocking of the wall became significant and a number of vertical rebar fractured at the wall base. Both the global drift capacity and the base
rotation of the wall were significantly greater than anticipated for this wall. Therefore, this presentation will examine the variation between observed and predicted performance, as well as the implication this has on proceeding with the wall design and proposed FRP retrofit approach.
Experimental Investigation of High-Strength Reinforcing Bars in Shear-Friction Applications
Presented By: Ahmed Alimran
Affiliation: Purdue University - West Lafayette
Description: In reinforced concrete, shear transfers across a plane defined by a crack or a cold joint through the shearfriction mechanism. Currently, the yield strength of reinforcing bars that cross the shear plane is limited to 60 ksi in the shear-friction design equations of US codes (ACI 318 and AASHTO LRFD). Because of the limited number of past shear-friction tests on specimens with high-strength reinforcing bars (HSRB), the benefits, if any, of using HSRB in shear-friction applications are unclear. Additional tests are needed to draw conclusions on the influence of HSRB on shear-friction strength and behavior prior to revising US design codes.
As part of an ongoing project, 12 large push-off specimens (see figure) were tested to investigate the effects of HSRB on shear-friction performance. The specimens incorporated varying reinforcement yield strengths (ASTM A615 Grade 60 and Grade 100), bar sizes (No. 4 and No. 5), and interface conditions (roughened, smooth, and keyed). All specimens had a 16-in. by 14-in. interface and a consistent reinforcement ratio. For the push-off specimens with a rough interface, it was observed that specimens with HSRB had higher capacities that the specimens with Grade 60 reinforcement. However, a similar trend was not observed for
the other interfaces when HSRB was used. Overall, the test results indicated that specimens with a rough interface had the highest load carrying capacities, followed by specimens with a shear-key interface. The presentation will include a summary of the experimental results to-date and the plans for the remainder of the project.
Seismic Performance Design Criteria for Bridge Bent Plastic Hinge Regions
Presented By: A K M Golam Murtuz
Affiliation: Portland State University
Description: The main objective of this ongoing research is to quantify the material strain limits to be used for seismic assessment of existing sub-standard reinforced concrete bridge bents considering
operational performance design criteria. Limited confidence exists in the current material strain limit state for operational performance criteria due to lack of experimental results considering the typical detailing of Oregon bridges and the cumulative damage effect resulting from an anticipated long-duration Cascadia Subduction Zone (CSZ) event. Component details for bridge bents such as geometry and reinforcing detail were determined through a statistical analysis of available bridge drawings built before 1990 in the State of Oregon. Three full-scale bridge column-foundation subassembly specimens were constructed and subjected to reverse cyclic lateral loading following CSZ and conventional laboratory loading protocols. The unique experimental setup allowed simulating the variation in axial loading due to secondary effects in the column during testing. Material strains along with global and local deformation quantities were measured with a suite of external and internal sensors mounted to the specimens. Despite having sub-standard seismic detailing, all three specimens showed ductile behavior under reverse cyclic lateral loading by achieving a minimum displacement ductility of 8.0. Foundation uplift was observed during testing and it was concluded to have impacted the displacement ductility achieved by the test specimens.
The obtained results suggest that the material strain limits currently used for design in Oregon should be revised to ensure operational performance criteria.
Testing a Full-Scale Reinforced Concrete Bridge Deck with GFRP and Steel Reinforcement using a New Rolling Load Simulator (ROLLS)
Presented By: Laura Tauskela
Affiliation: Queen's University
Description: A study is underway to investigate the fatigue behavior of a slab-on-girder bridge deck tested using a unique full-scale Rolling Load Simulator (ROLLS). This novel testing apparatus is capable of simulating full-size truck tire loads and is the first of its kind in Canada and likely one of very few in the world. The overall dimensions of the concrete deck are 15.24 m x 3.89 m x 0.21 m and the spacing of the steel girders is 3.05 m. The deck is conceptually divided into four sections based on reinforcement type and loading plan. The reinforcement types consist of conventional steel rebar, glass fiber reinforced polymer (GFRP) bars, and a
novel system of GFRP stay-in-place formwork. The first three sections are subjected to three million cycles of rolling loads using ROLLS. A fourth section with GFRP bar reinforcement is subjected to three million cycles of static pulsating loads using a hydraulic actuator at the same load level and frequency as the rolling loads. At various cycling milestones, monotonic load tests are performed to monitor the stiffness degradation. The literature suggests that
rolling loads provide a more critical loading case in terms of the fatigue life of a bridge deck. As well, GFRP bars have been shown to increase the fatigue life of bridge decks compared with conventional steel reinforcement. This study will allow for an improved understanding of the fatigue damage, mechanical degradation and cracking mechanisms of a full-scale reinforced concrete bridge deck under realistic load conditions.
Fatigue Behaviour of Reinforced Concrete Beams Rehabilitated using Sustainable Ultra High Performance Concrete Strips
Presented By: Ganesh P
Affiliation: Acsir - Academy of Scientific & Innovative Researc
Description: Ultra-high performance concrete (UHPC) turns out to be an effective candidate for the strengthening of damaged reinforced concrete (RC) beams, especially structures like bridges and high rise buildings. However, the cement dosage of UHPC is generally in a range of 800-1100 kg/m3, which is an environmental burden due to surplus CO2 emission. In view of this, sustainable UHPC mix was developed by replacing cement by ground granulated blast-furnace slag (GGBS) of about 40% as an alternative strengthening material. There is a need to study the fatigue behaviour of these structures in addition to monotonic loading as
most of them are subjected to traffic and wind loads. This paper presents the experimental and numerical studies to determine flexural fatigue response of RC beams rehabilitated with sustainable UHPC. UHPC strips thickness of 5, 10, and 15 mm were considered to rehabilitate the RC beams. Beams were preloaded under static loading about 60 and 80% of the maximum load of control beams and then tested under fatigue loading with stress ratio of 0.1 and frequency of 2 Hz. It was found that the damaged RC beams can be successfully rehabilitated by using a thin precast (5 mm) sustainable UHPC strip. Delamination of strip
was not observed in any of the rehabilitated beams. A finite element model was developed to predict the load-deflection behaviour and number of cycles to failure of the rehabilitated beams. It can be concluded that sustainable UHPC is an excellent prospective candidate for the rehabilitation of damaged RC flexural elements.
Estimating Strains in Deep Beams Using Measured Cracking Information
Presented By: Jarrod Zaborac
Affiliation: University of Texas Austin
Description: One of the most common benchmarks for the assessment of in-service reinforced concrete
structures is measured cracking information, such as crack width or spacing. These measurements are typically compared to preestablished limits, and structural elements are then sorted into qualitative condition states (e.g., “good” or “severe”). While these methods are useful for tracking damage progression, they neglect important influential factors that affect cracking behavior. Reinforcement detailing is one such factor. For the fact that many aged structures requiring assessment are not compliant with modern detailing standards, it is important to understand the influence that out-of-date reinforcement detailing may have on the structural assessment of existing structures. Ongoing research at the University of Texas at Austin has sought to develop procedures for assessing shear-distressed reinforced concrete beams using measured cracking information. Most recently, ten deep beams (i.e., shear-span-to-depth ratios less than approximately 2.0) with various levels of crack control reinforcement were tested. The crack patterns and widths were extensively documented over several load levels; furthermore, markers were mounted in a grid on one side of each beam and marker displacements were recorded during the tests. It is envisioned that by using the measured displacement field to estimate total strains, as shown in Figure 1, in combination with the measured cracking information, that a more effective method for correlating measured cracking information to in-service strains can be developed.
Enhanced Imaging of Structural Concrete Through Data Fusion of Ultrasonic and Radar Signals
Presented By: Sina Mehdinia
Affiliation: Portland State University
Description: There are many critical concrete structures in the world which require maintenance. Reliable and accurate tools to determine the integrity of concrete structures are critical, particularly in the context of postearthquake damage assessment. The objective of this ongoing research is to leverage the latest research in medical imaging and advanced data analytics to enhance the imaging of structural concrete. In this research, several concrete specimens with different features and geometries were built and analyzed. Signals from these specimens were collected with a hand-held 2.7 GHz ground penetrating radar instrument and an ultrasonic array with 24 shear transducers. In a first step, the instrument’s signal attenuation and radiation patterns were characterized by an experimental setup. Afterwards, some preprocessing methods such as direct wave removal are implemented and a synthetic aperture focusing technique (SAFT) approach was used to compute and reconstruct images. Moreover, parameter optimizations and image fusion techniques are investigated to obtain the highest resolution. In this presentation, an overview of the methodology is presented, and some preliminary results of fused images are discussed. Finally, the ultimate goal of this research is to automate and quantify damage assessment of structural concrete using novel procedures and algorithms.