Browsing by Author "Abbas, Ebrahim K."

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    Corrosion Assessment for Failed Bridge Deck Closure Pour
    Abbas, Ebrahim K. (Virginia Tech, 2011-12-02)
    Corrosion of reinforcing steel in concrete is a significant problem around the world. In the United States, there are approximately 600,000 bridges. From those bridges 24% are considered structurally deficient or functionally obsolete based on the latest, December 2010, statistic from the Federal Highway Administration (FHWA). Mainly, this is due to chloride attack present in deicing salts which causes the reinforcing steel to corrode. Different solutions have been developed and used in practice to delay and prevent corrosion initiation. The purpose of this research is to investigate the influence of corrosion on the failure mechanism that occurred on an Interstate 81 bridge deck. After 17 years in service, a 3ft x3ft closure pour section punched through. It was part of the left wheel path of the south bound right lane of the bridge deck. The bridge deck was replaced in 1992 as part of a bridge rehabilitation project, epoxy coated reinforcement were used as the reinforcing steel. Four slabs from the bridge deck, containing the closure, were removed and transported to the Virginia Tech Structures and Materials Research Laboratory for further evaluation. Also, three lab cast slabs were fabricated as part of the assessment program. Corrosion evaluation and concrete shrinkage characterization were conducted in this research. The corrosion evaluation study included visual observation, clear concrete cover depth, concrete resistivity using single point resistivity, half-cell potential, and linear polarization using the 3LP device. Shrinkage characteristics were conducted on the lab cast slabs only, which consisted of monitoring shrinkage behavior of the specimens for 180 days and comparison of the data with five different shrinkage models. Based on the research results, guidance for assessment of other bridge decks with similar conditions will be constructed to avoid similar types of failures in the future.
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    The Effect of Powder Actuated Fasteners on the Seismic Performance of Protected Zones in Steel Moment Frames
    Eatherton, Matthew R.; Toellner, Bradley W.; Watkins, Charles E.; Abbas, Ebrahim K. (2014-10-08)
    Steel moment resisting frames rely on large inelastic strains in the beam plastic hinge region to dissipate seismic energy during an earthquake and protect the building against collapse. To limit the potential for premature fracture and because of a lack of test data, fasteners, attachments and defects are prohibited in the plastic hinge region, also referred to as the protected zone in the AISC Seismic Provisions. However, unauthorized attachments and defects occur in many buildings in practice. A set of twelve full-scale moment connection tests were conducted to explore the effect of powder actuated fasteners (PAF) and puddle welds on the seismic performance of steel moment connections. Both reduced beam section and extended end plate connections were tested with W24x62 and W36x150 beams. Five specimens included PAF or puddle welds representing typical steel deck attachment to the top flange of the beam. Three of the specimens included PAF in a grid over the top and bottom flange and on the web. All twelve specimens passed the qualification criteria for special moment resisting frames (SMRF) in the AISC Seismic Provisions as they were subjected to a cyclic displacement protocol up to 4% story drift while retaining 80% of their nominal plastic moment capacity. This suggests that moment connections with PAF and puddle welds within the bounds of what was tested, will produce ductile SMRF type seismic performance. Furthermore, PAF and puddle welds were found to have negligible effect on cyclic envelope, moment capacity, energy dissipation and strength degradation prior to fracture.
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    Fatigue Assessment for the Failed Bridge Deck Closure Pour at Mile Marker 43 on I-81
    Rivera, Elias; Abbas, Ebrahim K.; Wright, William J.; Weyers, Richard E.; Roberts-Wollmann, Carin L. (Virginia. Department of Transportation, 2014-04)
    Fatigue of reinforcing steel in concrete bridge decks has not been identified as a common failure mode. Generally, the stress range occurring in reinforcing steel is below the fatigue threshold and infinite fatigue life can be expected. Closure pour joints, however, may be vulnerable to fatigue if some specific design details are present. This research shows that fatigue was a likely contributor to the I-81 closure pour failure. It is much less likely that corrosion directly caused a strength failure but it is very likely that corrosion accelerated the onset of fatigue. The joints in the I-81 deck had vertical joint faces that did not provide any means for shear transfer across the joint. The joints were located under a wheel load path and were located away from beams or other means of deck support. This created atypical conditions where shear forces across the joint due to wheel loads were carried only by the reinforcing steel. The stress range in the reinforcing steel is greatly magnified under this scenario thereby making fatigue a possibility. New closure pour joints can easily be designed to prevent fatigue by providing structural support for both sides of the joint. Existing joints, however, need to be evaluated to determine if fatigue vulnerability exists. Lacking knowledge of the joint internal details, a simple differential deflection test can be performed to detect fatigue vulnerability. If the two sides of the joint are deflecting vertically relative to each other under wheel loads, than fatigue can be considered a possibility. No deflection indicates that fatigue is unlikely.
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    A Low Cycle Fatigue Testing Framework for Evaluating the Effect of Artifacts on the Seismic Behavior of Moment Frames
    Abbas, Ebrahim K. (Virginia Tech, 2015-12-01)
    Structural steel components erected in real buildings include a wide range of artifacts. In this case, the word artifact is used to describe both defects and fasteners that create discontinuities in the steel such as notches, nicks, welds, powder actuated fasteners, self-drilling screws, repaired defects, and others. Although artifacts occur in real structures and their presence may affect the ductility of elements subjected to large inelastic strains, there is a dearth of experimental data on the seismic behavior of structural systems with artifacts. For instance, full-scale testing of moment resisting connections is expensive which makes it economically infeasible to experimentally examine the wide range of possible artifact types, artifact locations, and structural configurations. A framework has been developed for evaluating the effect of artifacts on special moment resisting frame (SMRF) plastic hinge regions using relatively economical coupon tests. Cyclic bend tests and monotonic tension tests on flat plate coupons that include artifacts are used to calibrate fracture parameters for different low cycle fatigue models such as the Cyclic Void Growth Model (CVGM), Stress-Weighted Damage Model (SWDM) and Cyclic Damage Plasticity Model (CDPM) which are then used in conjunction with finite element (FE) models to predict fracture initiation in full-scale SMRF connections. The framework is general and can be applied to many types of artifacts and seismic structural systems. Fracture propagation has been studied also using CDPM for full-scale tests using FE finite element software LS-DYNA. Alternatively, recommendations for future work is proposed for developing a new test setup, studying artifacts sensitivity to material thickness, and a method of demonstrating equivalence for the artifacts.