Vibration Based Damage Detections of Scour in Coastal Bridges

This article appeared in Homeland Security Affairs (April 2012), supplement 4, article 2"The ability to ensure the resiliency and to predict the future performance of coastal bridges is very dependent on identifying damages in critical components of the bridge rapidly after an event. Traditional vibration based damage detection efforts focused mainly on the detection of fatigue cracking. Although detecting fatigue cracking is important, it does not contribute significantly to the total number of bridge failures in the United States. A critical review of the up-to-date literature showed that hydraulic loading, including scour, is responsible for about 50% of the failed bridges. To this end, the primary focus of this project is the development and evaluation of damage features capable of rapidly identifying and quantifying the extent of deterioration of critical coastal bridge structures due to scour at submerged piers following extreme storm events. This paper illustrates the use of the curvature of horizontal mode shapes and introduces the 'Modified Curvature Damage Factor.''

Partial-interaction behaviour of composite steel-concrete bridge beams subjected to fatigue loading / by Rudolf Seracino.

Bibliography: leaves 140-144.xix, 156 leaves : ill. ; 30 cm.Determines the effect of partial-interaction and interfacial friction on the fatigue behaviour of composite bridge beams and develops a set of design rules for the assessment of the residual strength and performance of composite bridge beams.Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 199

Rapid Restoration of Deteriorated Prestressed Concrete Bridges Using Mechanically Fastened Fiber Reinforced Polymer

This presentation introduces a methodology to rapidly address deteriorated prestressed concrete bridge superstructures using prestressed mechanically-fastened fiberreinforced polymer (MF-FRP). Currently, departments of transportation (DOTs) must post load restrictions or closures on bridges with deteriorated prestressed concrete superstructures that can no longer carry original design loads. These posted restrictions and closures result in detours that increase travel time and vehicle operating costs for detoured vehicles, impacting commerce, public transportation, and emergency services. Often, load restrictions and closures must remain in place for several years to allow for budgeting, design, and contracting cycles prior to scheduling and completion of permanent repairs or superstructure replacement which must occur to remove posted restrictions. Therefore, a methodology which is capable of restoring prestress losses and strength reduction in mild to moderately deteriorated prestressed concrete bridge superstructures such that the useful service life of the bridge can be extended for 3 to 5 years while a permanent solution is planned and budgeted is desired. Further, a retrofit solution that can be installed rapidly by DOT maintenance personnel, can immediately restore traffic upon installation, and can be easily inspected and maintained is necessary for successful implementation into existing DOT policies and procedures

Modified Layered-Sectional Analysis for Forensic Investigation

This paper describes a modification to the layered-sectional analysis approach, which provides the engineer with a tool to assess structural behavior of concrete beams with localized damage, a problem not well suited to classical, closed-form solutions. The modified layered-sectional analysis (MLSA) framework is applied to a forensic investigation case study in which two prestressed double-tee beams are exposed to a short duration, intense fire in a parking structure. The results of the MLSA are within 1% of the case study load test, which indicates that the MLSA could be a useful, computationally efficient tool for the investigating engineer to predict the postfire serviceability and strength of damaged beams, and potentially eliminate the need for expensive load testing. A short parametric study is included for the research engineer interested in the MLSA for predicting the postdamage behavior of non-standard materials such as enhanced sustainability concrete (ESC)

Bond behavior of near-surface mounted FRP strips bonded to modern clay brick masonry prisms: influence of strip orientation and compression perpendicular to the strip

In this paper the results of 18 pull tests performed on clay brick masonry prisms strengthened with near-surface mounted carbon fiber-reinforced polymer (CFRP) strips are presented. The pull tests were designed to add to the existing database and investigate variables significant to masonry construction. FRP was bonded to solid clay brick masonry; FRP aligned both perpendicular and parallel to the bed joint; and in the case of FRP reinforcement aligned parallel to the bed joint, compression applied perpendicular to the strip was used to simulate vertical compression load in masonry walls. Results including bond strength, critical bond length, and the local bond-slip relationship are presented as well as a discussion on the effect of the new variables on these results

In-plane shear behavior of masonry panels strengthened with NSM CFRP strips: I: experimental investigation

An experimental investigation was conducted to study the in-plane shear behavior of masonry panels strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer strips (CFRP). As part of the study four unreinforced masonry panels and seven strengthened panels were tested in diagonal tension/shear. Different reinforcement orientations were used including vertical, horizontal, and a combination of both. The effect of nonsymmetric reinforcement was also studied. The results of these tests are presented in this paper, and include the load-displacement behaviors, crack patterns, failure modes, and FRP strains. The results showed that the vertically aligned reinforcement was the most effective, with significant increases in strength and ductility observed. The dowel strength of the vertical reinforcement did not likely contribute significantly to the shear resistance of the masonry. Instead, it was likely that the vertical reinforcement acted in tension to restrain shear induced dilation and restrain sliding. In some panels cracking adjacent to the FRP strip, through the panel thickness was observed. This type of cracking reduced the bond between one side of the FRP strip and the masonry, and led to premature debonding. A comparison of the test results with the results of other tests from the literature is also presented in this paper

In-Plane shear behavior of masonry panels strengthened with NSM CFRP strips: II: finite-element model

A combined experimental and numerical program was conducted to study the in-plane shear behavior of clay brick masonry walls strengthened with near surface mounting carbon-fiber-reinforced polymer (CFRP) strips. This paper is focused on the numerical program. A two-dimensional finite-element (FE) model was used to simulate the behavior of FRP-strengthened wall tests. The masonry was modeled using the micromodeling approach. The FRP was attached to the masonry mesh using the shear bond-slip relationships determined from experimental pull tests. The model was designed in a way so that FRP crossing a sliding crack (perpendicularly) would prevent crack opening, normal to the direction of sliding (dilation), and increase sliding resistance. This sliding resisting mechanism was observed in the experimental tests. The FE model reproduced the key behaviors observed in the experiments, including the load-displacement response, crack development, and FRP reinforcement contribution. The FE model did not include masonry cracking adjacent to the FRP and through the wall thickness (as observed in some experiments). This type of cracking resulted in premature FRP debonding in the experiments. Debonding did not occur in the FE model because this type of masonry cracking was not modeled

Crack Density and Elastic Properties of Sustainable Concretes

This paper examines relationships between changes in the microstructure and selected elastic properties of various concrete mixtures exposed to moderately elevated temperatures. The crack density parameters before and after exposure were estimated from the shear modulus measured wet and dry of 1 in. thick by 4 in. diameter (25 x 100 mm) disks. Mixtures examined included both granitic and lightweight coarse aggregates in combination with cementitious systems containing either 20% fly ash, 60% fly ash, termed enhanced sustainability, or 60% slag cement. This study found that the changes in crack density parameter resulting from exposure to elevated temperatures appear to be more sensitive to differences between cementitious materials than to differences between aggregate type or cementitious material proportions. A critical finding was that the relationship between initial crack density parameter and changes in crack density parameter were similar regardless of fly ash content

FRP-strengthened RC slabs anchored with FRP anchors

An abundance of tests over the last two decades has shown the bending capacity of flexural members such as reinforced concrete (RC) beams and slabs to be enhanced by the bonding of fibre-reinforced polymer (FRP) composites to their tension face. The propensity of the FRP to debond, however, limits its effectiveness. Different types of anchorages have therefore been investigated in order to delay or even prevent debonding. The so-called FRP anchor, which is made from rolled fibre sheets or bundles of lose fibres, is particularly suitable for anchoring FRP composites to a variety of structural element shapes. Studies that assess the effectiveness of FRP anchors in anchoring FRP strengthening in flexural members is, however, limited. This paper in turn reports a series of tests on one-way spanning simply supported RC slabs which have been strengthened in flexure with tension face bonded FRP composites and anchored with different arrangements of FRP anchors. The load–deflection responses of all slab tests are plotted, in addition to selected strain results. The behaviours of the specimens including the failure modes are also discussed. The greatest enhancement in load and deflection experienced by the six slabs strengthened with FRP plates and anchored with FRP anchors was 30% and 110%, respectively, over the unanchored FRP-strengthened control slab. The paper also discusses the strategic placement of FRP anchors for optimal strength and deflection enhancement in FRP-strengthened RC slabs