Changes In Flexural Rigidity Research Articles

Validation of bridge health monitoring system using temperature as a proxy for damage

In this paper, damage indicators are presented for bridges based on measured data collected under uncontrolled traffic conditions. The test bridge considered is a small stiff concrete culvert with low dynamics, making it suboptimal for monitoring with accelerometers. Largely static strain responses are measured, with the variability in the vehicle weights and configurations addressed by handling the data in statistical terms. Continuously recorded temperature data are used in an alternative and innovative way to validate damage indicators. Temperature change causes stiffness change in concrete structures. It is posited that temperature can be used as a proxy for bridge damage as, while the effects are clearly different, both cause changes in flexural rigidity and therefore in bridge response to load. It is demonstrated here, using field data, that the damage indicators are sensitive to temperature change. Strain and temperature data for a 2-year period are obtained for a culvert bridge in Slovenia. The defined damage indicators are calculated for the strain data and validated using the simultaneously recorded temperature data. Two ways of using the proposed damage indicators together with the information about temperature for bridge structural health monitoring (SHM) are also presented: one is including the mean and standard deviation of the damage indicators and a compensation for the temperature effect and another to obtain directly the modified Z score, which is used for identifying outliers, and draw a 2D risk map having damage indicator and temperature on the two axes.

In-service change in the flexural rigidity of the VVER-1000 fuel assemblies

In-service dimensional stability of the VVER-1000 reactor fuel assemblies (FA) depends to a great extent on their flexural rigidity. A decrease in the flexural rigidity in the process of the FA operation in the reactor may lead to such FA bowing as will make it difficult for the absorber rods of the reactor control and protection system to move in the FA guide channels. This is not admissible from the point of view of the reactor operation safety.This paper describes a method and a facility for the hot cell testing of the irradiated VVER-1000 FA flexural rigidity. The method is based on measurements of the FA bowing induced by cross-sectional loading. The load applied to the spacer grids is perpendicular to the grid face, and the FA bowing is measured optically using a TV camera. The facility can also be used to test the flexural rigidity of the FA skeleton after all of the fuel rods are removed. Several tens of VVER-1000 FAs with a burnup of ∼4 to ∼65МWday/kgU were tested by Dimitrovgrad Research Institute of Atomic Reactors. The generalization and an analysis of the test results have made it possible to identify the major factors that contribute to the in-service change in the flexural rigidity of the VVER-1000 FAs and to determine the experimental dependence of its change on burnup.It has been shown that an increase in the burnup causes the flexural rigidity of TVSA and TVS-2 FAs with a rigid skeleton to decrease to the minimum value of ∼5kgf/mm, the burnup being 45–50МWday/kgU, and then to start growing again. It has been found out that it is the fuel bundle, specifically the change in the force of the fuel rod compression in the spacer grid, which is responsible for the change in the FA flexural rigidity. The maximum TVSA and TVS-2 FA bowing is in the range of 8–11mm whereas the burnup is 48–63МWday/kgU. The newly adopted TVSA and TVS-2 FA designs have contributed to the safe operation of the VVER-1000 control and protection system's absorber rods.

The E117K mutation in β-tropomyosin disturbs concerted conformational changes of actomyosin in muscle fibers

The effect of the skeletal myopathy-causing E117K mutation in human β-tropomyosin on actomyosin structure during the ATPase cycle was studied using fluorescent probes bound to actin subdomain 1 and the myosin head. Multistep changes in flexural rigidity of actin filament and in spatial arrangement of actin subdomain 1 and myosin SH1 helix in troponin-free ghost muscle fibers were revealed. During the ATPase cycle E117K tropomyosin inhibited the rotation of subdomain 1 by 46% and the tilt of the SH1 helix by 49% compared with wild-type. At strong-binding stages the proportion of strong binding sub-states in the actomyosin population is decreased by the mutation. At weak-binding stages abnormally high numbers of switched-on actin monomers were observed, thus indicating a disturbance in concerted conformational changes of actomyosin. These structural alterations are likely to underlie the contractile deficit observed with this mutation.

A moving-window least squares fitting method for crack detection and rigidity identification of multispan bridges

In this study, a moving-window least squares fitting method is proposed for rapid identification of cracks and flexural rigidities in multispan bridges. First, the dynamic deflections of a continuous bridge were locally measured under a dynamic point load. Their integrations over time, referred to as ‘integration-over-time deflections’, were used to derive ‘integration-over-time slopes’. These virtually static measurements over a short segment of the bridge were then fitted into a cubic curve in the least squares sense. Finally, the coefficient of the square term of the fitted curve was used to determine both the magnitude and location of local flexibility because of cracking and/or changing in flexural rigidity of the bridge. For multispan continuous bridges, an iterative procedure was developed to ensure that the end moments of various spans are compatible with the identified cracks and rigidity changes. To illustrate the proposed method, prismatic girder bridges with multiple cracks of various depths or non-prismatic girder bridges were analyzed. Sensitivity analysis was conducted on the effects of weighting factor, noise level, load type, window length, and bridge discretization. Numerical results demonstrated that the proposed method can accurately detect cracks and identify the change in flexural rigidity. The five-point equally weighted algorithm is recommended for practical applications. The spacing of two discernible cracks is equal to the window length. The identified results are insensitive to noise because of integration of the dynamic measurements. Copyright © 2011 John Wiley & Sons, Ltd.

発泡樹脂/Al三層積層材の曲げ剛性の実験的評価と中立バンドモデルの構築

Flexural rigidity of a porous resin/Al laminate is estimated experimentally by means of the 3-points bending test. It can be seen from the results that the change in the magnitude of flexural rigidity of the laminate is convex with respect to its forming magnification. Therefore there exists the optimal value of the forming magnification of porous resin for the frexial rigidity. The neutral band in which the bending stress is free around the neutral plane of the porous resin/Al laminate beam is devised and the neutral band model is used for the calculation of the frexural rigidity of the laminate beam. The results obtained are good agreement with the experimental ones of the convex change in flexural rigidity with the forming magnification.

Effects of mechanical fatigue on the bending properties of the porcine bioprosthetic heart valve.

The mechanisms underlying the failure of porcine bioprosthetic aortic heart valves are not well understood. One possible explanation is that delaminations of the layered leaflet structure occur through flexion, leading to calcification and further delaminations, and finally resulting in valve failure. We investigated the changes in flexural rigidity of the belly of aortic valve cusps subjected to accelerated durability testing. We used three-point bending wherein a load was applied to the center of each specimen by a thin stainless steel bar calibrated to a known load-displacement relationship. Ten circumferential and 15 radial specimens from valves fatigued to 0, 50, 100, and 200 million cycles were flexed both with and against the curvature of the cusp. Linear beam theory was applied as a means to compare the relative bending stiffness between groups. Although specimens aligned to the circumferential direction were stiffer when bent against the cuspal curvature, the radial oriented specimens exhibited no bending directional dependence. Both the radial and circumferential specimens experienced a significant decrease in the bending stiffness with an increased number of accelerated test cycles. Overall, our results suggest that it is the fibrosa that experiences the greatest loss of stiffness with mechanically induced fatigue damage.

Mechanical properties of perforated and partially demineralized bone grafts.

Changes in flexural rigidity and compression strength of 18 sheep tibias were investigated after laser perforation and partial demineralization. Test bones were divided into three groups: Group 1, no treatment; Group 2, laser hole grid; and Group 3, laser hole grid and partial demineralization. Starting in the anterior direction at the tibial tuberosity, the flexural rigidity was determined using a nondestructive four-point bending test. The elliptical distribution of the flexural rigidity before and after a specific treatment was compared. After the bending test, a cylindrical center section of each test bone was loaded axially to failure to determine subsequent changes in compression strength. Results showed that perforation alone produced minimal reduction of rigidity and insignificant changes in compression strength. However, additional partial demineralization resulted in larger reductions. In compression testing, perforated and partially demineralized bone specimen showed marked decrease of the ultimate failure stress. The observed increase in failure strain appeared to be related to compression of the laser holes. The findings of this study suggest that partial demineralization and perforation can be applied to diaphyseal bone grafts and that their decreased mechanical properties are a function of the bone volume reductions produced by both processes.

Colonoscope flexural rigidity measurement.

A testing device is developed that determines the stiffness, or flexural rigidity, of an endoscope at specific locations down its length by subjecting it to a compressive axial force, a situation similar to the actual forces applied to the endoscope during a clinical procedure. The endoscope is made to deform in a similar fashion to a slender buckled column and the force causing this deformation is related to the flexural rigidity using column buckling theory. A direct relationship between the critical load needed to cause buckling and the square of column length L is demonstrated experimentally and is expected theoretically, giving confidence in the application of column buckling theory to endoscope testing. Additional confidence in the validity of the column buckling test results is obtained by their similarity to data obtained by subjecting the endoscope to a transverse load, determining deflection, and modelling the endoscope as a bent elastic beam. Several makes and models of endoscopes were tested, with flexural rigidity values typically ranging between 160 to 240 Ncm2. The effect of a metal stiffener inserted in an endoscope's accessory channel is quantified, as is the change in flexural rigidity down the insertion shaft of a graded-stiffness endoscope. Significant differences in flexural rigidity were obtained between identical endoscopes, each sharing similar usage histories, indicating the need for flexural rigidity measurements for each individual endoscope of a particular model line, though a more extensive study is required to reliably determine scope-to-scope stiffness variations for a particular model line.

Switches in subduction direction and the lateral termination of mountain belts: Pyrenees-Cantabrian transition, Spain

The switch in subduction polarity at the transition from the Pyrenees to the Cantabrians implies an abrupt change in the gross direction of plate movement. The Pyrenees formed in response to the northward subduction of continental crust beneath Europe during the Palaeogene whereas the Cantabrians developed during the southward subduction of Biscay oceanic crust beneath Spain. As yet, no attempt has been made to explain the mechanism and geometry of this apparent switch in plate kinematics. The transition from northward to southward subduction occurs across a discrete lineament, the Pamplona Fault, oriented transversely with respect to the long axis of the adjacent mountain belts. Regional mapping reveals a 180° switch in the facing direction of thrusts and associated folds across the Pamplona Fault. Balanced structural cross-sections, constructed either side of the Pamplona Fault, exhibit marked contrasts in bulk shortening, depth to detachment, gross structural geometry, and the thickness and completeness of the pre-orogenic Mesozoic succession. The Pyrenean-Cantabrian transition zone is thus envisioned as a fundamental crustal lineament of pre-orogenic origin. A new model for the Cenozoic tectonic evolution of north Spain has the Pamplona Fault separating a series of transtensional basins in the Pyrenees from a passive margin in the Cantabrians. Subsequent plate collision between Spain and Europe reactivated the faults that controlled pre-orogenic 'syn-rift' sedimentation in the present Pyrenean area. In the Cantabrians, however, plate collision signalled a shift from a passive margin to an active margin consuming Biscay oceanic crust beneath a northern Spain subduction zone. An implication of this model is that the foreland crust was affected variably by 'backarc' heating during the early stages of Spain-Europe collision. This is expressed by the changing depth of the Ebro Basin, the foreland basin that developed in response to Pyrenean-Cantabrian orogenesis, whose thickness of the Tertiary succession varies laterally according to changes in flexural rigidity.

A flexural isostatic model of lithosphere shortening and foreland basin formation: Application to the Eastern Cordillera and Subandean belt of NW Argentina

A numerical model of lithosphere shortening has been developed to combine flexural isostatic and structural balancing. This allows us to quantitatively reconcile lithosphere shortening, thrust sheet emplacement, and foreland basin formation. Lithosphere shortening is accommodated by thrusting in the upper crust and by distributed deformation in the lower crust and the lithospheric mantle. This leads to loading by thrust sheet emplacement, crustal thickening, and thermal perturbation. Additional loading and unloading are generated by sedimentation and erosion, respectively. The model is kinematically controlled, each fault having its position, geometry, and movement prescribed. The model is applied to the Subandean late Oligocene to Recent foreland fold and thrust belt of NW Argentina at 22°15′S. The Subandean belt of NW Argentina contains three major stratigraphic units, the Lower, Middle, and Upper Terciario Subandino Formations. By modelling these formations we attempt to determine whether the Terciario Subandino Group can be explained as a foredeep fill in response to thrust sheet loading, and, if so, what is the required effective elastic thickness. A successful model must predict not only foreland stratigraphy but also exhumation, topography, and crustal thickness. We see a change in the wavelength of sedimentary deposition in the Subandean basin through time that can be accounted for by a change in flexural rigidity. Accommodation space for the Lower Terciario Subandino Formation can be generated using an elastic thickness of 70 km. For the Middle/Upper Terciario an elastic thickness of 15 km produces the correct basin geometries. Shortening estimates of 110 km have proved sufficient to generate the observed foreland stratigraphy, Bouguer anomaly, and topography across the Subandean belt and Eastern Cordillera. However, an additional 140 km of shortening is required to generate the observed Bouguer anomaly and topography across the western Andes. This discrepancy could be due to earlier shortening in the western Andes or to crustal thickening by magma addition.

Fracture in reinforced concrete beams under repeated loads

In this work the behaviour of reinforced concrete beams in bending under repeated and reversed loading is studied. At first, a numerical investigation is carried out using a mechanical model based on the assumption of suitable constitutive laws for concrete and steel in the regime of reversed loads whilst also taking into account the confining effect of the stirrups. The adequacy of the model is, thereby, experimentally verified by some comparisons with the results obtained from tests on full-scale beams. The analysis of the results, concerning the ultimate load carrying capacity, ductile and brittle behaviour, change in flexural rigidity and cracking distribution, confirmed the theoretical previsions.

Formulation and application of a three-dimensional structural model for upper internal structures

A finite element structural model is developed for the upper internals which is capable of treating material nonlinearities and geometric nonlinearities arising from large displacements when subjected to dynamic loads. This structural model can be used either by itself or in an interactive mode with a hydrodynamics code. The upper internal structures which are located above the core and below the head cover may play a significant role in the hydrodynamics of an energy excursion by mitigating its response. The upper internal structure (UIS) is essentially a massive, perforated rigid body which is connected to the reactor head by support columns with a cylindrical cross section. The major response of interest is the buckling of these support columns which results from the compressive forces they sustain when the upper internals are loaded vertically upward by dynamic loads. In addition to buckling, these columns sustain plastic deformations and changes in cross section making geometric and material nonlinearities accountable. For the case of substantial change in the shape of the column cross section, it will be more convenient to treat the behaviour of the elements stiffness in terms of moment-curvature relations which account for the changes in flexural rigidity with change in cross section. Two factors considered of importance in developing the model are: (1) whether an imperfection is necessary in the initial mesh of the columns to trigger buckling and to what extent does the magnitude of the imperfection effect the results; (2) whether the buckling pattern is symmetric or asymmetric. It was established by these studies that elastic buckling is not affected by the magnitude of the imperfection; for plastic buckling, the results are more sensitive to the magnitude. The studies also showed that the UIS mass is sufficiently large so that it cannot be laterally displaced. By checking the deformed shape, it was observed that the column always attempts to reach the symmetric buckling mode. Even if the asymmetric shape is triggered, it is always at a load higher than that required to trigger a symmetric response. The behavior of the model has also been compared with the SRI tests simulating highly energetic CDAs. The model predicts the magnitude of the axial deflection quite well.

Large Strains of Drum Heads Studied with Silicone Rubber Models

A technique for producing accurate models is described. The models were subjected to internal pressure and the displacements of points on the outer surface were measured with a travelling microscope. From these measurements the radii of curvature and the rotation of the elements were determined graphically and the bending moments calculated. The greatest bending moments were found to be proportional to the percentage increase in head height and almost independent of Poisson's ratio of the material except for the change in flexural rigidity. The effect of large strains on the bending moments in any drum head can therefore be calculated if the relation between increase in head height and pressure has been determined and the bending moments for one pressure are known.