Abstract
Durch den schlechten Zustand vieler älterer Brücken und Änderungen in den Regelwerken ergeben sich häufig Defizite bei der Nachrechnung von Bestandsbrücken nach Nachrechnungsrichtlinie. Für ...den Fall, dass die erforderliche Bauwerkssicherheit nicht nachgewiesen werden kann, können Bauwerksmessungen zeitlich begrenzt oder als Dauermonitoring durchgeführt werden, um Erkenntnisse über die zeitlich veränderliche Beanspruchung zu gewinnen. Zentral hierfür ist die Ableitung von Zustandsindikatoren für das Bauwerk, die letztendlich den Handlungsbedarf für Betreiber und Ingenieure anzeigen. Im einfachsten Fall wird hierfür z. B. ein Ausnutzungsgrad ermittelt, der allerdings keinen Rückschluss auf das Risiko ermöglicht und streng genommen nur eine binäre Bewertung zulässt. In diesem Beitrag wird daher eine Vorgehensweise erläutert und am Beispiel der Hamburger Köhlbrandbrücke umgesetzt, die es erlaubt, einen Zuverlässigkeitsindex als zeitlich veränderlichen Zustandsindikator bezogen auf den Beulnachweis aus den dynamischen Monitoringdaten abzuleiten.
Abstract
Structural reliability assessment by structural monitoring – probabilistic buckling check of the Hamburg Köhlbrand bridge
The bad condition of many older bridges and changes in the code provisions often result in deficits after recalculation according to the recalculation guidelines. In case the necessary structural safety is not provided, temporary or permanent structural monitoring can be employed in order to gain knowledge about the time variant actions. For this, the derivation of condition indicators is key, since they indicate a need for action for the owners and the engineers. In the simplest case, a utilization will be derived which, however, does not allow for an assessment of the risk and strictly speaking only enables a binary assessment. In this paper, a method is described and demonstrated on the Hamburg Köhlbrand bridge which allows for the calculation of a reliability index as a time variant condition indicator on the basis of the dynamic monitoring data with regard to the buckling check.
Most structural health monitoring is carried out for a limited number of key measurement points of a bridge, and incomplete measurement data lead to incomplete mechanical equation inversion results, ...which is a key problem faced in bridge damage identification. The ability of digital images to holographically describe structural morphology can effectively alleviate the problem of damage identification due to incomplete test data. Based on digital image processing technology, a matrix similarity damage identification method based on a structural digital orthoimage was proposed. Firstly, a steel truss–concrete composite beam specimen with a complex support bar system was designed and fabricated in the laboratory, and the digital orthoimage of the test beam was obtained by the perspective transformation of the original image of the test beam. The body contour of the structure was extracted from the digital orthoimage of the test beam, and wavelet threshold denoising was performed on the lower edge profile to obtain the deflection curves of the structure under different working conditions. The verification results show that the maximum error of the deflection curve is 3.42%, which proves that the digital orthoimage can accurately and completely reflect the deformation of the structure. Finally, based on the digital orthophoto of the test beam, a matrix similarity test before and after the damage was carried out, and the results show that the singularities of the similarity distribution are consistent with the location of the damage; furthermore, the accurate positioning of the damage in different working conditions is achieved.
•Novel mechanically-fastened FRP flexural reinforcing developed for reinforced concrete.•Reinforcing system is easy to install and cost-effective.•Flexural tests indicate reinforcing provides ...strength gains of nearly 50%.•Environmental and fatigue durability were experimentally assessed.
While externally bonded fiber-reinforced polymer reinforcing has become an accepted technology for the flexural strengthening of reinforced concrete members, less information is available on flexural strengthening using mechanically fastened FRP (MF-FRP). This study presents the development of a vacuum-infused, hybrid glass–carbon MF-FRP system for the flexural strengthening of reinforced concrete beams. Two different FRP fabric architectures were considered to assess the impact of fiber orientation on behavior. The resistance of the MF-FRP composite strips to freeze–thaw cycling and saltwater submersion was assessed with single-fastener tension–bearing testing. Test results indicate that the MF-FRP system should display adequate residual capacity in typical cold-climate bridge applications. The flexural strengthening capabilities of MF-FRP composite strips were evaluated using four-point bending tests of MF-FRP-strengthened, steel-reinforced concrete beams and non-strengthened beams. The flexural test results for two glass–carbon MF-FRP reinforcing systems show an average increase in ultimate capacity of nearly 50% with good ductility. Flexural fatigue testing was conducted on four MF-FRP reinforced specimens. The cyclic flexural test results indicate that the strength gains that can be realized with the MF-FRP systems used here may be limited by fatigue performance, and that fatigue is an area that warrants further study.
Analysis of the variability in the responses of large structural systems and quantification of their linearity or nonlinearity as a potential non-invasive means of structural system assessment from ...output-only condition remains a challenging problem. In this study, the Delay Vector Variance (DVV) method is used for full scale testing of both pseudo-dynamic and dynamic responses of two bridges, in order to study the degree of nonlinearity of their measured response signals. The DVV detects the presence of determinism and nonlinearity in a time series and is based upon the examination of local predictability of a signal. The pseudo-dynamic data is obtained from a concrete bridge during repair while the dynamic data is obtained from a steel railway bridge traversed by a train. We show that DVV is promising as a marker in establishing the degree to which a change in the signal nonlinearity reflects the change in the real behaviour of a structure. It is also useful in establishing the sensitivity of instruments or sensors deployed to monitor such changes.
•First application of a Delay Vector Variance (DVV) based nonlinearity estimation of full scale experiments on large structures.•First application of DVV based comparison of sensors measuring dynamic responses of full scale large structures.•Comprehensive study on pseudo-dynamic and dynamic responses.•Demonstration of comparing dynamic systems using estimated nonlinearity as a measure.•Establishing the potential of DVV in monitoring and quantitatively comparing events from output-only conditions.
Non-stationary spatially variable ground motions (SVGMs) are commonly modelled as multivariate oscillatory processes based on evolutionary power spectral density (EPSD) functions. The existing ...conditional simulation algorithms require the known EPSD functions. The EPSD functions are usually assumed to be identical for all locations, which is unreasonable for long-span bridges because variable soil conditions are practically observed at different bridge piers. This paper proposes a conditional simulation algorithm for non-stationary SVGMs in consideration of non-uniform site conditions. The spatial interpolation tool, termed inverse-distance-weighted (IDW) interpolation, is introduced to estimate the EPSD functions at sites without ground motion measurement. Subsequently, the covariance matrix of the random Fourier coefficients of the multivariate oscillatory processes can be calculated. The Kriging estimation is adopted to obtain the unknown random Fourier coefficients, from which the time histories of the non-stationary SVGMs can be conditionally simulated. The proposed conditional simulation algorithm is first validated through a numerical example, in which the EPSD functions of non-uniform sites are represented by a non-stationary Kanai-Tajimi spectrum with different soil parameters. Then, the algorithm is applied to the Jiuzhou Channel Bridge, a navigation channel bridge of the Hong Kong-Zhuhai-Macau Bridge (HZMB), with complex soil and water conditions. Based on the limited in-situ seismic measurement data, the site characteristics in the bridge area are analysed, and the ground motion time histories at all piers can be generated.
A novel shape memory alloy wires-based smart roller bearing (SMA-RBs) has been developed and its cyclic behavior under reverse cyclic loadings has been experimentally investigated. However, its ...efficacy and performance in enhancing the seismic performance of bridge structures have not been well understood and proven. A new self-centering hysteresis model for SMA-RBs has been proposed to properly simulate their hysteretic behavior, which has been experimentally validated through a pseudo-static test. A methodology is proposed to determine the four damage states of SMA-RB (i.e. slight, moderate, extensive, and collapse) considering the contribution of SMA wires. The smart SMA-RBs are utilized for a cable-stayed bridge in China. The vulnerability of two reference bridges, i.e. the floating system (FS) and rigid system (RS), and one isolated bridge equipped with SMA-RBs (SMA-RBS) are compared at component and system levels. The applicability of three commonly used intensity measures (IMs), i.e. PGA, PGV, and Sa(T
1
), are evaluated and PGV turns out to be the optimal IM for long-span cable-stayed bridge systems. Results show that incorporating SMA wires in roller bearings can decrease the failure probabilities of the bearing. The piers and towers with SMA-RBs lead to lower seismic fragility over the towers and piers in the reference bridges. The RS is the most vulnerable bridge whereas the SMA-RBS is the least vulnerable bridge among the four bridges. The SMA-RBS experience a much lower collapse damage probability compared to RS ad FS.
We consider the problem of sorting signed permutations by reversals, transpositions, transreversals, and block-interchanges and give a 2-approximation scheme, called the GSB (Genome Sorting by ...Bridges) scheme. Our result extends 2-approximation algorithm of He and Chen 12 that allowed only reversals and block-interchanges, and also the 1.5 approximation algorithm of Hartman and Sharan 11 that allowed only transreversals and transpositions. We prove this result by introducing three bridge structures in the breakpoint graph, namely, the L-bridge, T-bridge, and X-bridge and show that they model "proper" reversals, transpositions, transreversals, and block-interchanges, respectively. We show that we can always find at least one of these three bridges in any breakpoint graph, thus giving an upper bound on the number of operations needed. We prove a lower bound on the distance and use it to show that GSB has a 2-approximation ratio. An O(n 3 ) algorithm called GSB-I that is based on the GSB approximation scheme presented in this paper has recently been published by Yu, Hao, and Leong in 17 . We note that our 2-approximation scheme admits many possible implementations by varying the order we search for proper rearrangement operations.
Glass fiber-reinforced polymer pultruded profiles have great potential in the construction industry, presenting certain advantages when compared with traditional materials, including the potentially ...improved durability under fluctuating levels of environmental factors. The paper presents analysis of glass fiber-reinforced polymer composite, acquired from cable-stayed Fiberline Bridge exploited for 20 years in the fjord area of Kolding, Denmark. Fragment of composite material used for Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis tests was therefore subjected to natural aging as a result of temperature amplitudes, permanent solar radiation as well as aggressive impact of sea salt contained in the moisture in the air around the coastal area. Complex comparative analysis presented in this paper, and based on Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis tests, pertained to both unspool composite glass fiber-reinforced polymer material (composite 1) and the one after 20 years of natural aging (composite 2). Dynamic mechanical analysis was allowed to detect thermal effects based on the changes in the modulus or damping behavior. The differential scanning calorimetry experiments were performed on the glass fiber-reinforced polymer material in order to determine the mass variation and the energy changes suffered by the materials, as a function of temperature and time.
The application of geodetic methods to examine structures consists in the determination of their displacements relative to an established geodetic reference datum or in the definition of the geometry ...of their individual components. Such examinations form a picture of changes happening between specific points in time. Modern measurement technologies used in geodetic engineering enable undertaking more and more challenging measurements with increasing accuracy. The purpose of this article is to present a measurement technique involving a Leica TDRA 6000 total station to measure displacements in engineering structures. The station features a direct drive technology to achieve an accuracy of 0.25 mm in 3-dimensional measurements. Supported by appropriate software, the unit makes a perfect instrument for the monitoring of civil engineering structures. The article presents the results of measurement of static and dynamic displacements in a few engineering structures. The measurements were carried out both in laboratory conditions and on actual, operated civil engineering structures.
The shape of a doubly clamped bridge structure depends on its deflection. At large deflections, where the system exhibits nonlinear behaviour, the shape effect becomes significant. We present a ...general method, based on variational analysis, for computing corrections to the nominal linear regime shape function. The method is used to compute the first non-trivial correction and quantify the corresponding improvement in the large deflection regime. The model obtained is also validated using FEM simulations.
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