Scaled Bridge Model Research Articles

Updating the Finite Element Model of Large-Scaled Structures using Component mode Synthesis Technique

It is difficult to update the finite element (FE) model of the large-scale or complex structures such as bridges by using the regular methods since the dynamic analysis of complex structures always result in the heavy computational burden. A new updating method based on component mode synthesis (CMS) was proposed to improve the efficiency of FE model updating of large-scale structures. The effectiveness of the proposed method was validated by updating the FE model of a scaled bridge model with measured modal parameters.

Performance of an AASHTO Beam Bridge Prestressed with CFRP Tendons

Corrosion-induced deterioration of steel RC highway bridges is one of the major distress types that can render a structurally deficient bridge before reaching the design life. One feasible solution to the problem is to replace the conventional steel reinforcement with noncorrosive carbon fiber–reinforced polymer (CFRP) reinforcements. However, the CFRP reinforcement as an internal reinforcement has not been explored in AASHTO-type prestressed concrete beam bridges. AASHTO-type beams have an I-type cross section with a bottom flange, and on integration of the deck slab, the final shape is a bulb-T section. This paper discusses the experimental investigation of a precast prestressed AASHTO control beam and a bridge model. A 12.5-m-long one-third scale AASHTO-type control beam was experimentally investigated for its flexural behavior when reinforced and prestressed with CFRP. Subsequently, a one-third scale bridge model made of five such beams was constructed, instrumented, and tested under both service and ultimate load conditions. As anticipated, the control beam and the bridge model failures were initiated by rupturing of the prestressing CFRP tendons at the bottom layer. The observed flexural response of the bridge model was in close agreement with that of the control beam. As expected, the failure mode was progressive, with extensive cracking of the bridge model, which gives significant warning prior to the ultimate collapse, overcoming issues related to the otherwise brittle behavior of the CFRP-reinforced structures. It is therefore highly recommended to provide the CFRP tendons in different layers along the depth of the beams to effectively address the issues related to brittle failure exhibited by CFRP reinforcements.

Performance of a scaled FRP deck-on-steel girder bridge model with partial degree of composite action

The applications of FRP decks have been increasingly implemented in the United States since the mid-1990s. Although extensive research has been conducted on stiffness and strength evaluations of various types of FRP decks, studies on FRP deck-on-steel girder systems are limited. The performance of the FRP deck-on-steel girder system depends substantially on the connectors used. Recently, a prototype shear connector was developed and its advantages were illustrated through both laboratory study and field applications, where partial degree of composite action could be achieved between the deck and stringers. This paper aims to study the effectiveness of the shear connector at bridge-system level, including the static and fatigue performance of the shear connector and the bridge system, the degree of composite action of the system; and more importantly, the influence of the partial degree of composite action on load distribution factor and effective flange width since no provision is provided in AASHTO Specifications. For this purpose, a 1:3 scaled FRP deck bridge model was tested, with an FRP sandwich honeycomb deck connected to steel girders using the prototype shear connector. The test program consisted of three phases: Phase I and Phase II included static and fatigue load tests on the scaled bridge model. In Phase III, a T-section was cut-out from the bridge model and then loaded under three-point bending until failure. A Finite Element model was constructed to simulate the tests. It was shown that the shear connection was able to provide partial composite action of about 25%, and sustain a cyclic fatigue loading equivalent to 75year bridge service life span. It is shown that AASHTO Specifications can still be applicable for load distribution factor, while the effective flange width needs to be re-defined for bridge-system with partial degree of composite action. The findings from this paper can be used for design purposes.

Quality factor in clamping loss of nanocantilever resonators

Clamping loss caused by elastic wave radiation to a support is one of the most dominant loss mechanisms in predicting the quality factor of very or ultra high frequency nanocantilever resonators. To consider nanosurface effects and different scales of the resonator and support, we propose a multiscale model combining a scale-bridging model for the resonator and a perfectly matched layer to estimate the loss in the support. The proposed model is used to investigate the surface effect on the nanoresonator and also shows the tradeoff between the resonant frequency and the quality factor with or without the surface effects.

Evaluation of effective flange width by shear lag model for orthotropic FRP bridge decks

Abstract In bridge engineering, the three-dimensional behavior of a bridge system is usually reduced to the analysis of a T-beam section with a reduced width of deck in relation to center-to-center spacing of stringers, over which the longitudinal normal stresses are assumed to be uniformly distributed, which is termed as effective flange width. It is defined in the AASHTO specifications primarily for concrete slabs and has inherent applicable limitations because of its empirical nature. This paper provides an analytical shear lag model for effective flange width for orthotropic bridge decks, applicable to various materials including Fiber-Reinforced Polymer (FRP) and concrete decks. To verify this solution, a Finite Element (FE) parametric study is conducted on 44 simply-supported FRP deck-on-steel girder bridges. The results from the shear lag model correlate well with the FE results. The accuracy of this model is further verified by close correlations with an existing empirical solution. It is also illustrated that the shear lag model, with the introduction of a reduction factor, can be applied to predict effective flange width for FRP deck-on-steel girder bridges with partial composite action, by favorable comparisons between the analytical and testing results for a T-beam section cut from a one-third scaled bridge model, which consists of an FRP sandwich deck attached to steel girders by mechanical connectors.

Stiffness and Strength Evaluations of a Shear Connection System for FRP Bridge Decks to Steel Girders

This paper reports on research investigating a nongrouted sleeve-type connection used to attach fiber-reinforced polymer (FRP) decks to steel girders. The connection system was investigated for stiffness, strength, fatigue resistance, and degree of composite action. Static and fatigue tests were conducted first at the component level on push-out specimens to obtain P-Δ (load-displacement) and S-N (stress range–fatigue life) relationships, from which design formulas were developed. Then tests were conducted at the system level on a 1∶3 scaled-bridge model by using this sleeve-type connection, and the results showed this shear connection can satisfy requirements from AASHTO specifications for fatigue, strength, and function. Further, three-point bending tests were conducted on a T-section model cut from the scaled bridge, and approximately 25% composite action was achieved for two different connection spacings. The structural efficiency of this shear connection is shown, and this connection design is applie...

Prediction of afflux on undistorted scale bridge model

This paper presents the results and findings from several sets of experimental data on afflux around bridge waterways in overbank flow condition. The paper also investigates the accuracy, capability, and suitability of one-dimensional hydraulic river modelling software (HEC-RAS and ISIS) to model flow through bridge structure. To eliminate a scaling effect between the laboratory-scale experiments and model techniques, all experimental results were scaled up using an undistorted-scale model in which both the vertical and horizontal scale ratio was 100. A total of six methods of predicting afflux, the energy method, the momentum method, the water surface profile (WSPRO) method, Yarnell's method (in HEC-RAS), the U.S. Bureau of Public Roads (USBPR) method, and the arch bridge method (in ISIS) were compared with scaled up experimental results. The results for ISIS are significantly different from the measured data and the output from HEC-RAS. The energy method and the momentum method in HEC-RAS are the most accurate methods to compute the afflux around the bridge waterways.

Health monitoring of bonded composite repair in bridge rehabilitation

Structural rehabilitation with carbon fiber reinforced composite materials has proven to bean excellent way to enhance/repair steel reinforced concrete structures and prolongtheir service lives. However, disbonds between composite repair patches and hoststructures continue to be a great concern of this technology. In this paper, a built-inpiezoelectric sensor network based structural health monitoring system is introduced formonitoring the disbonds between composite repair patches and the host structures.This diagnostic system combines the sensor network, diagnostic hardware anddata analysis software allowing for real-time monitoring of the integrity of thebonded repair. The effectiveness of detecting disbonds using the system has beendemonstrated on a full scale bridge model in a laboratory setting. The bridge model wasloaded incrementally to failure, and disbond monitoring was carried out during theloading intervals. Test results showed that the system could detect the disbondsbefore they have a noticeable effect on the global stiffness of the bridge model.

Damage Identification of Shear Connectors with Wavelet Packet Energy: Laboratory Test Study

Shear connectors are widely used to link the slab and girders together in slab-on-girder structures. Assessment of the integrity of shear connectors is an important issue in the maintenance and health monitoring of such structures. In this study, a 1:3 scaled bridge model was constructed with removable anchors linking the slab and girders as shear connectors. Each anchor consisted of a threaded bar penetrating through the soffit of a girder and anchored in the slab by an embedded nut cap with welded steel bar. Different damage scenarios were simulated by removing some of these connectors. A signal-based damage detection method in which the damage feature is characterized by the wavelet packet energy changes was applied to the damage identification of the shear connectors. Using measurements of hammer impact responses, the locations of the loosening of the shear connectors were effectively detected. This paper demonstrates that the wavelet packet-based energy index is a sensitive local damage indicator. The results also show that comparison of the relative vibration between the slab and the girders is a more effective technique for evaluating the shear connector damage than comparison of the vibration of the slab before and after shear connector damage. This finding is particularly interesting because data from the intact (undamaged) bridge is not required. The suitability and efficiency of the approach is expected to be applied in situ to assess the integrity of shear connectors in existing structures.

Polymorphism in ferroic functional elements

The present study describes an approach for the scale-bridging modeling of ferroic materials as functional elements in micro- and nanoelectronic devices. Ferroic materials are characterized by temperature-dependent complex ordering phenomena of the internal magnetic, electronic, and structural degrees of freedom with several involved length and time scales. Hence, the modelling of such compounds is not straightforward, but relies on a combination of electronic-structure-based methods like ab-initio and density-functional schemes with classical particle-based approaches given by Monte-Carlo simulations with Ising, lattice-gas, or Heisenberg Hamiltonians, which incorporate material-specific parameters both from theory and experiment. The interplay of those methods is demonstrated for device concepts based on electroceramic materials like ferroelectrics and multiferroics, whose functionality is closely related with their propensity towards structural and magnetic polymorphism. In the present case, such scale-bridging techniques are employed to aid the development of an organic field effect transistor on a ferroelectric substrate generated by the self-assembly of field-sensitive molecules on the surfaces of ferroic oxides. Electronic-structure-based methods yield the microscopic properties of the oxide, the surface, the molecules, and the respective interactions. They are combined with classical particle-based methods on a scale-hopping basis. This combination allows to study the morphology evolution during the self-assembly of larger adsorbate arrays on the (defective) oxide surface and to investigate the interplay of low-temperature magnetic ordering phenomena with the ferroelectric functionality at higher temperatures in multiferroic oxides like the hexagonal manganites. The combination of density-functional data with classical continuum modelling also yielded a model Hamiltonian for the quick determination of the properties of a gate structure based on bio-functionalized carbon nanotubes.

Study on mechanical response of an old reinforced concrete arch bridge

The structural behaviour of an old six-span reinforced concrete arch bridge, which has been in service for about 43 years, is investigated. Static and dynamic response of the bridge were obtained from the field monitoring. Based on the similarity theory of model design, a scaled one-span bridge model was fabricated by organic-glasses. To simulate different damages on the arch ribs, seven notches were introduced to the bridge by gradually cutting the arch ribs with saw cutting. Mechanical responses (e.g. strain distribution, deflection, frequency, mode shape, etc.) of the damaged bridge models are achieved. Since the laboratory experimental results shows agreement with the field monitoring results, it can be derived that the scaled bridge model can represent the actual structural behaviour. Effects of the damage location, damage extent on the structural response were discussed in detail. Numerical simulation was performed as well, and the numerical results show in good agreement with the experimental results. Copyright © 2006 John Wiley & Sons, Ltd.

Dynamic assessment of shear connectors in slab–girder bridges

Shear connectors are of primary importance in slab–girder bridges to provide composite action. Their damage will reduce the load-carrying capacity of the structure. To test the suitability and efficiency of various vibration-based damage identification methods to assess the integrity of the shear connectors, a 1:3 scaled bridge model was constructed in the laboratory. Some removable anchors were specially designed and fabricated to link the beams and slab that were cast separately. Each anchor consists of a threaded bar that penetrates through the soffit of the beam and ties up into an embedded nut cap to simulate a shear connector in real bridges. Different damage scenarios were introduced by pulling out some connectors. Vibration tests were carried out in each damage scenario. Various damage detection methods have been applied and results show that a local approach was able to detect all the damage successfully and consistently. This new method does not need any reference data for the structure, and therefore it is suitable for application to the prototype bridges. The proposed local method was also compared with some global methods, including optimal model updating techniques. The sensitivity region of this local vibration method for damage detection is also investigated.

Shaking table tests of a scaled bridge model with rolling-type seismic isolation bearings

Concurrent with the growth of the application of the seismic isolation technique to civil structures, a large variety of isolation systems has been developed during the past two decades. This paper investigates the seismic behavior of a 1/7.5 scaled bridge model isolated by rolling-type bearings. Shaking table tests of the scaled bridge model have been conducted to verify the effectiveness of the rolling-type bearing as a seismic isolation device. Test results reveal that the seismic force transmitted by the rolling-type bearing is independent of the earthquake intensities when the sloped rolling mechanism is completely triggered. An approximate expression is derived for predicting the peak acceleration response of a structure isolated by the rolling-type bearing. It is shown that the maximum structural acceleration may be estimated by the proposed formula. As an appropriate option, viscous dampers may be incorporated to reduce the larger displacement and eliminate unfavorable oscillation of the bridge deck, which may occur under strong earthquakes.

Seismic Performance of Steel Girder Bridges with Ductile Cross Frames Using Buckling-Restrained Braces

Ductile end cross frames have been proposed in the past for seismic design of steel plate girder bridges. In this paper buckling-restrained braces (BRBs) are investigated as ductile end cross frames and compared against the performance of yielding X braces. Component experiments on the BRBs showed that these braces dissipated energy very efficiently and have stable hysteretic behavior. Shake-table experiments on a large scale bridge model investigated the performance of braces with both pin-ended connections and fixed-end connections. Despite slippage, the pin-ended connections are considered more effective as flexural action in the relatively short braces is prevented. The base shear in the bridge model in response to 2.0 times the El Centro earthquake was 69% of the elastic base shear at an average drift of 2.5% during experiments. The relatively large deformation capacity of the BRBs, although not as great as the X braces, is necessary to achieve a significant reduction in base shear. The maximum cross frame displacements with the BRBs are consistently smaller than those in X braces at the same level of base shear.

Semi-active control of sliding isolated bridges using MR dampers: an experimental and numerical study

Sliding base-isolation systems used in bridges reduce pier drifts, but at the expense of increased bearing displacements under near-source pulse-type earthquakes. It is common practice to incorporate supplemental passive non-linear dampers into the isolation system to counter increased bearing displacements. Non-linear passive dampers can certainly reduce bearing displacements, but only with increased isolation level forces and pier drifts. The semi-active controllable non-linear dampers, which can vary damping in real time, can reduce bearing displacements without further increase in forces and pier drifts; and hence deserve investigation. In this study performance of such a 'smart' sliding isolation System, used in a 1:20 scaled bridge model, employing semi-active controllable magneto-rheological (MR) dampers is investigated, analytically and experimentally, under several near-fault earthquakes. A non-linear analytical model, which incorporates the non-linearities of sliding bearings and the MR damper, is developed. A Lyapunov control algorithm for control of the MR damper is developed and implemented in shake table tests. Analytical and shake table test results are compared. It is shown that the smart MR damper reduces bearing displacements further than the passive low- and high-damping cases, while maintaining isolation level forces less than the passive high-damping case.

An Investigation of the Effects of Layer Thickness on the Fracture Behavior of Layered NiAl/V Composites

The effects of vanadium layer thickness (100, 200 and 400 μm) on the resistance-curve behavior of NiAl/V, microlaminates are examined in this paper. The fracture resistance of the NiAl microlaminates reinforced with 20 vol.% of vanadium layers is shown to increase with increasing vanadium layer thickness. The improved fracture toughness (from an NiAl matrix toughness of 6˜.6MPam to a steady-state toughness of 1˜5MPam obtained from finite element analysis) is associated with crack bridging and the interactions of cracks with vanadium layers. The reinitiation of cracks in adjacent NiAl layers is modeled using finite element methods and the reinitiation is shown to occur as a result of strain concentrations at the interface between the adjacent NiAl layers and vanadium layers. The deviation of the reinitiated cracks from the pure mode I direction is shown to occur in the direction of maximum shear strain. Toughening due to crack bridging is also modeled using large-scale bridging models. The intrinsic toughness levels of the microlaminates are also inferred by extrapolating the large scale bridging models to arbitrarily large specimen widths. The extrapolations also show that the small-scale bridging intrinsic toughness increases with increasing vanadium layer thickness.

Microbuckle propagation in a unidirectional carbon fibre-epoxy matrix composite

Out-of-plane microbuckle growth is observed in a unidirectional carbon fibre-epoxy matrix composite under compressive loading. Experimental measurements of the overall kink-band width confirm that a growing microbuckle propagates in a crack-like manner rather than in a dislocation-like manner. The microbuckle is modelled as a bridged Mode I crack with compressive bridging tractions. A large scale bridging model with a crack tip toughness and a constant bridging stress is successful in correlating the length and width of a growing microbuckle with the remote stress.

Microbuckle propagation in carbon fibre-epoxy composites

Observations of microbuckle propagation in uni-directional carbon fibre-epoxy material are described. The fibres buckle either in the plane of the specimen or out-of-plane, depending on the constraints on the free surface. Large scale bridging models of in-plane and out-of-plane microbuckles are reported. The in-plane and out-of-plane microbuckles are modelled as mode II and mode I cracks, respectively. Sliding behind the microbuckle tip is resisted by a constant shear stress of 90 MPa for the in-plane microbuckle, and by a constant normal stress of 220 MPa for the out-of-plane microbuckle. For both the in-plane and out-of-plane microbuckles a microbuckle tip toughness in the range 10–17 KJ/m 2 is inferred from the experiments. The observed relative displacements across an out-of-plane microbuckle agree with theoretical values using the mode I bridging model. Micrographs of the propagating microbuckle tip show that the details of the failure mechanism are similar for both in-plane and out-of-plane microbuckling. Both develop kink bands with a width of between 25 and 70 μm and with a propagation angle β of between 25° and 30°. A process zone extends about 250 μm ahead of the kink band tip, wherein the fibres buckle and break. Fibres in this region become almost straight again on unloading. When the deduced large scale bridging model of microbuckling failure for unidirectional material is applied to failure at a sharpened slit in multi-directional laminates, reasonable agreement is found between the theoretical and the observed compressive fracture toughnesses.

Ductile phase toughening mechanisms in a TiAlTiNb laminate composite

Toughening mechanisms in a laminate composite composed of alternating layers of brittle γ-TiAl and ductile TiNb reinforcements were studied. The TiNb phase comprising about 20% of the composite volume, contributed to toughening by both crack renucleation and bridging mechanisms, yielding a steep resistance curve and effective toughness more than ten times higher than the matrix value. In part, the extraordinary toughening is derived from large scale bridging effects, which occur when the size of the bridging zone is not small compared to the crack and specimen dimensions. Large scale bridging model predictions based on independent evaluations of the fundamental composite properties, including the reinforcement stress-displacement function, were in good agreement with the experimental observations. We demonstrate how the models can be used to optimize the composite properties for specific applications.

Strengthening of Continuous Composite Bridges

The purpose of this first phase of a continuing research program is to examine the potential for strengthening continuous composite bridges by post‐tensioning. Testing of a one‐third scale bridge model and finite element analysis are used to determine the effects of various straight‐tendon posttensioning schemes. Because of both longitudinal and transverse distribution, the effects of posttensioning are complex. When asymmetrical posttensioning arrangements are applied to the bridge, the resulting stresses add to the dead load stresses in some regions of the model bridge. Symmetrical posttensioning of negative moment regions results in smaller stress reductions than symmetrical posttensioning of positive moment regions. Symmetrical posttensioning of positive moment regions has significant beneficial effects in both negative and positive moment regions. Vertical loads applied to the posttensioned model bridge either increase or decrease tendon forces, depending on the positions of the loads and tendons. Testing and analysis indicate that symmetrical posttensioning could improve service load stresses in continuous composite bridges.