Search

The viscoelastic property of pile-soil interactions is modeled by fractional derivative method and is used to characterize the structural dynamics of pile and rheological behavior of a thawing frozen soil. A study of the thawing frozen soil impacts on pile structure’s dynamic characteristic is carried out. The frequency spectrum analysis and empirical modal decomposition are used to identify the pile structure dynamic properties. The rocking mode vibration in which pile behaviors like rigid body supported by viscoelastic soil is extracted to capture the viscoelastic property of pile-soil interactions. The rocking mode exhibiting time-varying frequency features is modeled with fractional derivative model and the fractional derivative order is identified. This study proposes a quick and reliable method to identify the viscoelastic property of pile-soil interactions.

Most of the man-made structures in cold regions could expose in seasonally frozen conditions which could have significant impact on the soil-pile systems of structures. Little research has been conducted to investigate the thawed frozen soil effects on the dynamic performance of pile structures. An experimental investigation of the thawed frozen soil effects on the dynamic behavior of a pile structure is presented. Free-decay response approach is used in summer to estimate the dynamic properties of a pile partially embedded in Fairbanks silt one year ago. The frequency spectrum analyses are used to evaluate system's vibration properties. The empirical modal decomposition is used to decompose response signal for system parameter identification. Results show that two dominant modes can be used to characterize pile dynamic response, one is a component at 14 Hz and the other one is at 920 Hz. The former is a pile rocking mode in which pile behaves like a rigid body; the latter is the first order structural bending mode of the embedded pile. The rocking mode exhibits nonlinear characteristics in the time-frequency domain which is dominated by strong soil nonlinearity. The structural modes of embedded pile exhibit weak nonlinear characteristics. The damping ratios are identified, which can be used to characterize pile-thawed frozen soil interactions. A theoretical nonlinear model including equivalent nonlinear soil spring and nonlinear damping coefficients is developed to correlate with the experimental results.

In this paper, we investigate vehicle–bridge interactions and propose a new method for assessing bridge conditions based on nonlinear vibration analysis. A vehicle model is presented, and the dynamic load on the bridge is quantified based on bridge road roughness. The vibration of a river bridge under a moving vehicle is recorded and analyzed. The Fourier spectrum of the bridge response due to vehicle loading exhibits complicated cluster bands in addition to multiple peaks, some of which are correlated with the bridge natural modes characterized by finite element method analysis and free decay testing, and some of which are correlated with the vehicle dynamic load spectrum. To characterize the unidentified narrow band in the bridge response spectrum, the Lyapunov exponent of the response is estimated, which is found to be a positive value indicating the nonlinear properties of the bridge’s large response under vehicle loading. This finding correlates with the bridge inspection, which shows that some supporting roller bearings do not properly contact the superstructure of the bridge. To elaborate this phenomenon, a model of beam with nonideal supporting condition is analyzed, and a narrow band spectrum is characterized using He’s variational-iteration method. This research offers insight to using the vehicle–bridge interaction to monitor the health status of a bridge by using nonlinear properties, as well as linear properties.

A novel technique to identify bridge damage using genetic algorithms and simulated annealing is proposed in this article. In the proposed method, the cross-sectional area of the damaged member is set as a variable that can be updated. An objective function was investigated to estimate the current condition of the damaged members. This function is the relationship between the measured strain and the analytical strain at the damage location. To obtain better agreement, the parameters were then identified using a genetic algorithm and simulated annealing to minimize the objective function. The proposed method was verified by a truss bridge and can directly estimate the damage based on strain measurements.

As all bridges get deteriorated over time, structural health monitoring of these structures has become very important for the damage identification and maintenance work. Evaluating a bridge’s health condition requires the testing of a variety of physical quantities including bridge dynamic responses and the evaluation of the functions of varied bridge subsystems. In this study, both the acceleration of the deck and the dynamic rotational angle of the bearings in a long-span steel girder bridge were measured when the bridge system was excited by passing-by vehicles. The nonstationary dynamical phenomena including vibration mode interactions and coupling are observed in response spectrogram. To elaborate the phenomena, the linear vibration mode properties of the bridge are characterized by finite element analysis and are correlated with the specific modes in test. A theoretical model is presented showing the mechanism of the mode coupling and instability originated from the friction effects in bearing. This study offers some insights into the correlation between complex bridge vibrations and the bearing effects, which lays a foundation for the in situ health monitoring of bridge bearing by using dynamical testing.

Quantifying the non-stationary properties of bridge under passing vehicle has been an important topic in structural health monitoring of bridge. There are many methods of time–frequency representation used for the study of dynamics of bridge under passing vehicle, including spectrogram, wavelet, Hilbert–Huang transform, and so on. This article uses adaptive optimal kernel time–frequency representation to quantify the non-stationary properties of the response of bridge under passing vehicle and illustrates and discusses its advantages over conventional time–frequency methods.

A method to identify optimal strain sensor placement for examining structural static responses is presented. The method is based on the use of numerical optimization. Based on an assumed set of applied static forces, the optimal sensor placement can be obtained, and the measured strains can be used to provide the information needed to describe the structural stiffness. For example, the cross-sectional area can be determined by minimizing the difference between the analytical and measured strains. This approach is used to identify the optimized sensor placement. The objective of this study is to identify the minimum number of static strain sensors and the optimal sensor layout needed to evaluate a bridge’s structural condition. This study includes an automatic model parameter identification method, optimal static strain sensor placement, damage detection, and application to an actual bridge.

Frozen soils, including both those seasonally frozen and perennially frozen, exists extensively in Alaska and other cold regions. During past earthquakes, widespread damage was observed in deep foundations in the ground, and frozen ground appears to be the direct cause of at least some of that damage. The aim of this paper is to investigate the effects of seasonally frozen soil on deep foundations during lateral loads induced by earthquakes, ice, wind, vehicular impacting, and other loads with a short duration, and to recommend simplified tools for design practices. Two identical reinforced concrete-filled steel pipe piles were tested to large deformations at unfrozen and frozen soil conditions to demonstrate the effects of seasonally frozen soil on the lateral behavior of steel pipe piles. The pile tested at unfrozen condition behaved as a rigid pile, and the other at deep seasonally frozen condition formed a very shallow plastic hinge. Pile performance data in deep seasonally frozen silts were u...

Strain gage sensors have been used to evaluate the local behavior of structures; however, there are limited studies for its application in bridge dynamic feature identification. In this study, fiber Bragg grating strain gages were installed on the lower chord members of a bridge, and dynamic features were identified successfully using strain gage readings when vehicles passed over the bridge. The results were also verified using a finite element model. The innovation presented in this article is the use of fiber Bragg grating strain gage readings to identify the dynamic features of a long-span, steel-girder bridge. To clarify the effect of truck dynamic load, the load spectrum of the truck is characterized. This article introduces a new method for identifying the dynamic parameters of bridges.

A free-decay response signal approach is proposed for reliable estimation of frozen soil–pile dynamic properties of a partially embedded pile. Theoretical consideration and approximations are given for the free vibration of pile structures, with 20% of the pile cantilevered aboveground and the remaining embedded in Fairbanks silt. Winter measurements were taken for free-decay response of the pile. A comprehensive frequency spectrum analysis that includes fast Fourier transform, power spectrum density, and spectrograms is used to evaluate the system's vibration properties. Empirical mode decomposition is then used to decompose the signal to extract specific components for parameter identification. Results show that the response exhibits time-variant and nonlinear characteristics in the time–frequency domain. Experimental data show that the tested system exhibits weak nonlinearity. Dominant system parameters, used to characterize frozen soil–pile interactions, are identified. Two dominant frequencies for a stiff pile embedded 20 ft (6.096 mm) deep in frozen Fairbanks silt are 97 Hz and 1080 Hz. Damping was found to be approximately 0.016.

Most of the furniture manufactured in Australia is made from the eucalypt timber species. Although in the past old-growth eucalypt timbers were primarily used for the production of furniture and other appearance products, a global trend to promote the sustainable use of timber resources has stimulated the industry to adapt to the change by utilizing plantation and regrowth timbers. Reference materials on the properties of Australian species provide data on old-growth timbers but limited publications are available which compare the properties of plantation and old-growth timbers for high-value wood products. So, a research study was undertaken with the goal of investigating the suitability of seven plantation-grown Australian hardwoods for furniture (15 to 40 years of age of harvest). Selected properties of the timbers (density, modulus of elasticity [MOE], and modulus of rupture [MOR]) were assessed and compared with the data on old-growth timber of each species. The results of the study showed that the densities of young plantation timbers were not much lower than those of old-growth wood. The ratio of plantation to old-growth wood varied between 0.82 (for 18-year-old Corymbia maculata) and 0.99 (for 40-year-old Eucalyptus cladocalyx). The ratio of plantation to old-growth wood for MOE and MOR varied between the species as well as between the age of the trees. It was concluded that special care should be taken when using young plantation timbers for furniture production. Although 15-year-old timbers could be confidently used for non-structural appearance components of furniture, they should not be considered as reliable engineering material for structural components of furniture due to the high variability of their engineering properties.

Consider that the Mable Creek silt in central Alaska liquefied during the November 2002 earthquake. Subsequently, frozen samples of these fine-grained soils were retrieved for laboratory st...

This research present a multi-direction bridge finite element model updating method based on the static and dynamic test. A fiber optics structural health monitoring system was installed on the bridge site and 73 fiber optic sensors captured the static and dynamic data in local-level. A portable accelerometer system was used to record the ambient loading test and 15 force-balanced accelerometers were placed along bridge center to record the bridge global behavior. The original model was built according to the construction draw. The bridge model was updating by using multi-level test data. A new multi-direction model updating approach was established to separate the model updating into several stages based on the member’s direction. In each stage, the uni-direction members were updating in local-global level. This study found the multi-direction model updating can reduce the number of objective functions and variables in each stage and bridge model updating in the uni-direction has limited influence on the other directions. It is necessary to update steel girder bridge’s finite element model in the multi-direction in order to ensure the model’s accuracy.