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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.

Technology that measures bridge responses when a vehicle is crossing over it for structural health monitoring has been under development for approximately a decade. Most of the proposed methods are based on identification of the dynamic characteristics of a bridge such as the natural frequency, the mode shapes, and the damping. Specifically, many time–frequency domain approaches have been used to extract complex spectrum signatures from the complicated vibrations of a bridge due to the interactions of a vehicle with the bridge, which usually involves nonlinear, nonstationary, stochastic, and impact vibrations. In this paper, a method known as complete ensemble empirical mode decomposition with adaptive noise is applied for the first time to analyze the acceleration response of a bridge to a moving vehicle, and the purpose is to extract the spectrum signature of the vehicle–bridge response for structural health monitoring. The time–frequency Hilbert-Huang transform (HHT) spectrum of the decomposed mode from complete ensemble empirical mode decomposition with adaptive noise is presented. The results are well-correlated with finite element analysis. The advantages of the complete ensemble empirical mode decomposition with adaptive noise method are demonstrated in comparing the data from conventional methods, including power spectra, spectrograms, scalograms, and empirical mode decomposition.

This study investigates the characteristics of bridge–abutment interaction based on the vibration spectra of the recorded vibration responses of the abutment, which characterize the vibration transformation from the bridge to the abutment. To this aim, the abutment response excited by a moving truck on the bridge is used to evaluate the transmissibility of the bridge–abutment path. The test results are compared with the vibration spectrum of the bridge vibration responses. It is found that the vibration transformations from the bridge to the abutment and the abutment to the bridge have an identical specific frequency. The interactions between the bridge–abutment paths qualified using a passing vehicle can be used for structural health monitoring.

This research studies the nonlinear dynamic feature of the Chulitna river bridge in Alaska USA. The acceleration response of the bridge under moving truck loads are evaluated for dynamic invariants. The Fourier spectrum of a free-decay response (after the vehicle passes) exhibits a salient line spectrum, which is correlated to calculated linear modes from a 3-D finite element analysis. The bridge deck is used shell elements and truss members are simulated with beam elements. At some locations on bridge, the Fourier spectrum of the bridge response to vehicle loading exhibits a complicated narrow bandwidth suggesting the possibility of nonlinear characteristics. Chaos dynamics invariants of the response are examined based on the largest Lyapunov exponents, correlation dimension, and K-entropy and used to identify the nonlinear dynamic features. The bridge was found to have following characteristics: (a) modal parameters extracted from free-decay response exhibit linear properties. The free vibrations have relatively small amplitude which is not sensitive to possible structure damages; (b) at some locations, measured responses to moving loads exhibit chaos nonlinear dynamics properties with specific signatures. All of the derived nonlinear dynamics invariants including Lyapunov exponents, correlation dimension, and K-entropy support this observation; and (c) in addition to linear modal parameters, the multiple nonlinear dynamics invariants with damage-sensitive features can be used as additional candidates for the ongoing bridge health monitoring.

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.

The Chulitna River Bridge is a 790-ft five girder, five-span steel bridge on the Parks Highway between Fairbanks and Anchorage, Alaska. This bridge was built in 1970 and widened in 1993. Under the no-live load condition, five support bearings are not in contact. Heavily loaded trucks often travel across this bridge to the oil fields in Prudhoe Bay, Alaska. A virtual finite element modeling, dynamic field testing of the “ambient vibrational response,” and structural health monitoring system are used to analyze, evaluate, and monitor the structural performance. As the first stage of the research, this article presents results from the dynamic testing and evaluation of the structural responses of the bridge. In the dynamic field testing, 15 portable accelerometers were placed on centerline along the bridge length to record the structural response, and an ambient free-decay response was used to evaluate the dynamic properties of the bridge structure. Natural frequencies and modal damping ratios were identified and characterized using Hilbert–Huang transform and fast Fourier transform methods. Compared with conventional approaches, this study demonstrates that (1) the Hilbert–Huang method was found to be effective and suitable for modal parameter identification of a long steel girder bridge using ambient truck loading; (2) the nonlinear damping was, for the first time, identified based on Hilbert–Huang transform’s amplitude–time slope; (3) modal frequencies are very sensitive to sensor location so their position should be optimized.

This paper aims to explore fundamental characteristics of bridge vibration spectra to potentially evaluate soil-abutment interactions and changes in abutment earth pressures. To this aim, the bridge response to the excitation of an approaching vehicle on road is utilized to evaluate the transmissibility of the road-soil-abutment-bridge (r-s-a-b) path. By comparing the FFT spectrums of bridge acceleration responses before and upon a vehicle traversing over an abutment, we found that the response spectrum consists of specific frequency of vehicle excitation, even though the bridge response before vehicle traversed over the abutment has a much smaller magnitude. This suggests that the bridge response before the vehicle traversed over the abutment is sensitive enough to be used to characterize the dynamic features of r-s-a-b transmissibility. Hilbert–Huang Transform method is used to extract the non-stationary information of the moving vehicle excitation from the bridge responses to characterize the r-s-a-b transmissibility. It is found that specific signature associated with the specific frequency of vehicle excitation can be extracted from the Hilbert spectrum of empirical modal decomposition signals, and this signature could be readily quantified as a monitoring index which exhibits time-varying property.

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...

A set of dynamic field tests were conducted on the Chulitna River Bridge recently. The Chulitna River Bridge, built in 1970, is located at Historic Mile Post 133 on the Parks Highway between Fairbanks and Anchorage, Alaska. Ambient free-decay response approach is used to estimate the dynamic properties of the bridge. Stationary and dynamic tests on the acceleration responses of the bridge recorded at different locations and in different directions during traveling vehicle passing the bridge. The natural frequencies are identified are characterized by the FFT methods. Results show that there are several components at 1.50, 2.20, 2.85, 3.23, 4.58 Hz are characterized, 2.85, 3.23, 4.58 Hz are bridge vertical mode; 1.50, 2.20 Hz are the longitudinal mode of bridge. Compared with the finite element model results, the measured results matched very well. The modal parameters identified from the bridge responses recorded at different locations are compared with each other to check their consistency, and are compared with FEM analytical results. The results demonstrated that (1) the modal parameters consistent with the FEM results; (2) The modal frequencies results are very sensitive to measurement locations, as such, multiple measurement points are necessary, and the optimization of measurement location is critical to conduct the test efficiently; (3). The identified modal properties of the Chulitna River Bridge could be used as benchmark in on-going health monitoring studies of this bridge.

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.

The November 3, 2002 Denali-Alaska earthquake (Mw=7.9) caused significant liquefaction associated damage to various infrastructure built on fine-grained soils. The seismic response, liquefaction potential, and excess pore pressure generation of soils in cold regions, especially those of fine-grained nature, have not been studied thoroughly and therefore are not well-understood. This paper presents results from an extensive laboratory study on the characteristics of excess pore pressure generation and liquefaction potential of fine-grained soils. Laboratory-constituted soils specimens were tested in four categories: (1) tests on specimens subjected to no thermal conditioning or freeze–thaw cycles; (2) tests on specimens conditioned at 24, 5, 1, 0.5, and −0.2 °C; (3) tests on specimens subjected to 1–4 freeze–thaw cycles; and (4) tests on specimens conditioned at near-freezing temperatures of 0.5 and −0.2 °C through different freeze–thaw paths. Strain-controlled, undrained, cyclic triaxial tests were performed at shear strain levels of 0.005–0.8%. Specimens conditioned at different temperatures were found to generate significantly different pore pressures with cyclic loading. The excess pore pressure generation at near or slightly below freezing was found to change dramatically. A transitional change in the dynamic soil behavior, attributed to unfrozen- or frozen-dominant pore water, was discovered. The threshold shear strain was also found to be influenced by the temperature. Subjecting the soil specimens to 1, 2 and 4 freeze–thaw cycles caused a reduction in excess pore pressure generation and slight change in the threshold shear strain. The temperature conditioning path to reach the target temperature was found to be important on the development of excess pore pressure at near and slightly below-freezing temperatures.

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.

This paper summarizes field-testing of eight decked bulb-tee girder bridges as well as development of three-dimensional finite-element (FE) models. Using the calibrated 3D FE models, parametric studies have been performed to study the effect of shear connectors and intermediate diaphragms on live-load distribution and connector forces. It was found that: (1) in all cases studied, the live- load distribution factor (DF) for a single-lane loaded bridge was smaller than one for a double-lane loaded bridge; (2) connector forces caused by wheel loads were not uniform along the longitudinal joint—adding intermediate diaphragms tended to reduce the difference among horizontal shear forces in connectors; (3) the maximum horizontal shear force increased with the increase of the connector spacing—intermediate diaphragms reduced the maximum horizontal shear force in connectors; (4) the maximum vertical shear force and in-plane normal tensile force in connectors do not necessarily increase with the increase of the co...

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.

Summary The objectives of this research are (a) to establish a structural health monitoring system for bridge safety evaluation that is suitable for cold, remote regions and (b) to identify the bridge responses under variations in temperature. To achieve this, fiber optic sensors with temperature compensation were selected that were suitable for cold regions. This technique allows monitoring equipment to operate far from the sensor installation site, which avoids exposing much of the equipment to extremely cold temperatures and makes a power supply more accessible. The bridge temperature behavior is studied based on the real-time field measurement data, and the relationship between the thermal loading and the bridge response is presented.

Consider that seasonal frost will have a significant effect on soil-structural stiffness (lateral seismic response) and therefore, these phenomena should be accounted for when designing structures located in northern states. As early as 1973, Stevens reported that soil stiffness can increase during freezing by as much as two orders of magnitude. This paper provides the findings from three laterally loaded field tests on 16 inch diameter steel jacketed reinforced concrete pilings embedded in seasonally frozen silt with the pile tips approximately 1-ft above permafrost. Two test piles were driven 20 feet into Fairbanks silt about 1.5 miles from Fairbanks, Alaska at a CREEL test site. A 24 inch steel jacketed reinforced concrete reaction pile was located between and in line with the test piles. Both test piles were embedded in Fairbanks silt. Except for 1-ft gravel layer atop the ground at the north pile, the subsurface soil conditions at both test piles was essentially the same. Three quasi-static lateral load cyclic tests were conducted on the piles throughout the year; one in September when the soil was thawed, the other two in January and March with frost depths of 4.5 and 7.5 feet respectively. Where possible, the recommended FHWA guidelines for conducting tests on laterally loaded piles were followed for this research. During thawed conditions, displacement control was used for conducting the cyclic load tests. However, during winter months, it was quickly determined that load control was required for conducting the cyclic load tests. Soil temperatures for these tests ranged from thawed to – 0.4 F (-18 C). Shear demand on the piles increased by over 400 percent. The results of these tests showed that the test pile behaved similar to the same pile idealized as fix cantilever beam with the location of the fixed end being just below the ground surface. Depth to fixity was less than 0.75 pile diameters for the frozen condition. In this case, a 16-inch steel jacketed reinforced concrete pile may be considered fixed when the pile is embedded in frozen Fairbanks silt in interior Alaska. For the thawed condition, since the pile experienced short foundation behavior, the depth of fixity for a long foundation still must be determined by other methods. In this study, the depth of pile embedment for the thawed condition acted like a short pile and this precluded finding an equivalent depth of fixity. The soil springs used to model the pile in the frozen condition are significantly stiffer in the frozen condition in comparison to the unfrozen condition. The spring stiffness needed to model the pile increased by two orders of magnitude, from thawed to frozen. A soil spring representing the top few inches of soil and a 1 inch long pile section, the force required to displace a soil spring 0.5 inches went from 310 pounds in summer (when the surface was thawed) to over 27,500 pounds in winter (when the surface was frozen).

Frozen ground is significantly stiffer than unfrozen ground. For bridges supported on deep foundations, the bridge stiffness is also measurably increased in the winter months. Significant changes in the bridge pier boundary conditions due to seasonal freezing require additional detailing to ensure a ductile performance of the bridge during the design earthquake event. This paper reports the latest results obtained from a project aimed at systematically investigating the effects of seasonal freezing on the seismic behavior of highway bridges in cold regions. Presented here are the results obtained from numerical simulation of the overall dynamic performance and field monitoring study of the bridge selected for study in this project. By using OpenSees computational platform, a three-dimensional FE model of the bridge foundation is established to investigate the impact of seasonal frost on the bridge substructure behavior. In the meantime, a bridge is instrumented with a network of accelerometers to monitor its dynamic and seismic behavior. Earthquake-induced vibration data have been collected and analyzed. The results show that seasonal frost has significant impact on the overall dynamic behavior of bridges supported by pile foundations in cold regions, and these effects should be accounted for in seismic design.

A semianalytical technique is proposed for the analysis of a meridional rib stiffened shell of revolution which accounts for the discrete stiffness of the rib in a rational manner. The method uses discrete field concepts, finite Fourier series expansion of the dependent variables in the circumferential direction and Galerkin FEM in the meridional direction to analyse such a class of shells. In the process the two-dimensional physical problem is reduced to a one-dimensional mathematical model, thereby increasing computation efficiency. This scheme can be employed to study the size and effect of the ribs on the shell behavior more efficiently than a full-blown FEM. Through the use of a numerical example, the effect of the ribs in a typical hyperbolic shell of revolution is illustrated. Shell deflection and stress resultants are compared for both stiffened and unstiffened shell subjected to wind pressure. The analysis is applicable to such linear elastic models where small deflection theory is valid.

Variations in temperature within a typical interior deck-stringer section of a composite-girder highway bridge are investigated for mid-Missouri weather exposures. The exposures correspond to ambient air temperature extremes and were selected from National Weather Service data for the period 1946 through 1965. Equations to simulate these weather extremes and a finite element analysis are used to calculate bridge temperatures as a function of time. The results show that the temperature at the top of a bridge deck may be as high as 150°F (66°C) for a midsummer day and as low as -10°F (-23°C) for a cold winter day. The temperature differential between the top and the bottom of the deck for a hot day was 39°F (22°C) and for a cold day was 31°F (17°C). The maximum deck temperature occurred at 2:00 p.m. for the hot day and at 1:00 p.m. for the cold day. The minimum deck temperature occurred at 4:00 a.m. for both the hot and the cold day.