J. Leroy Hulsey

Performance and Design of Laterally Loaded Piles in Frozen Ground

AbstractFrozen 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...

Ambient loading and modal parameters for the Chulitna River Bridge

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.

Seasonal Freezing Effects on the Dynamic Behavior of Highway Bridges

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.

Characterization of non-stationary properties of vehicle–bridge response for structural health monitoring

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.

Experimental Investigation of a Bridge under Traffic Loadings

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.

Characterization of Nonstationary Mode Interaction of Bridge by Considering Deterioration of Bearing

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.

Quantification of Dynamic Properties of Pile Using Ensemble Empirical Mode Decomposition

This paper investigated dynamical interactions between pile and frozen ground by using the ensemble empirical mode decomposition (EEMD) method. Unlike the conventional empirical mode decomposition (EMD) method, EEMD is found to be able to separate the mode patterns of pile response signals of different scales without causing mode mixing. The identified dynamic properties using the EEMD method are more accurate than those obtained from conventional methods. EEMD-based results can be used to reliably and accurately characterize pile-frozen soil interactions and help designing infrastructure foundations under permafrost condition.

Optimal static strain sensor placement for truss bridges

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.