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Additional file 1: Supplementary Figure 1. (A) Boxplot show the relative abundance and difference of nine phyla of bacteria among four groups of laying hens. Wilcoxon rank-sum test: *, P < 0.05; **, P < 0.01, ***, P < 0.001; ****, P < 0.0001. (B) Five-fold cross-validation with five repeats were used to evaluate the importance of indicator bacterial genera, including HE versus HP, YE versus YP, HE versus YE, HP versus YP.

Quantifying the uncertainty in the dynamic properties of large-scale complex engineering structures presents significant computational challenges. Monte Carlo simulation (MCS) method is extensively employed to perform uncertainty quantification (UQ) because of its generality, stability, and easy implementation. However, a brute-force MCS approach may be unaffordable and impractical when the target model contains a large number of uncertain parameters. In this circumstance, MCS requires a potentially burdensome (if not computationally intractable) number of model evaluations to obtain a credible estimate of the global statistics. In this study, a general framework for analytical UQ of model outputs using a Gaussian process (GP) metamodel is presented, where case inputs are characterized as normal and/or uniform random variables. A detailed derivation of important low-order statistical moments (mean and variance) is given analytically. This analytical method is adopted to characterize the uncertainty of modal frequencies of two bridges with assumed normally- and uniformly-distributed parameters. Meanwhile, the brute-force MCS approach is used for comparison of GP metamodel-derived statistics. Results show that the GP method outperforms the MCS methodology in terms of computational cost, with consistency in the "true" values obtained by MCS. It demonstrates that this GP method is feasible and reliable for modal frequency UQ of complex structures. © 2014 Elsevier Ltd.

The main objective of this study is to assess the structural integrity of the I-24 parallel bridges at the Cumberland River crossing in western Kentucky. Due to its importance, the bridge is evaluated for the 250-year event and the maximum credible 500-year event. The scope of the work included: 1) Field testing of the main bridge; 2) Finite element modeling and calibration; 3) Time-history seismic response analysis for the main spans; and 4) Seismic evaluation for both the main and the approach spans. The seismic analysis for the 250-year event indicates that the main spans of the bridge can resist the event without yielding or loss-of-span at the supports. However, the anchor bolts on some of the piers are expected to fail in shear. Retrofitting measures are recommended. The seismic analysis for the 500-year event shows that few members of the main spans would yield due to the event. Also, the capacity of the bearing shear bolts of few piers of the main and approach spans are exceeded, and retrofitting measures are recommended.

This report presents the seismic evaluation of the approaches and parallel bridges on I-24 crossing the Tennessee River between Marshall and Livingston counties in Western Kentucky. The main bridges are steel tied-arch bridges. The bridges are situated within the influence of the New Madrid Seismic Zone. The seismic evaluation program consisted of field testing, 3-dimensional finite element modeling and seismic response analysis. The dynamic properties of the main bridges are determined through field testing, and are used to calibrate the finite element models. The finite element model is then subjected to time histories of the 250-year and 500-year earthquake events. Stresses and displacements for these events are found to be within the acceptable limits. Analytical results indicate that the main bridge will withstand the 250-year and 500-year earthquakes without any significant damage and no loss-of-span. The supports with fixed bearings on the pier of the main bridge need to be retrofitted for the 500-year earthquake event. The approach spans are analyzed using the response spectrum method with simplified single-degree-of-freedom models. Some supports on the approach spans are found to be vulnerable to shear failure of anchor bolts under the 250-year earthquake. All supports on the piers of the approach spans need to be retrofitted for the 500-year earthquake event. Additional anchor bolts or other retrofit measures at the bearings are recommended.

This report presents the baseline modeling of the Maysville cable-stayed bridge which connects Maysville, Kentucky and Aberdeen, Ohio over the Ohio River. The objective of this study is to establish the bridge baseline model via the dynamics-based technique and finite element method. The scope of research includes finite element modeling and modal analysis, field free vibration testing, finite element model calibration using field test results, and cable dynamic testing and modeling. It is demonstrated that a cable-stayed bridge is a highly pre-stressed structure. The stress stiffening of cable elements plays an important role in both static and dynamic analysis. The large deflection analysis has shown that large deflection has the limited effect on the member deflections. Dominate dynamic response modes in the low frequency range contain vertical and transverse directions. The free vibration modes of the bridge are complicated and coupled. A good agreement of frequencies has been found between finite element modeling and in field free vibration testing after calibrating the finite element model. But, the better matching for higher modes is not expected and not realistic, as the experimental model properties of the bridge come from the output-only measurement. The calibrated finite element model may be used as a baseline in the future structural analysis and monitoring of the Maysville cable-stayed bridge.

The John A. Roebling suspension bridge, formerly the Covington-Cincinnati suspension bridge over the Ohio River was completed in 1867 and is still serving the Northern Kentucky community. The objective of this study is to assess the bridge load capacity via the dynamics-based technique. The scope of research includes finite element modeling and modal analysis, field ambient vibration testing, finite element model calibration to field test results, and bridge load-capacity evaluation. It is demonstrated that stress stiffening of cable elements plays an important role in both static and dynamic analyses of the Roebling suspension bridge. Large deflection behavior has been shown to have a limited effect on the member forces and deflections. Dominant vibration modes in the low frequency range are shown to be in the transverse direction. Higher free vibration modes of the bridge are coupled. In the structural evaluation under dead loading, the main cable area is reduced by 10% to 40% to simulate deterioration and corrosion of the cables. It is observed that the safety margin of the main cables remains fair (larger than one) even for the conservative 40% cable area reduction and extreme live loading pattern that equals 40% of uniform dead loading. Similarly, the truss member forces are within the maximum capacity. The current load limit posting for the Roebling bridge is adequate. In case the load limit will be increased in the future, it is recommended that a detailed study be conducted to evaluate the need to strengthen the top chord truss members in order to increase the loading capacity of the truss.