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Full-scale experimental case studies have shown that the induced trench construction method effectively reduces the vertical earth load that is exerted on culverts installed beneath high embankments. Induced trench culverts are traditionally designed on the basis of Marston’s theory; however, various theoretical shortcomings of this formulation have recently come to light. In this paper, a new induced trench theoretical formulation is presented. The proposed analytical model employs inclined shear planes within the embankment fill; such geometry is consistent with experimental findings reported in the literature and leads to positive arching resulting from a reduction in vertical stress and an increase in horizontal stress (thus increasing the lateral earth pressure coefficient within the induced trench zone). A series of parametric studies is performed using finite element software. The proposed theoretical formulation is shown to be in good agreement with the numerical results, and correlations are developed to provide guidance in selecting the appropriate values of (i) the induced trench lateral earth pressure coefficient and (ii) the height to the plane of equal settlement. Two instrumented full-scale induced trench case studies are discussed, and the proposed theoretical formulation is shown to produce results that are in good agreement with the experimental data.

When culverts are installed beneath high embankments, earth loads become excessive and the induced trench construction method is a viable design option to reduce the culvert loads to acceptable levels. However, limited field studies evaluating the performance of induced trench twin culverts are reported in the literature and the practicality and effectiveness of the induced trench construction method (in general) has been subject to recent criticism. This paper describes the performance of twin 3048 mm inside-diameter reinforced concrete culverts constructed with an induced trench beneath 15.3 m of fill. Research instruments and autonomous data acquisition systems were installed during construction to monitor (i) culvert earth pressures, (ii) embankment deformations, and (iii) groundwater elevations in the vicinity of the compressible fill. The experimental observations recorded throughout the construction phase are presented herein; the embankment deformations are indicative of effective positive arching within the induced trench region, and the average earth pressure at the culvert crown was reduced to approximately 48% of the overburden soil pressure. The experimental data are compared with those reported in the literature by others, and the conclusions attained from this study demonstrate the effectiveness of the induced trench construction method.

Advancements in sensing and computer technologies have made vibration-based techniques in structural health monitoring viable methods of structural assessment. An accurate estimation of modal parameters using vibration tests may be achieved only if an optimum monitoring time is chosen. In this paper, the limitations of the currently available criteria are discussed in detail. A new set of criteria is recommended for monitoring time that encapsulates the effect of input excitation other than white noise. The new criteria consider bias and variance error trade-offs for achieving the optimal monitoring time and the number of windows used in the Welch method for spectral analysis. The recommendations in this paper allows one to select an optimum monitoring time for excitations with narrow and broad band spectral densities. A series of numerical parametric studies were conducted to validate the new recommendations. The proposed criteria are also validated using ambient vibration test data collected from a cable stayed bridge in Canada. The experimental study results were also used to demonstrate the trade-off between the spectral analysis parameters on the accuracy of estimations.

This paper presents the application of a hybrid structural health monitoring approach for condition assessment of cable-stayed bridges. Information from the structure’s quasi-static response, global vibration behaviour, visual inspection, traffic data, global positioning system, and local vibration test of cables are incorporated into the assessment process. Signal processing techniques and monitoring parameters to achieve an accurate identification is discussed in detail. A rigorous hybrid assessment method was used to evaluate the structural integrity of cables through incorporating visual inspection, ultrasound test, and local and global vibration analysis data. The framework was applied to a long-span case-study bridge in New Brunswick, Canada. Condition of primary structural members including stay-cables, bridge girders, and the orthotropic steel deck were successfully identified. Other structural parameters such as the bridge deck non-structural mass was also evaluated.

Tapered piles are used in place of cylindrical piles for their improved geotechnical performance. When tapered piles are subjected to axial dynamic loading, as is the case with machine foun...

Advances in research and development have led to the application of high-strength timber plates to flooring-slab construction. It is envisaged that floors built from timber plates will have...

This paper presents a series of experimental and analytical studies on the ductility requirements of bolted double-angle shear connections. Five full-scale connection configurations were tested, and their load-deformation behaviour was monitored using the digital image correlation technique. The yield line patterns observed from the experiments differ from the assumed pattern used in the derivation of the ductility equations currently available in design guidelines. The identified deformation contours were used as the basis for further development of analytical formulations applicable to the flexibility requirements of connections. The yield line theory was employed to evaluate the induced moment on the connections at the ultimate shear capacity. The details of the experimental setup including test parameters, loading scenarios, and the digital image correlation technique are fully outlined. Finally, the developed formulation was validated through a comparison with previously published experimental results. The results show the proposed solution provides an accurate estimation of the moments induced on double angle shear connections at ultimate capacity rotations.

Cross-laminated-timber (CLT) floor slabs have clustered modal frequencies, with higher order modes significantly influencing motions caused by dynamic footfall forces. Presented analyses address dependence of predicted slab motions on construction details and modal frequency filtering decisions. Based on the results, ideas are presented for creating robust vibration serviceability design methods applicable to CLT floor slabs. Those ideas are consistent with ISO limits on human toleration of motions under defined conditions, and design code classifications of building occupancy conditions. Ongoing research is implementing them.

New ultralight materials like cross-laminated-timber (CLT) enable attainment of longer floor spans than are possible with traditional shallow-profile timber construction. Their low modal mass to stiffness ratios make ensuring satisfactory dynamic responses under normal building occupancy conditions a primary design consideration. This paper presents numerical techniques for accurate prediction of modal frequencies, which are essential input to contemporary floor vibration serviceability design criteria. Recommendations are made for minimum requirements for design level prediction of modal responses of CLT floors, based on numerical and experimental studies of effects engineering design variables have on such characteristics.

Practicing engineers generally obtain stiffness and damping coefficients for dynamic design of pile foundations from design charts. The design charts require multiple interpolations and produce approximate frequency-independent coefficients. Explicit expressions consistent with the underlying theory for the vertical vibration of single piles are presented in this technical note. These expressions are easily implemented in a computer program, such as a spreadsheet, for design use. The proposed method preserves the frequency-dependent nature of the dynamic coefficients and enables one to account for the true condition of the pile tip. The effectiveness of the proposed method is illustrated with numerous examples.

A sandwich pipe (SP) is an effective design alternative, providing effective load carrying capacity and thermal insulation to pipelines, especially when the pipe is going to be utilized in deep and ultra-deep water applications. However, the design and development of a reliable SP requires an in-depth understanding of the behavior of such a system under various loading conditions. In this paper, the behavior of SPs subject to pure bending, which is one of the governing loading conditions for offshore pipelines, is investigated. In order to perform this investigation, a series of numerical parametric models, using the finite element (FE) method, was developed. The linear eigenvalue buckling analysis and the nonlinear post-buckling analysis were conducted to explore the systems' response. The influence of several significant structural parameters on the pre-buckling, buckling and post-buckling responses of SPs was investigated. The parameters investigated included various combinations of several geometrical and material properties, as well as the consideration of various possible intra-layer adhesion mechanisms. Moreover, the recent high strength steels used in formation of oil and pipes exhibit certain degree of yield anisotropy; it is therefore crucial to understand the effect of material's yield anisotropy on such system's response. This issue has also been considered in this research.

Sandwich pipes (SPs) offer sensible and cost-effective design alternative for extraction of oil and gas in deep and harsh waters. By employing the potential thermal insulation properties offered by the core material used in SPs, and the structural integrity provided by the sandwich mechanics, SPs can be optimally designed to provide safe transportation system for oil and gas under specific loading and environmental conditions. In this paper, the influence of the structural parameters that would significantly impact the characteristic behavior and pressure capacity of SP systems, having various intra-layer adhesion properties, are investigated. SPs response is simulated by the finite element (FE) numerical method, accounting for the material and geometrical nonlinearities, and considering the intra-layer condition. Finally, the results of more than 12,000 nonlinear FE models are used to develop three simplified practical equations, capable of evaluating the pressure capacity of SPs having various intra-layer mechanisms and material configurations, with an acceptable accuracy. As one of the main objectives of this study, the influence of the intra-layer adhesion configuration on the optimal design of such pipes at various water depths is also investigated. The optimization procedure previously recommended by the authors is extended to establish the optimal structural configurations.

Sandwich pipe systems can be considered as potentially optimum design configurations for overcoming the shortfalls of single-walled pipes for deep-water applications. This potential design alternative has gained considerable attention in recent years. In this paper the stability of these systems is investigated. The possible equilibrium paths are evaluated and the effect of the various significant parameters on the characteristic behavior of the system is discussed. The Finite Element (FE) software package ABAQUS is used to construct more than 3000 FE models of the sandwich pipes with practical configurations. Four design configurations are considered for the sandwich pipes with respect to the adhesion among the interfaces. The post-buckling behavior of each of these configurations is determined, with emphasis on a wide practical range of parameters. The behavior of these configurations is examined and the efficiency of each system is discussed. Finally, a simplified and fairly accurate equation is developed and recommended for calculating the pressure capacity of sandwich pipes. The parameters of the proposed equation are also fully defined.

Sandwich Pipes (SPs) have been developed to overcome the required flow assurance and pressure capacity issues in deep and ultra-deep waters. This research aims at studying the influence of certain structural parameters on the pressure capacity (also referred to as the plastic buckling pressure) of Sandwich pipelines. The use of high grade steel pipes, as the internal or external pipes, has also been considered as one of the design parameters in this study. Moreover, a comprehensive parametric study, considering a practical range of the parameters that influence the response of SPs (and considering 3840 SP configurations) was conducted. The results from this large array of pipes were used to formulate a practical equation, capable of estimating the plastic buckling pressure of SPs. The accuracy of the proposed equation was evaluated by comparing the results with the experimental and numerical results available in the literature. The comparative results demonstrated that the proposed equation could predict the buckling capacity of such pipes with a reasonable accuracy. Furthermore, the proposed equation was used, along with a general optimization procedure, to establish the most optimum and cost-effective combination of structural parameters for SPs suitable for use in various water depths.

Sandwich Pipes (SP) can be considered as an enhanced design configuration for Pipe in Pipe (PIP) systems. By improving the structural properties of the core layer and the components’ interface adhesion, SP systems can be an effective design alternative for deepwater applications. However, designing such a hybrid structure demands more knowledge of the response of the system under the governing loading and environmental conditions. A SP system would be a suitable design alternative for offshore pipelines that are subjected to very large hydrostatic pressure in deepwater. Therefore, full understanding of the behavior of such systems under the external hydrostatic pressure is a prerequisite for designing optimum SPs. In this paper a set of parametric models are generated based on practical design configurations. The Finite Element (FE) software package, ABAQUS, is used to create the models and analyze them. The FE models are analyzed through eigenvalue buckling and post-buckling analyses with the assumptions of linear and nonlinear buckling. Appropriate initial imperfections and FE parameters are administered. Moreover, the integrity of FE models is investigated through a mesh convergence study and also by considering various types of element locking mechanism. The results of these three methods of analysis are compared and the discrepancy between the results obtained through the linear analysis in comparison to the nonlinear post-buckling analysis is highlighted. Moreover, the influence of using various material plasticity models on the buckling and post-buckling responses is also investigated. Different models describing the materials stress-strain curves in the form of the elastic perfectly plastic, elastic followed by plastic exponential hardening, as well as the existence of the Luder’s bands are also considered. Furthermore, the effect of core material’s stiffness on the buckling and post-buckling response of the system is also examined. Based on the equivalent plastic strain, it will be shown that in order to ensure system’s effective composite sandwich action, the core must have a certain minimal stiffness. Finally, the influence of the enhancement in the steel grade used to form either the internal or external pipe on the stability response of both PIP and SP systems will be illustrated.Copyright © 2010 by ASME