Journal of Bridge Engineering

To understand the mechanical properties of superlarge-diameter piles in complicated geologic conditions, the authors carried out centrifuge model tests that simulated the bearing characteristics of single rock-socketed piles that had different cover thicknesses and rock-socket lengths. Valuable results were obtained from the centrifuge model tests. The overlying stratum of a single superlarge-diameter rock-socketed pile shares a certain proportion of the upper load, so it is not wise to neglect its bearing capacity in this type of design. The shaft resistance and tip resistance did not work synchronously with an increase in the upper load. Shaft resistance was mobilized prior to tip resistance and carried the majority of the upper load when the rock-socket length exceeded three times the pile diameter. There is an optimal rock-socket length for a certain thickness of overlying stratum. A centrifuge test was performed to investigate the behavior of a pile group socketed in bedrock with an inclined surface. The load distribution in the pile group was not even, and piles that had longer rock-socket lengths shared more load than piles that had shorter rock-socket lengths. The inclined surface caused differential settlement under concentrated vertical loading, which might result in safety issues with the superstructure.

Hybrid reinforcement for concrete bridge-deck slabs is being investigated through a collaboration project between the Ministry of Transportation of Quebec (MTQ) and the University of Sherbrooke. This paper presents design concepts, construction details, and results of live-load field tests of the twin hybrid-reinforced bridges (P-15502N and P-15502S) on Sainte Catherine Road in Sherbrooke, Quebec (Canada). These hybrid-reinforced slab-on-girder bridges are simply supported over a single span of 43,415 mm. Their 200-mm-thick concrete deck slabs are continuous over four spans of 2,650 mm each, with an average overhang of about 1,000 mm on both sides (measured perpendicular to the girder axis). The deck slabs were reinforced with glass fiber–reinforced polymer (GFRP) reinforcing bars in the top mat and with galvanized steel bars in the bottom mat. One of the two bridges (P-15502S) was instrumented with fiber-optic sensors (FOSs) in the bridge-deck slab (over and between the girders). The instrumented bridge was tested for service performance with three calibrated truck loads prior to placement of the asphalt layer to check for flexural cracks. The construction details and the results of the live-load field tests are presented. The field tests yielded very small strains in the GFRP reinforcing bars, which clarified the arch-action effect in the restrained hybrid-RC bridge decks.

Records show that research leading to the successful introduction of integral-type structures such as continuous beams and frames actually began in the 1930s. Simple stub-type abutments have been found to perform well and are recommended for widespread use. The purpose of this analysis was to consider the behavior of the superstructure and substructure/backfill soil when they are subjected to thermally induced lateral movement and vertically imposed load at deck level. With the Oasys Safe finite-element analysis programs, finite-element models were developed to represent a typical stub-type integral abutment bridge configuration and backfill/foundation soil profile. It was found that the behavior of the superstructure of an integral bridge was predominantly influenced by the loading magnitude, irrespective of backfill soil properties. The results suggest that when designing the superstructure, the design requirements to resist the imposed loading may be sufficient to accommodate any effects attributable to the thermal load.

Most of the vibration-based ambient modal identification methods in the literature are structured to process vibration data collected from a dense array of sensors centrally to yield modal information. For large systems, for example bridges, one of the main disadvantages of such a centralized architecture is the cost of dense instrumentation, predominantly consisting of the sensors themselves, the data acquisition system, and the associated cabling. Recent advances in wireless smart sensors have addressed the issue of sensor cost to some extent; however, most of the algorithms—with the exception of very few—still retain an essentially centralized architecture. To harness the full potential of decentralized implementation, the authors have developed a new class of algorithms exploiting the concepts of sparsity (using wavelet transforms) within the framework of blind source separation. The problem of identification is cast within the framework of underdetermined blind source separation invoking transformations of measurements to the wavelet domain resulting in a sparse representation. Although the details of these decentralized algorithms have been discussed in other articles, in this paper, for the first time, these algorithms are studied experimentally on a full-scale structure using wireless sensors. In a truly decentralized implementation, only two sensors are roved along the length of a pedestrian bridge, and the performance of the proposed algorithms is studied in detail. A pedestrian bridge located in Montreal, Quebec, Canada, is chosen primarily to highlight the methodology used to address modal identification under low-sensor density and for pedestrian loading. Issues arising from several modes being excited on this bridge and the presence of narrowband pedestrian excitations are addressed. The accuracy of modal identification that is achieved using the proposed decentralized algorithms is compared with the results obtained from their centralized counterparts.

In numerical simulations of engineering structures, several physical phenomena are represented by partial models, and the selection of the important partial models is usually based on engineering judgment. The quantitative assessment of how these partial models influence various response quantities is possible using variance-based sensitivity analysis. However, this provides information only on local positions in the structure. The present paper extends the sensitivity analysis at local positions to the integrative sensitivity analysis of the entire structural load-bearing behavior. In addition to the assessment of the partial model’s sensitivity, the method includes the local response significance factor, which relates the sensitivity to the response significance at each position in the structure. The integrative sensitivity analysis is applied to the numerical simulation of semi-integral concrete bridges to evaluate the partial model’s influence with respect to the entire integral structure. The quantitative assessment of the integrative sensitivity for varying pier heights and different loading conditions in the serviceability limit state and the ultimate limit state allows conclusions with practical engineering relevance.

The design of cable-stayed bridges is typically governed by the dynamic response. This work provides designers with essential information about the fundamental vibration modes, proposing analytical expressions based on the mechanical and geometrical properties of the structure. Different bridge geometries are usually considered in the early design stages until the optimum solution is defined. In these design stages, the analytical formulation is advantageous, because finite-element models are not required and modifying the bridge characteristics is straightforward. The influence of the tower flexibility is included in this study, unlike in previous attempts on mode estimation. The dimensions and proportions of the canonical models proposed in the analytical study stem from the previous compilation of the dimensions of a large number of constructed cable-stayed bridges. Five tower shapes, central or lateral cable-system layouts and box- or U-shaped deck sections, have been considered. The vibration properties of more than 1,000 cable-stayed bridges with main spans ranging from 200 to 800 m long were extracted within an extensive parametric analysis. The Vaschy-Buckingham theorem of dimensional analysis was applied to the numerical results to propose the formulation for period estimation. Finally, the formulas were validated with the vibration properties of 17 real cable-stayed bridges constructed in different countries. The importance of the tower flexibility is verified, and the errors observed are typically below 15%, significantly improving the estimations obtained by previous research works.

The Canadian highway bridge design code provides dimensions and reinforcement detailing of concrete bridge barriers reinforced with glass fiber–reinforced polymer (GFRP) bars. However, there are no guidelines on the repair of such concrete elements in case of damage caused by vehicle accidents. Therefore, the main objective of this study is to evaluate the feasibility and efficiency of available techniques to repair damaged GFRP-RC bridge barriers. To fulfill this objective, three full-scale, 6.0-m-long, PL-2 concrete bridge barriers, totally reinforced with GFRP bars, were constructed and tested under an equivalent static load, simulating a vehicle crash test. Two different repair techniques, planting and near-surface-mounted (NSM) fiber-reinforced polymer (FRP) bars, were used to repair the damaged barriers. Repaired barriers were retested under similar conditions to evaluate the effectiveness of the repair techniques. It is concluded that the repaired GFRP-RC bridge barriers achieved similar capacities to their counterpart control (undamaged) barriers.

In this paper, a refined double-beam finite-element model is constructed for composite cable-stayed bridges. Using this refined model, the authors aimed at performing more accurate three-dimensional (3D) analyses of cable-stayed bridges by considering all the geometric nonlinearities, including large 3D rotation issues, using catenary cable elements for cables, and taking into account member eccentricities between cable anchor points with the deck and member neutral axes. To consider member eccentricities and avoid using rigid links to connect the eccentricities, a validated two-step procedure is developed to transfer member forces and stiffness from the fluctuating neutral axis lines to a straight reference line. Through a numerical example, the effect of member eccentricity is discussed, and it is clearly shown that member eccentricity has a larger influence on displacements and bending moments than on modal responses. Through a detailed comparison example with previous research and existing software, the refined model presented in this paper demonstrates higher accuracy.

Planning retrofit actions on bridge networks under tight budget constraints is a challenging process. Because of the uncertainties associated with this process, a probabilistic approach is necessary. In this paper, a probabilistic methodology to establish optimum pre-earthquake retrofit plans for bridge networks based on sustainability is developed. A multicriteria optimization problem is formulated to find the optimum timing of retrofit actions for bridges within a network. The sustainability of a bridge network and the total cost of retrofit actions are considered as conflicting criteria. The sustainability is quantified in terms of the expected economic losses. The uncertainties associated with seismic hazard and structural vulnerability are considered. The methodology is illustrated on an existing bridge network. Genetic algorithms are used to solve the multicriteria optimization problem. The effects of deterioration on bridge seismic performance are considered. The effects of the time horizon on the Pareto optimal solutions are also investigated.

A series of optimal sensor placement (OSP) techniques is discussed in this paper. A framework for deciding the optimum number and location of sensors is proposed, to establish an effective structural health monitoring (SHM) system. The vibration response from an optimized sensor network reduces the installation and operational cost, simplifies the computational processes for a SHM system, and ensures an accurate estimation of monitoring parameters. In particular, the proposed framework focuses on the determination of the number of sensors and their proper locations to estimate modal properties of bridge systems. The relative importance of sensing locations in terms of signal strength was obtained by applying several OSP techniques, which include effective influence (EI), EI-driving point residue (EI-DPR), and kinetic energy (KE) methods. Additionally, the modified variance (MV) method, based on the principal component analysis (PCA), was developed with the assumption of independence in modal ordinates at each sensing location. Modal assurance criterion (MAC) between the target and interpolated mode shapes from an optimal sensor set was utilized as an effective measure to determine the number of sensors. The proposed framework is verified by three examples: (1) a numerically simulated simply supported beam, (2) finite-element (FE) model of the Northampton Street Bridge (NSB), and (3) modal information identified using a set of wireless sensor data from the Golden Gate Bridge (GGB). These three examples demonstrate the application and efficiency of the proposed framework to optimize the number of sensors and verify the performance of the MV method compared to the EI, EI-DPR, and KE methods.

The long-term assessment of large and complex civil infrastructures, such as prestressed concrete bridges, based on finite-element (FE) modeling remains a challenging task. The construction process, the influence of erection methods, the characterization of concrete properties, geometric accuracy, and environmental conditions are key factors involved in the development of robust FE models. Data collected using permanently installed monitoring systems is the most reliable strategy to improve such assessments. The availability of monitoring data are increasingly being used in the validation of design assumptions, updating of FE models, and safety factors. In this work, the long-term behavior of a long segmental bridge built in Portugal (Lezíria Bridge) is evaluated using FE model updating. The combination of several factors, including (1) the bridge’s scale, (2) the monitoring database, (3) the comprehensive scanning of important characteristics of the bridge, and (4) the FE modeling approach, makes this case study unique. Although the sensor trends are satisfactorily predicted, extrapolation of shrinkage and creep models, the influence of interior and exterior environments, and thickness variations of the structural elements are identified as areas for further research.

There has recently been considerable research published on the applicability of monitoring systems for improving civil infrastructure management decisions. Less research has been published on the challenges in interpreting the collected data to provide useful information for engineering decision makers. This paper describes some installed monitoring systems on the Hammersmith Flyover, a major bridge located in central London (United Kingdom). The original goals of the deployments were to evaluate the performance of systems for monitoring prestressing tendon wire breaks and to assess the performance of the bearings supporting the bridge piers because visual inspections had indicated evidence of deterioration in both. This paper aims to show that value can be derived from detailed analysis of measurements from a number of different sensors, including acoustic emission monitors, strain, temperature and displacement gauges. Two structural monitoring systems are described, a wired system installed by a commercial contractor on behalf of the client and a research wireless deployment installed by the University of Cambridge. Careful interpretation of the displacement and temperature gauge data enabled bearings that were not functioning as designed to be identified. The acoustic emission monitoring indicated locations at which rapid deterioration was likely to be occurring; however, it was not possible to verify these results using any of the other sensors installed and hence the only method for confirming these results was by visual inspection. Recommendations for future bridge monitoring projects are made in light of the lessons learned from this monitoring case study.

In the days of the AASHTO standard bridge design specifications, engineers used simple equations for calculating the HS-20 live-load moment for a simple span bridge. Engineers computed and compared the lane load moments to the truck load moments. The larger moment controlled the design. The second axle of the design truck was not placed at midspan but rather at a 2 ft 4 in. (0.711 m) offset from midspan. The correct orientation of the offset required that the truck’s resultant force reside on the opposite side of the midspan from the second axle. As an example, for a 50 ft (15.240 m) span, this 2 ft 4 in. (0.711 m) offset yielded a $628\hspace{0.17em}\text{kip-ft}/\text{lane}$ ($851\hspace{0.17em}\text{kN-m}/\text{lane}$) truck moment compared with a $620\hspace{0.17em}\text{kip-ft}/\text{lane}$ ($841\hspace{0.17em}\text{kN-m}/\text{lane}$) truck moment without an offset. By the 1990s, a new AASHTO specification was introduced based on LRFD. The old HS-20 live-load model was modified to combine its component lane load and truck load cases into a single load case called HL-93. This combined load case impacted the traditional 2 ft 4 in. (0.711 m) offset and made it vary according to span length. This paper proposes to derive an equation for determining the correct truck offset to produce maximum moment using HL-93 loading on simple spans greater than 40 ft (12.192 m). The scope of this paper does not include the tandem vehicle, because it does not govern spans greater than 40 ft (12.192 m) in length.