Journal of Bridge Engineering

A drive-by method is proposed to identify the modal frequencies of railway bridges from the dynamic responses of two-axle vehicles. The theoretical closed-form solution and frequency components of the vehicle response are derived based on the vehicle–bridge interaction (VBI) model composed of a two-axle vehicle and a simply supported bridge. The time-domain subtraction method (TSM) is improved and explained for two connected two-axle vehicles to reduce the effect of the track irregularity on the frequency identification of the bridge. The accuracy of the closed-form solution is verified by the finite-element (FE) analysis, indicating that both the vertical and pitching responses can be used for bridge frequency identification. Parametric studies are also conducted to investigate the factors that may affect the frequency identification. The results indicate that the TSM has a good performance and robustness against the track irregularity to ensure good frequency identification. The bridge frequencies with different stiffness can be well-identified regardless of the symmetry and damping of the vehicle, which shows a good prospect for indirect bridge monitoring.

This paper develops a novel reinforcement frame as the shear connector in the composite deck, which was expected to deliver large pre-pouring stiffness. To investigate its shear resistance, nine specimens were designed, including eight specimens using a reinforcement frame and one comparative specimen using classic headed shear studs. The pre-pouring stiffness of all the specimens was tested by hanging weight. Compared with the classic headed shear studs, the reinforcement frame significantly enhanced the pre-pouring stiffness of the composite deck hundreds of times. The four-point bending tests were performed to obtain the shear resistance of the composite deck. The composite decks using the reinforcement frame could achieve the same or even larger load-carrying capacity with those using headed shear studs. The wave-shaped rebar effectively limited the diagonal cracking. Based on physical testing, the finite–element model was developed and provided good agreement with the test results. The influence of the design parameters on the pre-pouring stiffness and ultimate shear resistance is discussed. Based on the physical tests and finite–element analysis, the demarcation condition for the two typical failure modes is observed.

Seismic assessment is of critical importance for structures in regions where earthquakes are prevalent. Such assessment in terms of determining the inelastic capacity of structures is often performed in laboratories of universities, government, and industry through quasi-static cyclic testing programs. In these programs, selecting an appropriate loading protocol is crucial for achieving an accurate assessment of inelastic capacity. Appropriate loading protocols need to be representative of the seismic demands to which a structural component may be subjected during seismic events. A standard loading protocol available in the literature may not necessarily yield a meaningful response. For the quasi-static cyclic test program, a loading protocol should be developed specifically for the site, structural component, or system. In this study, an incremental dynamic analysis–based approach is introduced to develop component-specific quasi-static cyclic loading protocols, which is illustrated for a single-column-reinforced concrete bridge bent in Vancouver, British Columbia. Here, different target displacement ductility demand levels, that is, 2, 4, and 8, and different sources of earthquakes, that is, crustal, intraplate, and subduction earthquakes, were considered. The number of inelastic cycles and cumulative ductility damage were the primary target demand parameters in the loading protocol development. Conventional loading protocols were found unrealistically more damaging than those proposed for crustal and intraplate earthquakes. The proposed loading protocols for subduction earthquakes were consistent with those developed by other researchers for the same but employed the classical constant ductility design approach to achieve the target displacement ductility levels.

This work proposes an efficient identification scheme for simultaneous input and parameter estimation of the hysteretic systems. For this purpose, a quasi-Monte Carlo (QMC)-simulation-based approach is adopted, where the sigma point generation scheme is coupled with a minimum variance unbiased estimator. In this process, additional bounds and constraints on the parameters are introduced to control the stability and convergence. The accuracy of the proposed algorithm is validated using a synthetic experiment on a frame whose nonlinear behavior is characterized by the Bouc–Wen–Baber–Noori model, that is, with degradation and pinching. Once the proposed algorithm is validated, its performance is further demonstrated using the shake table test of a full-scale bridge pier. The identified parameters in this case are utilized for damage quantification using a modified Park and Ang damage index. Overall, this study shows the robustness of the proposed algorithm for combined input estimation and condition assessment of inelastic reinforced concrete structures with a significant level of accuracy.

This paper will examine in detail a posttensioned concrete (PTC) girder bridge with dapped-end connections, with a re-entrant corner diagonal crack that is typical of these types of bridges. This paper aims to identify the possible causes of the existing damage and the potential modes of failure of the bridge's girder using nonlinear finite-element analysis (FEA). Failure analysis of the bridge girder will consider the effects of supplying the bridge with different dapped reinforcements and subjecting the bridge's prestressed tendons to losses in their prestressing forces. Various failure scenarios and cases will be simulated in numerical models. Numerical analysis results will be compared with design guidelines for bridge girders. Overall, the investigative results indicated that the combined impacts of insufficient hanger reinforcement and prestress losses in the girder's end-section was the probable cause of the bridge's re-entrant corner diagonal crack.

Suspension bridges with three cable planes provide an excellent solution to the suspension bridges’ downwarp problem with ultrawide decks, which implies their enormous demand and popularization prospect in the engineering scenarios. In this paper, a method for uniform allocation of dead load in the transverse direction to three cables of the suspension bridge with three cable planes (SB-3CP), which transforms the spatial stress mode into a plane model to simplify the calculation, is proposed. By altering the cross-sectional area of each hanger, the axial forces of the three hangers in the same cross section of the SB-3CP are equal. Therefore, the cross-sectional area and shape of the three cables are equal, improving the suspension bridge outlook in both the cross-sectional and facade views of the suspension bridge. Meanwhile, under the uniform allocation of the dead load, the side main cable bears a higher share of the dead load, which is conducive to improving the entire bridge’s torsional rigidity. In this study, conditions for compatibility of deformation and energy conservation are utilized to derive the relationship between the axial rigidity of the three hangers in the same cross sections. The effects of axial rigidity of hangers, flexural rigidity of the deck in the transverse direction, and length between the hanging points on the difference in the axial rigidities of the three hangers are analyzed and discussed in detail. Finally, an SB-3CP with a main span of 2,320 m and a width of 75 m was taken as an example. The cross-sectional areas of each hanger of the bridge were calculated using the proposed method. Then, its accuracy was validated through the finite-element analysis. This method’s design effect was verified by comparing the differences in the main cable diameter and torsional rigidity between the SB-3CP with uniform and nonuniform dead load distributions.

The ability of shallow bridge foundations to dissipate earthquake energy via rocking has gained significant attention by bridge engineers owing to recent efforts to quantify the performance of rocking footings. This paper presents a new formulation for estimating the moment capacity of rocking bridge foundations resting on all types of soils under varying saturation and surface flux boundary conditions. The proposed formulation uses the moment capacity equation originally employed for saturated soils, classical effective shear strength parameters, and a representation of the soil–water retention curve (SWRC) to accommodate partially saturated conditions that may commonly exist below the shallow foundations of bridge substructures. A closed-form equation is incorporated in this formulation for the matric suction and effective saturation profiles to directly implement surface flux boundary conditions when analyzing the moment capacity of rocking foundations supported on partially saturated soils. The formulation implements a new method to predict the air entry suction for partially saturated soils, representing a key step towards improving the accuracy of moment capacity. A parametric study is performed to investigate the sensitivity of the moment capacity to primary design variables and various surface flux boundary conditions. The analyses demonstrate that flow conditions have a negligible and strong influence on the moment capacity of coarse- and fine-grained soils, respectively. Predictions from the proposed formulation were compared against two sets of experimental data obtained from large-scale shaking table (on sand) and snap-back (on plastic silt) tests and indicated good agreement with experiments.

The prefabricated segmental column using posttensioning technology has become an ideal candidate for rapid and environmentally friendly construction. To avoid damage to the segment joint during a seismic event and enhance its energy dissipation (ED), a precast segmental concrete-filled steel-tube (PSCFST) bridge column with internal or external ED bars is proposed. The seismic performance and resilience of the PSCFST bridge columns with internal or external ED bars are investigated. Moreover, the fiber-section model and numerical analysis are used to analyze the optimal setup angle of the external ED bar. More importantly, the deformation mechanism of the PSCFST specimen with internal or external ED bars is provided. Then, two PSCFST columns and one reference monolithic reinforced-concrete (MRC) column were designed and tested under pseudostatic loading. Owing to the confinement effect of the steel tube on the concrete of each segment, the PSCFST column has desirable performance without obvious damage, whereas the plastic hinge region of the MRC column is severely damaged. After the test with a maximum drift of 5%, the residual drift of PSCFST columns is very small, only 0.175–0.209%, whereas the residual drift of the MRC specimen is 3.632%. To investigate the resilience performance of PSCFST column, one column was reloaded after the replacement of the external ED bars. Compared with the original specimen, the reloaded column shows excellent self-centering behavior, no obvious damage, and very small residual displacement.

An innovative load rating method for skewed highway bridges with steel girders is proposed in this paper. In the proposed method, a field test coupled with a grillage analysis is used to determine the actual safe load-carrying capacity of a bridge and the key factors that contribute to the capacity. Because the actual behavior of the bridge is incorporated via the field test, the method provides a justifiable evaluation of system behavior. The effect of additional system stiffness due to bridge skew is determined using a grillage analysis. The proposed method allows the factors that contribute to the load rating, such as critical span adjustment, longitudinal and lateral load distribution, unintended composite action, slab flexure, and additional system stiffness, to be quantified and qualified. The proposed method is illustrated using a case study of a symmetric steel girder bridge with a 43° skew angle. The case study demonstrates that the proposed method provides an accurate determination of the skew effect, compared to approximate methods of analysis, because the location of the girder and moment under consideration, the cross frames and parapets, and the location of the applied loading are explicitly incorporated.

Glass suspension footbridges or glass-bottomed suspension footbridges, such as the Zhangjiajie Grand Canyon Glass Bridge in China, are increasingly constructed in scenic regions as tourist attractions due to the glass-bottomed and transparent characteristics. Being installed in the second phase as a constant load, the glass deck is not designed to participate in the load bearing of the whole structure and thus the structure requires larger load-bearing capacity from other parts and a slightly different load-bearing system. More importantly, the glass deck weakens structural integrity and results in slightly smaller structural stiffness, which may result in globally lower natural frequencies. These structures may inevitably be more sensitive to the pedestrian-induced excitations. This paper investigates the human-induced vibrations of a typical glass suspension footbridge in China. The investigations are first performed based on intensive parametric studies. Except for the boundary conditions, the interlayers of glass, the vertical rise–span ratio and the axial stiffness of main cables, other governing parameters of the modal parameters for this type of structures are also identified, including the pavement load of the bridge deck system, the central buckle, and the prestress of wind-resistant cables. It may guide designers to take effective measures to improve the dynamic behavior of this type of structure. Next, the vibration serviceability assessments were performed based on different standards and guidelines such as the UK National Annex (NA) to Eurocode 1 (2008), the Bro2004 specification of Sweden, the HiVoSS guideline, and the ISO standard. Comparisons show that the UK NA to Eurocode 1, the HiVoSS guideline, and the ISO standard are more suitable for the vibration serviceability evaluations. These three codes consider the pedestrian-induced vibrations in both lateral and vertical directions and also consider both a small number of pedestrians and crowd-induced loads with different densities. Furthermore, comfort limits are not defined by only one limiting value but sorted into different levels. This may provide reference for the vibration serviceability evaluations of the other glass suspension footbridges. The assessments also show that changing the structural parameters can only partially reduce vibration levels and may result in different modal parameters to dominate the vibration responses. Thus, they recommend taking vibration mitigation measures to improve the vibration serviceability and suggest performing careful response calculations to ensure the effectiveness of vibration serviceability design if via changing the structural parameters. Finally, tuned mass dampers (TMDs) are installed to the structure. The results show that the popular TMD may effectively reduce the vibration levels.