Journal of Bridge Engineering

Metal deck forms are frequently used in the steel building and bridge industries as formwork for the wet concrete slab. Although the forms are often relied on for stability bracing during construction in buildings, conventional connection details between the forms and girder top flanges in the bridge industry possess an eccentricity that limits the bracing performance of the forms. A research study to assess and improve the bracing potential of permanent metal deck forms (PMDFs) used in bridge applications was conducted. Recommendations from the research study were implemented on two steel I-girder bridges located on the IH-610 north loop in Houston. The use of the PMDF bracing resulted in the elimination of 680 intermediate diaphragms from the bridges. Before the implementation project, laboratory buckling tests were conducted on a twin-girder system with members and bracing that were identical to those used in the implementation project. To the authors’ knowledge, this project represents the first time that metal deck forms were relied on for stability bracing of steel I girders in the bridge industry. This paper documents laboratory testing, design, and construction of the two bridges in which PMDFs were used as construction bracing for the steel I girders in the bridge superstructure. Laboratory test results showed that the forming system, which was at the lower span limit of PMDF systems frequently used in steel bridge systems, could provide suitable bracing for the two implementation bridges. Using metal deck forms for bracing, the bridges were designed with no intermediate diaphragms/cross frames. A total of 680 intermediate diaphragms that would have been required in a bridge with conventional bracing were eliminated. The implementation of the research recommendations in the design of steel bridges can result in substantial improvements on the efficiency and economics of bracing systems for steel bridge superstructures.

Two similar bridges constructed with a live-load continuous connection were tested for live-load distribution and joint continuity. Girder distribution factors (GDFs) were compared with AASHTO equivalent values. For positive moments on all girders as for negative moments on interior girders, results using AASHTO equivalent GDFs were found to be generally conservative. However, for negative moments on exterior girders, test results exceeded AASHTO values, significantly so with two-lane results. GDF results were verified with a finite-element analysis (FEA) model, which produced behavior similar to the field tests. With respect to joint continuity, it is estimated that a simple span would produce a maximum positive moment about 7% higher than the actual structure, whereas a completely continuous structure would produce a maximum positive moment about 16% lower than that of the actual structure. For negative moments, the actual structure experienced about 28% of that of a continuous structure. Shear reactions were also investigated. Recommendations are proposed for evaluating transverse distribution of live load as well as the longitudinal distribution of live load, accounting for the effect of joint continuity.

The real behavior of existing structures is usually associated with large uncertainty that is often covered by the use of conservative models and code practices for the evaluation of remaining fatigue lives. To make better decisions related to retrofit and replacement of existing bridges, new techniques that can quantify fatigue reserve capacity are required. This paper presents a population-based prognosis methodology that takes advantage of in-service behavior measurements using model-based data interpretation. This approach is combined with advanced traffic and fatigue models to refine remaining fatigue-life predictions. Study of a full-scale bridge revealed that this methodology provides less conservative estimations of remaining fatigue lives. In addition, this approach propagates uncertainties associated with finite-element, traffic, and fatigue-damage models to quantify their effects on fatigue-damage assessments and shows that traffic models and structural model parameters are the most influential sources of uncertainty.

An analytical model and corresponding closed-form equations capable of determining the internal forces, moments, and deflections about the weak and strong axes, as well as the angle of twist along the span and the rigid body rotation of a prismatic long-span beam with overhangs at both ends and with an initial horizontal curvature are presented. The beam was supported on two nonlinear elastic bearings, each with an initial slope, and temporarily held by a crane at the middle point of its total span. The beam cross section was assumed to be doubly symmetrical and made of a continuous, homogeneous, and linear elastic material. The effects of cross-sectional distortion, shear deformations, initial vertical curvature, and residual stresses and prestressing were not included in the analysis. An example is presented and discussed in detail showing the effectiveness and accuracy of the proposed method.

The most slender and flexible footbridges are stress ribbon bridges. One kind of these elegant and simple bridges consists of two hanging steel ribbons, usually made of steel, which carry concrete deck panels and are anchored between two heavy abutments. At the anchorage and on intermediate supports the ribbons are often supported by saddles that are curved so that the additional bending stresses in the ribbon, which occur there, stay within allowable limits. The magnitude and the distribution of the bending stresses, the transverse pressure the ribbons exert on the saddle, and stress changes in the region of the detachment point caused by live loads are crucial for the dimensioning of these ribbons. A clear understanding of these issues via parametric studies, analytical solutions, and confirmation by finite-element (FE) analyses are provided in this paper. The findings presented here can also be used for other saddle systems, such as those used in cable-stayed and extradosed bridges.

Using the Vincent Thomas Bridge (VTB) as a feasibility case study, near-fault loading protocols for qualifying buckling-restrained braces (BRBs) for use on long-span bridges were developed and are presented in a companion paper. In this paper, full-scale component testing demonstrated the ability of BRBs to sustain several consecutive near-fault loading protocols, and therefore, they are recommended as qualified for potential use on the VTB and other similar long-span bridges near seismic faults. Near-fault protocol test results led to the proposal of a new procedure for measuring unbalanced BRB compression and tension forces by testing two nominally identical braces. Other novel test variables included the use of stainless steel (SS) for several BRB yielding cores and high strain rates, characteristic of near-fault loading, in two dynamic tests. Design considerations were identified for BRBs using highly ductile SS considering its significant strain-hardening properties, as well as the increased brace force response due to the high strain rate observed for both steels.

Buckling-restrained braces (BRBs) are reliable energy-dissipating axial members that recently became popular in the seismic design of buildings. Using the Vincent Thomas Bridge (VTB) as a case study, this research investigates the feasibility of using BRBs for seismic response mitigation of long-span bridges, especially those located adjacent to seismic faults. A satisfactory set of BRBs was identified through a parametric study using a finite-element model of the bridge. Simulated deformational demands on the BRB elements included loading features that are not reflected in current BRB design and testing provisions. Therefore, two new BRB loading protocols were developed for physical testing and prequalification. The simulated seismic response of the bridge was improved by using BRB parameters consistent with those that are commercially available. Therefore, the use of existing BRB technology was deemed feasible as a relatively maintenance-free seismic response mitigation system for long-span bridges near seismic faults. A companion paper discusses a testing program of full-scale BRBs subjected to these new protocols along with the implications for seismic-capacity-based design and testing procedures.

This paper presents an investigation on the practicability and structural efficiency of prestressed carbon-fiber–reinforced polymer (CFRP) strips with a gradient anchorage in the framework of a bridge-strengthening application in Poland. The nonmechanical anchorage system avoids the installation of metallic bolts and plates, with the exception of a temporary support frame. Two 18.4-m-long large-scale prestressed concrete girders were produced following the drawings of the existing bridge construction. One girder served as a reference, and the second one was strengthened with two prestressed CFRP strips. In this case, the initial negative cambering was leveled out by a layer of dry shotcrete. CFRP strips with a prestrain of 0.58% were applied for flexural upgrading. Both girders with a total length of 18.4 m were finally statically loaded up to failure to assess the strengthening efficiency in flexure of the retrofitting technique used. Tensile failure of the CFRP strips was reached, indicating an optimal use of the composite reinforcement. The strengthened girder exhibited a ductile behavior up to strip rupture with a distinct steel yielding and a subsequent pronounced increase of the load-carrying capacity. For service load considerations, an enhancement of the cracking load of approximately 16% was noticed. In terms of ultimate load, a significant improvement of approximately 25% compared to the reference girder was reached. Although some practical problems need optimization, the presented results are very promising and make this strengthening system an alternative for future retrofitting applications in bridge engineering.

A 55-year-old bridge showed large cracking in the approach bridge caused by restraint of deformation and support settlement. After repair, it was uncertain at which crack width the traffic loads on the bridge should be further restricted. The shear capacity was calculated by counting on the aggregate interlock capacity of a supposedly fully cracked cross section. An aggregate interlock relationship between shear capacity and crack width based on an unreinforced section was used to find the maximum allowable crack width. Limits for crack widths at which load restrictions should be imposed were found. The large structural capacity of the cracked concrete section shows that the residual bearing resistance based on the aggregate interlock capacity of reinforced concrete slab bridges with existing cracks is higher than expected. This expected capacity could be calculated with the inclined cracking load from the code provisions. The procedure outlined in this paper can thus be used for the shear assessment of fully cracked cross sections of reinforced concrete bridges.

Fatigue service life of steel bridges subjected to cyclic live loads was studied using operational strain measurements of a full-scale bridge. Fatigue fracture can be brittle and sudden, potentially leading to catastrophic bridge collapse. A service-life index and function were proposed for determination of the ultimate service life and remaining service life of bridges. The proposed method was used to study fatigue behavior of a bolted connection of a full-scale steel bridge. A regression model was developed for calculation of the life index and the service life function. Instead of common practice of using nominal stress data, realizations of the maximum stresses were generated using the bootstrap method. This paper shows that the proposed model is applicable for service-life prediction of existing steel bridges using only a finite number of operational measured strains from heavy truck loads.

Current practice in California requires up to a 60-day waiting period for closure pour after falsework release for both staged construction and bridge widening. The relatively long waiting period is intended to mitigate damage to the connected bridge deck as differential displacement develops between the new and previously constructed decks. The current waiting period does not take into account the displacement capacity of the closure slab, which depends on the dimensions and reinforcement details of the slab. In this paper, time-dependent deflection of two bridges under construction was measured up to approximately 12 months, and full-size tests were conducted to investigate the behavior of closure slabs when subjected to differential displacement. The objective of the tests was to determine the deformation capacity of the slab so that time-dependent deflection of the bridge can be directly taken into account when determining the waiting period for slab closure. Parameters in the test program included the length and thickness of the slab and the use of couplers in the slab reinforcement. Results indicated that attention needs to be paid to large stiff closure slabs, leading to a long waiting period, as brittle failure may occur at relatively small differential displacement.

In cantilever-erected concrete box-girder bridges, a great number of longitudinal posttensioning tendons curve twice in the top flange to fit their anchor position. The radial force attributable to the curved tendons produces transverse bursting stresses, resulting in tension in the concrete of the top flange. In practice, longitudinal cracking is sometimes observed in the convex side of the horizontally curved tendons. Thus, it can be inferred that the transverse bursting stresses induced by horizontally curved tendons are partially responsible for the cracking. To seek an analytical solution to such scenarios, this study used a semi-infinite slab model with proper boundary conditions. By introducing the Airy stress function and its derivative on the boundary, an analytical formula for transverse tensile stresses was developed, and this formula was verified to have good accuracy as compared with finite-element analysis. Analysis revealed that the transverse bursting stresses were predominately affected by the curved angle and the distance of the two inflection points. Finally, this paper proposes countermeasures to control this unfavorable effect.

Ductile fracture of steel structural members under combined shear and tension was observed in past strong earthquakes, but studies on ductile fracture under the combined stress state have been very limited in the field of steel structures. This study aims to experimentally and numerically investigate the coupling effect of shear stress and tensile stress on ductile fracture of both mild steel and high-strength steel. Two series of specimens are manufactured in which they are under pure shear and combined shear and tension. Meanwhile, a generalized simulation process, including generalization of the whole stress-strain data up to the fracture and fracture parameter calibration using only tensile coupons, is proposed to simulate ductile fracture of different structural steels. The generalized simulation process is proven to be capable of simulating ductile fracture under the combined stress state with good accuracy and simplicity.

Current structural design philosophies rely on the inelastic capacity of structures for resisting seismic excitations. To assess such capacity, cyclic loading protocols have been used as a common practice in laboratory and numerical evaluations. The main objective was to obtain quasi-static loading protocols that reflect the increase in the inelastic demands of bridge columns subjected to long duration ground motions caused by subduction megathrust earthquakes. To study the demands imposed on the structural system, results from nonlinear time-history analyses considering numerous subduction ground motions imposed on structures with a wide range of structural periods and target ductilities were used. Because the number of inelastic cycles and the expected damage can be closely related, statistical analyses of the number of inelastic cycles and the cumulative inelastic demands were used to develop the loading protocols. Due to the observed dependence of the demand parameters on the structural period, different protocols were developed for short-, medium-, and long-period responses. The proposed cyclic deformation histories are more representative of the inelastic demands from subduction earthquakes; therefore, their application would improve the seismic assessment of bridge columns exposed to such hazards.

Widely used failure modes and effects analysis (FMEA) can be very effective in assessing the relative risks of the failure modes of a bridge scour countermeasure. In this study, an approach is developed for assessing the relative risks of failure modes of a bridge scour countermeasure overcoming the limitations of risk priority numbers (RPNs) associated with individual failure modes. Appropriate application of the RPNs is established by ensuring that high values of RPNs, indicating a relatively higher risk of failure, have higher severity and occurrence ratings compared with the low RPNs, indicating low risk. Replacement of the use of RPNs with risk priority codes (RPCs) enables engineers to prioritize the risks for any severity-occurrence pair using the same scale as the ratings, unlike the RPNs. Given the simplicity and effectiveness of this technique, RPCs are shown to be preferable for assessing and prioritizing the relative risks of the failure modes of a bridge scour countermeasure.

The purpose of this paper is to evaluate the impact factor (IM) in LRFD bridge design specifications for fatigue design and to propose a method for determining reasonable IMs for the fatigue design of steel I-girder bridges that can more rationally consider the effect of the deterioration of the road surface condition (RSC) during its whole lifecycle. The deterioration process of the RSC was investigated under the given traffic and environmental conditions, and the number of truck passages taken for the RSC to deteriorate from one class to the next was investigated. A three-dimensional coupled vehicle–bridge model was developed to simulate the interaction between the bridge and vehicle, with both the bridge and fatigue load models adopted from an existing LRFD code. The IM of the stress range (IM__SR), which is calculated using the stress range instead of the maximum stress used traditionally, was used for the fatigue analysis of steel girders. Numerical simulations were performed to study the IM__SR of steel I-girder bridges under different RSCs while taking into consideration the effect of two other important parameters: bridge span length and vehicle speed. Results show that the RSC has a greater impact on the IM__SR than on the traditional IM, and the IM__SR is greater than the traditional IM calculated using the maximum stress. By considering the cumulative fatigue damage caused by the passage of each truck under different RSCs and the deterioration process of the RSC during its whole lifecycle, simple and reasonable expressions were proposed for the IMs for fatigue design of steel I-girder bridges under the given traffic and environmental conditions.

This paper presents finite-element analyses and analytical models of innovative, small-scale, prototype deck panels examined under monotonic bending. The deck panels consisted of two glass fiber–reinforced polymer (GFRP) facesheets separated by webs formed from E-glass–woven fabric placed around trapezoidal-shaped, low-density, polyurethane foam segments. The proposed panel exhibited a higher structural performance in terms of flexural stiffness, strength, and shear stiffness than those of conventional sandwich panels. Analytical models were used to predict critical facesheet wrinkling in the sandwich panel. Furthermore, a three-dimensional model using simulation software was developed for analysis of the proposed panel system under monotonic four-point loading. The finite-element results in terms of strength, stiffness, and deflection were found to be in good agreement with those from the experimental results. A parametric study was also conducted to further evaluate the effects of the stiffness of the top facesheet fiber layers, the mass density of the polyurethane foam, the existence of web layers, and the introduction of an overlay above the top facesheet. A flexural beam theory approach was used to predict the flexural strength of the sandwich panel.

An application of two-dimensional (2D) time-domain full waveform tomography is presented to evaluate existing foundations using surface-based seismic wave fields. The full waveform inversion (FWI) technique is based on a finite-difference solution of 2D elastic wave equations and the Gauss–Newton inversion method. Both compression-wave (P-wave) and shear-wave (S-wave) velocities are inverted independently and simultaneously to increase the credibility of characterized profiles. The FWI technique was applied on both synthetic and real experimental data sets. Inverted results of synthetic data revealed that individual embedded foundation elements (piles) and soil between piles were distinguished. For real experimental data, seismic surface wave fields were measured next to two drilled shafts with a 1.2-m diameter and a 15-m length and then inverted by the FWI technique. The waveform analysis successfully profiled embedded shaft elements and subsurface soil stratigraphy, and shaft lengths of 15 m were also predicted.

The longitudinal stiffness of multispan suspension bridges plays an important role in load-resisting systems. In this paper, a model defined as the kinematic multispring (KMS) model is proposed for simulating the longitudinal deformation behavior of multispan suspension bridges. Tower springs and cable springs constitute a series-parallel system in the KMS model. The stiffness formulas for cable springs were derived on the basis of the energy principle. The elastic elongation of the cable was considered and proved to be nonnegligible, especially for long-span bridges. The effect of the inclined angle of the cables was first considered in the formulas for the cable elastic stiffness. The elastic stiffness and the geometric stiffness of the cables were found to be relevant. Compared with numerical models, the KMS model proposed in this paper was proven to be accurate and applicable.

With the use of a computational fluid dynamics (CFD) numerical simulation, in this study an unusual exponentially modified sinusoidal (EMS) oscillation was forcibly imposed on deck section to simulate amplitude-varying self-excited forces. This approach facilitated the investigation of the influence of EMS transient oscillation and amplitude on self-excited forces and flutter derivatives. Study results show that for an ideal thin plate, the sensitivities of $H_2^{*}$, $H_4^{*}$, $A_2^{*}$, and $A_4^{*}$ to oscillation decaying/diverging ratio ($\xi$) were higher than those of $H_1^{*}$, $H_3^{*}$, $A_1^{*}$, and $A_3^{*}$. With different amplitudes, $\xi$, and reduced wind velocities, the self-excited forces of one flat plate and two bluff bridge decks were numerically calculated and the flutter derivatives were extracted and compared with the theoretical and experimental results. If $|\xi |$ < 0.1, its influence was almost negligible, by which the traditional sinusoidal oscillation technique was validated. The heaving and torsional amplitudes had different influences on each flutter derivative. The influences were also related to deck cross sections and reduced wind velocities. The proposed numerical simulation of EMS oscillation enables a better understanding of the influence of oscillation amplitude and $\xi$ on bridge deck flutter derivatives.

This paper discusses the dynamic behavior of twin-box girder bridges under high-speed railway traffic. On the basis of several representative examples derived from recently built high-speed bridges, this contribution examines the effects of transverse bending in the upper slab of these structures and evaluates the bending moments in resonance conditions. The analysis was carried out according to one of the reference norms for the assessment of dynamic effects in high-speed bridges (Eurocode). The results demonstrate that the predicted dynamic response for shorter-span bridges can be unexpectedly higher than the static effects caused by the design loads as a result of transverse resonances induced by the absence of transverse diaphragms between the box girders and the movement of the sliding supports. Moreover, these strong impact coefficients may occur even when the maximum level of vertical vibrations in the deck is not severe.