Box-girder Highway Bridges Research Articles

Experimental and numerical investigation on deck system of a 102 m simply supported prestressed UHPC box-girder highway bridge

To address two main challenges (excessive mid-span deflections and numerous cracks in the main girder) in long-span prestressed concrete (PC) box-girder bridges, this paper proposes a long-span simply-supported UHPC box-girder bridge. In comparison to conventional PC box-girder bridges with three-dimensional prestress, the proposed UHPC box-girder consists only one-dimensional (longitudinal) prestress, and the thickness of the bottom/top plate and web of the UHPC box-girder are relatively thin and are strengthened with dense diaphragms and stiffening ribs. The 4th Beijiang River Bridge adopts this type of bridge with a span of 102 m, which is the longest span simply supported prestressed UHPC box-girder highway bridge in the world. Considering the fact that the thickness of the top plate of the UHPC box-girder is relatively thin (only 20 cm) and the transverse prestress is removed from the top plate, thus, under the direct action of wheel loads, the risk of bridge deck cracking may correspondingly increase. To investigate the mechanical behavior of the deck system of UHPC box-girder bridges, a 1:2 scaled experimental specimen associated with the field bridge is tested. The mechanical behavior of the new deck system is investigated and discussed. It is found that because the support strength of the stiffening rib is significantly weaker than that of the web, the UHPC deck slab should still be regarded as a two-way slab rather than a one-way slab in the elastic stage. In addition, although the test load location is unfavorable to the UHPC deck slab and the first crack appears on the UHPC deck slab, this deck system finally suffers from bending failure of the transverse rib. Furthermore, finite element analysis is carried out to study the mechanical behavior of this new deck system. Parametric analysis considers some factors including the reinforcement ratio in the transverse rib, the height of the transverse rib, and the space between transverse ribs. The results provide a good reference for design and optimization in the new deck system of UHPC box-girder bridges.

Effects of Deck-Abutment Pounding on the Seismic Fragility Curves of Box-Girder Highway Bridges

ABSTRACT Earthquake-induced pounding in bridges is a complex contact phenomenon in which the dynamic responses of structures, including collisions between deck and abutments, are strongly related to structural properties and earthquake excitation. The goal of this study is to develop and compare the seismic fragility curves of overall system and individual components of regular and irregular box-girder highway bridges in two cases: with pounding and without pounding. For this purpose, four levels of altitudinal irregularity, ranging from regular to highly irregular, are considered. To extend the results for all bridges in the same class, different sources of uncertainties related to earthquakes, structural geometries, and material properties are taken into account. The analytical fragility curves have been developed based on nonlinear time history analyses in OpenSees finite element software for the cases with and without pounding effects. The process has been repeated for each two-, three-, and four-span classes at four irregularity levels. The fragility function parameters for the two cases with and without pounding have been compared for all classes considered in this study. Using fragility functions, this paper clarifies the interactive roles of irregularity and pounding between deck and abutments for seismic vulnerability of multi-span box-birder highway bridges. The results indicate that collisions often show an adverse effect on all structural components. It has also been observed that the detrimental effect of pounding on seismic fragility is more apparent in irregular bridges when compared with regular ones. In addition, the study introduces a conversion coefficient to clarify the effects of pounding on the fragility of bridge components and the overall system. This coefficient can be applied in both conventional analytical methods like static or simplified analysis and technical earthquake models like HAZUS, adjusting fragility values for pounding and irregularity effects.

Utjecaj kuta djelovanja potresa na seizmičko ponašanje betonskih mostova na autocestama

This study aims to evaluate the effect of earthquake angle on the seismic performance of a concrete highway bridge. As a numerical example, a twin prestressed concrete box-girder highway bridge was analysed using finite element methods. The bridge was subjected to the 1992 Erzincan earthquake ground accelerations in 19 directions with values ranging from 0° to 90° in 5-degree increments. To evaluate the effects of different earthquake angles on seismic performance, variations in the maximum displacements, internal forces and principal stresses on the bridge deck, columns, isolator and foundation were studied . The results changed considerably for different earthquake angles. Variations in the displacement, internal forces and principal stresses occurred at different incidence angles. In other words, there is no unique angle of incidence for each structure.

Quantification of the effects of the spatial variation of ground motions on the seismic response of highway bridges

The stochastic responses of highway bridges to spatial variation of ground motions (SVGM) are analysed in this paper. A model of spatially varying ground motions is used to investigate the relative importance of the incoherency effect, the wave passage effect and the site effects on the stochastic dynamic response of an asymmetrical R.C box girder highway bridge with variable inertia. In this study, the incoherency effect is investigated using two widely used models while the wave-passage effect is incorporated using various wave velocities. Then, the random vibration theory is applied to study the effect of the non-uniform seismic excitations on the bridge structure. The bridge response is evaluated in terms of the mean values of the maximum displacements and the bending moments. Analyses of both stationary and transient response are performed. The results show that the stochastic dynamic responses related to site effects are mostly much greater than those calculated using uniform, delayed and incoherent seismic excitation assumptions. As a result, analytical models used for the stochastic dynamic analysis of long span highway bridges should take into account all the SVGM components, particularly the site-response effects.

The Effect of In-Span Hinges and Span Numbers on the Seismic Vulnerability of Curved Box-Girder Highway Bridges Considering Material and Geometric Uncertainties

AbstractAround 15% of seismically designed Californian box-girder bridges incorporate at least one in-span hinge. This class of bridges can be further divided into two subclasses (i.e., single-fram...

Developing a multi-variable vulnerability function for a class of multi-span continuous concrete box-girder highway bridges with emphasis on near-field earthquakes

The most common tools in seismic performance assessment of highway bridges are single-variable fragility curves. However, fragility curves are not confidently reliable due to utilizing only a single intensity measure (IM). Alternatively, single- and multi-variable vulnerability functions, of which the latter is scarce and rather complex, have been proposed for that purpose, yet without considering the effects of the strong vertical component of near-field earthquakes. This study aimed to develop a multi-variable vulnerability function for multi-span continuous concrete box-girder bridges, accentuating near-field earthquakes. Ten bridge models corresponding to the 1971-1990 design era were considered and analyzed, subjected to three-component records of 164 earthquakes using OpenSees framework. First, 28 IMs related to horizontal and vertical ground motions, and 12 engineering demand parameters were utilized, and a set of potentially optimal IMs were determined through optimality investigation. Then, to ensure that identified IMs are authentically optimal candidates, Lasso regression was employed, introducing 12 IMs as optimal. Finally, Step-wise regressions were conducted to reduce the complexity of the proposed equation. Results revealed peak ground acceleration, peak ground velocity, and velocity spectrum intensity of the horizontal component of ground motion, and acceleration spectrum intensities of both horizontal and vertical components as optimal ones.

Inelastic seismic response of box-girder bridges due to torsional ground motions

The torsional components of strong ground motions (TGMs) may result in unanticipated displacement and force demand particularly in highway bridges due to their complex dynamic characteristics. For this purpose, the present study investigates the effects of TGMs on the inelastic seismic response of continuous concrete box-girder highway bridges with seat type abutments. Three-dimensional finite element (3D FE) models of bridges with varying skew angles, number of bent columns, and column height-to-diameter ratios were developed using OpenSees, and a series of nonlinear response history analyses were conducted. Comparison of seismic response of bridges subjected to only translational and both translational and TGMs revealed that TGMs may result in uneven and asymmetric failure of the shear keys. Therefore, deck rotations are significantly amplified due to induced instantaneous eccentricity when deck comes in contact with shear key(s). The amplified impact forces due to TGMs further amplify the deck rotations, which in return result in higher inelastic displacement and force demand. Last but not the least, the induced torsion due to TGM combined with axial-flexure-shear interactions may result in complex failure modes, higher shear stresses, and reduction in lateral deformation and flexural capacity of the bridge columns.

Probabilistic seismic assessment of RC box-girder highway bridges with unequal-height piers subjected to earthquake-induced pounding

This paper uses the probabilistic seismic assessment to study the effects of pounding and irregularity on the seismic behavior of typical concrete box-girder bridges with four levels of altitudinal irregularity. To extend the results for all bridges in the same class, uncertainty related to the earthquake, structural geometries, and materials are considered. Pounding is likely to take place in two cases: the first one concerns the seat-type abutments, and the second is at the in-span hinge of multi-frame bridges. Accordingly, the present study is an attempt to investigate the behavior of irregular bridges considering the effects of pounding in both cases. In the first case, the effects of changes in the gap size on engineering demand parameters (EDPs) were investigated. Then, correlations between earthquake parameters and the pounding force were evaluated. Furthermore, the pounding force exerted on the abutment was compared for different bridge irregularity levels. In the second part of the paper, the effects of pounding of adjacent bridge segments in the decks of non-continuous bridges were studied for equivalent Two-Degree-of-Freedom structures, for which the probability of non-occurrence was estimated. In the end, the relationship between structural or seismic parameters and the pounding force was evaluated in case of pounding. The results of the study show that the gap size between the abutment and the deck has the highest effect on the abutment passive deformation, pounding force, and base shear. Also, the substructure irregularity of bridges reduces the correlation between the gap size and the EDPs, except for the column ductility. Moreover, decreasing the ratio of periods of the adjacent frames diminishes the effect of the type of the earthquake but increases the probability of pounding.

Seismic fragilities of single‐column highway bridges with rocking column‐footing

SummaryRocking isolation has been increasingly studied as a promising design concept to limit the earthquake damage of civil structures. Despite the difficulties and uncertainties of predicting the rocking response under individual earthquake excitations (due to negative rotational stiffness and complex impact energy loss), in a statistical sense, the seismic performance of rocking structures has been shown to be generally consistent with the experimental outcomes. To this end, this study assesses, in a probabilistic manner, the effectiveness of using rocking isolation as a retrofit strategy for single‐column concrete box‐girder highway bridges in California. Under earthquake excitation, the rocking bridge could experience multi‐class responses (eg, full contacted or uplifting foundation) and multi‐mode damage (eg, overturning, uplift impact, and column nonlinearity). A multi‐step machine learning framework is developed to estimate the damage probability associated with each damage scenario. The framework consists of the dimensionally consistent generalized linear model for regression of seismic demand, the logistic regression for classification of distinct response classes, and the stepwise regression for feature selection of significant ground motion and structural parameters. Fragility curves are derived to predict the response class probabilities of rocking uplift and overturning, and the conditional damage probabilities such as column vibrational damage and rocking uplift impact damage. The fragility estimates of rocking bridges are compared with those for as‐built bridges, indicating that rocking isolation is capable of reducing column damage potential. Additionally, there exists an optimal slenderness angle range that enables the studied bridges to experience much lower overturning tendencies and significantly reduced column damage probabilities at the same time.

The Impact of Asphalt Wearing Surface Thickness on Response of Two-Span Continuous Cast-in-Place Prestressed Concrete Box Girder Highway Bridge

The Impact of Asphalt Wearing Surface Thickness on Response of Two-Span Continuous Cast-in-Place Prestressed Concrete Box Girder Highway Bridge

Fatigue behaviour at elevated temperature of RC slabs strengthened with EB CFRP strips

Abstract Reinforced concrete (RC) structures such as concrete box-girder highway bridges may suffer fatigue damage due to cyclic loads. Externally bonded (EB) carbon fibre reinforced polymer (CFRP) strips can be used to increase the fatigue (and static) load bearing capacity of such elements and to increase the service life of the elements. The EB CFRP strips under the asphalt layer can reach elevated temperatures of up to 50 °C during summer when the asphalt is directly exposed to solar radiation. Therefore, in this study, the fatigue behaviour at an elevated temperature of RC slabs strengthened with EB CFRP strips is evaluated. The focus is on the strengthening of lateral cantilevers of deck slabs of concrete box-girder highway bridges. The fatigue behaviour of RC elements is a complex phenomenon that is influenced by many parameters such as the maximum load, stress oscillation level on the longitudinal steel reinforcement, shear span-to-depth ratio, and quality of concrete. This phenomenon becomes even more complicated when elevated temperatures are considered. Majority of the existing experimental works on fatigue behaviour of EB-strengthened RC structures showed that the typical fatigue failure at room temperature is caused by fatigue failure of the longitudinal steel reinforcement followed by strip debonding. In this study, it was investigated if a different type of failure can be observed at elevated temperatures owing to the changes in epoxy properties.

Probabilistic Vulnerability Assessment of Horizontally Curved Multiframe RC Box-Girder Highway Bridges

AbstractNumerous concrete box-girder bridges in California are horizontally curved and also have at least one in-span hinge. The curvature and in-span hinges in multiframe bridges lead to significant differences in bridge dynamic response during seismic excitations. In this article, a set of analytical fragility curves for horizontally curved highway bridges are developed based on nonlinear time history analyses in OpenSEES, focusing on subclasses of seismically designed multiframe concrete box-girder bridges with multicolumn bents and seat type abutments. Component damage levels are explored for joint seals, columns, bearings, abutments, unseating of decks, foundations, and shear keys, and system level damage states consistent with HAZUS-MH definitions. Curvature was identified to be an important factor that adversely affects the fragility of multiframe bridges. Median value modification factors are proposed to scale fragility curves to account for the deck radius effects.

Effects of soil-structure interaction on construction stage analysis of highway bridges

The aim of this paper is to determine the effect of soil-structure interaction and time dependent material properties on behavior of concrete box-girder highway bridges. Two different finite element analyses, one stage and construction stage, have been carried out on Komurhan Bridge between Elazi<TEX>$\breve{g}$</TEX> and Malatya province of Turkey, over Fırat River. The one stage analysis assume that structure was built in a second and material properties of structure not change under different loads and site conditions during time. However, construction stage analysis considers that construction time and time dependent material properties. The main and side spans of bridge are 135 m and 76 m, respectively. The bridge had been constructed in 3 years between 1983 and 1986 by balanced cantilever construction method. The parameters of soil-structure interaction (SSI), time dependent material properties and construction method are taken into consideration in the construction stage analysis while SSI is single parameter taking into consideration in the one stage analysis. The 3D finite element model of bridge is created the commercial program of SAP2000. Time dependent material properties are elasticity modulus, creep and shrinkage for concrete and relaxation for steel. Soft, medium, and firm soils are selected for evaluating SSI in both analyses. The results of two different finite element analyses are compared with each other. It is seen that both construction stage and SSI have a remarkable effect on the structural behavior of the bridge.

EFFECT OF SKEW ANGLE ON SEISMIC VULNERABILITY OF RC BOX-GIRDER HIGHWAY BRIDGES

In this study, the seismic vulnerability of post-tensioned reinforced concrete box-girder highway bridges with moderate-to-large skew angles to various levels of ground motion intensity is investigated. The fragility curves are generated by performing incremental nonlinear dynamic analysis (IDA) on the bridges of skew angles of 0, 30, and 60°s. A total of 45 ground motion pairs are considered to develop the fragility curves. The damage states are presented and quantified based on the column rotational ductility and superstructure displacements at the abutments. Furthermore, the fragility curves constructed are compared against those recommended by HAZUS. It is demonstrated that as the skew angle increases, skew bridges become more vulnerable to seismically induced damages. It is also shown that the HAZUS fragility curves may not lead to a consistent prediction of the vulnerability of skewed bridges.

Failure of concrete T-beam and box-girder highway bridges subjected to cyclic loading from traffic

Concrete cast-in-place T-beam highway bridges are often constructed by casting the girders and the deck separately, creating a cold joint between the girders and the deck. Under certain circumstances, cracking and visible slippage can occur in this joint, resulting in fracture of the reinforcing steel crossing the joint, greatly reducing the composite action between the flange and the web. After observing the movement of this joint at some bridges, a detailed evaluation was performed on 12 five-girder T-beam bridges on Interstate 40 (I-40) in the southwestern US, and a potential failure mechanism was identified in all of them. In addition, alkali silica reaction (ASR) had been known to affect bridges in the area; therefore the study evaluated whether ASR had contributed to the failures. Several factors were identified as contributors to the failure mechanism, including a limited recognition in the original design standard of cyclic loading, high volume of heavy truck traffic, and transverse moments caused by unbalanced wheel loading. After the investigation, recommendations were made for instituting special inspections of construction joints in similar existing bridges.

Load and Resistance Factor Design of Integral Bent Caps

Cast-in-place concrete box girder highway bridges with integral bent cap substructures are the preferred bridge type in California. In the AASHTO LRFD Bridge Design Specifications, two methods are available for the design of integral bent caps: the sectional method for flexural members and the strut and tie method (STM) for flexural and deep members. Although many bent caps are considered deep beams according to the AASHTO load and resistance factor design provisions, practicing engineers elect to use the sectional method exclusively for design because of its familiarity and the lack of guidance for using STM. Design examples that used STM have been published, but none of these examples deals with integral bent caps. When applying STM to integral bent caps, several issues, unique to this geometry, need to be addressed. These issues are discussed, and three different integral bent cap design examples are presented. The design of the three bent cap examples was also carried out by using the sectional method. The application of the sectional method to integral bent caps presented its own issues. These issues are discussed, and the results of both methods are compared.