Journal of Bridge Engineering

Bearings are important bridge elements that must be considered when evaluating potential ways to extend overall bridge service life. Elastomeric bearings have proven durability but with certain combinations of load and movement, their capacity to accommodate the required load and translation can be exceeded. Additional movement capacity can be provided by means of sliding surfaces. Many bearing types, including cotton duck pads and high-load multirotational bearings, also use sliding surfaces to accommodate bridge movements. Currently, polytetrafluorethylene (PTFE) is the material commonly used for sliding surfaces; however, this material wears under certain service conditions. Higher performing materials are available that can provide significantly greater wear resistance and enhanced service life. Two such high-performing sliding surface materials were investigated to study and predict their service life: ultrahigh-molecular-weight polyethylene (UMWP) and glass-filled reinforced PTFE (GFR-PTFE). This paper describes research and proof-of-concept testing to determine the feasibility of achieving increased service life with bearings that use sliding surfaces for movement through the use of alternative high-performing materials in lieu of conventional plain PTFE. This paper describes the experimental testing program, which compared material wear and coefficient of friction (COF) over a range of parameters including contact pressure, rate of movement, and accumulated total movement. Both UMWP and GFR-PTFE showed significantly greater wear resistance than conventional PTFE when subjected to initial testing with high contact pressure (20.7 MPa or 3,000 psi) and high rate of movement (63.5 cm/min or 25 in./min), but also exhibited higher COFs. Plain PTFE was shown to wear at a very high rate under the initial testing parameters, resulting in substantial thickness loss within less than 2 mi of accumulated sliding length. Glass-filled reinforced PTFE exhibited the best wear resistance with no material thickness loss in initial testing over approximately 8 mi of accumulated sliding length. Ultrahigh-molecular-weight polyethylene exhibited some initial thickness reduction, which may have been related to material compressibility. The testing confirmed the effects of both contact pressure ($P$) and rate of velocity of movement ($V$) as contributing factors to sliding-surface wear. For PTFE and GFR-PTFE, the testing also showed a direct correlation between the rate of material wear and the factor of $P$ times $V$ ($\mathit{PV}$), where increased levels of $\mathit{PV}$ resulted in increased rates of material wear. Also, wear rates at these $\mathit{PV}$ levels were nearly uniform. There were also levels or thresholds of $\mathit{PV}$ below which the rate of material wear was very low or nearly zero.

Bearings are important bridge elements that must be considered when evaluating potential ways to extend overall bridge service life (SL). Many bearing types, including cotton duck pads and high-load multirotational bearings, use sliding surfaces to accommodate bridge movements. Elastomeric bearings have improved durability but with certain combinations of load and movement, the capacity of elastomeric pads to accommodate the required translation can be exceeded. Additional movement capacity can be provided by means of sliding surfaces. Currently, polytetrafluorethylene (PTFE) is the material used for sliding surfaces. However, PTFE wears under service conditions, primarily under fast rates of movement owing to truck load. This paper provides a summary of recommended design steps that could be used to quantitatively predict the SL of sliding surfaces. The method incorporates a process that estimates and compares demand (load) with supply (resistance). The demand is the imposed pressure and horizontal movement on the sliding surface that causes wear, and is primarily the result of applied thermal and traffic loads and the rate of movement. The supply is the sliding material thickness and its capacity to undergo horizontal movements and subsequent wear before failure, and is a function of the sliding material properties. The supply is expressed in terms of a deterioration model based on test data. Finally, by comparing the demand to supply, one could determine whether a given sliding surface could provide the desired SL without failure. Deterioration models are developed for commonly used sliding surfaces such as PTFE, as well as higher-performing sliding surface materials, such as glass-filled reinforced PTFE. These models are based on the results of previous work and new experimental tests, and are used as part of the overall process to predict SL. The recommended design steps are general in nature and could be used for various sliding surface types. An example based on the analysis of a prototype bridge is provided to illustrate the process.

Recent tsunami and hurricane-caused destruction, and the possibility of both tsunami inundation and storms of even greater magnitude and frequency making landfall in the future, has focused attention on the vulnerability of coastal structures, and bridges in particular. Findings from a series of experiments measuring forces on a 1:35 scale bridge model impacted by a solitary wave with varying percentages of air relief openings (AROs) between girders are presented here. A range of water depths, wave amplitudes, and elevations of the model above the still-water level (SWL) are considered. Results show significant reduction of vertical uplift forces when AROs are added to the bridge model, particularly when the girders are fully elevated above the SWL or only slightly submerged, but relatively little effect on horizontal forces in the direction of wave propagation is observed. Buoyancy calculations show added hydrostatic force does not alone contribute to uplift forces, but rather a combination of hydrostatic force, wave impact force, and deformation of the wave must all be considered.

Finite-element (FE) modeling of RC structures under combined loading has received considerable attention in recent years. However, the combination of torsion and axial compression has been rarely studied in spite of its frequent occurrence in bridge columns under earthquake loading. This paper aims at creating a nonlinear FE model to predict the behavior of RC bridge columns under combined torsion and axial compression. A number of circular and square columns were analyzed. The developed FE model was calibrated on local and global behavior through comparison with test data. The overall torque–twist behavior of the members was captured well by the developed FE models. The predicted values of strain in the longitudinal and transverse reinforcement matched closely with the experimental results. An increase in transverse steel ratio was found to increase the torsional capacity and limit the damage of columns under torsion. It was further observed that at a low level of axial compression, the torsional capacity of columns is enhanced. In addition, the FE analysis showed a good agreement on the identification of the damage mechanism and the progression of failure. The shape of the cross section is found to play a major role in the distribution of torsional damage in the columns. Square columns exhibited a more localized damage due to presence of warping, whereas circular columns exhibited damage distributed along their length.

The lateral vibration of railway bridges induced by moving trains has traditionally been solved through numerical integration. Although it provides practical prediction, the numerical approach does not explicitly reveal the underlying driving mechanism of the train–bridge interaction. In this paper, a closed-form solution is derived for the lateral vibration of a simply supported bridge subjected to hunting forces from running wheel sets. Through complex Fourier expansion, this solution leads to the formulation of three influential factors with explicit physical meanings, namely, the effective unit moving load on the bridge, the arrangement of all moving wheel sets, and the frequency response function of the bridge. On the basis of these factors, a simplified formula to estimate the maximum vibration of the bridge is proposed. The closed-form solution and the simplified formula are validated through comparison with results from numerical integration. The resonance conditions of the bridge due to moving hunting forces are derived using the simplified estimation.

Specifications used in the design of bridges that cross barge-navigable waterways typically use, as a subcomponent of the impact-load calculation process, a barge force–deformation (crush) relationship. Such relationships model the nonlinear stiffness of the impacting barge and directly influence computed impact forces. Primarily because of logistical challenges, few studies have been conducted to experimentally quantify barge force-deformation data. A variety of analytical studies have been conducted to partially address this lack of experimental data, and to facilitate development of improved crush relationships. However, there remains a need for experimental data to validate analytically derived crush relationships, particularly at high barge-deformation levels. In this paper, an integrated experimental and analytical investigation of barge force–deformation behavior under high-energy impact loading is presented. Results from impact tests involving reduced-scale replicates of jumbo-hopper barge bows and impactors with two distinct surface geometries (e.g., circular and rectangular) are reported. Measured force and deformation data confirm several key findings previously identified through numerical simulation; for example, that rounded bridge surfaces produce smaller impact forces than flat (i.e., rectangular) surfaces.

The impact-echo method is applied to evaluate the grout quality in tendon ducts of posttensioned structures nondestructively in the present study. As the main evaluation index, the dominant frequency (DFQ) is obtained from the frequency-domain spectrum, which is transformed from the original time-domain signal. The influences of several factors on the DFQ are investigated in detail both experimentally and numerically. These factors include size effect, slab thickness, tendon duct depth, affected range, DFQ shift, and grout strength. The experiments are conducted in the construction field on posttensioned box girders under various grouting conditions. The DFQs of each test point in a test area are integrated to draw a contour image based on their coordinates. Through the analysis of the contour image, grout quality in the tendon ducts can be evaluated accordingly. Grout defects are detected in some box girders and verified by chiseling these suspected ducts. The numerical studies, which can provide some insights into the experimental findings, show good agreement between the experimental and numerical results.

Out-of-plane distortion of transverse cross-bracing systems in bridge superstructures has been known to cause localized fatigue cracking. The cracking is a result of the differential displacement of adjacent bridge girders, which causes high stress concentrations in unstiffened web-gap regions at the interface of girder and stiffener connection plates. Fatigue cracking within the web gap can occur because of cyclical loading scenarios. Rehabilitation efforts have shown to be unpredictable in preventing crack propagation once through-thickness crack profiles have developed. Therefore, understanding the mechanisms causing fatigue crack propagation in such detail is essential in developing effective repair methods. In this study, numerical analyses of typical web-gap connections are conducted using the extended FEM to characterize crack directionality and growth rate. Simulations varying the web-gap length, stress range, loading ratio, and initial crack length were used to determine the primary variables effecting crack growth in the web-gap region. Increasing the web-gap length was noted to stabilize crack propagation rates, resulting in stable growth, which can be correlated to the Paris Law. Elongation of horizontal initial crack lengths resulted in reorientation of crack growth. In stiffer web gaps, a combined high stress ratio and long initial crack length resulted in crack profiles propagating into the flange-web interface with eventual crack arrestment. The study suggests that horizontal extension of initial cracks has the potential to cause the crack to arrest, after stable propagation, without adversely compromising local structural integrity of bridge superstructures.

In current practices, the elastic design principle for the seismic design of pile foundations is an overly conservative strategy. In this regard, cyclic lateral loading tests were conducted to investigate the seismic failure mechanism and ductile behaviors of elevated RC pile-cap foundations. Two six-pile specimens with different aboveground heights were constructed and embedded in a single layer of cohesionless soil. Hysteretic characteristics and observed damages of the pile groups were presented, together with the corresponding soil pressure and pile curvature responses. From the test results, the sequence and positions of the pile plastic hinges were established. Ultimate limit states of the pile groups were determined according to test data, as well as numerical analysis results. Test results revealed a ductile flexural failure mode for both specimens. Plastic hinges were detected first at the top of outer piles, then underground at a depth of 4–6 times the section width. A displacement ductility capacity of 3.5 was observed for the elevated pile-cap foundation. Test results also indicated a linear relation between the displacement ductility factor and the cap rotation, which was important for determining the displacement at the top of piers.

Four $1/4\text{-scale}$ precast segmental bridge columns (PSBC) with different reinforcement types and arrangements and one monolithic reference column (MRC) were designed and tested under cyclic quasi-static loading. Both UPC (PSBC with unbonded tendons only) and UPCE (PSBC with unbonded tendons and bonded mild steel bars) use unbonded posttensioned (PT) strands to connect the segments. Bonded energy dissipation (ED) bars were added in UPCE to increase the ED ability of unbonded PSBC. Specimens BPC (PSBC with fewer bonded PT bars) and BPCII (PSBC with more bonded PT bars) use bonded PT bars to combine the segments together. The unbonded length was set in ED bars to delay the low-cycle fatigue damage. Test results showed PSBC only has minor concrete cracks or crushing at lower joints. The unbonded PT PSBC with ED bars had higher lateral strength, lower residual drift, and comparable ED with MRC. The bonded PT bar PSBC with appropriate bar arrangement also showed high lateral strength and medium energy-dissipation ability. However, bonded PT PSBC experienced large PT stress loss, which leads to a residual drift of 3% when unloading from 6% drift.

This paper presents the results of a testing program developed to assess the performance of circular RC bridge columns constructed with ASTM A706 Grade 80 [550] high-strength steel (HSS) reinforcement. Two pairs of columns were tested (four columns in total). The columns were subjected to lateral cyclic loading to determine the effects of steel reinforcement grade (yield strength) and of moment–shear span ratio on column performance. Each pair consisted of one column constructed with Grade 80 [550] HSS reinforcement and a control column constructed with Grade 60 [420] reinforcement. The first pair had a moment–shear span ratio of six (6), and the second pair had a moment–shear span ratio of three (3). All four columns were designed to have similar nominal bending-moment capacities. Results indicate that the columns constructed with Grade 80 [550] HSS reinforcement achieve similar resistance, similar maximum lateral displacements, and similar curvature ductility values when compared with the control columns constructed with Grade 60 [420] reinforcement. However, columns constructed with Grade 80 [550] reinforcement exhibited lower hysteretic energy dissipation than the control columns. Results also indicate that, independently of the steel grade, as the moment–shear span ratio decreases, the maximum drift ratio decreases, despite an increase in the displacement ductility.

Expansion devices are one of the main causes for high maintenance costs in bridges. In this paper, a seamless bridge system is presented that results in bridges with long service lives by eliminating the joints over the bridge length, approach slab, and a segment of the roadway. The idea of a seamless system was originally developed in Australia for use with continuously reinforced concrete pavements (CRCP). In this system, bridge movements are dissipated in the transition zone located at the bridge ends beyond the bridge abutments. Thermal compression forces are transferred partly to base soil and partly to the CRCP, and the thermal contractions are handled by opening and closing microcracks in the transition zone. Crack width and spacing are important parameters in the design of seamless bridge systems. This paper presents the modification to the Australian seamless system so that it could be extended to U.S. practice, where most pavements are either jointed plain concrete or flexible. Analyses and design procedures are presented. The main difference between the Australian version of the seamless system and the proposed version for U.S. practice is in the type of transition region. The main challenge for U.S. practice is to have almost zero movement and force at the end of the transition zone. This objective is achieved by constructing a secondary slab below the transition region and connecting the two using closely spaced small piles. Numerical and analytical studies have been carried out to comprehend the performance of the proposed system, and an experimental study was carried out to provide proof of the concept and merits of the proposed design recommendations. Results of this experimental work are presented elsewhere.

Expansion joints are one of the main causes for high maintenance costs in bridges. In this paper, a seamless bridge system is presented that provides for bridges with long service lives by eliminating the joints over the length of the bridge, the approach slab, and a segment of the adjoining roadway. Bridge movements in seamless systems are dissipated in a transition zone located at the bridge ends beyond the abutments. Thermal compression forces are transferred to the base soil, and thermal tensile forces are handled through opening and closing of microcracks in the transition zone. Crack width and spacing are important parameters in the design of seamless bridge systems. In the seamless system presented, the transition zone consists of a top slab and a secondary slab installed a few feet deep in the base soil. The two slabs are connected via small piles. At the end of the transition zone where it interfaces the roadway, which can be either jointed rigid or flexible pavement, there is a joint called an end joint. The bridge and transition zone movements should be reduced to amounts small enough so that no mechanical joint or grade beam would be required at the end joint. Development of the design provisions for the seamless bridge system is presented in a companion paper. A small pile–concrete slab connection detail has been proposed. In this paper, parametric studies have been carried out on a prototype bridge to develop an experimental program that simulates a segment of the proposed transition system. The experimental program studies the general behavior of the proposed transition system under cyclic loading, its stiffness, and capability in effectively reducing the bridge movements at the end joint, the development of cracks, the behavior of the proposed small pile-concrete slab connection detail, and the effect of geomaterial on the transition behavior. Finite-element analysis using Abaqus and SAP2000 computer programs was used to further study the behavior of the experimental system.

This paper investigates the effect of spectral shape (intensity and width of the constant acceleration region) and postyield stiffness ratio on equivalent viscous damping for short-period RC bridge columns ( $\text{effective period}<1\text{s}$). The modified Takeda degrading stiffness hysteretic model, with parameters appropriate to bridge columns (often termed thin Takeda in the literature), is used for analysis. Insight regarding the importance of these parameters is provided, and a new equivalent viscous damping model is proposed that includes the effect of spectral shape and postyield stiffness ratio, as well as effective period and ductility. The proposed damping model is compared with two existing models. The results indicate that significant improvement is achieved in predicting the peak displacement using the proposed damping model when compared with existing models.

The time histories of Cascadia Subduction Zone (CSZ) local tsunami horizontal and vertical loads and the overturning moment on four selected Oregon coastal bridges are computed for different load scenarios. These scenarios, containing the tsunami-free surface elevation and flow horizontal velocity components, are developed using various CSZ rupture models. One of the bridges is selected to evaluate the effect of various bridge geometry characteristics on the resultant tsunami loads. Maximum tsunami horizontal and downward vertical loads are found to occur approximately simultaneously when the tsunami flow reaches the landward side of the bridge cross section and overtops the barrier. A comparison between tsunami loads on a deck-girder bridge and a box-girder bridge under identical tsunami flow condition reveals that on box-girder bridges, (1) maximum horizontal loads are slightly larger, (2) downward vertical loads are smaller, and (3) uplift loads are significantly larger. It is shown that bridge cross sections with a seaward slope (the landward side of the bridge cross section is higher than the seaward side, so the tsunami travels landward) can be beneficial in reducing the uplift force. An analysis of a deck-girder bridge with a closed railing system shows an increase in the maximum tsunami horizontal, downward vertical, and uplift loads in comparison with an identical bridge that has an open railing system. Modifications are made to a previously proposed general method to estimate the specific local tsunami loads on Pacific Northwest coastal bridges from the results of computed tsunami loads. The modified tsunami load-estimation method is shown to be reasonably accurate in estimating the tsunami loads on bridge superstructures.

The collision of barges against bridge piers is an extreme loading condition that usually governs the design of bridges that span navigable waterways. The magnitude and time variation of impact forces depend on several aspects, such as mass and speed of the barges, stiffness of the impacted structure, and structural behavior of the barge. The latter has a considerable influence, not only because it defines the maximum possible impact force but also because it defines the energy absorption capacity of the barge. The structural behavior of barges has been studied using scale models and numerical methods. However, the total deformation reached in these studies was limited to the size of the barge bow. Hence, there is uncertainty in the behavior for high-energy collisions, where deformations may well exceed this deformation range. This paper studies the structural behavior of barges using detailed nonlinear finite-element (FE) models. Load–deformation relationships are established on the basis of the model results for different shapes and sizes of impacted structures. These relationships can be applied in simplified dynamic analyses for design, considering the large deformations expected for high-energy impact scenarios. Simplified analysis methods for symmetrical and oblique flotilla impacts are presented and validated against full FE models.

Bridge accessories, such as parapets, service ducts, and track slabs, are commonly used in railway bridges, but their real effects on the structural behavior of the bridges are still unknown because very few studies have been reported on this significant aspect. In engineering practice, lack of information on the contribution of bridge accessories may cause problems for bridge design, bridge health evaluation and monitoring, bridge management and operation, and bridge maintenance. Given this background, field tests were performed on a railway bridge with typical bridge accessories to confirm their contribution to bridge rigidity (or stiffness), as well as their effects on the sectional normal strain distribution. Both displacements in the midspan and strain results on key sections were measured in the field test and reported in this paper. Based on the field test observations, a numerical model capable of simulating the present railway bridge was built and was used to investigate the effects of the bridge accessories and their expansion joints. Longitudinal normal stress distributions on concrete slabs, steel main girders, and single-parapet panels were given, and parametric analysis considering different arrangement methods of expansion joints in the bridge accessories was also performed. Based on the numerical results, a stress concentration on the concrete slab near the expansion joints was confirmed. The results obtained in this study can be used for improving the design method used in new railway bridges and the maintenance of old railway bridge structures.

Culverts are an important part of ground-transport networks. With regard to constantly increasing traffic volumes and heavy vehicle weights, and given the attention focused on assessment and load rating of community infrastructure, a reliable understanding of the behavior of culverts is needed. In this study, nonlinear continuum-based finite-element (FE) models of RC culverts in conjunction with backfill soil were developed and analyzed. The FE models capture geometrical and physical nonlinearities of the RC culvert and the surrounding soil. After validating the FE models, a parametric study was conducted, and the effects of concrete compressive strength, reinforcing ratio, geometry (span over rise ratio), and stiffness of backfill on the peak-load capacity and fatigue behavior of the inverted U-shaped culvert, with little or no skew, were evaluated. It was concluded that stiffness of backfill can be the mobilizing mechanism of the arching action in the top slab, while enhancing the load capacity and fatigue strength of the inverted U-shaped RC culverts. In addition, ignoring the effect of backfill in the structural assessment of RC culverts can lead to significant underestimation of ultimate load capacity and fatigue life.

Current railroad bridge inspection and rating practices include observing bridge movement under live loads to help assess bridge conditions. Recent research has shown that transverse displacements of timber trestle bridges can capture critical changes in bridge serviceability (the ability to safely carry out railroad operations) as a function of railroad loading, speed, and direction. Measuring bridge movement under trains in the field is difficult and expensive because a fixed reference point is not normally available, thus creating the need to erect independent scaffolding to create good reference points near a timber bridge. This research demonstrates the potential of using reference-free accelerations collected with wireless smart sensors to estimate railroad bridge transverse displacements under live train loads. Focus is placed on timber trestle bridges, which comprise approximately 24% of the total inventory length of railroad bridges in the United States. The results show that wireless smart sensors can estimate transverse displacements of timber railroad trestles and could become an effective tool for campaign monitoring of railroad bridges (with applications toward helping overall bridge assessment).

Expansion joints will experience increasing deterioration and damage under repeating vehicle loading. A severely damaged expansion joint will induce significant dynamic vehicle load effects on the bridge deck near the expansion joint, whereas it may not cause such a large effect on the global bridge responses, e.g., deflection and bending moment at the bridge midspan. The impact factors (IMs) in bridge design codes are usually determined from global bridge responses. Therefore, it may be inappropriate to use the IMs in bridge design codes for the design of deck slabs for which the transverse bending moment is usually the controlling internal force. In this study, a three-dimensional vehicle-bridge model is used to study vehicle impact on the deck slab of prestressed concrete box-girder bridges caused by damaged expansion joints. Results show that the damage condition of expansion joints has a significant effect on the vehicle impact on the bridge deck slab, whereas it has a limited effect on the global bridge responses, especially for long bridges. The relationships between the vehicle impact on the deck slab and a few important parameters are also investigated, and some useful conclusions are obtained.