Reinforced Concrete Slab Bridges Research Articles

Long Short-Term Memory-Based Methodology for Predicting Carbonation Models of Reinforced Concrete Slab Bridges: Case Study in South Korea

Reinforced concrete slab (RCS) bridges deteriorate because of exposure to environmental factors over time, resulting in reduced durability. Particularly, the carbonation of RCS bridges corrodes the rebars and reduces the strength. However, carbonation models derived from short-term experiments exhibit low reliability with respect to existing bridges. Therefore, a long short-term memory (LSTM)-based methodology was developed in this study for generating carbonation models using existing bridge inspection reports. The proposed methodology trains the LSTM model by combining data extracted from reports and local environmental data. The learning process uses padding and masking methods to consider the history of environmental data. A case study was performed to validate the proposed method in three different regions of Korea. The results verified that the coefficient of determination of the proposed method was higher than those of the existing carbonation models and other regression analyses. Therefore, the developed methodology can be used for predicting regional carbonation models using the data from existing bridges.

Effect of Temperature on the Modal Variability in Short-Span Concrete Bridges

The dynamic characteristics of bridges are known to be affected by damages as well as by environmental factors such as temperature. Therefore, the changes in the dynamic characteristics caused by damages and environmental factors should be considered when evaluating the health of the structure. Accordingly, this study conducted long-term monitoring and modal identification of short-span concrete bridges, i.e., a RC (reinforced concrete) slab bridge a RC rahmen (rigid-frame) bridge. The investigation revealed that temperature is the factor having the greatest influence on the variability of the dynamic characteristics as the natural frequencies of the bridge decrease with higher temperatures. Model updating verified that such modal change resulted from the temperature dependency of the elastic modulus of concrete. The RC slab bridge showed higher temperature dependency than the RC rahmen bridge owing to the presence of elastomeric bearings. Apart from the effect of temperature, non-negligible modal changes caused by other environmental factors were also identified. The results of this study are expected to provide valuable data for the health evaluation of bridges.

Estimating the Load Rating of Reinforced Concrete Slab Bridges Without Plans

This article documents the development of a multiple regression model for the estimation of the inventory rating of reinforced concrete slab bridges. Given the lack of information on the superstructure elements in the National Bridge Inventory, the authors developed a data set by using the information found in as-built drawings provided by multiple state departments of transportation. The data consisted of 50 reinforced concrete slabs for which their inventory rating was computed. Various model combinations were considered, and their estimated errors were evaluated by performing a repeated tenfold cross validation. A five-variable model that included the year built, the span length, the slab thickness, the support type, and the skew was selected based on the lowest mean error and variance. The model had an adjusted coefficient of determination (adjusted R2) of 0.817, which was considerably higher than a previously developed model. The difference in adjusted R2 is attributed to the inclusion of slab thickness as an independent variable as well as to the quality of the data used.

Simple Procedure for Load Rating Reinforced Concrete Slab Bridges without Plans

AbstractIn New Mexico, bridges without plans are currently an issue as in other states in the US. Standard techniques cannot be used for load rating due to the lack of design plans that contain nec...

Development of Headed Bars in Slab-Column Joints of Reinforced Concrete Slab Bridges

Development of Headed Bars in Slab-Column Joints of Reinforced Concrete Slab Bridges

A nondestructive method for load rating of bridges without structural properties and plans

Load rating describes the processing of quantifying the safe live load carrying capacity of an existing bridge. For most bridges, this load rating is derived as an analytical solution based on the structural design details and operational condition state. However, for structures without plans or insufficient structural details available it is difficult to formulate an analytical solution, especially for concrete structures where internal reinforcement details are needed to determine section capacity. For structures within this category, the potential solutions involve destructive evaluation to characterize the materials and components, proof load testing, or engineering judgement-based characterization. In this paper, a nondestructive method for load rating of reinforced concrete (RC) slab bridges without structural plans is proposed. To determine a bridge’s load rating factor, the capacity as well as dead load and live load effects need to be determined. In the proposed approach, a series of finite element analyses were conducted to describe the modal properties of a large population of bridges with different geometric characteristics. Results and geometric inputs were then used to develop an artificial neural network model that predicts the flexural rigidity of a bridge based on the measured modal frequencies derived from vibration testing. Due to the uncertainty in internal geometry of concrete, nondestructive approaches are presented to obtain the cross-section dimensions of bridge as well as the elastic modulus and compressive strength of concrete. Next, the cross-sectional area of the internal reinforcing steel is estimated through a quasi-static load test coupled with an optimization approach. These structural and material properties are then used to determine load effects and ultimately the bridge’s capacity. As a validation of the proposed approach, a skewed RC slab bridge with structural plans was tested and analyzed as if plans were not available. The bridge was instrumented with accelerometers and strain gages to record its response under ambient vibration, impact excitation, and quasi-static live load testing. Results show that the proposed nondestructive approach can be used to satisfactorily determine the load rating factor of the test bridge and can ultimately be used for load rating of concrete slab bridges without structural information.

Performance Evaluation of a Reinforced Concrete Slab Bridge Retrofitted with Carbon Fiber Reinforcement Polymer Laminate System

As a result of a drawing oversight, a nine-span continuous reinforced concrete slab bridge on westbound I-10 near Lordsburg, New Mexico, was built with only half of the required positive moment steel reinforcement. Bridge 9367, constructed in April 2006, was retrofitted with a carbon fiber–reinforced polymer (CFRP) laminate system in November 2006 to correct for this error. Diagnostic load tests were conducted before and immediately after the retrofitting of the bridge. A finite element analysis of the bridge was also conducted to evaluate the strength and serviceability of the slab bridge and to determine whether the addition of the CFRP system effectively met these limit states. The addition of the CFRP to the bridge increased the rating factors to greater than the legal load limit. Before the bridge retrofit, stresses in the steel reinforcement exceeded the limits set to control excessive concrete cracking and inelastic deformations. Inclusion of the CFRP reduced these stresses but only slightly below the limits. Creep rupture and fatigue of the CFRP were not considered issues. Two additional load tests were conducted 8 months and approximately 9 years after the retrofit. The first evaluation showed that in the short term, the slab stiffness was increased with a decrease in measured strains immediately after the installation of the CFRP. However, comparison of the strains from the load tests conducted later showed that the magnitudes had greatly increased and were approximately equal to the preretrofit strains. Ultimately, Bridge 9367 was replaced due to excessive cracking and large measured strains.

Dynamic Behavior of Pre-stressed Slab Bridges

In last 10 years pre-stressed in-situ slab bridges has become one of the used bridge deck type for new bridges in Latvia. This structure is used for overpasses on road junctions where height of the bridge deck and space under the superstructure is limited by the levels of roads. This research show and discuss dynamic test results performed from 2008 to 2015. One reinforced concrete (RC) and three pre-stressed RC slab bridges were tested. One ribbed RC and three pre-stressed RC ribbed slab bridges were tested. Results show that for PRC bridges span/depth ratio correlate with damping ratio- higher span/depth ratio show decrease in damping ratio. For even pavement condition DAF values are lower than 1,4.

Spatial time-dependent reliability analysis of reinforced concrete slab bridges subject to realistic traffic loading

Resistance and loads are often correlated in time and space. The paper assesses the influence of these correlations on structural reliability/probability of failure for a typical two-lane reinforced concrete (RC) slab bridge under realistic traffic loading. Spatial variables for structural resistance are cover and concrete compressive strength, which in turn affect the strength and chloride-induced corrosion of RC elements. Random variables include pit depth and model error. Correlation of weights between trucks in adjacent lanes and inter-vehicle gaps are also included and are calibrated against weigh-in-motion data. Reliability analysis of deteriorating bridges needs to incorporate uncertainties associated with parameters governing the deterioration process and loading. One of the major unanswered questions in the work carried out to date is the influence of spatial variability of load and resistance on failure probability. Spatial variability research carried out to date has been mainly focused on predicting the remaining lifetime of a corroding structure and spatial variability of material, dimensional and environmental properties. A major shortcoming in the work carried out to date is the lack of an allowance for the spatial variability of applied traffic loads. In this article, a two-dimensional (2D) random field is developed where load effects and time-dependent structural resistance are calculated for each segment in the field. The 2D spatial time-dependent reliability analysis of an RC slab bridge found that a spatially correlated resistance results in only a small increase in probability of failure. Despite the fact that load effect at points along the length of a bridge is strongly correlated, the combined influence of correlation in load and resistance on probability of failure is small.

Reconstruction of the Reinforced-Concrete Railway Bridge in km 3,668 – Argentinská of the Track Bubeneč – Holešovice in Prague

This article provides a brief review of a reconstruction of the railway bridge in kilometer 3,668 of the railway-track Prague Bubeneč – Prague Holešovice. Specifically, the object is a 10-span reinforced-concrete slab bridge of spans app. 10x 20m carrying two railway-tracks. The reconstruction comprised of a superstructure waterproofing replacement, reconstruction or replacement of cornices and bridge seat at abutment O2 and replacement of all bearings and expansion joints.The bridge’s operation had to be maintained during reconstruction so replacement of bearings and expansion joints was carried out on an uplifted superstructure. Reconstruction of upper part (cornices, waterproofing and expansion joints) was conducted transversally by halves of bridge so operation was maintained at least on one of the railway-tracks.During the process, after consulted with SŽDC, some technical aspects of the original technical documentation from 2008 were changed according to an actual in-situ conditions and contractor demands. These changes involved a design of new cornices and a significant reduction in a number of temporary supports so the structures had to be analyzed for the temporary construction states again. After completing all works on bridge deck and enabling operation of both tracks, the bridge reconstruction continued with reconstruction of the superstructure’s bottom face and existing parts of substructure including building-up of new pile caps.

Appraisal of Strengthening Cost for Increasing Flexural Strength of Reinforced Concrete Slab Bridges in Thailand

The highway live loadings, HS20-44, stipulated by Association of State Highway and Transportation Officials (AASHTO) are different from Thai truck weights according to government gazettes issued by Department of Highways. This article aimed to study the strengthening costs of the bridges due to Thai trucks. The reinforced concrete solid slab bridges with the span length ranging from 5 to 10 meters were selected to study. It was found that the bridge responses due to Thai trucks were greater than those from AASHTO loads. The average strengthening costs were approximately 6,958 Baht/sq.m and highest at 7 m-span length. The results of this study would be a reference data to create an alternative plan for bridge strengthening in Thailand in order to sustain the bridge safety level recommended by AASHTO.

Recommendations for the Shear Assessment of Reinforced Concrete Slab Bridges from Experiments

Upon assessment of existing reinforced concrete short-span solid slab bridges according to the recently implemented Eurocodes that include more conservative shear capacity provisions and heavier axle loads, a number of these structures were found to be shear-critical. The results from recent experimental research on the shear capacity of slabs indicate that slabs benefit from transverse load distribution. Recommendations for the assessment of solid slab bridges in shear are developed on the basis of these experiments. A load spreading method for the concentrated loads is proposed and the applicability of superposition of loading is studied. The resulting most unfavourable position for the design trucks is provided and implemented in the so-called Dutch “Quick Scan” method (QSEC2). Cases of existing bridges are studied with the previously used QS-VBC as well as with the QS-EC2 that includes the recommendations. As a result of the assumed transverse load distribution, the shear stress to be considered at the support based on the recommendations becomes smaller.

Investigation of AASHTO Live-Load Reduction in Reinforced Concrete Slab Bridges

This paper presents the results of a three-dimensional (3D) finite-element study that investigated the effect of the multipresence factor of the load-reduction factors used in the AASHTO Bridge Design Specifications. Typical one-span, two-equal-span continuous, simply supported, three- and four-lane reinforced concrete slab highway bridges were selected for this study. AASHTO HS20 design truck loads are first placed transversally in all lanes, positioned side-by-side and close to one edge of the bridge slab; this fully loaded condition served as a reference case. Reduced loading patterns are then investigated using 3D finite-element analysis (FEA), with design loads in two out of three lanes (reduced 2/3), three out of four lanes (reduced 3/4), and two out of four lanes (reduced 2/4). The longitudinal bending moments and deflection results obtained for the FEA for reduced and fully loaded bridges are directly compared. Furthermore, a correlation between the reduced-load cases and AASHTO reduction factors ...

Identification of a Distribution of Stiffness Reduction in Reinforced Concrete Slab Bridges Subjected to Moving Loads

The method for identifying arbitrary stiffness reduction in damaged reinforced concrete slab bridges under moving loads is proposed and dynamic signals measured at several points are used as response data to reflect the properties of the moving loads sensitivity. In particular, the change in stiffness in each element before and after damage, based on the system identification method, is described and discussed by using a modified bivariate Gaussian distribution function. The proposed method in this work is more feasible than the conventional element-based damage detection method from the computational efficiency because the procedure of finite-element analysis coupled with microgenetic algorithm using six unknown parameters irrespective of the number of elements are considered. The validity of the technique is numerically verified using a set of dynamic data obtained from a simulation of the actual bridge modeled with a three-dimensional solid element. The numerical calculations show that the proposed technique is a feasible and practical method that can prove the exact location of a damaged region as well as inspect the complex distribution of deteriorated stiffness, although there is a modeling error between actual bridge results and numerical model results as well as a measurement error like uncertain noise in the response data.

Higher Level Evaluation of a Reinforced Concrete Slab Bridge

In New Mexico, many reinforced concrete slab (RCS) bridges provide service on interstates I-10, I-25, and I-40. The load rating for this type of bridge largely depends on the live-load moment in the slab. Consequently, the objective of this study was to determine a more accurate value for the equivalent strip width using higher level evaluation techniques. A continuous RCS bridge was evaluated starting with an AASHTO load and resistance factor rating analysis. A diagnostic test was then conducted to measure live-load strains which showed that the slab stiffness fit within cracked and gross section behavior. Furthermore, slab moments from finite element analysis agreed reasonably well with experimental moments derived using the average of the cracked and gross section modulus. From refined analysis, the equivalent strip widths for positive moment were 26.1 and 22.1% greater than those calculated by the AASHTO approximate method for the exterior and interior spans, respectively. The refined widths for negative moment were greater than AASHTO by 13.1 and 11.1%. This increase in the equivalent strip width reduced the live-load effects, which proportionally increased the rating factors.

Influence of Skew Angle on Reinforced Concrete Slab Bridges

The effect of a skew angle on simple-span reinforced concrete bridges is presented in this paper using the finite-element method. The parameters investigated in this analytical study were the span length, slab width, and skew angle. The finite-element analysis (FEA) results for skewed bridges were compared to the reference straight bridges as well as the American Association for State Highway and Transportation Officials (AASHTO) Standard Specifications and LRFD procedures. A total of 96 case study bridges were analyzed and subjected to AASHTO HS-20 design trucks positioned close to one edge on each bridge to produce maximum bending in the slab. The AASHTO Standard Specifications procedure gave similar results to the FEA maximum longitudinal bending moment for a skew angle less than or equal to 20°. As the skew angle increased, AASHTO Standard Specifications overestimated the maximum moment by 20% for 30°, 50% for 40°, and 100% for 50°. The AASHTO LRFD Design Specifications procedure overestimated the FEA maximum longitudinal bending moment. This overestimate increased with the increase in the skew angle, and decreased when the number of lanes increased; AASHTO LRFD overestimated the longitudinal bending moment by up to 40% for skew angles less than 30° and reaching 50% for 50°. The ratio between the three-dimensional FEA longitudinal moments for skewed and straight bridges was almost one for bridges with skew angle less than 20°. This ratio decreased to 0.75 for bridges with skew angles between 30 and 40°, and further decreased to 0.5 as the skew angle of the bridge increased to 50°. This decrease in the longitudinal moment ratio is offset by an increase of up to 75% in the maximum transverse moment ratio as the skew angle increases from 0 to 50°. The ratio between the FEA maximum live-load deflection for skewed bridges and straight bridges decreases in a pattern consistent with that of the longitudinal moment. This ratio decreased from one for skew angles less than 10° to 0.6 for skew angles between 40 and 50°.

Effect of reinforcement corrosion on reliability of highway bridges

This paper presents several aspects of a method for reliability assessment of reinforced concrete (RC) slab bridges with corroded reinforcement. It is assumed that corrosion will lead to a reduction in cross-sectional area of the reinforcing steel and/or a reduction in bond strength. Two types of corrosion are considered: general and localized corrosion. The method includes a non-linear finite element structural model and probabilistic models for traffic loads, corrosion propagation, bond characteristics, material properties, element dimensions and reinforcement placement. Reliability is estimated in terms of the reliability index using the first-order reliability method (FORM). For illustrative purposes, bridge reliabilities are calculated for a deteriorating, simple-span RC slab bridge, for ultimate strength and serviceability limit states.

Evaluation of Existing RC Slab Bridges

The objective of this study is to evaluate the American Association of State Highway and Transportation Officials (AASHTO) rating procedure for reinforced concrete (RC) slab bridges by using nondestructive load testing. Three RC slab bridges, each with three continuous spans, were selected for this study. These bridges had minor to severe deterioration. For each bridge, the rating factors were calculated using AASHTO specifications. Nondestructive load tests were carried out on all three bridges. Four dump trucks, each filled with gravel, were used for loading. The trucks were placed in three different load positions to cause maximum positive moment in the middle span, maximum positive moment in the end span, and maximum negative moment at the intermediate supports. The analytical models were updated using the results from load testing and then were used to calculate new rating factors for each bridge. The current AASHTO rating procedure was found to be too conservative.

Reliability of Deteriorating RC Slab Bridges

Reinforced concrete (RC) bridges deteriorate with time. This results in reduction of their resistance, and, consequently, of their reliability. Corrosion of embedded reinforcing steel is one of the main causes of deterioration. The paper presents a method for reliability assessment of RC slab bridges with corroded reinforcement. The method includes a traffic load model, a corrosion model, and a nonlinear finite element structural model. Two types of corrosion--general corrosion, including spalling and debond between concrete and the corroded reinforcement, and localized corrosion--are considered. Reliability is estimated in terms of the reliability index using the first-order reliability method. Uncertainties associated with material properties, geometry, loads, and corrosion parameters are taken into account. A sensitivity analysis of a simple span bridge is carried out to examine the influence of these uncertainties on the bridge reliability. Reliability assessment of a deteriorated three-span continuous bridge illustrates the application of the method.

Nonlinear Finite Element Analysis of RC Slab Bridge

A step‐by‐step modeling and analysis procedure for nonlinear finite element analysis of complete constructed facilities is presented. A comprehensive microcomputer‐based software that was developed for this study is briefly described. The procedure is demonstrated by conducting analyses of an existing reinforced concrete (RC) slab bridge. The experimental knowledge base gained from nondestructive tests conducted on this bridge is used to construct and validate the analytical models. A sensitivity study is carried out to explore the effects of various modeling parameters on the structure response. Analysis results indicate that the manner of modeling support conditions significantly affects the bridge strength. The collapse mechanism of the bridge that is predicted agrees with results from destructive tests conducted on a similar RC slab bridge.