Medium Span Bridges Research Articles

Effect of soil-foundation-structure interaction and pier column non-linearity on seismic response of bridges supported on shallow foundations

Traditionally, shallow spread footing-type foundations are used for medium span bridges supported on hard soil and rock strata. Such bridges are modelled with fixed supports and no soil–foundation–structure interaction (SSI) is normally considered. The investigation presented herein utilized a sub-structuring technique and finite element method (FEM) model for the analysis of a four-span bridge designed for five different rock classes and subjected to an ensemble of actual ground motions. SSI was incorporated through Winkler springs while non-linear behaviour of reinforced concrete pier column was modelled by an equivalent linear model. The results of the study were evaluated to delineate the effect of SSI and pier column non-linearity on seismic response parameters of bridges founded on rock. It was found that the soil–foundation–structure interaction couldn’t be neglected in all cases of rock classes and input ground motions. Furthermore, pier column non-linearity influenced bridge displacement and base shear more significantly than SSI. Impact of foundation rocking was also examined and was found to be rather insignificant on bridge response parameters due to high rocking impedance of properly designed bridge foundations.

COST AND PERFORMANCE OPTIMIZATION OF PRECAST POST TENSIONED PRE-STRESSED GIRDER BRIDGE SUPERSTRUCTURES

Bridges are the most costly components of a road transportation network. Pre-stressed concrete girders with cast in place concrete decks are widely used for short to medium span bridges. The design and subsequent cost of a bridge depends on key geometric variables such as bridge width, number of lanes, number and length of spans, slab thickness, number and spacing of girders. Some of these variables are dictated by traffic demands and highway geometry, while others are related to structural demands. Typically, designing a bridge usually involves experience and expert judgement of the bridge engineer. This study is aimed at cost and performance optimization of pre-stressed concrete girder bridges using a parametric study of the design variables and their effects on cost and performance of the bridge. A spreadsheet is developed for analysis and design of deck slab and girders using one dimensional beam line analysis and AASHTO LRFD distribution factors. The spread sheet also calculates the overall cost of the bridge superstructure. This spreadsheet is then used to perform a parametric study by iterating through all design parameters. It is shown that, contrary to conventional wisdom, the cost and performance of bridge superstructure are not necessarily competing factors. Relationships for slab thickness and girder spacing are presented that result in optimal performance and cost of the bridge superstructure.

Stress-laminated-timber decks: state of the art and design based on Swedish practice

Stress-laminated-timber (SLT) bridge decks are a valid alternative to conventional short- and medium-span bridges in terms of cost and performance. SLT decks are made from a number of planks or glulam beams positioned side by side and stressed together using high-strength steel bars. A concentrated load can therefore be distributed from the loaded beams onto adjacent beams due to the resisting friction caused by the pre-stressing of all beams in the deck. This paper describes the state of the art of SLT bridge decks, with special emphasis on Swedish practice. The effect of butt joints on deck deflection and solution applied to accommodate the loss of pre-stress are shown. Simple design tools for the preliminary design of road bridges are illustrated. Best practice with regard to some detailing, water protection and durability is also discussed. Finally, possible developments of SLT bridges are discussed.

Improvement of extrapolation of traffic load effect on highway bridges based on Rice’s theory

It is a primary strategy in assessment, maintenance and rehabilitation of existing bridges in China to analyze structural safety using real traffic load data. For medium and large span bridges, the most common approach to extrapolate extreme load effect takes advantage of the Rice's theory. The method, however, has a problem of determining optimal starting effect interval for tail histogram curve fitting of crossing rate. At present, the problem is generally solved using the approach proposed by Cremona. But the approach is essentially subjective in computing procedure. This paper carries out the test and verification of Cremona’s approach, discovering remarkable discreteness of extrapolated extreme load effects, and in-depth study reveals further flaws-improper understanding of statistical concept, miscalculation of significance level, and deviation of extrapolation by linear fitting method. To solve these issues, this paper develops a new method of determining optimal starting interval for tail histogram fitting. Instead of direct application of the Kolmogorov theory to crossing rate histogram, the new method starts analysis with the sample empirical distribution of effect at arbitrary time in stochastic process. By characteristics analysis of Kolmogorov distribution variable, it figures out whether the stochastic process variable complies with the hypothesis of the Rice's theory or the fitting curve tails with its theoretical curve (identification of optimal starting interval). Through in-depth analysis and case study, it can be seen that the proposed method can best reduce subjectivity in analysis procedure and improve on the load effect extrapolation based on Rice’s theory.

Dynamic and static identification of base-isolated bridges using Genetic Algorithms

In the paper, an identification approach based on a Genetic Algorithm (GA) is applied to the case study of a base-isolated, post-tensioned concrete bridge investigated in earlier contributions of literature. It is known that bearing isolators greatly influence the overall response of small- and medium-span bridges under dynamic loads, but in previous works it was seen that the characterisation of their elastic stiffness under small displacements may be inaccurate. In this work, based on in-situ test measurements obtained under static and dynamic loading conditions, inverse techniques based on GAs are successfully applied to the examined structural system, providing an efficient and well-calibrated structural identification of its main properties. Compared to other identification tools and classical correlation techniques, the main advantage deriving from the use of inverse approaches based on GAs typically manifests in the possibility to estimate a greater number of material parameters (e.g. properties of concrete as well as stiffness of the bearing isolators, etc.), and to critically assess the accuracy of the identification. Based on rather good correlation between test measurements and finite element (FE) model updating, it is expected that the same technique could be applied to various structural typologies and systems.

An innovative steel-concrete joint for integral abutment bridges

Integral abutment bridges are becoming rather common, due to the durability problems of bearings and expansion joints. At the same time, among short- and medium-span bridges, multi-beam steel-concrete composite deck with hot-rolled girder is an economical and interesting alternative to traditional pre-stressed concrete solutions. The two concepts can be linked together to design integral steel-concrete composite bridges with the benefits of two typologies. The most critical aspect for these bridges is usually the joints between deck and piers or abutments. In this paper, an innovative beam-to-pier joint is proposed and a theoretical and experimental study is introduced and discussed. The analyzed connection is aimed at combining general ease of construction with a highly simplified assembly procedure and a good transmission of hogging and sagging moment at the supports in continuous beams. For this purpose, the traditional shear studs, used at the interface between steel beam and upper concrete slab, are also used at the ends of steel profiles welded horizontally to the end plates. To better understand the behaviour of this kind of joints and the roles played by different components, three large-scale specimens were tested and an FE model was implemented. The theoretical and experimental results confirmed the potential of the proposed connection for practical applications and indicated the way to improve its structural behaviour.

Long term application of bus monitoring system to short and medium span bridges and damage detection

In this study, as one solution to the problem for condition assessment of existing short and medium span reinforced/prestressed concrete bridges, a new monitoring method using a public bus as part of a public transit system (bus monitoring system) is proposed, along with safety indices, namely, characteristic deflection, which is relatively free from the influence of dynamic disturbances due to such factors as the roughness of the road surface, and a structural anomaly parameter. A basic study was conducted by using the results of technical verification experiments and numerical analysis simulation. This paper describes the details of not only how to assess the bridge condition by public bus vibration measured in operating on Ube City bus network as a specific example for verify the system but also what kind of consideration we need to apply the system to existing bridges in overseas country.

Expected seismic performance of irregular medium-span simply supported bridges on soft and hard soils

This paper presents the parametric study of irregular RC bridge structures subjected to strong seismic records. We determine the expected damages and the concentration demands on short piers of bridges with columns of unequal height located on soft and rigid soil sites. Medium length span bridges are analyzed using the most common structural configurations built in many countries with several height pier configurations. The structures were subjected to strong seismic ground motions recorded on soft and hard soils of earthquakes generated at subduction seismic sources. The parameters of interest in the study are the strength and stiffness characteristics of the substructure and the influence of the dynamic characteristics of the seismic records. The parameter combinations produced more than three hundred 3D non-linear time history analyses conducted with the Perform-3D software. Based on the evaluation of damages indexes, we determine the pier expected damages and the importance of the soil type, on the behavior of irregular pier bridge substructures. It is also quantified the impact of the pier configuration in the global behavior of the bridges and the influence of the shortest pier in the expected damages of the other piers. In most of the cases, the piers adjacent to the tallest piers of the bridge were the elements more affected by the irregularity.

Impact Coefficient Analysis of Long-Span Railway Cable-Stayed Bridge Based on Coupled Vehicle-Bridge Vibration

Compared with medium and small span bridges, very limited attention has been paid on the research of the impact coefficient of long-span railway bridges. To estimate the impact effects of long-span railway bridges subjected to moving vehicles, a real long-span railway cable-stayed bridge is regarded as the research object in this study, and a coupled model of vehicle-bridge system is established. The track irregularities are taken as the system excitation and the dynamic responses of the vehicle-bridge system are calculated. The impact effects on main girder, stayed cable, bearings, and bridge tower are discussed at various vehicle speeds. The results show that different components of the long-span railway cable-stayed bridge have different impact coefficients. Even for each part, the impact coefficient is also different at different local positions. It reveals that the impact coefficients in the actual situation may have significant differences with the related code clauses in the present design codes.

Verification tests for practical application of a health monitoring system for short- and medium-span bridges based on public bus vibrations

In Japan, there is a huge number of short- and medium-span bridges in service, and it is becoming a major social concern how these bridges can be maintained in good condition during their whole lifetime. In this paper, we propose a method for assessing the condition of existing short-span (10–20 m span length) reinforced concrete bridges based on data obtained by monitoring public bus vibrations. This paper describes the details of not only a prototype monitoring system using information technology and sensors, which is capable of providing more accurate knowledge about bridge performance than traditional ways, but also a few specific examples of bridge condition assessment using public bus vibrations measured when driving on bridges, based on the data from the system.

Road Bridges WD7-WD8 on Route Sucharskiego, Poland - Innovative Steel-Concrete Composite Deck Solutions

In the range of small- and medium-span bridges, multi-beam steel–concrete composite decks consisting of high-strength hot-rolled girders are an economical and interesting alternative to traditional pre-stressed concrete solutions. The use of reinforced concrete cross-beams at the supports allows for a further optimization because of the easy and simple construction. This deck typology was introduced in Europe already in the 1990s and is now becoming a common solution for many standard bridges. This article describes the application of this typology to some of the viaducts on Route Sucharskiego, Poland. The principles of the deck concept, steel grade choice, concrete cross-beam function, fabrication detailing and construction phase are described in detail.

Identification of dynamic displacements and modal frequencies of a medium-span suspension bridge using multimode GNSS processing

Global Navigation Satellite System (GNSS) positioning technology has been employed in the dynamic monitoring of long-span bridges in the recent years. However, it has difficulties to meet the higher accuracy requirements of the dynamic monitoring of small or medium span bridges, due to the presence of measurement noise from multipath, cycle slips, ionosphere delay, orbital errors, etc. To verify the feasibility of using current GNSS technology to monitor these bridges, a series of monitoring experiments have been carried out on the Wilford suspension bridge in Nottingham (UK) with GNSS and a triaxial accelerometer. Three GNSS data processing modes, i.e. Real-Time Kinematic (RTK), network RTK and Post-Processing Kinematic (PPK), were considered. An innovative multimode adaptive filtering (MAF) that combining adaptive filter with Chebyshev highpass filter was used to identify the dynamic displacements of the bridge from the multimode GNSS data. To validate the GNSS results, the dynamic displacements were also computed from double integration of the accelerometer-measured accelerations. The differences of the displacements between the GNSS and accelerometer results were obtained. The standard deviation and the mean deviation of these differences are less than 1mm, which is good enough for the monitoring purposes. The modal frequencies of the bridge can be accurately identified from GNSS measurements, and successfully validated by those from the accelerometer data. Using the multimode GNSS data and the proposed the MAF algorithm, with sub-millimeter level accuracy GNSS can be used to monitor the vibration response of small or medium span bridges as well as long-span bridges.

Closure to “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. II: Finite-Element Analysis and Experimental Investigation” by Yaohua Deng and George Morcous

Closure to “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. II: Finite-Element Analysis and Experimental Investigation” by Yaohua Deng and George Morcous

Discussion of “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. II: Finite-Element Analysis and Experimental Investigation” by Yaohua Deng and George Morcous

Discussion of “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. II: Finite-Element Analysis and Experimental Investigation” by Yaohua Deng and George Morcous

Discussion of “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. I: System Description and Design” by Yaohua Deng and George Morcous

Discussion of “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. I: System Description and Design” by Yaohua Deng and George Morcous

Closure to “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. I: System Description and Design” by Yaohua Deng and George Morcous

Closure to “Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. I: System Description and Design” by Yaohua Deng and George Morcous

The Best Position to Determine the Hinge in the Cantilever Bridge

The simple-supported beam bridge is a common structure form widely used in small and medium span bridges. When the span is longer, the maximum bending moment is accordingly bigger. The maximum positive and negative bending moment numerical of beam decreases obviously because of cantilever bridge with cantilever beams to reduce the amount of materials. This article analyzes the current commonly used cantilever bridge with large span. The two-span cantilever bridge is analyzed under various loads about the internal force according to the condition of the absolute value of the maximum positive and negative bending moment being equal. It carries on the contrast and analysis about simple-supported beam bridges and obtains the best location of the hinge in the cantilever bridge. Moreover, it provides some reference for the optimum design of similar bridges and projects.

Investigation of Uncertainty Changes in Model Outputs for Finite-Element Model Updating Using Structural Health Monitoring Data

This article aims to investigate the effect of uncertainties on the predicted response of structures using updated finite-element models (FEMs). Modeling uncertainties are quantified by fuzzy numbers and are incorporated into the fuzzy FEM updating procedure. The impact of the amount and types of data used on the performance of the updated model is investigated. In order to perform the complex FEM updating calculations, which generally take too much time for complex models, a Gaussian process (GP) is used as a surrogate model. The central composite design (CCD) method is used to sample the input parameter space for more accurate GP models. Genetic algorithms (GA) are employed to solve the inverse fuzzy model updating problem. Additional constraints are presented to capture the variation space of the uncertain response parameters. The University of Central Florida benchmark test structure, which is designed to represent short-span to medium-span bridges, is used in the scope of uncertainty quantification study. Static and dynamic experimental test data obtained from the benchmark structure under different loadings and conditions are used for the demonstration. A damage case, in which the stiffness reduction in boundaries is simulated by using flexible pads, is considered. The results show that appropriate data sets, which contain the least uncertainty, should be generated instead of involving the entire set of measurements obtained from different tests. Nevertheless, uncertainty quantification should be employed to find the variation range of uncertain responses predicted by simplified FEM models.

Structural model updating using dynamic data

Parameter estimation through model updating is a powerful technique that has gained widespread popularity for condition assessment of aging infrastructure. Among the available techniques, the sensitivity method is perhaps the most popular approach to perform model updating in industrial-scale systems. However, convergence issues are inherent to the method, due to ill-conditioning of the sensitivity matrix and measurement errors. To overcome the afore-mentioned concerns, regularization techniques were successfully applied in simulated and experimental scenarios. Model updating is performed using the University of Central Florida Benchmark Structure which is a laboratory specimen intended to capture the behavior of short to medium span bridges. The finite element model of the Benchmark is updated using (1) a modal parameters-based and (2) a frequency response function (FRF)-based error functions where both methods consider sparse data. In the simulated study, the aim is to evaluate the robustness of both error functions under random noise and ill-conditioning. Finally, the methods are successfully validated using experimentally obtained dynamic data. Based on the obtained results, it is concluded that the FRF-based method is more robust under simulated noise and can handle more unknown parameters in the optimization problem. However, advantages and challenges inherent to each method are presented only in light of those experienced by the authors.

Application of modern timber structure in short and medium span bridges in China

A series of problems about Chinese bridges with short and medium span recent years were analyzed in this paper. The necessity and feasibility of modern timber structure applied in short and medium span bridges in China were also put forward. The results showed that the short and medium span bridges had many problems, such as monotonous structural forms, serious environmental pollution, multiple bridge defects and difficulty in maintenance. With the development of connection and maintenance technology of modern timber structure and its advantages of light self-weight, environmental coordination, high carrying capacity, excellent durability and abundant structural forms, it was necessary and feasible to apply modern timber structure in short and medium span bridges in China. More emphasis on the construction of modern timber structure should be conducted to expand its application scopes and improve the construction proportion of short and medium span timber bridges.