Ontario Bridge Research Articles

Infrastructure deterioration modeling with an inhomogeneous continuous time Markov chain: A latent state approach with analytic transition probabilities

AbstractMarkov chains have been widely used to characterize performance deterioration of infrastructure assets, to model maintenance effectiveness, and to find the optimal intervention strategies. For long‐lived assets such as bridges, the time‐homogeneity assumptions of Markov chains should be carefully checked. For this purpose, this research proposes a regime‐switching continuous‐time Markov chain of which the state transition probabilities depend on another, latent, Markov chain that characterizes the overall aging regime of an asset. With the aid of a state‐augmentation technique, closed‐form solutions for the transition probabilities are analytically derived, making the statistical analysis simple. A case study is presented using the open Ontario Bridge Condition data for provincial highway bridges. The case study demonstrates that the proposed method allows to (1) estimate a statistically superior model to the homogeneous Markov chain and (2) obtain results with comparable accuracy in approximately 48% of the computation time of the state‐of‐the‐art inhomogeneous Markov chain.

Soil-pile-structure interaction effects on seismic demands and fragility estimates of a typical Ontario highway bridge retrofitted with fiber reinforced elastomeric isolator

This study investigates the seismic performance of a seismically isolated soil-pile-structure system incorporating the effects of isolation system, soil layers of low stiffness and strength, pile inclination, pile-soil-pile interactions, and bridge-embankment interaction. A coupled three-dimensional nonlinear finite element model of an existing bridge in Ottawa, Ontario is developed as a representative of the 44% of the total bridges in Ontario that have been built prior to 1970. A seismic retrofit technique which involves isolating the bridge superstructure utilizing a novel type of elastomeric isolator called Fiber Reinforced Elastomeric Isolator (FREI) is adopted. Two bridge conditions, namely, monolithic (pre-retrofit) and isolated (retrofitted) are considered to investigate the effect of Soil-Structure Interaction (SSI) on the seismic performance of the bridge prior to and after the retrofit in its longitudinal and transverse directions, independently. Analytical fragility curves are developed for the bridge components based on the outputs of an Incremental Dynamic Analysis (IDA) using 45 synthetic ground motion records. It is shown that seismic isolation can effectively reduce the superstructure acceleration by allowing the deck to experience large lateral displacements. Therefore, the transferred shear forces to the columns and their supporting piles are decreased significantly. While seismic isolation of the bridge is found to be beneficial for bridge components, it has a detrimental effect on the extensive and collapse damage states of abutment piles in the longitudinal direction. This conclusion is limited to the conventional abutment models where the abutment backwall damage has not been taken into account. Using more complex physics-based abutment spring systems may reveal that using the seismic isolation systems can mitigate the probability of extensive damage and collapse to abutment piles by allowing the abutment to serve as a fuse and dissipate the imposed energy by its fracture mechanism.

Steel buried structures: condition of Ontario structures and review of deterioration mechanisms and rehabilitation approaches

Buried steel structures, commonly referred to as buried bridges, culverts, or soil–steel structures are a valuable bridge crossing solution. Owners manage their bridge assets by evaluating their condition and rehabilitating as required. Ontario’s resources for managing and rehabilitating buried steel bridge structures are limited, and an investigation into the maintenance and rehabilitation practice of Ontario’s assets demonstrates a lag in their maintenance and rehabilitation. Knowledge regarding rehabilitation of these structures is dispersed and unconcise, leaving owners challenged to understanding how to best manage and rehabilitate their assets. This paper investigates the age, condition, and rehabilitation of steel buried bridges in Ontario and reviews the commonly encountered deterioration and distress mechanisms along with the state-of-the-art rehabilitation practices. With an understanding of structural behavior, deterioration, and rehabilitation opportunities for structures nearing the end of their service lives, owners will be better equipped to effectively manage their inventory and leverage the economic, social, and environmental value of buried structures.

Blind comparison of non-invasive shear wave velocity profiling with invasive methods at bridge sites in Windsor, Ontario

Canadian seismic design guidelines classify subsurface ground conditions based on the average shear-wave velocity (VS) of the upper 30 m (VS30). We seek to optimize a robust earthquake site classification procedure for Ontario bridge sites, assessed primarily from blind comparison of non-invasive and invasive shear-wave velocity (VS) depth profiling techniques. Non-invasive seismic testing is performed at 6 bridge sites in Windsor, Ontario co-located with invasive penetration and/or borehole VS measurements. Non-invasive surface wave dispersion and site amplification functions are jointly inverted to retrieve VS profiles at each site. Bridge sites tested are found to be mostly characterized with sediments up to ~30 m thick overlying seismic bedrock. Excellent agreement of VS30 estimates is obtained between both invasive and non-invasive methods and we notably determine an overall average relative difference in VS between methodologies of 9% for soil layers. Earthquake site classification based on VS is consistent at all sites regardless of methodology.

The performance of epoxy coated reinforcement: experience of the Ontario ministry of transportation

The Ontario Ministry of Transportation has a mandate to specify cost-effective methods and materials for the construction and maintenance of provincial highway structures. In support of this mandate, the Bridge Durability Work Group initiated a performance evaluation of epoxy-coated reinforcement (ECR) in the Ontario bridge environment. Findings of the investigation, which are summarised in this paper, strongly indicate that the long-term performance of the ECR is not likely to provide the corrosion resistance or associated maintenance free service life that was originally forecast. Several Ministry structures constructed with ECR have already been rehabilitated, before achieving even a 20-year service life. Today, the Ministry must develop and adopt strategies at the time of design for service life that far exceed the expectations of only a few years ago; typically, in accordance with the new Canadian Highway Bridge Design Code, the design life of new structures is anticipated to be 75 years. A significant body of research to date indicates that ECR can at best provide marginally longer service life than black reinforcement.

Design and Performance of Jointless Bridges in Ontario: New Technical and Material Concepts

It is well recognized that leaking expansion joints at the ends of bridge decks have led to the premature deterioration of bridge components. The elimination of these maintenance-prone joints not only yields immediate economic benefits but also improves the long-term durability of bridges. In Ontario, Canada, “jointless” bridges have been used for many years. Recently, the use of two main types of these bridges has increased dramatically. The first type is an “integral abutment” bridge that comprises an integral deck and abutment system supported on flexible piles. The approach slabs are also continuous with the deck slab. The flexible foundation allows the anticipated deck movements to take place at the end of the approach slab. Control joint details have been developed to allow movements at this location. The second type is a “semi-integral abutment” bridge that also allows expansion joints to be eliminated from the end of the bridge deck. The approach slabs are continuous with the deck slab, and the abutments are supported on rigid foundations (spread footings). The superstructure is not continuous with the abutments, and conventional bearings are used to allow horizontal movements between the deck and the abutments. A control joint is provided at the end of the approach slab that is detailed to slide in between the wing walls. Some of the design methods and construction details that are used in Ontario for integral and semi-integral abutment bridges are summarized. A review of the actual performance of existing bridges is also presented.

Bridge Testing—A Surprise Every Time

Experience with field testing of highway bridges in Ontario, Canada, during recent years shows that nearly every bridge has some aspect of behavior that can escape the attention of even experienced bridge designers and analysts. This paper lists some of the various surprises encountered in bridge testing that may have a significant influence on the load‐carrying capacities of bridges. In particular, reference is made to the behavior of bridges with steel girders and concrete deck slabs, and of steel truss bridges. Lessons drawn from tests on these bridges are summarized, so they can provide an advantage in the load‐carrying capacity evaluation. It is also shown that in some cases the appearance of a bridge can be misleading with regard to its true load‐carrying capacity. In such cases, field testing is shown to be the most effective means of evaluating the bridge.

Pavement damage implications of Ontario Bridge Formula axle group weight limits

The Ontario Bridge Formula (OBF) is the basis for the regulation of highway truck weights in Ontario. Allowable loads on tandem and tridem axle groups increase with increasing axle group spread. Analyses of the moments induced in simple-span bridges by the allowable axle group loads show that the moments increase with the increasing loads allowed on wider axle spreads. Pavement damage load equivalency functions developed from the Canroad pavement test series are used to estimate the. pavement damage impacts of these allowable axle loads. Relative pavement damage is shown to increase by 50% for the range of loads allowed on tandem axle groups and by 125 % for the load range allowed on tridems. If equal pavement damage were used for regulating axle group loads, then the range allowed for tandems would be 15 400–16 500 kg, instead of the OBF-allowed 15 400–19 000 kg; and 19 100–20 000 kg, instead of the OBF-allowed 19 500–28 600 kg, for tridems. Key words: highway bridges, highway pavements, bridge loads, trucks, load equivalencies.

Axle load shifts during truck braking and their implications for bridge and pavement design

The axle load shifts of four truck types during braking are estimated using theoretical braking models and the implications of these axle load shifts for bridge and pavement design are explored. The truck types examined are a three-axle straight truck, a five-axle tractor semi-trailer, a seven-axle tractor semi-trailer with two air-lift belly axles, and a seven-axle B-train tractor-double trailer, each loaded to legal Ontario limits with weigh-out commodities. Each of the truck types experienced a substantial load transfer to the front steering axles under braking, mainly from the rear tandem axle groups, where the front axle load increase varied from 38 to 48%. The bridge design implications of the load shifts are examined in terms of the Ontario Bridge Formula and the moments induced in simple-span bridges compared with the moments induced by a reference design truck. For the braking model used, the decelerations and associated shifts in axle load do not lead to higher forces for bridge design and evaluation. The pavement damage implications are analyzed in terms of load equivalency functions derived from some load tests conducted at a number of pavement sites across Canada in 1986. These equivalencies increased up to 50% of the static values for the three-axle truck at maximum braking. It is suggested that the major damage implications are at intersections in urban areas and that increased structural sections could be designed to handle the increased equivalencies. Key words: bridge design, pavement design, truck braking, truck loads, pavement damage, bridge damage.

Permit vehicle control in Ontario

Issuing special permits for transportation of large indivisible loads or heavy construction equipment in Ontario is based on the strength of the highway bridges and pavements. The volume of such permit applications has increased many fold over the last 10 years requiring significantly increased effort for their evaluation.The Ontario bridge formula provides a direct relationship between the bridge strength and the regulatory weight limits. Using this relationship, simplified guidelines have been developed to allow speedy evaluation of permit applications without requiring a detailed evaluation of the bridges and pavements enroute. The two-vehicle concept for transporting very long prefabricated components, developed through an in-depth analysis of bridge structures, is included in the guidelines. Over the number of years, the industry has taken full advantage of these guidelines in improving their equipment, making movement of large components a routine matter. This paper summarizes the technical background of these guidelines. Use of the guidelines is illustrated with examples. Key words: transportation, highway bridges, pavements, weight regulations, special permit, truck weights, heavy loads.

Reliability-based design criteria for timber bridges in Ontario

The new Ontario Highway Bridge Design Code (OHBDC) is based on limit states theory and therefore uses a load and resistance factor format. This paper deals with the development of the basis for the timber bridge design provisions (OHBDC). Three structural systems are considered: sawn timber stringers, laminated nailed decks, and prestressed laminated decks. The latter system has been successfully used in Ontario for the last 7 years.The acceptance criterion in calculation of load and resistance factors is structural reliability. It is required that bridges designed using the new code must have a reliability equal to or greater than a preselected target value. Reliability is measured in terms of the reliability index. The safety analysis is performed for a structural system rather than for individual members. The live load model was developed on the basis of available truck survey data. Material properties are based on extensive in-grade test results. Numerical examples are included to demonstrate the presented approach. Key words: bridge deck, design code, prestressed timber, reliability, reliability index, stringers, structural safety, timber bridges.

Dynamic loading and testing of bridges in Ontario

The Ontario Highway Bridge Design Code (OHBDC) contains provisions on dynamic load and vibration that are substantially different from other codes. Dynamic testing of 27 bridges of various configurations, of steel, timber, and concrete construction, and with spans from 5 to 122 m was therefore undertaken to obtain comprehensive data to support OHBDC provisions. Standardized instrumentation, data acquisition, and test and data processing procedures were used for all bridge tests. Data was gathered from passing trucks, and scheduled runs by test vehicles of various weights. Accelerometer responses were used to determine bridge vibration modes, and dynamic amplifications were obtained from displacement or strain measurements. The form of the provisions adopted for dynamic load and vibration was confirmed by the test results, subject to minor adjustment of values. Observations on the distribution of dynamic load, and its relationship to span length and vehicle weight, may provide a basis for future refinement of the dynamic load provisions. If the stiffness of curbs and barrier walls is not included in deflection calculations, bridges designed by deflection could be penalized. Key words: bridges, vibration, bridge testing, bridge design codes.

The Ontario bridge code—Development and implementation

The Ontario Highway Bridge Design Code was first issued in 1979 and has since been used for the design and evaluation of most bridges in Ontario. The code is in metric SI units, written in a limit states format, and calibrated to a target safety index value of 3.5. It has produced bridges with a more consistent safety level and capable of carrying design live loads twice those previously prescribed. Feedback from users was obtained and their concerns considered in formulating the provisions of the seeond edition in 1983. New bridge codes can be written in a short time and implemented most readily within a relatively small jurisdiction having control of all highways, bridges, and vehicles. Communications between the writers and potential users are important throughout the preparation and implementation phases. It is essential that a commentary volume be issued with a code to ensure correct understanding and interpretation of new provisions. Computer programs should be available, incorporating the code technology before the use of a new code becomes mandatory. Future code needs and likely areas of new development are outlined in the paper. Key words: calibration, codes, computer systems, highway bridges, loadings, safety, structures.

Calibration of the Ontario Bridge Design Code 1983 edition

The paper summarizes the calibration procedure used to calculate load and resistance factors for the Ontario Bridge Design Code 1983 edition. The limit states considered include serviceability and ultimate limit states during service and in construction. The acceptance criterion is closeness to a predetermined target safety level. Safety is measured in terms of a reliability index. The results of calibration are discussed for composite steel–concrete girders, pretensioned concrete girders, post-tensioned concrete decks, and timber decks. The analysis of construction design criteria is demonstrated on segmental bridges. Key words: code calibration, bridges, reliability index, load and resistance factors, limit states.

Dynamic response of bridges to multiple truck loading

An analytical procedure called the iterative dynamic substructuring method (IDSM) is described for determining the response of a beam–slab bridge system traversed by multi-axle trucks. The trucks are idealized as systems of beams mounted on springs and the bridge as a grid. The IDSM applies mode superposition analysis to the bridge and truck as separate structures connected only at the time-dependent contact points. The bridge is subjected to forces equal to the time-dependent forces on the truck springs, while the truck is subjected to “ground” motion displacements. Since the forces in the spring and the ground motion are interdependent, an iterative procedure is necessary to achieve compatibility of forces and displacements at the contact points.The IDSM is employed to study the response to multiple vehicle loading of the Conestogo River bridge which was field tested by the Ontario Ministry of Transportation and Communications. The purpose of the analysis is to compare single with multiple vehicle loadings under various conditions of truck speeds and positions. The results are used to assess the validity of the reduction in impact factors applied to multiple vehicle loading in the Ontario Bridge Code.

Soil–steel structure design by the Ontario Code: Part 2. Structural considerations

The paper presents provisions of the Ontario Bridge Design Code for the structural design of the metallic shell of soil–steel structures, and also discusses the development background of these provisions. A simplified method of determining live load effects in the metallic shell is presented. The method is based on results of a well-tested plane strain finite element program. An empirical method for determining live load effects, which is based on tests of full-size structures, is also given. A worked example is given to illustrate the usage of the design provisions.

Rigid Frame Highway Bridges In Ontario

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