Canadian Highway Bridge Design Code Research Articles

Design of precast UHPFRC retaining walls – Experimental and numerical validations

This paper focuses on the design as well as on the experimental and numerical validations of the mechanical behavior of a precast ultra-high performance fibre reinforced concrete (UHPFRC) retaining walls. The design, made in accordance with the Canadian Highway Bridge Design Code ( CSA S6, 2019 ), led to the fabrication of a full-scale UHPFRC retaining wall with 3% fibre content which had dimensions of 3 m in height, 2 m in length, 2 m in width, with two vertical and horizontal stiffeners, and very thin vertical and horizontal panels of 40 and 65 mm, respectively. The experimental tests showed that the UHPFRC retaining wall exceeded by 42% the ultimate limit state (ULS) design factored bending moment and showed a very ductile behavior under flexural loading. At service limit state (SLS), the retaining wall had maximum crack opening between 0.15 and 0.28 mm, and a maximum lateral displacement of 4 mm. The finite-element model developed for the application captured accurately the flexural behavior of the UHPFRC retaining wall and was used later in parametric studies to optimize the design. The retaining wall optimal design includes UHPFRC with 3% fibre content and stiffeners with variable cross-section which allows volume reductions of 73% for concrete and 86% for rebars in comparison to the conventional reinforced concrete design.

Structural reliability assessment of steel bridges using OSIM visual inspection data and Bayesian updating

Structural reliability theories are used in the calibration of load and resistance factor design (LRFD) in the Canadian Highway Bridge Design Code (CHBDC). The LRFD approach contains certain assumptions about uncertainties in the load and capacity estimation that prevent it from fully exploiting the information gathered during visual inspections. This paper presents a reliability-based framework for analyzing the visual inspection data obtained according to the Ontario structure inspection manual (OSIM). Existing deterioration models are adapted. The Bayesian interference is utilized to estimate the updated structural properties according to the prior information from the bridge maintenance and deterioration models and the new information collected from visual inspections. The criteria set by the CHBDC are used to analyze components and systems reliability. The value of the proposed framework for bridge evaluation and optimizing maintenance is demonstrated through the full implementation of a case-study bridge in the Canadian Province of NB.

Transient Thermal Analysis of Concrete Box Girders: Assessing Temperature Variations in Canadian Climate Zones.

This study examines the temperature distributions and thermal-induced responses in reinforced concrete bridge elements, focusing on the Canadian climate regions. The Canadian Highway Bridge Design Code (CHBDC) currently utilizes a fixed thermal gradient profile that does not account for regional climatic variations. Historical environmental data determines the effective maximum temperatures in the CHBDC. In order to investigate temperature behaviors and distributions, a transient finite element (FE) model is developed using recorded and calculated 3-month thermal loads data for representative cities in different climate regions. The results indicate that the predicted daily maximum effective mean temperatures and extreme daily positive vertical thermal gradients do not align. A linear correlation exists between the daily maximum effective mean temperature and the daily maximum air temperature, with a coefficient of determination (R2) of 0.935. The proposed effective mean temperatures obtained from the FE thermal analysis are higher than the CHBDC recommendations. New thermal gradient profiles are proposed for Canadian climate zones, consisting of two straight lines and a linear gradient at the top and bottom sections. A comparison between the proposed profiles and the CHBDC and AASHTO specifications reveals that a single fixed thermal gradient profile is inadequate to account for the variation in thermal gradients across Canadian climate regions.

The effect of projected air temperatures on concrete box girders thermal gradients and effective temperatures in Canada

This study examines the impact of environmental thermal loads on the temperature behavior of bridges, focusing specifically on concrete box girders. Currently, the Canadian Highway Bridge Design Code (CHBDC) employs a single thermal gradient model for the entire country, which fails to account for the differences in the geographical conditions in the Canadian climate regions. Accordingly, in some cases, the temperature distributions along the girder depth and their thermally induced responses might not be determined accurately. To address this issue, a transient FE thermal analysis was conducted to develop positive and negative thermal gradients and the maximum effective temperatures (METs) for concrete box girders under extreme thermal load conditions of the projected air temperature for the years 2050–2100 and the historical solar radiation. Different parametric studies were conducted to determine how the geometric parameters of box girders affect the temperature distribution and found that the girder depth is a critical factor. Based on the analysis, a formula is proposed to predict the MET for concrete box girders. In addition, different adjustments were recommended to consider the effect of girder depth on the thermal gradients and METs of the box girders.

Predicting Maximum Effective Temperatures and Thermal Gradients for Steel I-Girder in Canadian Climate Regions

The constant fluctuation of thermal loads on steel members, especially during construction, causes non-uniform distributions of temperatures, resulting in possible constructional and structural defects leading to unfavorable thermally induced responses and potential safety risks. The Canadian Highway Bridge Design Code (CHBDC) provides one thermal gradient variation profile without accounting for the differences in the geometrical parameters of the steel members and the variations in the climate regions of Canada. Therefore, in this study, three-dimensional finite element (FE) thermal simulations were conducted to investigate the maximum effective temperatures and positive vertical thermal gradients for different Canadian climate regions. Parametric studies were performed to conduct the FE thermal analysis using the thermal model validated in ANSYS. The comprehensive study results showed that Canada could be divided into two main zones for vertical thermal gradient calculations, meaning that one stationary thermal gradient profile cannot be applicable to all climate regions of Canada, as recommended by the CHBDC. Based on the FE thermal analysis results, empirical formulas as a function of the significant parameters were proposed to predict the maximum effective temperature and thermal gradient variations of the steel I-girder. The predicted maximum effective temperature and thermal gradient variation values were found to be highly correlated with the FE values with coefficients of determination R2 of approximately 0.97 and 0.98, respectively.

Capacity of piles subject to downdrag: a comparison of North American bridge design codes and observations from a full-scale test pile program

Negative skin friction caused by ground settlement is an important consideration for deep foundations in limit states design. However, there are inconsistencies in the methodology whereby negative skin friction and associated drag force are considered in assessing the geotechnical capacity or geotechnical ultimate limit state (ULS) in various design codes. This includes two current North American bridge design codes, the Canadian Highway Bridge Design Code, and AASHTO LRFD Bridge Design Specifications. A test pile program was developed to observe effects of ground settlement on pile settlement, capacity, and drag force. Two instrumented steel H-piles were driven through a compressible clay layer to a hard end-bearing stratum, subjected to ground settlement by constructing a 1.5 m high embankment, followed by static load testing. A load-transfer model was calibrated from the test pile program observations. Test results and the calibrated model were used to compare geotechnical ULS requirements of the two bridge design codes. It is demonstrated that drag force did not detrimentally impact pile capacity. The results showed that for conditions of the test pile program, assessing the geotechnical ULS can be more conservative when adhering to the current AASHTO LRFD Bridge Design Specifications than the Canadian Highway Bridge Design Code.

Enhancing the capacity evaluation of Canadian bridges with structural monitoring data

The Canadian highway bridge design code (CHBDC) uses the concept of a target reliability index for evaluating the load-carrying capacity of existing bridges. This index, which is based on risk to human life, is related to three aspects of uncertainties inherent in a bridge: element behaviour, system behaviour and inspection level. Analysis is yet another uncertainty in bridge evaluation. It is assumed that all bridge inspections are manual. Citing examples of tests on many instrumented bridges, another level of inspection is proposed, carried out with the help of electronic instruments and tests under controlled vehicle loads. Simple additions to the clauses of the CHBDC are proposed, which can be used to determine the optimum load-carrying capacities of existing bridges where structural monitoring information is available.

Scenario-based earthquake damage assessment of highway bridge networks

In earthquake-prone regions, the evaluation of seismic impacts on bridges is crucial to mitigation, emergency, and recovery planning for highway networks. The degree of bridge damage determines the cost and time required for repairs and the level of post-earthquake functionality including disruption of transportation network, increased costs due to reduction of traffic flow and restricted access to emergency routes. The article presents the methodological development and implementation of an interactive web application for rapid geospatial assessment and visualisation of earthquake damage scenarios of municipal highway bridge networks based on open access datasets. The proposed framework consists of the following successive models: hazard, inventory, damage, and impact. The seismic hazard model generates spatial distribution of the shaking intensity for earthquake scenarios in terms of ground motion intensity measure using ground motion prediction equations based on seismic hazard model for Eastern Canada. The shaking intensities are then modified with local site amplification factors based on the Canadian highway bridge design code values. The inventory model provides a database of existing bridges based on open-access data which are then classified according to their seismic vulnerability. The damage model assesses seismic performance of classes of bridges by applying respective fragility functions represented as probabilistic relationships between the intensity measure and the degree of expected damage. The impact model evaluates the post-earthquake traffic-carrying capacity of the highway network based on the predicted damage including repair cost as a percentage of replacement cost of bridges and inspection priority. The web-application is demonstrated with a bridge network in Quebec City including 117 bridges subjected to 180 earthquake scenarios. The proposed methodology is particularly useful to facilitate direct communication of potential impacts to emergency managers and city transport officials.

LRFD calibration for soil failure limit state using the Stiffness Method

The paper describes load and resistance factor design (LRFD) calibration for the resistance factor used in the Stiffness Method internal stability soil failure limit state for geogrid mechanically stabilized earth (MSE) walls. The Stiffness Method was recently adopted in the current American Association of State Highway and Transportation Officials LRFD Bridge Design Specifications in the US, and will appear in the next edition of the Canadian Highway Bridge Design Code. The paper describes the details of the calibration of the soil failure limit state which is unique to the Stiffness Method. Calibration outcomes include consideration of the concept of level of understanding in the selection of nominal load and resistance values which is unique to LRFD foundation engineering practice in Canada. A practical conclusion from these calculations is that if product line-specific creep test data are available to estimate the reinforcement secant creep stiffness used for design, then a resistance factor of 1.0 is reasonable for US practice. If only minimum average roll value tensile strength data are available, then a value of 0.95 is recommended for US practice. For Canadian practice, the corresponding values for typical level of understanding are 0.90 and 0.85, respectively.

Ultimate capacity of large-span soil-steel structures

The ultimate limit states provided by current design codes and standards were based on full-scale field and laboratory tests performed on soil-steel structures (SSS) of spans less than 10.0 m. Recently, the spans of SSS have increased up to 32.4 m with the tendency to exceed this record. The ultimate capacity of SSS utilizing the deepest corrugation profile, i.e., 237 mm depth and 500 mm pitch, has not been yet investigated under earth and truck loading. The current study evaluates the ultimate capacity of the world’s largest-span SSS with 32.4 m span and 9.57 m rise, using three-dimensional (3D) nonlinear finite element simulation. The investigation covered both the maximum backfill height and ultimate truck loading conditions. The 3D finite element modelling technique under ultimate loading was validated by full-scale test measurements of 10.0 m span soil-steel structure subjected to tandem axle loading. The critical straining actions obtained from the steel structure at ultimate condition was used to evaluate the ultimate limit states provided by the Canadian Highway Bridge Design Code (CHBDC, 2019) and AASHTO (AASHTO LRFD, 2019). The results revealed that the ultimate capacity of the SSS was reached without conforming to all ultimate bounds provided by the current design codes. Finally, a limit state function was proposed to account for the structure instability that may occur to the steel structure under ultimate loading condition. The proposed function successfully predicted failure in the steel structure under all cases considered in the current analysis before failure occurred in the numerical results.

Comparative analysis of international codes of practice for pile foundation design considering negative skin friction effect

Negative skin friction (NSF) effect on pile foundation design attracts the attention of geotechnical engineers and requires comprehensive research. However, the ways of consideration of NSF for the pile foundation design vary with different design codes. This study aims to compare design code requirements adhering to Construction Codes and Regulations (i.e., SNiP), Eurocode 7 (EC7), Canadian Highway Bridge Design Code (CHBDC), and AASHTO for the pile foundation design subjected to NSF and provide insights for the understanding effect of NSF on the behavior of pile foundation. The overall objective is achieved by designing three cases of a driven pile for given design conditions in Astana city. Then, a sensitivity analysis was performed to estimate the effects of the dimensions of the pile foundation and the shear strength of soils on the bearing resistance. The comparative analysis shows that pile foundation design adhering to CHBDC and AASHTO results in a more conservative strategy than SNiP and EC7 when considering Kazakhstani soil engineering conditions.

Calibration of resistance factors for gravity retaining walls

ABSTRACT Geotechnical design codes have been migrating from the traditional allowable stress design towards load and resistance factor design (LRFD). In this paper, calibration of the geotechnical resistance factors for sliding and overturning limit states of gravity retaining walls is performed using a reliability-based method. For each limit state, the LRFD approach is applied to design the gravity retaining wall, and its probability of failure is estimated using the Random Finite Element Method (RFEM). An example gravity retaining wall is analyzed using the described methodology, and the results suggest that for a given resistance factor the sliding failure probability is greater than the overturning failure probability, and a positive correlation between the soil effective internal frictional angle and unit weight random fields significantly reduces the failure probability. For reasonable ranges of the target maximum lifetime failure probability, the required resistance factor for the sliding limit state is close to that for the overturning limit state. In addition, the sliding resistance factor given by the Canadian Highway Bridge Design Code seems slightly unconservative, while the recommended overturning resistance factor is slightly conservative. The current analysis can be used to guide the calibration of these geotechnical resistance factors used in design codes.

Preliminary Analysis and Instrumentation of Large-Span Three-Sided Reinforced Concrete Culverts

This paper investigates the structural performance and soil–culvert interaction of large-span precast concrete three-sided culverts (TSCs). Three TSCs with flat top slabs have been instrumented with 30 pressure cells and 56 strain gauge vibrating wire sensors. The test culverts cover a range of spans from 7.3 to 13.5 m, each under a different installation condition. The instrumentation plans were established based on the results of three-dimensional finite-element analyses. This paper makes a contribution to (1) recommendations on the design of instrumentation plan and sensors selection criteria; (2) details of the instrumentation installation procedure and corresponding modifications to accommodate specific conditions of each culvert; and (3) field measurements and analysis of the data from a culvert covered with 3.2 m of backfill soil. Useful guidelines are provided for instrumenting similar structures. The field data were used to evaluate the current design practice and evaluate the Canadian Highway Bridge Design Code (CSA 2014) provision regarding earth loads on TSCs. The obtained data reveal the nonuniform distribution of the earth pressures on the top slab with an average vertical arching factor of 1.05. Also, the strain gauge measurements indicate the development of bending moment at the base of the sidewall, which was attributed to the rotation of the strip footing predicted from the developed preliminary numerical analysis.

Dynamic load testing of a modular truss bridge using military vehicles

Determination of appropriate load factors ensures bridge assessments completed using limit states design are applicable for all potential loading scenarios. Extremely limited research has been completed to determine accurate Dynamic Load Allowance (DLA) values for military vehicle loading of bridges, specifically independent values for tracked and wheeled vehicle types. An experimental testing program was used to assess the dynamic load effects caused by these vehicle categories by subjecting a bridge to loading from multiple different vehicle types at different speeds, while controlling deck surface condition. It was found that tracked vehicles generated approximately half the dynamic bridge response of wheeled vehicles. Using this knowledge, tracked vehicle DLA value recommendations relevant for this bridge are made for use in the North Atlantic Treaty Organization (NATO) Military Load Classification (MLC) system, and in the Canadian Highway Bridge Design Code (CHBDC) and American Association of State Highway and Transportation Officials (AASHTO) bridge code. Further research in this area could lead to strategic increases in tracked vehicle mobility.

Effect of mat anchorage on flexural bonding strength between concrete and sand coated GFRP bars

In the present study, the impacts of using six different configurations of handmade mat anchorages on the improvement of bonding between normal concrete and GFRP bars have been investigated. To do so, 63 beam specimens of three different concrete mixes were cast. The beams were cast in accordance with RILEM recommendations and all tests were conducted under the same condition. The results indicated that the use of anchorage system could substantially enhance the bond between concrete and GFRP bars. However, the increase of both diameter and length of the anchorage did not significantly affect the bonding between concrete and GFRP bars. In addition, test results showed that the increase of anchorage number did not enhance the bond behavior of the anchorage system. Indeed, as the concrete compressive strength increased, the developed stress in GFRP bars increased. Moreover, the results have been compared with the empirical relations proposed by international codes and guidelines. The comparison showed that the suggested empirical relations by American Concrete Institute, Canadian Standard Association, Canadian Highway Bridge Design Code and Japan Society of Civil Engineers for the development length yield quite conservative results.

Reply to the discussion by Fellenius on “Comparison of Canadian Highway Bridge Design Code and AASHTO LRFD Bridge Design Specifications regarding pile design subject to negative skin friction”

Reply to the discussion by Fellenius on “Comparison of Canadian Highway Bridge Design Code and AASHTO LRFD Bridge Design Specifications regarding pile design subject to negative skin friction”

Discussion of “Comparison of Canadian Highway Bridge Design Code and AASHTO LRFD Bridge Design Specifications regarding pile design subject to negative skin friction”

Discussion of “Comparison of Canadian Highway Bridge Design Code and AASHTO LRFD Bridge Design Specifications regarding pile design subject to negative skin friction”

Seismic reliability assessment of base-isolated bridges in Quebec

The aim of this work is to estimate the seismic reliability of a simple typical two-span lifeline base-isolated bridge designed to behave essentially elastic or as per the Canadian Highway Bridge Design Code, for seven localities in Quebec. Two limit states are considered for possible failure due to unacceptable damage: flexure at the pier-base and displacement within the seismic isolation systems (SIS). The main problem random variables considered and modeled are seismic hazard, temperature, pier base dimensions, and material mechanical properties. The Monte Carlo method was used to evaluate the probability of failure and the reliability of each limit state. Preliminary results reveal that notwithstanding the large temperature and seismic hazard variabilities between the seven sites in Quebec, the global bridge reliability indices are almost uniform, approximately 3.45 ± 0.02. Furthermore, the security factor (i.e., 1.25) on the SIS displacement capacity results in reliability indices for SIS displacement that are not levelled with the flexural reliability indices and requires further examination and consideration.

Earth pressure distribution around flexible arch pipes

The Canadian Highway Bridge Design Code (CHBDC), the American Association of State Highway and Transportation Officials (AASHTO) and the Swedish Design Manual (SDM) are regarded as fundamental manuals for the design of flexible corrugated metal pipes. However, these manuals do not consider properly several factors that may affect the soil-structure interaction, such as the backfill soil stiffness, the pipe burial depth, the effect of compaction loads, and the trench geometry, including the trench width and the slope of the side of the excavation. To examine these factors, this paper utilizes a detailed finite element model of a flexible corrugated metal arch pipe. The model was developed and validated by using a field case study in Sweden. In a comprehensive parametric study, the numerical analysis and the empirical methods are used to investigate the applicability and accuracy of these methods for estimating the interaction behaviour of flexible culverts installed in semi-shallow and shallow trenches.

Live load distribution factors for simply-supported composite steel I-girder bridges

The Canadian Highway Bridge Design Code (CHBDC) provides formulas for determining the live load distribution factors for composite slab-on-girder bridges. These formulas were developed by neglecting the contribution of secondary elements such as lateral bracing in bridges, leading to conservative design in some cases and unsafe design in others. This paper presents a practical-design-oriented parametric study, using three-dimensional (3D) finite-element modeling, to investigate the live load distribution factors of composite braces steel I-girder bridges under CHBDC truck loading conditions at ultimate, serviceability and fatigue limit states. The key parameters considered in this study included girder stiffness and spacing, span length, number of girders, and number of design lanes. The comparison of results suggested that the CHBDC equations underestimate the girder moments for the 15 m spans and overestimates the response for greater spans. On the other hand, CHBDC generally overestimates the shear distribution factors, with significant difference observed at fatigue limit state. Based on the database generated from this study, a set of empirical expressions were developed for the moment and shear distribution factors for rational prediction of the girder design moment and shear force. A design example is presented to illustrate the use of the developed equations.