Designing Timber Bridge Superstructures: A Comparison of US and Canadian Bridge Codes (original) (raw)
Comparative Analysis of Design Codes for Timber Bridges in Canada, the United States, and Europe
Transportation Research Record: Journal of the Transportation Research Board, 2010
The United States recently completed its transition from the allowable stress design code to the load and resistance factor design (LRFD) reliability-based code for the design of most highway bridges. For an international perspective on the LRFD-based bridge codes, a comparative analysis is presented: a study addressed national codes of the United States, Canada, and Europe. The study focused on codes related to timber bridges and involved the following parameters: organization format, superstructure types, loads, materials, design for bending, design for shear, deflection criteria, and durability requirements. The investigation found many similarities and some distinctive differences between the three bridge codes. Although the United States and Canada have different design load configurations, these result in similar bending moments and shear effects over a typical span range. However, the design load configuration in the European code produces bending moment and shear effects tha...
Designing Timber Highway Bridge Superstructures Using AASHTO-LRFD Specifications
New Horizons and Better Practices, 2007
The allowable-stress design methodology that has been used for decades to design timber bridge superstructures is being replaced in the near future. Beginning in October 2007, bridge designers will be required by the Federal Highway Administration (FHWA) to utilize the Load and Resistance Factor Design (LRFD) design specifications published by the American Association of State Transportation and Highway Officials (AASHTO). Until recently, significant discrepancies existed between the two design methodologies as they pertain to the design of timber bridges. However, several modifications and improvements to the LRFD bridge design specifications were recently incorporated into the latest edition of the LRFD bridge design standards in an effort to mimic allowable-stress design techniques using current timber design standards. Timber bridge supstructures designed using the latest LRFD design requirements will still not be identical to those designed with allowable-stress design procedures, primarily due to new requirements for higher design vehicle live-loads and modified live-load distribution equations within AASHTO-LRFD design specifications. In addition, timber bridges designed using allowable-stress design methods prior to 2007 will be not be required to use AASHTO-LRFD methods for load rating purposes.
New Canadian Highway,Bridge Design Code design provisions for fibre-reinforced structures1
2000
This paper presents a synthesis of the design provisions of the second edition of the Canadian Highway Bridge Design Code (CHBDC) for fibre-reinforced structures. New design provisions for applications not covered by the first edition of the CHBDC and the rationale for those that remain unchanged from the first edition are given. Among the new design provisions are those for
New Canadian Highway Bridge Design Code design provisions for fibre-reinforced structures
Canadian Journal of Civil Engineering, 2007
This paper presents a synthesis of the design provisions of the second edition of the Canadian Highway Bridge Design Code (CHBDC) for fibre-reinforced structures. New design provisions for applications not covered by the first edition of the CHBDC and the rationale for those that remain unchanged from the first edition are given. Among the new design provisions are those for glass-fibre-reinforced polymer as both primary reinforcement and tendons in concrete; and for the rehabilitation of concrete and timber structures with externally bonded fibre-reinforcedpolymer (FRP) systems or near-surface-mounted reinforcement. The provisions for fibre-reinforced concrete deck slabs in the first edition have been reorganized in the second edition to explicitly include deck slabs of both cast-in-place and precast construction and are now referred to as externally restrained deck slabs, whereas deck slabs containing internal FRP reinforcement are referred to as internally restrained deck slabs. Resistance factors in the second edition have been recast from those in the first edition and depend on the condition of use, with a further distinction made between factory-and field-produced FRP. In the second edition, the deformability requirements for FRP-reinforced and FRP-prestressed concrete beams and slabs of the first edition have been split into three subclauses covering the design for deformability, minimum flexural resistance, and crack-control reinforcement. The effect of sustained loads on the strength of FRPs is accounted for in the second edition by limits on stresses in FRP at the serviceability limit state.
Ultimate Strength of Timber-Deck Bridges
Transportation Research Record, 1986
Contained in this paper is a discussion on the procedures for evaluating the ultimate strength of timber deck bridges. Three structural systems are considered: sawed timber stringers, nailed laminated decks, and prestressed laminated decks. The load and resistance are treated as random variables. Their parameters are determined on the basis of material tests, load surveys, and analysis. The bridge performance is measured in terms of the reliability index. Various safety analysis methods are discussed. The procedures used in calculations were selected on the basis of accuracy, requirements for input data, and simplicity of use. System reliability models were used to include load sharing between deck components. Reliability indices were calculated for three structures. It has been observed that the degree of load sharing determines the safety level. Reliability is highest for the prestressed laminates. Sawed stringers can be considered as a series system in the system-reliability sens...
Reliability-based geotechnical design in 2014 Canadian Highway Bridge Design Code
Canadian Geotechnical Journal, 2016
Canada has two national civil codes of practice that include geotechnical design provisions: the National Building Code of Canada and the Canadian Highway Bridge Design Code. For structural designs, both of these codes have been employing a load and resistance factor format embedded within a limit states design framework since the mid-1970s. Unfortunately, limit states design in geotechnical engineering has been lagging well behind that in structural engineering for the simple fact that the ground is by far the most variable (and hence uncertain) of engineering materials. Although the first implementation of a geotechnical limit states design code appeared in Denmark in 1956, it was not until 1979 that the concept began to appear in Canadian design codes, i.e., in the Ontario Highway Bridge Design Code, which later became the Canadian Highway Bridge Design Code (CHBDC). The geotechnical design provisions in the CHBDC have evolved significantly since their inception in 1979. This pap...
Canadian Journal of Civil Engineering, 2014
Recent research efforts have focused on the development of performance based seismic design methodologies for structures. However, the seismic design rules prescribed in the current Canadian Highway Bridge Design Code (CHBDC) is based largely on force based design principles. Although a set of performance requirements (performance objectives) for different return period earthquake events have been specified, there is no explicit requirement in the CHBDC to check the attainment of such performance objectives for the designed bridges. Also, no engineering parameters have been assigned to the specified performance objectives. This paper correlates seismic performance objectives (both qualitative and quantitative) with engineering parameters, based on the data collected from published experimental investigations and field investigation reports of recent earthquakes. A simple method has been developed and validated with experimental results for assessing the performance of bridges designed according to CHBDC. It has been found that the design rules prescribed in CHBDC do not guarantee that specified multiple seismic performance objectives can be achieved. An implicit seismic design rule in the form of performance response modification factor has been outlined for the performance based seismic design of bridges.
Romanian Journal of Transport Infrastructure, 2015
The norms and standards for design of timber bridges, as well as other structures built from this material, were obsolete, design standards that were used dated from 1978 to 1980. The introduction of European Standards has created a new legislative framework in the field of designing and building timber bridges. Currently the design of such constructions use Norm NP 005-2003 and SR EN 1995-1-1: 2004 Eurocode 5: Design of timber structures. Part 1-1: General. Common rules and rules for buildings, SR EN 1995-2: 2005 Eurocode 5: Design of timber structures. Part 2: Bridges, along with their national annexes. The aim of this paper is to analyze the design of the beams for timber bridges in parallel, using on one hand Norm NP 005 - 2003, and on the other hand provisions of European standards. The design requirements for both norms as well as the results of a case study for a structural element of a timber bridge will be presented.
Erratum: New Canadian Highway Bridge Design Code design provisions for fibre-reinforced structures
Canadian Journal of Civil Engineering, 2007
This paper presents a synthesis of the design provisions of the second edition of the Canadian Highway Bridge Design Code (CHBDC) for fibre-reinforced structures. New design provisions for applications not covered by the first edition of the CHBDC and the rationale for those that remain unchanged from the first edition are given. Among the new design provisions are those for glass-fibre-reinforced polymer as both primary reinforcement and tendons in concrete; and for the rehabilitation of concrete and timber structures with externally bonded fibre-reinforcedpolymer (FRP) systems or near-surface-mounted reinforcement. The provisions for fibre-reinforced concrete deck slabs in the first edition have been reorganized in the second edition to explicitly include deck slabs of both cast-in-place and precast construction and are now referred to as externally restrained deck slabs, whereas deck slabs containing internal FRP reinforcement are referred to as internally restrained deck slabs. Resistance factors in the second edition have been recast from those in the first edition and depend on the condition of use, with a further distinction made between factory-and field-produced FRP. In the second edition, the deformability requirements for FRP-reinforced and FRP-prestressed concrete beams and slabs of the first edition have been split into three subclauses covering the design for deformability, minimum flexural resistance, and crack-control reinforcement. The effect of sustained loads on the strength of FRPs is accounted for in the second edition by limits on stresses in FRP at the serviceability limit state.
Standard Designs for Hardwood Glued-Laminated Highway Bridges
Standard plans and specifications for hardwood glued laminated highway bridges have been developed and published. The plans are based on recent research to identify laminating processes, resin systems, structural properties of efficient beam cross sections, and preservative treatment processes. The results of these efforts are summarized. The standard plans are based upon nationally recognized allowable strength design methodologies and are for HS-25 or IML-80 loads. The standard plans, which are for northern red oak, red maple, and yellow poplar bridges, include details for design and construction of highway bridge superstructures and substructures The standard plans and specifications are being revised. The status of efforts to incorporate design efficiencies suggested by ongoing research and to convert the standard plans to a load resistance factor design basis are also presented.
Load and Resistance Factor Calibration For Wood Bridges
Journal of Bridge Engineering, 2005
The paper presents the calibration procedure and background data for the development of design code provisions for wood bridges. The structural types considered include sawn lumber stringers, glued-laminated girders, and various wood deck types. Load and resistance parameters are treated as random variables, and therefore, the structural performance is measured in terms of the reliability index. The statistical parameters of dead load and live (traffic) load, are based on the results of previous studies. Material resistance is taken from the available test data, which includes consideration of the post-elastic response. The resistance of components and structural systems is based on the available experimental data and finite element analysis results. Statistical parameters of resistance are computed for deck and girder subsystems as well as individual components. The reliability analysis was performed for wood bridges designed according to the AASHTO Standard Specifications and a significant variation in reliability indices was observed.
2020
This paper presents some of the innovations that are included within the new Bridge Design Standard for Steel and Composite Construction AS/NZS 5100.6, which will be the first harmonized standard between Australia and New Zealand for the design of bridges. As Chairs of the Committees responsible for AS/NZS 5100.6 and AS/NZS 2327, the authors of this paper present the challenges faced from the introduction concrete compressive strengths up to 100 MPa and quenched and tempered steels with a yield strength up to 690 MPa. Perhaps one of the most innovative aspects of this standard is the introduction of an appendix that provides design rules for steel products that are not manufactured to Australia and New Zealand standards. This appendix is underpinned by rigorous structural reliability analyses undertaken by Australian and New Zealand researchers, which included the present authors of this paper.
Bridge Structures, 2013
This paper tells the story of how a Bridge Construction Engineer and a Civil/Structural Engineering Professor learned from each other through the observation of bridge erection projects, and concurrent participation with industry organizations during development of the AASHTO LRFD Bridge Design Specifications (3rd-5th editions). Illustrations from several highway bridge projects in four states are used to explain a successful transitional journey from Service Load/Allowable Stress (SLD/ASD) to Load and Resistance Factor Design (LRFD) in steel bridge superstructure erection. Stability analysis and construction practice included the following: evaluation of controlling strength and serviceability criteria, steel bridge erection load (␥ i) factors, reconciliation of state-assigned construction wind loadings to the AASHTO Design Guide for Bridge Temporary Works and ASCE 7 (Minimum Loads for Buildings and other Structures), computation of lateral flange bending stress (f l) utilized on straight, curved, haunched multi-girder bridges, as well as cross-box girder (straddle bent) piers during erection; member resistance during construction under local flange/web and lateral torsional buckling of single girders, girder slenderness (λ i), L/b ratio rules of thumb and controlling bracing lengths during critical stages in the construction sequence, bearing point development, bridge system slenderness and the securing of partially constructed bridges (during storm events). Bridge erectors often exercise individual preferences in applying construction means and methods toward achieving specified geometry within alignment tolerances, so the interface between LRFD designed bridge members, ASD rigging components and ASD/Load Factor Design (LFD) temporary foundation components is also discussed.
Assessing the Load Carrying Capacity of Timber Bridges Using Dynamic Methods
A reliable determination of the structural condition of timber bridges presently requires costly load testing. A new testing method is described which has recently been used to undertake field-testing of more than 20 timber bridges across NSW. The bridge assessment procedure involves the attachment of accelerometers underneath the bridge girders. The vibration response and natural frequency of the bridge superstructure is measured when a "calibrated sledgehammer" is used to hit the unloaded deck, and then again with a relatively small mass applied at mid-span. The difference in response allows load carrying capacity of the bridge to then be calculated.
Design Criteria for Portable Timber Bridge Systems: Static versus Dynamic Loads
1999
Design criteria are needed specifically for portable bridges to insure that they are safe and cost effective. This paper discusses different portable bridge categories and their general design criteria. Specific emphasis is given to quantifying the effects of dynamic live loads on portable bridge design. Results from static and dynamic load tests of two portable timber bridges showed that dynamic loads can be significantly greater than static loads. Under smooth bridge entrance conditions, the mean dynamic bridge deflections were 1.13 times greater than static bridge deflections. Under rough bridge entrance conditions, mean dynamic bridge deflections were 1.44 times greater than static bridge deflections.
Seismic performance-based design of bridges with quantitative local performance criteria
2010
Performance based design of bridges for earthquake resistance is still not explicitly used in design. However, most codes specify a level of performance for bridges under various earthquake inputs. In principle, design rules suggested in the code should meet stipulated performance criteria. However, it has been highlighted in the past that design rules are not directly related with stipulated performance criteria. After the presentation of performance criteria and their relation with post-earthquake functional requirements, the article examines the case of the Canadian Bridge Design Code (CAN/CSA-S6-06). Performance of bridges designed with this code is predicted and compared to expected levels. It is shown that compliance with design rule does not guarantee an adequate performance. This article attempts to correlate qualitative performance criteria with post-earthquake functional requirements, and critically examines code specified design rules and their cost effectiveness. Some im...
A Comparison of Canadian, Mexican, and United States Steel Design Standards
The steel design standards for buildings of the three countries of Canada, Mexico, and the United States are compared in this paper. The special emphasis is on the criteria for the stability design of plates, columns, beams, and beam-columns. It is shown that while the theoretical and experimental basis for all three codes is common, the final form of the criteria is not the same: different formulas are used for columns, beams, and beam-columns. Other differences arise from the fact that all three countries use different units. However, the designed proportions of the structural elements and structures are often not significantly different in the final execution. Each code has advantages and disadvantages in its details of design.