Proposal for modification of load and resistance factors in the AASHTO LRFD bridge design code

2010 ◽  
pp. 657-657
Author(s):  
A Nowak ◽  
P Paczkowski
Keyword(s):  
Design Code ◽  
Bridge Design ◽  
Resistance Factors ◽  
Load And Resistance Factors ◽  
Aashto Lrfd

Calibration of the Ontario Bridge Design Code 1983 edition

1984 ◽  
Vol 11 (4) ◽  
pp. 760-770 ◽  
Author(s):  
Hid N. Grouni ◽  
Andrzej S. Nowak
Keyword(s):  
Reliability Index ◽  
Calibration Procedure ◽  
Design Code ◽  
Bridge Design ◽  
Limit States ◽  
Safety Level ◽  
Acceptance Criterion ◽  
Resistance Factors ◽  
Concrete Girders ◽  
Load And Resistance Factors

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.

Calibration of the Ontario Highway Bridge Design Code 1991 edition

1994 ◽  
Vol 21 (1) ◽  
pp. 25-35 ◽  
Author(s):  
Andrzej S. Nowak ◽  
Hid N. Grouni
Keyword(s):  
Reinforced Concrete ◽  
Reliability Analysis ◽  
Prestressed Concrete ◽  
Highway Bridge ◽  
Live Load ◽  
Design Code ◽  
Reliability Indices ◽  
Resistance Factors ◽  
Load And Resistance Factors ◽  
Selection Of

The paper describes the calculation of load and resistance factors for the Ontario Highway Bridge Design Code (OHBDC) 1991 edition. The work involved the development of load and resistance models, the selection of the reliability analysis method, and the calculation of the reliability indices. The statistical models for load and resistance are reviewed. The considered load components include dead load, live load, and dynamic load. Resistance models are developed for girder bridges (steel, reinforced concrete, and prestressed concrete). A reliability analysis is performed for selected representative structures. Reliability indices are calculated using an iterative procedure. The calculations are performed for bridge girders designed using OHBDC 1983 edition. The resulting reliability indices are between 3 and 4 for steel girders and reinforced concrete T-beams, and between 3.5 and 5 for prestressed concrete girders. Lower values are observed for shorter spans (up to 30–40 m). The acceptance criterion in the selection of load and resistance factors is closeness to the target reliability level. The analysis confirmed the need to increase the design live load for shorter spans. Partial resistance factors are considered for steel and concrete. The criteria for the evaluation of existing bridges are based on the reliability analysis and economic considerations. Key words: bridge code, calibration, load factor, resistance factor, reliability index.

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

2020 ◽  
Vol 57 (7) ◽  
pp. 1092-1098
Author(s):  
James R. Bartz ◽  
James A. Blatz
Keyword(s):  
Skin Friction ◽  
Drag Force ◽  
Limit State ◽  
Highway Bridge ◽  
Ultimate Limit State ◽  
Design Code ◽  
Bridge Design ◽  
Negative Skin Friction ◽  
Design Specifications ◽  
Aashto Lrfd

Negative skin friction acting on piles has long been included in the design of bridge foundations subject to ground settlement. However, currently there are inconsistencies in how negative skin friction and drag force are incorporated into the calculation of the geotechnical ultimate limit state (ULS), partly due to differences in the design codes. The latest editions of the Canadian Highway Bridge Design Code and AASHTO LRFD Bridge Design Specifications are compared with the analysis of a hypothetical steel H-pile, driven through a settling clay layer into a dense, nonsettling layer. The results show that foundation designs can be significantly more conservative and costly when adhering to the AASHTO code because this code includes the drag force in the geotechnical ULS. It is concluded that adhering to the CHBDC can result in a reduced foundation system by considering the actual force distribution in the pile.

Calibration of design code for buried structures

2001 ◽  
Vol 28 (4) ◽  
pp. 574-582 ◽  
Author(s):  
Andrzej S Nowak ◽  
Chan-Hee Park ◽  
Peter Ojala
Keyword(s):  
Reinforced Concrete ◽  
Reliability Index ◽  
Water Pressure ◽  
Earth Pressure ◽  
Highway Bridges ◽  
Design Code ◽  
Buried Structures ◽  
Reliability Indices ◽  
Resistance Factors ◽  
Load And Resistance Factors

The reliability-based calibration procedures were applied to develop load and resistance factors for the Ontario Highway Bridge Design Code (1979, 1983, and 1991) and recently the Canadian Highway Bridges Design Code (2000). However, the load components for buried structures were not considered. The development of a statistical model for earth pressure requires a special approach. Therefore, this paper deals with the reliability-based calibration of the design code for buried (cut-and-cover) structures. A typical running structure consists of reinforced concrete walls forming a rectangular box section, while an underground station may have a one- to six-cell box. The major load components include earth pressure, water pressure and weight of the concrete. Other load components such as live load are relatively small. Statistical parameters are derived for representative structures and structural systems. The correlation between load components is estimated based on the available field data. Structural performance is measured in terms of the reliability index. Reliability indices are calculated for a representative spectrum of running structures and stations. In general, the reliability indices for existing buried structures are higher than those for bridges or buildings. The target reliability index has been selected on the basis of calculated reliability indices, comparison with other structures, and cost analysis (consequences of failure). The optimum load and resistance factors are calculated and recommended for the design code to achieve a uniform safety level.Key words: buried structure, code calibration, load models, reinforced concrete, reliability analysis, resistance models.

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