Influence of Material Toughness on Fracture Reliability in Steel Bridges

2021 ◽  
pp. 036119812110566
Author(s):  
Frank A. Artmont ◽  
Thomas P. Murphy
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Structural Reliability ◽  
Limit State ◽  
Base Material ◽  
Steel Bridges ◽  
Steel Bridge ◽  
Limit States ◽  
Control Approach ◽  
Probabilistic Distribution

The fracture limit state of the AASHTO LRFD Bridge Design Specifications is addressed by requiring minimum impact toughness values for base material and mitigating potential fracture initiators through proper structural detailing. This fracture control approach has been successful in minimizing the number of fractures in steel bridges designed since its inception; however, it is not a calibrated limit state and the structural reliability against sudden brittle fracture has not been previously established. Accordingly, the objective of this study was to quantify the relationship between material toughness and fracture reliability in steel bridge members, considering the probabilistic distribution of fracture toughness and applied stress for a variety of structural steels and assumed crack sizes. The master curve approach is used to account for the probabilistic distribution of fracture toughness, and reliabilities are determined using Monte Carlo simulation and the Hasofer-Lind approach. The results indicate that the fracture reliability for modern bridge steels is consistent with the reliability of AASHTO strength limit states, and that certain steels currently available on the market can provide enough reliability against fracture to essentially eliminate brittle fracture as a limit state of concern. This finding holds the potential for a new way of approaching the design of fracture-critical members.

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

Limit State of Torsion of Ship Hulls with Large Hatch Openings

2001 ◽  
Vol 45 (02) ◽  
pp. 95-102
Author(s):  
Yuren Hu ◽  
Bozhen Chen
Keyword(s):  
Cross Section ◽  
Structural Reliability ◽  
Limit State ◽  
Safety Margin ◽  
Plastic Shear ◽  
Torsional Moment ◽  
Limit States ◽  
Ship Hulls ◽  
Design Values ◽  
Bound Theorem

The limit state of torsion of ship hulls with large hatch openings is studied. A method to determine the distribution of the plastic shear flow on the hull cross section in the limit state by using the lower-bound theorem is presented together with the corresponding linear programming problem. The limit torsional moment of the hull cross section is obtained based on the distribution of the shear stress in the limit state. Three example limit states for typical containerships of different sizes with large hatch openings are calculated. The calculated limit torsional moments are compared with the design values of wave torque calculated by using the equations given by main classification societies in their rules. A rough estimate of the safety margin is obtained. The results show that for large containerships, it is necessary to pay attention to the safety with respect to torsion. The present method can serve as an effective tool in structural reliability analysis of ships with large hatch openings when the failure mode of torsion is taken into account.

scholarly journals Reliability Estimation for Highway Bridges

2020 ◽  
Author(s):  
Nafiseh Kiani
Keyword(s):  
Reliability Index ◽  
Structural Reliability ◽  
Limit State ◽  
Highway Bridges ◽  
Reliability Estimation ◽  
State Function ◽  
Limit States ◽  
Resistance Factors ◽  
Load And Resistance Factors ◽  
Reliability Methods

Structural reliability analysis is necessary to predict the uncertainties which may endanger the safety of structures during their lifetime. Structural uncertainties are associated with design, construction and operation stages. In design of structures, different limit states or failure functions are suggested to be considered by design specifications. Load and resistance factors are two essential parameters which have significant impact on evaluating the uncertainties. These load and resistance factors are commonly determined using structural reliability methods. The purpose of this study is to determine the reliability index for a typical highway bridge by considering the maximum moment generated by vehicle live loads on the bridge as a random variable. The limit state function was formulated and reliability index was determined using the First Order Reliability Methods (FORM) method.

scholarly journals Reliability of Buried Pipes in Heterogeneous Soil Subjected to Seismic Loads

2021 ◽  
Vol 11 (1) ◽  
pp. 6708-6713
Author(s):  
H. Benzeguir ◽  
S. M. Elachachi ◽  
D. Nedjar ◽  
M. Bensafi
Keyword(s):  
Structural Reliability ◽  
Limit State ◽  
Bending Moment ◽  
Longitudinal Direction ◽  
Point Of View ◽  
Ultimate Limit State ◽  
Buried Pipe ◽  
Limit States ◽  
Ground Acceleration ◽  
Buried Pipes

Dysfunctions and failures of buried pipe networks, like sewer networks, are studied in this paper from the point of view of structural reliability and heterogeneity of geotechnical conditions in the longitudinal direction. Combined soil spatial variability and Peak Ground Acceleration (PGA) induce stresses and displacements. A model has been developed within the frame of geostatistics and a mechanical description of the soil–structure interaction of a set of buried pipes with connections resting on the soil by a two-parameter model (Pasternak model). Structural reliability analysis is performed considering two limit states: Serviceability Limit State (SLS), related to large "counter slope" in a given pipe, and Ultimate Limit State (ULS), corresponding to bending moment.

The Surface Treatment Influence on the Occurrence of the Critical State Relating to the Needle as the Operating Tool

2015 ◽  
Vol 818 ◽  
pp. 7-10
Author(s):  
Františka Pešlová ◽  
Adriána Pavúčková ◽  
Michaela Ďurovcová ◽  
Luba Hajdúchová ◽  
Mariana Janeková ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Brittle Fracture ◽  
Chemical Elements ◽  
Research Work ◽  
Base Material ◽  
Economic Losses ◽  
Limit States ◽  
Rapid Degradation ◽  
Experimental Part ◽  
Selection Of

The research work deals with the evaluation of limit states of machine needles failure where significant operational wear was anticipated. It focuses on the description of limit states, their causes and subsequent brittle fracture as a result of degradation. The experiment dealt with an evaluation of prepared microstructures followed by the fractography observation. Due to the fact that chemical composition of the material was not originally determined distribution of the chemical elements by linear and area method was performed within the experimental part. The work confirmed incorrect selection of the base material that although coated was typical by rapid degradation and failure which resulted in economic losses.

scholarly journals Structural Reliability Analysis of Ship Hulls Accounting for Collision or Grounding Damage

2020 ◽  
Author(s):  
Branka Bužančić Primorac ◽  
Joško Parunov ◽  
C. Guedes Soares
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Limit State ◽  
Random Variables ◽  
Bending Moment ◽  
State Equation ◽  
Limit States ◽  
Moment Capacity ◽  
Ship Hulls ◽  
Structural Reliability Analysis

AbstractClassical structural reliability analysis of intact ship hulls is extended to the case of ships with collision or grounding damages. Still water load distribution and residual bending moment capacity are included as random variables in the limit state equation. The probability density functions of these random variables are defined based on random damage parameters given by the Marine Environment Protection Committee of the International Maritime Organization, while the proposed reliability formulation is consistent with international recommendations and thus may be valuable in the development of rules for accidental limit states. The methodology is applied on an example of an Aframax oil tanker. The proposed approach captures in a rational way complex interaction of different pertinent variables influencing safety of damaged ship structure.

scholarly journals Reliability-Based Optimal Inspection for Fracture-Critical Steel Bridge Members

2003 ◽  
Vol 1845 (1) ◽  
pp. 39-47 ◽  
Author(s):  
Hsin-Yang Chung ◽  
Lance Manuel ◽  
Karl H. Frank
Keyword(s):  
Structural Reliability ◽  
Steel Bridges ◽  
Steel Bridge ◽  
Event Tree ◽  
Fatigue Reliability ◽  
Safety Level ◽  
Rule Approach ◽  
Reliability Control ◽  
Scheduling Plan ◽  
Inspection Scheduling

To prevent fatigue failure of members in steel bridges, one usually needs to perform frequent periodic bridge inspections and employ detailed inspection methods. This is especially true for fracture-critical members or details. Carrying out these inspections puts a large burden on a transportation agency’s bridge maintenance budget. A systematic reliabilitybased method for inspection scheduling is proposed to yield the most economical inspection strategy for steel bridges that, at the same time, guarantees an acceptable safety level through the planned service life. A methodology is presented for evaluating the fatigue reliability of a specified detail classified according to AASHTO fatigue categories. A Miner’s rule approach is used to evaluate the fatigue reliability. The inspection scheduling problem is modeled as an optimization problem with a welldefined objective function that includes the total expected cost of inspection, repair, and failure formulated on the basis of an event tree framework and appropriate constraints in inspection intervals and minimum (target) structural reliability. An optimal inspection-scheduling plan can thus be obtained for any specified fatigue details (fracture-critical details) in steel bridges. Examples presented demonstrate the advantage of the reliabilitybased optimal inspection scheduling in cost saving and structural reliability control over alternative periodic inspection plans. Two numerical examples for a steel bridge in Texas are presented to demonstrate the proposed reliability-based optimal inspection scheduling.

REQUIRED FRACTURE TOUGHNESS OF STEEL TO PREVENT BRITTLE FRACTURE DURING EARTHQUAKES IN STEEL BRIDGE PIERS

2003 ◽  
pp. 93-102 ◽  
Author(s):  
Eiichi SASAKI ◽  
Taiji ARAKAWA ◽  
Chitoshi MIKI ◽  
Atsushi ICHIKAWA
Keyword(s):  
Fracture Toughness ◽  
Brittle Fracture ◽  
Bridge Piers ◽  
Steel Bridge

Probabilistic Risk Analysis of a LNG Carrier Loading Pipeline

2012 ◽  
Author(s):  
Gilberto Francisco Martha de Souza ◽  
Erick Miguel Portugal Hidalgo ◽  
Dennis Wilfredo Roldán Silva ◽  
Marcelo Ramos Martins
Keyword(s):  
Brittle Fracture ◽  
Structural Reliability ◽  
Limit State ◽  
Simulation Method ◽  
Crack Size ◽  
Probability Of Failure ◽  
State Function ◽  
Loading And Unloading ◽  
Material Fracture ◽  
Accident Scenarios

The loading and unloading operation of a LNG carrier is dependent on the perfect performance of the loading/unloading equipment, such as valves, tanks and pipes. The rupture of a ship pipeline (part of the manifold or other secondary pipes) used for LNG loading or unloading can cause the leakage of the fluid causing not only the complete stop of the loading or unloading operation but also exposing the ship and other terminal facilities to a risk associated with LNG leakage. The paper applies structural reliability concepts to evaluate the probability of failure of a pipeline due to the presence of a crack in the pipe wall. The analysis considers the probability of occurrence of brittle fracture associated with a through thickness crack propagation. The limit state function as for brittle fracture analysis is presented and as for reliability analysis three random variables are considered: material fracture toughness, crack size and pipe thickness. The Monte Carlo simulation method is used to calculate the probability of failure. Based on those results, the paper proposes the use of the cause-consequence diagram to evaluate the accident scenarios associated with the pipe rupture, which failure probability was previously calculated. The events that appear in the diagram are associated with alarm and control systems that are used as monitoring system for loading and unloading operations. Those failure probabilities can be calculated using reliability database. The consequences of each scenario can be defined based on literature review. The main analysis result will be the risk profile associated with a pipe brittle fracture. The method is used for the analysis of a LNG carrier operating in a Brazilian harbor.

scholarly journals RELIABILITY OF IMPERFECT STRUCTURES (SIMPLE NON-LINEAR MODELS)

2002 ◽  
Vol 8 (2) ◽  
pp. 83-87
Author(s):  
Eugeniusz Bielewicz ◽  
Jarosłlaw Goórski
Keyword(s):  
Monte Carlo ◽  
Applied Load ◽  
Structural Reliability ◽  
Linear Models ◽  
Limit State ◽  
Random Variables ◽  
Limit States ◽  
Non Linear ◽  
Non Linear Operator ◽  
Imperfect Structures

Limit states of simple, spatial, non-linear models of structures with two degrees of freedom are considered. Geometric and material imperfections are taken in the form of random variables. The simulation of these random variables and the Monte Carlo technique are employed. Two possibilities in the assessment of the reliability of structures are presented: 1) Simulation of random imperfections and the Monte Carlo operation give as a result a histogram of the limit loads. Assuming that the probability distribution of the applied load is known, the structural reliability can be obtained according to the exact formula. 2) In order to obtain the histogram of the limit state of the structure, the values of the applied load are also simulated at every Monte Carlo step. The factor which amplifies the load responsible for the structure failure is derived. The set of all these factors leads to the model reliability calculation. The estimation of the limit state of an imperfect structures can be described as a transformation of random input data into random output results. In the transformation operation the non-linear operator of the model under considerations is of the greatest significance. The effects of stable and unstable operators are discussed.

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