Reliability-based design of wood structures: background to CSA-086.1-M89

1993 ◽  
Vol 20 (3) ◽  
pp. 349-357 ◽  
Author(s):  
Ricardo O. Foschi ◽  
Bryan Folz ◽  
Felix Yao
Keyword(s):  
Calibration Procedure ◽  
Code Design ◽  
Limit States ◽  
Wood Structures ◽  
Design Procedures ◽  
Reliability Based Design ◽  
Working Stress ◽  
Adjustment Factors ◽  
Duration Of Load ◽  
The Impact

The limit states design version of the 1989 Canadian code for engineering design in wood (CSA-086.1-M89) is, for the most part, reliability-based. This paper discusses the methodology employed in the calibration procedure and the reliability levels adopted. Particular emphasis is given to the results obtained for duration of load and system (load sharing) strength adjustment factors, to serviceability limit states, and to the design of columns. Final comments address the impact of the new code in comparison to the traditional working stress design procedures. Key words: code, design, reliability, timber construction, wood.

Reliability-based design of mechanically connected built-up wood columns

1991 ◽  
Vol 18 (2) ◽  
pp. 171-181 ◽  
Author(s):  
S. K. Malhotra ◽  
A. P. Sukumar
Keyword(s):  
Data Base ◽  
Reliability Analysis ◽  
Rational Model ◽  
Limit States ◽  
Wood Structures ◽  
Factors Affecting ◽  
Analysis And Design ◽  
Additional Information ◽  
Reliability Based Design ◽  
First Order Second Moment

Built-up wood structural components and systems have been in use in the building industry for decades. Though easy to construct, they are rather complex to analyze because of numerous factors affecting their strength and behaviour. This paper explains the development of a reliability-based design formulation in limit states for built-up columns, using a rational mathematical model for the analysis and design. Also, a brief discussion is given on a set of simplified design rules for layered columns which have been incorporated into the Canadian Standards Association Standard CAN3-086.1-M89 "Code for engineering design in wood (limit states design)." The rational model as well as the simplified rules are subjected to reliability analysis.The Canadian specifications for the design of wood structures in limit states format have been available since December 1984. These specifications are essentially a soft conversion of the previous working stress design code. The 1989 edition of the code is mostly based on the principles of reliability-based design. Some portions of the code are still not fully based on reliability approach, as additional information is needed for the establishment of a reliable data base upon which the "uncertainty factors" could be redefined in a more rational and logical manner. This paper provides that type of information and the details of reliability analysis as applied to mechanically connected built-up timber columns. The reliability analyses are performed based on first-order second-moment methods, using a data base of column strengths. The data base consists of experimental as well as simulated results. Two reliability analysis programs, BUCREL (built-up column reliability analysis) and POINT (reliability analysis using design point algorithm), are developed. Design recommendations are derived in a reliability-based design format. Key words: buckling, columns, design specifications, efficiency, joints, layered columns, rational model, reliability, resistance factor, slip, spaced columns, timber, wood.

Duration of load in wood: Canadian results and implementation in reliability-based design

1993 ◽  
Vol 20 (3) ◽  
pp. 358-365 ◽  
Author(s):  
Felix Z. Yao ◽  
Ricardo O. Foschi
Keyword(s):  
Design Guidelines ◽  
Fatigue Load ◽  
Load Duration ◽  
Reliability Based Design ◽  
Theoretical Approaches ◽  
Timber Construction ◽  
Adjustment Factors ◽  
Load Effects ◽  
Accumulation Of Damage ◽  
Duration Of Load

This paper summarizes some Canadian experimental results for duration of load effects in wood, and discusses the theoretical framework utilized for their interpretation and implementation in design guidelines. The theory is based on a model for accumulation of damage, and it is used in the context of reliability assessment of a structure under load over its service life. The paper also compares results from other theoretical approaches. Finally, the background to currently recommended design adjustment factors for duration of load is discussed. Key words: fatigue, load duration, reliability, timber construction, wood.

Limit states and reliability-based design for a non-codified problem of aqueduct buoyancy

2006 ◽  
Vol 43 (8) ◽  
pp. 869-883
Author(s):  
Gil Robinson ◽  
James Graham ◽  
Ken Skaftfeld ◽  
Ron Sorokowski
Keyword(s):  
Design Methods ◽  
Model Parameters ◽  
Safety Factors ◽  
Design Code ◽  
Limit States ◽  
Reliability Based Design ◽  
Simulation Techniques ◽  
Working Stress ◽  
Engineering Problems ◽  
Partial Safety Factors

Limit states design methods and engineering judgement have been used to assess buoyancy issues for remediation of the 85 year old Shoal Lake Aqueduct in Manitoba. The study demonstrates how these methods can be applied to non-codified engineering problems. Four separate buoyancy analyses were completed using (i) partial safety factors from the Ontario Highway Bridge Design Code, (ii) project-specific partial safety factors, (iii) Monte Carlo simulation techniques, and (iv) working stress design (WSD) methods. Engineering judgement was required to develop a buoyancy model, interpret data for modeling parameters, and provide meaningful values for parameters that could not be measured. Results from the analyses show that more uniform reliability is provided when measured variability of the model parameters is accounted for. The reliability is not quantifiable when working stress design methods are used. Key words: limit states, probability, non-codified problem, aqueduct, buoyancy.

scholarly journals Comparison of reliability evaluation methods between China and Canada standards for wood structures featuring duration of load

2020 ◽  
Vol 66 (1) ◽  
Author(s):  
Qiongyao Wu ◽  
Shuang Niu ◽  
Enchun Zhu
Keyword(s):  
Reliability Analysis ◽  
Analysis Method ◽  
Safety Level ◽  
Wood Structures ◽  
Load Effect ◽  
Key Factor ◽  
Live Loads ◽  
High Level ◽  
Partial Factor ◽  
Duration Of Load

Abstract Duration of load (DOL) is a key factor in design of wood structures, which makes the reliability analysis of wood structures more complicated. The importance of DOL is widely recognized, yet the methods and models through which it is incorporated into design codes vary substantially by country/region. Few investigations of the effect of different model assumptions of DOL and other random variables on the results of reliability analysis of wood structures can be found. In this paper, comparisons are made on the reliability analysis methods that underlie the China and the Canada standards for design of wood structures. Main characteristics of these two methods, especially the way how DOL is treated are investigated. Reliability analysis was carried out with the two methods employing the same set of material properties and load parameters. The resulted relationships between reliability index β and resistance partial factor γR* (the β–γR* curves) for four load combinations are compared to study the safety level indicated by the two methods. The comparison shows that the damage accumulation model (Foschi–Yao model) in the Canada analysis method is highly dependent on the type and duration of load, resulting in more conservative design than the China analysis method in loading cases dominated by dead load, but less conservative design in cases of high level of live loads. The characteristics of the load effect term of the performance function are also found to make considerable difference in reliability levels between the two methods. This study aims to provide references for researchers and standard developers in the field of wood structures.

Anchor rod forces and maximum bending moments in sheet pile walls using the factored strength approach

1996 ◽  
Vol 33 (5) ◽  
pp. 815-821 ◽  
Author(s):  
A B Schriver ◽  
A J Valsangkar
Keyword(s):  
Water Pressure ◽  
Limit State ◽  
Bending Moment ◽  
Ultimate Limit State ◽  
Sheet Pile ◽  
Limit States ◽  
Working Stress ◽  
Geotechnical Design ◽  
Ultimate Limit State Design ◽  
Sheet Pile Wall

Recently, the limit states approach using factored strength has been recommended in geotechnical design. Some recent research has indicated that the application of limit states design using recommended load and strength factors leads to conservative designs compared with the conventional methods. In this study the influence of sheet pile wall geometry, type of water pressure distribution, and different methods of analysis on the maximum bending moment and achor rod force are presented. Recommendations are made to make the factored strength design compatible with conventional design. Key words: factored strength, working stress design, ultimate limit state design, anchored sheet pile wall, bending moment, anchor rod force.

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.

scholarly journals Development of PM<sub>2.5</sub> source impact spatial fields using a hybrid source apportionment air quality model

2015 ◽  
Vol 8 (7) ◽  
pp. 2153-2165 ◽  
Author(s):  
C. E. Ivey ◽  
H. A. Holmes ◽  
Y. T. Hu ◽  
J. A. Mulholland ◽  
A. G. Russell
Keyword(s):  
Air Quality ◽  
Source Apportionment ◽  
Large Scale ◽  
Major Ions ◽  
Current Knowledge ◽  
Direct Method ◽  
Hybrid Approach ◽  
Sensitivity Analyses ◽  
Adjustment Factors ◽  
The Impact

Abstract. An integral part of air quality management is knowledge of the impact of pollutant sources on ambient concentrations of particulate matter (PM). There is also a growing desire to directly use source impact estimates in health studies; however, source impacts cannot be directly measured. Several limitations are inherent in most source apportionment methods motivating the development of a novel hybrid approach that is used to estimate source impacts by combining the capabilities of receptor models (RMs) and chemical transport models (CTMs). The hybrid CTM–RM method calculates adjustment factors to refine the CTM-estimated impact of sources at monitoring sites using pollutant species observations and the results of CTM sensitivity analyses, though it does not directly generate spatial source impact fields. The CTM used here is the Community Multiscale Air Quality (CMAQ) model, and the RM approach is based on the chemical mass balance (CMB) model. This work presents a method that utilizes kriging to spatially interpolate source-specific impact adjustment factors to generate revised CTM source impact fields from the CTM–RM method results, and is applied for January 2004 over the continental United States. The kriging step is evaluated using data withholding and by comparing results to data from alternative networks. Data withholding also provides an estimate of method uncertainty. Directly applied (hybrid, HYB) and spatially interpolated (spatial hybrid, SH) hybrid adjustment factors at withheld observation sites had a correlation coefficient of 0.89, a linear regression slope of 0.83 ± 0.02, and an intercept of 0.14 ± 0.02. Refined source contributions reflect current knowledge of PM emissions (e.g., significant differences in biomass burning impact fields). Concentrations of 19 species and total PM2.5 mass were reconstructed for withheld observation sites using HYB and SH adjustment factors. The mean concentrations of total PM2.5 at withheld observation sites were 11.7 (± 8.3), 16.3 (± 11), 8.59 (± 4.7), and 9.2 (± 5.7) μg m−3 for the observations, CTM, HYB, and SH predictions, respectively. Correlations improved for concentrations of major ions, including nitrate (CMAQ–DDM (decoupled direct method): 0.404, SH: 0.449), ammonium (CMAQ–DDM: 0.454, SH: 0.492), and sulfate (CMAQ–DDM: 0.706, SH: 0.730). Errors in simulated concentrations of metals were reduced considerably: 295 % (CMAQ–DDM) to 139 % (SH) for vanadium; and 1340 % (CMAQ–DDM) to 326 % (SH) for manganese. Errors in simulated concentrations of some metals are expected to remain given the uncertainties in source profiles. Species concentrations were reconstructed using SH results, and the error relative to observed concentrations was greatly reduced as compared to CTM-simulated concentrations. Results demonstrate that the hybrid method along with a spatial extension can be used for large-scale, spatially resolved source apportionment studies where observational data are spatially and temporally limited.

scholarly journals Toward a Consistent Definition between Satellite and Model Clear-Sky Radiative Fluxes

2020 ◽  
Vol 33 (1) ◽  
pp. 61-75 ◽  
Author(s):  
Norman G. Loeb ◽  
Fred G. Rose ◽  
Seiji Kato ◽  
David A. Rutan ◽  
Wenying Su ◽  
...  
Keyword(s):  
Tropical Pacific ◽  
Radiative Effect ◽  
The West ◽  
Model Calculations ◽  
Radiative Fluxes ◽  
Clear Sky ◽  
Cloud Radiative Effect ◽  
Adjustment Factors ◽  
The Impact ◽  
Global Mean

AbstractA new method of determining clear-sky radiative fluxes from satellite observations for climate model evaluation is presented. The method consists of applying adjustment factors to existing satellite clear-sky broadband radiative fluxes that make the observed and simulated clear-sky flux definitions more consistent. The adjustment factors are determined from the difference between observation-based radiative transfer model calculations of monthly mean clear-sky fluxes obtained by ignoring clouds in the atmospheric column and by weighting hourly mean clear-sky fluxes with imager-based clear-area fractions. The global mean longwave (LW) adjustment factor is −2.2 W m−2 at the top of the atmosphere and 2.7 W m−2 at the surface. The LW adjustment factors are pronounced at high latitudes during winter and in regions with high upper-tropospheric humidity and cirrus cloud cover, such as over the west tropical Pacific, and the South Pacific and intertropical convergence zones. In the shortwave (SW), global mean adjustment is 0.5 W m−2 at TOA and −1.9 W m−2 at the surface. It is most pronounced over sea ice off of Antarctica and over heavy aerosol regions, such as eastern China. However, interannual variations in the regional SW and LW adjustment factors are small compared to those in cloud radiative effect. After applying the LW adjustment factors, differences in zonal mean cloud radiative effect between observations and climate models decrease markedly between 60°S and 60°N and poleward of 65°N. The largest regional improvements occur over the west tropical Pacific and Indian Oceans. In contrast, the impact of the SW adjustment factors is much smaller.

Eighteenth Canadian Geotechnical Colloquium: Limit States Design For Foundations. Part I. An overview of the foundation design process

1996 ◽  
Vol 33 (6) ◽  
pp. 956-983 ◽  
Author(s):  
Dennis E Becker
Keyword(s):  
Design Process ◽  
Theoretical Models ◽  
Mean Value ◽  
Limit States ◽  
Foundation Design ◽  
The North ◽  
Working Stress ◽  
Characteristic Value ◽  
Partial Load ◽  
Resistance Approach

This paper examines the foundation design process in terms of level of safety associated with current state-of-practice, sources of uncertainty and how they are handled, importance of engineering judgement and experience, and the role of codes of practice. Working stress, limit states, reliability-based design approcahes are described and discussed in terms of their historical development, fundamental bases and differences, advantages, and limitations. Limit states are conditions under which a structure no longer performs its intended function. Limit states design considers seperately the two classes of ultimate and serviceability limit states using partial factors of safety. The European factored strength approach and the North American factored overall resistance approach are compared and discussed. The factored resistance approach is a logical extension of working stress design and has the significant advantage that it reflects not only uncertainty in strength, but also in theoretical models, site conditions, construction tolerances, and failure mechanisms. The partial load and resistance factors are interrelated and are a function of characteristic values. A consistent, rational basis for the selection of the geotechnical characteristic value is required. The use of a conservatively assessed mean value is recommended, and an approach for its interpretation is presented. Key words: limit states design, working stress design, characteristic value, partial factors, factored resistance, load and resistance factor design.

scholarly journals Probabilistic Prediction of Maximum Tensile Loads in Soil Nails

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Yongqiang Hu ◽  
Peiyuan Lin
Keyword(s):  
Correction Factor ◽  
Earth Pressure ◽  
Random Variable ◽  
Probabilistic Prediction ◽  
Limit States ◽  
Simple Formulation ◽  
Load Model ◽  
Soil Nail ◽  
Reliability Based Design ◽  
The Difference

This paper presents the development of a simplified model for estimation of maximum nail loads during or at completion of construction of soil nail walls. The developed simplified nail load model consists of two multiplicative components: the theoretical nail load and the correction factor. The theoretical nail load is computed as the product of lateral active Earth pressure at nail depth and the nail tributary area. The correction factor is introduced to account for the difference between the theoretical and the measured nail loads. A total of 85 measured nail load data were collected from the literature; out of which, 74 were used to develop a simple formulation for the correction factor, whereas the remaining 11 were used for validation. After the validation, the model was updated using all 85 data. The updated simplified nail load model was demonstrated to be accurate on average (mean of model factor equal to 1), and the spread in prediction quantified as the coefficient of variation of the model factor was about 40%. Here, model factor is the ratio of measured to estimated nail load. The randomness of the model factor was also verified. Finally, the model factor was demonstrated to be a lognormal random variable. The proposed simplified nail load model is beneficial due to its simplicity and quantified model uncertainty; thus it is practically valuable to both direct reliability-based design and load and resistance factor design of soil nail wall internal limit states.

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