scholarly journals An Efficient Approach to Obtain Optimal Load Factors for Structural Design

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Juan Bojórquez ◽  
Sonia E. Ruiz
Keyword(s):  
Reinforced Concrete ◽  
Mexico City ◽  
Structural Reliability ◽  
Building Code ◽  
Load Factor ◽  
Optimization Approach ◽  
Load Combination ◽  
Load Factors ◽  
Optimal Load ◽  
Concrete Elements

An efficient optimization approach is described to calibrate load factors used for designing of structures. The load factors are calibrated so that the structural reliability index is as close as possible to a target reliability value. The optimization procedure is applied to find optimal load factors for designing of structures in accordance with the new version of the Mexico City Building Code (RCDF). For this aim, the combination of factors corresponding to dead load plus live load is considered. The optimal combination is based on a parametric numerical analysis of several reinforced concrete elements, which are designed using different load factor values. The Monte Carlo simulation technique is used. The formulation is applied to different failure modes: flexure, shear, torsion, and compression plus bending of short and slender reinforced concrete elements. Finally, the structural reliability corresponding to the optimal load combination proposed here is compared with that corresponding to the load combination recommended by the current Mexico City Building Code.

scholarly journals Force reduction factors for the seismic provisions of the National Building Code of Canada

1987 ◽  
Vol 14 (4) ◽  
pp. 447-454 ◽  
Author(s):  
J. H. Rainer
Keyword(s):  
Building Code ◽  
Load Factor ◽  
Limit States ◽  
Load Factors ◽  
Earthquake Resistant Structures ◽  
Structural Configurations ◽  
Force Reduction ◽  
Factor Α ◽  
Reduction Factors

A derivation of force reduction factors for the seismic provisions of the National Building Code of Canada (NBCC), 1985, is presented. This includes the following: classification of seismic actions, applicable limit states, change in load factor, derivation of force reduction factors, and classification of structural configurations. Quantitative comparisons are made between the derived force reduction factors and the response modification factors of the Applied Technology Council and good agreement was found. It is suggested that seismic requirements should be considered as accidental actions with a load factor αQ = 1.0. These results can form the basis for possible modifications to the 1985 NBCC seismic provisions. Key words: earthquake resistant structures, building code, loads, load factors.

scholarly journals Calibration of the Live Load Factor for Highway Bridges with Different Requirements of Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-10 ◽  
Author(s):  
Lang Liu ◽  
Qingyang Ren ◽  
Xu Wang
Keyword(s):  
Structural Reliability ◽  
Highway Bridges ◽  
Calibration Method ◽  
Mean Value ◽  
Load Factor ◽  
Live Load ◽  
Load Effect ◽  
Load Factors ◽  
Short Period ◽  
Traffic Volumes

Highway bridge load rating has been moving toward structural reliability since the issuance of AASHTO LRFR specifications; however, the recommended load factors were carried out by a few reliable truck data. The objective of this study is to calibrate the live load factor in AASHTO LRFR Rating Specification by using huge amount of WIM data collected in California for more than ten years between 2001 and 2013. Since traffic volumes, vehicular overloads, and traffic components are highly related to the load effect induced, a set of calibration equations is proposed here, in which the nominal standard load effect models are used and different requirements of loading are taken into account. By the analytical model of platoons of trucks and the extrapolation of the gathered WIM data over a short period of time to remote future over a longer time period, the expected maximum live load effects over the rating period of 5 years are also obtained. Then, the live load factor is calibrated as the product of the codified value multiplied by the ratio between the nominal standard load effect and the expected mean value. The results show that the products of the two ratios present rather constant, implying the proposed method and load configurations selected are effective. In the end, the live load factors of 1.0 and 0.7 along with load configurations are recommended for a simple span length less than 300 ft. The recommended calibration method and live load factors will eliminate the unnecessary overconservatism in rating specifications.

Safety and limit states design for reinforced concrete

1976 ◽  
Vol 3 (4) ◽  
pp. 484-513 ◽  
Author(s):  
J. G. MacGregor
Keyword(s):  
Reinforced Concrete ◽  
Concrete Structures ◽  
American Concrete Institute ◽  
Building Code ◽  
Structural Safety ◽  
Reinforced Concrete Structures ◽  
Limit States ◽  
Load Factors ◽  
New Formula ◽  
State Of Art

This state-of-art paper reviews the concept of limit states design. Following a brief review of statistical definitions the sources of variability in reinforced concrete structures are reviewed. Methods of defining structural safety are reviewed. Following a derivation of the procedures used to compute load and [Formula: see text] factors, a series of [Formula: see text] factors compatible with the 1975 National Building Code of Canada load factors are computed. With the exception of the value for shear the new [Formula: see text] factors are lower than the current American Concrete Institute and Canadian Standards Association values by about the amount of the ratio of load factors in National Building Code of Canada and American Concrete Institute. The computed [Formula: see text] for shear is considerably lower than the corresponding value from the American Concrete Institute Code. An Appendix traces the development of the American Concrete Institute load and [Formula: see text] factors.

Load factor calibration for the proposed 2005 edition of the National Building Code of Canada: Companion-action load combinations

2003 ◽  
Vol 30 (2) ◽  
pp. 440-448 ◽  
Author(s):  
F M Bartlett ◽  
H P Hong ◽  
W Zhou
Keyword(s):  
Companion Paper ◽  
Building Code ◽  
Wind Loads ◽  
Load Factor ◽  
Live Load ◽  
Dead Load ◽  
Limit States ◽  
Snow Load ◽  
Load Factors ◽  
Snow Loads

The 2005 edition of the National Building Code of Canada (NBCC) will adopt a companion-action format for load combinations and specify wind and snow loads based on their 50 year return period values. This paper presents the calibration of these factors, based on statistics for dead load, live load due to use and occupancy, snow load, and wind load, which are summarized in a companion paper. A target reliability index of approximately 3 for a design life of 50 years was adopted for consistency with the 1995 NBCC. The load combinations and load factors for strength and stability checks recommended for the 2005 NBCC were based on preliminary values from reliability analysis that were subsequently revised slightly to address major inconsistencies with past practice. The recommended load combinations and factors generally give factored load effects similar to those in the 1995 NBCC, but are up to 10% more severe for the combination of dead load plus snow load and are generally less severe for the combination of dead load, snow load, and live load due to use and occupancy. Load factors less than one are recommended for checking serviceability limit states involving specified snow and wind loads. Importance factors for various classifications of structure are also presented. Revisions to the commentaries of the NBCC are recommended that will provide guidance on dead load allowances for architectural and mechanical superimposed dead loads and cast-in-place cover slabs and toppings.Key words: buildings, code calibration, companion action, dead loads, live loads, load combinations, load factors, reliability, safety, snow loads, wind loads.

Subsea Pipeline UHB OOS Design: Structural Reliability Analysis

2017 ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Reliability Analysis ◽  
Survey Data ◽  
Structural Reliability ◽  
Design Parameters ◽  
Load Factor ◽  
Data Sets ◽  
Subsea Pipeline ◽  
Upheaval Buckling ◽  
Structural Reliability Analysis ◽  
Load Factors

Upheaval buckling (UHB) is a major design concern for a trenched and buried subsea pipeline operating at high temperature and pressure. A predictive assessment is necessary during the detailed engineering design and optimisation to evaluate and define any measure that may be utilised for UHB mitigation such as deep trenching, backfilling, blanket or spot rockdumping. A pre-emptive UHB structural reliability analysis (SRA) has to be performed prior to pipeline installation based on the typical trench imperfection out of straightness (OOS) statistics. The SRA results are updated once survey data is made available. A rockdump schedule can be established by incorporating appropriate safety or load factors to address uncertainties in the design parameters and as-built OOS survey measurement accuracy. This paper examines the basis for processing the OOS features from survey data and stochastic distributions assumed for SRA with a view to improving the SRA OOS analysis. A number of OOS issues are considered. To cut conservatism an alternative distribution and interpretation is proposed for the key SRA input parameters with regards to imperfections and survey resolution. The random imperfection height assumption used in the current SRA practice for UHB is thus challenged — the rationale and argument for an alternative approach are constructed through a review of stochastic process theory, additional integrity criteria, a parametric analysis and evaluation of multiple OOS survey data sets. To add to the strength of the argument, a range of engineering issues are discussed in the context of stochastic distributions of imperfections. A worked example and case study is presented leading to a rationally reduced load factor and rockdump volume requirement for OOS UHB mitigation and protection.

UHB Model Uncertainty for Structural Reliability Analysis of Pipeline OOS Design

2018 ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Universal Design ◽  
Limit State ◽  
Load Factor ◽  
Design Curve ◽  
Design Load ◽  
Structural Reliability Analysis ◽  
Load Factors ◽  
Curve Method

Design load factor structural reliability analysis is critical for pipeline postlay OOS design to mitigate global UHB for a trenched and buried subsea pipeline configuration operating at elevated temperature and pressure. During the detailed engineering phase it is necessary to evaluate and define any measure available to be finalised for UHB mitigation such as deep trenching selection, enhanced blanket or spot rockdumping. In order account for inherent uncertainties in the design variables, a pre-emptive SRA is normally performed for the probabilistic UHB design load factors prior to pipeline installation according to the typical trench imperfection statistics and some specified survey accuracy. As per the current practice the semi-analytical universal design curve method is used in the limit state for design load factor predictions. The SRA results will be updated once the OOS survey data become available. A rockdump schedule can then be established by FEA incorporating appropriate safety or load factors to address uncertainties in the design parameters and as-built pipeline OOS survey measurement accuracy. This paper examines the UHB model uncertainties in the load factor and backfill cover assessment with a view to improving the SRA OOS analysis. Sources of uncertainties and variability in the UHB design are discussed first. Some disparity and inconsistency arising between the SRA and FEA models for the limit state are considered. Alternative UHB models are investigated by taking Timoshenko shear stiffness and associated deformation with pipe-soil interactions into consideration. A comparison is made with the conventional universal design curve method, the improved model and FE modelling to demonstrate the findings and conclusions. Of these, the pipe-soil interaction and its representation in the SRA limit state assessment are identified as a significant factor.

scholarly journals The impact of the quality of materials on the differentiation of the reliability of a reinforced concrete beam

2019 ◽  
Vol 262 ◽  
pp. 06009
Author(s):  
Izabela Skrzypczak ◽  
Lidia Buda-Ożóg ◽  
Joanna Kujda
Keyword(s):  
Quality Control ◽  
Reinforced Concrete ◽  
Reinforced Concrete Beam ◽  
Reliability Indicators ◽  
Load Factors ◽  
Materials Used ◽  
Available Information ◽  
The Impact ◽  
Concrete Elements

Eurocod PN-EN 1990 „The basis for structural design” includes general principles for the differentiation of reliability taking into account the consequences of failure. Constructions are classified into three reliability classes RC1 to RC3, for which target reliability indicators have been defined. For the RC2 reliability class the basic values of partial coefficients in relation to materials and loads for persistent and transient computational situations were given. However, Eurocod PN-EN 1992-1-1, „Design concrete structures”, proposes to reduce partial coefficients by including quality control of production and available information on the heterogeneity of the materials used. The evaluation of standard recommendations regarding material partial coefficients was made on the basis of analysis of the reinforced concrete bending beam. The standard recommendations provide different levels of reliability. Elements designed in accordance with EN 1992-1-1 to reduce the value of partial factors with tighter quality control and reliability of reinforced concrete elements at RC2 reliability level may not be sufficient for load factors more than 0. 4.

SETTING A DIAGRAM APPROACH TO CALCULATING VIBRATED, CENTRIFUGED AND VIBROCENTRIFUGED REINFORCED CONCRETE COLUMNS WITH A VARIATROPIC STRUCTURE

2020 ◽  
pp. 22-34
Author(s):  
Л. Р. Маилян ◽  
С. А. Стельмах ◽  
Е. М. Щербань ◽  
М. П. Нажуев
Keyword(s):  
Experimental Data ◽  
Reinforced Concrete ◽  
Bearing Capacity ◽  
Cross Section ◽  
Concrete Columns ◽  
Reinforced Concrete Columns ◽  
The Cross ◽  
Concrete Elements ◽  
Diagram Approach

Состояние проблемы. Железобетонные элементы изготавливаются, как правило, по трем основным технологиям - вибрированием, центрифугированием и виброцентрифугированием. Однако все основные расчетные зависимости для определения их несущей способности выведены, исходя из основного постулата - постоянства и равенства характеристик бетона по сечению, что реализуется лишь в вибрированных колоннах. Результаты. В рамках диаграммного подхода предложены итерационный, приближенный и упрощенный способы расчета несущей способности железобетонных вибрированных, центрифугированных и виброцентрифугированных колонн. Выводы. Расчет по диаграммному подходу показал существенно более подходящую сходимость с опытными данными, чем расчет по методике норм, а также дал лучшие результаты при использовании дифференциальных характеристик бетона, чем при использовании интегральных и, тем более, нормативных характеристик бетона. Statement of the problem. Reinforced concrete elements are typically manufactured according to three basic technologies - vibration, centrifugation and vibrocentrifugation. However, all the basic calculated dependencies for determining their bearing capacity were derived using the main postulate, i.e., the constancy and equality of the characteristics of concrete over the cross section, which is implemented only in vibrated columns. Results. Within the framework of the diagrammatic approach, iterative, approximate and simplified methods of calculating the bearing capacity of reinforced concrete vibrated, centrifuged and vibrocentrifuged columns are proposed. Conclusions. The calculation according to the diagrammatic approach showed a significantly better convergence with the experimental data than that using the method of norms, and also performs better when using differential characteristics of concrete than when employing integral and particularly standard characteristics of concrete.

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