Harmonizing structural safety levels with life-quality objectives

2003 ◽  
Vol 30 (3) ◽  
pp. 500-510 ◽  
Author(s):  
M A Maes ◽  
M D Pandey ◽  
J S Nathwani
Keyword(s):  
Life Cycle ◽  
Life Cycle Cost ◽  
Human Life ◽  
Limit State ◽  
Life Quality ◽  
Essential Element ◽  
Structural Safety ◽  
Human Consumption ◽  
Design Decision ◽  
Limit States

Life-quality objectives are identified as an essential element in design decision making. Of particular concern is the question of optimal safety levels that are consistent with reasonable expectations of individuals in a present-day society. Using sound principles of decision analysis and utility theory, a lifetime utility function is developed. It is shown to be related to human consumption, life duration including the cumulative effects of mortality and discounting, and the relative amount of time spent on work versus leisure. Questions regarding the acceptability and affordability of changes in life quality can be addressed using the utility functions developed. As an application, design safety levels for the Confederation Bridge are examined and discussed. Life-quality objectives can also be included in a life-cycle cost optimization. This allows us to perform a level IV probabilistic design approach including costs and consequences without having to estimate the value of human life, but instead including the effect of consequences on changes in life quality of individuals at risk. This results in a useful tool to determine optimal limit state design safety levels, as is illustrated in a parametric analysis in the case of a single limit state.Key words: lifetime utility, life-quality index, risk acceptance, limit states design, target reliability levels, risk reduction, minimum life-cycle cost, structural safety.

scholarly journals An Automated Procedure for Assessing Local Reliability Index and Life-Cycle Cost of Alternative Girder Bridge Design Solutions

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Ilaria Venanzi ◽  
Riccardo Castellani ◽  
Laura Ierimonti ◽  
Filippo Ubertini
Keyword(s):  
Life Cycle ◽  
Life Cycle Cost ◽  
Design Solution ◽  
Bridge Design ◽  
Limit States ◽  
Technical Standards ◽  
Local Character ◽  
Repair Costs ◽  
Design Solutions ◽  
Girder Bridge

Stakeholders of civil infrastructures have to usually choose among several design alternatives in order to select a final design representing the best trade-off between safety and economy, in a life-cycle perspective. In this framework, the paper proposes an automated procedure for the estimation of life-cycle repair costs of different bridge design solutions. The procedure provides the levels of safety locally guaranteed by the selected design solution and the related total life-cycle cost. The method is based on the finite element modeling of the bridge and uses design traffic models as suggested by international technical standards. Both the global behavior and the transversal cross section of the bridge are analyzed in order to provide local reliability indexes. Several parameters involved in the design, such as geometry and loads and materials’ characteristics, are considered as uncertain. Degradation models are adopted for steel carpentry and rebars. The application of the procedure to a road bridge case study shows its potential in providing local safety levels for different limit states over the entire lifetime of the bridge and the life-cycle cost of the infrastructure, highlighting the importance of the local character of the life-cycle cost analysis.

Applications of Vector Evaluated Genetic Algorithms (VEGA) in Ultimate Limit State Based Ship Structural Design

2014 ◽  
Author(s):  
Owen Hughes ◽  
Ming Ma ◽  
Jeom Kee Paik
Keyword(s):  
Genetic Algorithms ◽  
Structural Design ◽  
Limit State ◽  
Structural Safety ◽  
Wall Structure ◽  
Ultimate Limit State ◽  
Thin Wall ◽  
Limit States ◽  
Multi Objective ◽  
Ultimate Limit

Ship structural design often deals with multiple objectives such as weight, safety, and cost. These objectives usually conflict with each other, and optimizing a particular solution with respect to a single objective can result in unacceptable results with respect to the other objectives. A reasonable solution to a multi-objective problem is to investigate a set of solutions, each of which satisfies the objectives at an acceptable level without being dominated by any other solution. Genetic algorithms have been demonstrated to be particularly effective to determine excellent solutions to these problems. In this paper a multi-objective GA, called Vector Evaluated Genetic Algorithm (VEGA) is formulated and used to optimize a large and complex thin-wall structure (a complete cargo hold of a 200,000 ton oil tanker) on the basis of weight, safety and cost. The structure weight and cost and all of the stresses are calculated using a realistic finite element model. The structure adequacy is then evaluated using the ALPS/ULSAP computer program (Paik and Thayamballi, 2003) which can efficiently evaluate all six ultimate limit states for stiffened panels and grillages. This example was chosen because the initial design is severely inadequate. The results show that the proposed method can perform ultimate strength based structural optimization with multi-objectives, namely minimization of the structural weight and cost and maximization of structural safety, and also that the method is very robust.

Life Cycle Cost Considerations in Seismic Design Optimization of Structures

2012 ◽  
pp. 1-22 ◽  
Author(s):  
Bora Gencturk ◽  
Amr S. Elnashai
Keyword(s):  
Life Cycle ◽  
Life Cycle Cost ◽  
Critical Parameter ◽  
Problem Formulation ◽  
Civil Infrastructure ◽  
Limit States ◽  
Structural Capacity ◽  
Rc Structure ◽  
Simplified Analysis ◽  
Structural Engineers

The life-cycle cost (LCC) of a structure in seismic regions, which includes the initial and the post-earthquake repair cost, is a critical parameter for structural engineers and other stakeholders. The LCC analysis has been gaining prominence in recent years since civil infrastructure sustainability has been identified as one of the grand challenges for engineering in the 21st century. The objective of this chapter is to first identify the components in LCC evaluation that directly affect the outcomes, and propose strategies to improve the reliability of the analysis. The shortcomings of existing studies on LCC optimization of structures are identified. These shortcomings include simplified analysis techniques to determine the structural capacity and earthquake demand, use of generalized definitions for structural limit states, and inadequacies in treating uncertainty. In the following, the problem formulation and a brief review of existing literature on LCC optimization of structures are provided. A LCC model is presented, and techniques are proposed to improve the above mentioned shortcomings. Finally, LCC analysis of an example reinforced concrete (RC) structure is employed to illustrate the methodology.

Demonstration of a prototype design synthesis capability for space access vehicle design

2020 ◽  
Vol 124 (1281) ◽  
pp. 1761-1788
Author(s):  
L. Rana ◽  
B. Chudoba
Keyword(s):  
Life Cycle ◽  
Conceptual Design ◽  
Life Cycle Cost ◽  
Best Practice ◽  
Synthesis Process ◽  
Vehicle Design ◽  
Design Decision ◽  
Design Synthesis ◽  
Design Life ◽  
Synthesis Methodology

ABSTRACTThe early conceptual design (CD) phase of space access vehicles (SAVs) is the most abstract, innovative and technologically challenging phase of the entire aerospace design life cycle. Although the design decision-making during this phase influences around 80 percent of the overall life cycle cost, it is the most abstract and thus least understood phase of the entire design life cycle. The history of SAV design provides numerous examples of project failures that could have been avoided if the decision-maker had had the capability to forecast the potential risks and threats correctly ahead of time during the conceptual design phase. The present study addresses this crucial phase and demonstrates a best-practice synthesis methodology prototype to advance the current state of the art of CD as applied to SAV design. Developed by the Aerospace Vehicle Design (AVD) Laboratory at the University of Texas at Arlington (UTA), the Aerospace Vehicle Design Synthesis process and software (AVDS) is a prototype solution for a flight vehicle configuration–flexible (generic) design synthesis capability that can be applied to the primary categories of SAVs. This study focusses on introducing AVDS, followed by the demonstration and verification of the system’s capability through a sizing case study based on the data-rich Boeing X-20 Dyna-Soar spaceplane.

Reliability Evaluation of Structural Safety Factor Using a Global Resistance Approach

2019 ◽  
Author(s):  
Sergio Santos ◽  
Marcio Tacques R. Monteiro Junior ◽  
Luiz Fernando Martha ◽  
Claudia Interlandi
Keyword(s):  
Limit State ◽  
Point Of View ◽  
Structural Safety ◽  
Structural Behaviour ◽  
Limit States ◽  
Average Value ◽  
Model Code ◽  
Resistance Approach ◽  
Model Code 2010 ◽  
Ultimate Limit

<p>This paper presents a discussion on different ways of assessing the safety of concrete structures applying Reliability Analyses. The usual design approach based on the Ultimate Limit States (ULS) is confronted with the Global Resistance Format, as defined in <i>fi</i>b Model Code 2010. The Global Format considers the several uncertainties present in the structural behaviour through a pre-defined limit state in which one or more loading variables are increased by a <i>λ </i>factor, until a collapse situation is attained. In this evaluation, the variables related to the actions and to the resistances are taken with their average value. The obtained values for the <i>λ </i>factor shall be compatible, in the safety point-of- view, with the β reliability factors corresponding to the required safety levels. A conventional building is analyzed, and the obtained reliability factors corresponding to the two approaches are presented. It is shown that the application of the Global Resistance Format can lead to more economical structures.</p>

scholarly journals Probabilistic Approach to Limit States of a Steel Dome

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5528
Author(s):  
Paweł Zabojszcza ◽  
Urszula Radoń ◽  
Waldemar Szaniec
Keyword(s):  
Normal Distribution ◽  
Limit State ◽  
Probabilistic Approach ◽  
Random Variables ◽  
Structural Safety ◽  
Ultimate Limit State ◽  
Limit States ◽  
Serviceability Limit State ◽  
First Case ◽  
Ultimate Limit

In this paper, Numpress Explore software, developed at the Institute of Fundamental Technological Research of the Polish Academy of Sciences (IPPT PAN), was used to conduct reliability analyses. For static-strength calculations, the MES3D module, designed by the authors, was employed. Ultimate limit state was defined as condition of non-exceedance of the capacity value, resulting from the stability criterion of the bent and compressed element. The serviceability limit state was defined as the condition of non-exceedance of allowable vertical displacement. The above conditions constitute implicit forms of random variable functions; therefore, it was necessary to build an interface between the Numpress Explore and MES3D programs. In the study, a comparative analysis of two cases was carried out. As regards the first case, all adopted random variables had a normal distribution. The second case involved a more accurate description of the quantities mentioned. A normal distribution can be adopted for the description of, e.g., the randomness in the location of the structure nodes, and also the randomness of the multiplier of permanent loads. In actual systems, the distribution of certain loads deviates substantially from the Gaussian distribution. Consequently, adopting the assumption that the loads have a normal distribution can lead to gross errors in the assessment of structural safety. The distribution of loads resulting from atmospheric conditions is decidedly non-Gaussian in character. The Gumbel distribution was used in this study to describe snow and wind loads. The modulus of elasticity and cross-sectional area were described by means of a log-normal distribution. The adopted random variables were independent. Additionally, based on an analysis of the elasticity index, the random variables most affect the failure probability in the ultimate limit state and serviceability limit state were estimated.

scholarly journals A special limit state of reinforced concrete frameswith laterally reinforced nodes in the case of emergency impacts

Vestnik MGSU ◽  
2021 ◽  
pp. 1462-1472
Author(s):  
Vitaly I. Kolchunov ◽  
Pavel A. Korenkov ◽  
Dinh Quoc Phan
Keyword(s):  
Reinforced Concrete ◽  
Progressive Collapse ◽  
Limit State ◽  
Experimental Studies ◽  
Structural Safety ◽  
Structural Systems ◽  
Theoretical Studies ◽  
Limit States ◽  
Ground Floor ◽  
Experimental And Theoretical Studies

Introduction. The increasing number of domestic and foreign publications on structural safety and survivability of buildings and structures evidences a great interest in the study of the problem of protecting bearing systems from progressive collapse. The relevance of these studies is determined by the ongoing rise in the number of man-induced, natural and terrorist impacts on buildings and structures. In this regard, the decisive factor is the expansion of experimental and theoretical studies, focused on ensuring the required level of survivability of bearing systems under such special impacts and, respectively, developing methods for protection from progressive collapse. Materials and methods. This work presents new results of experimental studies on models of a fragment of a multi-storied building made of monolithic reinforced concrete, whose nodes, connecting the girder and the column, are reinforced with laterally reinforced meshes designed to resist operational static loads and a special emergency impact caused by the failure of one ground-floor column in the framework. Results. The article presents the results of experimental and theoretical studies on the stress-strain state and crack resistance of reinforced concrete frames or fragments of multi-storied frameworks of buildings, made of monolithic reinforced concrete. Nodes of these buildings are laterally reinforced. The data on force-induced resistance of structures were obtained for cases of the static operational loading of a structure and special emergency impacts caused by the instantaneous withdrawal of one column on the ground floor. A comparative analysis of the pace of cracking, crack development and opening is made. The co-authors have made a benchmark assessment of parameters of limit and beyond-the-limit states, as well as elements of structural systems, having nodes with/without laterally reinforced meshes. Conclusions. The co-authors have identified the nature of actual deformation and destruction of elements in the bearing system, whose nodes are laterally reinforced. The co-authors have experimentally identified the principal properties of structural elements to allow for a more rigorous assessment of deformability and the bearing capacity of the effect produced by the lateral reinforcement on the resistance of structural systems in beyond-the-limit states.

scholarly journals A Markovian-based methodology for the life-cycle cost analysis of bridge maintenance interventions under changing deterioration rates

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Fernando D ◽  
Walbridge S ◽  
Wan B
Keyword(s):  
Life Cycle ◽  
Cost Analysis ◽  
Life Cycle Cost ◽  
Intervention Strategies ◽  
Structural Safety ◽  
Life Cycle Cost Analysis ◽  
Bridge Maintenance ◽  
Optimal Intervention ◽  
Frp Strengthening ◽  
The Impact

Markovian transition probability matrices employing condition states are often used in bridge management systems to determine optimal intervention strategies. This approach assumes a constant deterioration matrix throughout the entire analysis period. In addition, decisions to carry out interventions are normally based on deterioration to predefined condition states, which are generally not linked to structural safety. However, in order to adequately model and evaluate certain intervention options, such as fiber-reinforced polymer (FRP) strengthening, it is necessary to model the impact of the intervention on the deterioration rate, as well as the safety of the structure. This paper presents a Markovian approach to model interventions that impact deteriorating rates. A model employing this approach is proposed, which also accounts for the safety of the structure. A simplified methodology to determine the optimal intervention strategy based on steady state probabilities is also presented. The proposed model and methodology are illustrated in a hypothetical bridge example, where one of the interventions is FRP strengthening of a concrete girder bridge. Keywords: Changing Deterioration Rates; Markov Chains; Bridge Maintenance Interventions; Optimal Intervention Strategies; Life-cycle Cost Analysis;

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