Comparative and Uncertainty Assessment of Design Criteria for Stiffened Panels

2004 ◽  
Vol 48 (03) ◽  
pp. 231-247
Author(s):  
Ibrahim A. Assakkaf ◽  
Bilal M. Ayyub
Keyword(s):  
Failure Modes ◽  
Prediction Models ◽  
Limit State ◽  
Uncertainty Assessment ◽  
Offshore Structures ◽  
Paper Strength ◽  
Limit States ◽  
Ship Structures ◽  
Steel Panels ◽  
Strength Models

Stiffened and gross steel panels (plates) are very important components in ship and offshore structures, and therefore they should be designed for a set of failure modes that govern their strength. They form the backbone of most ships' structure, and they are by far the most commonly used element in a ship. They can be found in bottom structures, decks, side shell, and superstructures. To evaluate the strength of a stiffened or gross panel element, it is necessary to review various strength-predicting models and to study their biases, applicability, and limitations for different loading conditions acting on the element. In this paper, strength limit states for various failure modes of ship panels are presented. For each limit state, commonly used strength models were collected from many sources for evaluating their limitations and applicability and to study their biases and uncertainties. Wherever possible, the different types of biases resulting from these models were computed. The bias and uncertainty analyses for these strength models are needed for the development of load and resistance factor design (LRFD) rules for stiffened and gross panels of ship structures. The uncertainty and biases of these models were assessed and evaluated by comparing their predictions with ones that are more accurate or real values. The objective of this paper is to summarize strength prediction models of stiffened and gross panels that are suitable for LRFD development for ship structures. Monte Carlo simulation was used to assess the biases and uncertainties for these models. Recommendations for the use of the models and their biases in LRFD development are provided.

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.

Reliability analysis of wood I-joists

1993 ◽  
Vol 20 (4) ◽  
pp. 564-573 ◽  
Author(s):  
R. O. Foschi ◽  
F. Z. Yao
Keyword(s):  
Reliability Analysis ◽  
Carrying Capacity ◽  
Failure Modes ◽  
Limit State ◽  
Load Carrying Capacity ◽  
Limit States ◽  
Element Analysis ◽  
Strength Limit ◽  
Reliability Method ◽  
Load Carrying

This paper presents a reliability analysis of wood I-joists for both strength and serviceability limit states. Results are obtained from a finite element analysis coupled with a first-order reliability method. For the strength limit state of load-carrying capacity, multiple failure modes are considered, each involving the interaction of several random variables. Good agreement is achieved between the test results and the theoretical prediction of variability in load-carrying capacity. Finally, a procedure is given to obtain load-sharing adjustment factors applicable to repetitive member systems such as floors and flat roofs. Key words: reliability, limit state design, wood composites, I-joist, structural analysis.

scholarly journals Reliability Analysis of Anchored Geotechnical Structures for the Design Limit States

2020 ◽  
Vol 8 (2) ◽  
pp. 35-47
Author(s):  
Sohaib K Al-Mamoori ◽  
Laheab A. Al-Maliki ◽  
Khaled El-Tawel
Keyword(s):  
Reliability Analysis ◽  
Reliability Index ◽  
Failure Modes ◽  
Limit State ◽  
Tensile Failure ◽  
Limit States ◽  
Geotechnical Parameters ◽  
Retaining Structure ◽  
Geotechnical Structures ◽  
Bending Failure

Reliability has been considered of magnificent importance in engineering design specially in geotechnical engineering due to the unpredictable conditions of soil layers. It is essential to establish well- designed failure modes that could guarantee safety and durability of the proposed structure. This study aims to suggest a reliability analyses procedure for retaining walls by the mean of a reliability index β using the specifications of AASHTO Bridge Design 2002, Eurocode 7, and DIN EN 1993-5 norms. Two failure modes; Tensile failure of tendon (G1) and Failure by bending (G2) were studied and compared by using equation of the Design Limit State (DLS) and by taking some basic geotechnical parameters as Random Variables RV. The analyses demonstrated that the reliability index β and probability of failure Pf are the most important parameter in the reliability analysis. Also, the suitable height (H) for the retaining structure (for all angles ϴ) equals to 6 m and the most critical angle is ϴ= 45º to prevent the failure by tensile of tendon. While the bending failure reliability analysis shows that all heights of retaining structure are suitable. After comparing the two cases it was found that (G1) is more dangerous than (G2).

DESIGN OF BOLTED CONNECTIONS SUBJECT TO TORSION AND SHEAR IN THE ULTIMATE LIMIT STRESS STATE

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Mohamed S. Abu-Yosef ◽  
Ezzeldin Y. Sayed-Ahmed ◽  
Emam A. Soliman
Keyword(s):  
Failure Modes ◽  
Focal Point ◽  
Design Method ◽  
Limit State ◽  
Bending Moment ◽  
Steel Structures ◽  
Ultimate Limit State ◽  
Shear Forces ◽  
Limit States ◽  
Ultimate Limit

Steel connections transferring axial and shear forces in addition to bending moment and/or torsional moment are widely used in steel structures. Thus, design of such eccentric connections has become the focal point of any researches. Nonetheless, behavior of eccentric connections subjected to shear forces and torsion in the ultimate limit state is still ambiguous. Most design codes of practice still conservatively use the common elastic analysis for design of the said connections even in the ultimate limit states. Yet, there are some exceptions such as the design method proposed by CAN/CSA-S16-14 which gives tabulated design aid for the ultimate limit state design of these connections based on an empirical equation that is derived for ¾ inch diameter A325 bearing type bolts and A36 steel plates. It was argued that results can also be used with a margin of error for other grade bolts of different sizes and steel of other grades. As such, in this paper, the performance of bolted connection subject to shear and torsion is experimentally investigated. The behavior, failure modes and factors affecting both are scrutinized. Twelve connections subject to shear and torsion with different bolts configurations and diameters are experimentally tested to failure. The accuracy of the currently available design equations proposed is compared to the outcomes of these tests.

Reliability Analysis of Land Pipelines for Hydrocarbons Transportation in Mexico

2004 ◽  
Author(s):  
David De Leon ◽  
Carlos Cortes
Keyword(s):  
Mechanical Properties ◽  
Stress Concentration ◽  
Internal Pressure ◽  
Failure Modes ◽  
Limit State ◽  
Response Analysis ◽  
Initiation Toughness ◽  
Limit States ◽  
Internal Corrosion ◽  
Maximum Stresses

Pipelines are the most economical way to transport hydrocarbons. In Mexico, PEMEX manages more than 60,000 Km of oil and gas land and marine pipelines. Therefore, their structural integrity must be carefully assessed. Pipeline managers require reliable and realistic codes in order to back up their decisions about design, maintenance and operation. In particular, for safety prediction, the failure modes and uncertainties involved in each loading condition need to be incorporated in the analysis in order to specify the pipelines use thresholds that keep them over acceptable safety levels within their operating lifetimes [1, 2]. For these reasons, a structural reliability formulation appears to be the appropriate framework to perform the evaluation. In this paper, the land pipeline reliability is estimated for the internal pressure, bending and tension failure mode conditions. These loading conditions are applied individually and tension and bending in a combined fashion, and random variability on the internal pressure, steel mechanical properties as well as the degradation effect of internal corrosion due to the transported fluid is included. So far, seamless pipeline is considered as used in Mexico. A set of internal pressures and mechanical properties are randomly generated through Monte Carlo simulation and the pipeline response under each simulated condition is obtained by making use of commercial software. The response analysis resorts on the nonlinear finite element method and it involves the calculation of maximum stresses and stress concentration factors under no corroded and corroded conditions. The following limit states are assessed: 1) the margin between maximum stresses due to internal pressure, tension and bending and the material capacity and 2) the margin between stress concentration factor and fracture initiation toughness. The above described limit states are calculated for no corroded condition and, once the critical failure modes are identified, corrosion effect is included on them. The failure probability is estimated from the response statistics for the considered limit state. The Cornell reliability index and the respective safety factor are also estimated. These results may be further extended and used for risk assessments and code calibration for design, inspection and maintenance of pipelines in Mexico.

Long-Term Fatigue and Extreme Design of Steel Risers

2009 ◽  
Author(s):  
Michele A. L. Martins ◽  
Andre´ S. Do´ria ◽  
Eduardo S. S. Silveira
Keyword(s):  
Limit State ◽  
Joint Probability ◽  
Offshore Structures ◽  
Joint Probability Distribution ◽  
Full Time ◽  
Extreme Statistics ◽  
Limit States ◽  
Sea State ◽  
Zero Crossing

Environmental loads are the main source of dynamic excitation of offshore structures. Due to the random nature of these loads, one should consider statistical properties when designing such structures. Recent codes for the design of steel risers address the use of environmental contours or full long-term analysis to take into account the statistics of load effects. Moreover, sea states for fatigue design should also be carefully selected so as to include the region of the scatter diagram which most contributes to the total damage. This paper looks into fatigue and ultimate limit states of steel risers. The first part shows a comparative study of three design criteria for extreme statistical analysis. These criteria are based on design storm, environmental contour, and full long-term statistics. A joint probability distribution found in the literature for a Brazilian location was used to describe the correlation between the significant wave height and the zero crossing wave period. The second part deals with the analysis of the coefficient of contribution for fatigue and long-term extreme statistics. Several full time domain analyses were performed and the most important sea state region for each limit state is shown in two examples of steel catenary risers. A discussion about sea state selection is then presented.

scholarly journals Recent Industrial Developments of Marine Composites Limit States and Design Approaches on Strength

2020 ◽  
Author(s):  
Beatrice Barsotti ◽  
Marco Gaiotti ◽  
Cesare Mario Rizzo
Keyword(s):  
Failure Modes ◽  
Three Dimensional ◽  
Offshore Structures ◽  
Structural Domain ◽  
Limit States ◽  
Ship Hulls ◽  
Starting Point ◽  
Current Design ◽  
The One ◽  
Marine Composite

Abstract To further exploit the potential of marine composites applications in building ship hulls, offshore structures, and marine equipment and components, design approaches should be improved, facing the challenge of a more comprehensive and explicit assessment of appropriately defined limit states. The structure ultimate/limit conditions shall be verified in principle within the whole structural domain and throughout the ship service life. What above calls for extended and reliable materials characterization on the one hand and for accurate and wide-ranging procedures in structural analyses. This paper presents an overview of recent industrial developments of marine composites limit states assessments and design approaches, as available in open literature, focusing on pleasure crafts and yachts as well as navy ships and thus showing a starting point to fill the gap in this respect. After a general introduction about composites characterization techniques, current design practice and rule requirements are briefly summarized. Both inter-ply and intra-ply failure modes and corresponding limit states are then presented along with recently proposed assessment approaches. Three-dimensional aspects in failure modes and manufacturing methods have been identified as the main factors influencing marine composite robustness. Literature review highlighted also fire resistance and hybrid joining techniques as significant issues in the use of marine composites.

IMPACT OF PREDICTING BRITTLE FAILURE MODES ON SELECTION OF LIMIT STATES OF VERTICALLY-IRREGULAR TALL BUILDINGS

2017 ◽  
Vol 4 (1) ◽  
Author(s):  
Aman Mwafy ◽  
Sayed Khalifa ◽  
Bilal El-Ariss
Keyword(s):  
Failure Modes ◽  
Limit State ◽  
Tall Buildings ◽  
International Standards ◽  
Performance Criteria ◽  
Far Field ◽  
Limit States ◽  
Earthquake Records ◽  
Irregular Buildings ◽  
Definition Of

The proper definition of structural failure of irregular structures is a critical element in building vulnerability assessment. Shear force demands may be the main cause of failure under earthquake loading. This increases the uncertainty related to the definition of the limit states of irregular buildings. The present study thus focuses on the assessment of brittle shear failure on the performance criteria of vertically irregular tall buildings. Five 50-story structures are designed using international standards to represent code-conforming tall buildings with main vertical irregularities. Detailed simulation models are used to assess the failure modes of the buildings under the effect of far-field and near-source earthquake records. Experimentally verified shear strength models are adopted to monitor the shear supply-demand response of the reference structures. Based on the comprehensive results obtained from incremental dynamic analyses, it is concluded that shear modeling is essential for the reliable assessment of vertically irregular buildings. The characteristics of earthquake records and the irregularity type significantly influence the limit states of the reference buildings. Unlike the behavior of the buildings under the far-field earthquake scenario, which is controlled by flexure, the collapse prevention limit state is significantly influenced by the member shear response under the effect of near-field earthquakes. Accordingly, improved limit state criteria are proposed, which supports the reliable earthquake loss estimation of tall buildings with different vertical irregularities.

Development of geotechnical limit state design

1995 ◽  
Vol 32 (1) ◽  
pp. 128-136 ◽  
Author(s):  
Geoffrey G. Meyerhof
Keyword(s):  
Limit State ◽  
Offshore Structures ◽  
Soil Parameters ◽  
Ultimate Limit State ◽  
Offshore Structure ◽  
Limit States ◽  
Limit State Design ◽  
Earth Structures ◽  
Earth Retaining Structures ◽  
Operational Constraints

The historical development of limit state design in geotechnical engineering is reviewed. Total and partial factors of safety used for the design of land–based and offshore structures are compared. It is found that the factors of safety in different codes for the ultimate and serviceability limit states design of earthworks, earth retaining structures, and land-based and offshore foundations are very similar. Partial factors in the ultimate limit state design are linked to the variability of the loads and soil parameters, the design approximations, and construction tolerances. They influence the nominal probability of failure of the type of structure considered and the seriousness of failure, which differ for land-based and offshore structures. These probabilities are compared with human fatality risks of common experiences. The serviceability limit states are governed by structural and operational constraints and the intended service life of the land-based or offshore structure. The corresponding partial factors are generally taken as unity. Key words : codes, earth structures, foundations, human risks, limit states design, probability of failures, factors of safety.

scholarly journals Fragility curves for non-engineered masonry buildings in developing countries derived from real data based on structural surveys and laboratory tests

2021 ◽  
Author(s):  
Viviana Iris Novelli ◽  
Raffaele De Risi ◽  
Ignasio Ngoma ◽  
Innocent Kafodya ◽  
Panos Kloukinas ◽  
...  
Keyword(s):  
Failure Modes ◽  
Fragility Curves ◽  
Limit State ◽  
Rift System ◽  
Ultimate Limit State ◽  
East African Rift System ◽  
East African ◽  
Local Data ◽  
African Countries ◽  
Limit States

AbstractMalawi is located within the southern branch of the active East African Rift System, where earthquakes of moment magnitude (Mw) 7.0 or greater can occur along major faults. The majority of dwellings in the country are non-engineered unreinforced masonry constructions, built by local artisans with little input from engineers. These constructions are highly vulnerable to seismic events due to poor-quality materials and lack of construction detailing. This study presents a new methodology to assess the seismic fragility curves of typical dwellings located in the Central and Southern Malawi. On-site inspections of buildings are carried out to assess geometrical and structural features of 646 façades, and an experimental campaign is performed to characterise the mechanical properties of local construction materials. The collected data allow the identification of different building typologies in terms of quality of materials and construction techniques. The critical failure modes for each of the inspected façade at their ultimate limit state are evaluated analytically. Damage limit states are defined and adopted to derive simplified Static Push-Over (SPO) curves, transformed into incremental dynamic analysis (IDA) curves by using SPO2IDA. The IDA curves are then used to obtain fragility curves for the specific damage limit states. The fragility curves presented herein are the first to be calculated for these building typologies, based on local data, and unfortunately, they show that buildings in Malawi are far more vulnerable to earthquakes than estimated from previously available international reference data. The fragility curves developed in this study may prove useful for assessing the seismic risk of these building typologies in Malawi and other East African countries.

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