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.

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.

Service Life of Concrete Structures

2020 ◽  
Vol 309 ◽  
pp. 267-271
Author(s):  
Milan Holicky ◽  
Jiří Kolísko
Keyword(s):  
Service Life ◽  
Concrete Structure ◽  
Limit State ◽  
Concrete Structures ◽  
Technical Specification ◽  
Working Life ◽  
Degradation Process ◽  
International Standards ◽  
Limit States ◽  
Existing Structures

The concept of service life of structures is included in international standards ISO (under the term Design Working Life), in the European document EN 1990 (Design Service Life) and in the upcoming document CEN for assessment of existing structures - Technical Specification TS (Remaining Working Life). The mentioned documents contain mainly material-independent provisions for the design and assessment of all types of structures and for any category of actions. The submitted paper includes the definition of service life (performance time) tser, which is extended for any concrete structure, considering the resistance of a structure R(t) and the effect of action S(t). Both the aggregate variables R(t) and S(t) are usually random variables significantly dependent on time t. Due to the random variability of the variables R(t) and S(t), the service life tser, needs to be related to the probability that the performance of the structure is weakened or completely eliminated. Basically, serviceability limit states (SLS) and ultimate limit states (ULS) should be considered. In the case of concrete structures another limit state corresponding to the beginning of a specific degradation process (corrosion of reinforcement), denoted tinit, may be important. In specific cases of buildings and bridges a functional (moral) service life may be taken into account. The paper includes also a practical example of assessing the remaining working life of a concrete structure.

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).

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.

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.

scholarly journals Performance Criteria for Liquid Storage Tanks and Piping Systems Subjected to Seismic Loading

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Maria Vathi ◽  
Spyros A. Karamanos ◽  
Ioannis A. Kapogiannis ◽  
Konstantinos V. Spiliopoulos
Keyword(s):  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Local Strain ◽  
Performance Criteria ◽  
Piping System ◽  
Storage Tanks ◽  
Limit States ◽  
Liquid Storage ◽  
Piping Systems

In this paper, performance criteria for the seismic design of industrial liquid storage tanks and piping systems are proposed, aimed at introducing those industrial components into a performance-based design (PBD) framework. Considering “loss of containment” as the ultimate damage state, the proposed limit states are quantified in terms of local quantities obtained from a simple and efficient earthquake analysis. Liquid storage tanks and the corresponding principal failure modes (elephant's foot buckling, roof damage, base plate failure, anchorage failure, and nozzle damage) are examined first. Subsequently, limit states for piping systems are presented in terms of local strain at specific piping components (elbows, Tees, and nozzles) against ultimate strain capacity (tensile and compressive) and low-cycle fatigue. Modeling issues for liquid storage tanks and piping systems are also discussed, compared successfully with available experimental data, and simple and efficient analysis tools are proposed, toward reliable estimates of local strain demand. Using the above reliable numerical models, the proposed damage states are examined in two case studies: (a) a liquid storage tank and (b) a piping system, both located in areas of high seismicity.

scholarly journals Assessment of Seismic Vulnerability of Steel and RC Moment Buildings Using HAZUS and Statistical Methodologies

2017 ◽  
Vol 2017 ◽  
pp. 1-16 ◽  
Author(s):  
Iman Mansouri ◽  
Jong Wan Hu ◽  
Kazem Shakeri ◽  
Shahrokh Shahbazi ◽  
Bahareh Nouri
Keyword(s):  
Seismic Vulnerability ◽  
Fragility Curves ◽  
Limit State ◽  
Moment Frames ◽  
Limit States ◽  
Rc Frames ◽  
Dynamic Analyses ◽  
Damage States ◽  
Definition Of ◽  
Nonlinear Dynamic Analyses

Designer engineers have always the serious challenge regarding the choice of the kind of structures to use in the areas with significant seismic activities. Development of fragility curve provides an opportunity for designers to select a structure that will have the least fragility. This paper presents an investigation into the seismic vulnerability of both steel and reinforced concrete (RC) moment frames using fragility curves obtained by HAZUS and statistical methodologies. Fragility curves are employed for several probability parameters. Fragility curves are used to assess several probability parameters. Furthermore, it examines whether the probability of the exceedence of the damage limit state is reduced as expected. Nonlinear dynamic analyses of five-, eight-, and twelve-story frames are carried out using Perform 3D. The definition of damage states is based on the descriptions provided by HAZUS, which gives the limit states and the associated interstory drift limits for structures. The fragility curves show that the HAZUS procedure reduces probability of damage, and this reduction is higher for RC frames. Generally, the RC frames have higher fragility compared to steel frames.

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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