Time-dependent reliability of aging structures: From individual facilities to a community

Civil structures and infrastructure systems are often subjected to aggressive environmental or operational factors during their service life, which are likely to trigger a reduction in structural performance (e.g., stiffness, resistance). Moreover, many types of external loads may vary with time (e.g., the future cyclone actions in a changing global environment), potentially resulting in a severer load effect on structures. As a result, the impact of the time-variation of both structural performance and external load actions should be taken into account in structural reliability assessment under a probability-based framework. The built environment provides physical support to realizing the functionalities of a community. Different structures/facilities may be functionally dependent, exposed to similar service environment, and mutually correlated in terms of resistances and aging processes. This thesis is aimed to develop a mathematical framework for time-dependent reliability assessment of aging civil structures, with an emphasis on both the individual facilities and a community’s built environment. The framework takes into account the time-variant processes of both structural resistance and the load effects. For an individual structure, the reliability is measured by the probability of violating the limit state of resistance being greater than the load effect. With this regard, two types of load processes are considered, i.e., the discrete load process representing the occurrence of extreme events, and the continuous load process whose temporal correlation is reflected by an autocorrelation function (or equivalently a power spectral density function). Moreover, the impact of incompletely-informed variables (imprecise variables) on structural reliability is also studied. The reliability of a built environment is represented by the post-hazard damage ratio to the building portfolios with distributed and discretized structures, or the post-hazard serviceability of the infrastructure system (an electric grid system in this thesis) with interdependent components. Two types of natural hazards are considered, namely earthquake excitations and cyclone winds, whose large footprint leads to the spatial correlation of the load effects for different sites. With a view from individual facilities to a built environment, the proposed framework is applied to several examples to demonstrate its applicability. The work in this thesis suggests the importance of reasonably modeling the structural resistance and applied loads on both the temporal and spatial domains, especially in an attempt to achieve a resilient community

Time-Dependent Reliability of Aging Structures: Overview of Assessment Methods

Reliability assessment of engineered structures is a powerful and useful concept to estimate the structural capacity of withstanding hazardous events during their service lives. Taking into account the time variation of both structural resistance and the external load processes, the structural safety level is dependent on the duration of service period of interest, due to the accumulation of hazards by exposure in time. This paper presents an overview on the nonempirical assessment methods for time-dependent reliability of deteriorating structures. Generally, these methods can be classified into two types, namely simulation-based and analytical methods. The former is usually brute, and is especially suitable for solving high-dimensional reliability problems. Conversely, analytical solutions may improve the calculation efficiency significantly, and offer insights into the reliability problem that otherwise could be difficult to achieve through Monte Carlo simulation. Both the simulation-based and analytical methods will be reviewed in this paper. Furthermore, the application of time-dependent reliability methods in practical engineering is discussed. Recommendations for future research efforts are also presented

From Reliability-Based Design to Resilience-Based Design

Abstract Reliability-based design has been a widely used methodology in the design of engineering structures. For example, the structural design standards in many countries have adopted the load and resistance factor design (LRFD) method. In recent years, the concept of resilience-based design has emerged, which additionally takes into account the posthazard functionality loss and recovery process of a structure. Under this context, the following questions naturally arise: can we establish a linkage between reliability-based design and resilience-based design? Does there exist a simple resilience-based design criterion that takes a similar form of LRFD? This paper addresses these questions, and the answer is “yes”. To this end, a new concept of structural resilience capacity is proposed, which is a generalization of structural load bearing capacity (resistance). The probabilistic characteristics (mean value, variance, probability distribution function) of resilience capacity are derived. Applying the concept of resilience capacity, this paper explicitly shows the relationship between the following four items: time-invariant reliability-, time-invariant resilience-, time-dependent reliability-, and time-dependent resilience-based design methods. Furthermore, an LRFD-like design criterion is proposed for structural resilience-based design, namely, load and resilience capacity factor design (LRCFD), whose applicability is demonstrated through an example. The LRCFD method can also be used, in conjunction with LRFD, to achieve reliability and resilience goals simultaneously of the designed structure.</jats:p

Sustainability analysis: A stochastic formulation for evaluating the sustainability of engineering systems

During their life-cycle, engineering systems typically suffer from deterioration due to regular operation and exposure to extreme events and harsh environmental conditions. As a result, regular recovery strategies are often required to restore the system to a target safety and functionality level. There is a need to evaluate the associated impact of such strategies on the life-cycle sustainability of engineering systems. This work proposes a novel stochastic formulation, named Stochastic Life-cycle Sustainability Analysis (SLCSA), for evaluating the sustainability of engineering systems throughout their service lives. In the SLCSA, the sustainability of the system is evaluated for a fixed time horizon in terms of its environmental impact, which includes the impact of the construction, operation processes and recovery strategies that are associated with the various structural and mechanical components of the system. The formulation proposes state-dependent stochastic models that capture the effects of gradual and shock deteriorations in the evaluation of the environmental impact of the system. Moreover, the formulation accounts for the relevant uncertainties, such as those in the external conditions (e.g., environmental exposure and potential hazards), and those in the environmental emissions, associated with the materials and energy used throughout the system life-cycle. As an illustration, the proposed analysis is used to evaluate the life-cycle sustainability of a typical reinforced concrete (RC) bridge

Dynamic impact of ageing dump truck suspension systems on whole-body vibrations in high-impact shovel loading operations

Surface mining operations typically deploy large shovels, with 100+ tons per pass capacity, to load dump trucks in a phenomenon described as high-impact shovel loading operations (HISLO). The HISLO phenomenon causes excessive shock and vibrations in the dump truck assembly resulting in whole body vibration (WBV) exposures to operators. The truck suspension system performance deteriorates with time; therefore their effectiveness in attenuating vibrations reduces. No research has been conducted to study the impact of ageing suspension mechanisms on the magnitudes of WBV in HISLO operations. This study is a pioneering effort to provide fundamental and applied knowledge for understanding the impact of ageing on the magnitudes of WBV exposures. The effects of underlying ageing processes on a suspension performance index are mathematically modeled. The effects of scheduled maintenance and corrective maintenance on improving the performance index (PI) are also modeled. Finally, the proposed mathematical ageing model is linked to the truck operator\u27s exposure to WBVs via a virtual prototype CAT 793D truck model in the MSC ADAMS environment. The effects of suspension system ageing in increasing the WBV levels are examined in the form of both the vertical and horizontal accelerations under HISLO conditions. This study shows that the hydro-pneumatic suspension strut ageing results in deteriorating stiffness-damping parameters. The deteriorating suspension performance (with time) introduces more severe and prolonged WBVs in HISLO operations. The RMS accelerations increase significantly with time (suspension ageing). The vertical RMS accelerations increase to severe magnitudes of over 3.45, 3.75, and 4.0 m/s2 after 3, 5, and 7 years, respectively. These acceleration magnitudes are well beyond the ISO limits for the human body\u27s exposure to WBVs. This pioneering research effort provides a frontier for further research to provide safe and healthy working environments for HISLO operations --Abstract, page iii

OPERATIONAL MODEL ANALYSIS AND FINITE ELEMENT MODEL UPDATE USING AMBIENT VIBRATION DATA FOR AL-SINYAR TOWER

Buildings in Qatar rely on minimum structural code requirements implemented by design consultants’ offices. Qatar 2030 vision considers increasing of structures’ sustainability and serviceability as a high priority, which require testing structures under real full scale modeling. The process of monitoring structures’ behavior over time for aerospace, civil and mechanical engineering infrastructure is referred to as structural health monitoring (SHM). In Qatar, most high-rise building stability design is based on wind loading. According to Uniform Building Code3 1997 (UBC1997) which classifies seismic zones on a scale of zero to four, Qatar’s seismic classification on the scale is zero which is the minimum seismic risk value. Qatar Meteorological data on wind speeds enabled analysis of extreme winds to be undertaken in structural designs. This study aims to identify dynamic properties of the structural by using wired and wireless accelerometers in order to assess structural performance to update Finite Element Model (FEM). By updating FEM, engineers are enabled to support clients to make quick and correct decisions in extreme emergency situations in the case of boundary conditions changes and loads such as seismic vibration and wind pressure changes, during a structure’s life. The objective of this research is to apply and evaluate a single output-only procedure on a reinforced concrete tower building, Al Sinyar Tower, which consists of 2B+G+52 floors in Al Dafna Area in Qatar, with a total built up area of 74,747 sqm and is the tallest residential building in Qatar with a total height of 230 m . A Finite Element model using Sap2000 program was used to model and analyze building values in order to compare results with the real test results. The different forms of response data from ambient vibration were scrutinized to evaluate structure performance. Mode shapes, natural frequencies, modal damping ratios were studied, while the results of tests carried under ambient conditions were used to update the Finite Element model based on modules of elasticity, density and also connections fixity. The thesis concluded that wired sensors are not practical to use for low frequencies measurements in high rise buildings and that it is tremendously challenging and difficult to deal with more than 1000 meter long cables, especially with a very sensitive devices. Frequencies values from wired sensors could not been captured, whereas wireless connection provided more reasonable values. Ambient vibration results based on as-built environment provided higher frequency values in comparison to FEM because the stiffness provided by cladding, façade and walls eventually increased the system’s stiffness, which cannot be revealed in FEM based on structural drawings only. The foremost concept of Model Updating is to have an ideal simulation of structure that can represent real structure behavior. The Final Updated model results founded satisfactory according to modal assurance criterion (MAC) value with 98.9% and frequency deference errors average of 7.6%