Target Performance Level Research Articles

Probabilistic optimum inspection planning of steel bridges with multiple fatigue sensitive details

Inspection planning of fatigue sensitive bridges is a complex process. This, in part, is due to various uncertainties associated with the damage propagation and the detection technique used to perform inspections. The planning process starts with identifying the most critical locations of fatigue damage occurrence. In this context, non-destructive testing (NDT) techniques, applied at different times along the service life, can be used to monitor the crack growth and support the fatigue life estimation. The next step is to establish an inspection plan which considers the available budget and the target performance level of the investigated bridge. This paper proposes a probabilistic approach for providing effective inspection plans for fatigue critical bridges. The proposed approach considers multiple fatigue critical locations in the bridge and chooses the best inspection option among a set of predefined types of non-destructive inspections for each detail. Uncertainties in the damage propagation are considered in addition to the uncertainties in the damage detection process. A multi-objective optimization problem, which accounts for various critical details in the bridge, is formulated to find the optimum inspection times and the required NDT technique for each inspection. An existing fatigue critical steel bridge is used to illustrate the proposed probabilistic approach.

Quantization and Bit Allocation for Channel State Feedback in Relay-Assisted Wireless Networks

This paper investigates quantization of channel state information (CSI) and bit allocation across wireless links in a multi-source, single-relay cooperative cellular network. Our goal is to minimize the loss in performance, measured as the achievable sum rate, due to limited-rate quantization of CSI. We develop both a channel quantization scheme and allocation of limited feedback bits to the various wireless links. We assume that the quantized CSI is reported to a central node responsible for optimal resource allocation. We first derive tight lower and upper bounds on the difference in rates between the perfect CSI and quantized CSI scenarios. These bounds are then used to derive an effective quantizer for arbitrary channel distributions. Next, we use these bounds to optimize the allocation of bits across the links subject to a budget on total available quantization bits. In particular, we show that the optimal bit allocation algorithm allocates more bits to those links in the network that contribute the most to the sum-rate. Finally, the paper investigates the choice of the central node; we show that this choice plays a significant role in CSI bits required to achieve a target performance level.

Reliability assessment on ultimate and serviceability limit states and determination of critical factor of safety for underground rock caverns

The observational design method which uses extensometers to measure the displacements during cavern construction and then adopt these data for back analysis does not always guarantee satisfactory performance because the displacements provide little information about the strength to stress ratio that ultimately determines the stability of the rock caverns. In this study, both the ultimate and serviceability limit states are investigated by means of the Finite Difference program FLAC3D. The global factor of safety obtained using the shear strength reduction technique is used as the criterion for the ultimate limit state and the calculated percent strain around the opening is adopted as the serviceability limit state criterion. High deformability, low shear strength and the high in situ stress state are the major factors that govern the underground rock cavern stability and serviceability. Through the identification of the key influencing parameters for calculating the factor of safety and the percent strain, numerical experimentations are performed in accordance with the methodology of 2k factorial design, from which polynomial regression models are developed for each rock mass condition. The First-Order Reliability Method (FORM) was used to determine the probability of failure for the limit states. Through the use of the automated spreadsheet search algorithm to determine the design point, to meet the different target performance levels, the required minimum FS is obtained and termed as the critical value. This proposed approach enables a cost-effective analysis to be conducted for a rational design of underground rock caverns.

KINERJA PELAKSANAAN KEGIATAN DINAS PARIWISATA KABUPATEN BADUNG

Decentralization on the basis of Law No. 32 of 2004 on Local Governmentwhich local governments are given discretion to manage their own household, sothe area has the authority and discretion in implementing policies in accordancewith the aspirations of the community. Governance and service area is based on theprinciples of transparency, participation and accountabilityIn this regard, this paper aims to determine the performance of the implementationof activities seen from the input, output and outcome and performance accountabilityBadung Tourism Offi ce.The result of the implementation of Badung Tourism Offi ce in 2008 are in accordancewith the plan, and 8 ( eight ) exceeded the target performance level indicators and8 ( eight ), an indicator similar to the target, the average level of achievementgoals through the formulation of indicators and targets at 116 percent of averageachievement levels of activity amounted to 102.64 percent.

A Comparative Evaluation of Performance Based Analysis Procedures According to 2007 Turkish Earthquake Code and Fema-440

Chapter 7 of the 2007 Turkish Earthquake Code (TEC) entitled “Assessment and Strengthening of Existing Buildings” sets standards for assessment and rehabilitation of existing buildings. Linear elastic and non-linear evaluation procedures of 2007 TEC are applied to reinforced concrete buildings. 2007 TEC gives two methods for assessment and rehabilitation of existing buildings. Linear elastic and non-linear static evaluation procedures are proposed for structural evaluation. A performance-based evaluation methodology is used under three levels of earthquake ground motion intensities with different return periods. The performance acceptance criteria are based on demand to capacity ratios at critical sections for the linear evaluation procedures (equivalent seismic load method and mode superposition method) and material strains for the non-linear evaluation procedures (the non-linear static pushover analysis). Member performance limits are described for three damage levels, considering the anticipated failure mode and ductility capacity of each member. Structural performance is then calculated by accounting for the distribution of member damages over the building.. Consistency between the results of the methods used for seismic evaluation of existing buildings is of prime importance. For this purpose, an irregular structure of in plane (A3 type) and 3 story is considered. The target performance level of the building is obtained by applying the linear and the non-linear evaluation procedures. The results are given comparatively on the target performance level of the building. Furthermore non-linear procedure results are compared between 2007TEC and FEMA-440 Capacity-Spectrum Method (CSM) and Displacement- Coefficient Method (DCM).

A knowledge-based software for the preliminary design of seismically isolated bridges

Seismic design of isolated bridges involves conceptual, preliminary and detailed structural design. However, despite the variety of commercial software currently available for the analysis and design of such systems, conceptual and preliminary design can prove to be a non-straightforward procedure because of the sensitivity of bridge response on the initial decisions made by the designer of the location, number and characteristics of the bearings placed, as well as on a series of broader criteria such as serviceability, target performance level and cost-effectiveness of the various design alternatives. Given the lack of detailed design guidelines to ensure, at this preliminary stage, compliance with the above requirements, a “trial and error” procedure is typically followed in the design office to decide on the most appropriate design scheme in the number and location of the bearing systems; the latter typically based on engineering judgment to balance performance with cost. To this end, the particular research effort aims to develop a decision-making system for the optimal preliminary design of seismically isolated bridges, assumed to respond as single degree of freedom (SDOF) systems. The proposed decision-making process is based on the current design provisions of Eurocode 8, but is complemented by additional criteria set according to expert judgment, laboratory testing and recent research findings, while using a combined cost/performance criterion to select from a database of bearings available on the international market. Software is also developed for the implementation of the system. The paper concludes with the application, and essentially the validation of the methodology and software developed through more rigorous MDOF numerical analysis for the case of a real bridge.

Seismic design of a precast r.c. structure equipped with viscous dampers

The seismic design of a two-storey precast reinforced-concrete building structure equipped with viscous dampers is presented in this paper with twofold purpose. The first goal is to verify the applicability of a practical procedure for the identification of the mechanical characteristics of the viscous dampers which allow to achieve target performance levels, originally proposed by the authors for moment-resisting building frames, also with reference to pendular structures. The second goal is to investigate the effectiveness of the use of viscous dampers (as compared with traditional lateral-resisting stiff braces) for the seismic design of precast not moment-resisting concrete structures.

Impact of Co-Channel Interference on the Performance of Adaptive Generalized Transmit Beamforming

The impact of co-channel interference on the performance of adaptive generalized transmit beamforming for low-complexity multiple-input single-output (MISO) configuration is investigated. The transmit channels are assumed to be sufficiently separated and undergo Rayleigh fading conditions. Due to the limited space, a single receive antenna is employed to capture desired user transmission. The number of active transmit channels is adjusted adaptively based on statistically unordered and/or ordered instantaneous signal-to-noise ratios (SNRs), where the transmitter has no information about the statistics of undesired signals. The adaptation thresholds are identified to guarantee a target performance level, and the adaptation schemes with enhanced spectral efficiency or power efficiency are studied and their performance are compared under various channels conditions. To facilitate comparison studies, results for the statistics of instantaneous combined signal-to-interference-plus-noise ratio (SINR) are derived, which can be applied for different fading conditions of interfering signals. The statistics for combined SNR and combined SINR are then used to quantify various performance measures, considering the impact of non-ideal estimation of the desired user channel state information (CSI) and the randomness in the number of active interferers. Numerical and simulation comparisons for the achieved performance of the adaptation schemes are presented.

An energy-based method for seismic retrofit of existing frames using hysteretic dampers

This paper proposes a method for the seismic retrofitting of existing frames by adding hysteretic energy dissipating devices (EDDs). The procedure is based on the energy balance of the structure, and it is used to determine the lateral strength, the lateral stiffness and the energy dissipation capacity of the EDDs needed in each story to achieve prescribed target performance levels for a given earthquake hazard. The performance levels are governed by the maximum lateral displacement. The earthquake hazard is characterized in terms of input energy and several seismological parameters, and further takes into account the proximity of the earthquake to the source. The proposed method deals with the effect of the EDDs explicitly in terms of hysteretic energy, bypassing equivalent viscous damping approximations, and directly quantifies the cumulative damage induced in the EDDs. The validity of the method is assessed numerically through nonlinear dynamic response analyses with near-fault and far-field ground motions, as well as experimentally through dynamic shaking table tests.

Assessment of RC moment frame buildings in moderate seismic zones: Evaluation of Egyptian seismic code implications and system configuration effects

Building code restrictive seismic design provisions and building systems type and configuration have remarkable implications on seismic performance of reinforced concrete moment framed structures. Seismic assessment of ductile versions of low- to mid-rise moment frames located in moderate seismic zones is carried out through comparative trial designs of two (4- and 8-story) buildings adopting both space and perimeter framed approaches. Code-compliant designs, as well as a proposed modified code design relaxing design drift demands for the investigated buildings, are examined to test their effectiveness and reliability. Fragility curves for the frames are generated corresponding to various code-specified performance levels. Code preset lower or upper bounds on either design acceleration or drift, respectively, that would control the final design are also addressed along with their implications, if imposed, on the frames’ seismic performance. The trial design study demonstrates that built-in static overstrength is generally larger for space frames than for perimeter frames, whereas the force reduction attributable to inelastic dynamic response differs from one frame type to the other for various investigated heights and for different target performance levels. Nonetheless, all trial designs are shown to meet the minimum performance implied by building code provisions but with varying margins. However, the study suggests that more consistent reliability for designed structures can be achieved by disaggregating the force reduction factor into its static and dynamic parts and that code default values of this factor for some building types would be better reduced for a more reliable performance.

Simultaneous selection of optimal parameters and tolerance of manipulator using evolutionary optimization technique

For precise industrial applications, a manipulator must have high positioning accuracy and repeatability. However, variations in performance of the manipulator are attributed to improper selection of dimensions of design and process parameters and its tolerance. There have been almost no attempts to optimize these parameters and tolerance of the manipulator, by which performance variations will be minimum. This paper presents an offline approach to select optimal parameters and tolerance simultaneously which minimizes the manufacturing cost and delivers the target performance level. To determine the optimal parameters and tolerances, a modification in differential evolution algorithm is proposed, which helps in incorporating the effect of uncertainty in optimization process. Proposed approach has been illustrated by selecting optimal parameters and tolerance of a 2-DOF RR planar manipulator. The performance of this approach has been compared with modified genetic algorithm. It is observed that differential evolution algorithm provides optimal results with lesser computations compared to genetic algorithm.

Incorporating Environmentally Compliant Manure Nutrient Disposal Costs into Least-Cost Livestock Ration Formulation

Livestock rations are formulated to minimize feed cost subject to nutritional requirements for a target performance level, which ignores the potentially substantial cost of disposing of nutrients fed in excess of nutritional requirements. We incorporate nutrient disposal costs into a modified least-cost ration formulation model to arrive at a joint least-cost decision that minimizes the sum of feed and net nutrient disposal costs. The method is demonstrated with phosphorus disposal costs on a representative dairy farm. Herd size, land availability and proximity, crop rotation, and initial soil phosphorus content are shown to be important in determining phosphorus disposal costs.

Incorporating Environmentally Compliant Manure Nutrient Disposal Costs into Least-Cost Livestock Ration Formulation

Livestock rations are formulated to minimize feed cost subject to nutritional requirements for a target performance level, which ignores the potentially substantial cost of disposing of nutrients fed in excess of nutritional requirements. We incorporate nutrient disposal costs into a modified least-cost ration formulation model to arrive at a joint least-cost decision that minimizes the sum of feed and net nutrient disposal costs. The method is demonstrated with phosphorus disposal costs on a representative dairy farm. Herd size, land availability and proximity, crop rotation, and initial soil phosphorus content are shown to be important in determining phosphorus disposal costs.

Cross-Modulation Interference and Mitigation Technique for Ultrawideband PPM Signaling

The detection issues of ultrawideband (UWB) signals depend on the type of modulation scheme that is used during the transmission. Cross-modulation interference (CMI) is a problem that is specific to UWB pulse-position-modulation (PPM) signaling. In this paper, the effects of CMI on the performance of noncoherent UWB receivers are analyzed. The probabilities of error for transmitted-reference (TR) and energy detector (ED) receivers in the presence and absence of CMI are derived. Optimal and suboptimal CMI avoidance algorithms, which are based on novel acquisition techniques, are proposed for Rake receivers. The results show that the performance degradation in both receivers, which is due to the CMI effects, can be significant, depending on the modulation index. TR receivers still can be functional in the presence of CMI, and the target performance level determines the modulation index to be used. It is unlikely that effects of CMI on the performance of ED receivers in the presence of CMI are more severe relative to TR receivers, and the performance level is not acceptable. As a result, PPM signaling is not an appropriate modulation technique for ED receivers that are operating in the CMI region, unless CMI mitigation algorithms can be developed. Furthermore, the proposed optimal and suboptimal algorithms are two promising schemes for avoiding the CMI effects and, consequently, for improving the performance of Rake receivers operating in the CMI region.

Performance-Based Optimization considering Both Structural and Nonstructural Components

Development of performance-based design (PBD) methodologies for buildings and a better understanding of the performance and damage to nonstructural components during ground motion events give rise to design problems that involve structural and nonstructural component performance. The current research effort is geared toward development of an automated PBD environment to optimize structural system performance. FEMA-350 and HAZUS procedures are used to evaluate confidence levels associated with the probability of a structure not meeting targeted performance levels. A genetic algorithm (GA) is used to solve this complex optimization problem where confidence levels are incorporated into a GA fitness function along with initial construction cost in a series of optimal design scenarios. Inelastic time-history analysis is used to evaluate the designs under different levels of hazard during execution of the evolutionary algorithm. Different optimization formulations are studied in order to explore the symbiotic relationship between seismic hazard magnitude, initial construction cost, and confidence levels for damage exceedance for structural and nonstructural components.

Design Methodology for Seismic Upgrading of Substandard Reinforced Concrete Structures

This article presents a design methodology for seismic upgrading of existing reinforced concrete (RC) buildings. The methodology is based on the modification of the deflected shape of the structure so as to achieve a near-uniform distribution of interstorey drift along the building height, thereby eliminating damage localization. Yield Point Spectra are utilized for the definition of demand and a direct displacement-based design approach is implemented. The fundamental steps of the method are described in detail, including a systematic evaluation of assumptions and limitations. A full-scale tested structure is used as a case study for assessment and verification of the proposed methodology. Alternative retrofit scenarios are set according to target response and performance levels. The role of the target deflected response shape and its influence on the outcome of the retrofit strategy is investigated. The viability of the alternative retrofit scenarios is studied for different ground motions including near-fault earthquake records.

Effectiveness of simple approaches in mitigating residual deformations in buildings

AbstractDevelopments in performance‐based seismic design and assessment approaches have emphasized the importance of considering residual deformations. Recent investigations have also led to a proposed direct displacement‐based design (DDBD) approach which includes an explicit consideration of the expected residual deformations as an integral part of the design process. Having estimated the expected residual deformations in a structure, engineers are faced with the problem of reducing them to meet the targeted performance levels under pre‐defined seismic hazard levels. Previous studies have identified the post‐yield stiffness as a primary factor influencing the magnitude of residual deformations in single degree of freedom and multiple degree of freedom structures. In this paper, a series of simple approaches to increase the post‐yield stiffness of traditional framed and braced systems for the purpose of reducing residual deformations are investigated. These methods do not utilize recentring post‐tensioned technology. This contribution addresses the feasibility of altering the lateral post‐yield stiffness of structural systems by: (i) using different reinforcement materials with beneficial features in their stress–strain behaviour; (ii) re‐designing the section geometry and properties of primary seismic‐resisting elements; and (iii) introducing a secondary elastic frame to act in parallel with the primary system. The efficiency of each of these techniques is investigated through monotonic and cyclic moment‐curvature and non‐linear time‐history analyses. Of these approaches the design and introduction of an elastic secondary system was found to be most effective and consistent in reducing residual deformations. A simplified design approach for achieving the desired increase of a system's post‐yield stiffness is also presented. Copyright © 2007 John Wiley & Sons, Ltd.

Bayesian adaptive estimation of arbitrary points on a psychometric function

Bayesian adaptive methods have been extensively used in psychophysics to estimate the point at which performance on a task attains arbitrary percentage levels, although the statistical properties of these estimators have never been assessed. We used simulation techniques to determine the small-sample properties of Bayesian estimators of arbitrary performance points, specifically addressing the issues of bias and precision as a function of the target percentage level. The study covered three major types of psychophysical task (yes-no detection, 2AFC discrimination and 2AFC detection) and explored the entire range of target performance levels allowed for by each task. Other factors included in the study were the form and parameters of the actual psychometric function Psi, the form and parameters of the model function M assumed in the Bayesian method, and the location of Psi within the parameter space. Our results indicate that Bayesian adaptive methods render unbiased estimators of any arbitrary point on psi only when M=Psi, and otherwise they yield bias whose magnitude can be considerable as the target level moves away from the midpoint of the range of Psi. The standard error of the estimator also increases as the target level approaches extreme values whether or not M=Psi. Contrary to widespread belief, neither the performance level at which bias is null nor that at which standard error is minimal can be predicted by the sweat factor. A closed-form expression nevertheless gives a reasonable fit to data describing the dependence of standard error on number of trials and target level, which allows determination of the number of trials that must be administered to obtain estimates with prescribed precision.

Optimizing random walk search algorithms in P2P networks

In this paper we develop a model for random walk-based search mechanisms in unstructured P2P networks. This model is used to obtain analytical expressions for the performance metrics of random walk search in terms of the popularity of the resource being searched for and the random walk parameters. We propose an equation-based adaptive search mechanism that uses an estimate of the popularity of a resource in order to choose the parameters of random walk such that a targeted performance level is achieved by the search. We also propose a low-overhead method for maintaining an estimate of popularity that utilizes feedback (or lack there-off) obtained from previous searches. Simulation results show that the performance of the equation-based adaptive search is significantly better than the non-adaptive random walk and other straight-forward adaptive mechanisms.

A Risk-Based Performance Analysis of Plate-andFrame Heat Exchangers Subject to Fouling: Economics of Heat Exchanger Cleaning

Fouling is one of the major uncertainties associated with the operation and maintenance of plate-and-frame heat exchangers (PHEs) in the steel and process industries. The decision regarding periodic maintenance (i.e., cleaning) to meet the target performance level is generally based on both thermal and economic behavior of the process. In this paper, we present a cost model that includes the risk level and the scatter parameter of random fouling growth models. Two models (namely, power law and exponential fouling growth) are integrated in the model. The non-dimensional cost function of reduced time is examined by considering dimensionless cost parameters, representing additional cost due to a decrease in effectiveness, pumping power cost, anti-foulant cost, cleaning cost, additional pumping power cost of the standby unit during cleaning, and miscellaneous costs. These dimensionless cost elements are examined for a PHE operating in the steel industry. The results are presented in terms of the risk level and scatter parameter for the underlying fouling models. Furthermore, a simplified closed-form solution is also obtained to study the optimal cycle time, which represents the minimum cost of operation and maintenance of heat exchangers. It is found that the optimum dimensionless cost increased by about 21 and 14% for the power law and exponential fouling models, respectively, as the risk level decreased from 0.5 to 0.01