Sez Atamturktur

Bayesian Updating of Soil Parameters for Braced Excavations Using Field Observations

ABayesianframeworkusing fieldobservationsfor back-analysisandupdatingofsoilparameters inamultistage bracedexcavation is presented. Because of the uncertainties originating from the poorly known soil parameters, the imperfect analysis model, and other factors such as construction variability, the soil parameters can only be inferred as probability distributions. In this paper, these posterior distributions are derived using the Markov chain Monte Carlo (MCMC) sampling method implemented with the Metropolis-Hastings algorithm. In the pro- posedframework,Bayesianupdatingis firstrealizedwithonetypeofresponseobservation(maximumwalldeflectionormaximumsettlement), andthenthisBayesianframeworkisextendedtoallowforsimultaneoususeoftwotypesofresponseobservationsintheupdating.Theproposed framework is illustrated with a quality excavation case and shown effective regardless of the prior knowledge of soil parameters and type of response observations adopted. DOI: 10.1061/(ASCE)GT.1943-5606.0000782.

Simplified Approach for Reliability-Based Design against Basal-Heave Failure in Braced Excavations Considering Spatial Effect

This paper presents a simplified approach for reliability analysis of basal heave in a braced excavation considering the spatial variability of soil parameters, The first-order reliability method (FORM) with a variance reduction technique is employed to model the spatial variability in lieu of the conventional random field modeling (RFM). The proposed approach yields results that are comparable with those obtained using the conventional RFM approach that relies on Monte Carlo simulation. The proposed approach requires much less computa- tional effort, is easy to use, and has potential as a practical tool for reliability-based design that has to deal with spatial variability of soils. DOI: 10.1061/(ASCE)GT.1943-5606.0000621.

Error and Uncertainty Analysis of Inexact and Imprecise Computer Models

Computer simulations are routinely executed to predict the behavior of complex systems in many fields of engineering and science. These computer-aided predictions involve the theoretical foundation, numerical modeling, and supporting experimental data, all of which come with their associated errors. A natural question then arises concerning the validity of computer model predictions, especially in cases where these models are executed in support of high-consequence decision making. This article lays out a methodology for quantifying the degrading effects of incompleteness and inaccuracy of the theoretical foundation, numerical modeling, and experimental data on the computer model predictions. Through the method discussed in this paper, the validity of model predictions can be judged and communicated between involved parties in a quantitative and objective manner. DOI: 10.1061/(ASCE)CP.1943-5487.0000233.

Bootstrapping for Characterizing the Effect of Uncertainty in Sample Statistics for Braced Excavations

A simple procedure for assessing the probability of serviceability failure in a braced excavation involving bootstrapping to char- acterize the effect of uncertainty in sample statistics is presented. Here, the failure is defined when an excavation systems response in terms of themaximumwalldeflectionorgroundsettlementthatexceedsthelimitingvaluespecifiedbytheclientorinanapplicablecode.Theanalysisfor the probability of failure (or probability of exceedance) necessitates an evaluation of the means and SDs of critical soil parameters. In geotechnical practice,thesemeansandSDsareoftenestimatedfromaverylimiteddataset,whichcanleadtouncertaintyinthederivedsample statistics. Thus, in this study bootstrapping is used to characterize the uncertainty or variation of sample statistics and its effect on the failure probability.Throughthebootstrappinganalysis,theprobabilityofexceedancecanbepresentedasaconfidenceintervalinsteadofasingle, fixed probability.Theinformationgainedshouldenabletheengineertomakeamorerationalassessmentoftheriskofserviceabilityfailureinabraced excavation. The study points to the potential of the bootstrap method in coping with the problem of having to evaluate failure probability with uncertain sample statistics. DOI: 10.1061/(ASCE)GT.1943-5606.0000734.

A novel vibration-based monitoring technique for bridge pier and abutment scour

Scouring degrades the overall health of a bridge by removing the bed material surrounding the piers and abutments. If undetected, scour may lead to the catastrophic failure of a bridge resulting in hundreds of millions in repair costs. The loss of a bridge due to undetected scour formations can also hinder emergency evacuations since riverbed scouring typically occurs in peak flow periods such as hurricane or flood events. To take requisite precautions against such catastrophic events, a monitoring system that can reliably detect scour formation, without being adversely affected by the environmental conditions, is essential. This article presents a novel scour monitoring technique that exploits the differences between the low-frequency ambient excitations exerted on a thin, flexible plate located in the flow versus the same device located in the sediment. The underlying principle is that a flexible plate excited by the turbulent flow vibrates at significantly higher amplitudes compared to an identical plate surrounded by sediment. To validate this principle, a simplified numerical model is developed to guide the design of the scaled laboratory device; next, a prototype model is built in the laboratory and tested in an indoor flume. The energy content of the sensor in the flow is measured to be one to two orders of magnitude greater than the sensor in sediment. The findings obtained at various flow conditions indicate that this technique can supply reliable information on the water/sediment interface, and thus scour and refill processes. Experimental results also demonstrate that the presence of a scour hole further improves the ability to detect the interface location. Additionally, the results show that maximum slope of the sensor energy content as a function of the sensor depth can be used as a feature to estimate the water/sediment interface.

Prioritization of Code Development Efforts in Partitioned Analysis

In partitioned analysis of systems that are driven by the interaction of functionally distinct but strongly coupled constituents, the predictive accuracy of the simulation hinges on the accuracy of individual con- stituent models. Potential improvement in the predictive accuracy of the simulation that can be gained through improving a constituent model depends not only on the relative importance, but also on the inherent uncertainty and inaccuracy of that particular constituent. A need ex- ists for prioritization of code development efforts to cost- effectively allocate available resources to the constituents that require improvement the most. This article proposes a novel and quantitative code prioritization index to ac- complish such a task and demonstrates its application on a case study of a steel frame with semirigid connections. Findings show that as high-fidelity constituent models are integrated, the predictive ability of model-based simula- tion is improved; however, the rate of improvement is de- pendent upon the sequence in which the constituents are improved.

Optimization-Based Strong Coupling Procedure for Partitioned Analysis

AbstractThe concept of partitioning a complex engineering problem into smaller, manageable components and investigating each individual component autonomously has been in use for many decades. Such partitioning approaches, however, rely on strong and occasional unwarranted assumptions regarding the interactions among different engineering components. Fluid and structure interaction, soil and structure interaction, and human and structure interaction are but a few of the many such partitioned analyses commonly needed in civil engineering applications. Recently, there has been a growing interest in combining the expertise developed separately in traditionally distinct fields to obtain a holistic treatment of engineering problems. Such holistic treatment would ultimately yield not only more realistic and accurate analyses of coupled systems but also improved optimality in engineering designs. This growing interest has resulted in development of mathematical coupling procedures for conjoining multiple, separa...

Efficient robust geotechnical design of drilled shafts in clay using a spreadsheet

Abstract This paper presents an efficient robust geotechnical design (RGD) approach that considers performance requirements, design robustness, and cost efficiency simultaneously. In this paper, design robustness is measured via the variation in the performance function of concern that can be evaluated using reliability analysis. Furthermore, the performance requirements of the system are also evaluated using reliability analysis. Thus, the evaluation of design robustness and the evaluation of performance requirements share common computational steps, referred to herein as computational coupling. This coupling for computational efficiency is a significant feature of the proposed RGD approach. Within the framework of the proposed RGD approach, design robustness, cost efficiency, and performance requirements can be considered simultaneously by means of multiobjective optimization. Furthermore, a practical and efficient procedure is developed for such optimization using a feature resident in a popular spread...

Ambient vibration testing and seismic behavior of historical arch bridges under near and far fault ground motions

This study investigates the effects of near and far fault ground motion on the seismic behavior of historical arch bridges through a combined numerical and experimental evaluation. The approach undertaken begins with finite element modeling of the arch bridge and identification of the most significant vibration modes of the bridge through ambient vibration testing. Uncertain parameters of the finite element model are then revised through systematic comparisons of the measured vibration models to those that are predicted by the model. The revised finite element model is used to predict the time history response for displacements and stresses through which the effect of the finite element model updating on model predictions are evaluated. Furthermore, displacements and stresses obtained considering both near and far fault ground motions are then compared. Results indicate that near fault ground motion imposes higher seismic demand on the arch bridge observed in both higher displacements and stresses.

Experimental evaluation of a vibration-based leak detection technique for water pipelines

Abstract Conventional water pipeline leak detection surveys employ labour-intensive acoustic techniques, which are usually expensive and not amenable for continuous monitoring of distribution systems. Many previous studies attempted to address these limitations by proposing and evaluating a myriad of continuous, long-term monitoring techniques. However, these techniques have difficulty to identify leaks in the presence of pipeline system complexities (e.g. T-joints), offered limited compatibility with popular pipe materials (e.g. PVC), and were in some cases intrusive in nature. Recently, a non-intrusive pipeline surface vibration-based leak detection technique has been proposed to address some of the limitations of the previous studies. This new technique involves continuous monitoring of the change in the cross-spectral density of surface vibration measured at discrete locations along the pipeline. Previously, the capabilities of this technique have been demonstrated through an experimental campaign carried out on a simple pipeline set-up. This paper presents a follow-up evaluation of the new technique in a real-size experimental looped pipeline system located in a laboratory with complexities, such as junctions, bends and varying pipeline sizes. The results revealed the potential feasibility of the proposed technique to detect and assess the onset of single or multiple leaks in a complex system.