Head- and Flow-Based Formulations for Frequency Domain Analysis of Fluid Transients in Arbitrary Pipe Networks

This paper discusses the development of a numerical model for a braced excavation to estimate the various design parameters that significantly influence the excavation's behavior. The results of the numerical model were compared with those of a reported case study of a braced excavation in sand, and close agreement between the results was observed. The developed model is used for parametric study to show theinfluenceofdifferentdesignparameters,suchasstrutstiffness,wallthickness,strutarrangementandtheembeddeddepthofthewallonstrut force, maximum moment developed in the wall, maximum lateral displacement of the wall, and maximum vertical displacement of ground surface.Itwasfoundthat,amongallthecombinationsstudied,aparticulartypeofstrutarrangementforaparticularratioofembeddeddepthand excavation depth produces the best possible result. A design guideline is also presented based on the results of this numerical study. DOI: 10.1061/(ASCE)GM.1943-5622.0000207. © 2013 American Society of Civil Engineers. CE Database subject headings: Bracing; Excavation; Displacement; Parameters; Struts; Walls; Bending; Numerical analysis. Author keywords: Braced excavation; FLAC; Stiffness; Displacement; Embedded depth; Design parameters; Strut force; Wall thickness; Wall bending moment.

More than 20% of the bridges in the United States were built more than 50 years ago, at a time in which intense precipitation events were much less common. However, very little work has been done on the use of scour risk-assessment models to assess how climate change increases bridge failure probabilities. This paper develops a risk-assessment framework based on HYRISK, a model developed to assess the probability of a bridge failure due to scour, and illustrates oneway in which current engineering risk-assessment models can be used to quantify the additional risks and expected economic losses associated with a changing climate. Application of this framework to all bridges in the United States that carry vehicular traffic over water finds that economic losses due to climate change factors will increase by at least 15% over current losses and that the expected number of annual bridge failures in the United States will increase by at least 10% over current failures. Climate-based risk measures, such as those developed as part of this study, could be included in asset management systems to help state DOTs prioritize maintenance, operation, and replacement schedules. DOI: 10.1061/(ASCE)IS.1943-555X.0000109. © 2013 American Society of Civil Engineers. CE Database subject headings: Bridges; Scour; Risk management; Climate change. Author keywords: Bridge scour; Risk assessment; Climate change.

Convex equations exist in different fields of research. As an example are the Hazen-Williams or Darcy-Weisbach head-loss formulas and chlorine decay in water supply systems. Pure linear programming (LP) cannot be directly applied to these equations and heuristic techniques must be used. This study presents a methodology for linearization of increasing or decreasing convex nonlinear equations and their incorporation into LP optimization models. The algorithm is demonstrated on the Hazen-Williams head-loss equation combined with a LP optimal operation water supply model. The Hazen-Williams equation is linearized between two points along the nonlinear flow curve. The first point is a fixed point optimally located in the expected flow domain according to maximum flow rate expected in the pipe (estimated through maximum flow velocities and pipe diameter). The second point is the calculated flow rate in the pipe resulting from the previous iteration step solution. In each iteration step, the linear coefficients are altered according to the previous step's flow rate result and the fixed point. The solution gradually converges closer to the nonlinear head-loss equation results. The iterative process stops once both an optimal solution is attained and a satisfactory approximation is received. The methodology is demonstrated using simple and complex example applications. DOI: 10.1061/(ASCE)WR.1943-5452.0000275. © 2013 American Society of Civil Engineers. CE Database subject headings: Optimization; Water distribution systems; Chlorine; Water supply. Author keywords: Convex; Optimization; Water distribution systems; Optimal operation; Successive linearization; Head loss.

Knowledge of reference potential evapotranspiration (PETref) conditions is important for a number of vegetation- and hydro- logical-related applications. Direct estimations of PETref are difficult and require sophisticated instrumentation. The Food and Agriculture Organization (FAO), therefore, proposed a method for the estimation of PETref using only meteorological data. This equation has been widely accepted as the standard method for the estimation of PETref because of its good fit with measured values. Nevertheless, it requires several meteorological variables (e.g., wind speed), which are rarely available. Where such data are not available, its application is hampered. To overcome this problem, a number of simpler, empirical equations requiring only a fraction of the meteorological input variables required by the FAO PETref have been developed. Before using these equations, it is important to evaluate their performance and choose the equation that will have the lowest possible bias in the estimation of PETref. Using daily meteorological observations obtained from seven meteorological stations on the island of Crete (southern Greece), the performance of 13 empirical equations (radiation- and temperature-based) for the estimation of PETref has been evaluated against the estimations of PETref using the FAO equation. Performance was evaluated on a daily and a monthly basis, and five different measures of goodness offit were used. The results showed that when the use of the FAO equation is not possible because of the unavailability of data, some empirical methods can serve as appropriate alternatives. The radiation-based equations generally performed better than those that included only temperature-related input variables. The equations proposed by Hansen and Turc were the most useful because they had an average monthly absolute error ranging from 5.7 to 17.7 mm and 5.5 to 19.2 mm, respectively. DOI: 10.1061/(ASCE)IR.1943-4774.0000283. © 2011 American Society of Civil Engineers. CE Database subject headings: Evapotranspiration; Evaluation; Performance characteristics; Validation; Greece. Author keywords: Evapotranspiration; Evaluation; Performance characteristics; Validation.

Due to the use of many warm-mix-asphalt (WMA) additives in the market, the effect of long-term aging on these WMA mixtures is generally unclear; hence, it is necessary to simulate their performance in the laboratory. The objective of this study was to investigate the influence of various WMA additives on the moisture susceptibility of mixtures containing moist aggregates following a long-term aging process. Mass loss (percentage), indirect tensile strength (ITS) of dry and conditioned specimens, deformation (flow), and dissipated energy values were measured. The experimental design included two aggregate moisture contents (0% and approximately 0.5% by weight of the dry mass of the aggregate), two lime contents (1 and 2% lime by weight of dry aggregate), one liquid antistripping agent (ASA), five WMA additives, and two aggregate sources. A common long-term aging procedure was used in this study. The test results indicated that long-term aging improved the moisture resistance of WMA mixtures regardless of WMA additive, ASA, and moisture content. In addition, aggregate source affected the moisture resistance regardless of WMA additive, ASA, and aggregate moisture content. The effects of various WMA additives on the dissipated fracture energy of unaged mixtures are generally similar except that mixtures with Asphamin have relatively lower dry dissipated fracture energy. In addition, the aggregate type affected the dissipated energy value of WMA mixtures regardless of aging states.

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 computational 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.

The ancient masonry city hall in L'Aquila, Italy (Margherita Palace) that was severely damaged during the L'Aquila earthquake in April 2009 has been subjected to ambient vibration tests to determine its dynamic characteristics such as the natural frequencies, mode shapes, and damping ratios. The processing of ambient vibration responses is performed with three output-only identification approaches: (1) the frequency-domain decomposition, (2) random decrement (RD) technique combined with the eigensystem realization algorithm (ERA), and (3) the natural excitation technique (NExT) combined with ERA. Measurements were made in the palace and in the civic tower using 15 sensors in three different configurations, and the ambient vibration tests involved the simultaneous measurements of longitudinal and lateral vibrations. Lateral vibration modes for the civic tower were identified clearly; a total of five modal shapes and frequencies were identified in the frequency range 0 to 7 Hz. The modal identification in the palace was more difficult because of the severe damage; however, the two bending modes in the perpendicular directions were identified. The comparison of the three experimental techniques shows good agreement, confirming the reliability of the three identification methods. The results of the modal identification have been used to update the finite-element model of the palace. DOI: 10.1061/(ASCE)ST.1943-541X.0000494. © 2012 American Society of Civil Engineers. CE Database subject headings: Historic buildings; Masonry; Finite element method; Vibration; Structural analysis; Earthquakes; Italy. Author keywords: Output-only modal identification; Frequency domain decomposition (FDD); Eigensystem realization algorithm (ERA); Random decrement (RD); Masonry structure; Finite-element model; Ambient vibration; Identification; EMA; Operational modal analysis.

This paper describes an application of the fast multipole boundary element method (FMBEM) in simulating the viscoelastic behavior of asphalt concrete (AC). FMBEM has some merits including easy meshing of complicated geometries, accuracy in solving singular fields, high calculation efficiency, and low data storage requirements. These merits lead to many applications in multiple time-step and multi-inclusion problems, such as prediction of AC creep behavior. In this paper, a fast multipole formulation and an algorithm for two-dimensional linear viscoelastic problems are introduced first. To consider the bonding between the asphalt matrix and aggregates, a viscoelastic interface model is used to simulate the interfacial imperfection. A numerical model of asphalt concrete is then constructed based on image processing techniques, and the model is capable of taking into account the effects of the size and content of the air voids. The creep compliance of AC is predicted by the developed FMBEM arithmetic and subsequently compared with the experimental results. It has been shown that the developed method can describe and simulate the correct creep evolutionary trend of AC. DOI: 10.1061/(ASCE)MT.1943- 5533.0000603. © 2013 American Society of Civil Engineers. CE Database subject headings: Asphalts; Concrete; Micromechanics; Viscoelasticity; Imaging techniques; Boundary element method. Author keywords: Asphalt concrete; Micromechanics; Fast multipole boundary element method; Viscoelastic properties; Image processing technique.

Climate-change-based global sea-level rise is of concern because it contributes to significant loss of coastal wetlands and mangroves and to increasing damage from coastal flooding in many regions of the world. Physical mechanisms that describe the dynamic global climate systems and the effect of this system behavior on sea-level rise are inherently complex. In this study, conducted using systematic analysis of historic data on temperature change and sea-level rise, a linear dynamic system model is proposed to predict global sea-level rise and mean surface temperatures. Unlike the semiempirical approaches proposed in the recent literature, this model incorporates the inherent interaction between temperature and sea-level rise into the model. The resulting model, recognized from the historic data, shows that the rate of sea-level rise is proportional to temperature, and this rise is also a function of the temporal state of the sea level. Similarly, the rate of temperature change is a function of the temporal state of the temperature and is also affected by the sea-level rise. The proposed model is also used to predict the sea-level rise during the 21st century. DOI: 10.1061/(ASCE)HE.1943-5584.0000447. © 2012 American Society of Civil Engineers. CE Database subject headings: Climate change; Sea level; Temperature effects; Dynamic models; Predictions. Author keywords: Climate change; Complex systems; Sea-level rise; Temperature change; Dynamic model.

More pronounced at relatively smaller magnitude events, significant variations to an extent of a factor of two in magnitude (duration) scaling factors (MSFs) explain the need to further study this issue, which is also recognized and recommended by the National Center for Earthquake Engineering Research Group. Inspired from this gap, the main motivation of this study is defined as to (1) compa- ratively assess the validity of existing magnitude scaling models and the accuracy of their predictions; (2) develop robust and practical to use semiempirical magnitude scaling models applied on CRR: separate sets for strain (cyclic mobility) or excess pore pressure (cyclic or flow liquefaction) problems. The writers' excess pore water pressure and shear strain accumulation models were used for the assessment of magnitude (duration) scaling factors. On the basis of the proposed framework, it is concluded that (1) MSFs are not only a function of number of equivalent loading cycles but increase with increasing ru or γmax thresholds and decreasing dilational response (i.e., decreasing relative density and/or increasing effective stress states) of soil layers, (2) significantly different set of MSFs than the NCEER recommen- dations can be estimated for different combinations of γmax (or ru), N1;60;CS, σ 0;0 , (3) for the assessment of critical structures (e.g., nuclear power plants), where significantly smaller shear strain performance targets are needed, use of existing models may produce significantly higher MSFs, leading to unconservative estimates of cyclic mobility potential. DOI: 10.1061/(ASCE)GT.1943-5606.0000596. © 2012 American Society of Civil Engineers. CE Database subject headings: Soil liquefaction; Earthquakes; Pore water; Pore pressure; Strain. Author keywords: Liquefaction; Magnitude scaling factor; Earthquake duration; Performance-based design; Pore water pressure; Shear strain; Number of equivalent uniform stress cycle.

A survey of current literature has revealed that the testing protocol for determining the time of setting of fly ash-soil mixtures is not available. Although the current ASTM standard recommends using the Vicat needle method with a water-to-fly ash weight ratio of 0.35, it was originally proposed for testing the time of setting of cement. The current study showed that the Vicat needle method yielded poor test results for some common fly ashes. Moreover, the water-to-fly ash weight ratio of 0.35 may not be appropriate for some fly ashes because the chemical components are varied in different fly ashes. Therefore, a British fall cone was adopted to determine the time of setting of fly ash paste and fly ash-soil mixtures. It suggests that the best starting water-to-fly ash weight ratio should be at its liquid limit. As the water content increases, the initial and final times of setting of fly ash paste increase accordingly. For the fly ash-soil mixture, the initial and final times of setting decrease as the ash-to-soil weight ratio increases. Finally, a linear correlation was established based upon the water content, ash-to-soil weight ratio, and the ratio of calcium oxide to silicon dioxide present in the fly ash. DOI: 10.1061/(ASCE) MT.1943-5533.0000604. © 2013 American Society of Civil Engineers. CE Database subject headings: Fly ash; Soils; Mixtures; Time factors. Author keywords: Time of setting; Fly ash-soil mixture; British fall cone method.

The soil cement deep mixing method has been used to improve soft clayey soils under embankment loading conditions. A compacted granular fill layer or geosynthetic reinforcement layer is placed over the top of soil cement deep mixed (DM) columns to reduce differential settlement between DM soil and the surrounding untreated soil, which, in turn, increases embankment stability. Typically, in conventional deep mixing methodology, the soil cement columns are closely spaced, indicating large area replacement ratios in the con- struction projects. Such practice could increase construction costs substantially. In this research, a new type of DM column, called a T-shaped DM (TDM) column, was designed and used as an alternative to the large-area-replacement-ratio DM columns employed in the field. Unlike in the conventional column, the cross section of the new column varies along the installation depth. Large amounts of cement slurry are injected and thoroughly mixed with the native shallow soil using specially designed mixing blades. At greater depths, deep mixing methodology is applied only to smaller-diameter columns, resulting in large-diameter columns near the surface and smaller-diameter columns deeper. Field trials were conducted to investigate the performance of TDM column-supported soft ground under embankment loading. For comparison, performance of conventional DM column-supported soft ground under similar embankment loading is presented. Differences in quality control studies and in situ plate loading tests on TDM and conventional DM columns are discussed. Under field embankment loading con- ditions, stress concentration ratio, excess pore water pressures generated in the soft clays, total monitored settlement, and lateral soil dis- placement near embankment toes are analyzed and discussed for both treatments. It is concluded that TDM columns have considerable advantages over conventional DM because they both mitigate settlement and enhance the performance of the embankments while reducing construction costs. DOI: 10.1061/(ASCE)GT.1943-5606.0000625. © 2012 American Society of Civil Engineers. CE Database subject headings: Embankments; Cement; Field tests; Pore pressure; Settlement; Soil mixing; Soft soils. Author keywords: Embankment; Cement; Field tests; Pore pressure; Settlement; Soil mixing; Soft soils.

Analysis of forecasts obtained by a forecasting model called STAFOM, a Muskingum-type model for real-time application, shows that the model provides accurate forecast stage estimates for most of the selected case studies and flood events in the Upper-Middle Tiber River basin in central Italy. However, three main issues affected STAFOM: (1) its kinematic nature, (2) the lateral inflows representation, and (3) the occurrence of sudden fluctuations in water levels observed at the ends of the equipped river reach. Therefore, this simple stage forecasting model is hereby improved by incorporating a methodology relating local stage and remote discharge along river channels. This latter procedure, based on the rating curve model (RCM), is capable of reconstructing a discharge hydrograph at a river site where only the stage is monitored, while the discharge is recorded at another section located far away and for which a significant lateral inflow contribution is expected. Application of the new model, named STAFOM-RCM, to several flood events that occurred along four equipped river reaches of the Upper-Middle Tiber River basin, shows that it improves the stage forecast accuracy both in peak and stage hydrograph primarily for long river reaches, thus allowing consideration of a longer forecast lead time; and hence, avoiding the use of the old two-connecting river branch scheme that amplified the fluctuations in observed water levels. DOI: 10.1061/(ASCE)HE.1943-5584.0000345. © 2011 American Society of Civil Engineers. CE Database subject headings: Floods; Forecasting; Inflow; Case studies. Author keywords: Real time; Flood forecasting; Lateral Inflows; Muskingum method; Adaptive procedure.

Corrosion of high-strength steel wires in a suspension bridge’s main cable has been attributed to the environment within the cable wrapping. A sensor network was developed to monitor and provide information in order to indirectly assess the environmental conditions and the deterioration of the interior of suspension bridge main cables. The overall functionality of both the individual sensors and the monitoring system was tested on a full-scale mock-up cable. The cable mock-up was covered in aluminum wrapping and an environmental chamber was built around it in order to subject the test specimen and sensor network to an aggressive corrosive environment created by cyclic temperature and humidity conditions. The temperature, relative humidity (RH), and corrosion rate levels were recorded by all sensors. The recorded data were analyzed in an attempt to determine general trends and correlations between the environmental variables themselves and their effects on corrosion rates. The recorded temperature fluctuations were highly dependent on the sensor depth within the cable; however, the RH levels were not. During cyclic testing, near-linear temperature increases and RH decreases were recorded close to the cable’s center. The baseline corrosion rate levels were affected by the RH levels, with significant increases in corrosion rates at RH levels greater than 50%. The temperature changes proved to impact the corrosion rates on a cyclic level, with high correlations between the temperature and corrosion rate readings recorded by linear polarization resistance corrosion rate sensors.

This work deals with the simple shear flow of neutrally buoyant, rigid, frictionless spheres immersed in a viscous fluid that exchange momentum through inelastic collisions. It is shown how kinetic theories are able to provide a full analytical description of the flow, once the influence of the viscous fluid is taken into account in a simple way through the dependence of the collisional coefficient of restitution on the Stokes number. This allows the capture of the characteristics of the experiments performed by Bagnold 60 years ago and the interpretation of the macroviscous and inertial regimes described by the same author as the limits for the coefficient of restitution equal to zero and to the value valid in absence of the viscous fluid, respectively. DOI: 10.1061/(ASCE)HY.1943-7900.0000701. © 2013 American Society of Civil Engineers. CE Database subject headings: Shear flow; Kinetics; Rheology; Coefficients. Author keywords: Simple shear flow; Kinetic theory; Granular-fluid mixture; Rheology.