Showing papers in "Ksce Journal of Civil Engineering in 2010"

Estimation of Markovian transition probabilities for pavement deterioration forecasting

Abstract: While it is impossible to estimate when a road section will collapse, the understanding of road section deterioration can help asset managers predict the condition of road sections and take appropriate actions for rehabilitations. Deterioration forecasting modeling is an essential element for an efficient pavement management system. Although the Pavement Management System (PMS) has been introduced and operated for optimal road maintenance since the late 1980s in Korea, some problems for accurate prediction of road deterioration remain due to the quality of pavement performance data and the different pavement structural, material and environmental conditions. In this paper, a methodology to estimate the Markov transition probability model is presented to forecast the deterioration process of road sections. The deterioration states of the road sections are categorized into several ranks and the deterioration processes are characterized by hazard models. The Markov transition probabilities between the deterioration states, which are defined by the non-uniform or irregular intervals between the inspection points in time, are described by the exponential hazard models. Furthermore, in order to verify the validity of the proposed method, the applicability of the estimation methodology presented in this paper is investigated by using the empirical surface data set of the national highway in Korea.

Experimental study on interfacial behavior of CFRP-bonded concrete

Abstract: External bonding of Carbon Fiber Reinforced Plastic (CFRP) sheets has come to be regarded as a very effective method for the strengthening of reinforced concrete structures. The behavior of CFRP-strengthened RC structures is mainly governed by the interfacial behavior, which represents the stress transfer and relative slip between concrete and the CFRP sheet. In this paper, the effects of bonded length, width, and concrete strength on the interfacial behavior are experimentally verified and a bond-slip model is proposed based on the experimental results. From the pull test for CFRP-bonded concrete, it is found that the bond strength increases as the bond width increases and the effect of concrete strength is minor. The proposed bond-slip model has nonlinear ascending regions and exponential descending regions, facilitated by modifying the conventional bilinear bond-slip model. Finite element analysis results of interface element implemented with bond-slip model have shown good agreement with the experimental results performed in this study. It is found that the failure load and strain distribution predicted by finite element analysis with the proposed bond-slip are in good agreement with results of experiments.

Influence of existing tunnel on mechanical behavior of new tunnel

Abstract: By quantifying the displacement and crack propagation during the excavation of a new tunnel constructed near an existing tunnel, the influence of the size of the existing tunnel, the distance between tunnel centers, and the earth pressure coefficient, K on the mechanical behavior of existing and new tunnels was investigated and analyzed. A series of experimental model tests was performed and analyzed. It was found that the displacements decreased and stabilized as the distance between tunnel centers increased depending on the size of the existing tunnel. Consequently, a 3.0D distance between tunnel centers for Model Test I and 1.2D for Model Test II are required conservatively to avoid the tunnels being influenced by each other. It was also found that regardless of the distance between tunnel centers, displacements are reduced and hence the stability of the pillar can be secured as the earth pressure coefficient increases. This fundamental insight provides the basis for a more rational design of closely spaced twin tunnels.

Trend analysis of research and development on automation and robotics technology in the construction industry

Abstract: Attention to development of automation and robotics technology in the construction industry seems to have been growing and there has been an increased awareness of the potential benefits of automation and robotics technology development. Although research and development (R&D) facilitates progress in the state of technology and-in the long run-yields significant savings in time and money for companies that take advantage of it, the costs of R&D in the short term are high and resources are limited. Analysis of trends in existing research is helpful in identifying where further R&D is needed and in suggesting directions for future research. In addition, it can be used to help predict the return on investment in individual technologies. This study was to identify global trends and issues in automation and robotics technology in the construction industry by analyzing papers published in the proceedings of the International Symposium on Automation and Robotics in Construction (ISARC). The results of that analysis show that various research topics are actively researched from the viewpoint of automation in construction and contributed by different countries and regions as well as different types of research institutions.

An integrated system for bridge management using probabilistic and mechanistic deterioration models: Application to bridge decks

Abstract: This paper presents a system for the maintenance management of aging highway bridges that integrates two different approaches for deterioration modeling. Probabilistic state-based/time-based models are used to predict the macro-response of bridge components for network level analysis, while reliability-based mechanistic models are used to predict the micro-response of bridge components for project level analysis. Probabilistic state-based/time-based models are developed using qualitative performance indicators (condition ratings) that are determined through visual inspections to identify the overall condition of damaged components in a bridge network. Reliability-based mechanistic models are developed using quantitative performance indicators (physical parameters) that are determined through detailed condition surveys, analytical assessments, and empirical investigations to identify the extent and severity of specific deterioration mechanisms for safety critical structures and/or highly damaged components. The condition rating data obtained from the Ministere des Transports du Quebec database and the condition assessment of the Dickson Bridge in Montreal, Canada were used to demonstrate the two approaches for predicting the deterioration of concrete bridge decks at the two levels of management of the integrated system.

GA-based multi-objective optimization of finance-based construction project scheduling

Abstract: From a financial management perspective, the profitability of a construction project is connected to the cash requirements of the project and the ability of a company to procure cash at the right time. Line of credit as a bank credit agreement provides an alternative way of managing the necessary capital and cash flow for the project. Today’s highly competitive business environment necessitates comprehensive scheduling with respect to cash providing provisions and restrictions. This paper presents a multi-objective elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) based optimization model for finance-based scheduling which facilitates the decision making process of the most appropriate line of credit option for cash procurement. Finance-based scheduling modifies the initial schedule of the project so that its maximum negative cash flow is limited to a specific credit limit. Furthermore, this paper suggests several improvements to basic NSGA-II and demonstrates how they significantly enhance the efficiency of the model in searching for non-dominated solutions. The proposed model is validated by a designed benchmark problem, and its performance and merits are illustrated through its application to a case example. It is shown that the model can effectively approach to the optimal Pareto set and maintain diversity in solutions.

Effect of suction on unconfined compressive strength in partly saturated soils

Abstract: Unconfined compression tests are performed in this study to evaluate the effect of matric suction on the strength and the deformation characteristics of dynamically and statically compacted silt soils. In order to estimate the suction stress, the change in suction and the volume change of the soil samples are measured, and the relationship between suction stress and unconfined strength is established. Under different conditions of the initial degree of saturation and the dry density in soils, the relationship between suction and the degree of saturation at failure can be expressed by a unique soil-water characteristic curve. This result shows a similar tendency to that of a predicted equation using the same parameters for the soil-water characteristic curves. The unconfined compressive strength is also affected by the suction stress which seems to work as a confining pressure for unsaturated conditions. These results demonstrate that the suction stress can be used for estimating the relationship between suction and the unconfined compression test.

Rheology investigation of crumb rubber modified asphalt binders

Abstract: The incorporation of crumb rubber into asphalt pavement mixes is designed to enhance binder properties through reducing the binder’s inherent temperature susceptibility During the interaction process, crumb rubber particles swell after absorbing a portion of the oils in the binder, resulting in the increase of binder viscosity In this study, the Crumb Rubber Modified (CRM) asphalt binders were produced using virgin binder of Performance Grade (PG) 64-22 and ambient rubber with various concentrations (10%, 15%, and 20% by weight of virgin binder) in the laboratory Rheological analyses (flow behavior, elasticity, loading dependence, and temperature dependence) of the control virgin binder and the CRM binders were conducted using a Bohlin Dynamic Shear Rheometer (DSR) II The results indicated that (1) the use of crumb rubber as a modifier seemed to improve the penetration resistance of the asphalt binder because of the increased viscosity at 60oC, (2) its advantage was more apparent at lower frequencies of loading, and (3) the asphalt binder with higher crumb rubber contents was observed to have better resistance to permanent deformation at higher temperatures and elasticity at lower temperatures

Influence of soil grading on properties of compressed cement-soil

Abstract: Compressed cement-soil block is known as low cost building materials. This paper studies the effects of soil grading and the characteristics of soil on the properties of compressed cement-soil such as compressive strength, dry density and water absorption. Compacting pressure of 10 MPa and 30% binder with respect to cement content of 10% were used. The results obtained from crushed soil particles were better than those from natural soil. Mixture of 35% soil and 65% sand produced the optimum of strength, dry density and water absorption. Strength and dry density increased with the fineness of soil particles. Moreover, soil properties also affect the strength properties of cement-soil. Its strength is significantly reduced with increasing plasticity index or liquid limit.

Comparative long term study of concrete mix design procedure for fine aggregate replacement with fly ash by minimum voids method and maximum density method

Abstract: Replacement of scarcely available natural sand with fly ash has economical and environmental advantages. However due to lack of knowledge people avoid using fly ash at construction sites, which is increasing area under land bank. The paper presents the results of experimental investigation, which indicated about 20% increase in the compressive strength and about 15% increase in flexural strength of concrete by the inclusion of fly ash as a partial replacement of sand as compared to control concrete. Sand was replaced by fly ash by Maximum density method and Minimum voids method. Addition of 0.5% super plasticizer could achieve about 30% increase in the compressive strength and about 20% increase in flexural strength of concrete by the inclusion of fly ash as a partial replacement of sand as compared to control concrete. Results indicated increase in workability for all the cases over control concrete. Concrete with fly ash was also found to be about 25% economical when cost per N/mm2 was compared. Based on experimental results correlations are developed to predict Compressive Strength, Flexural strength, cost per N/mm2, Slump and Dry Density for percentage sand replacement with fly ash.

Instantaneous baseline structural damage detection using a miniaturized piezoelectric guided waves system

Abstract: In recent years, new Structural Health Monitoring (SHM) methodologies with a concept of “instantaneous baseline damage detection” are being developed by many researchers since it has been found that the most of SHM technologies are too vulnerable to environmental and/or operational variations. In this context, this paper presents online instantaneous baseline structural damage detection using a low cost and low power, in-situ piezoelectric guided waves-SHM system. Firstly, four small, low cost and light weight smart Piezoelectric Ceramic (PZT) patches are surface-mounted and assumed to have the same bonding conditions to detect structural defects on an aluminum plate. Then, a miniaturized low power guided waves-SHM system with a Digital Signal Processing (DSP) module is employed for signal generation/excitation, signal sensing, and data processing. The instantaneous baseline damage detection based on Wavelet Transform (WT) and Cross Correlation (CC) analysis is carried out on the DSP module. Finally, effects of Lamb waves due to artificial ‘cut-damage’ at different locations are investigated using both “pitch-catch” and “pulse-echo” wave propagation schemes. Conclusively, this study shows a good potential for online and in-situ crack monitoring on panel structures such as an aircraft wing.

Shear connection system and performance evaluation of FRP-concrete composite deck

Abstract: Strong composition between FRP and concrete is an indispensable prerequisite to achieve the structural integrity of FRP-concrete composite deck. Accordingly, this study evaluates experimentally the behavioral characteristics of such shear connection systems realized by coarse sand coating and concrete wedge. The results show that coarse sand coating develops composite performance close to perfect composition in the shear direction but exhibits weakness against normal split. On the other hand, concrete wedge appears to be an efficient solution to resolve such problem. Therefore, a new shear connection system combining coarse sand coating and concrete wedge has been conceived and test revealed that the new shear connection system provides equivalent static performance together with significantly improved fatigue performance compared to the coarse sand coating composition. Following, the shear connection system combining both coarse sand coating and concrete wedge constitutes an efficient solution satisfying the strong composition requirement for the structural system.

The mechanisms of moisture damage in asphalt pavement by applying chemistry aspects

Abstract: Moisture damage occurring within asphalt pavement causes the pavement to undergo several types of distress, such as stripping, potholes, and others. The durability or integrity related to moisture damage plays an important role in other types of damage or distress, such as rutting and fatigue. The development of a Dynamic Shear Rheometer (DSR) moisture damage test is the result of an effort to estimate the moisture damage in a simple, practical testing setup. As a conceptual supporting step, in turn, this paper provides fundamental, general mechanisms to explain the asphalt-aggregate bond behaviors during wet conditions in a DSR moisture damage test. Shear-thickening and thixotropy are introduced to explain the asphalt-aggregate interface behaviors under wet conditions, in view of a colloidal system. Moreover, the self-assembly concept is introduced with regard to a supramolecular system. Both systems can be associatively applicable because of their conceptual similarities. The analysis of data recorded during wet conditions supports and explains qualitatively the reversible structure of the asphalt-aggregate interface.

Effect of air inlet hole diameter of venturi tube on air injection rate

Abstract: The oxygen concentration in water is a prime indicator of the water quality for human use as well as for the aquatic biota. The physical process of oxygen transfer or oxygen absorption from the atmosphere acts to replenish the used oxygen. This process is termed re-aeration or aeration. Venturi aeration is a method of aeration that has become popular in recent years. A venturi tube allows air bubbles to be inserted into flowing water from air inlet holes and so increases oxygen levels in the water. In the present study, a series of experiments on venturi tubes were conducted to investigate the effect of air inlet hole diameter on air injection. It was observed from the results that air inlet hole diameter on venturi tube played a significant role in air injection and there was an optimal diameter that maximizes air injection. Moreover, a multiple non-linear regression equation was obtained for venturi tubes relating air flow and water flow to Reynolds number, inlet diameter and air inlet hole diameter.

Development of a PDA model for water distribution systems using harmony search algorithm

Abstract: Hydraulic analysis of water distribution systems can be divided into DDA (Demand-Driven Analysis) and PDA (Pressure-Driven Analysis). Many studies have reported the superiority of the PDA over the DDA in the realistic simulation of hydraulic conditions under abnormal operating conditions. Many of the developed PDA models rely on iterative processes to solve the equations, which is a time-consuming task and even worse it is not possible to solve them in some cases. To improve the efficiency of the PDA, the present study proposes a new PDA model which interfaces a hydraulic simulator and an optimization algorithm with a customized searching scheme. The suggested model is applied to differently sized water distribution systems under abnormal operating conditions and its results are compared with ones by the DDA model and two other PDA models. As results, the DDA may generate unrealistic hydraulic results under the abnormal operating conditions while the three PDA models produce more realistic results. Moreover, the suggested PDA model with the new optimization process simulates the hydraulic conditions under the abnormal operating conditions in large water distribution systems efficiently compared to the other PDA models.

Shear Behavior of Rectangular-shaped Asperities in Rock Joints

Abstract: This study addresses the shear behavior of rectangular asperities on rock joints to highlight the role of asperity characteristics related to joint shear behavior. The shear strength and failure mode of a rectangular asperity are theoretically derived from force equilibrium analysis, and the relationship between shear strength and shear displacement of a unit asperity is obtained considering shear mechanisms and asperity characteristics. Two failure modes of a rectangular asperity are determined depending on its shape and critical aspect ratio: a dilative failure mode with an inclination of 45-ϕ f /2 and a non-dilative failure mode with shearing of asperity. The range of critical aspect ratio is 0.15 to 0.32 for general rocks. The shear strength of a rectangular asperity is also determined with peak friction angle, cohesion, basic friction angle, aspect ratio, and normal stress. Direct shear tests on artificial joints are performed to verify the theoretical analysis on a rectangular asperity and to explore the effect of asperity size distribution and progressive failure. Based on the analysis on a unit asperity, various effects, such as asperity geometric distribution, normal stress, and specimen size, are discussed in relation to the shear behavior of rock joints.

Genetic-programming-based modeling of RC beam torsional strength

Abstract: This study investigates the use of Genetic Programming (GP) to model Reinforced Concrete (RC) beam torsional strength. Experimental data of 76 rectangular RC beams from an existing database were used to develop the GP model. The following input parameters, which affect torsional strength, were selected: beam cross-sectional area, closed stirrup dimensions, stirrup spacing, closed stirrup cross-sectional area of one leg, stirrup and longitudinal reinforcement yield strength, stirrup steel ratio, longitudinal reinforcement steel ratio and concrete compressive strength. Moreover, a short review of well-known building codes in relation to the design of RC beams under pure torsion is presented. The accuracy of the codes in predicting the RC beam torsional strength was also compared with the proposed GP model using the same test data. The study concludes that the proposed GP model predicts RC beam torsional strength more accurately than building codes

Application of shear wave velocity for characterizing clays from coastal regions

Abstract: Demand for infrastructure development in coastal regions where the subsurface is often composed of soft clays, results from the desire for rapid industrialization. The frequently encountered coastal soil conditions often call for suitable ground improvement and modification techniques to prepare soft deposits for foundation construction. For appropriate site improvement, several engineering soil properties are desired which require expensive and time consuming field and laboratory testing. Under such circumstances, empirical correlations based on routinely determined soil properties would be very useful and economical in planning of the project. With this as a goal, undisturbed samples from three on-shore and off-shore sites of the coastal regions in India, where major infrastructure projects are being executed, were collected. These samples were tested for physical, chemical, mineralogical and geotechnical characteristics. In addition, shear wave velocity of specimens of these soils was determined by using bender elements. Based on this data, empirical correlations between void ratio, compression index and undrained shear strength with shear wave velocity of clays were developed. Because shear wave velocity can be easily determined in the laboratory, these correlations are found to be valuable for preliminary planning of the project. The utility of these correlations for preliminary characterization of the soft soil has also been demonstrated.

Effect of stress level on the bearing capacity factor, Nγ, by the ZEL method

Abstract: It has been known that soil shear strength parameters are stress level dependent. On the other hand, foundation size has a significant effect on the level of imposed stress on subsoil elements. In this study, the Zero Extension Lines (ZEL) method, which has wide applications in determination of bearing capacity and load-displacement behavior of foundations and retaining walls, is employed to consider the stress level dependent nature of soil shear strength parameters to predict the actual bearing capacity of foundations. The ZEL equations which are capable of considering variations in soil shear strength parameters have been employed to consider their dependency on stress level and solved numerically by a computer code developed for this study. The presented approach has been compared with experimental data showing reasonable predictions when the effect of stress level is taken into account. It is then utilized to develop some design charts showing modified values of N γ , as a function of foundation size and soil properties based on Bolton (1986) equation for stress level effect in cases of smooth and rough base foundations. The charts represent the decreasing tendency in N γ with an increase in foundation size and it shows the decreasing tendency in the reduction rate when the foundation size increases.

Reliability of Galvanostatic Pulse Technique in assessing the corrosion rate of rebar in concrete structures: Laboratory vs field studies

Abstract: Corrosion of rebar in concrete structures is one among the various causes impairing its long-term durability. Precise assessment of corrosion rate (CR) is of prime importance to evaluate the structural safety as well as for estimation of service life of concrete structures. Among the electrochemical techniques, Galvanostatic Pulse Technique (GPT) is very promising for field mapping due to its rapidity. The reliability of GPT in determining the CR under passive and active state of rebar has been carried out using small size laboratory specimens and large scale aged concrete structures. The CR determined by the GPT is compared with the CR obtained by Electrochemical Impedance Spectroscopy Technique (EIST) and weight-loss method. The study reveals that an anodic pulse of 100 μA with a pulse duration of 10 seconds is able to determine the CR from 1–663 μm/y (from negligible to higher corrosion activity) on the rebar network more precisely even up to 65 mm of cover concrete. For instance the rebar corroding at higher rate, the CR predicted by GPT is very close to the CR by weight-loss method whereas it is 20 times less by EIST. In the case of passive state of rebar, the CR predicted by EIST is very close to weight-loss method whereas GPT predicts 10 times higher. In aged structures, the change in microstructure of concrete and loss of moisture from the concrete make the potential of rebar and resistivity of concrete more unpredictable and mislead the status of rebar embedded inside the concrete.

Partnering in construction: Investigation of problematic issues for implementation in Vietnam

Abstract: Partnering in construction industry has been prosperous in recent years. This new approach has been proved applicable to construction projects in Vietnam and other developing countries; however, many problems have emerged during partnering implementation process. This paper has identified some prominent problematic issues of partnering in Vietnam construction projects through a questionnaire survey conduct. Partners’ attitudes governed by commercial pressure and dealing with large bureaucratic organization(s) are the most concerned problems with foreign organizations and local practitioners respectively. Factor analysis has pointed out seven underlying dimensions of problems existing in partnering process. These are: unsuitability of partnering application; lack of commitment to partnering; unfamiliarity with the partnering concept; poor communication between partners; lack of key stakeholders’ involvement; external constraint issues; and failure to compromise. This study could help practitioners in the Vietnamese market to comprehend issues in executing a partnering construction project. The understanding of these issues will increase the chance to succeed in partnering on construction projects.

Solution of the Advection-Diffusion Equation Using the Differential Quadrature Method

Abstract: Differential Quadrature Method (DQM) to integrate the one-dimensional Advection-diffusion Equation (ADE) is presented. This method was applied to two examples and the results were compared with the performance of the Explicit Finite Difference Method (EFDM) and Implicit Finite Differences Method (IFDM). Based on the comparison with the exact solution, and both the explicit and implicit finite difference solutions, it was concluded that the DQM provides similar results but less grid points; besides the results are converged quickly. A numerical comparison for a case in which the exact solution is known, DQM gives closer results to the exact values than EFDM and IFDM.

Frequency design in urban transit networks with variable demand: Model and algorithm

Abstract: The goal of this study is to present a methodology for modeling the transit frequency design problem with variable demand. A bilevel optimization model based on a non-cooperative Stackelberg game is used to describe the problem. The upper-level operator problem is formulated as a non-linear optimization model to maximize demand while considering fleet size and frequency constraints. The lower-level user problem is formulated as a capacity-constrained stochastic user equilibrium assignment model with variable demand, considering transfer delays between transit lines. An efficient algorithm is also developed for solving the proposed model. The upper-level model is solved by a gradient projection method. The gradient of the objective function is calculated at each iteration considering the fixed equilibrium overload delays determined by the lower-level model. The lower-level model is solved by an extant iterative balancing method, which was slightly modified for this study. An application of the proposed model and algorithm is presented using a small test network. The results of this application show that the developed algorithm converges well to an optimal point.

Performance-based value engineering application to public highway construction

Abstract: Public works sector programs such as highway construction and infrastructure projects are increasingly being criticized for delivering projects that fail to meet the following objectives: 1) Achieving expected project goals, 2) Achieving project delivery within a reasonable amount of time, or 3) Costs within their budgeted amounts Performance based value engineering methodology can help to find ways to improve solutions to these problems by providing a measured balance in cost, schedule, and scope via the generation of a large quantity of innovative alternatives This requires a motivated team of multi-disciplined professionals in cooperation with well-established project stakeholders who are stimulated and guided by the appropriate process This study shows the performance measurement based value engineering method and process, and case study applications The authors found that the project can significantly save cost and improve performance of project functions by using the appropriate VE process at the appropriate time In addition, this study shows an example of a VE case study that applies the performance measurement process, which led to a very innovative, less expensive way to provide innovative toll plaza modification project Finally, this study summarizes the benefits and effectiveness of the proposed methodology with recommendations

Regional low flow frequency analysis using Bayesian regression and prediction at ungauged catchment in Korea

Abstract: This study employs Bayesian multiple regression analysis using the ordinary least squares method for regional low flow frequency analysis. The parameter estimates using the Bayesian multiple regression analysis were compared to conventional analysis using the t-distribution. In these comparisons, the mean values from the t-distribution and the Bayesian analysis at each return period are not significantly different. However, the difference between upper and lower limits is remarkably reduced using the Bayesian multiple regression. Therefore, from the point of view of uncertainty analysis, Bayesian multiple regression analysis is more attractive than the conventional method based on a t-distribution because the low flow sample size at the site of interest is typically insufficient to perform low flow frequency analysis. Also, we performed low flow prediction, including confidence intervals, at two ungauged catchments using the developed Bayesian multiple regression model. The Bayesian prediction proves effective to infer the low flow characteristic at the ungauged catchments.

Improved link system between schedule data and 3D object in 4D CAD system by using WBS code

Abstract: Current 4D CAD systems can perform basic functions to construct a 4D simulation to visualize a construction schedule. One important function is to link the schedule to a 3D object because it is the most basic and essential process necessary to create a 4D simulation. Though the link process in existing systems is still somewhat complicated, it can be simplified by changing the information structure of the system. Because the 4D system includes the schedule, 3D objects, and 4D simulations, the database of the system stores various information. Accordingly, information management in a 4D system is an important factor to serve the user’s convenience and to simplify the link between a construction schedule and drawings. This study presents an effective information management methodology, an improved 4D system, using Work Breakdown Structure (WBS) as an information center. The artificial link process to generate a 4D simulation can be simplified by using the same WBS code for both schedule and drawing information. The suggested methodology was applied in a new 4D CAD engine developed in this study and verified by running practical data from a gas plant and a civil engineering project. The developed system enables project manager to generate a 4D simulation at WBS code level. This function can be a useful tool and a new approach to visualize schedule data in a large project.

A Study on the Reinforced Fibrous Concrete Elements Subjected to Uniaxial Tensile Loading

Abstract: The structural response of prisms of cross section 100×100 mm and length of 500 mm constructed with reinforced fibrous concrete and subjected to pure tensile loading has been presented in this contribution. The main focus was to study the effects of adding different metallic fibers in mono and hybrid form in the conventionally reinforced concrete on the tension stiffening and strain development. Two metallic fibers with different geometrical, mechanical and physical properties were investigated: amorphous metallic straight fibers and carbon steel hooked-end fibers. A total of four concrete mixtures: control, single fiber and hybrid fiber reinforced concretes were prepared. The fibers were investigated at content of 20 kg/m3 for single fiber reinforced concretes, and for hybrid fiber reinforced concrete, at content of 40 kg/m3. Through studying load-deformation response of composites and strain development in steel bar and concrete, it has been found that the metallic fibers improve tension stiffening effect and influence significantly the strain development. The effect of two metallic fibers on tension stiffening was seen to be different at different loading stages. On the other hand, when fibers were used in hybrid form, the behaviour of the composite was improved at all loading stages in terms of tension stiffening and resistance to cracking.

Investigations into the influence of object characteristics on the quality of terrestrial laser scanner data

Abstract: In contrast to other existing terrestrial surveying instruments, there are not many benchmark tests available for Terrestrial Laser Scanner (TLS) data quality specifications. This paper presents two possible approaches to the standardization of a TLS point data set. Firstly, the ranging accuracy from an instrument to the object is investigated by comparing measured distances by TLS with those of Total Station (TS). In this case, we use two different slope distances with one being about 25 m and the other, about 50 m in range. Secondly, the comparison of data intensity with six different materials, such as aluminum, a sheet of plywood, resin (black & white), steel (black), and laminate (yellow) is carried out. When comparing the distances measured by TS and those scanned by TLS, the standard deviations (Std.) of differences were found to be about 7 mm (50 m range) and 3 mm (25 m range). In the case of plane-fitting of point clouds, aluminum with white color gave better result than that of others, suggesting that the color of an object affects the intensity value of point clouds. It is expected that these results will contribute to the quality evaluation of TLS point clouds and the selection of standard targets.

Another View of Freight Forecasting Modeling Trends

Abstract: This paper reports on current freight forecasting models used inside and outside of the U.S. Our study first classifies available models into seven classes, and describes important modeling concepts and case studies applying these models. Our study summarizes primary independent variables (inputs) and outputs for these freight models in order to help understand the current status of freight forecast modeling. In addition, we found that a common characteristic of the case studies shows that freight modeling is not always done as a single project at one point in time nor do the most successful studies rely on a single class of the model. Due to resource constraints or evolving freight needs, public agencies can opt to stage their freight model development or combine and remove portions of certain classes as they see fit. Our paper concludes by discussing three types of hybrid models involving commodity supply chains, urban logistics tours, and economic tours which are considered for the future modeling trends.

2D finite element pollutant transport model for accidental mass release in rivers

Abstract: A numerical model to simulate the accidental pollutant transport in rivers was developed using the two-dimensional finite element method. RAM4 is developed as the scalar transport module of the software RAMS (River Analysis and Modeling System) which can provide a graphical user interface for various river topographies and has recently been released as a beta version. The significance of RAM4 is that it is able to treat the pollutant mass itself, which is instantaneously released at a certain point of a river. The development of this ability was motivated by the inadequacy of the previous method, whereby the instantaneous mass release was expressed by defining some initial concentration at a source point. This method is not able to balance the injected mass value in accordance with the numerical time step size and the magnitude of flow velocity at this point. RAM4 was connected with the RAMS graphic user interface so that the source point and the released mass value can be controlled with a user-friendly graphical tool. The hydrodynamic module of RAMS, named RAM2, is currently undergoing beta-testing. Therefore, RAM4 was applied to the real river using the popular hydrodynamic model, RMA2, in TABS-MD. Using the obtained flow field computed by RMA2, the model has been simulated for a number of example scenarios of mass dumping accidents in the Han River of Korea in order to verify the applicability of this method in a real situation.