Página 25 dos resultados de 2122 itens digitais encontrados em 0.029 segundos

‣ Aggregate calibration of microscopic traffic simulation models

Mahanti, Bhanu Prasad, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 101 p.; 3882088 bytes; 3893815 bytes; application/pdf; application/pdf
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The problem of calibration of microscopic simulation models with aggregate data has received significant attention in recent years. But day-to-day variability in inputs such as travel demand has not been considered. In this thesis, a general formulation has been proposed for the problem in the presence of multiple days of data. The formulation considers the day-to-day variability in all the inputs to the simulation model. It has then been formulated using Generalized least squares (GLS) approach. The solution methodology for this problem has been proposed and the feasibility of this methodology has been shown with the help of two case studies. One of them is with an experimental network and the other is with network from Southampton, UK. The results indicate that estimation of day-to-day OD flows is feasible. They also reinforce the importance of having good apriori information on the OD flows and locating the sensors so as to obtain maximum information.; by Bhanu Prasad Mahanti.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.; Includes bibliographical references (p. 97-101).

‣ A client side tool for contextual Web search

Lakshmanan, Hariharan, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 77 p.; 2740426 bytes; 2740233 bytes; application/pdf; application/pdf
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This thesis describes the design and development of an application that uses information relevant to the context of a web search for the purpose of improving the search results obtained using standard search engines. The representation of the contextual information is based on a Vector Space Model and is obtained from a set of documents that have been identified as relevant to the context of the search. Two algorithms have been developed for using this contextual representation to re-rank the search results obtained using search engines. In the first algorithm, re-ranking is done based on a comparison of every search result with all the contextual documents. In the second algorithm, only a subset of the contextual documents that relate to the search query is used to measure the relevance of the search results. This subset is identified by mapping the search query onto the Vector Space representation of the contextual documents. A software application was developed using the .NET framework with C# as the implementation language. The software has functionality to enable users to identify contextual documents and perform searches either using a standard search engine or using the above-mentioned algorithms. The software implementation details...

‣ Underpinning strategies for buildings with deep foundations

Kordahi, Ray Z. (Ray Zahi), 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 54 leaves; 1672022 bytes; 1671829 bytes; application/pdf; application/pdf
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Nowadays, numerous underpinning methods are available to provide safe, fast and practical solutions to nearly any geotechnical problem related to the foundations of a structure. This paper discusses these techniques with an emphasis on grouting and micropiling underpinning systems. Furthermore, some practical case studies such as the current Boston Central Artery Project (Big Dig), where these techniques were adopted, are presented showing the main stages of their construction execution and their main advantages and disadvantages.; by Ray Z. Kordahi.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.; Includes bibliographical references (leaf 54).

‣ Web services @ MIT; Web services at Massachusetts Institute of Technology

Tyagi, Sapna DevendraSingh, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 80 leaves; 3138978 bytes; 3138786 bytes; application/pdf; application/pdf
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There are several useful web services developed at MIT by students, faculty and researchers. However, they are scattered all over MIT. Most people at MIT are unaware of the availability of these web services and hence they cannot leverage them. The thesis provides a solution to this problem called Web Services @ MIT that tracks all the web services scattered over MIT at a single location, with a brief description of the service they provide. Web Services @ MIT is intended to facilitate exploitation of both centrally and locally developed web services in a highly distributed enterprise such as MIT. While there is a compelling need for such a service, no such service is currently available at MIT. Web Services @ MIT is a portal built on top of IBuySpy Portal Solution Kit that allows one to build intranet and Internet application using ASP.NET along with Microsoft .NET Framework.; by Sapna DevendraSingh Tyagi.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.; Includes bibliographical references (leaf 66).

‣ Corrosion resistance of concrete reinforcement

Ward-Waller, Elizabeth, 1982-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 40 leaves; 2650967 bytes; 2653556 bytes; application/pdf; application/pdf
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The objective of this thesis is to investigate the mechanism of corrosion of steel reinforcement in concrete and epoxy coated reinforcing bars as corrosion resistant alternatives. Several case studies explore the durability and deterioration issues for epoxy-coated bars discovered through 30 years of implementation in reinforced concrete structures. The methods for predicting the end of functional service life for structures reinforced with uncoated reinforcing bars and with epoxy-coated reinforcing bars are detailed and tested in a design problem in the final section of this report.; by Elizabeth Ward-Waller.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.; "June 2005."; Includes bibliographical references (leaves 39-40).

‣ Decision aids for tunnel exploration

Karam, Jad S
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 121 leaves; 6441135 bytes; 6446185 bytes; application/pdf; application/pdf
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Tunnels are subsurface passages which are often constructed without removing the overlying rock or soil. It follows that the lack of a priori knowledge of subsurface conditions poses major challenges in their preliminary design and planning. Considerable construction savings may be achieved through the proper collection and interpretation of information obtained through site exploration. However, exploration results are often not completely reliable and site exploration in itself involves a cost. Exploration planning is therefore a process of decision making under uncertainty. Einstein et al. (1978) provide a model that applies decision analysis to the tunnel exploration problem. This thesis first describes the model devised by Einstein et al. and provides numerical techniques for implementing it in a programming package. A package in Visual Basic for Applications is presented which implements the model for a generic tunnel. The thesis concludes by applying the devised package to the North Kenmore Tunnel (Washington State).; by Jad S. Karam.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.; Includes bibliographical references (leaf 121).

‣ Design of a building structural skin using multi-objective optimization techniques

Merello, Riccardo
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 57 leaves; 12808711 bytes; 12808369 bytes; application/pdf; application/pdf
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Multi-disciplinary System Design Optimization was used to design the geometry and to select the materials for the structural facade of a building. A multi-objective optimization model was developed, capable of optimizing the design of the facade on the basis of a lighting analysis of the interior, of a thermal analysis of the cooling loads corresponding to the skin configuration, and of a finite elements analysis of the supporting structure. The system also considers the need for transparency in the facade due to view requirements of the occupants, and the cost of cladding materials. A scalarization approach to MDO, via utility functions, was chosen, and the overall objective function was optimized using Genetic Algorithms.; by Riccardo Merello.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.; Includes bibliographical references (leaves 56-57).

‣ Modeling gap acceptance at freeway merges

Lee, Gunwoo
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 105 p.; 3987482 bytes; 3993185 bytes; application/pdf; application/pdf
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This thesis develops a merging model that captures the gap acceptance behavior of drivers that merge from a ramp into a congested freeway. Merging can be classified into three types: normal, forced and cooperative lane changing. The developed merging model uses a single critical gap function, which incorporates explanatory variables that capture all three types of merging behavior. Thus, the model combines all three types in a single model. The merging gap acceptance model is estimated using the maximum likelihood method with detailed trajectory data that was collected on two freeway sections in California. Estimation results show that the merging gap acceptance model is affected by traffic conditions such as average speed in the mainline, interactions with lead and lag vehicles, and urgency of the merge. Transferability tests for the stability of the model parameters between the two datasets are conducted. The single level gap acceptance model is implemented and compared with an existing gap acceptance model in the microscopic traffic simulation model, MITSIMLab. The results show that the proposed model is better than the existing gap acceptance model.; by Gunwoo Lee.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering...

‣ A consistent segment procedure for solution of 2D contact problems with large displacements

Baig, Muhammed Ali Ifran, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 146 leaves; 5804390 bytes; 5804258 bytes; application/pdf; application/pdf
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Solution of contact problems in solid mechanics using the finite element method is a challenging and non-trivial task. Stable and efficient contact algorithms are required for effective solution of general problems. In this thesis, a general algorithm is presented for the analysis of contacting bodies undergoing large displacements. A sub-segment approach is adopted, which allows the algorithm to pass the contact patch test. Passing the patch test is a fundamental requirement for optimal convergence of the finite element solution. The algorithm is a Lagrange-multiplier based one, with the contact tractions as the additional variables to be solved for. Interpolation orders for which the resulting mixed formulation remains stable and optimal are used to interpolate the contact traction variables. The inequality constraints arising in contact conditions are regularized using the constraint function method. Implicit time integration schemes are attractive for dynamic analysis of structures and solids when the response lies in the lowest few modes. But the schemes then have to be unconditionally stable to be able to utilize reasonably large time step sizes. Widely used schemes that are unconditionally stable in linear analysis, do not remain so in nonlinear analysis. A simple composite direct time integration scheme is presented which remains stable for long duration analyses involving large displacements. The nature of the method also makes it attractive for use in dynamic analysis involving contact. The numerical schemes presented are validated using example problems.; by Mirza Muhammad Ali Ifran Baig.; Thesis (Sc. D.)--Massachusetts Institute of Technology...

‣ Improving supply chain performance by implementing weekly demand planning processes in the consumer packaged goods industry

Rah, Myung-Hyun Elisa
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 63 leaves; 21658364 bytes; 21658022 bytes; application/pdf; application/pdf
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This thesis examines how simple weekly demand planning process can improve inventory levels and customers service levels at the Gillette Company. The processes designed by the project team has been tested and executed in a real production environment. The weekly forecast volumes generated by the demand planning team were successfully deployed by the manufacturing plant throughout the course of the project. By successfully executing this simple demand planning process, the project was able to shorten factory firm periods, eliminate the supply warehouse, and de-link demand plan to trade-flow commitments to improve overall supply chain performance.; by Myung-Hyun Elisa Rah.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.; Includes bibliographical references (leaves 61-63).

‣ Assessing the level of service for shipments originating or terminating on short line railroads

Alpert, Steven M
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 78, [6] p.
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This thesis measures railroad freight trip time and trip time reliability for freight rail shipments involving short lines in 2006. It is based on an underlying MIT study commissioned by members of the short line railroading industry, including the American Short Line Rail Road Association, and RaiLinc Corporation, a company that provides many railroad-related services. The data for this thesis is provided by several short lines through RaiLinc Corporation, which gathers and releases the data. Data from a 90-day window is gathered for 39 shipping lanes spread amongst several short line railroads, with a total of 6,747 movements analyzed. In addition, two shipping lanes of 69 total movements that were provided for preliminary analysis are presented in greater detail. Two short lines have also provided their own multiyear data on car movements. The significant result of this thesis is that there is an average time from shipper to customer of 8.3 days per load, with a standard deviation of 4.3 days. There is an average 2-day percentage, or highest percentage of loads to arrive in any 2-day window, of 44.7%. These numbers represent a moderate increase in trip time and trip time unreliability from the 1990-1991 numbers presented by a 1995 trip time study.; by Steven M. Alpert.; Thesis (S.M.)--Massachusetts Institute of Technology...

‣ A performance-based approach to retrofitting unreinforced masonry structures for seismic loads; Performance-based approach to retrofitting URM structures for seismic loads

Bouchard, Keith M. (Keith Michael)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 59, [47] leaves
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The structural inadequacy of existing unreinforced masonry (URM) buildings to resist possible seismic loading is a serious problem in many parts of the United States, including the Northeast and Midwest. The fact that many of these buildings are deemed historic structures or house critical facilities, like firehouses, emphasizes the need for an effective retrofitting program. The Federal Emergency Management Agency published a performance-based design code - FEMA 356 - in 2000 to use for analyzing and retrofitting existing structures. This code includes procedures for URM buildings. This paper applies these performance-based analysis procedures to a URM shear wall and compares the results to a modified analysis proposed by researchers. The wall is then rehabilitated using two common retrofit methods and again analyzed using the code. Recommendations are made for practicing engineers when evaluating URM structures for seismic loads.; by Keith M. Bouchard.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.; Includes bibliographical references (leaves 58-59).

‣ Earth pressure balance (EPB) tunneling induced settlements in the Tren Urbano Project, Rio Piedras, Puerto Rico; EPB tunneling induced settlements in the Tren Urbano Project, Rio Piedras, Puerto Rico

Abrams, Alejandro J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 73 leaves
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Underground construction of the Rio Piedras section of the Tren Urbano project involved the construction of twin tunnels (6.3m diameter) with Earth Pressure Balance machines in weathered alluvial soil. The depth of the cover over the tunnel crown varies from 13m to 10m. The twin tunnels, which connect the Rio Piedras Station and University of Puerto Rico Station, each have a length of 433 meters. Precast concrete linings offered the final structural support. Ground deformations were monitored throughout the construction of both twin tunnels. Volume loss is defined as the volume of ground loss as a proportion of the final tunnel volume and is measured in the plane perpendicular to the tunnel heading. Volume losses corresponding to the process of tunnel construction are identified in this thesis. Settlement troughs both over single and twin tunnels (when symmetric) are often described by a Gaussian curve. However, previous studies have suggested that the settlement trough due to twin tunnels is not symmetric with respect to the midpoint between the two tunnels.; (cont.) The current research shows that the superposition methods proposed by Suwansawat and Einstein (2007) are able to describe the observed settlement trough of the two bored tunnels with volume losses ranging from 0.9 to 1.8% for each bore. These results are up to a factor of 2 larger than volume losses predicted by empirical methods based on overload factors (Macklin...

‣ Investigation of shear lag effect in high-rise buildings with diagrid system

Leonard, Johan, M. Eng. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 62 leaves
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In the recent years, there have been many new skyscrapers built which soar into new heights. The most efficient building system for high-rises has been the framed tube system. However, the framed tube building suffers from shear lag effects which cause a nonlinear distribution of axial stresses along the face of the building. A particular structural system called a diagrid system has caught the attention of the public. The diagrid system is not a new invention. The idea had been around since 1960 and few buildings have been built with the diagrid system. However, the implementation in a larger scale of such tall building was not practical due to high cost related to the difficult node connections. It is only in recent years that the technology has allowed for more reasonable cost of making the diagrid node connections. Despite becoming the new trend in high-rise structures, there are not many technical publications related to diagrid building system. A recent thesis by Moon (2005) studied the various angles of the diagrid to find optimum angle. He has also reviewed the design considerations for diagrid building. This thesis attempts to build on the study by Moon related to the shear lag effect in diagrid building. Diagrid buildings of different configuration are modeled in SAP2000 and analyzed for shear lag effect and structural performance.; by Johan Leonard.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Pile design using wave equation analysis program application in offshore wind farm

Chauhan, Siddharth
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 leaves
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Pile driving has been of interest to geotechnical engineers for a very long time. Originally, empirical pile driving formulae were used to interpret pile displacements caused by a hammer blow. Smith (1960) proposed a numerical solution for wave propagation in an elastic pile using a finite difference scheme, with lumped mass representation and simple rheological laws for pile-soil interaction. Since then, many significant parameters affecting pile driving have been included in the wave equation analysis. The offshore industry finds much application of pile driving analysis, especially after recent developments in instrumentation and electronic computational tools. Positioning of wind farms offshore and designing a foundation for a floating platform is a challenge to geotechnical engineers. One of the methods to anchor the floating platform is to tether it down to the seabed with help of driven piles. This thesis considers a typical offshore site for designing a driven pile for floating wind farm. The Author has carried out a set of numerical simulations to analyze pile driving at this site using a commercial program (GRLWEAP), and illustrates how this program can be used in pile design.; by Siddharth Chauhan.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Frequency-based response of damped outrigger systems for tall buildings

Gamaliel, Renard
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 90 leaves
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The outrigger structural system for tall buildings is known to be effective in reducing lateral drift under quasi-static wind loading. Although keeping lateral deflection below the required value is certainly important, it is found that in most tall buildings without supplementary damping, the design for stiffness is usually governed by occupant comfort under lateral acceleration. This thesis describes the concept of incorporating fluid viscous dampers in the outrigger system to add supplementary damping into the structure. A 40-story building installed with the variant outrigger system is analyzed for dynamic response due to wind effects such as buffeting and vortex shedding. By constructing an 80-dof discrete lumped mass model, and using a frequency-based response approach, two configurations of dampers, namely series and parallel damping are studied in detail. The effect of increasing damper size to overall achievable building damping is monitored for both configurations. Additionally, design and constructability issues with regards to the implementation of the systems are discussed.; by Renard Gamaliel.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.; Includes bibliographical references (leaf 77).

‣ High density polyethylene (HDPE) containers as an alternative to polyethylene terephthalate (PET) bottles for solar disinfection of drinking water in northern region, Ghana; HDPE containers as an alternative to polyethylene terephthalate (PET) bottles for solar disinfection of drinking water in northern region, Ghana

Yazdani, Iman
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 115 leaves
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The purpose of this study is to investigate the technical feasibility of high density polyethylene (HDPE) containers as an alternative to polyethylene terephthalate (PET) bottles for the solar disinfection of drinking water in the Northern Region of Ghana, in a process know as SOLAIR. This study is in line with the intention of Pure Home Water, a registered non-profit organization in Ghana, to offer a variety of low-cost household water treatment and safe storage (HWTS) products as it continues to grow, including the possibility of offering a solar disinfection product in the future. If successful, SOLAIR is practically advantageous over SODIS, which uses smaller PET bottles, chiefly due to the ability to use a larger water container (2-25L), and one that is more likely to be available in a rural setting, given the widespread use of HDPE jerry cans as water collection and storage vessels in many developing countries. The main idea behind the SOLAIR system is to keep high dissolved oxygen (DO) levels in the water which, in turn, enhances disinfection. A study done by Meyer et al. (2000), in South Africa, showed that regular shaking of the water-filled HDPE container keeps DO at sufficiently high levels to augment disinfection.; (cont.) The SOLAIR results...

‣ Structural blast design

Kieval, Tamar S. (Tamar Shoshana), 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 45 leaves; 1738875 bytes; 1738681 bytes; application/pdf; application/pdf
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Blast design is a necessary part of design for more buildings in the United States. Blast design is no longer limited to underground shelters and sensitive military sites, buildings used by the general public daily must also have satisfactory blast protection. Integrating blast design into existing norms for structural design is a challenge but it is achievable. By looking at the experience of structural designers in Israel over the past several decades it is possible to see successful integration of blast design into mainstream buildings. Israel's design techniques and policies can be used as a paradigm for the United States. A structural design for a performing arts center is analyzed within the context of blast design. Improvements in the design for blast protection are suggested. These design improvements include camouflaging the structural system, using blast resistant glass, reinforced concrete, and hardening of critical structural members. It is shown that integration of blast design into modem mainstream structures is achievable. New techniques and creative problem solving must be used to adapt blast design to work alongside current design trends.; by Tamar S. Kieval.; Thesis (M. Eng.)--Massachusetts Institute of Technology...

‣ Wide-span cable structures

Santoso, Katherina, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 leaves; 3103507 bytes; 3103315 bytes; application/pdf; application/pdf
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In recent years, the application of cable structures in buildings has gained huge popularities. Although cable technology has been established since the 1950s, there is suddenly a surge in the number of its building application starting in the late 90s. This phenomenon is attributed to the recent advances in computational form finding, analysis and construction simulation, which make the design and construction of cable structures simpler and more economical. Although cable structures have been employed for different building applications, this thesis will concentrate only on the use of cable structures in wide span system. Five cable systems: simply suspended cables, pretensioned cable beams, pretensioned cable nets, tensioned straight cable nets and tensegric shells are studied for their mechanical properties and suitability for wide span uses. A case study is presented at the end of each system's description to illustrate its possible application. The paper will then conclude with a presentation of a general design methodology of a cable structure.; by Katherina Santoso.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.; Includes bibliographical references (leaves 69-70).

‣ Evaluating flexibility in railroad construction projects

Oh, Choong Ryun, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 104 p.; 5721659 bytes; 5733985 bytes; application/pdf; application/pdf
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This thesis aims to valuate flexibilities in a large-scale railroad construction project. In general, a railroad construction project involves a large amount of flexibilities due to its long construction period and conflicts among various participants. Therefore, railroad construction projects require investors to examine the feasibility of the project, taking into account managers' ability to make strategic decisions to deal with flexibilities during the construction. However. this important value is not considered in conventional valuation methods, such as Net Present Value (NPV) or Internal Rate of Return (IRR) analysis. This study introduces methods to identify and valuate the flexibilities involved in a project. Decision Tree Analysis (DTA) and Real Option Analysis (ROA) are mainly discussed as primary methods to avoid pitfalls of the conventional valuation methods. DTA helps managers to make future decisions in an effective way by providing graphical diagrams of decision opportunities. ROA appraises the value of mitigating risks by allowing managers to defer investing decisions until a situation that affects a project's success seriously becomes obvious. As a case study, the additional station construction projects in Incheon International Airport Railroad (IIAR) are analyzed to apply the methodologies to valuate the flexibilities. The case study shows that the use of DTA and ROA enables us to visualize the risks...