Thesis: Ph. D. in Environmental Chemistry, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 125-141). / Atmospheric aerosols are important due to their adverse effects on human health and their direct and indirect radiative effects on climate, which are significant and very uncertain factors contributing to global climate change. In estimating the direct radiative effect (DRE), the absorption from carbonaceous aerosols, including black carbon (BC) and brown carbon (BrC, a component of organic aerosol, OA), are highly uncertain. This thesis addresses this uncertainty by combining models and observations to better constrain the optical properties and radiative impact of carbonaceous aerosols. First, a global model simulation (GEOS-Chem) of BC is expanded to separately treat both the aging and physical properties of BC from different sources. By combining model and observations, the global BC lifetime is found to be overestimated in previous investigations, leading to higher estimates of its warming potential. The DRE of BC is estimated to be less than one quarter of the previously reported value. Second, a new method is developed to derive BrC absorption from measurements and used to identify BrC from total absorption observations. The absorption efficiency of BrC is found to be positively correlated with the emitted BC/OA mass ratio, which is related to combustion conditions. In addition, measured BrC absorption from biomass burning plumes is found to decrease with photochemical aging with a lifetime of one day. Third, a global model simulation of BrC is developed and tested against BrC absorption measurements from aircraft campaigns in the continental United States. The BrC absorption properties from biomass burning estimated based on laboratory measurements are found to overestimate the direct measurements of ambient BrC absorption. In addition, applying a photochemical aging scheme for BrC improves the model skill. The simulation suggests that the DRE of BrC has been overestimated previously due to the lack of observational constraints from direct measurements and omission of the effects of photochemical aging. Finally, the influence of mixing state on the global absorption of carbonaceous aerosols is estimated through simplified model experiments. This thesis suggests that policies for reducing emissions of carbonaceous aerosols may have a limited impact on mitigating global climate warming. / by Xuan Wang. / Ph. D. in Environmental Chemistry

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002. / Includes bibliographical references (p. 280-287). / High performance cementitious composites (HP2C) are a new generation of fiber reinforced cementitious composites (FRCC) with substantial improvements in mechanical behavior. The most important development in these HP2C materials may be the nearly elasto-plastic ductile behavior, which allows safe exploitation of the tensile and shear capacity in structural elements. This thesis presents a comprehensive investigation into the ductility enhancement of HP2C structures. Beginning at the micromechanical level, sources of ductility are examined and micro-to-macro relations are derived from homogenization theory and fracture mechanics. These micro-to-macro relations form the basis for a novel 3-D two-phase material model, which captures macroscopically observed behavior. Currently existing models which describe the mechanical behavior of FRCC are often micromechanical in nature. However, this macroscopic approach permits one to model the mechanical behavior of HP2C in a continuous fashion, i.e. through the various states of cracking in HP2C, while capturing - through the two-phase composite structure of the model - the micromechanical sources of energy dissipation in the fiber reinforced composite. / (cont.) The 3-D model is implemented in a finite element program to simulate the behavior of two HP2C applications: a flexural girder and a shear girder, which have recently been tested by the FHWA. It is shown how the two-phase model aptly and accurately predicts the structural behavior of HP2C. Next, a sensitivity analysis of the HP2C model parameters elucidates how changes in HP2C mechanical behavior, observed at material level, manifest themselves at the structural level. By setting limits on the permanent composite matrix strain, which accounts for cracking in HP2C, one can set service limits on HP2C structures.Hence, a comprehensive (micromechanical, macroscopic, and structural) method for the assessment of the ductility enhancement of HP2C structures is presented. A significant scientific benefit of this research is the HP2C model which links micromechanical processes to macroscopic behavior and ultimately to structural behavior. This research also provides a design tool, that is the finite element application, which can be used to predict the behavior of HP2C structures and suggest improvements in HP2C structural and material design. / by Eugene Chuang. / Sc.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2000. / Includes bibliographical references (p. 98-102). / by Luis Tomás Pérez-Prado. / S.M.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1915. / by Alejandro Bibolini, Jacob Cohen. / B.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 77). / The Grand Junction railroad lies at the heart of East Cambridge adjacent to the Kendall Square business district and the Massachusetts Institute of Technology campus. Over the last one hundred years the railroad has gone through substantial changes - from an important freight corridor to having just a few train movements per day. The recent purchase of the railroad by the Commonwealth of Massachusetts, planned relocations of existing freight yards, and future corridor improvements have made it possible to consider the addition of passenger services on the Grand Junction. Rising employment, population, and the congestion of the existing commuter rail facilities necessitate exploration of existing means to alleviate capacity. This study is part of larger study that explores the addition of passenger transit services on the Grand Junction with the goal of increasing frequency and capacity to the west along the Worcester/Framingham main line. The topics of this paper are service alternatives, scheduling, cost and performance. The study outlines all possible alternatives that are then screened for final analysis. Commuter rail and diesel multiple unit (DMU) services are the alternatives quantitatively analyzed. A schedule model estimates the maximum frequency, based on existing constraints, to be five trains per hour. Marginal cost modeling shows that based on estimated demand levels, DMU trains may be a more financially viable option for Grand Junction service. This conclusion is backed up by performance comparison of DMUs and commuter trains, showing that DMUs in the configurations proposed are quieter, more fuel efficient, and would likely have a smaller traffic impact along the densely populated Grand Junction corridor. A substantial and detailed study of DMU service along the Grand Junction is recommended. / by Jesus Iglesias Cuervo. / M.Eng.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2000. / Includes bibliographical references (leaf 134). / by Matthew John Horrigan. / S.M.

Thesis (S.M. in Transportation)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. [165]-167). / Public transport users depend on a reliable level of service on a daily basis. But system disruptions, caused by infrastructure problems, passenger events, and crew duty constraints, can result in reduced reliability for users. Understanding the impacts of those disruptions on customers is vital to evaluating the performance of the system and appropriately communicating delays to passengers. The goal of this thesis is to investigate the impact of certain disruptions on passenger journey times using several new metrics. The thesis has three primary components: First, a description and categorization of incidents that occur on a urban rail transport line over the course of 29 days with some degree of disruption; second, the development of a new measure of impacts on passengers resulting from those incidents using automated fare collection (AFC) data; and third, an exploration of the potential use of AFC data in real-time applications to monitor service. The proposed approach is applied to the Piccadilly Line, one of the London Underground's major rail lines. The line suffers from instances of significant disruption caused by aging technology and infrastructure, but it will not be upgraded for more than a decade. Therefore, insights from existing automated data sources, such as AFC, could play an important role in improving service without capital-intensive improvements. The passenger impact analysis method developed in the thesis relies on dividing the line into sections and aggregating all AFC transactions on all origin-destination (OD) pairs within each section. The resulting disruption impact index summarizes the effects of a disruption on the average passenger for each section of the line. In addition, the accumulation of passengers on a line is introduced as an indicator of delays relating to a disruption. These metrics are each compared with information provided by train-tracking information systems. The methods developed in the thesis were compared with actual passenger notifications on several study days. The results indicate that, despite the methods' limitations, there is potential for using AFC data, along with operational data, to provide more accurate and timely information to the users of the line. The application also leads to recommendations for how the method described for disruptions analysis could be extended to other types of analysis. / by Yonah Freemark. / S.M.in Transportation

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1924. / by Chung W. Chen. / B.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 41-42). / Increased demand for timber construction in the United States has placed a strain on the American timber reserve. At the same time, the annual demolition of thousands of buildings and wood structures results in thousands of tons of waste earmarked for incineration or landfill disposal. There exists a great potential to reuse most of the wood already standing in today's structures for tomorrow's construction. Identifying alternatives for virgin timber can create economic opportunity and help to mitigate an expensive and environmentally sensitive landfill problem. This thesis describes the opportunities, barriers, and benefits of using reclaimed lumber and timbers in new construction. Factors affecting the mechanical properties of wood are examined and changes in strength over time are quantified. Utilizing current research, various sources of reclaimed timber are studied and recommendations are made as to their potential for reuse in structural design. / by James Brandon Davis. / M.Eng.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1995. / Includes bibliographical references (p. 137-144). / by Joseph F. Ahadian. / M.S.