<p> The premature deterioration of RC structures is a major concern for infrastructure owners. Cracks accelerate the deterioration processes by providing preferential flow paths for water and aggressive agents. Therefore, to accurately estimate the degradation rate, methodologies to account for the effect of discrete and distributed cracks in service life prediction tools need to be developed. To account for the effect of cracks, their effect on moisture transport in concrete needs to be fully understood and quantified. </p><p> The research reported in this dissertation provides more insight to the effect of damage induced by freeze-thaw loading on moisture transport. This study includes an extensive experimental program on moisture transport in saturated and unsaturated damaged cement-based materials. Analytical study and numerical modeling are also used to determine the parameters that have significant effect on the mass transport. Furthermore, new nonlinear parameters are proposed to estimate the freeze-thaw damage in concrete using acoustic spectroscopy technique. Therefore, this study consists of four phases. </p><p> In the first phase, three objectives are studied: (i) how damage affects the saturated and unsaturated moisture transport as well as electrical resistivity of concrete. Conceptual models are developed based on the fundamentals of damage mechanics and fluid transport to analytically describe the effect of damage, (ii) whether one-dimensional analyses based on the Sharp Front Theory can explain the relationship between the saturated and unsaturated moisture transport in damaged concrete, and (iii) which transport property and therefore which measurement method is more sensitive to damage. The results show that damage differently affects each of the transport mechanisms, and saturated hydraulic conductivity is more sensitive to damage as compared to sorptivity and electrical resistivity. The 1D analysis, based on the sharp front theory, does not adequately describe the effect of damage on unsaturated transport. </p><p> In the second phase, damage was induced by freeze-thaw in mortar specimens. Mass transport properties were measured using electrical resistivity, rapid chloride permeability, sorptivity, drying, air permeability, water permeability, and desorption isotherm. The results indicate that the measured effect of damage depends on the mechanisms of transport used in the measurement technique and different techniques provide a different measure of the effect of damage. The water and air permeability are comparatively more sensitive to the presence of damage. </p><p> In the third phase, it is investigated whether classical isothermal unsaturated moisture transport can be used to simulate moisture ingress in damaged mortar and concrete. The results indicate that the unsaturated moisture transport model well simulates early stages of moisture ingress, where capillary suction is the prominent mechanism, for all damage levels. At later stages of moisture transport, where air diffusion and dissolution have significant contribution, simulation results diverge from the experimental results. In the fourth phase, it is investigated whether Nonlinear Impact Resonance Acoustic Spectroscopy (NIRAS) technique can be provided a method, using nonlinear parameter and nonlinear quality factor (Qfactor) parameter, to estimate the damage in the absence of prior knowledge of intact material? </p><p> The outcomes of this work can be used to develop methodologies to integrate the degree of damage measured on concrete structures using non-destructive testing into service life prediction models and therefore more accurately predict the service life of reinforced concrete structures. More accurate service life prediction models can help operators of infrastructure in scheduling the repair and maintenance activities. Service life prediction is a main deriver in life cycle costing and life cycle assessment analyses and therefore developing more accurate service life prediction models can help to more accurately quantify life cycle cost and environmental emissions and implications of concrete infrastructure. </p>

<p>This thesis addresses the difference between design camber predictions using the Precast/Prestressed Concrete Institute (PCI) methodology and constructed camber predictions for precast prestressed box girders. Existing bridges constructed with box girders with a range of spans, depths, sections, and fabricators are field measured for camber. A statistical analysis of the field data is preformed to compare design versus constructed camber. Revised multipliers for design are calculated based on statistical distributions of the field data. Additionally, girders are selected from various bridges and analyzed theoretically for camber using the Tadros equation. The girders are also analyzed for consideration of the two-stage pour sequence that is common in the construction of box girders in Colorado. The field data cambers and theoretical cambers are compared and analyzed. Recommended multipliers and high and low multipliers are found. The multipliers are found to be lower than the PCI and Martin multipliers and are recommended to be 1.65 for the prestress camber and 1.70 for the self-weight deflection. </p>

<p> Shear beams and shear walls were constructed using varying amounts of steel fibers and rubber to determine the effect of these constituents on concrete when subject to shear loads and reversed cyclic loadings. 22 concrete beams were tested using mixes with differing amounts of fibers and rubber. The beams were designed to fail in shear by applying a single downward point load at midspan using a MTS Universal Testing Machine. Using the recorded load and displacement data the behavior of each beam and the shear strength contribution for each mix were determined. For all mixes that included fibers and/or rubber the shear strengths increased 12% to 56% in comparison to the plain concrete mixes. Four concrete walls were also tested using four of the 22 beam mixes. The four selected mixes were chosen based on the comparable compressive strengths and mix constituents. The walls were designed to fail in shear by applying a lateral load to a top block cast on top of the shear wall. The walls were tested on a modular strong-block test system within a rigid steel frame so that the load could be applied by a hydraulic actuator. During testing, the displacement at 10 selected locations, the loads placed on the walls at each displacement, and the behavior were recorded and analyzed. The walls containing rubber experienced lower strengths, a brittle failure with severe spalling and damage, and dissipated a low amount of energy. The walls containing fibers exhibited strain hardening characteristics leading to a ductile failure mode, higher strengths, and little web damage. Using the findings from this study, it can be concluded that both fibers and rubber can be used to increase shear strength but only fibers were found to be a viable option for application in walls subject to reverse cyclic loadings.</p>

<p> The decision-making process used by construction foremen at a job site when the workflow is disrupted was investigated in this study. The foremen&rsquo;s decision-making process was mapped and then modeled to a heuristic model. This study focuses on cognitive decision or psychological heuristic models. The study shows that construction foremen use a heuristic decision model in their decision-making. The capability of heuristic to yield fast decision is very useful in construction because it is common for a construction foreman to experience several disruptions during the course of a single workday. With heuristic decision-making, a work-around decision can be rapidly and effectively made following a construction site disruption. Understanding the ability of heuristics to facilitate rapid and effective decision-making will help the construction industry to save time and increase productivity. </p><p> Research was conducted in order to map a decision process that foremen were using in their decision-making and to develop a model for a heuristic decision-making process. Interviews were conducted with 22 construction foremen in the electrical trade in 88 real disruption cases in order to understand how decisions were made after disruptions occurred. Interviews were subsequently conducted with 10 additional industry foremen in 10 real disruption cases to validate the data. Using this data, a heuristic decision-making model was developed. To validate this model, a survey was conducted with another 11 industry foremen. The findings indicate that construction foremen currently use a heuristic decision-making model known as &ldquo;determinant decision attribute&rdquo; (referred to as DDA) heuristics model. This DDA heuristic model was compared to the similar model with equal weighing and elimination by aspects (referred to as EW/EBA) to assess the performance of the heuristic. The DDA heuristic model correctly predicted, on average, 91% of the time what foremen&rsquo;s decisions were as to which decision task to choose to assign or re-assign to crew members. Whereas, the EW/EBA model correctly predicted, on average, 82% of the time, the foremen&rsquo;s decisions. A computer program was also developed for DDA heuristic model to help foremen expedite the process of their decision-making.</p>

A Cast Modular Ductile Bracing System (CMDB) has been developed as an alternative to special concentrically braced frames. The CMDB system introduces cast components at the ends and center of the brace in an attempt to produce a system with reliable strength, stiffness, and deformation capacity. A cruciform cross-section has been chosen for the cast component geometry, which is specially detailed to enhance energy dissipation and increase low cycle fatigue life thereby reducing the likelihood of fracture. In this dissertation, capacity design parameters are established that describe the axial strength and flexural strength of the cast components relative to the main hollow structural section member. These parameters are varied in 2D finite element models to understand the nature of the system and identify the best performing designs. The cruciform shape of the casting is varied to produce better performance and self-centering enhancements are introduced. 3D FE models of the CMDB system and a typical special concentrically braced frame, in combination with fracture indices, are used to compare the expected low cycle fatigue life of the two systems. The dynamic performance of the system is assessed through nonlinear finite element anaylses and conclusions are drawn. The performance of the system is proved experimentally.

No description available.

<p>The construction of the consecutive weirs and excavation along the Nakdong River in Korea changed many channel characteristics such as longitudinal slope, cross-sectional area, water stage which led to changes in erosion and sediment transport patterns. It is now necessary to assess the sedimentation problem upstream of the weirs and seek a way to mitigate the problem. </p><p> The study site of Sangju Weir has been selected for this study because it is a representative site for these types of problems and because sufficiency and availability of data. The purpose of this research is to: (1) estimate incoming sediment yield, define the trap efficiency and estimate the reservoir sedimentation rates of weirs and low-head dams using the Flow-Duration and Sediment Rating Curve (FD/SRC) method, along with the Series Expansion of the Modified Einstein Point Procedure (SEMEPP) to determine the long-term sediment yield for Sangju Weir from suspended load concentration measurement; (2) find the B/C ratio and break-even point between hydropower production revenues and sediment excavation costs using a Benefit and Cost Analysis (BCA); (3) suggest new operation rules for Sangju Weir and propose a systematic analysis procedure to find a better operation rules for mitigating sedimentation problems using the Multi- Criterion Decision Analysis (MCDA) method. </p><p> First, in this study, the Integrated Reservoir Sedimentation Estimation Procedure (IRSEP) was proposed to estimate the reservoir sedimentation at weirs and low-head dams. IRSEP integrates all conventional methods related to reservoir sedimentation: (1) Flow-Duration (FD), (2) Sediment-Rating Curve (SRC), (3) Series Expansion of the Modified Einstein Point Procedure (SEMEPP), and (4) Trap efficiency (TE), in order to estimate reservoir sedimentation rate. Steps (3) and (4) constitute the new elements of this type of analysis. Through stream flow runoff modeling and channel geometry analysis, the trap efficiencies in accordance with certain stages were defined. The trap efficiency of Sangju Weir was calculated for each sediment size fraction as a function of the variables, sediment load at daily discharges and particle size distribution of the sediment transported by the Nakdong River. The trap efficiency is also dependent on channel geometry, inflow discharge and reservoir stage determined by the operation rules at Sangju Weir. Then, the amount of reservoir sedimentation was calculated by multiplying the annual sediment load with trap efficiencies, which vary with discharge and water stage. As a result, the reservoir filling rates were examined. Second, the B/C ratio and break-even point between hydropower production revenues and sediment excavation costs were estimated using a Benefit and Cost Analysis (BCA) method based on daily-modeling. It is essential to determine the effects of the reservoir operation rules using the Multi-Criterion Decision Analysis (MCDA) technique in order to seek improvement in the operation rules to mitigate sedimentation costs, simultaneously considering the other decision makers&rsquo; interests. Finally, new operational rules for Sangju Weir and a systematic analysis procedure were proposed. </p><p> The conclusions of this research are summarized as follows: (1) the total incoming sediment load and the average trap efficiency (TE) at the lowest (EL37.2m) and highest (EL47.0m) stages were estimated as 425,000 tons/year, 50.1 % and 78.1%, respectively; and the maximum annual amount of reservoir sedimentation at Sangju Weir was estimated as 332,000 tons/year (207,000 m³/year) which corresponds to 0.76 %/year of the total reservoir storage of Sangju Weir. On the contrary, the minimum reservoir sedimentation rate was 0.49 %/year, which was come when the water stage was the lowest (EL37.2m). (2) Since the operation rules of Sangju Weir affects significantly the trap efficiency, a Benefit and Cost Analysis (BCA) based on daily-modeling was performed in order to find the break-even point between hydropower production revenues and sediment excavation costs. For daily sediment transport modeling, historical and predicted reservoir stream flow data (2015&ndash;2034) were generated by Tank model using seventy-six daily precipitation data. The B/C ratio obtained 20 years of daily simulation was calculated as 2.28. Also, the discharge and stage thresholds, balancing both hydropower production revenues and sediment excavation costs, are found as 600 m3/s and EL43.6m, respectively. (3) based on the daily Multi-Criterion Decision Analysis (MCDA) modeling, the most favorable Sangju Weir operation rules to mitigate reservoir sedimentation were found in Alternative 5 after including seasonal management of stage control according to the magnitude of the upstream inflow. [table omitted]</p><p> The systematic analysis procedure, the combination of the Integrated Reservoir Sedimentation Estimation Procedure (IRSEP) and the Multi-Criterion Decision Analysis (MCDA) method, are deemed useful to find optimum operation rules of weirs and low-head dams, which can mediate the disputes among various decision makers who have different interests related to reservoir operation. The proposed methodology could be applied to the other weirs of the Four River Restoration Project, and elsewhere. (Abstract shortened by ProQuest.)</p>

<p> This thesis presents the construction sequence of a liquefaction tank for simulating liquefaction for observation and laboratory testing. The project consists of constructing an acrylic tank to hold sand, a water reservoir, casting a porous stone to allow even water distribution, installing a pipe system and pump for water flow, manufacturing lateral support braces, and modifying a steel cart to install the whole assembly. </p><p> Sand collected from Junipero Beach within the city of Long Beach is used as the testing media in the tank. Sand collected at this location shows favorable liquefiable gradations and is located within a liquefaction hazard zone. Laboratory testing using the proposed liquefaction tank demonstrated that this apparatus is functional and able to induce liquefaction on the sample of Long Beach sand.</p>

<p> Cofferdams are often employed as temporary watertight structures made of sheet piles and internally braced with steel or reinforced concrete ring beams to retain surrounding soil. For urban cofferdam excavations, soil removal is performed following a bottom-up performance and concrete shear walls and foundations are installed in rock or competent soil. The main goal of this study is to compare the observed performance of two cofferdams projects and conduct a series parametric analysis to study the effects of installation activities of steel ring beams. The first case history is the One Museum Park West (OMPW) and the second is the construction of a cofferdam of a structure projected to be the tallest building in America and the deepest basement built in the city. These two cofferdams evidence the need of a strict deformation control plan applicable to every construction stage, including those considered as ancillary.</p>

Potentially high risk medical procedures are performed in hospital operating rooms (ORs) across the country on a daily basis. There are detailed and stringent procedures in place for routine practices, such as handwashing and instrument sterilization, and for the HVAC (heating, ventilation and air conditioning) systems, such as controlling humidity and ventilation rates. To maintain the sterile conditions, ventilation rates, measured in air changes per hour (ACH), are understandably higher than any other hospital space. While the highest air change rates may be required to provide a quality indoor environment to minimize the risk of surgical site infections (SSIs), there are significant capital and operating costs associated with these requirements. The ventilation requirements for ORs have increased over the past 10 years with minimal data to support that more air provides cleaner conditions. We hypothesized that a test of the air quality utilizing dynamic, surgical procedures would provide evidence showing increased ventilation does not necessarily provide cleaner conditions. The costs were estimated based on actual energy usage, while the air quality metrics were Environmental Quality Indicators (EQIs). This enabled a comparative analysis of the costs and benefits of different air change rates in an operating room to assist in defining the optimum air change rates. To compare the air quality in ORs under realistic conditions, a testing protocol using EQIs was developed and implemented by an interdisciplinary team, including medical clinicians, air quality experts and engineers experienced in ORs. The testing included a âmockâ surgical procedure directed by a Board certified surgeon in three actual operating rooms using standard gowning and sterilization practices with experienced staff to simulate actual conditions. The results showed that the air quality was significantly better at 20 ACH than at 15 ACH, but did not significantly improve at 25 ACH. The additional operating costs for 5 ACH at the typical facilities tested was approximately $4000 per year per operating room. For academic medical centers and hospital systems with many ORs, this could be significant savings, but the cost must be weighed against the risk of potentially increasing surgical site infections (SSIs).