Browsing by Author "Shuler, Scott, committee member"
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Item Open Access Analysis and evaluation of stormwater quantity and quality performance for three permeable pavement systems in Fort Collins, Colorado(Colorado State University. Libraries, 2013) Gruber, Eli, author; Roesner, Larry A., advisor; Grigg, Neil S., committee member; Shuler, Scott, committee memberUrbanization and the subsequent increase of effective impervious area (EIA) result in an increase in storm runoff volumes, peak flow rates and pollutant concentrations. Stormwater management has recently shifted towards a focus on site level low impact development (LID) techniques that aim to reduce the total stormwater runoff volumes in addition to attenuating peak flows and removing pollutants at or near the source of runoff. Permeable pavement systems (PPS) are a subset of LID stormwater best management practices (BMPs) of particular interest in dense urban areas because they can be installed in parking areas and low traffic roadways where the availability of land space for more traditional BMPs is not available. However, few studies have documented the performance of PPS in terms of reducing runoff volume, peak flow and pollutant loads in semi-arid environments such as Colorado. Such information is necessary to improve the selection of BMP/LIDs for stormwater management. Three PPS in Fort Collins, Colorado were monitored between 2009 and 2011 to evaluate pollutant reduction, runoff volume reduction performance and surface infiltration rates. The Mountain and Walnut permeable inter-locking concrete paver (PICP) sites, referred to collectively as Mitchell Block, were each designed with differing "no-infiltration" sub-base designs to compare performance between a system with a sand filter layer (Walnut) and one with only gravel layers (Mountain). The third site, referred to as CTL, is a porous concrete (PC) parking lot that allows full infiltration, and was only monitored for water quality and surface infiltration rates. Mountain, Walnut and CTL all had lower effluent median event mean concentrations (EMCs) than those found at two Fort Collins stormwater outfalls for; total suspended solids (TSS), total recoverable zinc (TR Zn), total phosphorous (TP), total nitrogen (TN), total organic nitrogen (TON), total Kjeldahl nitrogen (TKN) and ammonia (NH3). EMCs for TR copper (Cu), nitrate (NO3) and total dissolved solids (TDS) at all three sites were elevated compared to the outfall sites. The TR Cu result EMCs at the three PPS were elevated compared to effluent PPS data from the International Stormwater BMP Database, which may indicate higher source concentrations in these study areas. CTL had elevated TR chromium (Cr) concentrations, which is likely a function of the portland cement in the PC itself, leaching Cr into the exfiltrate. Walnut had lower effluent median EMCs for 10 of the 13 water quality parameters analyzed, including significantly lower concentrations for TON, TKN and TR Cu. Recorded effluent volumes and estimated influent volumes to the PPS at the Mitchell Block sites were used to calculate runoff volume reduction on an event-based and long-term basis. Both sites provided runoff reduction for over 70% of the monitored events, with Mountain and Walnut reducing 45% and 35% of the total runoff volume monitored at each site, respectively. These results confirm that "no-infiltration" PPS designs are capable of reducing large volumes of storm runoff. Field capacity (water retention capacity) of the two sites was investigated with regard to runoff reduction. Runoff volume reduction at Mountain exceeded the field capacity for the two longest storms monitored. This suggests that runoff volume reduction potential can exceed field capacity given long intermittent rainfall events. An investigation of hydrologic storm parameters indicated a discernible trend between runoff volume reduction and antecedent dry time, showing increasing runoff volume reduction with increasing antecedent dry time. The runoff volume reduction performance at Mountain was greater than Walnut based on 23% greater median and average volume reduction per storm in addition to 25% greater total aggregate volume reduction for common monitored events at the two sites. This study did not investigate the design characteristics that allowed Mountain to provide greater runoff volume reduction. Surface infiltration rates at all three sites were estimated using a single infiltrometer field test. The results indicated that sections of all three sites are experiencing varying degrees of clogging. CTL had the highest degree of clogging, with two of the three tests indicating zero infiltration. Maintenance is recommended to reduce clogging for all three sites.Item Open Access Application of symbolic computing in analysis of modal properties of structurally coupled twin tall buildings(Colorado State University. Libraries, 2011) Richards, Eric Lee, author; Bienkiewicz, Bogusz, advisor; Criswell, Marvin E., committee member; Shuler, Scott, committee memberThis thesis develops non-dimensionalized symbolic expressions for the normalized natural frequencies of two identical tall buildings structurally connected by a skybridge. Symbolic expressions for the modal shapes are also developed to express the coupled movements of the two buildings. The mass and stiffness of the two tall buildings are generalized and reduced to the skybridge level, and the equations of motion are evaluated with Maple 13 math and engineering software. A parametric study of the effects of coupling stiffness on the modal properties is carried out using formulas resulting from symbolic computing. The obtained symbolic expressions are compared with the results of numerical analysis performed using Risa-3D structural engineering analysis software. Findings of this thesis show a good agreement between the symbolic expressions and Risa-3D results. The developed symbolic equations are proposed as a tool for use in the preliminary analysis of tall buildings connected by a skybridge.Item Open Access Disruptive packing of binary mixtures(Colorado State University. Libraries, 2016) Zou, Shuai, author; Heyliger, Paul, advisor; Bareither, Christopher, committee member; Shuler, Scott, committee memberGranular materials are common in many areas such as civil engineering, food industry,and chemistry. The discrete element method has been demonstrated to be an eectivemethod to study the particle dynamics of such materials over the past several decades. Thepacking of monosized spherical particles has been well studied from both numerical andexperimental perspectives. However, the study of packings of a binary mixture that containsparticles of two dierent sizes has been limited because of the numerous variables that aectthe packing structure.The potential variables for packing of binary mixtures of spherical particles blended bygeometric disruptors in a gravity loaded ramp are evaluated in this thesis. The complexity ofthe disruptor geometry was used as the primary variable to study the resulting packing of twodierent-sized particles. The nal packing structure was quantied by coordination number,radial distribution function, packing density, and vertical position of the smaller-diameterparticles. Based on the analysis conducted in this thesis, the mean coordination number ofall particles, larger particles and smaller particles, generally increases with the complexity ofdisruptor geometry. The mean vertical position of smaller particles decrease with an increasein the complexity of the disruptor geometry. The radial distribution function of each type ofparticle in a binary mixture has the same characteristics of the radial distribution functionof mono-size particle packing. The methodology presented in this thesis can be eective toanalyze binary mixtures of spherical particles.Item Open Access Investigation of mechanistic deterioration modeling for bridge design and management(Colorado State University. Libraries, 2017) Nickless, Kyle, author; Atadero, Rebecca, advisor; Jia, Gaofeng, committee member; Shuler, Scott, committee memberThe ongoing deterioration of highway bridges in Colorado dictates that an effective method for allocating limited management resources be developed. In order to predict bridge deterioration in advance, mechanistic models which analyze the physical processes causing deterioration are capable of supplementing purely statistical models and addressing limitations associated with bridge inspection data and statistical methods. A review of existing analytical models in the literature was conducted. Due to its prevalence throughout the state of Colorado and frequent need for repair, corrosion-induced cracking of reinforced concrete (RC) decks was selected as the mode of deterioration for further study. A mechanistic model was developed to predict corrosion and concrete cracking as a function of material and environmental inputs. The model was modified to include the effects of epoxy-coated rebar, waterproofing membranes, asphalt overlays, joint deterioration, and deck maintenance. Probabilistic inputs were applied to simulate inherent randomness associated with deterioration. Model results showed that mechanistic models may be able to address limitations of statistical models and provide a more accurate and precise prediction of bridge degradation in advance. Preventative maintenance may provide longer bridge deck service life with fewer total maintenance actions than current methods. However, experimental study of specific deterioration processes and additional data collection are needed to validate model predictions. Maintenance histories of existing bridges are necessary to predicting bridge deterioration and improving bridge design and management in the future.Item Open Access Reliability assessment of the deteriorating reinforced concrete bridges subjected earthquake and foundation scour(Colorado State University. Libraries, 2016) Ren, Jingzhe, author; Ellingwood, Bruce, advisor; van de Lindt, John, committee member; Shuler, Scott, committee memberThis study assesses the structural reliability of a deteriorating reinforced concrete bridge subjected earthquake and foundation scour during its service life. This study relies on probabilistic models of natural hazards and structural deterioration based on in-service inspection and utilizes methods of time-dependent reliability assessment. The results of the study reveal the potential influences of competing hazards on structural response of bridges over their service lives. The thesis is structured in five chapters: (1) Introduction, including motivation and objectives of the study; (2) Literature review, addressing the background of natural hazards modelling and time-dependent reliability assessment; (3) Methods for modelling natural hazards and structural deterioration of bridges probabilistically; (4) Performance assessment of deteriorating bridges under competing hazards, providing numerical measures of structural reliability for a three-span reinforced concrete bridge based on a finite element model; (5) Conclusion and recommendations, summarizing the main research findings and discussing a possible direction for further studies.Item Open Access Semi-rigid steel frames subjected to mainshock-aftershock earthquake sequences(Colorado State University. Libraries, 2018) Admuthe, Sushant Ajay, author; Mahmoud, Hussam, advisor; Atadero, Rebecca, committee member; Shuler, Scott, committee memberIn a typical seismic event, large number of aftershocks are generally triggered due to the complex interaction within and between tectonic plates. Despite the fact that aftershocks are typically smaller in magnitude than mainshocks, their ground-motion intensity, measured by peak ground acceleration, is not always smaller. As a result, vulnerability of structures to extensive damage and complete collapse as a result of the aftershocks increases. In spite of their in evaluating the true risk of system failure and collapse, the inclusion of aftershocks in code provisions and guidelines for seismic risk assessment and performance-based engineering is lacking. In this study, three semi-rigid frames, with connection capacity of 50%, 60% and 70% of the plastic moment of the beam, were designed and their performance under mainshock-aftershock sequences assessed. The objective of this study, pertaining to the seismic performance of the frames, was twofold. First was to develop fragility functions for the frames under sequential mainshock-aftershock hazards as the basic ingredient for performance-based engineering. Second, was to evaluate the extent of spread of inelasticity and period elongation as a result of the sequential events. The first objective was realized through performing incremental dynamic analysis (IDA) using a new set of ground-motion records, with naturally available aftershock data. Scaling of the aftershocks for the IDA was performed while maintaining the Peak Ground Acceleration (PGA) relationship, established priori, between the respective mainshock and aftershock events. The results showed that the inclusion of the aftershocks increase the probability of reaching or exceeding a particular damage state. The increase in the probability is higher for the complete damage state and lower for the slight damage state. In other words, the probability, of the structure slightly or moderately damaged in the mainshock, to exceed the same damage state is not increased in aftershocks but in the case of extensive and complete damage, there is considerable increase in the probability of exceeding the same damage state in aftershock. In addition assessment of the spread of inelasticity and period elongation, performed using Short-Term-Fourier-Transformation, show that a relationship between the elongated period and connection capacities for different ground-motion intensities can be established.Item Open Access Shear strength and stiffness of a Sahara sand from Libya(Colorado State University. Libraries, 2011) Badanagki, Mahir, author; Carraro, J. Antonio H., advisor; Shackelford, Charles D., committee member; Shuler, Scott, committee memberModern geotechnical analyses rely upon a rigorous characterization of the dilatancy, critical state and stiffness parameters of geomaterials. In order to generate a fundamental database for these parameters for future geotechnical projects in Libya, the shear strength and stiffness of Libyan Sahara sand were systematically studied in drained and undrained axisymmetric compression. The dry funnel deposition method was employed in this study to create homogenous specimens and simulate the natural fabric of aeolian sand deposits from Libya. The fabric of Sahara sand was examined using a Scanning Electron Microscope (SEM). Static, monotonic, isotropically-compressed drained and undrained triaxial tests were performed on specimens with nominal height and diameter equal to 140 and 70 mm, respectively, to characterize the stress-strain-volumetric (or stress-strain-excess pore pressure) response and determine the intrinsic parameters of Libyan Sahara sand. Bender element tests were also performed to measure the shear wave velocity (Vs) and estimate the small strain shear modulus (Gmax) of Sahara sand at mean effective stress levels of 50, 100, 200 and 400 kPa. The intrinsic parameters that characterize isotropic compression, critical-state, dilatancy and small-strain stiffness of Libyan Sahara sand were determined to allow future analyses of mechanical behavior for this soil to be carried out using a rigorous theoretical framework for granular soils. The critical state soil parameters Γ, λ and k of the Libyan Sahara sand were determined to be equal to 1.92, 0.031 and 0.0002, respectively. The critical state friction angle (φc) of the soil was found to be equal to 31.9° based on results from both drained and undrained tests. The value of φc determined from drained tests was found to be in perfect agreement with the value of φc determined from undrained tests, as expected. The intrinsic parameters Q and R of the peak friction angle (φp) correlation (Bolton 1986) were determined to be equal to 8.5 and 0.98, respectively. This allowed prediction of φp values that differed by no more than about 1° from the actual values measured during the triaxial tests performed under a wide range of relative densities and mean effective stresses. The very small strain stiffness parameters Cg, ng and eg of the Libyan Sahara sand were equal to 548, 0.51 and 2.17, respectively. While the Libyan Sahara sand tested has about 25% of nonplastic fines, results from this fundamental study suggest that the isotropic compression, critical-state, dilatancy and small-strain stiffness characteristics of this soil can be reasonably interpreted according to (or predicted by) a rigorous framework that has already been validated for clean sands and/or sands containing fines.Item Open Access Testing of a full-scale mass timber diaphragm(Colorado State University. Libraries, 2018) Kode, Anirudh, author; van de Lindt, John W., advisor; Mahmoud, Hussam, committee member; Shuler, Scott, committee memberCross Laminated Timber (CLT) has only recently garnered attention as a new building material in the United States. Despite being introduced in Europe nearly 20 years ago, CLT is still not used widely in North America. One primarily reason is because CLT is not yet recognized as a structural system for seismically active regions of the U.S. One sub-assembly that has not been fully investigated are horizontal diaphragms for floors, roofs, or bridge decks. This thesis aims to test a single large scale CLT cantilever diaphragm subjected to a simulated seismic load. Data was collected and the behavior of the diaphragm documented to help begin to reduce this dearth of CLT data in the U.S. This data will also assist in refining CLT diaphragm design procedures that have recently been developed. Ten CLT panels were used to build the diaphragm, which was setup as a cantilever beam according to ASTM specifications. A 110-kip actuator was used to apply a concentrated load at one end of the diaphragm while a steel base serving as a fixed boundary condition was at the other end. The CUREE test protocol with a reference displacement of 75.6 mm (3 inches) was applied to the floor diaphragm specimen, which included a number of string potentiometers to collect displacement data. The diaphragm behaved in a predictable manner and the connectors failed in tension first even with a chord designed per the National Design Specification (NDS) for wood. Then the CLT panels separated resulting in a total failure. This data set will be made available to those working on CLT diaphragm provisions for refinement of on-going revisions.Item Open Access The effect of single, shaped surface flaws on ductility in cast aluminum dog bone specimens in uniaxial tension(Colorado State University. Libraries, 2017) Wardwell, Scott L., author; Mahmoud, Hussam, advisor; Atadero, Rebecca, committee member; Shuler, Scott, committee memberDuctile fracture of structural, metallic alloys is of great interest to the engineering community. This interest has sparked many attempts in an effort to describe the fracture process for these ductile materials. The theory that stands out is that ductile fracture is driven by the process of void nucleation, growth and coalescence which, as the name suggests, allows voids to be created through nucleation, then follows their growth and coalescence until material failure occurs. In this process, a damage criterion is often selected and used to model and predict how ductile fracture will occur. While this modeling yields results with enough accuracy to be useable in practical applications, it relies on some initial idealized void geometry. These geometries are usually of cylindrical or spherical nature and do not capture the essence of the actual void geometry of real materials. Surface flaws, on the other hand, are often modeled to mimic their actual appearance in real materials. This being the case, little research has been conducted on actual void geometry or highly specific, three-dimensional surface flaw geometry. This study explores these relatively untouched regions of geometrical interest and their effect on the ductile fracture process through physical testing of specifically shaped surface flaws on structural grade aluminum. Additionally, aluminum demonstrates unique properties with respect to ductility. Other ductile materials often yield in tension then continue to stretch and withstand additional loading up to some maximum material strength then stretch more until eventual failure. Many commercially available grades of aluminum however, fail almost immediately after reaching their maximum material strength. The results from this study are compared so that the effects of the specific shapes on ductility can be seen. The results suggest that, depending on the definition of ductility, it may be possible to easily increase material performance for ductile materials, which demonstrate the unique ductility profile seen in aluminum, by introducing specifically shaped surface flaws.