Seismic Design and Performance of Self-Centering Concentrically-Braced Frames

Chancellor, Nathan Brent Lehigh University 2014 해외박사(DDOD)

Conventional steel concentrically-braced frames (CBFs) are a stiff and efficient seismic lateral force resisting system, but they have limited ductility capacity due to brace buckling, low-cycle fatigue, and fracture. Under earthquake loading, conventional CBFs dissipate energy by yielding and buckling of braces and yielding of gusset plates. This behavior results in significant damage to the CBF after the earthquake and residual lateral drift. A new seismic lateral force resisting system, known as a self-centering concentrically-braced frame (SC-CBF), has been developed and studied by researchers at Lehigh University. The SC-CBF has an arrangement of members that is similar to that of a conventional CBF. The SC-CBF columns, however, are not rigidly attached to the foundation in the vertical direction, which enables the columns to uplift and enables the SC-CBF to rock on its foundation. Steel post-tensioning bars run vertically over the height of the CBF and are stressed to clamp the CBF to the foundation. Energy is dissipated through energy dissipation devices instead of through yielding and buckling of the CBF braces. The ductility capacity of the SC-CBF is increases compared to that of a conventional CBF, by enabling the CBF to rock on its foundation. The SC-CBF lateral force resisting system has been studied and a first generation design procedure for SC-CBFs has been developed. A laboratory testing program at Lehigh University tested a 4-story, 0.6-scale SC-CBF using hybrid simulation. The 4-story SC-CBF was subjected to 31 intense earthquakes at both the design basis earthquake (DBE) intensity level as well as the maximum considered earthquake (MCE) level. The SC-CBF performed very well. The first generation design procedure was developed through the study of 6-story SC-CBFs, but it is uncertain how well this design procedure would work for SC-CBFs with a greater number of stories. It was also not well understood how the behavior of the SC-CBF system would change as the height increases. This research investigates the seismic performance of SC-CBF structures across a range of heights, studies the accuracy of the first generation design procedure, studies the parameters influencing the peak member forces and peak drift demands for SC-CBFs under the DBE, and develops and validates a second generation design procedure for SC-CBFs that adequately predicts peak member forces and peak drift demands under the DBE for SC-CBFs across a range of heights. The effect of ground motion selection on the performance of the SC-CBF system in nonlinear time-history analysis was also studied. Finally, a comparison study was performed with conventional CBFs to understand how SC-CBF behavior might impact the performance of nonstructural systems. The results of these studies indicate that, while the SC-CBF system is useful even for taller structures, its effectiveness at limiting member force demands, as currently configured, generally diminishes with increasing height. The correlation between modal responses was studied and shown in many cases to be widely varying. A new modal combination technique and associated modal correlation coefficients are proposed to account for the correlation between the modal responses and to adequately predict peak member force demands. It is shown that considering both the foundation flexibility and second order effects are important for estimating peak drift demands, particularly for SC-CBFs less than 6 stories. It is also shown that using accepted techniques for selecting and scaling ground motions to the seismic hazard may not lead to an accurate estimate of the largest SC-CBF response for a given hazard level. A second generation design procedure for SC-CBFs is proposed and validated to show that it is capable of adequately estimating peak member force demands and peak roof drift demands under the DBE across a range of heights.

A Mixed Methods Study of Changes in Student Global Leadership Competency Development Through a Short-term Global Leadership Program at a Research University

Gravelle, Christine A Lehigh University ProQuest Dissertations & Theses 2020 해외박사(DDOD)

Global leadership has been identified as one of the premier aptitudes that students should learn before they enter the global workforce, and developing these competencies in global citizens has become a theme in universities. A popular method of learning these global leadership competencies is through short-term, immersive experiences. The purpose of this study, looking through the lens of intercultural effectiveness and experiential learning theory, was to compare how students’ global leadership competencies change after participating in a short-term, non-credit bearing, global leadership exchange program at a large, research university in the south. This mixed methods study compared students’ global leadership competencies utilizing a pre-post established assessment, the intercultural effectiveness scale, and written reflections. Although this study utilized a small sample size (n=12), and the findings of the quantitative data did not show statistically significant changes from pre-trip to post-trip (n=7); the reflections (n=8) confluence with the quantitative results captured participant themes of global leadership and global leadership competency development specifically around continuous learning, interpersonal engagement, and hardiness. Participants identified that an important component of the learning experience was the engagement with people from a different culture. This research can assist students, faculty, and staff in understanding how students articulate the importance of global leadership and global leadership competencies. This study can also support university administrators develop and implement an intentional global leadership development program using both quantitative and qualitative methods.

Perceptions of children of international school educators: An exploratory study of Third Culture Kids

Zilber, Ettie (Ethel) Lehigh University 2005 해외박사(DDOD)

What can be learned about the life experiences of TCK children of IS educators who have been raised in IS outside their home country? Perceptions of Adult Third Culture Kids (ATCKs) were explored as they reflected on their experiences as children of IS educator parents. A public call to professional associations resulted in a data base of potential participants from which six were selected according to: age 18--26, North American nationality, two parents employed in IS during child's adolescence, and current enrollment or graduation from university. Qualitative methodology elicited responses through guided interview and follow up questions which were sent and received via email. Four counselors with rich experience in IS were interviewed, for triangulation. Four themes emerged from the six case studies: (a) extremely tight bonds and relationships within educator families, (b) ambivalence about life experiences, (c) sensitivity to multiple and intersecting roles in IS community, and (d) positive achievement, attitudes and adjustment. Findings. (a) The plurality of roles is omnipresent, (b) The management of role plurality develops sensitivity to role diversity, (c) The intersection or blurring of roles causes ambivalent feelings, such as, well being, advantage, security and happiness, and, confusion, awkwardness, angst and frustration. The higher the visibility of the parent the greater the negative feelings of the child, particularly in secondary school, (d) The family bond has a deeper dimension than for other expatriate families, (e) The participants were proud, aware and appreciative of their parents' careers, (f) The relationships forged with other educators functioned like a surrogate extended family, (g) The adjustment to university relocation was due to a combination of factors, (h) The attitude toward the host nationals came from parent modeling and school profile, (i) The participants were high achievers and active in extra-curricular activities; 33% chose a career in education, (j) The IS orientation for new families had a long term impact on attitudes toward the sponsoring group. Implications. Findings may help educators make informed decisions about an overseas career. They may potentially impact recruitment, retention of educators in international schools and orientation and counseling of all members of the international school community. They may help administrators, counselors and colleagues better understand the educator-family unit. Conclusions and recommendations may help inform relationships among the IS community constituents.

Computational and theoretical studies of globular proteins

Pagan, Daniel L Lehigh University 2005 해외박사(DDOD)

Protein crystallization is often achieved in experiment through a trial and error approach. To date, there exists a dearth of theoretical understanding of the initial conditions necessary to promote crystallization. While a better understanding of crystallization will help to create good crystals suitable for structure analysis, it will also allow us to prevent the onset of certain diseases. The core of this thesis is to model and, ultimately, understand the phase behavior of protein particles in solution. Toward this goal, we calculate the fluid-fluid coexistence curve in the vicinity of the metastable critical point of the modified Lennard-Jones potential, where it has been shown that nucleation is increased by many orders of magnitude. We use finite-size scaling techniques and grand canonical Monte Carlo simulation methods. This has allowed us to pinpoint the critical point and subcritical region with high accuracy in spite of the critical fluctuations that hinder sampling using other Monte Carlo techniques. We also attempt to model the phase behavior of the gamma-crystallins, mutations of which have been linked to genetic cataracts. The complete phase behavior of the square well potential at the ranges of attraction lambda = 1.15 and lambda = 1.25 is calculated and compared with that of the gammaII-crystallin. The role of solvent is also important in the crystallization process and affects the phase behavior of proteins in solution. We study a model that accounts for the contribution of the solvent free-energy to the free-energy of globular proteins. This model allows us to model phase behavior that includes solvent.

"This damned business of colour": Passing in African American novels and memoirs (Charles Waddell Chesnutt, James Weldon Johnson, Nella Larsen, Shirlee Taylor Haizlip, Judy Scales-Trent, Gregory Williams)

Negrea, Irina C Lehigh University 2005 해외박사(DDOD)

The topic of this dissertation is an analysis of racial passing, as depicted in the novels The House Behind the Cedars by Charles Chesnutt, The Autobiography of an Ex-Colored Man, by James Weldon Johnson, and Passing by Nella Larsen, as well as in the memoirs The Sweeter the Juice by Shirlee Taylor Haizlip, Notes of a White Black Woman by Judy Scales-Trent, and Life on the Color Line by Gregory Williams. Starting from the premise that passing is a complex phenomenon that reinforces and subverts the racial system simultaneously, this dissertation focuses on the subversive side of passing that comes to light especially when the passer is found out---a side that becomes obvious in the reactions it provokes in white racists: horror, fear, disgust, and insecurity. One other new element that this dissertation brings into the field is a classification of passing that can be used as a tool for the analysis of similar literary works. The majority of passers fall into one of two categories: identificatory and performative. Identificatory passing is predicated on the passer's identification with the white ideology. It is permanent, and the passer breaks all ties with his/her African American ancestry. At the other end of the spectrum is performative passing, based on the view of race as performance---a matter of props, makeup, and/or behavior. The passer crosses the color line and "acts" white, but in most cases, s/he does not break his/her ties with his/her African American roots and community. Rather, the performative passer tries to acknowledge both his/her racial identities, refusing to be boxed in one narrow racial category. These types of passing do not exist in a "pure" state; there are characters who start as performers of race and end up identifying with whiteness, for example, but the two basic types exist, in one combination or another, in all the stories of passing ever written. These two different types of passing engender different types of subversion of the racial system, and they are discussed as well in this dissertation.

Anelasticity in freestanding aluminum thin films

El-Deiry, Paul A Lehigh University 2005 해외박사(DDOD)

Anelastic deformation is present in all metals, but it is generally negligible in bulk form and at low homologous temperatures. In thin films, anelastic deformation contributes a great deal to the overall mechanical properties. Anelastic deformation is any portion of the total deformation of a body that occurs as a function of time when load is applied and which disappears completely after a period of time when the load is removed. Two major anelastic mechanisms proposed for pure, metal thin films are reversible dislocation glide and grain boundary sliding. Dislocation glide is expected at low homologous temperatures while grain boundary sliding is expected at high homologous temperatures. With increasing grain boundary density (i.e. smaller grain sizes), grain boundary sliding is expected to dominate, and with larger grain sizes dislocation glide is expected to dominate. To investigate this phenomenon in thin metal films, a custom-built microtensile system was designed and fabricated. Uniaxial tensile tests were performed on four different thicknesses (1.00 mum, 0.75 mum, 0.50 mum, and 0.25 mum) of freestanding Al thin films. Strain rate sensitivity and stress relaxation experiments were performed to investigate anelasticity. Film quality turned out to be a major factor in all of the mechanical measurements made, including the ability to observe anelasticity. Uniaxial tensile experiments performed on Al and Cu micro-wires lead to the supposition that a dislocation gliding mechanism is responsible for the observed strain rate sensitivity. Stress relaxation experiments were performed at four different temperatures (38°C, 50°C, 60°C, and 70°C) on freestanding Al thin films. The results indicate that the freestanding films can be modeled by a linear anelastic solid. In addition, a time constant for fast relaxation (<0.5 seconds) was determined at each temperature. From these values, an activation energy was calculated. The small value of the activation energy (approximately 14 kJ/ol) suggests that only one mechanism is operating over the time scale of 0.5 seconds: dislocation glide.

Fatigue strength of AL-6XN stainless steel weldments

Metrovich, Brian Lehigh University 2004 해외박사(DDOD)

This study presents an assessment of the fatigue strength limit state of large scale welded joints fabricated from nonmagnetic AL-6XN superaustenitic stainless steel. Three welded details were tested under constant amplitude loading, subjected to both compressive and tensile stresses. The experimental program included longitudinal fillet welds, transverse groove welds, and simulated bulkhead attachments. Fabrication was of shipyard quality using the GMAW weld process. Two Ni-based weld metals, IN625 and IN622, were used. A total of 66 large-scale I-beams were tested. Over 186 fatigue cracks were observed, resulting in 82 through flange thickness fatigue cracks used in the assessment of fatigue strength, in addition to many uncracked details related to the constant amplitude fatigue limit (CAFL). Discontinuities associated with initiation of fatigue cracks were identified from the fracture surfaces and included: lack of fusion areas at the weld root of longitudinal fillet welds; internal lack of fusion planes, internal volumetric discontinuities, and micro-discontinuities at the reinforcement weld toe of transverse groove welds; and micro-discontinuities (tears or inclusions) at the bulkhead attachment weld toe in combination with regions of sharp weld toe reentry angle. Fatigue strength was evaluated analytically using fracture mechanics concepts. Initial discontinuities and fatigue propagation behavior observed during the experimental program were used to assess the fatigue strength of longitudinal fillet welds and simulated bulkhead attachments. The analytical models attempt to estimate the lower bound finite life fatigue strength curves for the longitudinal fillet weld and bulkhead attachment details, as well as the CAFL. Based on the experimental and analytical results, the following design recommendations were made: (1) Use AASHTO Category B for standard double sided longitudinal fillet welds, with a CAFL of 100 MPa. (2) Use AASHTO Category C for transverse groove welds subjected to nondestructive evaluation to avoid large internal defects, with a CAFL of 83 MPa. (3) Use AASHTO Category E for 200 mm long bulkhead attachments, with a CAFL of 41 MPa. (4) Use AASHTO fatigue classification categories to develop preliminary fatigue resistance curves for details not yet tested with AL-6XN stainless steel.

Metacognition and moral reasoning in the conflict positive classroom

Heydenberk, Roberta Stern Lehigh University 2002 해외박사(DDOD)

The purpose of this study was to determine whether conflict resolution skill development over the period of one school year of training increases students' use of metacognitive strategies and moral reasoning. This investigation was conducted over a four-year period in a low income elementary school in the Philadelphia School District and in two elementary schools in a suburban low income school district in lower Bucks County. Sample subjects were fourth and fifth grade students. Each of the student samples (10 treatment; eight comparison) were reported as group means. The pretest and posttest measures from all treatment and comparison classrooms were pooled and assessed for significant pretest to posttest differences using a one tailed t-test with an alpha level of .05 (Group I). Because significant pretest differences were found between groups for year three in Bucks County, the same analysis was conducted with the eight treatment and six comparison classrooms that showed no significant pretest differences (Group II). In these school settings, treatment group teachers were trained in conflict resolution strategies, and the treatment classes were monitored throughout the duration of the study to ensure classroom implementation of skills learned during training. The following hypotheses were examined: <italic>Hypothesis I</italic>. Conflict resolution skill development will positively affect use of metacognitive strategies. <italic>Hypothesis II</italic>. Conflict resolution skill development will positively affect students' moral reasoning. The Student Attitudes About Conflict standardized scale was administered to treatment and comparison groups to confirm program implementation. Differences between treatment and comparison groups on a one tailed t-test affirmed training effectiveness for the treatment groups at the alpha level of .05. One tailed t-tests with an alpha level of .05 established that treatment group students demonstrated significant improvement in both areas of investigation, metacognitive skills and in moral reasoning. Both research hypotheses were accepted. Consequently, the veracity of integrating conflict resolution into classrooms was affirmed.

The geomorphic evolution of the Black Hills of South Dakota and adjacent High Plains during the late Cenozoic: Knickzone propagation

Zaprowski, Brent Jason Lehigh University 2001 해외박사(DDOD)

Geomorphic research in the Black Hills and northern High Plains provides new insight into the late Cenozoic evolution of this salient of the Laramide Rockies. Traditionally, geologists have appealed to epeirogenic uplift or climate change to explain the post-Laramide unroofing of the Rockies. On the basis of field mapping and the interpretation of long-valley profiles, I conclude that the propagation of knickzones generated by base level fall, is the primary mechanism responsible for exhumation in the Black Hills. Long profiles of major drainages show discrete breaks in the slope of the channel gradient that are not coincident with changes in rock-type. I use the term knickzones to describe these features because their profiles are broadly convex over tens of kilometers. At and below the knickzone, the channel is incising into bedrock, abandoning a flood plain, and forming a terrace. Above the knickzone, the channel is much less incised, resulting in a broad valley bottom. Numerous examples of stream piracy are documented, and in each case, the capture is recorded in the same terrace units. These observations are consistent with migrating knickzones that are believed to have swept through Black Hills streams, rearranging the drainages. I demonstrate there are two knickzone fronts associated with mapped terraces. Preliminary field evidence of soil development shows that these terraces are time transgressive in nature. Digital elevation models from the Midwestern United States were used to test the validity of the climate model proposed by several authors. The results of the DEM study showed that streams change their long profiles in response to storm intensity rather than mean precipitation. Even though climate may play a role in the formation of terraces, the data clearly shows that migrating knickzones are responsible for the formation of terraces in the Black Hills and adjacent northern Great Plains.

Mathematical modeling of microchemical systems

Alfadhel, Khaled A Lehigh University 2005 해외박사(DDOD)

Mathematical models are important to analyze anomalous phenomena and the behavior of systems in science and engineering. They are the building stones for process design, control and performance optimization. When it comes to modeling schemes in chemical engineering, there are two schools of thoughts; continuum models and molecular level approaches. While the former require certain conditions and criteria pertinent to macro-scale processes, the latter involve a higher level of complexity and thus are considered more powerful at atomistic scale. However, for systems in the rarefied regime (microchemical systems) neither continuum nor molecular models are believed to be adequate [70]. This dissertation addresses the problem of modeling microchemical systems in which selective permeation and chemical reactions take place. Starting with the microfluidic modeling, it was found that velocity-slip, when not accounted for, predicts flow reversal on the walls that are parallel to the permeable membrane, and leads to errors in over-estimating the pressure gradient in rectangular microchannels. For higher Knudsen numbers (Kn), relative errors as high as 50% are possible. When the analytic pressure formulae derived in this work for slipping flow in rectangular microchemical systems are used to generate concentration profiles, which in turn are based on constitutive laws, simulation results revealed that a 4-cm long microchannel was capable of completely removing the permeate and totally consuming the unwanted species. The mathematically derived expressions for species and microfluidic flows offer influential modeling alternatives that are complicated enough to capture the physics of microchemical systems while maintaining a decent level of mathematical solvability. The last part of this dissertation illustrates a rigorous derivation and an analytical solution to the energy problem applicable to membrane microreactors incorporating velocity slip and temperature jump boundary conditions. Criteria under which several terms of the energy equation can be ignored will be highlighted. Investigation of the dimensionless viscous dissipation shows that it decreases with increasing Kn and with decreasing permeation. For rectangular microchannels with aspect ratios less than 1.0, the dimensionless cross-sectional-averaged viscous dissipation was found to become nearly independent of the aspect ratio when the value of Kn exceeds 0.3.