Department of Civil and Mechanical Engineering

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Tip casing heat transfer measurements of a film-cooled turbine stage in a short duration facility
(Massachusetts Institute of Technology, 2001) Van Poppel, Bret P.
An experimental study of the heat transfer to the tip casing of a fully scaled turbine stage was conducted. Pressure and surface temperature measurements were taken on the tip casing. Time-averaged heat flux data was computed and used to assess the influence of stage total pressure ratio, corrected speed and tip gap on casing heat flux. The experimental work was conducted in the MIT Blowdown Turbine Facility using a highly loaded, film-cooled turbine stage. The facility is a short duration experimental structure capable of testing turbine stages under fully scaled conditions to produce useful test durations of 0.5 seconds. The turbine stage tested consisted of film-cooled turbine blades and nozzle guide vanes. During the course of this research, semi-infinite heat flux gauges were designed and fabricated by painting and baking thin platinum films onto machineable ceramic substrates. These gauges were used to experimentally measure surface temperatures on the tip casing with an estimated frequency response of 60 kilohertz. A tip casing insert was designed as an instrument holder to orient the heat flux gauges and highly sensitive pressure transducers on the tip casing surface to spatially resolve heat flux and static pressure. A matrix of test conditions was devised to investigate the effects of various run conditions and tip gaps on tip casing flow. Both a 3.0% and a 1.5% tip-gap-to-span ratio were tested. Run conditions were established by varying the stage pressure ratio and the corrected speed. Results were compared within each test, between tests at the same tip gap, and between tests at different tip gaps. Time averaged data revealed the influence of rotor enthalpy extraction on casing heat flux. Pressure and corrected speed tests showed similar trends at both tip gaps. At design conditions, average endwall heat transfer was approximately 4% greater for the 1.5% tip gap.
Material Properties of the Grade 300 and Grade 270 Prestressing Strands and their Impact on the Design of Bridges
(Virginia Polytechnic Institute and State University, 2006) Hill, Aaron T.
The primary objective of this thesis was to test the material properties of the new Grade 300, low-relaxation prestressing strand. The purpose of this testing was to verify the advertised breaking strengths and relaxation properties of the Grade 300 strand. Additional properties, such as yield strength, modulus of elasticity, and elongation, were also examined. Several tests were performed on each specific type of strand. For example, six tension and eight relaxation tests were performed on the Grade 300, 0.5 in. diameter, 0.153 square in. area strand. From the tests, it is concluded that the advertised breaking strengths and relaxation properties from Strand-Tech Martin, Inc. were accurate and meet the industry standards for low relaxation strand. The secondary objective of this project was to comment on the benefits of the Grade 300 strand as it pertains to the bridge industry. It was concluded from the tests that the Grade 300 strand had a 10 per cent larger 1 per cent elongation stress compared to the bridge industry standard Grade 270 strand. Furthermore, the amount of loss due to relaxation for the Grade 300 strand was comparative to that of the Grade 270 strand. While additional testing needs to be done to include stress-corrosion, transfer length, development length, and flexural strength, the completed testing indicates that less strand will be required using Grade 300 strand versus Grade 270 strand to achieve a set span length and transverse girder spacing. In addition, with the industry gradually progressing toward using higher strength concretes, longer span lengths and larger transverse girder spacing can be achieved by using the Grade 300 higher strength strand. The final objective of this testing was to examine the procedures and testing methods outlined by ASTM A416, Standard Specification for Steel Strand, Uncoated Seven-Wire for Prestressed Concrete (2005), ASTM E328, Standard Test Methods for Stress Relaxation for Materials and Structures (2002), and ASTM A370, Standard Test Methods and Definitions for Mechanical Testing of Steel Products (2005). The breaking strength and yield strength tables in ASTM A416 (2005) need to be updated with the new Grade 300 strand information. Based on this testing, ASTM should also remove the recommendation of simply using aluminum foil and Standard V-Grips to grip the strand. Even though the standard Grade 270 and Grade 300 regular diameter strand met the material property requirements when using aluminum foil as a cushioning material, none of these samples broke clearly within the gage length of the strand. Furthermore, all of the super area strand samples failed prematurely at the grips due to the notching effect of the V-grip teeth. Thus, an alternative method involving aluminum tubing, aluminum oxide, and epoxy were used to create a cushioning device between the V-grip and the strand in order to achieve the true ultimate breaking stress of the strand. Finally, ASTM should comment on the impact of test length on the total relaxation measurements. Three test lengths were evaluated during the 26 relaxation tests. As the test length increased, the total measured relaxation decreased. Losses due to chuck slip and frame settlement were negligible as the strand test length increased.
An Integrated Approach For Engineering Mechanics And Design
(ASEE, 2007) Klosky, James Ledlie; Hains, Decker; Johnson, Timothy; Bruhl, Jakob C.; Erickson, Jared B.; Richards, John
As part of a major curriculum update undertaken over the last three years, the United States Military Academy at West Point has implemented a new course sequence in statics, mechanics and material science. This sequence involves teaching an introductory engineering course, CE300, to both engineering majors and non-majors, followed by CE364, a mechanics + material science course that is taken by those students majoring in Civil or Mechanical Engineering. The sequence integrates statics, mechanics of materials and a lesson block on material science; information that is traditionally separated across two or more courses, making it difficult for students to form the key connections between statics, mechanics and materials that are the bread- and-butter of the working engineer. Through tight coordination of these two courses, significant advances have been made in student attitudes, capabilities and, perhaps most importantly, engineering perspective. This sequence, CE300 + CE364, was created in response to curriculum changes arising from the Department of Civil & Mechanical Engineering’s slow-loop assessment process and a desire on the part of the Academy to implement a complete revision of the undergraduate engineering experience for non-engineering majors. CE300 – Fundamentals of Engineering Mechanics and Design became the first course in engineering for both majors and non-majors. This large change in the earliest part of the student’s engineering experience suggested two questions - could this course truly serve both engineering and non-engineering students and could the tight coordination of the two-semester pair of courses be effectively implemented? This paper explores these questions, the answer to which we believe is a resounding “yes!” CE300 is now the first course of a two-course sequence in basic statics and solid mechanics and builds the foundation in mechanics and design for all civil and mechanical engineering majors. The key finding of this effort, expanded on in this paper, is that by combining statics with introductory mechanics of materials, CE300 now includes exciting elements of design that are not generally taught in a traditional statics course. For instance, where students were previously constrained to answer only what forces acted on the members of a truss, they can now attach something more physical to that computation and get the feeling of accomplishment that comes with actually designing something by choosing an appropriate a material type and size for the truss member based on stress and/or deformation requirements. The second course in the sequence was originally CE364 – Mechanics of Materials and although it maintained its original name, the content now includes a more in-depth coverage of mechanics of materials and an introduction to material science, content that had previously been simply missing from the civil engineering curriculum. The result is a well-blended sequence of courses that provides an exciting introduction to engineering and gives engineering students the opportunity to begin the exciting process of design within the first five weeks rather than waiting for follow-on courses. This paper discusses the approaches and content of both courses as well as the linkage between the two. Assessment data related to student achievement and perceptions is also analyzed, and suggestions for further improvement of the sequence are included.
Teaching Engineering To The Disinterested: A Case Study In Teaching Engineering Principles To Non Engineering Majors
(ASEE Conferences, 2008) Himes, Gerald; Bruhl, Jakob C.; Hanus, Joseph P.
As our infrastructure ages, Civil Engineers, balanced by a firm core of social, economic and political theory, are a strategic asset for the future. Yet, the number of students that elect to undertake engineering majors for their undergraduate degree appears stagnated and even trending downwards in recent years. The Executive Director of the National Society of Professional Engineers, Patrick Natale, believes this trend is caused by selling the wrong message; that is, engineering is only the application of math and science. Rather, the message that should be communicated is that engineering is about innovative problem solving and creating what was not there before; about defining a problem and finding a new path to forge ahead; and building the future now. A medium for communicating this message is a broad-based introduction-to-engineering course early in the undergraduate curriculum. Many universities currently offer or are developing such courses. A consideration when developing these courses is the challenge of teaching engineering to those who are not fully committed to an engineering major. As a critical piece of the liberal education at the United States Military Academy, a sequence of engineering courses is required for all majors, including non-engineering majors. Many of the means and methods used in these courses are applicable to the introduction-to engineering courses at other universities. This paper focuses on a semester-long Engineering Design Project (EDP) - used in the third sequence course - for the design and construction planning of a base-camp to house, support and sustain a given population. The EDP is developed within a broad math, science, social, economic, and political context. Base-camp objectives are developed based on population requirements, constraints governing the solution and necessary base-camp functions. Specific techniques used include trade-off decision analysis, using Google © SketchUp to communicate the design, and a “K’nex-ercise” to illustrate the construction process. This paper assesses the effectiveness of the EDP to deliver the contemporary engineering message - innovative problem solving for building the future - and outlines the applicability of the EDP in other universities.
Watching Videos Improves Learning?
(ASEE Conferences, 2008) Bruhl, Jakob C.; Klosky, James Ledlie; Bristow, Elizabeth
Watching Videos Improves Learning? An Effective Use of Short, Simple, Instructor-Made Videos in an Engineering Course Abstract Keeping up with trends in technology use among students is always a challenge. Students, like much of society, are increasingly “pulling” their desired content from the web (news, entertainment, etc.) rather than simply acting as passive receivers. The growth of on-demand internet viewing on YouTube and NetFlix in combination with the diminished power of the big three networks is a great example of this trend. Education, however, remains generally out-of- sync with this trend; we still rely primarily on a “push” approach. Today’s students desire more and more control over how they get their information both in their courses and in their lives. This paper reports on a notably successful attempt to create a resource which augments traditional classroom instruction and can be used at the time and place of the student’s choosing. By creating short, simple videos using easy-to-use technology, instructors discovered that students not only appreciate having the resource available, they also improve their learning with its use. Students in the civil engineering program at the United States Military Academy who used these videos as they prepared for mid-term exams performed better than those students who chose not to make use of the resource. In addition to the marked improvement in academic performance, feedback from students was overwhelmingly positive. These videos are unique compared to other web-based learning objects in a number of ways. First, they are created using very simple, easy-to-learn technology and do not require assistance from outside the department. Second, they do not duplicate any of the material presented in the course or the traditional classroom activities; rather, they augment the course content and provide an additional resource for students to consult when studying and solving assigned problems. Third, they are short and focused on a single concept; they do not require a large time investment for a student to benefit. We believe that this resource blends traditional presentation and current technology in a unique way that is demonstrably beneficial and does not require significant time or computer “know-how” on the instructor’s part. This paper summarizes the initial implementation of short, instructor-created tutorial videos in our introductory engineering course, Fundamentals of Engineering Mechanics and Design, and includes quantitative support for the conclusion that using these videos improves academic performance and students’ attitudes. This paper also includes an explanation of how to create the videos using inexpensive and easy-to-learn resources, outlines our lessons learned, and concludes with a discussion of best practices. Introduction: Keeping up with trends in technology use among students is always a challenge. Our students, like much of society, are increasingly “pulling” their desired content from the web (news, entertainment, etc.) rather than simply acting as passive receivers. The growth of YouTube in combination with the diminished power of the big three networks is a great example of this trend.
Training Civil Engineers To Communicate Effectively
(ASEE Conferences, 2008) Bruhl, Jakob C.; Crispino, Eric
Abstract ABET requires that graduates of accredited institutions have “an ability to communicate effectively.” The importance of effective communication of technical information is also addressed in the ASCE Body of Knowledge. How schools meet this outcome varies by institution but about half of the schools surveyed for this paper require a specific course on the subject. Constraints at the United States Military Academy (programs can not extend beyond four years and a very large core curriculum) make it impractical to require a technical communications course. In order to educate our graduates about this specific type of communication rather than simply have them “learn by doing” in their engineering courses, the Civil Engineering program now includes an introduction to technical writing in the first engineering course our students take. By using a number of short, focused reading assignments from a technical writing guide, several short memorandum assignments, and a complete laboratory report, students taking Fundamentals of Engineering Mechanics and Design now leave with one more fundamental – the ability to effectively communicate technical information. This paper discusses our experience of teaching technical writing in an existing introductory engineering course and includes feedback from students and instructors as well as some of our lessons learned. Introduction One of the outcomes of ABET-accredited institutions is that graduates have “an ability to communicate effectively.”1 The ASCE Body of Knowledge expounds on this outcome stating that engineers must be capable of “interacting effectively with technical and nontechnical or lay individuals and audiences in a variety of settings.”2 The complete method schools use to prepare students to meet these outcomes varies but many include a specific course on technical communication. A survey of civil engineering curricula at 18 public and private institutions of varying size showed that only half have a specific requirement for technical communication and one offers a similar course as an elective (see Appendix A). Two of the nine schools requiring a technical communications course require two such courses, the rest require one course. Of those requiring a course, four require the course of their sophomores, three during the junior year, and two require the course in the senior year. Background Deciding which courses to require is a challenge for programs – especially those that desire to maintain a four year bachelor’s program. The United States Military Academy (USMA) must keep the program to four years and given the very broad core curriculum required of all USMA graduates, the first engineering course is not taken until the second semester of their sophomore year. With only 5 semesters to fit in an ABET accredited program, our leadership must be very...
On Demand Learning Augmenting The Traditional Classroom
(ASEE Conferences, 2008) Bruhl, Jakob C.; Klosky, James Ledlie; Bristow, Elizabeth
On-Demand Learning – Augmenting the Traditional Classroom: Details on the Effectiveness of Short, Simple, Instructor-Made Videos in an Engineering Course Abstract In the spring of 2007, short, focused, instructor-made videos intended to supplement classroom presentations were successfully incorporated as an additional learning resource in the last half of a fundamentals of engineering course at the United States Military Academy. Based on the success of this introduction, the use of these videos was dramatically expanded in the same course for the Fall 2008 semester. A detailed study of the effectiveness of this resource was undertaken, and this paper reports the effectiveness of this resource on academic performance and student perceptions of learning. We discuss usage trends and preferences throughout the semester as students discovered and acclimated to having additional instruction available whenever and wherever they were studying. The paper also discusses the usage of the video resource based on learning styles and previous academic performance. It is clear that visual or sequential learners are not the only ones who like this resource; the videos were equally used by global and verbal learners. Another concern addressed is the hypothesis that growing the use of video will lead students to abandon textbooks and other traditional resources in favor of watching videos and “pattern matching.” This concern proved invalid during the semester – students still used multiple resources to study and prepare assignments, including their textbook. The observation from Spring 2007 that watching these videos improves students’ perception of learning as well as their academic performance was corroborated on a broader scale in Fall 2008. The academic benefit is quantified using a predictor of performance based on students’ grade point average at the start of the semester. It is shown that those students who made use of the videos improved their academic performance as compared to those who chose not to use the videos. The authors conclude that significant benefit can be gained by creating and posting short, simple, instructor-made videos.
Assessing the Impact of New Teaching Methods by Predicting Student Performance
(ASEE, 2008) Bruhl, Jakob C.; Bristow, Elizabeth; Klosky, James Ledlie
Many teachers try new things in the classroom with the intent of making learning more effective. In most cases, assessment of the impact is anecdotal; the teacher surveys the students about the new technique and draws conclusions based on their feedback. In order to more definitively prove the impact, better assessment tools are needed. In a recent study, the authors attempted to predict performance in a course and then measure the improvement due to a major change in the available resources for study outside the classroom in our fundamentals of engineering course. To measure the effectiveness, we used the GPA of the students at the start of the semester to predict their performance in the course. We then assessed the impact by comparing actual grades in the course to the predicted grades. Using historical data as a baseline, we thus conclude with some certainty the amount of impact our change made in academic performance. This paper focuses on the method of assessment and measurement rather than the classroom changes.
Combined loading of a bridge deck reinforced with a structural FRP stay-in-place form
(Construction and Building Materials, 2009) Hanus, Joseph P.; Bank, Lawrence C.; Oliva, Michael G.
The investigation of a structural fiber-reinforced-polymer (FRP) stay-in-place (SIP) form used to construct and reinforce a deck for a prototype military bridge system is discussed in this paper. For this application the deck is subjected to combined bending and compressive longitudinal axial load because it also serves as the top chord of the truss for the bridge system. In an experimental program, deck specimens were tested in several configurations. The results are compared to ACI 440 design guide equations, and capacity prediction techniques are proposed for limit states associated with flexural and flexural-shear under the combined loading. It was found that the ACI 440 equations accurately predicted the flexural and flexural-shear capacities under combined loads provided that eccentricity due to the combined loading was accounted for in the calculations.
On the Similarity Solution for Condensation Heat Transfer
(ASME International, 2009-08-26) Tamm, Gunnar; Boettner, Daisie D.; Van Poppel, Bret P.; Benson, Michael J.; Arnas, A. Özer
Analytical solutions for laminar film condensation on a vertical plate are integral to many heat transfer applications, and have therefore been presented in numerous refereed articles and in most heat transfer textbooks. Commonly made assumptions achieve the well known similarity solution for the Nusselt number, heat transfer coefficient, and film thickness. Yet in all of these studies, several critical assumptions are made without justifying their use. Consequently, for a given problem one cannot determine whether these restrictive assumptions are actually satisfied, and thus, how these conditions can be checked for validity of the results. This study provides a detailed solution that clarifies these points.
Numerical Methods for Simulating Multiphase Electrohydrodynamic Flows with Application to Liquid Fuel Injection
(University of Colorado, 2010) Van Poppel, Bret P.
Over the past decade, there has been a growing amount of attention paid to the emissions from small engines in the size range of 200 cm3 or smaller. In 2002 the EPA published a study claiming small engine emissions were responsible for 9% Hydrocarbons (HC), 4% Carbon monoxide (CO), 3% NOx, and 2% particulate matter from all mobile sources in the United States [1]. As a result, there is considerable interest in controlling emissions for these small engines. One of the main reasons small engines produce high emissions is that they are carbureted. Carburetors mix fuel with air for combustion, but they are incapable of providing precise fuel timing. These deﬁciencies lead to partial combustion and decreased fuel eﬃciency while increasing emissions. Direct fuel injection may reduce the incidence of these pollutants. However, the cost of implementation is a barrier to large scale adoption. Fuel injectors used in the automotive industry are too costly to be implemented on small engines, with the average cost falling in the range of $35 dollar per unit (USD). In order to keep the production cost proﬁtable, costs will have to be substantially lower.
On the Analysis of the Aerodynamic Heating Problem
(ASME International, 2010-09-20) Arnas, A. Özer; Boettner, Daisie D.; Tamm, Gunnar; Norberg, Seth A.; Whipple, Jason R.; Benson, Michael J.; Van Poppel, Bret P.
A complete analytical solution to the problem of aerodynamic heating is lacking in heat transfer textbooks, which are used for undergraduate and graduate education. There are many issues that are very important from a convective heat transfer point of view. In practice, poor analyses lead to poor design, thus faulty manufacturing. Since, over the years analysis has given way to numerical studies, the instructors do not take the necessary time to go through analytical details. Thus the students just use the results without any awareness of how to get them and the inherent limitations of the analytical solution. The only intent of this paper, therefore, is to present the detailed analytical study of the aerodynamic heating problem.
Enhanced Sustainability Concrete Mixtures: Effects of Elevated Temperature Exposure on Changes in Microstructure and Elastic Properties and in Development of Modified Layered-Sectional Analysis for Forensic Investigation
(North Carolina State University, 2011) McCoy, Brad C.
Part I of this report discusses the findings of an investigation of the relationships between changes in microstructure and elastic properties of lightweight and conventional, enhanced sustainability concrete (ESC) mixtures resulting from elevated temperature exposure. The shear modulus (G) and dynamic elastic (Young’s) modulus (Ed) was determined from resonant frequency of nominal 25 mm (1 in.) thick by 100 mm (4 in.) diameter disk specimens, tested wet and dry, before and after exposure to 150 C (300 F) and 300 C (570 F). The crack densities () before and after exposure were estimated from wet and dry G values of the disk. A critical finding was that the relationship between initial crack density and changes in crack density were similar regardless of the fly ash content implying that ESC mixtures can be used similarly to conventional mixtures in elements exposed to elevated temperatures. This study confirmed the well-established effects of strength on damaged concrete members due to elevated temperature exposures and found statistically significant differences between changes in crack density of mixtures containing fly ash and those containing slag cement. Part II of this report describes the development of a modified layered-sectional analysis (MLSA) providing the engineer with a tool to assess structural behavior of concrete beams with localized damage, a problem not well suited to classical, closed form solutions. The MLSA framework was then used to examine how concrete materials with enhanced sustainability would perform in service after damage associated with a short intense fire. The elastic (Young’s) modulus of the ESC mixtures was determined in a companion study for undamaged and damaged conditions before and after exposure to 300 C. The elastic properties were incorporated into the MLSA, which predicted satisfactory structural performance of the evaluated ESC beams with localized damage due to fire.
Student Perceptions of the Civil Engineering Body of Knowledge
(ASEE Conferences, 2012) Barry, Brock; Katalenich, Scott; McCoy, Brad C.
Student Perceptions of the Civil Engineering Body of Knowledge: Comparison of Two Academic Institutions In 2008, the American Society of Civil Engineers (ASCE) updated their body of knowledge (BOK2) that defines how a combination of education and experience shall fulfill developmental requirements for entry into the civil engineering (CE) profession. A student seeking licensure asa professional engineer (PE) ought to attain a specified level of achievement in each of 24different foundational, technical, and professional outcomes in order to demonstrate the proficiency and preparedness the profession expects. Determining how potential and existing civil engineering students perceive the BOK2 has been a subject of interest, recently investigated by Angela Bielefeldt at the University of Colorado, Boulder (CU). Potential students can use the BOK2 to learn about their chosen field of study, visualize a roadmap for future development, and better understand the dedication their profession requires. Graduating seniors can use the BOK2 to assess their personal development, their own strengths and weaknesses, and coincidently identify the strengths and weaknesses of their undergraduate engineering program. Student feedback can help leaders in higher education to make positive changes in their school’s program in order to better prepare students for professional service. This study replicates Bielefeldt’s 2010 investigation under different conditions (i.e. at a military academy as opposed to a research-oriented academic institution) in order to provide confirmationthat the BOK2 framework is a useful tool for evaluating CE curriculums across a wide range ofinstitutions. We queried 42 seniors within a military academy’s CE program on their personalstrengths and weaknesses in the context of the 24 outcomes suggested by the ASCE BOK2. Inaddition, we asked these students to identify apparent curriculum weaknesses and rank order the24 outcomes in terms of perceived importance.This study is of interest to any undergraduate CE program administrator who is interested inassessing pedagogy and developing learning experiences to better prepare students forprofessional licensure. The study also assists practicing engineers to provide appropriatementorship and engineering experience to further prepare engineer interns for eventual licensureas a PE.
Infrastructure and the Operational Art: A Handbook for Understanding, Visualizing, and Describing Infrastructure Systems
(DTIC, 2014) Hart, Steven D.; Klosky, James Ledlie; Katalenich, Scott; Spittka, Berndt F.; Wright, Erik R.
The Army's understanding of infrastructure as an operational variable has been evolving over the past 30 years in response to significant events ranging from international conflicts to domestic weather-related disasters. These experiences have combined to drive a significant shift in infrastructure doctrine, which now demands that commanders and staffs understand, visualize, and describe the infrastructure variable to accomplish the Army s assigned infrastructure missions of protecting, restoring, and developing infrastructure all missions essential to restoring stability after conflict or disaster. Current Army doctrine, however, does not say how commanders and staffs are to approach these challenging tasks. This report presents a cognitive framework for understanding, visualizing, and describing infrastructure by using five conceptual models created to allow commanders and staffs to think critically, creatively, and completely about infrastructure problems. The report also includes the scholarship behind the models including verification, validation, and certification as well as example applications of the models to actual situations. Infrastructure is a concern for both civil society and the military, and the models work equally well in both. The authors actively solicit feedback from any reader on the use, application, and improvement of these models.
Crack Density and Elastic Properties of Sustainable Concretes
(ACI Materials Journal, 2014) McCoy, Brad C.; Leming, Michael L.; Seracino, Rudolf
This paper examines relationships between changes in the microstructure and selected elastic properties of various concrete mixtures exposed to moderately elevated temperatures. The crack density parameters before and after exposure were estimated from the shear modulus measured wet and dry of 1 in. thick by 4 in. diameter (25 x 100 mm) disks. Mixtures examined included both granitic and lightweight coarse aggregates in combination with cementitious systems containing either 20% fly ash, 60% fly ash, termed enhanced sustainability, or 60% slag cement. This study found that the changes in crack density parameter resulting from exposure to elevated temperatures appear to be more sensitive to differences between cementitious materials than to differences between aggregate type or cementitious material proportions. A critical finding was that the relationship between initial crack density parameter and changes in crack density parameter were similar regardless of fly ash content.
Design of SC Walls Subjected to Impactive Loading for Local and Global Demands
(SMiRT, 2015) Kim, Joo Min; Bruhl, Jakob C.; Varma, Amit
Steel-plate composite (SC) walls have been shown experimentally to have excellent resistance to impactive loading, such as from impacts resulting from internally generated missiles, external hurricane borne missiles, or other extreme event missiles. This is a significant advantage for SC walls, and also one of the primary reasons for their increasing use in safety-related nuclear facilities. This paper presents a comprehensive review and evaluation of the missile impact resistance of SC walls. This paper reviews design recommendations to prevent perforation (i.e. local failure) and assessment methodologies to estimate total and global displacement (i.e. global response) of SC walls subject to impact loads. This paper also describes numerical modelling methods to predict local and global behaviour and provides design recommendations for research engineers and design professionals in the nuclear power and protective construction industries.
Design of composite SC walls to prevent perforation from missile impact
(International Journal of Impact Engineering, 2015) Bruhl, Jakob C.; Varma, Amit; Johnson, William H.
This paper presents a three-step method for designing steel plate composite (SC) walls subjected to missile impact. This method can be used to compute the minimum required steel plate thickness for SC walls to prevent perforation due to missile impact. The design method was verified using the complete experimental database of 130 SC wall missile impact tests compiled as part of this research. The design method compares favorably with the observations and results from the experimental database and can be used within its range of applicability to design SC walls to prevent missile perforation. The paper also presents the development and benchmarking of 3D finite element models for predicting the behavior and local failure of SC walls subjected to missile impact. The models were benchmarked using test results from the experimental database and results were used to confirm the failure mechanism of SC walls subjected to missile impact. The benchmarked models were used to conduct analytical parametric studies to expand the database, and further verify the design method. The numerical modeling approach is recommended for future research and design of specific SC wall configurations to resist design basis missiles.
Changes in lower extremity peak angles, moments and muscle activations during stair climbing at different speeds
(Journal of Electromyography and Kinesiology, 2015) Lewis, Jacqueline; Freisinger, Gregory; Pan, Xueliang; Siston, Robert A.; Schmitt, Laura C.; Chaudhari, Ajit M.W.
Stair climbing is a common daily activity, yet there is no basic knowledge on how lower extremity joint angles, moments or muscle activations are affected by stair climbing speed. This information will determine whether speed matching is necessary for stair climbing studies. Moreover, changes in lower extremity biomechanics during stair climbing at different speeds will aid in the clinical interpretation of a patient’s maximal stair climbing speed. Thirty healthy participants provided consent. Kinematics, kinetics, and muscle activations were collected on a three step staircase. Subjects climbed the staircase at normal, slow and fast self-selected speeds. Linear mixed models for repeated measures were used to study the associations between speed and the lower extremity peak joint angles and moments, and muscle activations. The peak hip flexion and extension moments increased with increasing speed, while peak knee flexion moment did not vary consistently with speed. The peak muscle activations varied consistently with respect to the sagittal plane kinetics. These results suggest that in healthy subjects, the hip is the greatest contributor when modulating stair climbing speed, while additional knee contributions do not appear necessary to increase speed. Further stair studies should consider speed matching in order to accurately assess biomechanical differences.
Impact Assessment of SC Walls Using Idealized SDOF and TDOF Models
(ASCE, 2015) Bruhl, Jakob C.; Johnson, William H.; Reigles, Damon G.; Li, Jie; Varma, Amit; Kim, Joo Min
Steel-plate composite (SC) walls have been used recently in overseas and domestic nuclear power plant (NPP) projects. For safety-related NPP facilities these walls may be required to resist the effects of impact. Analysis of the structural global response of conventional reinforced concrete (RC) walls to impact loadings, such as those from tornado borne missiles or turbine-generated missiles and secondary wall impacts due to heavy load drops, is reasonably approximated using simplified dynamic analysis methods. For cases in which global bending dominates the response, an inelastic single-degree-of-freedom (SDOF) model is effective. For some impact loadings the response includes considerable localized deformation. Analysis for these cases requires a cascaded two-degree-of-freedom (TDOF) model with one mass and resistance representing the global flexural response and a second mass, resistance and damping representing the local deformation response. In this paper, the methodology to complete dynamic analysis of impact loadings on SC walls (both SDOF and TDOF models) is provided, and SDOF and TDOF model results are compared to SC wall dynamic response from nonlinear finite element models.

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