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Articles 1 - 30 of 38
Full-Text Articles in Engineering
Expedient Airfield Runway Repair Using Folded Fiberglass Mat, Christopher Tuan, William Dass
Expedient Airfield Runway Repair Using Folded Fiberglass Mat, Christopher Tuan, William Dass
Christopher Y. Tuan
For expedient airfield runway repair, the US Air Force has developed a folded fibreglass mat to cover craters repaired with a well-compacted granular base material. The objective of this study was to evaluate the adequacy of using polymer plugs to anchor the mat to a repaired asphalt pavement for heavy aircraft operations. The effort consisted of materials testing, field experiments and analytical modelling. An 89,800-kg (198,000-pound) load cart having the footprint of a single C-5 main gear was pulled on a mat with wheels locked to simulate full braking forces. Anchor bushings were instrumented to measure anchor loads. A simplified …
Dynamic Characteristics Of Streched-Membrane Heliostats, Christopher Tuan, A. Al-Einea, L. Murphy
Dynamic Characteristics Of Streched-Membrane Heliostats, Christopher Tuan, A. Al-Einea, L. Murphy
Christopher Y. Tuan
Stretched-membrane heliostats provide efficient two-axis tracking mirrors for use in solar thermal applications. The solution of the two-dimensional wave equation for a circular stretched membrane provided lower and upper bounds of the natural frequencies of the heliostat. The effects of the boundary condition on the mode shapes of the membrane were shown in the finite element analysis as well as in the vibration tests. Different natural modes were excited depending upon the number of supports around the circumference of the membrane. Damping in the heliostat was small. Damping ratios estimated from vibration decay curves were less than 3% of critical …
Thin Conductive Concrete Overlay For Bridge Deck Deicing And Anti-Icing, Sherif Yehia, Christopher Tuan
Thin Conductive Concrete Overlay For Bridge Deck Deicing And Anti-Icing, Sherif Yehia, Christopher Tuan
Christopher Y. Tuan
Concrete bridge decks are prone to ice accumulation. Bridge decks freeze before the roads approaching them freeze, making wintry highway travel treacherous. Road salts and deicing chemicals are effective for ice removal but cause damage to concrete and corrosion of reinforcing steel in concrete bridge decks. The resulting rapid degradation of existing concrete pavements and bridge decks is a major concern to transportation and public-works officials. The use of insulation materials for ice control and electric or thermal heating for deicing have been attempted, with unsatisfactory results. Conductive concrete is a cementitious admixture containing electrically conductive components to attain high …
Ponding On Circular Membranes, Christopher Tuan
Ponding On Circular Membranes, Christopher Tuan
Christopher Y. Tuan
Nonlinear circular membrane responses under partial and full ponding loads have been solved by the fourth-order Runge-Kutta numerical integration and by finite element simulation with good accuracy. Under partial ponding loads, a discontinuity exists in the curvature of the deformed membrane at the fluid boundary while an inflection point forms inside the ponding. An iterative finite element algorithm has also been developed for solving membrane ponding problems where inelastic material response becomes significant. The finite element simulation procedure was proven to be accurate when validated against test data from membrane forming experiments.
Viscoplastic Cap Model For Soils Under High Strain Rate Loading, Xiaoli Tong, Christopher Tuan
Viscoplastic Cap Model For Soils Under High Strain Rate Loading, Xiaoli Tong, Christopher Tuan
Christopher Y. Tuan
A viscoplastic cap model of the Perzyna type was developed for simulating high strain rate behaviors of soils. An associative viscous flow rule was used to represent time-dependent soil behaviors. The viscoplastic cap model was validated against experimental data from static and dynamic soil tests. The model was also compared with soil behaviors under creep and stress relaxation with good agreement. However, the model was unable to represent tertiary creep where strain softening became significant. The model was subsequently integrated into LS-DYNA for finite-element simulations of high strain rate behaviors of sandy and clayey soils in explosive tests. The significance …
Conductive Concrete Overlay For Bridge Deck Deicing, Sherif Yehia, Christopher Tuan
Conductive Concrete Overlay For Bridge Deck Deicing, Sherif Yehia, Christopher Tuan
Christopher Y. Tuan
Concrete bridge decks are prone to ice accumulation. The use of road salts and chemicals for deicing is an effective method for ice removal, but causes damage to concrete and corrosion of reinforcing steel in concrete bridge decks. This problem is a major concern to transportation officials and public works due to rapid degradation of existing concrete pavements and bridge decks. The use of insulation materials for ice control and electric or thermal heating for deicing have been attempted and met limited success. Conductive concrete may be defined as a cementitious composite that contains a certain amount of electronically conductive …
Design Of Concrete-Filled Circular Steel Tubes Under Lateral Impact, Yaohua Deng, Christopher Tuan
Design Of Concrete-Filled Circular Steel Tubes Under Lateral Impact, Yaohua Deng, Christopher Tuan
Christopher Y. Tuan
Infrastructures and key members are potentially exposed to accidental loads due to extreme situations such as collisions, impacts, and terrorist bombings. Consequently, the current design concept requires that the structures or key members possess adequate capacities to resist accidental loads. To understand the mechanical response of concrete-filled steel tube (CFT) beams subjected to impact loads, this paper presents numerical simulations on the CFT beam tests in an instrumented drop-weight impact facility using finite element code LS-DYNA. The adequacy of finite element modeling (FEM) has been validated against drop-hammer impact tests in the literature. Based on the dynamic increase factors (DIFs) …
Formation Of Circular Optical Membranes Under Free-Form Yielding, Christopher Tuan, David White
Formation Of Circular Optical Membranes Under Free-Form Yielding, Christopher Tuan, David White
Christopher Y. Tuan
High‐quality optical reflector surfaces are attainable with the use of pressure‐formed membranes. The formation technique involves gradual application of fluid pressure on initially flat, simply supported circular membranes until a desirable center deflection is reached. After the fluid is removed, a uniform pressure is subsequently applied to offset the surface slope error. Empirical testing of membrane‐forming technique was conducted at two scales to define the critical process variables that controlled material yielding. Aluminum membranes with 54‐in. (1.4‐m) diameter were constructed for the smaller scale and with 144‐in. (3.7‐m) diameter for the larger scale. The experiments were carried out with the …
Assessment Of Software For Blast Loading And Structural Response Analysis Using A Lightweight Steel-Joist Roof As A Test Case, Christopher Tuan
Assessment Of Software For Blast Loading And Structural Response Analysis Using A Lightweight Steel-Joist Roof As A Test Case, Christopher Tuan
Christopher Y. Tuan
The purpose of this paper is to evaluate the current multihazard loading environments when future blast loadings are included. While most of the currently available software programs for the physical testing of normal design loading conditions have been validated, the testing does not include the blast environment. It has not been determined whether these programs can be used when blast loads are included. Currently, designers use multiple software packages to perform multihazard analyses when blast loads are involved, making it difficult to compare the results. This analysis has as major topics air-blast and structural responses. The three standard air-blast codes …
Fatigue Strength Of End-Coped Crane Runway Girders, Xiaoli Tong, Christopher Tuan, Jianping Yang, Jiaqi Zhang, Qingrui Yue
Fatigue Strength Of End-Coped Crane Runway Girders, Xiaoli Tong, Christopher Tuan, Jianping Yang, Jiaqi Zhang, Qingrui Yue
Christopher Y. Tuan
Fatigue cracks were found on a series of end-coped crane runway girders after 14 years of service in a steel mill building in China. Two typical crane runway girders with different spans were studied in this paper. Finite element analyses were conducted to investigate the stress concentration at the coped ends. Analytical results showed the stress concentration effect was highly localized and the stress concentration factor decreased with increasing cope radius and decreasing total depth. The analytical results agreed well with the field measured data. Fatigue tests were conducted to determine the fatigue strength using eight 1/5-scaled end-coped girder specimens. …
Flexural Behavior Of Concrete-Filled Circular Steel Tubes Under High-Strain Rate Impact Loading, Yaohua Deng, Christopher Tuan
Flexural Behavior Of Concrete-Filled Circular Steel Tubes Under High-Strain Rate Impact Loading, Yaohua Deng, Christopher Tuan
Christopher Y. Tuan
Nine simply supported circular steel concrete-filled tubes (CFTs), two circular steel posttensioned concrete-filled tubes (PTCFTs), and one circular steel fiber–reinforced concrete-filled tube (FRCFT) have been tested in an instrumented drop-weight impact facility. The weight and the height of the drop-weight were varied to cause failure in some test specimens. The failure modes and local damages in those specimens have been investigated extensively. Failure in the steel tubes was commonly tensile facture or rupture along the circumference. Concrete core in the impact area commonly crushed under compression and cracked under tension. The use of prestressing strands and steel fibers significantly restrained …
Three-Dimensional Security Barrier Impact Response Modeling, Ratul Sarmah, Christopher Tuan
Three-Dimensional Security Barrier Impact Response Modeling, Ratul Sarmah, Christopher Tuan
Christopher Y. Tuan
The occurrence of terrorist vehicular bomb attacks has been frequently reported. Perimeter security barriers are designed and guilt to defeat vehicle penetration. Due to the complexity of designing a security barrier, the current practice is to physically crash test the barrier head-on with a threat vehicle, at a certain velocity as a validation of the design. As full-scale vehicular crash tests are costly, facility designers are often forced to use existing barriers without the benefit of designing new, innovative and cost-effective systems for a specific threat. With the present-day computing capability, conducting three-dimensional simulations of vehicular crash dynamics on a …
Drop Weight Testing On Sandwich Panels With A Novel Thermoplastic Core Material, Christopher Tuan
Drop Weight Testing On Sandwich Panels With A Novel Thermoplastic Core Material, Christopher Tuan
Christopher Y. Tuan
A series of drop weight tests were conducted to evaluate the dynamic flatwise compression strength and flexural strength of sandwich panels with a novel core structure. This sandwich core material, known as Norcore, consists of interconnected cells in a unique configuration of truncated pyramid with sloping cell walls. Core materials made of thermoplastic including virgin Lexan, polycarbonate, polycarbonate regrind, high impact polystyrene, and acrylonitrile butadiene styrene were tested. The test results showed that these sandwich panels have good strength as well as energy absorption capacities.
Conductive Concrete Overlay For Bridge Deck Deicing: Mixture Proportioning, Optimization, And Properties, Sherif Yehia, Christopher Tuan
Conductive Concrete Overlay For Bridge Deck Deicing: Mixture Proportioning, Optimization, And Properties, Sherif Yehia, Christopher Tuan
Christopher Y. Tuan
Bridge pavement surfaces are prone to ice accumulation, making winter travel hazardous. Current practice is to use road salt and deicing chemicals, that cause damage to concrete and corrosion of reinforcing steel. A thin conductive concrete overlay can generate enough heat to prevent ice formation on a bridge deck. Conductive concrete is a cementitious admixture containing electrically conductive components that attain stable and high electrical conductivity. Due to the electrical resistance and impedance in conductive concrete, heat is generated when connected to a power source, and can be used for deicing or anti-icing. Conductive concrete is a relatively new material …
Conductive-Concrete Overlays - An Innovative Solution For Bridge Deck Deicing, Sherif Yehia, Christopher Tuan
Conductive-Concrete Overlays - An Innovative Solution For Bridge Deck Deicing, Sherif Yehia, Christopher Tuan
Christopher Y. Tuan
Bridge decks are prone to ice accumulation, making winter travel treacherous. Road salts and some other deicing chemicals are cost effective, but may cause surface scaling, reinforcing-steel corrosion, or both. Another alternative is a thin, conductive-concrete overlay that, when connected to a power source, can generate enough heat through electrical resistance to prevent ice formation on the deck or melt ice after it forms. Using a conductive concrete overlay provides an environment-friendly deicing method that would prolong bridge service life by significantly reducing the use of road salt and deicing chemicals. When used on pedestrian bridges, sidewalks, and driveways, it …
Aurora Arch Bridge - Confined Concrete System Speeds Construction Of Walkway Span, Christopher Tuan
Aurora Arch Bridge - Confined Concrete System Speeds Construction Of Walkway Span, Christopher Tuan
Christopher Y. Tuan
The 30-m-long, single-span, pedestrian arch bridge under construction over Lincoln Creek in Aurora, NE, combines the best attributes of concrete, steel, and fiber-reinforced polymers (FRP), and is a type that is easily constructed, durable, and strong. Swooping top chords formed from concrete-filled steel tubes define the prominent design features of this bridge. Its straight bottom chords are post-tensioned concrete-filled steel tubes. In turn, FRP honeycomb panels form its bridge deck. By incorporating confined concrete, designers enhanced the strength and ductility of the top and bottom chords of the bridge.
Simulation Of Soil Behavior Under Blast Loading, J. An, Christopher Tuan
Simulation Of Soil Behavior Under Blast Loading, J. An, Christopher Tuan
Christopher Y. Tuan
A viscoplastic cap model was previously developed to address the high strain rate effect on soil behaviors. Although the model is an improvement over the inviscid cap model, it does not update soil density and bulk modulus as the shock wave propagates through the soil. Further, soil should be modeled as a three-phase porous media to accommodate various degrees of water saturation. This is especially true for the soil mass surrounding the source of energy release because each of the three phases responds differently to shock loading. A revised cap model comprising a Gruneisen equation of state for each of …
Numerical Analysis Of A Novel Thermoplastic Sandwich Core Material, Christopher Tuan, Robert Sierakowski
Numerical Analysis Of A Novel Thermoplastic Sandwich Core Material, Christopher Tuan, Robert Sierakowski
Christopher Y. Tuan
A numerical investigation of the behavior of a novel thermoplastic honeycomb core material was conducted. This sandwich core material, known as Norcore®, consists of interconnected cells in a unique configuration of truncated pyramid with sloping cell walls. A finite element model of the unit cell structure was constructed using shell elements. Mechanical properties of polycarbonate core specimens of 25.4 mm and 50.8 mm thickness without facings reported by the manufacturer were used for comparisons with finite element analysis.
Flexural Strength Analysis Of Non-Post-Tensioned And Post-Tensioned Concrete-Filled Circular Steel Tubes, Yaohua Deng, Christopher Tuan, Q. Zhou, Y. Xiao
Flexural Strength Analysis Of Non-Post-Tensioned And Post-Tensioned Concrete-Filled Circular Steel Tubes, Yaohua Deng, Christopher Tuan, Q. Zhou, Y. Xiao
Christopher Y. Tuan
Concrete-filled circular steel tubes (CFT) have recently gained significant attention for their enhanced strength and ductility over the conventional steel and reinforced concrete construction. The concrete compressive strength is significantly increased by the lateral confinement provided by the steel tube and local buckling of the steel tube is restrained by the concrete infill. This paper investigates the further enhancement of these composite actions due to post-tensioning the concrete cores inside circular steel tubes. The flexural behavior of a post-tensioned CFT as well as a non-post-tensioned CFT was studied experimentally and analytically. A numerical algorithm for predicting the moment capacities of …
Roca Spur Bridge: The Implementation Of An Innovative Deicing Technology, Christopher Tuan
Roca Spur Bridge: The Implementation Of An Innovative Deicing Technology, Christopher Tuan
Christopher Y. Tuan
The heated deck of Roca Spur Bridge is the first implementation in the world using conductive concrete for deicing. Conductive concrete is a concrete mix containing a certain amount of electrically conductive components in a regular concrete matrix, designed to enable conduction of electricity. Due to its electrical resistance, conductive concrete can generate enough heat to prevent ice formation on a paved surface when connected to a power source.
Uniform Pressure Formation Of Optical Membranes, Christopher Tuan, L. Murphy
Uniform Pressure Formation Of Optical Membranes, Christopher Tuan, L. Murphy
Christopher Y. Tuan
High‐quality optical reflector surfaces are attainable with the i use of pressure‐formed membranes. Those reflector surfaces offer the prospect of very light weight and low cost. The formation of those surfaces, using initially flat circular membranes with uniform pressure loading, is studied in this paper. Finite axisymmetric deformations, along with both linear and nonlinear material responses are considered. A wide range of focal‐length‐to‐diameter ratios are addressed, and the structural/optical response mechanisms that lead to optical distortions relative to ideal parabolic reflector shapes are also considered. Results show that elastic material response can often lead to a significantly larger deviation from …
Buckling Analysis Of A Cable-Stayed Circular Frame, Alexander Tuan, Christopher Tuan, Q. Li
Buckling Analysis Of A Cable-Stayed Circular Frame, Alexander Tuan, Christopher Tuan, Q. Li
Christopher Y. Tuan
Large parabolic dish concentrators have been widely employed in solar thermal applications. The supporting structure of a solar dish concentrator consists of a circular frame, a central post, and front and rear cables connecting the frame to the post. The tensions in the cables cause compressive stresses in the circular frame and the central post, and this support structure must be designed for stability. In this paper, the nonlinear buckling behavior of the supporting structure of a cable-stayed circular frame is studied in detail. A three-dimensional finite element model of the supporting structure is developed to predict the critical cable …
Conductive Concrete As An Electromagnetic Shield, A. Krause, L. Nguyen, Christopher Tuan
Conductive Concrete As An Electromagnetic Shield, A. Krause, L. Nguyen, Christopher Tuan
Christopher Y. Tuan
Conductive concrete mixture was originally developed for surface de-icing purposes but can be designed to perform as an electromagnetic shield. Testing procedures have been developed to measure the attenuation provided by conductive concrete without the cost and labor of building a large structure. This paper provides a description of the design, testing methods, and results obtained from the development of conductive concrete as an electromagnetic shielding material.
Evaluation Of Electrically Conductive Concrete Containing Carbon Products For Deicing, Christopher Tuan, Sherif Yehia
Evaluation Of Electrically Conductive Concrete Containing Carbon Products For Deicing, Christopher Tuan, Sherif Yehia
Christopher Y. Tuan
Evaluates electrically conductive concrete containing carbon products for deicing. Drawbacks about using steel shaving; Use of carbon and graphite products; Workability, finishability and compressive strengths; Electric resistivities of carbon concrete trial mixtures; Electric conduction mechanism in conductive concrete.
Evaluation Of Use Of Lithium Nitrate In Controlling Alkali-Silica Reactivity In Existing Concrete Pavement, Christopher Tuan, Hoasu Sun
Evaluation Of Use Of Lithium Nitrate In Controlling Alkali-Silica Reactivity In Existing Concrete Pavement, Christopher Tuan, Hoasu Sun
Christopher Y. Tuan
This study presents the findings from a 2-year field trial in which lithium nitrate was applied at a rate of 0.006 gal/ft2 twice a year on an existing concrete pavement in Norfolk, Nebraska, in an attempt to arrest ongoing alkali-silica reaction (ASR) distress. Various destructive and nondestructive means were used to measure the effectiveness of the treatments. Concrete cylinders were cored for petrographic examination and split tension testing. Powder samples were taken to determine the lithium content. Nondestructive evaluations used crack mapping, a Schmidt hammer, a velocity meter, and an impact echo apparatus. The amount of lithium that penetrated into …
Evaluation Of Ice-Melting Capacities Of Deicing Chemicals, B. Gerbino-Bevins, Christopher Tuan, M. Mattison
Evaluation Of Ice-Melting Capacities Of Deicing Chemicals, B. Gerbino-Bevins, Christopher Tuan, M. Mattison
Christopher Y. Tuan
Common deicing chemicals include sodium chloride, magnesium chloride, calcium chloride, calcium magnesium acetate, potassium acetate, potassium formate, and corn or beet-based deicer solution. Liquid deicers are commonly used for pre-wetting road salt, sand or other solid deicers, or mixed with salt brine as liquid deicer. Although manufacturers provide performance data under specific conditions, a standardized test is very much needed. Samples of sodium chloride, magnesium chloride, calcium chloride, potassium acetate, and beet juice-based chemical deicers were selected for performance evaluation. The SHRP Ice-Melting Capacity Test has been used in many research projects, but the results do not always correlate well …
Equipment Fragility Due To Shock Response, Christopher Tuan
Equipment Fragility Due To Shock Response, Christopher Tuan
Christopher Y. Tuan
Because of its simplicity, the shock response spectrum has become widely used as a means of describing the shock responses and fragilities of structures and equipment. This paper focuses on the drawbacks of using the shock response spectrum for defining equipment shock tolerance. A cantilever beam with a tip mass was used to model a hypothetical piece of equipment subjected to strong ground motion such as that caused by an explosion. The exact solution from a detailed modal analysis shows that multiple modes of response were excited. Contributions from higher modes can be more predominant than that from the fundamental …
Electrical Resistance Heating Of Conductive Concrete Containing Steel Fibers And Shavings, Christopher Tuan
Electrical Resistance Heating Of Conductive Concrete Containing Steel Fibers And Shavings, Christopher Tuan
Christopher Y. Tuan
Conductive concrete is a category of concrete containing electrically conductive components to attain stable and high electrical conductivity. Due to its electrical resistance and impedance, a thin conductive concrete overlay can generate enough heat to prevent ice formation on a bridge deck when connected to a power source. Steel fibers and steel shavings were used for the conductive materials in this study. A conventional concrete slab, 1.2 x 3.6 m (4 x 12 ft), has been constructed with a 9 cm (3.5 in.) conductive concrete overlay for conducting deicing experiments in the natural environment. The conductive concrete mixture was developed …
Development Of Kansas Guardrail To Bridgerail Transition Designs Using Barrier Vii, Christopher Tuan, Edward Post, Syed Atuallah, J. Brewer
Development Of Kansas Guardrail To Bridgerail Transition Designs Using Barrier Vii, Christopher Tuan, Edward Post, Syed Atuallah, J. Brewer
Christopher Y. Tuan
BARRIER VII computer code was used to evaluate the dynamic performance of five Kansas guardrail-to-bridgerail transition designs. The simulation results were compared with those of two FHWA-approved transition designs. The test vehicle model was a 4,500-lb, 1977 Plymouth impacting the barriers at 60 mph with an approach angle of 25 deg. The vehicle-crushing properties and guardrail-post stiffness had been validated using full-scale vehicle crash test data before the simulations were conducted. A methodology for wheel-snagging prediction was also proposed and validated against available test data. It was shown that reliable simulation results could be obtained if the input parameters for …
Review Of Live Loads Due To Human Movements, William Saul, Christopher Tuan
Review Of Live Loads Due To Human Movements, William Saul, Christopher Tuan
Christopher Y. Tuan
Present U.S. structural engineering practice assumes that live load components due to human occupancy and human movements for the design of assembly structures, such as grandstands, can be represented as statically applied uniform or line loads. A review of code values and procedures reveals a history of theoretical, experimental, empirical, and practical developments and events that provide insight into their sources and meanings. The mechanisms by which they have been implemented should prove to be interesting and informative to the design engineer and others concerned with the modernization of codes. The designer is provided with a perspective of a complex …