Differential Deflection Research Articles

Girder Differential Deflection and Distortion-Induced Fatigue in Skewed Steel Bridges

The prevalence of fatigue cracking in steel bridge girders due to out-of-plane web distortion motivates development of procedures to evaluate the effects of distortional fatigue. In a previous study sponsored by the Minnesota Department of Transportation (Mn/DOT) the frequency and magnitude of distortional stresses on a typical skewed, steel bridge with staggered, bent-plate diaphragms were assessed. The results revealed a diaphragm deformation mechanism that causes distortional fatigue in the girder web gap, leading to simple, accurate estimates of fatigue stress if bridge properties and differential vertical deflection between girders are known. In the present study, linear finite element models are used to represent composite steel bridges and identify bridge parameters that influence relative deflection of adjacent girders. Parameters found to have a significant effect on differential deflection include girder spacing, angle of skew, span length, and deck thickness. These results are incorporated in a simple procedure that is intended for use in management schemes for skewed, steel-girder bridges, with staggered, bent-plate diaphragms, susceptible to web gap distortional fatigue.

Detection ofBacillussubtilisSpores Using Peptide-Functionalized Cantilever Arrays

We move beyond antibody-antigen binding systems and demonstrate that short peptide ligands can be used to efficiently capture Bacillus subtilis (a simulant of Bacillus anthracis) spores in liquids. On an eight-cantilever array chip, four cantilevers were coated with binding peptide (NHFLPKV-GGGC) and the other four were coated with control peptide (LFNKHVP-GGGC) for reagentless detection of whole B. subtilis spores in liquids. The peptide-ligand-functionalized microcantilever chip was mounted onto a fluid cell filled with a B. subtilis spore suspension for approximately 40 min; a 40 nm net differential deflection was observed. Fifth-mode resonant frequency measurements were also performed before and after dipping microcantilever arrays into a static B. subtilis solution showing a substantial decrease in frequency for binding-peptide-coated microcantilevers as compared to that for control peptide cantilevers. Further confirmation was obtained by subsequent examination of the microcantilever arrays under a dark-field microscope. Applications of this technology will serve as a platform for the detection of pathogenic organisms including biowarfare agents.

Minimizing differential deflection in a pontoon-type, very large floating structure via gill cells

When a pontoon-type, very large floating structure is heavily loaded in the central portion, it will deform with its central deflection much larger than its corner deflections. The resulting differential deflection, if large enough, may cause machines and equipment sensitive to differential deflection to cease operation or the floating structure to be subjected to additional large stresses. In this paper, we introduce the so-called gill cells which are compartments within the floating structure with holes or slits at the bottom floor to allow water to flow in and out freely. It will be shown herein that these gill cells reduce the differential deflection and the bending stresses significantly while maintaining the structural stiffness integrity by using the example problem of a super-large floating container terminal.

Micro-elastohydrodynamic lubrication of coated cylinders using coupled differential deflection method

A numerical solution for the micro-elastohydrodynamic lubrication (EHL) problem of two coated elastic bodies in line contact is presented. This incorporates non-Newtonian behaviour of the lubricant, using an Eyring-type non-linear viscous model. The surface elastic deformations are computed from full elasticity analysis of layered elastic half-spaces. The coupled differential deflection method is used in the numerical solution of the micro-EHL mathematical model. Results are presented for smooth surface, steady-state problems that compare the influence of coating elastic modulus and coating thickness on calculated lubricant pressure and film thickness distributions. Some transient results are also included, where the effect of coatings on a single ridge feature and on a rough surface in rolling/sliding contact is examined.

BISMALEIMIDES (N, N′-BISMALEIMIDE-4, 4′-DIPHENYLMETHANE AND N, N′-BISMALEIMIDEO-4, 4′-DIPHENYLSULPHONE) MODIFIED BISPHENOLDICYANATE–EPOXY MATRICES FOR ENGINEERING APPLICATIONS

ABSTRACT An interpenetrating network of cyanate ester (CE)-bismaleimide (BMI)-epoxy matrix systems was developed. Epoxy systems modified with 4%, 8%, and 12% (by wt) of cyanate ester were made by using epoxy resin and cyanate ester with diaminodiphenylmethane as curing agent. The cyanate-ester-toughened epoxy systems were further modified with 4%, 8%, and 12% (by wt) of bismaleimides, namely N, N′-bismaleimido-4, 4′-diphenylmethane and N, N′-bismaleimido-4, 4′-diphenylsulphone. BMI-CE-Epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and heat deflection temperature (HDT) analysis. The DSC thermograms of cyanate-ester-modified epoxy and BMI-modified epoxy during cure show unimodal reaction exotherms. The studies indicate that thermal stability and resistance to water absorption of epoxy resin has been enhanced by the introduction of cyanate ester. The incorporation of bismaleimide into unmodified epoxy and CE epoxy enhanced the thermal and mechanical properties according to its percentage content. The morphologies of fractured surfaces of modified epoxy systems were compared with the unmodified epoxy system.

Live Load Deflection Performance of Glued Laminated Timber Girder Bridges

To demonstrate and possibly to promote the increased use of timber bridges in U.S. transportation systems, various agencies, including the United States Department of Agriculture Forest Products Laboratory and FHWA, have supported research to develop improved glued laminated timber bridges. This project is part of this research and identifies acceptable live load deflection characteristics of timber bridges. The relationship between live load deflection and the condition of the asphalt wearing surface is of particular interest. To accomplish this, eight glued laminated timber girder bridges were selected for testing. The performance of the bridges was investigated under live load tests and through bridge inspections. The structures were load tested with fully loaded tandem-axle dump trucks, and global and differential deflection data were collected. Field tests revealed that a significant amount of the asphalt wearing-surface deterioration is the result of differential deck panel deflection.

Live Load Deflection Performance of Glued Laminated Timber Girder Bridges

To demonstrate and possibly to promote the increased use of timber bridges in U.S. transportation systems, various agencies, including the United States Department of Agriculture Forest Products Laboratory and FHWA, have supported research to develop improved glued laminated timber bridges. This project is part of this research and identifies acceptable live load deflection characteristics of timber bridges. The relationship between live load deflection and the condition of the asphalt wearing surface is of particular interest. To accomplish this, eight glued laminated timber girder bridges were selected for testing. The performance of the bridges was investigated under live load tests and through bridge inspections. The structures were load tested with fully loaded tandem-axle dump trucks, and global and differential deflection data were collected. Field tests revealed that a significant amount of the asphalt wearing-surface deterioration is the result of differential deck panel deflection.

In vitro cuspal deflection and microleakage of maxillary premolars restored with novel low-shrink dental composites

The development of novel low-shrink resin-based composites (RBCs) may offer a potential reduction in polymerisation shrinkage stresses generated at the tooth/restoration interface compared with current methacrylate RBCs. In vitro cuspal deflection and microleakage of meiso-occlusal-distal (MOD) cavities restored with experimental oxirane and silorane (EXL596 and H1) and methacrylate (Z100 and Filtek Z250) RBCs were assessed. Standardised pre-molar MOD cavities were prepared (n = 10) and restored with each material. The flexure of buccal and palatal cusps was recorded 0.1 h following irradiation utilising a differential transformer deflection gauge. Each restored tooth was subjected to a thermocycling regime and microleakage of tooth sections were assessed following 24 h immersion in 0.2% fuschin dye. The degree of conversion (DC) of each RBC material was also assessed using Fourier transform infrared (FTIR) spectroscopy following 0.1, 0.5, 1, 4, 24 and 48 h post-irradiation. A total cuspal deflection was observed for EXL596 (2.5 +/- 0.9 microm) and H1 (6.0 +/- 1.8 microm) compared with Z100 (20.0 +/- 4.7 microm) and Filtek Z250 (16.5 +/- 3.3 microm) following 0.1 h. The cavities restored with EXL596 displayed significantly higher microleakage than any other RBC and H1 exhibited non-significant and significantly decreased microleakage compared with Z100 and Filtek Z250, respectively. The DC of EXL596 and H1 was significantly decreased compared with Z100 and Filtek Z250 following 0.1, 0.5 and 1 h. The 'living' polymerisation associated with the novel oxirane and silorane RBCs and the associated decrease in cuspal deflection may suggest a decrease in the magnitude of polymerisation shrinkage stress at the tooth/restoration interface. The decreased DC following 0.1 h of the oxirane compared with the methacrylate RBCs has provided information on the cure rate of cationic and free-radical polymerisation mechanisms, respectively. The inadequate marginal seal of cavities restored with EXL596 would preclude its use as a dental restorative. The reduction in cuspal deflection and decrease in microleakage of cavities restored with H1 compared with Filtek Z250 may be advantageous in terms of marginal integrity following placement. However, the non-significant difference in microleakage between the H1 and Z100 may only present modest decreases in the deleterious effects of shrinkage stress.

Synthesis and Characterization of 1,1-bis(3-Methyl-4-Cyanatophenyl) Cyclohexane-Epoxy-Bismaleimide Matrices

A new cyanate ester monomer, 1,1-bis(3-methyl-4-cyanatophenyl) cyclohexane has been synthesized and characterized. Epoxy modified with 4, 8 and 12% (by wt) of cyanate ester were made using epoxy resin and 1,1-bis(3-methyl-4-cyanatophenyl) cyclohexane and cured by using diaminodiphenyl-methane. The cyanate ester modified epoxy matrix systems were further modified with 4, 8 and 12% (by wt) of bismaleimide ( N,N′-bismaleimido-4,4′-diphenyl methane). The formation of oxazolidinone and isocyanurate during cure reaction of epoxy and cyanate ester blend was confirmed by IR spectral studies. Bismaleimide-cyanate ester-epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. The matrices, in the form of castings, were characterized for their mechanical properties; namely tensile strength, flexural strength and unnotched Izod impact test as per ASTM methods. Mechanical studies indicate that the introduction of cyanate ester (CE) into epoxy resin improves the toughness and flexural strength with reduction in tensile strength and glass transition temperature, whereas the incorporation of bismaleimide (BMI) into epoxy resin enhances the mechanical and thermal properties according to its percentage content. However, the introduction of both CE and BMI enhances the values of thermo-mechanical properties according to their percentage content. DSC thermogram of cyanate ester modified epoxy and BMI-modified epoxy show an unimodal reaction exotherms. The thermal degradation temperature and heat distortion temperature of the cured BMI-modified epoxy and CE-epoxy systems were increased with increasing BMI content. The morphology of the BMI modified epoxy and CE-epoxy systems were also studied by scanning electron microscope.

A 2-D Microcantilever Array for Multiplexed Biomolecular Analysis

An accurate, rapid, and quantitative method for analyzing variety of biomolecules, such as DNA and proteins, is necessary in many biomedical applications and could help address several scientific issues in molecular biology. Recent experiments have shown that when specific biological reactions occur on one surface of a microcantilever beam, the resulting changes in surface stress deflect the cantilever beam. To exploit this phenomenon for high-throughput label-free biomolecular analysis, we have developed a chip containing a two-dimensional (2-D) array of silicon nitride cantilevers with a thin gold coating on one surface. Integration of microfluid cells on the chip allows for individual functionalization of each cantilever of the array, which is designed to respond specifically to a target analyte. An optical system to readout deflections of multiple cantilevers was also developed. The cantilevers exhibited thermomechanical sensitivity with a standard deviation of seven percent, and were found to fall into two categories-those whose deflections tracked each other in response to external stimuli, and those whose did not due to drift. The best performance of two cantilevers showed a maximum difference of 4 nm in their deflections. Although nontracking cantilevers exhibited large differences in their drift behavior, an upper bound of their time-dependent drift was determined, which could allow for rapid bioassays. Using the differential deflection signal between tracking cantilevers, immobilization of 25mer thiolated single-stranded DNA (ssDNA) on gold surfaces produced repeatable deflections of 80 nm or so on 0.5-/spl mu/m-thick and 200-/spl mu/m-long cantilevers.

DEVELOPMENT AND CHARACTERIZATION OF VINYL ESTER OLIGOMER (VEO) MODIFIED UNSATURATED POLYESTER INTERCROSSLINKED MATRICES AND COMPOSITES

An intercrosslinked network of varying percentage of vinyl ester oligomer (VEO) modified unsaturated polyester matrices has been developed. Vinyl ester oligomer was prepared by reacting commercially available epoxy resins GY 250 (Ciba-Geigy) and acrylic acid and was used as toughening agent for unsaturated polyester (UP) resin. Unsaturated polyesters modified with 10%, 20% and 30% (by wt) of vinyl ester oligomer were made. E-glass reinforced composites were fabricated by hand lay–up technique using VEO-UP matrix systems. VEO modified unsaturated polyesters were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. The matrices in the form of castings and E-glass reinforced composites were characterized for their mechanical properties, i.e., tensile strength, flexural strength and unnotched-Izod impact test as per ASTM methods. Data obtained from mechanical studies and thermal characterization indicate that the introduction of VEO into unsaturated polyester resin improves the thermo-mechanical properties and negatively affects the moisture resistance according to its percentage concentration.

Preparation and characterization of bismaleimide‐modified bisphenol dicyanate epoxy matrices

AbstractAn intercrosslinked network of epoxy matrix systems modified by cyanate ester (CE) and bismaleimide (BMI) was developed. Epoxy systems modified with 4%, 8%, and 12% (by weight) cyanate ester were made by using epoxy resin and cyanate ester, with diaminodiphenylmethane as the curing agent. The reaction between the cyanate ester and the epoxy resin during the cure process of cyanate ester–modified epoxy systems was studied using Fourier transform infrared spectroscopy. The cyanate ester–toughened epoxy systems were further modified with 4%, 8%, and 12% (by weight) bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenylmethane). BMI–CE–Epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis, and heat deflection temperature analysis. The matrices, in the form of castings, were characterized for their mechanical properties such as tensile strength, flexural strength, and unnotched Izod impact test as per ASTM methods. Mechanical studies indicated that the introduction of cyanate ester into epoxy resin improved the toughness and flexural strength, with a reduction in tensile strength and glass‐transition temperature, whereas the incorporation of bismaleimide into epoxy resin influenced the mechanical and thermal properties according to its percentage content. However, the introduction of both cyanate ester and bismaleimide influenced the mechanical properties according to their percentage content. DSC thermograms of cyanate ester–modified epoxy and BMI‐modified epoxy showed unimodal reaction exotherms. The thermal degradation temperature and heat distortion temperature of the cured BMI‐modified epoxy and CE‐epoxy systems increased with increasing bismaleimide content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1596–1603, 2003

Analysis method for PSC-girder bridge deck slab with flexible girders

This paper deals with the assessment of load carrying capacity and safety of PSC-girder bridge decks. It has been observed from the result of load test and analysis that the differential deflection between girders in PSC-girder bridge deck reduces the negative bending moments in the deck slab. In this study, closed-form analysis method considering the effect of girder deflection is developed, based on the elastic plate theory. In this study, analytical solution with the elastic plate theory and numerical analyses with finite element modeling are performed and the results are compared with those of experimental studies for PSC-girder bridge. As a result, the differential deflection of the girders, which can greatly reducethe negative moments in a deck slab, tensile stresses of top slab is reduced. The analytical solution and 3-D shell modeling presented in this paper more accurate in estimating these results.

Preparation and characterization of bismaleimide/1,3-dicyanatobenzene modified epoxy intercrosslinked matrices

An intercrosslinked network of cyanate ester (CE)–bismaleimide (BMI) modified epoxy matrix system was made by using epoxy resin, 1,3-dicyanatobenzene and bismaleimide (N,N ′-bismaleimido-4,4 ′-diphenyl methane) with diaminodiphenylmethane as curing agent. BMI–CE–epoxy matrices were characterised using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. The matrices, in the form of castings, were characterised for their mechanical properties such as tensile strength, flexural strength and unnotched Izod impact test as per ASTM methods. Mechanical studies indicated that the introduction of cyanate ester into epoxy resin improves the toughness and flexural strength with reduction in tensile strength and glass transition temperature, whereas the incorporation of bismaleimide into epoxy resin influences the mechanical and thermal properties according to its percentage content. DSC thermograms of cyanate ester as well as BMI modified epoxy resin show an unimodal reaction exotherm. Electrical properties were studied as per ASTM method and the morphology of the BMI modified epoxy and CE–epoxy systems were studied by scanning electron microscope.

Microfabricated mechanical biosensor with inherently differential readout

We report measurements with a micromachined mechanical biosensor that inherently suppresses background effects by producing a differential signal with respect to a reference. The sensor comprises two adjacent cantilevers with interdigitated fingers between them that allow interferometric detection of the differential, i.e., relative bending. We demonstrate that differential detection can efficiently suppress unspecific chemical effects that result in cantilever bending. We show that the differential deflection noise is up to an order of magnitude lower than the absolute deflection noise in the low-frequency range of 0.0003–1 Hz, where many types of biologically relevant reactions occur. We also demonstrate the sensor’s applicability to biological receptor–ligand systems by reporting experimental results on direct differential detection of biotin–streptavidin binding.

Preparation and characterization of epoxy‐cyanate ester interpenetrating network matrices/organoclay nanocomposites

AbstractThe interpenetrating network matrices of epoxy and cyanate ester was made using epoxy resin and three different cyanate ester monomers namely 1,1‐bis(3‐methyl‐4‐cyanatophenyl) cyclohexane, bisphenol dicyanate and 1,3‐dicyanatobenzene and cured by using diaminodiphenylmethane. Epoxy modified with 4, 8 and 12% (by weight) of cyanate esters were made. Cyanate ester modified epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. Thermal studies indicate that the introduction of cyanate ester into epoxy resin improves the thermal degradation studies at the expense of glass transition temperature. DSC thermogram of cyanate ester modified epoxy show unimodel reaction exotherms. The matrices, in the form of castings, were characterized for their mechanical properties namely, tensile strength, flexural strength and unnotched Izod impact test as per ASTM methods. Mechanical studies indicate that the introduction of cyanate ester into epoxy resin improves the toughness and flexural strength with reduction in tensile strength. The morphology of the epoxy and cyanate ester‐epoxy systems were also studied by scanning electron microscope (SEM). The organophilic montmorillonite clay‐epoxy and cyanate ester‐epoxy nanocomposites are prepared and the formation nanocomposites are evaluated by X‐ray diffraction (XRD), dynamic mechanical analysis (DMA) and SEM. Copyright © 2003 John Wiley & Sons, Ltd.

Studies on thermal and morphological properties of 1,1‐bis(3‐methyl‐4‐cyanatophenyl)cyclohexane‐epoxy‐bismaleimide matrices

AbstractA new cyanate ester monomer, 1,1‐bis(3‐methyl‐4‐cyanatophenyl)cyclohexane has been synthesized and characterized. Epoxy modified with 4, 8 and 12% (by weight) of cyanate ester were made using epoxy resin and 1,1‐bis(3‐methyl‐4‐cyanatophenyl)cyclohexane and cured by using diaminodiphenylmethane. The cyanate ester modified epoxy matrix systems were further modified with 4, 8 and 12% (by weight) of bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenylmethane). The formation of oxazolidinone and isocyanurate during cure reaction of epoxy and cyanate ester blend was confirmed by IR spectral studies. Bismaleimide‐cyanate ester‐epoxy matrices were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and heat deflection temperature (HDT) analysis. Thermal studies indicate that the introduction of cyanate ester into epoxy resin improves the thermal degradation studies at the expense of glass transition temperature. Whereas the incorporation of bismaleimide into epoxy resin enhances the thermal properties according to its percentage content. However, the introduction of both cyanate ester and bismaleimide influences the thermal properties according to their percentage content. DSC thermogram of cyanate ester modified epoxy and bismaleimide modified epoxy show unimodel reaction exotherms. The thermal degradation temperature and heat distortion temperature of the cured bismaleimide modified epoxy and cyanate ester‐epoxy systems increased with increasing bismaleimide content. The morphology of the bismaleimide modified epoxy and cyanate ester‐epoxy systems were also studied by scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd.

Effect of creep and shrinkage in reinforced concrete frame–shear wall system with high beam stiffness

AbstractThe behaviour of frames and frame–shear wall systems with regard to creep and shrinkage with high beam stiffness has been largely unexplored until recently since no procedure has been available. For low beam stiffness the most widely used procedure available in literature for determining creep and shrinkage effects in reinforced concrete building frames and frame–shear wall systems designated herein as approximate procedure, AP has been recommended for buildings having flexible slab systems and with a limited number of storeys. Recently an accurate procedure termed Consistent Procedure (CP) has been developed which is applicable to low as well as high beam stiffness and requires no restriction on number of storeys. In this paper, using CP, studies are reported for frame–shear wall systems with high beam stiffness. The effect of introduction of shear walls on load transfer among vertical members considering creep and shrinkage is studied. It is shown that the presence of shear wall alters significantly the load transfer among vertical members. It is also shown that whereas differential vertical deflections between adjacent vertical members are small owing to high stiffness of beams, the load transfer between them can be significant. Copyright © 2003 John Wiley & Sons, Ltd.

Transient elastohydrodynamic point contact analysis using a new coupled differential deflection method Part 1: Theory and validation

The paper presents a transient analysis technique for point contact elastohydrodynamic (EHL) lubrication problems using coupled elastic and hydrodynamic equations. Full coupling is made possible by use of a novel differential deflection formulation. The way in which the differential deflection is incorporated into the overall solution method for a point contact is discussed. A range of spatial and temporal discretization methods are incorporated and compared. The method is validated under transient conditions by a detailed comparison with published work produced using a different, independent method incorporating a moving roughness feature. A comparison of the results with different discretization methods leads to the conclusion that spatial central differencing with a Crank-Nicolson temporal discretization is the most effective finite difference scheme, and this is generally equivalent to the finite element discretization given in detail in the paper. A comparison of the results produced for moving rough surfaces suggests that the finite element formulation is preferred.

Transient elastohydrodynamic point contact analysis using a new coupled differential deflection method Part 2: Results

The paper presents results obtained using a transient analysis technique for point contact elastohydrodynamic lubrication (EHL) problems based on a formulation that effectively couples the elastic and hydrodynamic equations. Results are presented for transverse ground surfaces in an elliptical contact that show severe film thinning at the transverse limits of the contact area. This thinning is caused by transverse (side) leakage of the lubricant from the contact in the remaining deep valley features. Comparison is made between the elliptical contact results on the entrainment centreline and the equivalent line contact analysis. This confirms the importance of edge effects as a likely cause of film collapse and scuffing failure. The surface profiles used in the analysis are taken from test discs used in scuffing experiments and from gears used in micropitting tests. Side leakage is found to be sufficiently severe to cause microasperity contact in the numerical examples presented. This contact mainly occurs close to the edges of the corresponding Hertzian area and correlates in position with the location at which scuffing is found to first occur in the earlier experiments. Comparisons are made with other numerical results for point contact configurations with sinusoidally varying surface features obtained by Zhu (2000) and considerable differences are seen in the calculated extent of asperity contact. The differences are thought to be due to the simplified treatment of the lubrication equation adopted by Zhu.