Accuracy of bubble velocity measurement with a four-point optical fibre probe

For the operation of high void fraction bubbly flows in bubble\ud columns, insight in primary parameters such as bubble size,\ud shape and velocity as well as gas volume fraction is essential.\ud At high gas volume fractions the flow system becomes\ud opaque, ruling out non-intrusive optical techniques. As an\ud alternative optical fibre probes can be used, which have the\ud advantage of low cost, simplicity of setup and easy\ud interpretation of the results.\ud By using four-point optical fibre probe, properties of bubbles\ud can be studied, such as bubble velocity, bubble size, etc.\ud However, the effect of bubble wobbling behaviour and\ud physical properties of liquids on the accuracy of the velocity\ud measurements has not been investigated in detail.\ud In the present study, the performance of a four-point optical\ud fibre probe was evaluated for five different liquids. The probe\ud performance and causes of inaccuracies are discuss

Thickness Design Curves for Portland Cement Concrete Pavements

Past experience indicates that thickness designs using portland cement concrete best agree with criterion used in the Portland Cement Association\u27s design method for 18-kip EAL of 2 to 3 million or less. For EALs greater than 2 to 3 million, past experience best agrees with criterion developed from the AASHO Road Test. Research herein indicates the two criterion become asymptotic to each other at approximately 2.5 million EAL. For a variation in thickness and elastic moduli in portland cement concrete, dense-graded aggregate, and sub grade elastic modulus, research indicates that a general conic equation (included herein) very closely duplicates the work at the bottom of the portland cement concrete caused by an 18-kip single axle load. The transition from a tensile strain to a work criterion is presented. Decreasing the thickness of dense-graded aggregate base caused a maximum increase of 0.15 inches in the thickness of portland cement concrete. Thus, the thicknesses of the portland cement concrete were averaged. The resulting thickness design curves are presented for a concrete elastic modulus of 4.2 million psi (Kentucky concrete strength)

Suggested Changes to Kentucky Statutes (Vehicle Weights and Dimensions)

The purposes of this report are: 1. To clearly define the terms \u27\u27tandem, tridem, and “triaxle. 2. To clearly define the term 600 pounds per inch width of tire as the width of the tread in contact with the pavement. 3. To make the axle load limits the same throughout the statutes. 4. To suggest elimination of indentified discriminatory legislation. 5. To recommend additional legislation: a. to clearly define the purpose and use of air-bag suspension systems -- those that can be raised or lowered by the driver, and b. to enable vehicle weight enforcement officers to use shipping documents as evidence to issue overweight citations without having to weigh the trucks. These documents may be in the possession of the driver, or in the files of the shipping and/ or receiving firms

Distributions of Strain Components and Work Within Flexible Pavement Structures

An investigation was made to determine the location along the centerline of the axle of the maximum strain energy density, or work, in the pavement as defined by classical physics. The location is under the inside edge of either dual tire. The most influential strain was the shear component. The distribution of shear strains and stresses with depth through the full-depth asphaltic concrete and into the subgrade was investigated. Using Simpson\u27s rule for an even number of increments, or using the trapezoidal rule, allows the summation of strain energy density calculated at various depths. This sum multiplied by a unit volume converts the strain energy density to work as defined by classical physics. The sum of work throughout the pavement structure provides a greater insight to the behavior of the pavement because all components of strain, or stress, are considered and the variation throughout the depth may be large according to the location within the tire print. The sum of strain energy density is much greater under the edge of the dual tire compared to that under the center of the dual tire, yet the magnitude of the strain energy density at the bottom of the asphaltic concrete may be nearly identical. For an 18-kip (80-kN) four-tired single axleload, the depth of maximum shear is approximately 35 to 40 percent of the thickness from the surface downward for a maximum pavement thickness of approximately 8 inches (203 mm); thereafter the depth of maximum shear moves toward the surface as the thickness increases. An investigation of shear stress indicated the maximum value was approximately 67 psi (0.46 GPa) due to an 18-kip (80-kN) single axleload and tire contact pressure of 80 psi (0.63 GPa). For an 80-kip (36-kN) tandem axleload and tire contact pressures of 100 psi (0.69 GPa), the shear stress increased o approximately 133 psi (0.92 GPa). As the tire contact pressures of 100 psi (o.69 GPa), the shear stress increased to approximately 133 psi (0.92 GPa). As the tire contact pressure increases, the shear stress may approach 200 psi (1.38 GPa). Recommendations include eliminating any construction plane between the 1- to 4-inch (25– to 102–mm) depth from the surface and determining the shear resistance of the asphaltic concrete mix to insure that the mix can withstand a higher shear stress that is currently being obtained. Target values of shear stress have not been recommended for adoption because a limiting value has not been found in the literature

Variable Serviceability Concept for Pavement Design Confirmed by AASHO Road Test Fatigue Data

Fatigue data from the AASHO Road Test were plotted for each level of serviceability. The Kentucky thickness design system uses the concept of a variable level of serviceability as a function of EALs. The Kentucky thickness design curve for the equivalent CBR was converted to an equivalent structural number and superimposed on each of the specific serviceability figures. The AASHTO Equation C–14 of the 1972 AASHTO Interim Guide was evaluated for each level of serviceability and superimposed on its respective figure. Equation C–14 fits reasonably well for serviceability levels of 2.0 and 2.5 but does not fit the remining serviceability levels. the Kentucky thickness curve is asymptotic to a portion of each figure and directly related to level of serviceability. Figure 6 is a composite of portions of Figures 1 through 5 created by lifting the portion of each level of serviceability for which the Kentucky thickness design curve was asymptotic to the data for specific range in EAL. The composite figure illustrates the potentiality of the AASHTO design method being expressed by one nomograph (not developed or shown herein) in which the serviceability level increases as EAL increases

Truck Design and Usage and Highway Pavement Performance

When the term highway pavement is used, most people think of the moderate to thick systems on which their vehicles travel on intermediate- or high-type roadways. These pavement systems are typically constructed of bituminous concrete or portland cement concrete. This is not to say that low-volume roads do not have a pavement system; however, in case of low-volume roads, the pavement system usually consists of unbound aggregates, sod, soil materials, or at the most very thin or moderate applications of a binding material. It is the high-type pavement systems to which the comments in this paper will be addressed specifically. These high-type pavements serve two primary functions. On the one hand, these pavements are the wearing surface upon which the tires of the vehicles travel. Because of high stresses at the tire-pavement interface, the surfacing materials must be extremely stable. The hard, bound surface provides a dust-free and smooth-riding surface. Secondly, the pavement system provides a means of transferring the total load of the vehicle to the supporting subgrade or earth foundation. The design of such a pavement system is thus a structural problem very similar to the design of bridges or office buildings

Deflection Behavior of Asphaltic Concrete Pavements

Deflection responses of a series of experimental test sections were obtained layer by layer during construction, upon completion of construction, and subsequent to construction. Deflections were obtained by use of Benkelman beams, the Road Rater, and the Dynaflect. Test results from one location within each test section were analyzed to determine which relationships were, or were not, meaningful. This was done as a pilot study and as a preliminary step toward final analysis of the data bank. The analyses are presented in this report

Variations of Fatigue Due to Unevenly Loaded Axles within Tridem Groups

The effect of unevenly distributed loads on the axles within a tridem has been shown to be very significant. Equations are presented that enable the equivalent load effect for equal load distribution to be adjusted for uneven loading. Considering the relative increase and the relatively small volume of trucks currently using tridems, the equation for all tridems without regard to locations on the vehicle is recommended at this time. Consideration should be given to using equations for individual load patterns as the volume of trucks using tridems increases and more weight data become available