Panel Dimensions Research Articles

Optimal design of grid-stiffened panels and shells with variable curvature

A design strategy for optimal design of composite grid-stiffened structures with variable curvature subjected to global and local buckling constraints is developed using a discrete optimizer. An improved smeared stiffener theory is used for the global buckling analysis. Local buckling of skin segments is assessed using a Rayleigh–Ritz method that accounts for material anisotropy and transverse shear flexibility. The local buckling of stiffener segments is also assessed. Design variables are the axial and transverse stiffener spacing, stiffener height and thickness, skin laminate, and stiffening configuration. Stiffening configuration is herein defined as a design variable that indicates the combination of axial, transverse and diagonal stiffeners in the stiffened panel. The design optimization process is adapted to identify the lightest-weight stiffening configuration and stiffener spacing for grid-stiffened composite panels given the overall panel dimensions, in-plane design loads, material properties, and boundary conditions of the grid-stiffened panel or shell.

The beam pattern of the IRAM 30–m telescope

Total power scans across the Moon around New Moon (mostly day time) and Full Moon (night time) at 3.4 mm (88 GHz), 2.0 mm (150 GHz), 1.3 mm (230GHz), and 0.86 mm (350 GHz) wavelength are used to derive the beam pattern of the IRAM 30-m telescope to a level of approximately -30 dB(0.1%) and, dependent on wavelength, to a full width of 1000 - 1400''. From the reflector surface construction and application of the antenna tolerance theory we find that the measurable beam consists of the diffracted beam, two underlying error beams which can be explained from the panel dimensions, and a beam deformation mostly due to large-scale transient residual thermal deformations of the telescope structure. In view of the multiple beam structure of the 30-m telescope, and of other telescopes with a similar reflector construction of (mini-)panels and panel frames, we summarize the antenna tolerance theory for the influence of several independent surface/wave front deformations. This theory makes use of different correlation lengths, which in essence determine the independent error distributions, and of the wavelength-scaling of the diffracted beam and of the error beams. From the Moon scans we derive the parameters for calculation of the 30-mtelescope beam in the wavelength range 3 mm to 0.8 mm as required for the reduction of astronomical observations, in particular of extended sources. The parameters of the beam are primarily for the time after July 1997 when the reflector was re-adjusted and improved to the illumination weighted surface precision of sigma _T = 0.065 - 0.075 mm.In the Appendix we explain the choice for this analysis of scans taken around New Moon and Full Moon.

Optimal Design of Grid-Stiffened Composite Panels

A design strategy for optimal design of composite grid-stiffened panels subjected to global and local buckling constraints is developed using a discrete optimizer. An improved smeared stiffener theory is used for the global buckling analysis. Local buckling of skin segments is assessed using a Rayleigh-Ritz method that accounts for material anisotropy and transverse shear flexibility. The local buckling of stiffener segments is also assessed. Design variables are the axial and transverse stiffener spacing, stiffener height and thickness, skin laminate, and stiffening configuration, where the stiffening configuration is herein defined as a design variable that indicates the combination of axial, transverse, and diagonal stiffeners in the stiffened panel. The design optimization process is adapted to identify the lightest-weight stiffening configuration and stiffener spacing for grid-stiffened composite panels given the overall panel dimensions, in-plane design loads, material properties, and boundary conditions of the grid-stiffened panel.

Seismic tomography survey under the La Gileppe Dam

Abstract A tomographic survey of 15 panels was performed under the La Gileppe dam (Belgium) to assess the degree of fracturing in the rock foundation which consists of steeply dipping beds of sandstone and shale. A particular aim of the study was to locate fracture zones likely to cause leakage under the dam. The panel dimensions range from 9 by 15 m (between 2 boreholes) to 60 by 40 m (between 4 boreholes). An explosive source and a 12 hydrophone string were used for the experiment. The data inversion was made with the Rai2D software of the L.C.P.C. (Laboratoire Central des Ponts et ChaussÉes), based on the SIRT algorithm with circular ray paths. The velocity values were influenced both by rock type and fracturing. The tomography method has been shown to image successfully low velocity fracture zones which could not have been determined by classical cross-hole tests. In some cases, tomograms showed cross shape images with a high velocity zone along the diagonals. These artefacts have been explained by numerical modelling as a result of the poor angular ray coverage of the section.

Shear Lag in Shear/Core Walls

Shear lag occurs not only in bridge decks and framed tubes, but also in shear/core walls. However, there have been relatively few studies on shear lag in wall structures. Moreover, most existing theories neglect shear lag in the webs and, although they are acceptable for bridge decks that normally have flanges wider than webs, they may not be applicable to shear/core walls whose webs can be much wider than flanges. To study the shear lag phenomenon in wall structures, a parametric study using finite-element analysis is carried out. Unlike previous studies that neglected shear lag in the webs, many layers of elements are used for both the webs and flanges so that shear lag in the webs can also be taken into account. The results indicate that the shape of the longitudinal stress distribution in an individual web or flange panel is quite independent of the dimensions of the other panels. Based on this observation, design charts and empirical formulas for estimating the shear lag effects are developed for practical applications.

Interface Horizontal Shear Strength in Composite Decks With Precast Concrete Panels

Six stay-in-place precast, prestressed deck panels were tested to evaluate the horizontal shear strength between the precast panel and the cast-in-place portion of the bridge deck. Presently, the Indiana Department of Transportation requires a minimum of 20 shear connectors regardless of panel dimensions. The shear connectors are placed across a broom finished deck panel surface. Broom finish with approximately 0.05 to 0.075 in. (1.27 to 1.91 mm) total amplitude deformations is specified instead of a raked finish with 0,25 in. (6.35 mm) total amplitude because of the reduced 2.5 in. (63.5 mm) thickness of the panels used in Indiana. In this study, composite behavior at ultimate, including horizontal shear and interface slip characteristics, was evaluated. It is concluded that stay-in-place precast, prestressed deck panels with a broom finished surface do not require horizontal shear connectors if the nominal average horizontal shear stress at the interface is less than 116 psi (0.8 MPa).

Full Depth Precast and Precast, Prestressed Concrete Bridge Deck Panels

Since 1970, there has been a dramatic increase in the use of full depth precast and precast, prestressed concrete deck panels for the rehabilitation and new construction of bridges. In order to document the various applications of bridge deck panels in North America, a questionnaire survey was sent to the departments of transportation (DOTs) of individual states and one province. Requested information in the survey included type of construction, deck dimensions, deck supporting system, panel dimensions and reinforcement, type of connecting system between panels and supporting system, type of joint between the adjacent panels, type of bonding material used to fill the joints, problems associated with the joints, reasons for adverse results, and type of protection system. The returned questionnaires were compiled and analyzed. This paper summarizes the significant results of this survey

General stability of composite panels reinforced with flexible rods taking account of the side boundary conditions

Reinforced panels are the basic load-bearing elements of various structures. Optimization of massive structures requires consideration of deformation of the panel cross-sections. This is particularly important in determining the bearing strength at buckling. The load scheme, conditions for fixation of the panel cross-section, and bend-torsional stiffness taking account of the deformation of the rod cross-section affect the buckling load in real structures. The stress distribution prior to buckling must be known to solve the buckling problem properly. The stress in the panel is proportional to the active load. The stress distribution is assumed to be known according to our previous method [1]. The load scheme and panel dimensions are shown in Fig. 1. The stress distribution in the panel prior to buckling can be found using Eqs. (1)-(3). A view of the cross-section is given in Fig. 1. The displacements in the panel at buckling for the boundary area are found using Eqs. (4)-(6), while the stresses in the skin and stiffness are found using Eq. (7). Roots k1 and k2 are those of the characteristic equation and β is a dimensionless coordinate. The problem was solved using variational theory. The potential energy is given by Eqs. (8) and (9) by orihogonalization of Eqs. (5). The basic equations are converted to Eqs. (10) by evaluation of the components in Eqs. (8) and (9). Its calculation (11) gives the compression load. Optimization of parameter α gives the critical strength P1 = 6.93 kN (without taking account of the boundary area) and P2 = 5.31 kN (taking account of the boundary area).

Extended longwalls: is bigger better? : E. D. Thimons, R. A. Jankowski & G. L. Finfinger, Engineering & Mining Journal, 195(4), 1994, pp 16B–16F, 16H

Since the first introduction of longwalls into the U.S. mining industry, longwall mining productivity has been continually on the increase. These productivity gains have resulted from a number of operational and equipment changes. One constant trend over the years has been to increase the size of longwall panels. Recently, some longwall mines have opted to make significant increases in the size of their panels. These extended longwall panels offer some major benefits in terms of fewer panel moves, less entry development, and increased resource recovery. At the same time, large increases in panel dimensions result in changes in the mining environment, and these changes can have potential positive and negative health and safety implications. On the positive side, reducing the number of panel moves can reduce injury rates since more accidents occur during moves than during actual mining. Additionally, the amount of continuous miner development work is reduced, and since the frequency of accidents is higher for continuous mining than for longwall mining, overall accident rates should be lower. conversely, extended panels can introduce concerns with respect to dust and methane levels, ground control issues, ventilation planning, and fire and escape considerations. How longwalls are getting bigger, how this canmore » impact health and safety, and some practices implemented by current extended longwall operations to improve conditions are discussed.« less

RESEARCH PROGRAMME MICROCLIMATES: PAINTINGS ON PANEL AND CANVAS

In an experimental set-up, the microclimates inside two differently constructed sets of microclimate boxes (MC-boxes) were registered at different points inside and outside. The first group of MC-boxes was integrated into woodell picture frames. Glass was sealed into the rabbet of the frame with silicon adhesive and wooden strips covered with a rubber gasket were added to the reverse over which a rigid metal plate was attached, creating a sealed box (Type A). The second group of MC-boxes was constructed by sealing glass into the rabbets of alulllilliulll frames with silicon adhesive and covering the reverse with Perspex sheets sealed with rubber gaskets, creating sealed boxes (Type B). The interior dimensions of both types of MC-box were approximately the same, as were the dimensions of the oak test panels. A free-standing wall was constructed and placed in an environmentally controlled room. The temperature of the wall was controlled by a closed water system. On each side of the wall three MC-boxes were placed at an angle of 5.5 degrees, for a period of 10 consecutive weeks, under varying conditions of relative humidity (RH) and temperature. The boxes were:

Mathematical model for estimating the economic effectiveness of production process in coal panels and an example of its practical application

The paper includes the application foundations of the integrational method of mine production process modelling to planning the extraction process in coal panels. The main idea of mathematical model creation based on the principle of the integration of elementary structural units according to spatial, engineering, and time structures of the production process in longwall and exploitation panels is briefly described. The model can be used as an investigation tool for making optimal planning decisions according to the economic criterion assumed. An example of practical application of the method is briefly described. It takes into consideration the impact of exploitation panel dimensions on the optimal longwall face length. Selected conclusions derived from the calculation results are presented.

Wave-number analysis of active structural acoustic control of sound transmission through a panel

Active control of sound transmission through elastic structures, such as panels using structural inputs, has received considerable attention in recent years. The active control technique of improving structural transmission loss (TL) by applying control forces directly to the transmitting structure using single or multiple piezoelectric actuators mounted on the structure rather than using acoustic canceling sources is known as active structural acoustic control (ASAC) method. This paper presents results of experimental investigations of ASAC method in improving the TL of a panel. Wave-number analysis was employed to understand the mechanism of improving the TL of a panel using multiple piezoceramic actuators. Experiments were conducted to measure near-field sound radiation from a baffled panel (dimensions: 1.75 m×1.14 m×1.27 mm) subjected to acoustic excitation for both with and without active control conditions. The active control of the panel TL was achieved by four piezoceramic actuators mounted on the panel. An array of four microphones placed about 1 m away from the panel were used as error transducers for a multiple-input multiple-output active control system. The transmitted acoustic field was measured by a two-dimensional array of microphones (array size: 22×14). The wave-number frequency spectra of the sound field were obtained by implementing Fourier transforms on the spatial domain data. Sound intensity measurements were also made to determine improvements in panel transmission loss. Comparison of measured wave-number spectrum for the active control condition with that of baseline (without control) showed that sound radiation from the acoustically fast lower-order modes at low wave numbers is significantly reduced. Results from the near-field acoustical holographic measurements will also be discussed. The relative reduction in sound power levels due to ASAC estimated from the near-field holographic measurements compared very well with those obtained from sound intensity measurements.

An assessment of critical anthropometric dimensions for predicting the fit of a half-mask respirator.

The purpose of this study was to determine if facial dimensions for a group of subjects were predictive of the fit factors measured while one brand of half-mask respirator was worn. Fit factors and 12 facial dimensions measured on 30 female and 38 male subjects were analyzed by correlation coefficients; weighted, multiple linear regression; and discriminant analysis. Data were analyzed for all subjects, gender subgroups, a race subgroup (whites only), and race/gender subgroups. Significant correlation coefficients with the log-transformed fit factors were found for four dimensions; four dimensions had significant coefficients in four or more multiple linear regression models. Only two dimensions had significant coefficients in four or more discriminant analysis models. Menton-subnasale (lower face) length was the only dimension included in all three of these groups. Gender-specific regression models had very high coefficient of determination values (R2 > 0.85). Discriminant analysis of the data for all subjects and race/gender subgroups found very good predictive scores for statistical software-generated models and menton-subnasale length alone; these scores were significantly better than those for the model with the respirator test panel dimensions (face length and lip width). These analyses found that facial dimensions were good predictors of respirator fit for those subjects wearing one brand of half-mask respirator. Lower face length was consistently indicated as being correlated or associated with fit. These results would indicate that dimensions other than those currently used may be more appropriate to define a half-mask respirator test panel.

The central pavilion in the IFEMA fairground. Madrid

The Central Pavilion, with its square floor and a large circular central patio, rises in the southernmost point of the Axis of the IFEMA Fairground. This article deals with the composition of its two clearly distinguished glass facades. One, the one facing the patio, has glass panels of 1.25x3.00 m in isolated glass, 10 +c+ 10, fitting between the floor and the roof of the slab by means of a simple woodwork. It offers a subtle superposition of plans with perforated veneer railing and glass sunscreens. The exterior facade looms up as double. On one side, the same system as the one in the patio is maintained, on the other side an open curtain is located on top of the facade along its entire perimeter In this way a large gallery around the entire building is defined. Due to its upper ventilation and determined central space, the acclimatization of the building is provided. The structure supporting the curtain wall (together with the system of aisles), the special cross-section and the dimensions of the glass panels 4.00x2.50 m in isolated glass 12 +c+10 bring out the horizontality of the facade.

Elastic instability of composite material laminates under uniform temperature variations

In this paper the behaviour of a simply supported rectangular composite plate with anti-symmetric lamination under the action of an in-plane unidirectional load and subjected to a uniform temperature variation is studied. When the in-plane displacements are constrained on the boundary, the existence of two characteristic curves has been established. Such curves are independent on the panel dimensions and allow the diagrams of the critical buckling load for laminates at different temperatures to be derived. As an example those curves are plotted for some typical carbon fiber reinforced plastic laminates. Finally the phenomenon of the thermal buckling is considered.

Practical design of laterally loaded masonry panels

This paper presents an integrated and practical approach to the design of laterally loaded masonry panels. Unreinforced, reinforced and prestressed rectangular panels are all covered, together with supports of variable fixity along two, three or all four sides. A description of panel types and serviceability requirements is given, followed by a review of the equations for ultimate moments of resistance. The yieldline equations for the ultimate limit state are presented in a form suitable for hand calculation, and are then restated solely in terms of the primary variables of lateral pressure, moments, and panel dimensions. Design charts derived from these equations are presented which enable direct design of rectangular panels with pinned or fixed supports under uniform lateral loads. Their use is illustrated with the aid of worked examples. The design of panels with partial fixity or superfixity at supports is then described. Finally, the method is extended to cover the design of retaining-wall panels subject to lateral earth pressures.

Out-of-plane resistance of concrete masonry infilled panels

Nine large-scale concrete masonry infilled panels (3.6 × 2.8 m) were tested to destruction under uniformly distributed lateral pressure applied in small increments. Load–deformation curves of the infills and the enclosing steel frame showed linear elastic behaviour prior to first cracking. Nonlinear behaviour due to cracking and arching action of infill was prominent in the postcracking range. Parameters investigated experimentally included the effects of boundary supports, joint reinforcement, panel thicknesses, panel opening, and characteristics of construction. In parallel with the testing program, computer-aided analytical techniques were developed to predict the first crack and ultimate loads. First crack prediction was based on a finite element analysis for bending of thick plates, while ultimate load prediction was based on a yield-line technique modified to account for the arching action of infill confined within a flexible frame. Having been verified by comparison with test results, the postcracking analysis program was used to conduct a parametric study. It was found that infill compressive strength, panel dimensions, and frame rigidity have significant effect on ultimate loads. While central openings do not affect the ultimate strength, they do, however, reduce postcracking ductility. Key words: masonry, infill panel, steel frame, experimental, out-of-plane, behaviour, strength, arching, yield-line technique, cracking.

Active control of low-frequency harmonic sound radiated by a finite panel

Quadratic optimization theory is applied to determine the minimum sound power output of a simply supported panel in a baffle when the radiation is controlled with additional ‘‘secondary’’ monopole sources. The theory presented produces analytical results for the optimal complex strengths of the secondary sources and the resulting value of minimum power output. The results are valid in the low-frequency limit when the panel dimensions are much smaller than the wavelength of the radiated sound. The results demonstrate the importance of matching the secondary source distribution to the type of panel mode and can be explained using Maidanik’s modal radiation classification scheme.

Further studies on pimel absorbers

Panel absorbers are very useful in reducing the noise propagated in pipes and ducts in applications where reactive mufflers cannot be used. A panel absorber is made of a rectangular panel backed by an air gap. It is believed that this is the first time detailed studies have been made on the applications of panel absorbers in pipes and ducts. Governing differential equations are derived considering the lumped and distributed spring mass systems. The ordinary and partial differential equations are solved and the expressions for the natural frequencies and the admittance of the panel absorber are obtained. Equations for the insertion loss and the transmission loss of the panel absorber are derived. Ten different types of aluminum panel absorbers have been designed, fabricated, and tested in the Sound and Vibration Laboratory at Auburn University. Panel absorber parameters such as panel thickness, panel edge support(boundary) conditions, panel absorber mounting, and panel dimensions were considered during the experiments. The location of the panel absorber along the length of the pipe was also examined. The experimental results are very encouraging. Insertion loss of the first panel absorber was 2.8 dB, whereas the insertion loss of the latest panel absorber with all the improvements is 18 dB.

Sound absorption and transmission by periodically supported double panel structures

Double panel structures are frequently used in modern lightweight constructions, e.g., as factory roofing. Measurements indicate that these structures may provide the majority of low‐frequency absorption in the spaces they enclose. Conventional infinite double panel models significantly underestimate the absorption provided by these structures. As a result the authors have instead modeled these surfaces as two parallel infinite arrays of simply supported rectangular panels separated by a finite depth airspace, thus introducing component panel dimension as a model parameter. When the incident wave field is plane, the panel motions and the reflected, interpanel and transmitted acoustic fields may be expanded in functions periodic in the panel dimensions and their component strengths determined by application of sets of boundary conditions. The fraction of the incident energy that is either dissipated by each panel layer or transmitted may then be calculated. Absorption coefficients calculated in this way are consistent with those measured for factory roof structures and indicate that panel damping may control low‐frequency sound absorption.