Large Roof Research Articles

Mechanism of aeroelastically unstable vibration of large span roof

Mechanism of aeroelastically unstable vibration of large span roof

Reducing the wind loading on large cantilevered roofs

A 1/100 scale aeroelastic model of a cantilevered roof, over a grandstand, has been tested in a turbulent boundary layer model of the natural wind over suburban terrain, to determine the response of the roof and the effectiveness of a leading edge slot in reducing the response. For the basic cantilevered roof configuration the leading edge displacement was shown to increase with wind speed to a power significantly higher than two, illustrating the wind sensitivity of these structures. Various plain leading edge slot configurations were tested and an optimum configuration determined which showed that a 25% reduction in response could be achieved for a slot width of 5% of the cantilever length. The data have been presented in terms of an equivalent triangular load distribution as a function of reduced velocity for direct design application.

Butler Folded Plate Greenhouse Roof

FOLDED plate structures have been used for centuries, generally to enhance the aesthetics of a building but also because of some inherent structural characteristics. There are many possible folded plate configurations with most categorized according to fold type, arrangement and resulting cross section. Concern for water removal from large area greenhouse roofs led R. G. Butler of Westboro, MA, to propose a folded plate roof constructed of triangular plates in a parallel fold arrangement to create an M cross section (Fig. la). He constructed a model of the roof using flat acrylic triangles as plates tilted at 45 deg with the horizontal. The sloping valleys were parallel to the building sides. The ridges were horizontal and at an angle to the sides. This paper discusses (a) the design, testing and structural evaluation of a folded plate roof model based on the Butler roof and (b) design, fabrication and erection of a 7.3 m x 7.3 m (24 ft x 24 ft) Butler roof greenhouse.

Lateral Stability of Beams with Elastic End Restraints

In the analysis of the lateral buckling of simply supported beams, the ends are assumed to be rigidly restrained against tip. Real supports are, of course, never perfectly rigid. This report examines the relation of the stiffness of the end axial rotation restraint to the buckling load when the stabilizing effect of an attached deck is taken into account. For the case of uniform load, it is found that as the restraint stiffness approaches zero, the buckling load also approaches zero. This has implications in the design of large roof systems where end restraint on one member is provided by the torsional rigidity of another member connected in‐line. Families of design curves are presented which show the effects of restraint stiffness, span‐depth ratio, and shear stiffness of attached roof deck. It is concluded that periodic bracing against axial rotation is essential for stability of long roof systems with several beams spliced together in‐line.

ON THE LARVAL REARING OF THE WHITE‐SPOTTED GREEN GROUPER, Epinephelus amblycephalus (BLEEKER), WITH A DESCRIPTION OF LARVAL DEVELOPMENT

ABSTRACTThe white‐spotted green grouper, Epinenephelus amblycephalus (Bleeker), a popular and cmercially important marine food fish in Hong Kong, has been used for intensive cage culture in coastal water for many years. The major constraints to its large‐scale development are, however, the shortage and uncertain supply of fingerlings from the wild. Research efforts have therefore been directed at producing large supplies of fingerlings, either for culture to marketable size or for restocking.Larvae of E. amblycephalus were reared through metamorphosis in 1000‐liter rectangular tanks covered with a large translucent roof. The newly hatched larvae measured 2.0 mm in total length and possessed a large yolk sac. Effects of temperature and salinity on the yolk sac larvae were examined in laboratory experiments. Recommended temperature and salinity for rearing of the early larvae are 24°C and 25–32 Ppt. In the laboratory larvae were fed fertilized oyster eggs, rotifers, Artemia nauplii, copepods and shrimp meat. The developnent stages from hatching through metamorphosis are described. Three mortality peaks were observed during the experiment. The highest larval survival rate through metamorphosis (i.e., 40 days) after hatching was 25%.

Biaxial Test Method for Characterization of Fabric Materials Used in Permanent Fabric Roof Structures

Abstract An experimental investigation was conducted to develop a test method and hardware for the purpose of characterizing the material behavior of coated glass fabrics for application in large roof structures. Because of the biaxial nature of stresses in fabric structures, an internally pressurized cylinder specimen was designed for use in a hydraulically actuated (MTS) testing machine. Biaxial cylinder fabrication and appropriate testing procedures were developed. Stress-strain and strength characteristics were determined for various fabric material types and material lots. Biaxial monotonic, step loading, stress rupture, and dynamic fatigue loading conditions were studied. Combined biaxial tensile plus shear loading were assessed by testing cylinders under biaxial and superimposed torsion loading conditions. The strength characteristics of damaged fabric materials were also extensively assessed.

Turbulent wind forces on a large span roof and their representation by equivalent static loads

The paper describes the measurement of the steady and fluctuating wind forces on a large span roof and their representation by equivalent static loads. The work was undertaken as part of a study for the Olympic Saddledome, Calgary, Canada, but has quite general applicability to other large span roofs. The procedure defines the shape of the structural loading in terms of simple patterns; in this case, harmonic Fourier functions were chosen. The force coefficients defining the amplitudes of these orthogonal loading patterns are each summarized by a mean coefficient [Formula: see text]; a root-mean-square fluctuating coefficient, [Formula: see text]; and a resonant magnification factor, (RMF)i. The equivalent static design pressure loading, pD(r,θ), over the roof surface is then represented by an expression[Formula: see text]in which r and θ are polar coordinates, q is the reference velocity pressure of the wind [Formula: see text], gi, is a statistical load combination factor, and μi(r,θ) is the shape of the ith pattern or function.Aerodynamic data defining these coefficients were derived from a boundary layer wind tunnel investigation, using an adaptation of the pneumatic averaging technique. As well as the distributed force coefficients, local pressure coefficients are also given. The dynamic content of the loading was found to be highly significant both on account of its magnitude, which was larger than the mean, and because of its variable distribution. Approximately one-quarter of the dynamic loading might be associated with resonance amplification. Key words: aerodynamics, arenas, design, dynamics, pressure, roofs, turbulent flow, wind loads, wind tunnel tests.

Bracing Requirements for Lateral Stability

The forces induced in braces depend on the magnitude of initial imperfections (lateral bending and twist) and magnitude of applied loads. A method for calculating these forces is presented here. Shear stiffness of attached deck is taken into account. Calculations show that, for beams which derive their lateral stability mainly from the stiffness of the attached deck, additional bracing against rotation or lateral deflection is not able to achieve an important increase in the load capacity of the systems. In those cases, bracings employed merely to straighten the initial imperfections need not be very strong. In cases where decking cannot be counted on to stabilize the roof system, bracings should be designed for stiffness (sufficient to enforce a higher buckling mode) and checked by the methods presented here for required strength. The results are of value to designers of large flat wood roof systems

Flexural axisymmetric free vibrations of a spherical dome: Exact results and approximate solutions

Exact expressions exist for the natural frequencies and mode shapes of the axisymmetric free vibrations of a spherical shell or dome. However, they are not easily amenable to numerical calculation and there are no reference standards of natural frequencies and modes available for use in engineering. The need for such reference standards is increasing nowadays because of the wide applications of shell structures in large building roofs, containers and vessels, and of the serious concern about their structural resistance to such dynamic forces as earthquakes and waves. Furthermore, the exact solution is even less practical for analysis of response to dynamic loading. This paper provides, first, the natural frequencies and modes for a wide range of conical angle, based on the exact solution. Compatible with these results, an approximate solution is then proposed which is suitable for dynamic response analysis and which easily provides natural frequencies and modal shapes which are accurate enough for engineering purposes.

Loss of Torsional Stiffness Caused by Beam Loading

A beam under load can be more easily twisted or deflected laterally than when not under load. This loss of apparent stiffness is an example of the general principle that stiffness associated with a buckling displacement diminishes to zero as the buckling load is approached. This phenomenon was first reviewed and derived for beam‐columns and then derived for beam‐torsion members. It was found that stiffness decays linearly for beam‐columns and parabolically for beam‐torsion members. The results are important to designers of large flat roofs in which one beam must provide axial rotation restraint for the next beam in‐line. Simple design equations are recommended.

Structural design in the eighteenth century: James Essex and the roof of Lincoln Cathedral Chapter House

The design of novel structural forms can happen either by a process of trial and error supported by testing, or by adopting some conceptual model of structural behaviour. These conceptual models are often simple analogies rather than sophisticated abstractions. This paper provides a case study of one particular example; a method used in the design of an unusually large roof structure during the eighteenth century. The study is a contribution from historical materials to the ‘natural history’ of design.

Wind tunnel studies of cable roofs

Behaviour of large cable roofs in turbulent wind is studied in the wind tunnel using both rigid and aeroelastic models. The similarity requirements are reviewed with special attention being paid to the effect of the air enclosed under the roof. A similarity law for the modeling of this enclosure is presented and its role in free vibration as well as wind induced vibration is investigated. A wind tunnel study of a large tension roof is described.

Efficient Large Panel Roofing

Abstract Large panel building roofs using prestressed short cylindrical panel-shells with dimensions of 3 by 12, 3 by 18, and 3 by 24 m developed in the U.S.S.R. are presented in this paper, and their technical and economic advantages in comparison with other roofs are shown.

Wind loads on cantilevered roof structures

This paper summarises the most important findings of the first stage of a large-scale project to investigate the wind loading on cantilevered roof structures such as those typified by a large grandstand roof. Some results of a general study of the flow field for typical grandstand configurations and an investigation of likely critical cases for the occurrence of large mean loads are given. The important inter-relationships between roof slope, yaw angle and sub-roof area blockage are described. The likelihood of occurrence of near-periodic load fluctuations due to vortex shedding is shown to be low. The form of the spectrum of both local and overall loads has been studied, and the relationship to the free-stream turbulence is discussed.

Grupo escolar en Irurzun - Navarra - España

The formal characteristics of this school complex are determined by the large roofs and the angled shape of the floorplans. The first is as a consequence of the interest in achieving a unity of concept and volume, at the same time maintaining the architectural tradition of the area. Insofar as the angular shape, this is the response to the idea of obtaining ideal conditions of light in each of the classrooms. The building consists of three upper levels, ground floor and semi-basement. In the last of these are found: the gymnasium, the dressing rooms for students and the technical premises serving the school. The ground floor, where the main access is found, includes a small administrative area, the dining room and kitchen, one classroom for girls, three for pre-school children, four for boys and one multifunctional room. The rest of the floors, with the same arrangement, house eight classrooms for girls and five for boys, along with a series of auxiliary premises, such as teachers' rooms, libraries, classrooms for various uses, archives, rooms for crafts, etc. . The construction is completed with an ample sports area and recreation zone.

The geological interpretation of gravity and magnetic surveys over the exposed southern margin of the Galway Granite, Ireland

AbstractGravity measurements across the southern margin of the Galway granite, on the Islands of Gorumna and Lettermullen, reveal small positive Bouguer anomalies of amplitudes less than 40 g.u. associated with the denser country rock. These anomalies suggest that the ‘country rock’ is no more than a thin wedge, thickening southwards. Such a structure may form part of a large roof pendant or roof section with the true granite margin lying further south. Magnetic anomaly profiles across the granite contact reveal that the rock groups, making up the country rock, have distinct magnetic character which may provide a means of mapping their southern extent beneath Galway Bay.

Foundations and earthworks for cylindrical steel storage tanks : Harris, G Ground Engng. V9, N5, July, 1976, P24–31

The design and construction techniques for steel storage tanks for storing oil and general bulk commodities are reviewed. The nature of storage tanks are described, the effects of settlement of tanks are discussed, and comments are made on tank loadings, foundations, water testing and settlement records, dyke compount areas, and underwriting considerations. Shell bearing plates are used for fixed roof tanks where shell bearing pressures are in excess of 100 kilopascals or where floating roof tanks are involved. Large size cone roof tanks have their roofs supported on columns and generally a center column. The dead load on columns normally ranges from 50 to 100 kn, whereas live load can add a further 100 to 150 kn per column. Foundation solutions for varying soil conditions are diagramatically illustrated and relate to shallow foundations in competant graound, foundations for poor ground conditions, fill replacement technique, piled foundations, and foundation preloading. Tests to ensure that the storage tank is water tight, and that the foundation is adequate to carry the loadings are discussed. The dyking (to retain spillage and prevent flooding and pollution) precaustions to be adopted in any instance will depend on the nature of the commodity being stored. Underwriting consideraions are discussed related to the storage of hydrocarbons.

Buckling of Hyperbolic Paraboloids

Large spherical dome roofs are being constructed regularly because of their beauty, adaptability, and low cost. A decade ago this type of roof was rather rare because of the high cost of construction and the significant unknowns in the design. Considerable research and development in design and construction has resulted in analysis procedures that have a high degree of reliability and are carried out at minimum cost (often the dome analysis is much more economical than the analysis of a similar size conventional type structure.) Ingenious fabrication and erection methods have paralleled the analysis development with resulting relatively low final costs. Designs have been carried to completion for roofs up to 850 ft in base diameter (the Astrodome is about 620 ft in base diameter). Preliminary feasibility designs have been made for roofs over one mile in diameter. The buckling analysis is an important part of dome design. Several large domes have failed in the last decade and present methods of buckling analysis have been used to explain the failures. Experience in the field and laboratory has allowed reductions in factors of safety from about 10 to as low as 1.5 with satisfactory results.

Las cubiertas de grandes luces. Soluciones actuales

This article deals generally with the problems connected with the construction of large span roofs, and also with the various types of designs that are currently in practice. It may be said that at present the only limitation to these designs is the imagination of the designer and the financial restrictions imposed on him.

A Comparative Study of Plecotus Auritus and P. Austriacus (Chiroptera, Vespertilionidae) Inhabiting One Roost

This study began in November, 1960 and involved studies of all bats living within one large and complex roof. Furzebrook House, built in 1885, was of brick with hollow walls and a black slate roof. The roof consisted of 9 distinct sections comprising some 385 m³ of which 60 % was accessible for searching. Eight species were caught in these accessible regions and because Plecotus spp. were the most numerous, they became the chief study. The study became more significant when Plecotus austriacus (Fischer) (first described by Bauer, 1960), was identified in the roof. Detailed descriptions of the two English Plecotus have already been published (cf. Stebbings, 1967). The aim of this report is to present evidence that might suggest reasons for the distribution of the two Plecotus in northern Europe, and particularly their northern limits.