Showing papers on "Portal frame published in 1991"

Probabilistic FEM for Nonlinear Concrete Structures. II: Applications

Abstract: This is the second part of an investigation on probabilistic finite element methods for nonlinear concrete structures. The study is concentrated on two reinforced concrete application examples including a simply supported beam and a portal frame. Nonlinearity in material and geometry, and randomness in loading, material, and geometry are considered. Extensive computations using a probabilistic finite element method imbedded in the computer code PFRAME developed at the University of Colorado, Boulder, are carried out to verify analytical results. The effect of Taylor series expansions about different values of various random variables on structural response is demonstrated in both application examples. Furthermore, using the simply supported beam example, it is shown that the probabilistic finite element method proposed is applicable to the assessment of structural safety of material and geometric nonlinear concrete structures. Further investigations are necessary in order to develop this probabilistic fin...

Random Vibration of Flexible, Uncertain Beam Element

Abstract: A stochastic finite element method is developed to analyze the random responses of geometrically nonlinear beams and frames with combined uncertain material and geometric properties under simultaneous spatial and temporal random excitations. The method is based on an equivalent linearization scheme, combined with the mean‐centered second‐order perturbation technique and the modal expansion approach. The procedure can be straightforwardly extended to incorporate other existing finite elements. Examples include large‐amplitude free vibration and dynamic random response of three simply supported beams and a portal frame with combined uncertain material and geometric properties. For the case of beams and frame with no structural uncertainties, the results obtained are in good agreement with alternative solutions. For the case of beams and frame with structural uncertainties, alternative representative results are also obtained using Monte Carlo simulation to compare and validate the present solution and method.

Effect of random material variability on seismic design parameters of steel frames

Abstract: Whereas an increase in material yield stress beyond the code specified characteristic value enhances plastic capacity, it may cause a reduction in overall ductility and energy absorption capability of steel frames. Since quality control of various shapes of sections used on site is difficult to impose, the effect of this random variability on design response parameters should be accounted for in earthquake-resistant regulations. Moreover, the required weak-beam/strong-column design principle in particular, and failure mode control in general, could be undermined if the yield stresses in beam and column assume two opposite extremes in a random sample. This paper addresses the problem of defining the expected range of response parameters in a steel frame with randomly varying yield stress. A simple portal frame is designed using code specified characteristic values and verified by non-linear transient dynamic analysis. The influence of yield stress variability, including the degree of correlation between beam and column material properties, on several response parameters is assessed through a Monte Carlo simulation study. Results are presented from both univariate and bivariate statistical analyses that quantify the relationship between input (material) and output (response) parameters. Assessment of the interdependence of output parameters given a particular model for yield stress variability is also undertaken. It is shown that certain response parameters exhibit more favourable statistical properties than others. Thus, the implications for seismic code design are discussed in the light of these results.

Thermal cutting installation - has vibration resistant bearing units

Abstract: The installation for thermal cutting has a workpiece support and a cutting unit mounted on a laterally movable carriage on portal frame which can be displaced in the longitudinal direction. The portal frame (5) is area supported on base rails (17, 18) using sliding bearings (15, 16). These bearings have a clearance-free fit and take up moments between the portal frame (5) and the base rails (17,18). The base rails (17, 18) have an outside profile which fit into the inside profile of the sliding bearings (15, 16). These profiles have areas whose normal vector has at least one component pointing in the lateral direction (6). The portal frame (5) in the radial direction (6) is fixed with respect to one rail (17), while with respect to the other rail (18) it is movable. There is a drive mechanism (29) consisting of a rack (30) and a doubly toothed belt (31) which meshes with the rack and is spanned over two turn-round rolls and one driving roll. The carriage (3) is supported at least two carrying rails by means of sliding bearings capable being loaded by both compressive and tensile forces. USE/ADVANTAGE - Used, for example, to cut steel sheets and iron plates by means of cutting torches and lasers. In comparison with known equipment, it more resistant to vibration excitation, and hence permits higher operating speeds of the carriage and the portal frame.

Appliance to facilitate construction of small buildings - has platform of adjustable height, mounted on wheeled chassis

Abstract: The frame facilitates the construction of buildings of a relatively low height. It consists of two uprights (3) which are mounted on feet (1). Each end of each foot is supported on a wheel (2). Each upright (3) supports an upper part (4) which can be height adjusted relative to the lower part (3). The upper parts support a cross-member (11) to form a portal frame. This cross-member is equipped with a carriage (12) which is provided with lifting tackle. The upper parts of the uprights support a platform (5) which can be raised and lowered to suit the height of the building. USE - Building industry.

Movable portal frame

Abstract: The utility model has the advantages of movable portal frame which is a hoisting device, in particular to a portal hoisting frame device. Compared with the existing portal frame, each component of the utility model is convenient for disassemble and assemble, and the bottom end of a pole support is provided with a universal castor. The pole support can be composed of two or more than two segments, and the bottom of each two closed pole supports can be connected with a telescopic pull rod. The utility model has the advantages of convenience for arrangement, transportation, dismounting and operation, good overall stability, lifting heavier objects and wide applicability, and after heavy objects are lifted, the utility model can move in all direction.

Simple electric hydraulic forklift

Abstract: The utility model relates to a simple electric hydraulic forklift which relates to a hoisting device for lifting, falling and transporting the weight, composed of an oil cylinder, an oil pump, an oil tank, a plunger piston, a valve plate, a safety valve, a hand-operated direction valve, a fork arm, a lifting frame, a portal frame, a support frame, a chain wheel, a chain and a wheel. The utility model is characterized in that an electric drive system and a device for controlling the swing angle of the portal frame are also provided. The utility model can regulate the front inclination angle or the back elevation angle of the portal frame according to the different requirements of the three processes of goods loading, goods transport and goods unloading, the centroid position of the goods is changed, and the alternating current or the direct current can be used according to different requirements. Thus, the simple electric hydraulic forklift has the characteristics of low cost, labor saving, safety, simple and compact structure, and light weight. The simple electric hydraulic forklift is particularly suitable for using under the escort handling occasions.

Flexible Beam and Frame Elements Under Nonwhite and Nonzero Mean Loads

Abstract: A finite element formulation combined with stochastic linearization and normal mode methods is developed for the study of geometrically nonlinear random vibration responses of beam and frame structures subjected to simultaneously spatial and temporal Gaussian stationary nonwhite and nonzero mean random excitations. Examples include dynamic random responses of simply supported beams, clamped‐clamped beams, a simply supported beam on an elastic foundation, and a fixed‐end portal frame under various random loadings. To compare and validate the present formulation and solutions, results are compared with alternative analytical solutions whenever available. The Monte Carlo simulation method is also used to generate solutions to compare with some of the present results when alternative solutions are not available.

Reliability-based plastic synthesis of portal frames

Abstract: A mathematical programming technique is described which minimizes the total average volume of steel reinforcement of a reinforced concrete frame for a specified failure probability. The structural material is assumed to exhibit a perfectly-plastic behaviour so that plastic collapse is the only possible failure mode. It consists of solving alternatively a reliability assessment problem, which incorporates recent developments in large-scale constrained concave quadratic programming and an optimal sizing problem (convex minimization) until the best reliability-based design against collapse is found.

Wall papering machine

Abstract: Apparatus consisting of a frame, which can be adapted onto any stepladder, equipped with a folding portal frame and a fixed cradle on which are installed a roll of wall paper and a semi-cylindrical reservoir filled with paste and including on its central shaft a roll of synthetic foam. This apparatus enables a width of wall paper to be unrolled, pasted and hung on the wall via its pasted surface, in one and the same location. This apparatus also enables the outlines of doors, windows, etc. to be cut out beforehand, before pasting, the paper then being hung after it has been cut in the way indicated previously.

Analysis of steel frame structures in fire.

Abstract: The main aim of the present research is to develop a method of analysis for structural frames exposed to fire including the effects of material and geometric non-linearities. A matrix stiffness method based on a secant stiffness approach is used providing a full temperature deformation history. The approach has previously been used for the analysis of continuous beams and is extended in the present work to include axial forces. These not only affect the longitudinal displacement, but also reduce the member stiffness and create secondary moments due to the p-delta effect. The influence of material unloading on the moment-axial force-curvature relationship is studied by examining a cross-section subjected to different combinations of bending moment and axial force at both ambient temperature and in fire. A computer program, based on the method is used to conduct a limited parametric study. This includes the influence of slenderness ratio, the magnitude of axial load and moment, the size of cross-section and grade of steel. Both uniform and non-uniform temperature profiles are considered for isolated beams, columns and simple portal frame. The importance of the p-delta effect is also investigated.

Reliability Constraint on Optimum Design

Abstract: The purpose of the paper is to emphasize the importance of the probability concern on optimum design work. The probability of failure of the structure can be considered as one of the optimum design constraints in addition to stress constraint, strain constraint, buckling constraint . . . etc. Examples of plane truss, space frame and a simple portal frame are presented. In truss analysis, the weakest link model is assumed to be available for both statically determinate and statically indeterminate problems. Probability of failure for individual elements and for the whole truss are calculated. In the simple portal frame problem, the risk value according to seismic loads at certain selected sites and to damage stages classified by yielding condition and mechanism types are calculated for various designs. The best designed structure might be considered as the structure with the lowest probability of failure and with equally ordered probability of failure for different components.