Showing papers on "Deflection (engineering) published in 1971"

Calculation of Stresses and Strains in Four-Point Bending Creep Tests

Abstract: An analysis of strains and stresses in four-point bending creep tests in the limit of small beam deflections resulted in a general equation which relates the load-point deflection, the applied load, the creep exponent (N), and the geometrical parameters of the loading system. Measurements of load-point deflection rates, which are experimentally easy to accomplish in ceramic systems, vs the applied load lead to the direct determination of the creep exponent and the creep compliance in a steady-state creep test. The creep compliance is a function of the temperature, grain size, and all other factors except stress. The elastic equation relating the load-point deflection and the outer fiber strain is strictly valid for viscous creep and approximately valid for nonviscous creep (i.e. N>1) if the ratio of the distance between the support points to the distance between the load points is not very large.

A rheological model for mechano-sorptive deflections of beams

Abstract: Most of the increase in deflection with time that occurs during the drying of initially green beams under load is known to be due more to the change in moisture content (a mechanosorptive phenomenon) than to the passage of time. A first approximation rheological model for this deflection is presented. The validity of the model was assessed by tests on small messmate stringybark (Eucalyptus obliqua) beams. It was found that during the initial drying about 85% of the total deformation was attributable to the proposed first approximation rheological model.

Stability and Load Capacity of Members with No Tensile Strength

Abstract: A mathematical solution is derived which permits the computation of critical load, deflection and stresses for eccentrically loaded slender prismatic compression members made of materials that have compressive strength but no tensile strength. A graphical presentation of the solution facilitates its applicaiton. In an example of application, the solution is used to compute the strength of masonry walls which were tested by the Structural Clay Products Institute. Even though there are limitations to our ability of predicting the behavior of a complex material such as masonry by a mathematical solution based on a simplified model, there is good agreement between computed and measured strength.

Reinforced concrete beams under load reversals

Abstract: A SERIES OF 12 REINFORCED CONCRETE CANTILEVER BEAMS WERE SUBJECTED TO REVERSALS OF OVERLOAD TO DETERMINE THE EFFECT OF LOAD HISTORY ON THE STRENGTH, DUCTILITY, AND MODE OF FAILURE OF THE BEAMS, THE RESULTS SHOWED THAT THE BEHAVIOR OF THE SPECIMENS UNDER LOAD REVERSAL WAS INFLUENCED PRIMARILY BY SHEER. CHANGES IN BEAM GEOMETRY OR LOAD HISTORY WHICH REDUCED THE SHEAR FORCE OR INCREASED THE SHEAR CAPACITY OF THE BEAM SIGNIFICANTLY INCREASED THE ENERGY ABSORBING CAPACITY AND THE NUMBER OF CYCLES TO FAILURE. /AUTHOR/

Acousto-Optic Light Deflection: Design Considerations for First Order Beam Steering Transducers

Abstract: A trade-off between performance and drive power is inherent in the design of present acousto-optic light deflection devices which use simple planar ultrasonic transducers. However, improved performance, measured in terms of bandwidth, is possible without a corresponding increase in power if the transducer is designed to steer the radiated ultrasonic beam in such a way as to track the frequency dependent Bragg scattering angle. The present work is directed towards optimizing the transducer design for the simplest type of beam steering. In this case the transducer consists of a phased array of piezoelectric elements which to a first order approximation steer the ultrasonic beam, even though the interelement phase shifts are held fixed. Well known results from optics are applied to ultrasonics to simplify the analysis of this structure. The design method is applied to several examples to demonstrate its usefulness. A particularly interesting result is that the 85 MHz bandwidth of the present lead molybdate light deflectors can be doubled without increasing drive power by incorporating first order beam steering. Manuscript received October 9, 1970. The author is with Bell Telephone Laboratories, Inc., Murray Hill, N.J. A. PINNOW

Theoretical Lateral Resistance of Nailed Joints

Abstract: This paper presents results of a theoretical analysis based on behavior of beams on elastic foundations and comparison with test data for deflection and proportional limit stresses of nailed joints under lateral load. A simple theoretical expression is derived which relates single shear load and joint slip for a laterally loaded, smooth round nail in a two-member wood joint. The expression accounts for nails of different sizes and materials, and for wood of different species by incorporating a foundation modulus determined from an elastic bearing constant proportional to the wood density.

Behavior of fiber glass reinforced concrete beams

Abstract: This investigation deals with the behavior of fiber glass-reinforced beams with varying percentages of reinforcement. Conventional beams having similar percentages of steel reinforcement are used as control beams. The feasibility of the use of short, randomly oriented wires to improve concrete qualities when incorporated with fiber glass tensile reinforcement is also investigated. Twenty rectangular beams 6 ft in span (1.83 m) and subject to concentrated loads were tested to failure. It was found that fiber glass-reinforced beams were able to take a higher load than the corresponding steel-reinforced control beams. Their cracking and deflection behavior were also favorably comparable to the steel-reinforced beams at working stress levels.

Large‐Deflection Solution of the Coaxial‐Ring‐Circular‐Glass‐Plate Flexure Problem

Abstract: Nonlinear deflections and radial surface stresses in thin elastic circular plates laterally deformed into symmetrical concave shapes are analyzed. The deformations are induced by loading each plate with a small center ring while the plate is resting on a ring of nearly the same diameter as the plate. The rings and plate are coaxial, i.e. concentric. Center deflections up to 3 and 4.5 times the plate thickness were predicted for ring-diameter ratios of 0.5 and 0.2, respectively. The predicted deflection profiles at various loads agreed quite well with those which were determined experimentally on a chemically strengthened glass plate. This analysis provides a new criterion for using the coaxial-ring loading method for flexural strength testing of brittle materials.

Multiple-Wheel Heavy Gear Load Pavement Tests. Volume 1. Basic Report

Abstract: : Flexible and rigid pavements were constructed and tested to obtain data on pavement and soil behavior under large aircraft loadings for use in developing criteria for evaluating and designing airfield pavements subjected to multiple-wheel heavy gear loads (WMHGL). The test sections incorporated instrumentation systems designed to determine the response of the pavement structures to static, dynamic (slowly moving), and vibratory loads and to traffic by full prototype loadings of a 12-wheel assembly (one main gear of a C- 5A aircraft), a twin-tandem assembly (one twin-tandem component of the Boeing 747 assembly), and a single wheel. Analysis of static load response data from the flexible pavement instrumentation program resulted in the establishment of maximum elastic deflection and vertical elastic stress versus depth curves. Comparisons showed that the same relationships were true for static and dynamic load tests, as well as for speed tests. The findings for the rigid pavement test section indicated that the Westergaard algorithm can be used for reasonable predictio of pavement response to test loadings. The data from the instrumentation program and the traffic tests were used in the analysis of the flexible and rigid pavement test sections. The analysis resulted in a modification of the basic flexible pavement CBR design method.

Criteria for the deflection of steel bridges

Abstract: THE OBJECTIVES WERE TO DETERMINE THE ACTUAL EFFECTS OF SLENDERNESS AND FLEXIBILITY ON THE QUALITY OF MULTISTRINGER STEEL HIGHWAY BRIDGES AND TO RECOMMEND RATIONAL DESIGN CRITERIA. THE INVESTIGATION CONSIDERED EFFECTS OF FLEXIBILITY AND SLENDERNESS ON PEAK STRESSES, STRESS RANGES AND DEFLECTIONS DUE TO LIVE LOADS AND THEIR DYNAMIC EFFECTS. THESE EFFECTS ARE DIRECTLY RELATED TO GROSS YIELDING, DECK CRACKING, AND FATIGUE DAMAGE, AND ARE CORRELATED WITH POSSIBILITIES OF BRIDGE DECK DETERIORATION AND HUMAN DISCOMFORT FROM BRIDGE MOTIONS. DESIGN STUDIES INDICATE THE PREDICTED EFFECTS OF REVISED DEFLECTION CRITERIA ON THESE MODES OF BEHAVIOR. IT APPEARS THAT RELAXED CRITERIA FOR SLENDERNESS AND FLEXIBILITY WOULD HAVE NEGLIGIBLE OR BENEFICIAL EFFECTS FOR ALL MODES OF RESPONSE OTHER THAN HUMAN DISCOMFORT FROM BRIDGE MOTIONS. THERE SEEMS TO BE NO NEED FOR DEFLECTION CRITERIA IN THE ABSENCE OF PEDESTRIAN TRAFFIC. PEDESTRIAN DISCOMFORT DOES NOT APPEAR TO BE DIRECTLY RELATED TO THE PRESENT DEFLECTION CRITERIA. A REVIEW OF AVAILABLE INFORMATION SUGGESTS THAT A CRITERION FOR THE COMFORT OF PEDESTRIANS SHOULD LIMIT THE ACCELERATION IN THE FUNDAMENTAL MODE OF VIBRATION AT THE MIDSPAN REGION OF THE BRIDGE. THE ACCELERATION CRITERION OFFERS CONSIDERABLE POTENTIAL FOR ECONOMY IN DESIGN OF BRIDGES WHICH CARRY PEDESTRIAN TRAFFIC. /AUTHOR/

A finite‐deflection analysis of shallow arches by the discrete element method

Abstract: The discrete element displacement method is used to analyse the finite-deflection behaviour of shallow arches. The arches are idealized as assemblies of shallow curved elements and the necessary properties of the displacement patterns in these elements are discussed. Numerical solutions of the geometrically non-linear problem are obtained by directly minimizing the total potential energy of the system.

Framed-Tube Structures for High-Rise Buildings

Abstract: The framed-tube system is regarded as an economic solution for high-rise buildings However, in view of the shear lag which occurs as a result of the flexibility of the spandrel beams, it is essential to predict accurately the structural behavior of the system A simplified yet accurate method is presented for the analysis of framed-tube structures subjected to wind loads By recognizing the dominant modes of structural action, the three-dimensional system is replaced by an equivalent plane frame by the addition at the corners of fictitious horizontal members with specially prescribed properties The plane frame can be analyzed by conventional methods, and it enables larger problems to be treated on a given computer The accuracy of the method is examined by comparing the results with those from tests on a 15-story perspex model, and from an analysis carried out by a standard three-dimensional space frame computer program

Dynamic Analysis of Plane Coupled Shear Walls

Abstract: The continuous method of analysis of coupled shear walls is reformulated in terms of deflection variables and used to study the dynamic behavior of plane coupled shear walls. The assumption that mid-points of the connecting beams are points of contraflexure is relaxed so that the resulting theory is applicable to the general case where the lateral loading on the piers can be arbitrarily distributed. The equations of motion with appropriate boundary conditions are given. The free vibration of coupled shear walls is studied and the fundamental frequency determined. Theoretical results are verified by dynamic testing on two models to show the theory is sufficiently accurate to provide information for dynamic analysis in seismic design.

Optimal structural design for given deflection under periodic loading

Abstract: This paper is concerned with the minimum-weight design of structures subjected to periodic loading, under the constraint of a prescribed deflection at a specified point of the structure. For elastic sandwich beams, the method of stationary mutual potential energy is extended to cover periodic loading and a sufficient condition for stationary weight is derived.

Inelastic Flange Buckling of Curved Plate Girders

Abstract: Local buckling of the flanges of horizontally curved plate girders is studied analytically. Buckling in both the elastic and inelastic range is considered. The mathematical model consists of the small deflection plate equations for an isotropic media in the elastic range and an orthotropic media in the inelastic range. Prebuckling stresses due to bending and nonuniform torsion and residual stresses due to the fabrication process are included in the mathematical model. The influence of the stress distribution and yielding of portions of the curved plate on the buckling coefficients is studied. Plate buckling curves relating the internal forces in curved beams to the flange dimensions, width-to-thickness ratio, required to prevent buckling are also presented.