Showing papers on "Flexural strength published in 1977"

Composite beams with formed steel deck

Abstract: The results are presented of 17 full-scale tests of composite beams incorporating formed steel decks. The results were analyzed in conjunction with 58 additional tests conducted by other investigators. This report evaluates shear connector capacity and beam flexural capacity and behavior, and compares such capacity and behavior with existing design criteria. The flexural capacity of a composite beam with formed steel deck can be more accurately and conservatively estimated if the slab force is considered to act at the mid-depth of the solid portion of the slab above the ribs, rather than at the centroid of the concrete stress block. The following empirical expessions are presented: to determine the capcity of stud shear connectors in the ribs of composite beams with formed steel deck; the estimation of the deflection of a composite beam with partial shear connection with or without formed steel deck; and the estimation of the stress in the bottom steel fiber of a composite beam with partial shear connection with or without formed steel deck.

Unstiffened Compression Elements

Abstract: Local buckling and post-buckling behavior of unstiffened elements in cold-formed steel structural sections are studied. Column and beam specimens tested and results obtained are presented. Two effective width equations for the post-buckling behavior have been compared with test results indicating good correlation. Two procedures for calculating the flexural buckling strength of columns including the effects of local buckling, based on tangent modulus and Column Research Council Methods, are presented. The column curves obtained using these two methods indicate good correlation with the results of tests on cold-formed steel columns.

Fracture Properties of Polycrystalline Lithia-Stabilized β“- Alumina

Abstract: The critical stress-intensity factor, K1C, and the fracture strength, σf, have been investigated on both hot-pressed and sintered lithia-stabilized β”-alumina. The hot-pressed material possessed a strong preferred orientation with many of the basal planes aligned perpendicular to the direction of hot-pressing. Both K1C and σf were found to be orientation-dependent. Two regimes of fracture were identified. In fine-grained material (<120 μm), the strength was slightly dependent on grain size. For larger grain sizes, the strength decreased rapidly with increasing grain size and the fracture mode was almost entirely transgranular. The K1C values for sintered β”-alumina were in the same range as those obtained on the hot-pressed material.

Mechanical anisotropy in injection‐molded polypropylene

Abstract: By use of a mod with a film gate, two straight polypropylenes (PP) with different melt flow index (MFI) and a glass fiber-reinforced polypropylene (FRPP) were injection molded at various molded at various temperatures into square plates with orientational anisotropy. The anisotropies of tensile property, tensile impact strength, and flexural property were studied on the molded sample cut mainly in the machine direction (MD), 45°-direction (45°), and transverse direction (TD). Both the orders of the yield strength and tensile impact strength of the FRPP, and those of the necking stress and tensile impact strength of the straight PP, were MD >45° >TD, which are reasonable tendencies. The orders of the yield strength and flexural modulus of the straight PP were MD > TD > 45°, which suggests the presence of shear deformation between the lamellae in the skin layer. The variation of the flexural modulus with the angle to the MD fitted well to Hearmon's equation. Generally, for straight PP, the anisotropy of various properties increased as the MFI and cylinder temperature became lower, or as the skin layer became thicker. For the FRPP, the anisotropy increased as the cylinder temperature became higher, or as the degree of the orientation of glass fibers became higher.

Bulk material containers

Abstract: A container for use in the bulk handling of flowable particulate materials is disclosed comprising a closed, generally rectangular parallelpiped on upper container body portion, having side walls, end walls and a roof, and a lower base portion; conduits permitting the introduction and withdrawal of particulate materials to and from the container body; the lower base portion supporting a vertical flexure panel at each corner thereof, the vertical flexure panels supporting opposed pairs of longitudinal and transverse flexure panels between the tops thereof; exterior outer skin members bonded as side and end walls and roof of the container body portion to the curved flexure panels; a plurality of horizontal, non-intersecting internal end wall stiffeners bonded to each of the end walls, each terminating at opposite ends in a junction with one of the pair of vertical flexure panels; a plurality of vertical, non-intersecting internal side wall stiffeners bonded to each of the side walls, each terminated at opposite ends in a junction with one of the longitudinal flexure panels and the lower base portion; and a plurality of transverse, internal, non-intersecting roof stiffeners bonded to the roof, and each terminated at opposite ends in a junction with one of the pair of longitudinal hinge panels; whereby the side walls, end walls and roof may deflect independently of each other to provide overall container flexural capability while avoiding areas of high stress concentration.

Strength and ductility of cast-in-place beam-column joints

Abstract: The results of an experimental study of the behavior of cast-in-place reinforced concrete beam-column joints, subjected to slow load reversals simulating seismic loading are presented. Variables were the amount and size of joint reinforcement, and stress vs. strain characteristics of the joint steel. It was found that loading history does not affect the strength but seriously affects the stiffness of beam-column sub-assemblies; that the ACI equation predicts the cracking shear well but that the 45 degree truss analogy does not predict the behavior of reinforced joints. Stress vs. strain characteristic of the joint steel has a significant effect on confinement provided and the energy dissipating capacity of beams depends significantly on the anchorage provided at the joints. To ensure that the plastic hinge is formed in the beam, the column flexural strength should be based on the core alone.

Ice Engineering - study of Related Properties of Floating Sea-Ice Sheets and Summary of Elastic and Viscoelastic Analyses

Abstract: : This report summarizes approximately 12 yr of research effort by the Civil Engineering Laboratory (CEL) for developing engineering data and analytical capability for calculating operational bearing capacity of sea-ice sheets. The objectives of the report are: (1) to summarize the CEL elastic and viscoelastic experimental programs; (2) to review the two CEL-developed finite- element techniques for analyzing the structural behavior of the material; and (3) to present bearing capacity limits for both short- and long-term ice-sheet operations. At the outset of this research program little engineering data and only limited analytical techniques were available to assist the practitioner in evaluating ice-sheet bearing strength. Though much still remains to be learned, it is now possible to make qualitative engineering predictions on bearing strength as a result of the comprehensive laboratory and field research program directed at defining the tensile strength, compressive strength, flexural strength, elastic modulus, creep behavior, and their relationship to temperature and salinity. Bearing strength analysis, using the CEL-developed finite-element computer codes, can now be based on the material properties corresponding to the actual temperature and salinity gradient existing across the vertical profile of the ice plate.

Behavior and design of prestressed concrete beams with large web openings

Abstract: Results of tests on 18 full-size prestressed, pretensioned concrete tee beams representing one-half of a structural double tee section are reported. The variables investigated were opening size, location of opening along the span, type and amount of web shear reinforcement, and amount of primary flexural reinforcement. Behavior of beams with openings was found to be similar to that of a Vierendeel truss. For the sizes of openings studied, distribution of shear force above and below an opening was dependent on the relative flexural stiffnesses of the struts. Based on these findings, a method of analysis was established. Criteria for strength design are presented and a fully worked numerical example is included to illustrate the application of the proposed design method.

A general relation between tensile strength and specimen geometry for concrete-like materials

Abstract: The tensile strength of concrete-like materials varies wiries when different test procedures or even different shapes and sizes of specimens are employed. Correlations have previously been established but restricted to particular test conditions. The approach here presented, based on the “weakest link of the chain” concepts, offers the possibility of correlating the results of the different tensile tests of concrete-like materials. For that purpose, the amount of material under a tensile stress greater than 0.95 of the maximum tensile stress in the specimen must be evaluated. Relating the maximum tensile stress at the moment of failure with the above mentioned volume (Highly Stressed Volume), a decreasing function is obtained. The function fitted can be used to obtain a tensile strength value of the material, free from the influence of the characteristics of tests and specimens. In this experimental work, the function is established by testing seven different mortar mixes, subjected to nine different test conditions. Centered-point and third-point loading flexural tests and splitting tests were carried out on specimens of different sizes. Direct tension on a briquertte was also applied. The test results showed a decreasing linear regression between the logarithm of the maximum tensile stress at the moment of failure and the logarithm of the highly stressed volume. The slope of that line remained fairly constant for the seven mortar mixes tested.

Defect-initiated fracture and the bend strength of WC-Co hardmetals

Abstract: The wide scatter in the results of the transverse rupture test on specimens of hardmetals of the same grade, and the overlap in the results of tests on different grades, have. been rationalized by examining the fracture surfaces of individual specimens. It is found that a major reason for the scatter in the test is that fracture is usually initiated at pores and other defects of various sizes, and the fracture stress depends on the defect size according to a Griffiths-type relation. This observation and other considerations concerning the position of the initiation site are used to provide a quantitative explanation of the results of transverse rupture tests; it is shown that the scatter in the results is due to the combined effects of test variability and material variability, and consequently the test does not measure an intrinsic material property.

Mixed-Mode Fracture of Graphite/Epoxy Composites: Fracture Strength:

Abstract: The paper presents results on the fracture strength of Gr/Ep (T300/5208) [0/±45 and [0/±45/90] symmetric laminates in the pres ence of angle cracks. It is concluded that the fracture strength can be predicted irrespectively of the crack orientation if one uses the effective normal crack length in the equation developed for normal cracks. However, the application of the present model to isotropic, homogeneous materials may not be so satisfactory as is, say, the maximum tangential stress criterion.

Silicon nitride-silicon carbide composite material

Abstract: A densified silicon nitride-silicon carbide composite material formed by hot-pressing a mixture of silicon nitride (Si 3 N 4 ) powder, which forms the matrix, up to 40 volume percent and preferably from 5-30 volume percent silicon carbide (SiC) powder, and a densification aid such as magnesium oxide (MgO). The average size of the silicon carbide particles is to be less than about 5 microns. The densified composite material is characterized by higher thermal conductivity and strength at high temperatures relative to silicon nitride. The flexural strength at 1400° C. of the composite material being at least double that of sintered silicon nitride.

The modulus of elasticity and flexural strength of some acrylic bone cements.

Abstract: The modulus of elasticity and flexural strength were measured for three bone cements, CMW Bone Cement, Surgical Simplex, and Palacos R, with various additions and prepared as in actual use. A distinct afterpolymerization was demonstrated in all three brands. The addition of blood lowered the E-modulus whereas radio-opaque media seemed to render them somewhat stiffer. The rupture values demonstrated the inhomogeneity of the final product in all three brands. The possible clinical significance of the findings is discussed.

Effect of Stacking Sequence on the Notched Strength of Laminated Composites

Abstract: : The effect of laminate stacking sequence on the notched and unnotched tensile strength of quasi-isotropic graphite/epoxy laminates is investigated. Notch geometry includes circular holes and center cracks. Experimental data is presented for two different stacking sequences of quasi-isotropic graphite/epoxy laminates. One stacking sequence produces large interlaminar tensile stresses along straight free-edges of a tensile coupon, while the second yields compression at the same free-edges. Three different notch sizes are used for the circular hole and center crack in conjunction with both stacking sequences. Each data point is represented by a minimum of fifteen replicates so that statistical distributions of notched and unnotched strengths can be obtained. The experimental data indicates that unnotched tensile strength is reduced by the presence of interlaminar tensile stresses at the straight free-edge, while notched strength appears to be independent of stacking sequence for notch sizes which produce tensile failure prior to delamination at the straight free-edge. Experimental results are also compared against theoretical notch strengths obtained from the average stress criterion and the point stress criterion, two recently developed criteria for predicting notch strength of laminated composites.

A Flexural Method for Evaluation of Metal-Ceramic Bond Strengths:

Abstract: A test technique is presented for evaluating metal-ceramic bond strengths. The test piece consists of a four-point loaded metal beam with porcelain bonded to the central tension side of the beam. The test produced failures at predictable locations and was able to differentiate between metal surface treatments.

Prediction of Bending Strength of Long Bones From Measurements of Bending Stiffness and Bone Mineral Content

Abstract: The relationship between fracture strength in bending, bending stiffness and bone mineral content for 56 fresh canine radii, ulnae and tibiae was determined from three- and four-point bending tests on a MTS testing machine and from measurements of bone mineral content at the fracture site using the Norland-Cameron Bone Mineral Analyzer. The high correlation of bending stiffness (0.962) and mineral content (0.901) with fracture bending moment permits estimates of fracture strength using current noninvasive methods of measuring stiffness and mineral content.

Fracture Resistance Characterization of Graphite/Epoxy Composites

Abstract: The resistance method has been applied to graphite/epoxy composites. The method is based on the assumption that the damage growth at the crack tip can be modeled as a self-similar crack extension through compliance matching. Experimental data for center-cracked tension specimens reveal a linear relationship between crack-growth resistance and initial crack length. For the [0/′45], laminate, the effective increment of crack length at fracture and the corresponding crack-growth resistance essentially are independent of initial crack length. The average amount of this crack extension in the [0/′45] 2 , and [0/′45], laminates is higher than the values obtained from a best fit of fracture strength data reported in the literature. However, the present method results in an improved prediction of fracture strength for the [0/90/′45], laminate.

RC Beam-Column Joints under Large Load Reversals

Abstract: An experimental investigation to determine the shear strength of reinforced concrete beam-column joints is presented. The test specimens consisted of six exterior beam-column subassemblages. The primary variable were the amount of transverse reinforcement in the joint, the magnitude of axial load on the column, and the severity of the load reversals applied to the beam. The experimental results indicate that the shear resisted by the concrete in the joint was considerably greater than the values suggested by current recommendations. The increase in shear strength is assumed to be influenced by the ratio of the sum of column flexural capacities to that of the beams framing into the joint. It is concluded that this ratio should be considered when designing a beam-column joint.

Shaped articles of foam plastics

Abstract: Shaped part based on rigid urea formaldehyde or melamine formaldehyde foam of at least partially open cell structure and having density of 5 to 150 kgs/cu.m. The cells of the foam material adjoining the periphery of at least one external surface of the shaped part are impregnated with a silicate, and the external surface is coated with a silicate lacquer which forms a continuous top coat. A reinforcing sheet material is bonded to the top coat. The shaped part is of improved fire proofness, and compressive, tensile, and flexural strength of the foam.

Preliminary Development of a Fundamental Analysis Model for Crack Growth in a Fiber Reinforced Composite Material

Abstract: A mathematical model for the strength of fiber reinforced composites containing specific flaws is described. The approach is to embed a local heterogeneous region surrounding the crack tip in an anisotropic elastic continuum. By consideration of the individual failure events activated near the flaw tip, a strength prediction can be made from basic properties of the composite constituents. Computations for arbitrary flaw size and orientation have been performed for unidirectional composites with linear elastic-brittle constituent behavior. The mechanical properties were those of graphite epoxy. With the rupture properties arbitrarily varied to test the capability of the model to reflect real fracture modes in fiber composites, it is shown that fiber breakage, matrix crazing, crack bridging, matrix-fiber debonding, and axial splitting all can occur during gradually increasing load prior to catastrophic fracture. Qualitative comparisons with experimental results on edge-notched unidirectional graphite epoxy specimens have also been made.

Optical fiber for communication

Abstract: An optical fiber for communication comprises an optical fiber covered with a coating of a high-molecular elastomer having a flexural modulus of not less than 200 kg/cm2 at room temperature, the difference between the flexural moduli of said elastomer at room temperature and about -50° C being not more than 1000 kg/cm2.

Optimum Reinforced Concrete T-Beam Sections

Abstract: A method is proposed for the determination of the optimum depth and area of flexural reinforcement for reinforced concrete T-beam sections. To evaluate an objective function, a ratio of steel to concrete costs is necessary. The problem is solved using the Lagrange multipliers method. Three examples are presented to illustrate calculation procedures, and some characteristics of the optimum solutions are considered. The method can serve as the basis for developing general rules for selecting effective depths and reinforcement ratios for T-beams including rectangular sections.

Load–deflection curves for fibre-reinforced concrete beams in flexure

Abstract: Synopsis The paper examines the effects of the addition of various fibres, including fibrillated and monofilament polypropylene, as well as round straight, Duoform, crimped and hooked steel, upon the flexural load-deflection properties of a basic concrete matrix at three different ages. The flexural and splitting strengths of the beams were increased with the addition of steel fibres, especially for those with efficient forms of mechanical anchorage, such as Duoform and hooked steel. The fracture toughness of reinforced beams was increased considerably for all the fibres used.

Plastics-sheathed, multi-core, optical cable - having plastics-coated glass fibre cores and high-tensile, elastic, polyamide or polyethylene terephthalate mantle

Abstract: An optical cable has several optical cores and a plastics mantle surrounding the same. The cores are centrally arranged inside the cable, each consisting of a glass filament covered by a firmly fitting, tensile, elastic, plastics mantle e.g., of a polyamide (I) or a poly(ethylene) terephalate (II). Th cores are loosely and untwisted (i.e., uncorded) inside an extruded, two-ply envelope of dissimilar plastics e.g., an envelope having an inner layer of a fluoro polymer, and an outer layer of tensile, elastics plastics, e.g., of (I) or (II). The plastics mantle is arranged over the two-ply envelope. The cables can be used for light-transmission, esp. transmission of control impulses, and in communication transmission generally. The cables combine good mechanical strength i.e., resistance to tensile, compressive and flexural stresses, with effective flame-resistance.