Direct Tension Test Research Articles

溶融亜鉛めっき高力ボルト (F8T) の単純引張り時性状

Recently, hot dip galvanized high strength bolts are used in structures, because of a protective surface coating to prevent corrosion and reduce maintenance costs. In such cases, commonly, oversize tapped nuts of which tapping may be tapped either after or before galvanizing are assembled. On the other hand, at the present time, International Organization for Standardization has submitted some drafts of international standard for bolts, nuts and washers. In the drafts hot dip galvanized surface finishing in accordance with ISO 1461, dimensions and so forth are discribed. In the international standard ISO 1461, which relates to hot dip galvanized coating on fabricated ferrous products, threads only be required to fit after galvanizing if a suitable allowance has been made for the coating in making the thread. Therefor only oversize tapping or retapping after hot dip galvanizing is required so far as the male thread is hot dip galvanized. The behavior of galvanized high strength bolts assembled with oversize tapped nuts may differ from the behavior of normal high strength bolts. This difference in behavior may be primarily caused by the zinc layer on the threads, oversize tapping of nuts and galvanizing process. This is apparent that before a connection can be analyzed, the behavior of single bolt subjected to the typical loading conditions of tention, shear and shear and combined tension must be known. In this paper, the behavior of galvanized bolts assembled with various oversize tapped nuts is discussed through the load-elongation relationships and the mode of failure in direct tension test putting a stress on the effects of oversized tapping of nuts as well as galvanizing process. In conclusion, I suggested the suitable oversize of nut thread for each bolt diameter and galvanizing process when tapping the female thread before hot dip galvanizing. Test specimens are F 8 T high strength bolts specified in JIS B 1186-1979. Nuts are tapped 3 kinds of oversize thread before galvanizing. In practice, the bolt preload force is usually introduced by tightening the nut applying torque to nut. This results in different stress conditions in the bolt. Thus the behaivior observed in torqued tension tests shall be discussed in my the other paper.

Splicing of reinforcement bars with epoxy joints

The splicing of reinforcement bars in tension using epoxy-sleeve joints is described. The optimum length of the splicing sleeve required and the optimum bonding layer of epoxy resin in the joint were determined in direct tension tests. The performance of the epoxy-sleeve joint made to these optimum dimensions is then compared to that of a lap splice made according to the provisions of CP 110 in a beam flexure test. A sleeve length of 12 bar diameters and an optimum average thickness of 2 mm of the bonding layer of epoxy are shown to develop the full strength of the splices bar. Tensile reinforcement bars spliced using epoxy-sleeve joints are shown to perform satisfactorily as flexural reinforcement in beams and compare favourably with the standard CP 110 lap splice. Epoxy-sleeve joints are shown to produce stiffer beams and reduced crack width at the joints.

The influence of pore pressure upon concrete

Synopsis The effects of pore pressures within porous material have caused debate, especially in relation to internal uplift in gravity dams and the areas over which water pressures act. The background to these divergent views is reviewed in the paper. By using a direct-tension test method and experimental principles already reported, equipment was built capable of testing three specimens, subjecting them to uplift pressures, neutral pore pressures and external tensile stresses; strains were continuously monitored for periods of a few minutes to several days. Tests have been carried out in which uplift developed and caused failure or was progressively replaced by external load, or concrete was subjected to neutral pore pressures in conjunction with external load. The results established that Terzaghi's effective stress equation was applicable to concrete in any stress condition, and that the effective porosity of concrete was initially of the order of 0·5 to 0·65 and increased with crack propagation to unity.

F10T 高力ボルト単純引張り時の荷重・変形性状

Bolts in tension are common in tension type connections and in beam-to-column connections. Some of them may also subject the bolts to combined tension and shear. It is apparent that before not only a connection can be analyzed but to determine the manner of turn of nut method, the behavior of a bolt itself must be known. Therefore, the behavior of a single bolt subjected to the typical loading conditions of tension is discussed in this paper, further in conclusion I proposed some approximate equations to predict the load-elongation relationships for most popular high strength bolts which have different grip conditions. The behavior of a bolt subjected to an monotonic axial load seems to be governed by mostly its threaded part under and included in nut as well as its body part. To determine the actual mechanical properties of a bolt, I examined direct tension test using 420 specimens putting a stress on amount of thread under nut. These specimens are F10T high strength bolts specified in 1979 JIS B 1186 (Specification for high strength bolts in japanese industrial standard). The tested nominal bolt diameters are 4 kinds of M16 through M24, also the bolt length for every size are 6 kinds which varied from approximately 3 to 10 times of diameter. The amount of thread under nut varied from 0 to 8 threads for every bolt length. In practice, the bolt preload force is usually introduced by tightening the nut applying torque to nut. This tigetening procedure results in different stress conditions in bolt. Therefore, the behavior observed in a torqued tension test may differs from the results obtained from a direct tension test. Thus, the behaviors in torqing a bolt until failure will be discussed in my further paper.

Determination of tensile and compressive creep behaviour of ceramic materials from bend tests

We have developed equations that permit the determination of individual compressive and tensile creep rates from four-point bend test measurements made on trapezoidal bars. The equations developed are for the general stress dependence case. Finnie first proposed this type of analysis and solved the equations for the case of linear stress dependence. We present graphs that show solutions to the equations for the stress squared case. Creep measurements were performed on trapezoidal HS-130 Si3 N 4 bars to determine the ratio of compressive to tensile creep (β). The values determined on four separate tests using two different temperatures and beam dimension ratios b 2/b 1 gave fairly consistent results. The β′s for previously unstrained material are: 0.24, 0.14, 0.17, and 0.17 with the average value of β=0.18. For the case of prestrained Si3N4, β is 0.48. To further test the usefulness of this analysis, data from a conventional (rectangular bars) four-point bend test were taken from the literature and analysed using the equations developed in this paper and the average determined value of β. The individual tensile and compressive creep rates determined in this manner were found to agree very closely with other literature data measured in direct tension and compression tests.

Stress–strain behaviour of two compacted clays in tension and compression

Zones of total stress tension and steep stress gradient occur in soil structures such as multilayer pavements and earth dams, and direct tension tests and simple bending tests on soils could be used advantageously to investigate soil behaviour under these conditions. The Paper describes the observed behaviour in direct tension and bending of two clays compacted with standard Proctor effort at different moisture contents ranging from below to above optimum. The investigation is in terms of total stress and is concerned with both stress-strain behaviour and strength condition. It is shown that the elastic bending theory is not satisfactory for analysing bending in soils and an alternative differential method of analysis is used which does not require the assumption of any preferred stress- strain laws. The maximum tensile strains at failure are observed to increase with the increase of moulding moisture content irrespective of the type of test or the optimum moisture content. This supports the view that clays should be compacted at high moisture contents when considerable tensile deformation of a soil structure is expected. The values of both the initial tangent modulus and of the secant modulus (at maximum stress) for both clays are markedly greater in tension than in compression, and the relative values are influenced by the moulding moisture content. Thus the use of identical values for tension and compression in analysis of soil structure is not justified. Des zones de contrainte de tension totale et de gradient élevé se produisent dans des structures de sol telles que les multicouches et les barrages en terre. Des essais de tension directe et de simples essais de flexion sur les sols pourraient être utilisés avantageusement afin d'étudier le comportement du sol dans ces conditions. L'étude décrit le comportement observé dans une tension non drainée et une flexion de deux argiles compactées au Proctor standard à diverses teneurs en eau inférieures. et supérieures à l'optimum. L'étude est en termes de contraintes totales et elle est concernée par le comportement de contrainte de tension ainsi que par les conditions de résistance. II est montré que la théorie de la flexion élastique n'est pas satisfaisante pour analyser la flexion dans les sols, et une autre méthode différente d'analyse est utilisée qui n'exige pas l'hypothese d'aucune loi spéciale de contrainte déformation. On observe que les déformations maximum de traction à la rupture augmentent avec l'accroissement de la teneur en eau, indépendamment du genre d'essai ou de la teneur optimum en eau. Cela confirme que les argiles devraient être compactées à des teneurs en eau élevées lorsque l'on s'attend à une déformation de traction considérable du sol. Les valeurs du module initial tangent et du module sécant (à contrainte maximum) pour chacune des argiles sont, d'une façon marquée, plus grandes en tension qu'en compression, et les valeurs relatives sont influencées par la teneur en eau. Ainsi, l'utilisation de valeurs identiques en traction et en compression dans l'analyse de la structure du sol n'est pas justifiée.

An Unconfined Direct Tension Test for Compacted Clays

Abstract Although problems associated with total stress tension arise in soil structures such as earth embankments and multilayer pavements, no standard tension test for soils exists. An unconfined direct tension test, either strain controlled or load controlled, is described, which can be used to determine the tensile (total) stress-strain characteristics of compacted clays. The overall tensile strains in the specimen are determined by observing the displacement of two surface markers spiked into the specimen with a displacement measuring optical device (DMOD) capable of measuring to one-micrometer displacement. An alternative radiographic technique of monitoring strains has shown that the distribution of average tensile strains in the specimens is substantially uniform. Moreover, the failure of the tension specimen occurs in midsection, indicating a uniaxial transmission of tensile force to the specimen. Comparison of standard triaxial unconfined compression tests with unconfined tension tests shows that elastic moduli are not equal in compression and tension for compacted clays at a given moisture content.

歯科用せっこう硬化体の破面学的研究

From the fractographical point of view the relation between tensile strength and microstructure was studied for several dental plasters and stones by means of diametral compression test, scanning electron microscopy and x-ray diffraction. The following results were obtained. 1. Most of the specimens prepared from various dental plasters and stones fractured in the diametral plane containing the applied load axis. This fact shows the diametrical compression may set up a theoretical tensile stress normal to the diametral plane of the specimen. In practice, the plastic deformation of the specimen at the contact area increased with W/P ratio ; the load is distributed over the extended contact area. The fracture producing a "triplecleft" pattern was rarely observed in the present investigation of wet specimens. 2. The values of tensile strength obtained in the present investigation were nearly equal to the values in direct tension test by Nakamura et al. Consequently, it may be considered that the diametral compression test is a valid one for dental gypsum products. 3. In each specimen the longitudinal growth of dihydrate crystals increased and the tensile strength decreased as the W/P ratio increased. Therefore, the behavior of dihydrate crystals is a parameter of tensile strength in each specimen ; the decrease of tensile strength can be caused by the longitudinal growth of dihydrate crystals which brings about the decrease of contact of dihydrate crystals and the increase of the volume of porosity in the set mass. 4. Three crystal habits of hemihydrates were observed ; S type (dense stubby crystals), E type (dense elongated crystals) and A type (porous agglomerate of fine crystals). 5. Hemihydrate crystals were also observed in the fractured surface. These residual hemihydrates were dominantly observed at lower W/P ratio, although their quantity is not equivalent in each of the specimen even at the same W/P ratio according to the x-ray diffraction patterns. The set mass contained the residual E type of hemihydrates was stronger than that contained S type. 6. It is considered that the fundamental structure of set mass is composed of two phases : dihydrate and hemihydrate. Both crystals should be considered as parameters contributive to the phisical properties of set mass.

Model Studies on Mechanics of Jointed Rock

A generalized physical model is tested triaxially in order to relate properties of the intact material and of the discontinuities to the strength and deformability of a jointed rock mass. The behavior of jointed models can be divided into three characteristic zones. At low confining stresses there is either sliding along preexisting joints or brittle failure through intact material and across joints with strength depending on the number of intersected joints. At intermediate confining stressed sliding or failure may occur again, but the failure mode changes from brittle to ductile. At high confining stresses no sliding and only ductile failure occurs. The three zones and the upper and lower bounds of strength are easily obtained by a few confined compression tests on the intact material, by sliding tests along joints, and by a direct tension test. If this characteristic behavior is valid for other materials, as seems likely because of the basically similar underlying mechanism, it may become possible to determine the behavior of a jointed rock mass by relatively simple experiments.

Stresses and failure in rings of rock loaded in diametral tension or compression

The failure of rock materials in the form of rings subjected to line loadings on either their internal or external surfaces is studied. Formulae for the stresses and some numerical values are given. Experimental results for three fine-grained rocks are given and values of the tensile strengths so obtained are compared with those from direct tension, indirect tension (Brazilian) and bending tests. It is found that the calculated tensile stresses at failure for rings loaded in either fashion, and for bending tests, are considerably higher than those for direct tension or the indirect tensile (Brazilian) test. It is suggested that this is due to the fact that in the two latter cases the stresses are uniform (or nearly so) over the section in which failure takes place, while in the three former they vary almost linearly across it. This suggests that a criterion for failure must not simply involve the stresses at a point, but also their rate of change with position.

わが国慣用の各種PC定着装置の耐力試験 : B.B.R.V.および安倍式定着装置の場合

As mensioned in the previous report, the series of direct tension test is being carried out on various anchorage systems for the purpose of obtaining the basic data for standardizing the testing method and for specifying the bearing capacity requirement on post-tensioned anchorage systems for practical use. In this report, the direct tensioned and sustained loading test, results on B.B.R.V. anchorage for 13-φ 5mm cables and Abe anchorage for φ24mm strands were discussed and also summarizing the results of this test series, some suggestion on the testing method for bearing capacity on post-tensioned anchorage systems were proposed. The B.B.R.V. anchorage, here tested, is one of those anchorages using cold-formed rivet head at the ends of the wires of cable and being anchored by nut and stressing washer. In Abe anchorage, a strand is anchored in the same way as B.B.R.V. system using threaded cast-steal pipe which is called socket. However, the ends of the wires are buried with zinc. On the both anchorage, the direct tensile failing and sustained loading tests were carried out bearing the nut of the anchorage against the bearing plate of the Amsler type testing machine. The test results showed both of them have sufficient anchorage capacity until some wires of the cable or the strand failed in tension. The apparant average failure load was over 95% of the specified tensile strength of the cable or the strand. In the tests, the sinking of the head of the wires into the washer on B.B.R.V. anchorage and the sinking of the buried zinc into the socket on Abe anchorage was recognized. But these sinking did not affect the failure of the anchorage. From the test results, here mensioned, following remarks must be made. In B.B.R.V. anchorage, the length of the each wire of the cable differ with each other and so is the stress of it. For this reason, it is desirable that the quantity of washer bearing the head of the wires is not so hard that the head can not sink into it to average the stress of them. In Abe anchorage, much attension must be paid for controling the temperature of the buried zinc not to injury the wires.

わが国慣用の各種PC定着装置の耐力試験 : フレシネ式定着装置の場合

For the purpose, of obtaining the basic data for standardizing the testing method and for specifying the bearing capacity requirement on post-tensioned anchorage systems for the practical use, direct tension tests are being carried out on various anchorage systems. In this report the direct tension and sustained loading test results on Freyssinet Wedge anchorage for 12-φ 5mm or 12-φ 7mm cable were discussed in terms of bearing capacity, slippage of wires from the anchorage cone and sinking of male cone into female cone. Two types of spesimens were prepared in the tests, one having the female cone cast into the solid steel pipe case and another cast into the concrete block. The former was used for the tensile failing and sustained loading tests by Amsler type testing machine and the latter for the tencile strength tests by hand treating oil jack. In the direct tension tests, the anchorage cone cast into concrete block showed the sufficient anchorage capacity until the wire was failed in tension or the concrete block in compression. The apparent average failure load was 95% of the specified tensile strength of cable. However, in tests on specimen having the female cone cast into the steel pipe case the excessive slippage of wire from the cone as well as the obvious sinking of male cone into female cone was recognized prior to the shear failure of wire at the bend near the anchorage cone. The failure load was about 85% of the Specified strength of cable. From the results it can be concluded that the anchorage capacity is remarkably related to the testing method. From the sustained loading tests under specified allowable tensile load of cable itwas sure that a little time-dependent slippage of wire or slinking of male cone occured during first 30 hours justafter the loading and after that no obvious deformation were recognized.

Comments on an indirect tensile test on concrete cylinders

Summary A test which originated in Brazil for determining the tensile strength of concrete involves applying a compressive load to opposite generators of a cylindrical specimen. The specimenfaiL~ in tension along the diametral plane containing the load. Experiments with this teot have shown that: (1) Packing strips of relatively soft material are necessary between the specimen and the platens of the testing machine. Plywood strips ½ in. wide and ⅛ in. thick are satisfactory for the purpose, but the material and dimensions of the strips have little effect, provided they can conform to small irregularities in the surface of the specimen. (2) Cylinders 6 in. in diameter by 6 in. long may be usedfor concrete containing aggregate up to ¾ in. maximum size. Longer specimens may tend to give more uniform results, while smaller specimens may give higher average values. (3) The new test gives results higher than those given by a direct tensile test, but lower than the modulus of rupture of beams. It tends to give more uniform results than the direct tension or transverse test, but less uniform results than a compression test on cubes.

Adhesion of Rubber and Textiles. III. Examination of Test Technique

Abstract The variation with the rate of stripping of the load required to break rubber-to-fabric bonds is discussed for unvulcanized and vulcanized rubbers, and this is followed by a discussion of the load variation with period of vulcanization. The two features which are evident in stripping tests are separated, and a simple direct tension test is proposed as a more reliable measure of adhesion. An improved stripping test is proposed and this, together with the direct tension test, is discussed in a final section on the relation between the two tests and their application to practical problems.

Adhesion of Rubber and Textiles. IV. Function of Staple Fiber in Rubber to Fabric Adhesion

Abstract An investigation of the adhesion of rubbers to a series of fabrics woven from spun staple and continuous filament viscose, acetate rayon, and nylon is described. Using the direct tension test, it is shown that adhesion strength is a property of the staple fiber and is directly related to its tensile strength. The number of projecting fibers has been determined and compared with the broken-off ends recovered from a natural rubber cement after stripping from the fabric. The size-distribution histograms of the recovered fiber ends are also given and discussed. Recommendations are made for utilizing the results so far obtained in this investigation for the production of improved rubber-textile articles.