Geoffrey L. Kulak

Field studies of bolt pretension

Abstract Pretensioned bolts must be used when it is required that an axially loaded connection does not slip when force is applied or for connections loaded in direct tension. Studies that report on the attainment of bolt pretension are generally available only for laboratory conditions, however. This paper reports on the results of two independent investigations that used an ultrasonic bolt length measurement device to establish the pretension in bolts installed in the field. Six different sites were used by one researcher to obtain the pretensions in 232 bolts of different sizes, grades, and which used different installation methods. A total of 104 bolts at three different sites were monitored by the other team. In all cases, installation was done by the erector of the structure: the research teams were not involved in the installation process in any way.

Local buckling rules for structural steel members

Abstract Specifications governing the design of structural steel members provide rules for both the overall strength of the member (beam, column, or beam-column) and for capacity as governed by local buckling. Generally speaking, the development of rules for local buckling has not received the same amount of attention as has the examination of the strength or overall stability of the member. Recently, however, both analytical and experimental studies of local buckling have increased in number. In the report provided herein, a comparative review of the local buckling rules of a number of specifications is presented. The intention is that those responsible for the various specifications, norms, or building codes will be able to make a critical assessment of their own rules governing local buckling of steel members. With some exceptions, the material is generally presented in a factual fashion: those who identify cases within their own specification that stand out from the general trend will have to make their own examination of the reasons why their particular rule is at variance with others.

Tubular members — large and small

Members of circular hollow cross-section have a long history of use and wide application in civil engineering structures. In the smaller sizes, usually called hollow structural sections, improvements in connection design have greatly increased their use. Design methods for these members are reasonably well-defined. Design rules for manufactured or fabricated pipe of the kind used for transmission of fluids such as water, gas, or oil are not quite so well established, however. Likewise, there are still areas in the design of fabricated steel tubes of the sizes used for stacks, masts, conveyor galleries, or in offshore structures that need further study. An overview of the state of the art in these several areas is presented.

Flexural tests of longitudinally stiffened fabricated steel cylinders

Abstract Fabricated steel cylinders with large R t ratios are often used in conveyor galleries, offshore platforms, storage tanks, towers, vessels, and the like. The use of longitudinal stiffeners in these large cylinders has proven to be an efficient way to promote structural stability. The increase of load capacity is significant. However, the attachment of the stiffeners complicates the problem by introducing additional buckling modes and new design parameters. Four large-scale specimens were tested. The collected data included the load versus deformation behavior, as well as the geometric imperfections and welding residual stresses of the specimens. The objective of the research program was t investigate the local buckling behavior and ultimate load capacity of longitudinally stiffened steel cylinders subjected to bending. The results showed two failure modes, a shell buckling mode and a general buckling mode. The occurrence of both modes and the corresponding capacity depend on the shell properties, as well as on the spacing and angle of arc covered by the stiffeners. The general buckling mode has strength and ductility much higher than those predicted by existing design guidelines.

Tests of fabricated steel cylinders subjected to transverse loads

Abstract The inelastic shear behavior of large-diameter cylindrical shells subjected to transverse loads was investigated. Two specimens of 1270 mm diameter were tested under different boundary conditions. The tests were preceded by finite element simulation in order to help plan the tests and to offer insight into the findings. Measurement of the geometric imperfections and the welding stresses was made prior to testing and the testing itself was carried out in both the pre-buckling and the post-buckling ranges. The finite element predictions and predictions made using other design equations compare favorably with the test results.

Ultimate shear strength of large diameter fabricated steel tubes

Abstract Large diameter fabricated steel tubes subjected to transverse shear forces and bending moments can fail either in a local compression buckling mode because of flexure or in a diagonal buckling failure mode as a result of shear forces. Drawing on recent work by the writers at the University of Alberta, the ultimate shear strength is investigated through a parametric study to determine the factors affecting failure. A nonlinear regression analysis is then carried out using the available experimental data to derive an empirical relation for the ultimate shear strength. The formula is compared to the current design approach and found to perform better throughout the range of applicability.

Longitudinally-stiffened large diameter fabricated steel tubes

Abstract Fabricated steel cylinders are often used as conveyor galleries, stacks or masts, or as members in offshore structures. The cylinders are fabricated by first cold rolling steel plates to form short cans and then joining these together by circumferential girth welds to yield long spans. Circumferential stiffeners are almost always present, in order that the circular shape of the tube is maintained and as an assistance when the cylinder is being handled. Longitudinal stiffeners may be used as well. If they are present, they will be welded to the cylinder surface, thereby improving the behaviour under axial compression or beam bending. The paper addresses the design of the type of cylinder commonly used as a conveyor gallery. In this application, diameters of from 2·5 to 4·0 m are typical and the radius to thickness ration, R/t, ranges from about 100 to 400. Spans can reach 60 m. The results of four large-scale flexural tests on large diameter fabricated steel cylinders that had longitudinal stiffeners and a parametric study of hypothetical cylinders of this configuration are used as the basis of the study. The paper reviews current design standards in the light of those test results, presents the results of the parametric study and makes recommendations for the design of longitudinally-stiffened fabricated steel cylinders.

Strength and installtion characteristics of tension control bolts

Publisher Summary Tension control bolts are a configuration of high-strength bolt in which a splined end extends beyond the threaded portion of the bolt. To install the bolt, a special electrically powered wrench that has two coaxial chucks is used. The inner one slips over the splined end of the bolt and the outer one envelops the nut. The two chucks turn relative and opposite to one another to tighten the bolt. At some point, the splined end of the bolt shears off at an annular groove that is located between the threaded portion of the bolt and the spline. If properly calibrated, preload is achieved at this point. Factors that control the preload include bolt material strength, thread conditions, such as lubrication, dirt, and thread damage, the diameter of the groove, and the surface condition at the nut-to-washer interface. The testing program reported herein measured the preload in a large sample of bolts (about 850) taken from several different manufacturers. Differing conditions of bolt age and exposure before installation were also included.

Shear capacity of large fabricated steel cylinders: A truss model

Abstract Failure of large diameter steel cylinders fabricated from hot rolled sheet steel plates and subjected to transverse beam shear occurs when large diagonal buckles develop in the panels formed by the circumferential stiffeners. The load-carrying capacity then drops to a slightly lower level than the ultimate strength level. Whereas the ultimate strength has been shown to be significantly reduced in the presence of fabrication residual stresses, the postbuckling load level is not affected. Further, this load level is stable. It is advocated, therefore, that the postbuckling load be used as a conservative design base for calculation of shear capacity. A general truss model is developed herein as a description of the load-carrying mechanism in the postbuckling range. Predictions obtained using the model are compared with available test results and a design chart is developed that will enable designers to handle most practical cases.

Fatigue strength of a groove weld on steel backing

Abstract Groove welding made from one side is a common fabrication technique for joints in steel structures. If a steel backing bar is used, current (1988) North American specifications require that it be removed after welding and the weld ground flush if the detail is oriented transversely to the direction of stress and loaded in fatigue. This is an expensive, and in some cases impractical, procedure. British specifications permit the detail to be used but assign a very restrictive fatigue category. In the investigation reported herein, data concerning the fatigue strength of a groove weld with steel backing bar have been obtained experimentally. The backing bar was attached with intermittent fillet welds. A finite element analysis was used to assist in interpretation of the test results. The analysis showed that high local stresses are present at the toe of the fillet weld. However, high stresses also exist at the flush-ground face of the groove weld, and in the physical tests all fatigue cracks started at this side of the detail. When this detail is present in a structure that is subjected to a fatigue loading, Category C of the AASHTO or CSA specifications will provide a suitable basis for design. The selection of categories Class F or G from the British Standard (depending upon the proximity of the fillet welds to the edge of the plate) is too conservative.