Design Guidelines For Structures Research Articles

Present activities for the preparation of a Japanese draft of structural design guidelines for the experimental fusion reactor

Since November 1990, systematic research has been carried out in preparation for a Japanese draft of structural design guidelines for the experimental fusion reactor. This report summarizes the major results of the work and the status of these efforts. A classification of components and definition of operating conditions are proposed on the basis of the ITER-CDA design, in the light of the safety characteristics of the fusion reactor and relevant conventions for the existing fission reactor design code. Specific issues regarding the structural design of the experimental fusion reactor are discussed based on the experimental and analytical work. The validity of the existing structural design method is confirmed for the use of irradiated 316 SS, irrespective of the significant reduction in uniform elongation capability caused by heavy neutron irradiation. Further important phenomena are treated such as magnetic damping, magnetic stiffness and fracture due to electromagnetic forces. Finally, the issues concerned with welding and non-destructive examinations are discussed with relevance to component classification.

The PRESSS Program Current Status and Proposed Plans for Phase III

The current status of the coordinated Precast Seismic Structural Systems (PRESSS) program is summarized and plans for the final phase outlined. PRESSS Phase III is built around two large-scale super-assemblage experiments, one of a frame building and the other of a panel structure. Precast concrete elements will be used to the maximum in both structures. The buildings will be designed using a displacement-based design procedure developed as part of the PRESSS program and the results of experimental programs forming PRESSS Phase II. The purposes of PRESSS Phase III are to demonstrate the viability of precast concrete design for regions of high seismicity, to establish clearly the predictability and dependability of performance of properly designed precast concrete buildings under seismic response, and to emphasize the advantage of precast concrete seismic performance, including reduced damage levels compared with equivalent reinforced concrete or steel structures. A final objective of the PRESSS program will be to develop design guidelines for precast concrete structures in zones of high and moderate seismicity which can be incorporated into the model building codes.

New Guidelines for Fatigue Design of HSS Connections

The current specifications for fatigue design of hollow structural section (HSS) connections are both outdated, and, in view of recent research results fairly inaccurate. Analyses of a large number of connections have been carried out, incorporating results from other researchers. The result is this paper, which contains an outline for improved fatigue design guidelines for HSS structures that are welded directly together without the use of additional stiffeners. To clarify the use of these guidelines and show the difference between the proposed and existing design methods, three HSS connections are analyzed with existing design guidelines as well as with the proposed guidelines.

ELEVATED TEMPERATURE LOW‐CYCLE FATIGUE BEHAVIOR OF HK40 ALLOY

Abstract— By conducting creep tests and creep‐fatigue tests at temperatures of 800°C, 900°C, and 1000°C, on centrifugal cast HK40 alloy (which is used for example for the steam reformer tubes of fuel cell plants) and varying the strain rate during the loading and unloading process, the influence of strain history on the life of the material has been clarified. Furthermore, the data obtained from these tests were subjected to analyses by means of life evaluation methods utilizing the life fraction rule, strain range partitioning method, and damage rate approach, and comparative studies were conducted on each life evaluation method. As a result, problematic points concerning the application of the life fraction rule, strain range partitioning method, and damage rate approach have been clarified and data which would be useful in establishing design guidelines for structures to be used under conditions such as involves the interaction of creep and fatigue have been obtained.

DESIGN OF CONCRETE STRUCTURES USING FUSION-BONDED EPOXY-COATED REINFORCEMENT.

The paper reviews structural aspects of fusion-bonded epoxy- coated reinforcement (FBECR) which may differ from that of non- coated reinforcement, proposes guidelines for structural design using FBECR in respect of those differences, and presents a rationale for these proposals. The study shows that coating of reinforcement to BS 7295 will not adversely affect mechanical properties, fatigue endurance or bendability of reinforcement. Bond behaviour is affected, however. A review of data demonstrates that anchorage and lap strength of reinforcement is reduced by an FBE coating where concrete cover is less than three times bar diameter. The paper concludes with proposals for design detailing with FBECR, and for changes to methods for bond testing; and it identifies areas in which further data are required. Conclusions from the study raise questions about the value of the BS 4449 test specification when applied to coated bond reinforcement.

Floor vibrations from aerobics

Recent vibration problems with floors used for aerobics have shown the need for better guidelines for structural design and evaluation. Such guidelines were introduced for the first time in the Supplement to the 1985 National Building Code (NBC), but more recent experience with one particular floor has shown the need for some improvements to these guidelines. The paper describes the investigation of the floor and the use of the floor to estimate the loading function for aerobics, and recommends changes to the NBC design criteria. The paper provides guidance on estimating parameters used in the criteria and discusses repair alternatives related to the floor problem. Key words: floor vibration, aerobics, design criteria, repair.

Coupling of surface waves by two crossed dielectric waveguides

The coupling of surface waves by two crossed dielectric slab sections with curved transition waveguides is investigated by the method of staircase approximation. the coupling problem of the nonuniform structure is analyzed in terms of the scattering of incident surface wave by the crossed structure as a whole. The scattering characteristics of the crossed waveguides are calculated with a particular attention directed to the effect of radiation due to bending of the curved transition waveguides on coupling properties of the structure. Some useful guidelines for the design of the coupling structures are thereby suggested.

Influence of variations in creep curve on creep behavior of a high-temperature structure

It is one of the key issues for a high-temperature structural design guideline to evaluate the influence of variations in creep curve on the creep behavior of a high-temperature structure. In the present paper, a comparative evaluation was made to clarify such influence. The evaluation results showed that, in almost all cases of a creep behavior pattern in which creep strain accumulated during a stress cycle caused significant relaxation of the corresponding deformation-controlled stress in the following cycles, the variations in creep behavior with the creep curve were qualitatively similar to those in fundamental creep properties. On the other hand, in many cases of another creep behavior pattern in which creep strain accumulated during a cycle doesn't cause the significant stress-relaxation in the following cycles, the variations in creep behavior for earlier cycles are different from those in fundamental creep properties. Even in these cases, however, those get qualitatively similar after several cycles when their stress-time histories are stabilized. Additional consideration was given to the influence of the relationship between creep rupture life and minimum creep rate, i.e., the Monkman-Grant's relationship, on the creep damage evaluation. The consideration suggested that the Monkman-Grant's relationship be taken into account in evaluating the creep damage behavior, especially the creep damage variations. However, it was clarified that the application of the creep damage evaluation rule of ASME B.&P.V. Code Case N-47 to the “standard case”which was predicted from the average creep property would predict the creep damage on the safe side.

Seafloor scour--Design guidelines for ocean-founded structures

Seafloor scour--Design guidelines for ocean-founded structures

Analytical and experimental vibration and buckling characteristics of a pretensioned stayed column

Modal vibration tests to determine lateral modes of vibration of a stayed column and static axial compression tests to determine the column's buckling and postbuckling behavior have been performed. Effects of stay tension levels and vibration-load interaction are presented. Two finite element models are used to analyze the column, a three-dimensional frame using NASTRAN and an equivalent two-dimensional frame using an exact dynamic stiffness matrix. Both analyses correlated well with the linear vibration and buckling experimental data. Results indicate premature buckling of the column due to vibration-load interaction and nonlinear oscillations due to stay slackening. Postbuckling behavior of the column is unusual because of stay slackening and results in a postbuckling restoring force of less than the bifurcation buckling load. Guidelines for design of pretensioned structures are presented which consider buckling, postbuckling and vibration behavior.

Interference effects in laser micromachining of thin films on silicon

Some recent designs of new electronic circuits on silicon have been implemented by laser removal of thin metallic film from the composite structure. The presence of an insulating dielectric region between the thin metallic film and the silicon substrate gives rise to a complex laser-micromachining process whose understanding is crucial to successful applications. In this paper we explore the laser-machining process at 1.06 μm for a tantalum nitride thin-film resistors material on top of a dielectric film on silicon. We experimentally verify the existence of strong optical interference effects in laser machining of these resistors and determine their influence on various laser-trimming parameters. Good correlation is obtained between an analytical model for these interference effects and the experimental data. For structures containing a single SiO2 layer with thickness up to 1 μm between the tantalum film and silicon, it is observed that from a laser-trimming standpoint, a SiO2 thickness of 9000 or 5400 Å is preferred to all others. A selection of either one of these thickness will lead to a wider laser-trimming-process window. These results could, therefore, be viewed as structure design guidelines for laser trimming by material removal at 1.06 μm.