摘要:

A decision theory approach is proposed for selecting the optimal accident countermeasure when estimates of future accidents at a site and expected proportion of the accidents likely to be prevented by a countermeasure are uncertain. The decision model is transformed into a microcomputer program and a numerical example is used to illustrate the aptness of the approach and its ability to allow analysts to combine empirical data with informed judgment to make decisions systematically. The potential of the program to be expanded to operate with an extensive built-in knowledge base of accident and countermeasure attributes is discussed.Key words: decision theory, probability, expert systems, utility, uncertainty.

ISSN:0315-1468    

DOI:10.1139/l88-020

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

While the basic concept of guiding individual drivers en route to their destination using on-board computers was introduced more than two decades ago, a practical implementation of this concept has only become possible as part of the current microcomputer–communications revolution. This paper assesses the potential role of these on-board route guidance systems as a means of better assisting drivers to make routing decisions and to improve the quality of the data available to the central traffic control system. The assessment indicates that the potential capabilities of these systems are controlled by the type of communications between the on-board units and the central control system, the level of on-board intelligence that is provided, and the integration of these activities within the traffic control model.Key words: traffic control, individual route guidance, driver information systems.

ISSN:0315-1468    

DOI:10.1139/l88-021

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The longitudinal movement of a structure supporting continuously welded track relative to that track results in interactive forces (interactions) being induced in both the rails and the structure. The differential movement may arise from thermal effects, volume changes in the structure, substructure deformations, or other factors. These resulting interactions are the focus of this paper.A design tool allowing the estimation of the limiting values of these interactions is presented for use by track and structure designers.The presentation begins with a discussion of the thermal stresses and movements induced in at-grade tangent continuous welded rails (CWR). The interaction of CWR and the structure is then presented, followed by a brief overview of the behaviour of CWR with rail expansion joints. The work addresses tangent tracks and will adequately apply to curved tracks with large radii, say, in excess of 500 m. Adjustments for track curvature would be required for tighter radii.Key words: trackwork, continuous welded rail, bridges, thermal stresses, force interactions.

ISSN:0315-1468    

DOI:10.1139/l88-022

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The limit states design of structural components involves the use of resistance factors which account for the variabilities and uncertainties which exist in both load effect and element resistance. In this paper, the rational development of such resistance factors is examined for axially loaded K, T, and Y joints between steel circular hollow section members subject to predominantly static loading. The development of these factors is primarily oriented to the design of such joints in offshore structures under extreme environmental loading conditions, but onshore applications to buildings are also considered. A level II method of reliability analysis has been used for the derivation of the resistance factors. The joint strength criteria from seven prominent code and noncode design documents have been considered, and recommendations for resistance factors to be used in the design of offshore and onshore tubular joints are made.Key words: steel, offshore structures, tubes, joints, reliability analysis, structural safety.

ISSN:0315-1468    

DOI:10.1139/l88-023

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

As a result of environmental changes in the design requirements, many old industrial structures for chemical, power plants, and processing mines now face the problem of changing their process equipment to meet the new code requirements. In most cases, new pieces of equipment, such as scrubbers and filters, are introduced to the process cycle. This kind of equipment is usually very heavy and creates massive loads on the existing foundation.Many existing concrete foundations are unable to safely support the additional loads. It is necessary to increase the existing foundation capacity using the underpinning technique. Normally, the underpinning procedure includes shoring and jacking up of the existing structure. Due to the dynamic nature of loading, it is often required to shut down the plant for the foundation underpinning. However, the high cost of such a shutdown (0.5 to 1.0 million dollars a day) makes it necessary to develop new underpinning techniques to double the capacity of the concrete foundation while the plant is in full production. This paper describes the case of underpinning a chemical plant near Regina. Three design alternatives were proposed for the underpinning. A suitable design method was adopted and the construction was completed during the spring of 1985.Key words: underpinning, strengthening, footings, steel grillage, concrete repair, pile cap, deep beam, construction procedure.

ISSN:0315-1468    

DOI:10.1139/l88-024

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Columns, stacks, conveyor galleries, and other similar civil engineering structures are often constructed in the form of an unstiffened tube or as a discretely stiffened tube that behaves in an essentially unstiffened manner. Tubes of this type are used extensively in the materials-handling operations of industrial plants. These are fabricated circular steel cylinders, typically 2.4-4 m in diameter, with radius-to-thickness ratios in the range of 150–400. They support and enclose conveyor systems, and they customarily span distances up to about 50 m. The task of the designer is similar to that faced with plate girders: the bending capacity, shear capacity, and the combined effects of shear and bending all must be examined. The results of a test program established to examine the flexural strength of large diameter fabricated steel tubes is reported herein. Although the number of tests is not great, the program is distinguished by the fact that the tests were done using relatively large specimens made in a way similar to that which would be employed in full-size tubes. These tests are believed to represent the best information currently available, and the results should be useful to both designers and other researchers who are approaching the problem using analytical tools.Key words: buckling, conveyors, pipes, steel, structural engineering, tubes.

ISSN:0315-1468    

DOI:10.1139/l88-025

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The Tsing Yi South Bridge was constructed in the early 1970s to provide access between Tsing Yi Island and the mainland at Kwai Chung. It has a prestressed concrete box girder superstructure consisting of five independent units which are monolithic with their piers and have expansion joints at the mid-span shear hinges and the abutments. During routine maintenance it was found that the superstructure cantilevers were deflecting excessively, and consequently a thorough inspection and appraisal were commissioned. These included a complete visual inspection, concrete core extraction, radiographic inspection of prestressing tendons and a programme of load testing. The bridge was also reanalyzed to check its long-term performance. Subsequently, a rehabilitation scheme was designed to recover part of the deflection. This involved the introduction of additional prestress near the box girder's top flange.Key words: prestressed concrete, structural assessment, creep, shrinkage, radiographic inspection, rehabilitation, external prestressing.

ISSN:0315-1468    

DOI:10.1139/l88-026

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A model for evaluating the fatigue life of a prestressed concrete girder bridge is presented. Experimental studies indicate that fatigue is a random phenomenon. Therefore, the approach is based on probabilistic methods. The fatigue life of the prestressed concrete girder is estimated from the fatigue properties of its components, namely, the cast-in-place slab, precast beam, prestressing steel, and, if partially prestressed, the tension reinforcement. The model utilizes the availableS–Ncurves for structural materials and Miner's rule to evaluate the fatigue life under variable amplitude loading. A model for determining the distribution function of time to first cracking is also presented. To demonstrate the developed models, a typical prestressed concrete girder bridge is analyzed. On the basis of this investigation, it is concluded that fatigue in prestressed concrete girder bridges designed according to the American Association of State Highway and Transportation Officials specifications is not a limiting design criterion.Key words: bridges, fatigue, prestressed concrete, structural reliability.

ISSN:0315-1468    

DOI:10.1139/l88-027

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

In this article, a general methodology for simulation of water resources management is suggested. The research has been conducted in three different levels: a deep analysis of the historical management procedures, the development of some alternative ways to optimal management, and the establishment of planning criteria at short, middle, and long term. The main constraints, divided into three categories according to the severity of probable losses, have been defined as a function of several expected goals: hydro power, flood control, recreational activities, etc. The model was applied with excellent results to the upper region of the St. François river basin (Québec, Canada).Key words: simulation, resources management, mathematical models, optimization.

ISSN:0315-1468    

DOI:10.1139/l88-028

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A large disposal field (31 × 69 m) was designed in agreement with legal recommendations. A full scale test with clear water revealed that the field exfiltration rate was much lower than anticipated. This paper describes the design, the instrumentation performed with eleven piezometers, the ground-water conditions as modified by the disposal field, how the true exfiltration rates have been determined after due consideration of natural precipitations and evaporation losses, and also the method used to improve the performance. The value of the infiltration rate into the soil, initially established by percolation tests, was confirmed by permeability tests performed in the piezometers. However, the true exfiltration rate of this disposal field was only 8% of the rate predicted by the conventional, legal design. It is established that this exfiltration rate cannot be derived by simple transposition of the results of percolation tests as presently done by by-laws. Alternatively, more rigorous methods are described. For a good design, it is necessary to perform hydrogeologic studies much more detailed than those presently required by by-laws. Finally, for improving the design and service life of such disposal fields, several suggestions are made to avoid water mounds and to reduce the risk of clogging.

ISSN:0315-1468    

DOI:10.1139/l88-029

出版商:NRC Research Press    

年代:1988

数据来源: NRC