摘要:

A straightforward approach is presented for the productivity calculations in shovel-truck type operations applicable to earthmoving, quarrying, and open cut mining. The approach is based on finite source queueing models where the loading times of the shovel are modelled as Eriang distributions and the truck backcycle times follow exponential assumptions. The state of the system is defined as the number of Eriang phases left in the system and yet to be processed; this requires keeping track of which phases the trucks are in. The balance equations for such queueing models are derived and a sequential calculation procedure requiring minimal computational effort is put forward by which the shovel utilization and hence the operation productivity may be calculated. Example calculations, together with a field study illustrating the applicability of the queueing models, are also presented.

ISSN:0263-0257    

DOI:10.1080/02630258608970435

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An automated approach for the analysis of plates on an elastic foundation is presented. The approach combines automatic mesh generation with nonlinear analysis to analyse plates of arbitrary shape on an elastic foundation subject to uplift. Two separate complete systems are presented, the first employing an ACM element to analyse rectangularly-shaped plates and the second employing a heterosis element to analyse plates of arbitrary shape. Solutions of the systems are presented and compared to theoretical results. A convergence study is also presented.

ISSN:0263-0257    

DOI:10.1080/02630258608970436

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An investigation of the parameters affecting the optimization of curvature ductility in a reinforced concrete frame sub-assembly subjected to seismic loads is presented using the feasible directions method. Four design variables are used: width of beam cross section, effective depth of cross-section, area of tension steel, and compression reinforcing. Two other variables, concrete compressive strength and yield strength of reinforcement, are treated as preassigned parameters because these quantities are usually taken as integer values in structural design. Curvature ductility is maximized for a given demand moment when one uses: the lowest yield strength steel and the highest concrete strength available; equal amounts of tension and compression reinforcement; the largest cross-section permitted by the design constraints; and sufficient reinforcement to just satisfy the demand moment constraint.

ISSN:0263-0257    

DOI:10.1080/02630258608970437

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Different models of uncertainties from the simplest interval representation to fuzzy sets and random numbers are reviewed. Mathematical theories spawned by these conceptual models are described, including interval analysis, possibility and fuzzy set theories, probability theory and the theory of evidence. The relationship among these theories is delineated from the perspective of understanding human reasoning. The discussion emphasizes conceptual understanding and physical intuition rather than mathematical theorems and axioms. It is intended to remove some of the mysteries surrounding existing viewpoints on uncertainties, which may have hindered wider understanding and acceptance of these viewpoints by practicing civil engineers. Subsequent parts of this paper will discuss the process of uncertainty propagation in a rules framework with reference to the various kinds of uncertainty representations.

ISSN:0263-0257    

DOI:10.1080/02630258608970438

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Power plants use cooling towers for waste heat transfer either into air or water, with the result that both the cost of electricity and the environment are greatly affected by the type and operation of the cooling system. Systems analysis of both aspects shows that differentiated cooling management, dependent on specific site conditions at a particular time of year, is more profitable than permanent cooling with fixed emission standards throughout the year. As shown for the German Lower Main River, it would not be economically disadvantageous to transfer less waste heat to the river during hot summer periods, thus gaining ecological advantages. Similarly, in winter when the power plant is working to full capacity, cooling could be reduced, resulting in a lower cost and higher energetic efficiency, without ecological risks.

ISSN:0263-0257    

DOI:10.1080/02630258608970439

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This paper concludes that traditional methods used in risk analysis have to be modified for adaption to the civil engineering industry. The main reason is that civil engineering systems are humanistic systems while traditional methods have been developed for mechanical systems. Consequently, the proposed method, indication of risk, is based on traditional methods such as fault tree analysis but modified according to the needs of the civil engineering industry. For humanistic systems, the method is based on the theories of possibility and fuzzy sets instead of the traditional theory of probability. The method is intended to be used to identify critical phases of the analysed systems and for optimizing system control. The method presented is exemplified by a risk analysis of a computer calculation. It is concluded that the method fulfils its intentions and deserves to be developed and examined further.

ISSN:0263-0257    

DOI:10.1080/02630258608970440

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0263-0257    

DOI:10.1080/02630258608970441

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor