摘要:

Maximum pressure head rises, which result from total closure of the valve from an initially fully open position, are calculated and plotted for the valve end and for the midpoint of a simple pipeline. Uniform, equal-percentage, optimum, and parabolic closure arrangements are analysed. Basic parameters such as pipeline constant, relative closure time, and pipe wall friction are considered with closures from full valve opening only. The results of this paper can be used to draw the maximum hydraulic grade line along the pipe with good accuracy for the closure arrangements considered. It is found that the equal-percentage closure arrangement yields consistently less pressure head rise than does the parabolic closure arrangement. Further, the optimum closure arrangement yields consistently less head rise than the equal-percentage one. Uniform closure produces pressure head rise that usually lies between those produced by the parabolic and the equal-percentage closure arrangements, except for the range of low pressure head rise combined with low or zero friction, where the rise due to uniform closure approaches that produced by optimum closure.

ISSN:0315-1468    

DOI:10.1139/l85-027

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Following the generalized coordinate method of Vlasov, simple beam theory has been extended to treat torsional, distortional, and shear lag effects in straight, thin-walled box beams of uniform section. Single-cell or multicell sections with side cantilevers can be analysed, and the structure can be single-span or continuous. An example suitable for use in design is given, and all the calculations have been performed on a nonprogrammable hand calculator. The method is suitable for quick preliminary design and for reassessment of load capacity of a bridge. Comparisons are made with the results of finite strip computations. It is expected that when the method of hand analysis is programmed, computing times will be so short that interactive design procedures will become feasible, making it possible to develop relatively simple design rules which consider adequately the types of structural action specific to box beams. A physical understanding of box beam behaviour is facilitated by the use of the theory given here. As the elastic solution developed satisfies equilibrium, it can be factored to give a lower bound to the collapse load, for use in limit state design.Key words: analysis, box beams, bridges, distortion, interactive design, microcomputers, shear lag, torsion, warping.

ISSN:0315-1468    

DOI:10.1139/l85-028

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Groundwater quality management requires a good understanding of the contaminant migration phenomena within the porous media. A horizontal experimental tank (gross area of 63 m2) was built at Ecole Polytechnique de Montréal. An automatic data acquisition system, developed around a Timex-Sinclair ZX81 microcomputer, monitors, through 30 probes located in observation wells, the migration of a saline tracer. The dispersive properties of a limestone aggregate are derived from the spatial and temporal distribution of the tracer concentration.Key words: groundwater, quality, dispersion coefficient, automatic data acquisition, experimental tank, laboratory model, microcomputer.

ISSN:0315-1468    

DOI:10.1139/l85-029

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The rates of pipe breakage with increasing pipe diameter and times are investigated. Failure rates for cast-iron pipe are found to decrease with increasing diameter. Changes in pipe failure rates for the various modes of failures are examined in detail. Asbestos-cement and cast-iron pipe overall failure rates are found to increase with time, but for different reasons. Analysis of the modes of failure shows that joint failure is predominant for cast-iron pipe systems with bolted and universal joints whereas the predominant mode of failure for asbestos-cement pipe systems is circumferential cracking.Key words: asbestos cement, cast iron, cracking, diameter, failure rate, joint, regression analysis.

ISSN:0315-1468    

DOI:10.1139/l85-030

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Basin lag time is an important variable in the calculation of peak discharge resulting from a specified precipitation input. For the case of ungauged basins, the lag time must be estimated, normally from one or more expressions relating lag time to basin physical characteristics. A number of such expressions exist but each was developed for a particular range of basin size and geographic region. To overcome the problem of using an expression that may not be appropriate, a tentative general expression for basin lag time has been developed using data from basins representative of many regions in North America and ranging in area from 0.5 ha to 5840 km2. The tentative expression has only one basin characteristic, basin length divided by the square root of basin slope,, and applies to natural basins with minimal effective lake and swamp storage. When more data become available, the expression will be modified to include the effects of urban development and significant storage.Key words: lag time, peak discharge, prediction equation, ungauged basins.

ISSN:0315-1468    

DOI:10.1139/l85-031

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A linear programming screening model is developed to formulate a set of comprehensive water resource management plans using individual projects to deal with problems of flooding, water quality impairment, and municipal water supply shortfalls for the Grand River Basin Study. The value of the model is described as being the forcing of a system-wide approach by analysts, identifying interdependencies, directing technical analyses, and the formulation of management plans. Postoptimality procedures are used to test the sensitivity of derived management plans to parameters used to describe the Grand River Basin.Key words: water resources, management modelling, Grand River, linear programming.

ISSN:0315-1468    

DOI:10.1139/l85-032

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The stiffened tied arch bridge has a tie consisting of a stiff flexural member, which tends to distribute live loads uniformly over the arch. Various approximate methods for analyzing this system are presented, including Maillart's method, a simplification of that procedure, the single-redundancy method, and an elastic foundation approach. Comparisons are made with a computer analysis to determine the accuracy of each procedure. Increased familiarity with this structure should lead to more frequent consideration of this type of bridge by designers.An optimization study was carried out for spans in the range of 50–150 m. This investigation indicated that a girder-to-arch stiffness ratio of about 9 is desirable.Key words: analysis, arch, bridge, optimization, stiffened, structure, tie.

ISSN:0315-1468    

DOI:10.1139/l85-033

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

This paper presents an ultimate shear-bond equation for composite deck-slabs failing in shear-bond. The equation is based on recent experimental evidence of composite deck-slabs exhibiting early end-slip prior to ultimate load, and contains the steel deck thickness as a parameter, which other existing equations do not. The presence of the steel deck thickness parameter can result in a reduction of up to 75% of the presently required number of laboratory performance tests. A total of 196 test results was used to substantiate as well as to compare the results of the equation developed. The results of the developed equation were, in general, within the commonly accepted scatter range of ±15% of the corresponding experimental results.Key words: bonding, composite structures, shear strength, shear tests, slabs, structural engineering, ultimate strength, steel decking.

ISSN:0315-1468    

DOI:10.1139/l85-034

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Since 1981, an Ontario provincial government study has been undertaken on the 53 concrete water tanks built in the province since 1956. Results of mainly external, but some internal, inspections, condition surveys, and ratings on an ascending 0–9 scale revealed a wide range in performance. This varied from failed tanks, rated 0 (two tanks), to very good performance, rated 9. The ratings were generally related to the tank types and construction method used. The best performance was exhibited by posttensioned bonded (PTB) types. The survey results and defects analysed revealed various problems and causes. These varied from specific construction methodology faults, such as slipform jack rods (pipes) left in the walls of certain types of tank, which filled with water and froze, to common defects, such as cold joints, experienced in all types, leading to leakage and freezing, and ice expansion in voids in tank walls during the winter. Actual concrete tensile stresses induced by internal ice formations, thermal gradients, and shrinkage stresses were found to be higher than those used in most designs or allowed in international codes or standards. As a result of the study, a provincial government rehabilitation programme for ministry-built tanks in need of repairs and leakproofing was started in mid-1982 in the order of priority ratings established during the study.

ISSN:0315-1468    

DOI:10.1139/l85-035

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The results of two pilot studies are presented: one concerning snow on farm roofs in the Ottawa area carried out in 1966, and the other an eight-winter investigation of the influence of surface roughness and slope on snow accumulation on nine 2.4 m × 2.4 m unheated, north-facing experimental roofs built in a sheltered woods at the National Research Council Canada in Ottawa. The results indicate a trend towards reduced snow density as slopes increase and a smaller accumulation of snow on smooth (metal) surfaces than on rough shingled roofs as slopes increase. More data on full-sized roofs across Canada are required to verify this. It is suggested that a less conservative slope-reduction relation might be considered for smooth roofs in the Ottawa area and for other areas with similar climate.Key words: snow loads, sliding snow, sloping roofs, snow depths, snow densities, surface roughness, pilot survey.

ISSN:0315-1468    

DOI:10.1139/l85-036

出版商:NRC Research Press    

年代:1985

数据来源: NRC