摘要:

An experimental study has been made on a scale model of a rectangular canal in the hydraulics laboratory of Laval University in order to simulate the destruction of a solid continuous ice cover under the effect of the tangential forces created by the flow.The canal was 6 ft (1.8 m) wide and 46 ft (14 m) long. At the lower end, an ice retention structure of reticular form was built. The ice was simulated with a wax poured in a continuous and uniform layer; whose properties correspond to that of natural ice at an average scale of 1/25. Ice covers corresponding to thicknesses of 8 to 20 in. (20.3 to 50.8 cm) were simulated at that scale.Tests consisted essentially in increasing progressively the discharge feeding the canal until complete failure of the ice cover and accumulation of the pieces in front of the grid retaining structure.Three important phenomena have been observed and measured. By chronological order the first one is the submersion of the frontal edge of the cover. This happens at a relatively constant Froude number but much higher than the one characterizing the stability of unconsolidated ice jams.An increase in discharge makes the ice cover unstable as it oscillates in the flow. This state is followed closely by the failure of the cover, the movement of the pieces with the flow and their accumulation in front of the retaining structure where they form a dry jam. This phenomenon of failure of the ice cover could be interpreted in the first approximation with two dimensionless numbers one being the Froude number and the other characterizing the ratio of failure forces to gravity forces. We have found that an exponential relationship relates these two numbers and the correlation coefficient for the 25 tests is satisfactory.Finally, we have measured the thrust exerted by the dry jams on the ice retaining structure. There is a very direct hydrostatic relationship between the thrust and flow conditions with a dry jam.These laboratory results are interesting to assess the discharges and water levels required in rivers to break-up ice covers of various resistances. One can estimate these conditions for the case of weakened ice covers before spring break-up. However, more importantly, it is possible to approximate the worst conditions of flooding with an early break-up towards the end of the winter when the ice still has its maximum strength.

ISSN:0315-1468    

DOI:10.1139/l76-001

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A statistical study has been done to investigate (i) the variation of spectral responses of structures due to artificially generated earthquake records with identical statistical properties, (ii) the effect of duration of strong shaking phase of artificial earthquakes on the response of structures, and (iii) the number of earthquake records needed for time-history response analysis of a structure in a seismic region. The results indicate that the flexible structures are more sensitive to the inherent statistical variations among statistically identical earthquake records. Consequently several records must be used for time-history response analysis. A sample of eight or more records appear to provide a good estimate of mean maximum response. The duration of strong shaking can significantly affect the maximum response. Based on the results, it is suggested that for the purpose of estimating peak response, the strong shaking duration of the input earthquake motion should be at least four times the natural period of the structure. The maximum responses due to statistically identical ground motion records are observed to fit approximately the type 1 extreme value distribution. Thus, it is rationally possible to choose a design value based on the mean, standard deviation of the spectral response values and tolerable probability of exceedance.

ISSN:0315-1468    

DOI:10.1139/l76-002

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

In this paper a linear programming technique is used as an aid in selecting storage reservoirs for a hydroelectric power development system at the feasibility stage of investigation, and for maximizing system guaranteed hydroelectric power by optimum regulation of discharge through power plants and from diversions for a selected time period. The linear programming technique is used as an allocation or screening model that provides information on system operation and response which would be useful in the preliminary design of hydroelectric power producing facilities and from which basic data and guidelines could be extracted for extending the investigation to the study of long-term system response by use of simulation models.

ISSN:0315-1468    

DOI:10.1139/l76-003

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A method for evaluating the spatial variations in strong seismic motions for a linear, homogeneous, and horizontally stratified soil layer system is presented. The procedure accounts for the focal depth and the epicentral distance, the corresponding angle of incidence, and the relative contributions of both shear and Rayleigh waves. The inclined propagation of shear waves is studied using the multiple reflection refraction theory. The range of possible values of Rayleigh wave phase velocity in the soil layer system is determined, and using an averaging procedure the Rayleigh wave amplification factors are computed. The influences of various factors on the spatial variations in seismic response are discussed. The method is general so that it can be used for various problems involving spatial motion computations. The application of the method in computing the responses of a soil–pile system is described and some typical results given.

ISSN:0315-1468    

DOI:10.1139/l76-004

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The 28 day strength of concrete cylinders cured under standard laboratory conditions can now be reliably predicted at early ages by use of (a) the Modified Boiling Test or (b) the Autogenous Curing Test. The availability of early strength indicators for concrete can be used to great advantage during construction provided these strengths can be related to the strength of the structural elements.To permit an estimate to be made of the strength of in-place concrete on structures appurtenant to the Welland Channel By-pass, the temperature rise of the structural elements was monitored with an automatic 16 point recording potentiometer. The time temperature curve of the in-place concrete was compared to that of 6 in. by 12 in. (150 mm by 300 mm) concrete cylinders taken during casting of the structure and cured autogenously for 48 h, thus permitting an estimate of the in-place concrete strength to be made from the results of the 48 h autogenous strengths.On the basis of the in-place concrete strength estimates, decisions were made regarding the application of post tensioning forces and/or the removal of formwork and supporting shoring.

ISSN:0315-1468    

DOI:10.1139/l76-005

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A freeway project in the vicinity of Cambridge, Ontario was stalled in the planning stage because of citizen reaction to the route proposal. A multidisciplined team was assembled under the direction of the recently formed Waterloo regional government. The team studied the need for and alternatives to a new transportation corridor for a major section of Ontario's Highway 8 between Kitchener and Cambridge.The study examined present and future transportation needs. Alternatives were evaluated as they affected community goals, including environmental, social, economic, and transportation considerations. It was a reactive process involving three levels of government, various institutions, regional bodies, and the public.The study had several unique features. The project team conducting the study was a joint venture of staff from five affected governing bodies and a private consulting consortium working under the direction of a steering committee. The study was constrained in time by other feasibility studies and ongoing official plan study schedules but was not compressed in scope. Public participation involved uniquely differing interest groups and communities (urban, semi-urban, and rural).In this paper, the major features of the project organization, the traffic systems analysis, the corridor evaluation, and the public participation program are described.

ISSN:0315-1468    

DOI:10.1139/l76-006

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A method is described for proportioning fly ash concretes to produce similar compressive strengths as normal Portland cement concrete at 3, 7, 28, and 90 days. The method is primarily based on the Abrams' law relating compressive strength and water–cement ratio. Curves are also presented, for estimating the most economical fly ash to cement ratio for a particular strength and cost of fly ash.

ISSN:0315-1468    

DOI:10.1139/l76-007

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A methodology to design a stormwater sewer system using a nonlinear programming approach is developed. It is divided in five steps: (1) hydrology, (2) set up of the technological constraints, (3) optimization with the Rosen's projected gradient method with the pipe diameters considered as continuous variables, (4) standardization of the diameters, and (5) post-optimal analysis of the piezometric surface. The cost function includes the purchase and installation and the excavation costs of every pipe. It is a convex programming problem; therefore the minimum solution is an absolute minimum. A subsequent paper to appear in this journal will illustrate the complete design procedure and the effect of certain parameters on the design.

ISSN:0315-1468    

DOI:10.1139/l76-008

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Often in the early stages of planning a major development it is necessary to consider a large number of alternative individual projects and alternative sequences of projects. The main problem at this stage is to screen out the less desirable projects quickly so that only a manageable number of the more promising ones remain for detailed study. A number of simple techniques are presented which can be used to assist the screening process. These include a method for finding the sequence of projects which will meet one or more projected demands at minimum discounted cost, and making a sensitivity test of the results; a method for finding the sequence of projects which would yield the maximum present value of benefits; and a way of finding the optimal planning horizon for facilities where there are economies of scale. A comparison is given between results obtained by the sequencing technique presented and results from a more rigorous but more elaborate and time consuming method for the case of multiple demands.

ISSN:0315-1468    

DOI:10.1139/l76-009

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

This study treats wave motion within rectangular and sloping rockfill embankments with impervious cores. The non-Darcy flow in the rockfill is solved by a finite difference one-dimensional model. The characteristic directions are used to control the discretization of the solution domain. The entrance boundary condition (outcrop point) is computed from the external wave motion on the face of the rockfill. An equivalent rectangular section is used to approximate a sloping embankment, and waves on slopes are classified as 'fast' or 'slow rising.' The mathematical model yields phreatic line profiles with time. The model is supported by several wave flume experiments.

ISSN:0315-1468    

DOI:10.1139/l76-010

出版商:NRC Research Press    

年代:1976

数据来源: NRC