摘要:

Over the past few years several snowmelt simulation models have been developed as an aid to streamflow forecasting in mountainous regions. This paper describes the major difficulties encountered when simulation of Prairie snowmelt conditions is attempted, not only for the purpose of forecasting streamflow, but also soil moisture, evaporation, and snow distribution patterns. Simulation is discussed in terms of the energy equation for the snowpack and it is shown that the improvement of the model depends on the following factors: (i) the adjustment of the radiation flux at the snow surface for slope and aspect, (ii) the development of procedures which will allow estimates of the areal distribution of sensible heat, (iii) successful modelling of the diurnal freeze–thaw cycle common to Prairie snowpacks, (iv) an investigation of the energy exchange processes during the period when the snow cover is discontinuous or patchy, (v) knowledge of the coupling of heat and mass transfer processes in frozen soils, and (vi) the extrapolation of point estimates of significant parameters to an areal basis.

ISSN:0315-1468    

DOI:10.1139/l75-044

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Experimental results are presented on three externally reinforced concrete block walls subjected to in-plane cyclic lateral loading, the walls being confined by flexible steel frames. All three specimens were of similar construction, the varying parameter being the steel reinforcement ratio in the outer skins. The load deflection curves, stiffness degradation characteristics, energy absorption capacity, as well as axial stress in the confining frame columns, are discussed. The externally reinforced walls held their integrity even under a large number of cycles of reversed load. In this respect, externally reinforced masonry behaves under cyclic loading at least as well as internally reinforced masonry. It is concluded that changes in steel reinforcement ratios do not materially affect the failure load although this ratio may have an important effect on the stiffness degradation and the energy absorption capacity of the assembly. The evaluation of the axial forces in the columns on the basis of the truss analogy appears to be substantiated by the test results.

ISSN:0315-1468    

DOI:10.1139/l75-045

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

A five-step, computer-aided design procedure representing a significant change from current seismic design practices is proposed.In the first step, the ‘design earthquake’ and the safety and serviceability criteria are established, and appropriate values of a damping coefficient and displacement ductility factor are assumed. An iterative preliminary analysis procedure, centered around specified values of a seismic coefficient and a drift index, is used to determine the design story shears using modal analysis.Then, a preliminary design is carried out using a simplified story-wise optimization procedure. This is followed by inelastic static and dynamic analyses of the design. The maximum values of story shears and ductilities and their overall pattern, so obtained, are compared against those used initially. The procedure is repeated until a satisfactory agreement is obtained and the final design story shears are determined. In the fourth step, these shears are used to attain the final optimum design through a procedure similar to that used in the preliminary design, but using an improved story subassemblage and a more formal linear optimization technique.Finally, the reliability of the optimum design is evaluated by determining its nonlinear response to severe earthquakes and its serviceability. The design procedure is demonstrated on a 10-story 3-bay frame.

ISSN:0315-1468    

DOI:10.1139/l75-046

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

This paper explains the nature of progressive collapse, with examples, and enlarges considerably on commentary C, supplement No. 4 of the 1975 National Building Code of Canada. Attendant philosophical problems related to code coverage and the design for progressive collapse are considered in discussions of risk, abnormal events that might initiate progressive collapse, and design procedures to reduce the risk of progressive collapse. An example illustrates some of these procedures and indicates how, in a general way, design problems may be approached.

ISSN:0315-1468    

DOI:10.1139/l75-047

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

A feeder bus system for a suburban community commuter rail station is designed. The paper develops a design methodology utilizing cost–effectiveness methods. A demand model for feeder bus ridership is developed with input variables – location of rail users, income of users transit fare, level of transit service, and walk time to bus route. In applying the methodology to a study area which included three commuter rail stations it was found that all feeder bus systems would operate at a loss. Bus routes with loops in residential areas and direct service to the rail stations had the best ridership levels. The cost–effectiveness approach and the model developed are effective design methods.

ISSN:0315-1468    

DOI:10.1139/l75-048

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The forces and overturning moments exerted by waves on a vertical circular caisson, extending from the ocean bottom through the water surface, have been measured for a range of wave heights and periods. The wave loads were measured on a 1:60 scale model of a rigid circular caisson, 60 ft (18.3 m) in diameter, in a water depth of 145 ft (44.2 m). A digital computer was used for the acquisition, processing, plotting, and storage of data. Experiments were conducted for a range of conditions described by water depth on incident wavelengthd/Lfrom 0.179 to 0.786, wave steepnessH/Lup to 0.076, and caisson diameter on incident wavelengthD/Lfrom 0.074 to 0.325. The experimental results were compared with values computed by the diffraction theory of MacCamy and Fuchs and showed that the theory is suitable for use over the range of conditions described above.

ISSN:0315-1468    

DOI:10.1139/l75-049

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Using dimensional analysis and regression techniques a series of diagrams, involving five dimensionless flow parameters, showing the interrelationship of the discharge intensity, flow depth, mean bed material size and discharge, and channel slope for mobile boundary channels have been prepared. The universal flow diagrams (UF diagrams) cover 10 grain size ranges, from 0.1 to 40 mm, with each diagram based on an analysis of 1300 or more data items. Examples are given showing the use of the UF diagrams for design and analysis of channel and river problems.

ISSN:0315-1468    

DOI:10.1139/l75-050

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The recent United States Atomic Energy Commission study (WASH-1400), using a simplified analysis, has estimated the probability of earthquake initiated accidents of typical U.S. nuclear plants to be in the range 10−5to 10−8per year, and has concluded that these are sufficiently small compared to other causes as to be safely ignored in assessing overall plant safety.An event tree model is presented in this paper to assess the failure probabilities from seismic events of single and multiple component safety systems. The ground motion, response spectra, and failure criteria are treated as probabilistic quantities. The model is applied to a Canadian site and failure probabilites are predicted for several levels of design. The sensitivity of uncertainties in the input data on the failure probabilities is also investigated.The results show the importance of considering common mode failures when determining seismically initiated system failure probabilities. Also, in assessing system failure probabilities of the order of 10−6it is shown that the input with the highest sensitivity is the probability distribution of large magnitude earthquakes and the component failure probabilities.It is recommended that the design basis earthquake be determined from the desired system failure probability level, and that more effort should be placed on estimating the probability of occurrence of large magnitude earthquakes and in determining component failure probabilities.

ISSN:0315-1468    

DOI:10.1139/l75-051

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

This paper reports one phase of a research program at the University of Washington on the seismic response of flat plate to column connections. In particular the behavior of connections containing integral beam stirrup reinforcement in the slabs is discussed. The paper compares different approaches for designing that stirrup reinforcement, outlines the benefits of placing stirrup reinforcement in the slab, and gives guidelines as to the design and proper detailing necessary for that stirrup reinforcement. The effects of concentration of the flexural reinforcement in the immediate column region are also examined. Ductility ratios, energy absorption, energy dissipation, and degeneration of stiffness characteristics of the specimens are reported together with the lateral loads for first yielding and maximum capacity of the specimens.

ISSN:0315-1468    

DOI:10.1139/l75-052

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

It has not yet been recognized that modification of the natural seasonal discharge of rivers might result in significant consquences to the ecology of the adjacent marine environment. An example of such regulation is the St. Lawrence system in which, in order to optimize power production, large quantities of water from the spring runoff are retained in storage lakes and returned to the river during the low natural discharge period of autumn and winter. It has been estimated that under present conditions the spring and summer runoff at the entrance to the Gulf of St. Lawrence has been reduced by between one third and one half.This drastic alteration of the natural runoff has caused significant changes in the physics and dynamics of the waters of the Estuary, Gulf, and adjacent coastal region. It is argued that such modifications produce a profound impact on the biological balance of the whole ecosystem, as well as changes in the seasonal heat budget.

ISSN:0315-1468    

DOI:10.1139/l75-053

出版商:NRC Research Press    

年代:1975

数据来源: NRC