摘要:

One of the most important factors affecting the rate of heat transfer by natural convection is the temperature–density relationship of the convecting fluid. The importance of this factor is greatly amplified when the heat is being transferred to a medium that has a maximum density at a given temperature. Water at low temperatures offers such a behavior, its density attaining a maximum value near 3.98 °C. thereafter decreasing with decreasing temperature. This phenomenon is responsible for unusual flow patterns in areas of water exposed to near freezing temperatures.This investigation is a theoretical analysis of the transient natural convection of water contained in a square enclosure with constant wall temperature. Initially the water is assumed to be at a uniform temperature above 0 °C, the wall temperature being suddenly applied.An alternating direction implicit finite-difference schema was used to solve the coupled system of partial differential equations. The transient flow and temperature fields, and local and overall heat transfer are greatly affected by the inversion of flow patterns caused by the maximum density. Their respective values for different flow situations are presented in this study.

ISSN:0315-1468    

DOI:10.1139/l79-062

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

A study of the structural effects caused by traffic loading on highway bridges is presented. The objective is to provide guidance for the selection and calibration of the highway live loads, which are specified for design. Bridge loading events with one, two, …, five trucks present are simulated separately in five categories. The results are combined to form a probability distribution for each effect. The idealized trucks used in the simulation procedure are mathematical models of 6380 trucks that were weighed and measured during the 1975 truck survey in Ontario. For each effect, the mean largest value and the corresponding coefficient of variation are calculated based on two traffic densities. The largest effects caused by truck queues in traffic jams are predicted also.The effects are divided into three groups based on their sensitivity to multiple presence. For the first and third groups, the largest effects are caused by loading events with one truck and a queue of trucks respectively. For the second group, loading events with two trucks present may be the dominant cause of large effects. In the calibration process the magnitudes of live loads are adjusted in order that their application causes effects approximately proportional to mean largest effects.

ISSN:0315-1468    

DOI:10.1139/l79-063

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Local instability of thin facings in sandwich panels often leads to wrinkling at stresses lower than yield stresses. An investigation was carried out by the authors on the behaviour of the facings of rectangular sandwich panels having thin aluminum faces and styrofoam core when subjected to edgewise compression and (or) out-of-plane bending. A set of the panels had no additional reinforcement at the edges whereas others were either totally or partially reinforced with wood framing integrated along the edges. Existing formulae developed to predict these stresses were found to overestimate results obtained from a test programme conducted by the authors. New expressions are presented for wrinkling and ultimate loads for sandwich panels with various edge conditions. A comparison is made between existing and newly derived expressions.

ISSN:0315-1468    

DOI:10.1139/l79-064

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Up until the 1950s, government ships were the only means of servicing offshore lighthouses. Early in the 1960's, the Canadian Coast Guard started to use helicopters to service all their isolated lighthouses. A helicopter transports people and replacement parts for navigational aids at a fraction of the time and cost required by a ship. Now all major offshore lighthouses are being built with heliports; in addition, heliports are being erected on some old lighthouses.Heliports on offshore lighthouses are private, exclusive-use heliports for light and medium helicopters. Their size is the minimum safe size for the helicopter landing.In designing offshore heliports, consideration is given to easy and economical construction procedures; the supporting structure of a heliport is light or made of light members for easy erection.

ISSN:0315-1468    

DOI:10.1139/l79-065

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The present system for pick-up and delivery of small shipments by trucks within an urban area is not very efficient. This is often due, in part, to poor vehicle utilization, competition between freight and passenger movements using available common right-of-way, highly congested and dense city centres, and current business practices. The lack of coordination between truck shipment activities often leads to route duplication, street congestion, long waits at loading/unloading facilities, and underutilization of available truck capacity.Because provision of consolidation terminals appears to be one of the promising alternatives for alleviating some of the problems of the current freight distribution structure, this study has been undertaken to gain better insight into the feasibility and desirability of this alternative. For this purpose, the City of Calgary, which had a population of 500 000 in 1977, was chosen for identifying the economic benefits of applying the concept of consolidation terminals operation to the movement of small shipments within the city. The results revealed that a system with a single consolidation terminal located at an appropriate site is economically feasible and would significantly reduce the number of trucks and truck trips needed for urban goods movement.

ISSN:0315-1468    

DOI:10.1139/l79-066

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

This investigation deals with the flexural and serviceability behaviour of limited prestressed beams under repeated loads and considers the concrete in the tension zone by relating the distribution of stresses in steel at and in between cracks. The consideration of crack stability and bond efficiency in achieving additional load-carrying capacity and the resulting economy are discussed from design considerations. The widening and deepening of cracks and their overall stability under severe conditions of repeated loading were studied by tests on limited prestressed beams having different distributions of steel and the results were used for comparison. The destruction of the bond between concrete and steel located between adjacent cracks under repeated loads was investigated in detail and the results were interpreted from endurance limit considerations. Theoretical analysis included computation of deflections and moments by considering the concrete located in the tension zone. Effects of repeated loads on load deflection hysteresis, crack pattern and stability, efficiency of bond between steel and concrete between adjacent cracks, contribution of concrete in tension towards increase in rigidity of beam, and endurance limit for working moments, stresses in steel and concrete expressed as percentage of ultimate are discussed in detail. It is seen that this method of accounting for the strength of concrete in the tension zone closely predicts the behaviour of beams.

ISSN:0315-1468    

DOI:10.1139/l79-067

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Although a large number of ferry and roll on/roll off services exist in Canada, little research has been carried out on the design of their terminals. In the planning and design of a new or re modelled terminal system, one of the most important tasks is to determine the required number and size of components of the terminal complex. Although advances in design methodology and specific techniques have recently been made for other modal terminals, ferry terminal design has largely been piecemeal and nonscientific. This paper reports a systematic design methodology for ferry and roll on/roll off terminals. In addition to a description of specific techniques developed, design criteria and a case study are reported as well.

ISSN:0315-1468    

DOI:10.1139/l79-068

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

By present design procedures bottom chords of welded structural steel trusses are designed as simple tension members. Little regard is given to the interaction of shear and tension stresses that occur at the bottom chord joints. A study of this interaction on the ultimate capacity of a truss joint consisting of a structural tee tension chord and double angle web members is presented. Based on theoretical considerations and experimental results, an interaction equation is suggested as a design aid to determine the allowable tensile stress at critical joints with transverse shear present.

ISSN:0315-1468    

DOI:10.1139/l79-069

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The mechanics of mixing of neutral substances in natural streams and methods for engineering applications of the understanding developed to date constitute the subject of this paper.Diffusion and differential advection are identified as the main processes governing mixing in natural streams and are reviewed in some detail. The interaction between these two processes is shown to enhance the rates of spreading in the longitudinal direction and this effect is termed dispersion.Methods for predicting the concentration resulting from injection of a neutral substance in a stream, as a function of time and location, are outlined and the various pertinent simplifications and associated assumptions are discussed. It is shown that in steady-state situations, such as those resulting from continuous releases at constant rate, analytical predictions are possible using a transformation that substitutes distance across the channel by the corresponding fraction of discharge. However, transient mixing, such as that resulting from slug or time-dependent injections, is a relatively complex process and requires use of numerical techniques of computation.A method for generating hydraulic information necessary for applications from limited data is presented. This can be used when detailed hydraulic data are not available or when only limited accuracy of prediction is required.Engineering application is shown to depend on knowledge of the transverse mixing coefficient. In straight, prismatic channels, this reflects the combined effects of turbulent diffusion and dispersion due to secondary currents. However, in natural streams, this coefficient incorporates additional effects, such as transverse dispersion due to helical motions at river bends and river nonuniformity. The former effect has been well documented but virtually nothing is known about the latter.Experimental data regarding the transverse mixing coefficient are reviewed for straight and meandering laboratory channels as well as natural streams. It is shown that the available field data are not sufficient to permit predictions of the transverse mixing coefficient in terms of stream hydraulics. Qualitatively, it can be stated that when the mixing coefficient represents an average value over several meanders, the curvature of river bends appears to be of less significance than had been thought previously and the effect of an ice cover seems to be better accounted for if the transverse mixing coefficient is nondimensionalized with the frictional velocity and the depth rather than the hydraulic radius.Finally, an example of practical application is presented.

ISSN:0315-1468    

DOI:10.1139/l79-070

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The design of formwork for vertical surfaces is dependent upon the magnitude of the lateral pressure assumed to act on the form face. This paper describes an experimental investigation to determine the variation of the lateral pressure exerted by fresh concrete with depth of immersion of the vibrator, duration of vibration, and power of the vibrator while keeping the rate of pour, form dimensions, and slump nominally constant and measuring the temperature.It was concluded that the lateral pressure is dependent upon the vibration parameters of depth of immersion of the vibrator, duration of vibration, and power of the vibrator and varies inversely with the temperature of the concrete mix.The experimental results were compared with the CIRIA (Civil Industries Research and Information Association, United Kingdom) and ACI (American Concrete Institute) design recommendations. It was concluded that the CIRIA arching criterion should be used with caution as it was not conservative for low friction formwork surfaces, and that both the CIRIA stiffening criterion and the ACI recommendations are conservative.

ISSN:0315-1468    

DOI:10.1139/l79-071

出版商:NRC Research Press    

年代:1979

数据来源: NRC