摘要:

The greater rationality of limit states design as compared to working stress design is developed to show that limit states design leads to a more consistent probability of failure and that neither overly safe and therefore uneconomic structures nor structures with insufficient safety should result from this design methodology.This rationality is extended in the limit states design method in that the performance of the structure and its components is checked against the various limit states at the appropriate load levels. Thus the limit states of serviceability are checked at specified load levels and of strength and stability at the factored load levels.Functions are presented for the two sides of the inequality:A comparative design of a 20-storey structure selected to provide a wide range of variables shows that limit states design as proposed results in a structure comparable to that designed by working stress method with a moderate saving in the weight of steel. Some simple design examples are worked out to show the basic similarities between working stress design and limit states design and that the two methods are of about equal complexity or simplicity. It is believed, because the designer will have to check the ultimate resistance against the effect of the factored loads, that he will develop a greater awareness of the behavior of the material and members with which he is working.

ISSN:0315-1468    

DOI:10.1139/l74-001

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The selection of a design wave is best obtained by the use of a relationship showing the construction costversusthe anticipated damage cost. In the present paper, the influence of the main parameters affecting the optimum design criteria has been studied in reference to practical cases.Indeed, this criteria has been applied to three different wave conditions obtained from a wave climate study conducted by the Hydraulics Division of the National Research Council of Canada in the Gulf of St. Lawrence. The damages were evaluated using results from breakwater scale models carried out in the Hydraulics Laboratory of Laval University. Three different types of armour units have been considered: that is, quarry stones, tetrapods, and ‘dolosse’.For the sake of comparison, we have studied, in addition to the three wave conditions and the three types of armour units mentioned above, the influence of the economic losses due to malfunction of the structure and of the choice of an annual interest rate. We have also taken into account the water depth at the structure, a parameter which was found often to play an important role in limiting the value of the design wave.

ISSN:0315-1468    

DOI:10.1139/l74-002

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The magnitudes of loads imposed by snow depend upon a number of climatological and meteorological variables and as a result exhibit marked variations geographically, due to local effects within a particular region, and with time. The snowload formation process, which depends both on the macro- and microclimates of such meteorological variables as the depth of the snowfall, the snowfall density, wind speed, air temperature etc., as well as, the size and geometry of particular roofs and the influence of their immediate environment, is discussed.A model of the snow load formation process based on a mass balance approach, which takes into account the deposition of snow by individual snowfalls and the depletion of the snow load by wind action and thermal effects, is introduced. The use of this approach requires the establishment of statistical descriptions of the various meteorological variables, as well as a knowledge of the physical process of snow accumulation and depletion for a particular roof. The statistical properties of some of the more important meteorological variables are discussed. Also presented are some model derived data of snow accumulation and depletion for particular roofs located in different terrain.It is shown that even relatively simple statistical descriptions of the relevant meteorological data and snow accumulation and depletion mechanisms can lead to realistic predictions of roof snow loads. Snow loads on a flat roof are generated by a digital simulation technique and compared with full scale observations. Annual extreme values of the simulated snow load process are presented and compared with currently specified design values. Comments are made regarding the practicability of this approach.

ISSN:0315-1468    

DOI:10.1139/l74-003

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

This paper reviews the basic principles of vacuum sewer systems and the introduction of vacuum sewers to Canada. A vacuum sewer uses air pressure instead of gravity as the driving force for waste water transport. Waste water is moved in plugs, separated by air gaps, at high velocities through small diameter pipes. The pressure differential of about one-half atmosphere is created by a central vacuum pump. Specially designed vacuum toilets, valves, and a central collection tank complete the system. The advantages of a vacuum sewer system over a conventional gravity system are its ability to transport waste water horizontally and to a certain extent upgrade, its much lower water usage, and its lower capital cost. However the length, capacity, and lift potential of vacuum sewers are limited by the available pressure differential, which precludes their use in many cases.

ISSN:0315-1468    

DOI:10.1139/l74-004

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

A testing program was conducted at the University of Windsor in order to examine the effect of dynamic (repeated) loading on the strength of composite slabs. The slab specimens were made of 18 gauge (1.21 mm) T30 Hi-Bond Steel sheets with a 6 in. (15.24 cm) nominal depth concrete slab. The width was 18 in. (0.457 m), and span 8 ft (2.44 m). The design and failure of the slabs was governed by bond. Several pull-out specimens were also tested.The following conclusions were reached:(1) Specimens subjected to low values of dynamic load up to 60% of the static bond failure load) for 2 million cycles do not show any reduction in failure load due to bond when tested statically. Since a factor of safety is always applied the load would not exceed 60% of the bond failure load. Therefore no reduction factor should be applied to the bond stresses for slabs when subjected to dynamic load.(2) The lower limit for dynamic bond failure is about 87% of the static failure load.(3) The ultimate collapse load for all slabs tested varied only about 10%. This load is considerably greater than the bond failure load.(4) The allowable bond stresses should be determined from beam tests and not from pull-out specimens.

ISSN:0315-1468    

DOI:10.1139/l74-005

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

Starting from the fundamental concepts of mass transfer of gases into liquid, a comprehensive mathematical equation, relating the mass oxygen-transfer rate to the various parameters in diffused aeration systems, is developed.The important variables involved are the liquid film coefficient, temperature, waste water characteristics, bubble size, diffuser submergence, airflow rate, and the contact time. The contact time between the air bubbles and the oxygen absorbing liquid can be varied by changing the operating conditions of the aeration system in terms of the direction of air and liquid movement. Investigations on four such combinations are presented.The influence of the above-mentioned variables, individually or in combination, on the mass oxygen-transfer rate and overall oxygen transfer coefficient are discussed. The presentation is supported with laboratory data collected from aeration studies over a period of 3 years. With proper understanding of the influence of operating parameters on mass transfer coefficients, it should be possible to modify the design and operation of aeration basins in order to obtain increased oxygen transfer.

ISSN:0315-1468    

DOI:10.1139/l74-006

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

In interacting shear wall and flat slab-column construction it is desirable to be able to evaluate the contribution of the columns to the stiffness of the lateral load resisting system. This paper presents a relatively simple method whereby this contribution can be determined, both in terms of the reduction in lateral displacement and the reduction in overturning moment in the shear walls. For the case of a continuous flat slab connection, the bending of the slab induces axial forces into the exterior columns, which therefore causes a portion of the moment to be carried by the columns. Axial forces can also be induced into the exterior columns by means of a very stiff top beam extending from the shear wall to the exterior columns. Design curves are presented for both types of stiffening so that the method can be applied easily by the designer. Comparisons of specific examples with results obtained by a more exact computer-oriented method show that the method gives reliable results.

ISSN:0315-1468    

DOI:10.1139/l74-007

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

When water flows at high velocity over a surface, quite small boundary irregularities may trigger cavitation which can, in turn, cause extensive damage. Concrete surfaces downstream from high head outlet gates are particularly vulnerable to cavitation damage.Operating experience and previous experimental work suggest that cavitation damage can be greatly reduced and, in some cases, eliminated by entrained air in the water.Experiments were carried out with a special high head test facility in Vancouver to obtain additional data on the effect of air entrainment. These tests confirmed its effectiveness. In this paper, previous evidence is reviewed, the experiments are described, and the results presented. Finally suggestions are made about the design of hydraulic structures which involve high velocity flow.

ISSN:0315-1468    

DOI:10.1139/l74-008

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

With the recent trend toward long-span floors in buildings, there has been an accompanying increase in the incidence of complaints of unacceptable floor vibration after occupancy. This paper details acceptable vibration limits for human tolerance. In addition, the magnitudes and time durations of motions of floors of different constructions resulting from foot-falls (persons walking) are examined.The relative floor vibrational behavior resulting from variables such as unsupported span, type of structure (open web joist-concrete deck or reinforced concrete, etc.) composite or noncomposite deck-structure, etc., is discussed. The relative effect of each variable is outlined and ranked. Guidance on the relationship of variables is provided for the designer of long-span floors. Approaches to ‘correcting’ floors exhibiting an unacceptable floor vibrational behavior are discussed. Case histories of floors that have been modified to improve vibrational response are also given.

ISSN:0315-1468    

DOI:10.1139/l74-009

出版商:NRC Research Press    

年代:1974

数据来源: NRC

摘要:

The majority of communities in the Northwest Territories lack the water, sewage, and garbage facilities available in southern Canada. Recently, the Government of the Northwest Territories proposed a multimillion dollar ten-year program to upgrade the water and sanitation services of the sixty-odd communities under its jurisdiction. In this paper, which is a first report on an ongoing project to upgrade the sanitary conditions of settlements in the Northwest Territories, we develop a methodology whereby the cost of the alternative water, sewage, and garbage systems for each community can be determined, compared, and evaluated. This analysis defines the level of service to be recommended in each community.Cost data for sanitary installations in the north are generally not available and therefore need to be estimated. The costs associated with alternative systems are assessed as a function of some one hundred variables, including population, demand for water, distance to the water source, topography, terrain, weather conditions, severity of climate, existence of roads, availability and cost of gravel, general remoteness of the community, freight rates, etc.The basis for comparison of the various level of service alternatives is the net present value of the investment required over the duration of the program, including capital as well as operating expenditures. Actual data for some forty-five communities are used in the calculations.

ISSN:0315-1468    

DOI:10.1139/l74-010

出版商:NRC Research Press    

年代:1974

数据来源: NRC