摘要:

Resolutions of conflicts within an economic–environmental system are challenges that engineers often face, since they are expected to provide the decision-makers with the trade-offs involved among the various levels of the waste generating economic activities, the resulting environmental quality, and spending for attaining it. This paper presents a methodology for resolving such conflicts. The methodology is based on a waste management network model which allows for an efficient and systematic search among the possible waste management systems linking generated wastes with the environment, and also for their evaluation on the basis of the balance of their burdens on the various environmental forms and the operating budget. Recycling, discharge and effluent standards, charges, damage costs, and various budgeting schemes can be handled. Dynamic analyses for long-range financial planning under an expected increasing rate of waste generation are possible. For a simple hypothetical case, the model is set up, available data are reduced to usable forms', and trade-off curves are obtained through simulation analysis.

ISSN:0315-1468    

DOI:10.1139/l75-001

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

This paper gives details of the hydraulic investigation carried out for the proposed new bridge crossing over the Carrot River on Highway No. 23, near Carrot River, Saskatchewan. Geotechnical studies indicated that due to the very low shear strength of the highly plastic clay comprising the banks of the Carrot River, the river banks would not be capable of supporting the approach fills to the bridge. Highways Department engineers came up with the rather novel idea of placing a compacted clay fill or berm across the river at the bridge site in order to stabilize the banks. This introduced the problem of passing river flows through and over the berm. It was proposed that low flows should be carried through the berm by a culvert, and high flows should be passed over the berm by a spillway. Hence, the design envisaged a bridge over an earth fill and a spillway over a culvert, all at one site. A model study was considered essential because of the uncertain hydraulics and because a hydraulic failure could result in bridge failure.

ISSN:0315-1468    

DOI:10.1139/l75-002

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The provisions of the present Canadian and U.S. seismic codes are examined with respect to their requirements on the distribution of seismic forces and overturning moments throughout the heights of building structures. Assuming the code design base shears to be correct, it is shown that the prescribed distribution of lateral forces may underestimate the shear forces in the upper stories of the building. It is further shown that the contribution of the higher modes is not directly related to the height-to-width ratio of the building, but rather to its fundamental period of vibration. By idealizing the building as an average uniform cantilever deflecting partly in a shear mode and partly in a bending mode and by taking a root-sum-square combination of the modal responses to a standard seismic acceleration spectrum, the envelope of the resultant maximum shears throughout the building height is obtained; the maximum overturning moments throughout the building height are obtained in a similar manner. By comparing these with the cantilever overturning moments computed from the shear envelope referred to above, the moment reduction factors applicable to the various levels of a building are calculated. New empirical relationships are then developed to approximate the shape of the maximum shear and overturning moment envelopes.

ISSN:0315-1468    

DOI:10.1139/l75-003

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Canadian structural standards for buildings are moving toward a unified limit states philosophy with common safety and serviceability criteria for all materials and types of construction. Structural steel and cold formed steel will have limit states design rules by 1975 and concrete, masonry, and wood will follow later.This paper compares the new rules with existing NBC/CSA requirements on the basis of probability of failure calculated by simplified theory. The main emphasis is on load combinations of dead, floor, and wind loads for office and residential buildings where failure occurs by yielding of steel. Other aspects of the new limit states design rules—column formula for structural steel, performance factors for composite structures, the importance factor which reflects the seriousness of failure, and safety factors during construction, are also considered.The results indicate that the new rules provide more consistent safety than existing rules for different combinations of loads and materials; and that simple rules are sufficiently accurate, keeping in mind the predominating influence of human error on failures and the simplifications used in analyzing complex building structures.

ISSN:0315-1468    

DOI:10.1139/l75-004

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Weibull's theory of brittle fracture is applied to the determination of strength of Douglas-fir wood in tension perpendicular to the grain. Results from tests on blocks of glued-laminated material uniformly stressed in tension are used to derive ultimate stresses, at a given survival probability, for pitched-tapered beams, curved beams, and griplam nail connections. The results of the theory are shown to be in agreement with experimental data. Allowable stresses are derived for blocks, pitched-tapered beams, curved beams, and the particular nailed connection studied.

ISSN:0315-1468    

DOI:10.1139/l75-005

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The combined mechanisms of oxidation of iron sulfides followed by sulfatation of both the surrounding calcite and the hydration products of Portland cement are well known. Nevertheless, cases where important breakdown of concrete structures have occurred, with less than 2% shale in the coarse aggregate fraction seem to be very rare.Based mainly on petrographic examination, the expansive mineral phases were identified in the black shale and in the concrete paste. It is believed that sulfuric acid, formed within the shale by oxidation of the pyrrhotite, has transformed the calcite into gypsum. In the concrete, this newly formed gypsum or that formed by sulfatation of the portlandite Ca(OH)2has reacted in turn with the tricalcium aluminate of the cement paste to form ettringite. Both reactions, within the shale or with the cement paste, occur with an important volume increase.

ISSN:0315-1468    

DOI:10.1139/l75-006

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The objective was to determine experimentally and analytically two-dimensional steady-state temperature distributions produced in the cross-sectional planes of steel–concrete composite simple span bridges. The upper and lower surfaces were exposed to different temperatures.The research included the development of finite element solutions for steady-state temperature distributions from known boundary conditions and the calculation of strains and stresses. Temperature and stress distributions were generally nonlinear with linear strains through the finite elements. Temperatures were predicted to ±1 °F (±5/9 °C). The experimental strains are linear through the composite section, with the computed finite element strains giving generally slightly higher stresses. The conventional and finite element method computed stresses were compared.For positive curvature, the conventional method underestimated the compressive stress in the top flange by about 20% while the bottom flange tensile stresses were identical. For negative curvature, the conventional method overestimated the bottom flange compressive stresses between 15 to 27% and the top flange tensile stresses from 10 to 61%. The concrete slab stresses were overestimated for positive curvature and slightly underestimated for negative curvature. Slab stresses were relatively small when compared with the permissible concrete stress. Temperature stresses in the steel beam were shown to be significantly large, about 30% of the permissible steel stress, to warrant consideration in the design of these bridges. The stresses were calculated for short term steady-state temperatures. Transient conditions existing in the field produce greater thermal stresses.

ISSN:0315-1468    

DOI:10.1139/l75-007

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Urban strategy planning studies are directed towards the estimation of the transport demand and other servicing implications of a range of urban development alternatives. These studies attempt to isolate those concepts which might lead to costly and intractable infrastructure problems. Several analytical tools that may be used to explore the implications of strategic development alternatives are described.A land use-transport model is described which may be used to estimate the implications of alternative public development policies. These policies may include servicing and transportation options, basic and service employment location alternatives, and zoning. The model calculates an internally consistent co-distribution of population and employment along with the associated travel demands for each set of public policies. A corridor-level traffic assignment technique is described which may be used along with the land use-transport model to develop corridor travel demand estimates for each development concept. Computer-based procedures for estimating the servicing requirements of alternative development concepts are also described. These procedures directly employ the land use allocations calculated by the land use model. The use of the analytical tools is illustrated with information from the Hamilton area.

ISSN:0315-1468    

DOI:10.1139/l75-008

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The fatigue behavior of the negative moment region of continuous steel–concrete composite beams under Canadian temperature conditions was studied. Tests were conducted on three 26 ft 0 in. (7.92 m) long beams, continuous over a central support, and on 11 conventional push-out specimens. These were supplemented by a theoretical study of the internal forces in the beams using an iterative method of analysis.The close agreement between measured and theoretical strains and deflections indicated that good interaction was achieved throughout the length of the beams. The beams sustained 500 000 cycles of loading with no serious deterioration of composite action. The pattern of stud failures was consistent from beam to beam and reflected closely the calculated distribution of horizontal shear force at the steel–concrete interface. Stud shear connectors in the negative moment region where the slab had cracked in tension were found to be slightly less effective than studs in the positive bending moment regions.Neither the detailed study of individual connectors in the beams nor the results of the push-out tests show evidence of a reduction in the fatigue life of studs at −20 °F (−29 °C) relative to room temperature. The beams also exhibited no significant difference in their overall performance at these two temperatures.

ISSN:0315-1468    

DOI:10.1139/l75-009

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Several approximate formulae for the determination of natural frequencies of interconnected walls and frames with uniform mass and stiffness throughout their height are compared and the range of their applicability discussed. It is found that none of the approximations give high accuracy for the entire range of the stiffness parameter αHencountered in practice. It is recommended that for the fundamental frequency the flexural beam approximation be used for the lower end of the range (αH < 7) and the large αHasymptotic formula be used elsewhere. This ensures that the error never exceeds 5%. For the higher modes there is a choice between three approximations, the maximum error associated with each being practically identical: 10% in the second mode and 5% in the third.

ISSN:0315-1468    

DOI:10.1139/l75-010

出版商:NRC Research Press    

年代:1975

数据来源: NRC