摘要:

The results of field tests on the response of floating ice sheets to moving loads are presented and discussed. To measure time-dependent deflections under moving loads, a convenient method that does not require reference to a fixed datum is developed. This method is based on integrating the output of a sensitive slope indicator. The data support the available theory in most respects. Deflection under a load moving at constant speed is maximized when the speed is equal to a critical value. The critical speed is essentially a function of ice thickness and water depth. Observed critical speeds for ice thicknesses and water depths in the ranges 0.3−1.4 and 1.8−54.3 m, respectively, are generally 10% higher than predicted values; these ranges include present data and earlier data by others. The data show further that critical deflection and strain can be up to 4.6 and 1.4 times the corresponding static loading values. Discussion of this finding points out that abrupt speed changes should be avoided.

ISSN:0315-1468    

DOI:10.1139/l81-001

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

With high-rate activated sludge as feed, various modes of digestion were studied on a laboratory scale at 20, 10, and 5 °C. This study was performed to develop design guidelines, operating criteria, and kinetic coefficients for low-temperature aerobic sludge digestion. To develop a possible scale factor for extrapolation of laboratory results to full-scale conditions, a field evaluation program was conducted to collect and analyze full-scale data from three independent sources.In this manuscript a summary of previously published data, as well as some of the latest research findings, have been presented. In addition, this paper outlines a new design procedure for use in "sizing" a typical aerobic digester; as well, a method for determination of oxygen requirements in the digester tanks is described.This design procedure is based primarily on a graphical solution involving several variables, whereby the percentage reduction of volatile suspended solids is plotted against the product of temperature and sludge age. Included in this presentation is a comparison between the use (and misuse) of kinetic data in traditional design procedures. The design methodology presented has already proven to be a valuable and cost-effective tool, especially for cold-climate package plant design.

ISSN:0315-1468    

DOI:10.1139/l81-002

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Load effects for four bridge design live load models are compared over a broad span range for three simple influence line shapes. The models are American Association of State Highway and Transportation Officials (AASHTO) HS20, Ontario Highway Bridge Design Code (OHBDC), Canadian National Standard CAN3-S6-M78 MS250, and one from the American Society of Civil Engineers (ASCE). Comparisons are made on a number of grounds including maximum effect, simplicity, and accuracy. The span range 30–300 m is considered.

ISSN:0315-1468    

DOI:10.1139/l81-003

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Though structures designed according to codes do not generally fail, it is interesting to know their true probability of failure in view of the economic consequences.A simply supported uniformly loaded box beam is considered. Based on real statistical data derived from tests or adequate and realistic assumptions, the factored momentMfand the resisting momentMrare calculated using Monte Carlo simulation. In order to take into account some important phenomena for prefabricated beams, such as residual stresses, initial crookedness, and end conditions, the random variable α, which multipliesMr, and its variation coefficientVαare introduced. The α coefficient is defined as the tested capacity divided by the code predicted capacity. After interpolation, the variableZ = Mr − Mfis assigned a normal (Gaussian) frequency distribution. Then, the probability of failure is evaluated using a well tested mathematical technique.

ISSN:0315-1468    

DOI:10.1139/l81-004

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The influence of P – Delta effects on the response of buildings subjected to earthquake ground motion is illustrated using time – history studies. It is shown that the influence of P – Delta effects is of great importance for buildings responding in a highly inelastic manner. However, for buildings responding in an elastic or slightly inelastic manner, the influence of P – Delta effects is relatively small. The stability factor approach for estimating the influence of P – Delta effects is reviewed. It appears that this approach gives reasonable results only for systems responding in an elastic or slightly inelastic manner. The strength and drift characteristics of buildings are briefly described. The results presented suggest that the response of certain types of well-designed buildings will not be significantly influenced by P – Delta effects. Finally, recommendations are made for assessing the significance of P – Delta effects for a given building design.

ISSN:0315-1468    

DOI:10.1139/l81-005

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The purpose of the paper is to open discussion on the development of Canadian structural codes and standards. It argues for a common simple limit states format for all civil engineering structures, with the loading function contained in structural use codes the same for all construction materials, and the resistance function contained in materials design standards the same for all structural uses. The format for loading and resistance functions and the degree of code complexity are discussed.

ISSN:0315-1468    

DOI:10.1139/l81-006

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The consecutive testing to failure of four test joints in each of two identical 7.3 m span × 1.8 m deep tubular steel trusses with cropped webs is described. The behavior of each of the test joints is discussed and compared to that of similar joints previously tested as isolated specimens. Following large chord-face deformations and bending of the webs in the truss plane, failure occurs by out-of-plane buckling of the compression web at those test joints with slender webs, or by yielding and tearing of the tension web at those with stocky webs. Stiffnesses are in close agreement for corresponding truss and isolated joints. Strengths of the truss joints are from 0–23% lower than those of the isolated joint specimens. Joint deformation contributes less than 5% to truss deflection.

ISSN:0315-1468    

DOI:10.1139/l81-007

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Simulation of the dissolved oxygen at the bottom of deep reservoirs using an existing one-dimensional mathematical model is discussed. A modification to the BOD and detrital components is presented and implemented in the mathematical model. A simulation of Boundary Reservoir in Saskatchewan is included to demonstrate the simulative capacity of the modified model.

ISSN:0315-1468    

DOI:10.1139/l81-008

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Since 1975 recommended design loads on cylindrical curved roofs in the Commentaries on Snow Loads in National Building Code documents have undergone significant changes. This paper presents data and some of the background to the changes, and discusses the problems that have arisen with the recommendations published in the 1977 Commentary. The intent is to make recommended design snow distributions and loads as realistic as possible without undue complication. Further improvements are suggested.

ISSN:0315-1468    

DOI:10.1139/l81-009

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Trinidad and Tobago is undergoing substantial economic growth resulting from petroleum revenues, the volume of transportation (including air travel) thus expanding rapidly. It is essential, therefore, to provide estimates of future traffic to allow sensible planning to be undertaken. Previous modelling work in this region has tended to be extrapolative. This paper describes work undertaken to evaluate the underlying causal relationships influencing the volume of air travel to the small (population 1.1 millions) twin-island Caribbean republic and to build a descriptive model. The well-tried method of multiple regression analysis was used. Locally available statistical data were utilized, the analysis revealing that airfare, per capita income, and population were the main influencing factors. Cultural ties between zones were taken into account, postwar migration emerging as a proxy variable to accommodate this. Backward projections were made using the calibrated equation and intuitively reasonable forward projections were derived. The paper contains as examples detailed descriptions of the results relating to four of the links studied as well as a presentation of overall results. The technique appears appropriate both to a rapidly changing economic environment and to small nations (for example, other Caribbean islands) in deriving projections for the design of air transport facilities and the planning of services.

ISSN:0315-1468    

DOI:10.1139/l81-010

出版商:NRC Research Press    

年代:1981

数据来源: NRC