摘要:

Formulations are presented for enhancing the serviceability of one-way floor systems subjected to dynamic loading through the use of constrained viscoelastic layers. The constrained layers are combined with the floors and the resulting systems are analyzed as sandwich structures using a double Fourier series approach. Results indicate that the damping of the resulting sandwich beams is governed by factors related to the elastic and geometric properties of the constrained layer and the constraining system (i.e. cover plates and beams) and the loss modulus of the viscoelastic material, and is highly influenced by the location of the viscoelastic layer in the sandwich beams. Optimum designs of the sandwich beams are obtained using the box algorithm optimization technique.

ISSN:0315-1468    

DOI:10.1139/l77-049

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The fracture of commercial Hem-Fir boards in the LR and LT modes was studied, using both saturated and air-dry specimens. Notched samples were tested in flexure (third-point loading). It was found that the concepts of linear elastic fracture mechanics could be applied, even when the crack extension was in a direction perpendicular to the initial notch. However, the physical interpretation of the apparent fracture toughness,, remains unclear. It was also found that the apparent flexural stsrength increased as the size of the uncracked ligament decreased. Finally, the results indicated that both the nominal flexural strength and the fracture toughness were greater for the saturated specimens, probably due to an increase in viscoelastic behaviour at high moisture contents.

ISSN:0315-1468    

DOI:10.1139/l77-050

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

As a result of improved facilities, reduced computing costs, and the availability of better programs, conversational computer programs are becoming effective design aids in structural engineering offices. The author outlines his work in writing conversational computer programs, and the techniques he has developed to make them successful.Some of the topics given attention are: the relationship between the engineering and the computer science aspects of the work; a technique for free-format data input; the planning of the dialogue to take place between the program users and the computer; the provision of technical support for the program users; the selection of the correct computer and the correct terminal for conversational programs; procedures for error checking, error correction and input data editing; electronic data transmission from program to program; development of the programs in a time-sharing environment; the use of modular programming; and trade-offs between the costs of the software and the hardware to support conversational programs. A limited amount of attention is given to the role of computer graphics in support of conversational computer programs.

ISSN:0315-1468    

DOI:10.1139/l77-051

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Long range planning is required in order to avoid impending environmental disasters in most northern communities. Present short range planning should consider more closely the basic needs of the inhabitants. These needs include piped water and sewer systems, more careful avoidance of sewage pollution of drinking water and the immediate environment, better cross cultural integration, greater emphasis on recreational facilities, awareness of the need for energy savings, less ice fogs, and relatively warm and sunny microclimates.The Scandinavians have been leaders in this field, and offer many examples of advanced planning of northern communities in Lapland, Iceland, and West Greenland. We should study their approach towards the solution of our common problems. Through dialogue with them a clearer understanding and possibly better solutions to existing problems will be found.A basic necessity in making the studies is a better understanding of the nature of the North and of the people. We must learn to workwithboth nature and the people.Now is the time for long range planning by considering climatic, environmental and cultural factors, and integrating them into a more harmonious system with the aim of a higher quality of life.

ISSN:0315-1468    

DOI:10.1139/l77-052

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Continuous flow, daily fill and draw, and batch aeration digesters were studied on a laboratory scale, to develop low temperature characteristics and design criteria for aerobic digestion of waste-activated sludge. These results were compared against full-scale data, from three independent sources. Raw sludge used in these studies was obtained from a municipal high-rate activated sludge plant. The digestion systems were operated at temperatures of 20, 10, and 5 °C, and at six different sludge ages. Measurements of all parameters studied were made under steady-state conditions.The results show that the effect of low temperature on aerobic digester performance is pronounced. The combined effect of temperature and sludge age is shown to be an important design parameter. Kinetic reaction rates and temperature coefficients were calculated on the basis of total volatile suspended solids. It was shown that batch and continuous feed system reaction rates are not interchangeable. The laboratory results further show that there is little difference between continuous flow and daily fill and draw digestion characteristics, except at 5 °C. Difficulties encountered in making a valid comparison between the laboratory and full-scale results are also discussed.

ISSN:0315-1468    

DOI:10.1139/l77-053

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A probabilistic analysis is presented for the response of offshore structures subjected to random forces due to ice floe movement. Analysis based on the averaged power spectral density of the ice force fluctuations is shown to result in unreliable designs in certain cases, owing to sensitivity to even small errors in the calculated natural frequencies of the structure. To overcome this drawback, an ‘enveloping, step function power spectral density’ is proposed. A single-degree-of-freedom system and a three-dimensional offshore tower are solved as examples.

ISSN:0315-1468    

DOI:10.1139/l77-054

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Two nonlinear parameter estimation techniques are used to obtain expected values, variances, and covariance estimates forLandkin the first-order BOD equation. The techniques are compared with a number of other BOD parameter estimation methods with respect to both estimated values ofLandkand necessary assumptions about the measurement error structure of BOD analyses. The techniques that historically have been used to estimate the parameters in the first-order BOD equation are shown to often give erroneous answers because of their use of an incorrect error structure.A case study application of the methodology to the raw influent and primary effluent of the Waterloo Pollution Control Plant is included.

ISSN:0315-1468    

DOI:10.1139/l77-055

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A steady-state, one dimensional dissolved oxygen (DO) model was developed for summer conditions for the Rideau River near Ottawa, Ontario. Model parameters were estimated for July 1975 conditions, and model acceptance was based on June 1975 conditions. Results of the model indicated that the tributaries in this section had only a marginal effect on DO concentrations. The major factor affecting DO concentrations was the distributed source–sink processes, which include photosynthesis, respiration, and sediment oxygen demand. River channel reaeration and aeration at dams had a minimal effect on DO.

ISSN:0315-1468    

DOI:10.1139/l77-056

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

A physical model is used to calculate roof loads due to rain on a snow covered roof. A snow depth of 0.5 m and the twenty-five year rainstorm in Hanover, New Hampshire, are used in the examples. For a flat roof with 10 m parallel flow to gutters, the total liquid weight can increase the roof load by about 50%. The weight of the transient liquid is greatly increased if the mode of flow is radial to central drains and is decreased if the roof is slightly inclined or if significant melt channels form in the basal layer. However, the wetting of the snow over its entire depth will still cause a significant weight of transient liquid. Snow drifting can cause very large, local loads but the effects of snow temperature and antecedent moisture are not too important.Depending on the circumstances, the largest load can occur for either a long duration, low intensity rainstorm or a short duration, high intensity rainstorm. The former occurs if the saturated layer makes a significant contribution to the total live load whereas the latter occurs when the liquid weight is due mainly to the unsaturated layer. Further study is needed to establish the joint probabilities of combined snow and rain loads, especially when rain and snowmelt occur simultaneously.

ISSN:0315-1468    

DOI:10.1139/l77-057

出版商:NRC Research Press    

年代:1977

数据来源: NRC

ISSN:0315-1468    

DOI:10.1139/l77-058

出版商:NRC Research Press    

年代:1977

数据来源: NRC