摘要:

Long-term behavior of high-alumina cement concrete is described with an emphasis on the loss of strength due to conversion. Failures in various countries, especially in England, are reviewed. The status of the cement in a number of countries is reported, and it is concluded that there are no grounds for including the cement in Canadian standards.The current discussion on the need for a standard for high-alumina cement concrete in Canada makes the subject of the structural behavior of this material topical. For this reason, experiences in other countries, and especially the recent problems in England, may be of interest.

ISSN:0315-1468    

DOI:10.1139/l75-034

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

A number of lightweight coastal protection structures, built on the Lake Erie shore are discussed in this paper. There were two constraints on the design; limited funds and a very precarious downdrift beach. Thus the structures were inexpensive and the protection was low-key to prevent damage downdrift. In 1972–1974 these structures were subjected to a combination of large waves and high water levels and thus they were tested well beyond their design limits.The paper discusses the structures, their performance under normal conditions, and their performance during and after the abnormally high water levels. It is found that inexpensive, low-key structures are sufficiently strong to survive normal conditions, but fail by overtopping and flanking under conditions beyond their low design limits.

ISSN:0315-1468    

DOI:10.1139/l75-035

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Among the problems associated with the extension of the winter navigation season on the Great Lakes and the St. Lawrence River, the obstruction of navigation posed by a continuous ice boom across a water body may possibly be solved by creating a gap or opening in the boom, through which vessels may pass, but which will promote retention of floating ice pieces by arching. A laboratory study of arching by fragmented ice floes across a gap in a surface obstacle was conducted in a 0.9 m wide hydraulic flume using simulated ice floes. Polyethylene blocks, 37 mm and 74 mm square by 6.4 mm thick, were used in both single-sized runs and combination-sized runs. The simulated ice was released upstream at a controlled rate and the occurrence or nonoccurrence of a stable arch was observed and recorded by time-lapse photography. The threshold of arching was found to be described by a correlation between the supply rate of simulated floesQi(in terms of total floe surface area per unit time), normalized byVb, the product of water surface velocity and gap width, anda/b, the ratio of block size to gap width of the formIn a corollary series of experiments an arch, once formed, was subjected to a disturbance simulating the passage of a vessel through the ice field. The area of ice floes released as a result of the disturbance before arching reoccurred was found to be, on average, equivalent tob2, the square of the gap width.

ISSN:0315-1468    

DOI:10.1139/l75-036

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Laboratory tests on freshwater ice were conducted by using model structures of various geometries. Vertical and sloping pile sections with diameters up to 36 in. (91.4 cm) were pushed through the ice with an active testing system. The test variables investigated were size, shape, velocity, and slope or angle from the vertical.The data gathered in this study indicates that nominal ice pressure varies indirectly with pile width/ice thickness (D/T) ratio in the range of 1:10. There was no apparent change in nominal ice pressure due to the change of the pile shape. Data gathered in the velocity tests suggests an inverse effect upon the ice pressure, especially at speeds greater than 3 in./s (7.6 cm/s). In the sloping pile tests it was found that the ice pressure decreased with an increase in the slope angle from the vertical position.An expression correlating the vertical and horizontal forces in the sloping pile tests that failed in bending was developed. Values for this linear correlation were found graphically.A comparison of the test results with other investigations is also presented.

ISSN:0315-1468    

DOI:10.1139/l75-037

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Stormwater runoff from a homogeneous residential area in Windsor, Ontario, was studied over a 1 year period of time. Hourly grab samples were taken and analyzed for 21 constituents. Seasonal and annual concentration data are reported along with the most significant correlations among constituent concentrations. Other influences on runoff quality are discussed. Rainfall for all 25 storms was measured, and discharge was measured for 13 storms. The discharge data and rainfall data were used to generate runoff hydrographs for 9 storms without measured hydrographs. The hourly discharges and concentrations were used to calculate loadings on an annual and seasonal basis. The loadings' variation on an hourly basis is listed. The results of an empirical analysis of the average annual loadings contained in percentage amounts of annual runoff are reported. Significant correlation was found between the preceding two variables for all constituents whose loads were calculated. A comparison is made between annual loadings of stormwater runoff and raw sewage for biochemical oxygen demand and total suspended solids and orthophosphates.

ISSN:0315-1468    

DOI:10.1139/l75-038

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Following the ideas of Newmark, a complete record of torsional ground motion is generated from the two translational components of an earthquake record. The approximate spectra developed by Newmark are generally confirmed. The assumptions and the limits of validity are discussed. Code provisions for this phenomenon are commented upon.

ISSN:0315-1468    

DOI:10.1139/l75-039

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

This paper describes the concept and the experimental study made to determine the design criteria for a drop structure comprised entirely of loose dumped rock. The three principal components of the design were: (1) the weir at the top of the slope, (2) the sloping portion downstream from the weir, and (3) the horizontal apron at the bottom. The rock weir was intended to prevent excessive drawdown and control upstream velocities. The sloping portion was a hydraulically steep reach, on which supercritical velocity occurred. The apron was intended to accommodate the transition back to subcritical flow at the end of the drop structure.The initial investigation involved study of the structure in two-dimensional flow. It was determined that the critical area for stability was in the terminal velocity region of the steeply sloping portion of the structure. The stone size and layer thickness required for channel stabilization was found to be a function of the channel slope and flow depth at terminal velocity. Eight combinations of variables were tested and included four different slopes, three different stone sizes, and two different layer thicknesses. Each combination was tested to failure.The failure process was unique in that there was an initial failure and an ultimate failure. Initial failure occurred when some stone at the lower end of the slope was displaced, exposing the subgrade. The exposed area was rapidly filled in by downstream migration of stones from further up the slope. The migration process continued until it was arrested at the top of the slope by the rock weir, and the structure became stable once again. A further large increase in discharge was required to precipitate a second or ultimate failure.Design criteria were formulated, including a recommended factor of safety based on initial failure, and the design was verified on a three-dimensional model.

ISSN:0315-1468    

DOI:10.1139/l75-040

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The static seismic loading provisions of the 1975 National Building Code of Canada include, as do a number of other seismic codes, an overturning moment reduction factor in order to recognize that the overturning moment computed from the static load distribution is likely to be larger than the actual maximum dynamic moment. The reduction factors specified in the various codes have been based on empirical data and on relatively simplistic evaluations of the contributing effects. The purpose of this paper is to make a dynamic evaluation of the dynamic shear moment relationship and the reduction factor for a class of uniform shear wall–frame buildings subjected to earthquake motions as specified by several design spectra. The results are presented to show the effect of damping, natural period, and the particular response spectrum for different shear wall–frame stiffness proportions.

ISSN:0315-1468    

DOI:10.1139/l75-041

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

This paper deals with the problem of cracking due to the thermal shock of concrete. Safe temperature differentials between concrete and air are given with sample calculations in arriving at the values. The required amount of insulation is shown for various weather conditions to cure the concrete in accordance with the CSA specification. Assuming that the stipulated insulation is attached to the formwork, the safe stripping times to avoid thermal cracks are given for various thicknesses of structures under various degrees of restraint. The salient points are illustrated with practical examples, and the vital data are presented in graphical form to make it usable.

ISSN:0315-1468    

DOI:10.1139/l75-042

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The moisture content – strength relationship for lumber was investigated by performing a dry out test. It was found that the increase in strength, as moisture content went down was discernible for initially strong material, whereas weak material did not increase in strength as indicated in the present building codes. However, stiffness did increase over the whole range of initial stiffness as moisture content dropped. It was also found that the present grading rules do not provide consistent overload factors for the different grades.

ISSN:0315-1468    

DOI:10.1139/l75-043

出版商:NRC Research Press    

年代:1975

数据来源: NRC