摘要:

The carrying capacity of square hollow structural section T-joints stiffened by a rectangular flange plate is investigated for both branch bending moment and punching shear. The ultimate moment or load is determined from the simple yield line method of which one of three failure modes is applicable depending on the plate length. A large number of combinations of branch, chord, and plate sizes are analysed to provide a statistical basis for making recommendations of optimum plate lengths and thicknesses for stiffened joints in Vierendeel truss applications.

ISSN:0315-1468    

DOI:10.1139/l82-017

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Vibration measurements have been correlated on five long-span floors in a two-storey shopping centre. The floors are used primarily as walking areas and have been considered satisfactory with respect to floor vibrations. Three of the floors are steel beam composite concrete deck construction, and two are precast, prestressed, concrete beam construction.Dynamic characteristics of the floors as determined by the heel impact test were compared with quiet occupancy criteria. Results suggest that quiet occupancy criteria can be increased by at least a factor of three for walking areas in shopping centres.Calculations of fundamental frequency and initial peak acceleration from heel impact for the five floors are also presented and the results compared with measured values.

ISSN:0315-1468    

DOI:10.1139/l82-018

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

For the construction of a rockfill dam in flowing water, caused by river closure or a dam collapse, generally a progressive lateral dumping of stones is considered. The aim of the study of this phenomenon in the hydraulic laboratory at the University of Sherbrooke was to determine an economic procedure for an actual power plant structure and, if possible, to draw some conclusions of general validity.Scale model techniques of river studies are well understood from the application of the laws of similarity of hydraulic flow and of bed load transport. It seems to be more difficult to extrapolate the results from scale model studies of a river closure, because of the uncertainty of extrapolation of some physical factors like turbulence intensity, form coefficient of solid material, friction and inertia forces of dumped particles, and their stability in connection with bottom roughness. The same uncertainty exists also in the extrapolation of the duration of closure for a specific frequency of dumping.

ISSN:0315-1468    

DOI:10.1139/l82-019

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

One of the properties of air-entraining admixtures that may influence their efficiency is their surface tension when combined with mixing water. Lignosol SF is a standard air-entraining agent. With the objective of identifying a product with improved qualities, Lignosol SF was fractionated and two of its fractions, respectively with low (foamate) and high (retentate) surface tension properties were investigated as potential air-entraining agents. Measurements were made both of air content in wet concrete mix and of the air-void characteristics of the hardened concrete.The results showed that at low concentrations and water:cement ratios the performance of all the three products above are similar. However, the foamate fraction becomes more effective in entraining air with increases in concentration and water:cement ratio. Further, this foamate resulted in the hardened concrete having bubbles with a smaller mean diameter than those in the retentate. The spacing factors for both these products were within recommended limits.Keywords: admixtures; air-entrainment; air-voids; concrete; freeze-thaw resistance; Lignosol; spacing factor.

ISSN:0315-1468    

DOI:10.1139/l82-020

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Since the construction of the Bennett Dam on the Peace River in British Columbia, the temperature of flow releases from G.M. Shrum Generation Station, located at the dam, has been 0.5 °C or higher during the winter months. As a result, the progression of ice cover below the dam is inhibited and a long reach of ice-free river persists throughout the winter. During February, 1979 below normal air temperatures persisted in the area and the cover progressed to a point 103 km downstream of the dam, or 19 km upstream of the Water Survey of Canada (WSC) stream gauge at Taylor. This was only the second occurrence of ice cover at the town of Taylor since 1972, when an increase in generating capacity at the G.M. Shrum Station raised maximum powerhouse releases to 1580 m3/s.A series of ice jams at the leading edge of the ice cover formed as the cover advanced, producing water levels within Taylor that approached the maximum historic summer flood levels. The ice movement, including ice cover advance and retreat, ice levels, and jam formation were monitored and documented. The data provided an opportunity to examine various river ice simulation models and assess their applicability to the Peace River.

ISSN:0315-1468    

DOI:10.1139/l82-021

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

One of the least understood aspects of flow in sewers is the nature of the transition from gravity to pressure or surcharged flow. A complete design of a storm sewer should consider both gravity and surcharged conditions. The available design and/or simulation models can handle gravity (open-channel) flow with various degrees of sophistication, whereas some consider surcharged flow. None of the available stormwater computer models include an adequate treatment of the transient pressures associated with surges that can occur at the transition from gravity to pressure flow. During the transition period there is a further complication because there is a mixture of air and water in the pipe.This paper deals with transients that occur when gravity flow is suddenly changed to pressure flow by the occurrence of a surge in the line. The pressure head fluctuations associated with this transient have been studied. Some of the factors affecting the pressure transients are: pipe size, pipe shape, flow velocity, Froude number, relative depth of flow, alignment of the pipe, pipe material, venting arrangements, and boundary conditions such as pumps, interceptors, and drop pipes. The paper also suggests a theory to predict the excess pressure rise due to these transients.Keywords: Fluid transients, gravity flow, instability, pipe flow, sewers, surcharged flow, surges, two-phase flow.

ISSN:0315-1468    

DOI:10.1139/l82-022

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Combined sewer diversions are designed to divert significant flows directly to the receiving water during rainstorms. To estimate pollutant loadings to the recipient water it is necessary to compute continuous hydrographs and pollutographs for the full period of potential overflow. Since a diversion is active only during part of a storm, diverting only part of the flow, a rating curve for the diversion structure must be obtained. Few structures have been adequately calibrated and their rating curves are not usually available.Overflow and diversion structures may be classified according to the shape of the sill or overflow control: end weirs, oblique weirs, and side spillways. Many structures experience hydraulic jumps of complex shape over much of the operating range. This paper reviews the hydraulics of side spillways and the SWMM-EXTRAN computer program. A new program called OVRFLO3 has been developed to dovetail with the SWMM package. Internal SWMM coding has not been changed. As a stand-alone program, OVRFLO3 will produce rating curves for side-weir diversion structures. The program has been applied to urban catchments in Hamilton, Canada.Validation of OVRFLO3 is discussed in the paper. Comparisons were also made between OVRFLO3, SWMM-EXTRAN, and a series of previous laboratory experiments conducted by others.

ISSN:0315-1468    

DOI:10.1139/l82-023

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

The Péligre Dam in Haïti, on the Artibonite River, was built in 1956 for an expected life of about 180 years. Based on sedimentation data collected in 1925 and 1926, the average rate of silting in the reservoir was estimated at 3.45 × 106 m3/year. In 1979, however, an average sedimentation rate of 9.6 × 106 m3/year was established.Systematic observations were undertaken in 1961, 1977, and 1979 to explain the phenomenon and to predict the future rate of silting in the reservoir. The studies led to simulation, by means of a mathematical model, of the processes involved and have permitted reconstruction of the hydro-sedimentological events since 1956 as well as prediction of the future rate of sedimentation.In order to develop a methodology that has widespread applicability for predicting the rate of sedimentation, the main physical processes responsible for the patterns of deposition were used as common denominators: degradation of watershed and rivers, effects of deforestation, urbanisation, and agriculture, effects of flocculation and consolidation, effect of the reservoir geometry, expected sediment inflow, water inflow versus outflow, etc.On the whole, the model indicates very well the acceleration of the silting rate with an average increase of about 18% per year. The study thus shows that the sediment inflow took the form of a quadratic or exponential growth curve instead of a straight line. After 23 years the average silting is three times that of the design. The results show in conclusion how we must be careful in predicting long-term sedimentation rates in a reservoir since the lifetime of the dam is notably reduced.Keywords: erosion, sedimentation, reservoir, lifetime, simulation, degradation, watershed, design.

ISSN:0315-1468    

DOI:10.1139/l82-024

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

The grillage analogy method for analyzing bridge superstructures has been in use for quite some time. The idealization of a bridge by a grillage is not axiomatic and is not without pitfalls. An attempt is made in this paper to provide guidance on grillage idealization of various types of structure, together with the relevant background information. Specifically, the paper deals with the idealization of slab, beam-and-slab, cellular, and voided-slab bridges. Idealization of slabs of linearly varying thickness is also discussed. Guidance is provided on the mesh layout.Keywords: analysis, beam-and-slab bridges, cellular structures, flexural rigidity, grillage, idealization, load, mesh, slab bridges, torsional rigidity, voided slab.

ISSN:0315-1468    

DOI:10.1139/l82-025

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Techniques for analyzing flow velocity profiles for streams where the flow depth is less than 1 m should be employed with caution. The two procedures for calculating flow resistance based on the logarithmic law, (1) mean and maximum velocity determinations and (2) intereept evaluation of log depth – velocity plots, should yield the same results for the various resistance coefficients and shear stress values, but they do not. The former procedure generally predicts higher values than the latter and is recommended for shallow streams where the field data were collected. For a 3.8 cm diameter flow sensor, the minimum distance from a boundary to the position of maximum velocity for a good velocity profile appears to be roughly 15–20 cm.The fluid shear stress values for ice covers on this shallow stream range from 0.1 to 17 Pa, depending upon ice type and duration of the cover. The shear stress under frazil ice slush showed a drop of about one tenth the initial value over a 2-week period at one location. The measured division of flow velocities about the maximum velocity associated with the bed and ice boundaries indicated that the mean velocities were not equal but often differed by as much as 25–30%, generally being higher in the section associated with ice, i.e., a rougher ice boundary.The most consistent method of determining the resistance coefficients was to define the cross-sectional shape of the river and ice cover accurately, subdivide the flow areas, use the mean velocity data calculated from the velocity profiles, and then compute the resistance values accordingly. The sensitivity of the roughness coefficient is discussed in terms of its impact on determining the total stage of an ice-covered river.

ISSN:0315-1468    

DOI:10.1139/l82-026

出版商:NRC Research Press    

年代:1982

数据来源: NRC