摘要:

A theoretical investigation of the buckling strength of continuous steel girders with top flange restraint is presented. Girders consisting of two equal spans are analyzed using a finite element technique to determine the effects of partial and full restraint conditions commonly found in bridge design. The effects of loading conditions, span length, and web stiffeners are also considered. A refinement is introduced for the purpose of modelling inelastic behavior due to combined bending and residual stresses. The theoretical method shows excellent agreement with experimental results obtained by others. A parametric study is conducted using the verified analytical technique.Key words: stability, buckling, plate girders, flange restraint, inelastic behavior.

ISSN:0315-1468    

DOI:10.1139/l90-016

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The uplift behavior of grouted rock anchors is little known despite their increasing use within the last few years and during which their field of application has been greatly broadened. The behavior of anchors is usually controlled at great cost after installation through field tests. Generally, their design is based on experience and an engineer with lesser experience finds it extremely difficult to design one. Furthermore, present methods for dimensioning anchors generally result in oversizing the anchors' grouted length without a corresponding improvement in the safety factor. To provide a more fundamental approach to designing grouted rock anchors, a finite element analysis of the uplift behavior has been carried out. The results of the analysis using isoparametric quadrilateral elements with eight nodes are presented in this article. Results of failure loads and modes obtained from anchors installed in the field are well predicted by the model.Key words: rock mass, grouted anchor, cement grout, finite elements, uplift of an anchor.

ISSN:0315-1468    

DOI:10.1139/l90-017

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The construction of shore protection is expensive, but the alternative of permitting erosion is also expensive. Yet any design of shore protection is based mostly on intuitive concepts. This paper presents an overview of what is lacking in our knowledge, a possible methodology for improving shore protection design and discussions about some of the most important (and often ignored) physical parameters to be considered if shore protection is to perform its task without interfering with the littoral environment.Key words: erosion, groins, seawalls, sediment transport, shore protection.

ISSN:0315-1468    

DOI:10.1139/l90-018

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

In the St. Lawrence estuary (Canada), tidal flats localized in the area of saline intrusion are covered with up to 30 cm of fine sedimentation during July, August, and September. This sedimentation is the result of waters coming from the turbidity zone. The upper half of the tidal flats are covered with a tidal marsh. This vegetation is very important in preventing the sediments from eroding. In the tidal marsh, measurements with automatic current meters were taken during periods longer than a month. These showed that, among the vegetation, currents are weak and steady during spring tides and neap tides, whereas next to the drainage systems, currents are heavily dependant on the range of the tide. Close to the shore, currents decrease significantly, thus helping fine sedimentation to occur. A mathematical simulation of the currents made on a line perpendicular to the shore shows the impact of the vegetation on the formation of the drainage system in the tidal flats. Water entrapment by the vegetation at the end of the flood initiates the creation of creeks and insures their continuity throughout the summer. As soon as the vegetation is destroyed, creeks fill up with sediments and disappear from the surface of the tidal marsh. Contrary to what could be assumed, the mathematical model also shows that spring tides, even though associated with strong currents, promote a very active sedimentation on the tidal marsh. In the St. Lawrence estuary, erosion of the mud flats deposits is observed during short periods of strong winds in summer. This high energy and high variability do explain the strong year to year variation in sedimentation observed in the tidal flats.Key words: currents, intertidal sedimentation, tidal creeks, tidal flats.

ISSN:0315-1468    

DOI:10.1139/l90-019

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

An experimental research involving tracer studies, carried out in four geometrically similar models of contact chambers and operated under an equal detention time criterion, is presented. The scale effect on dispersion characteristics is investigated to determine how closely the performance of a prototype can be predicted from a laboratory study on scaled-down models. A number of parameters and indices, including dispersion number, are considered in the investigation. It is observed from the output-generated curves that the coefficient of dispersion is influenced by scale. However, the normal variance and the dispersion number are, to a large extent, independent of scale, at least for longitudinal basins larger than 5.6 cm (2.2 in.) width and for all practical detention times.Key words: longitudinal dispersion, dispersion number, model study, scale.

ISSN:0315-1468    

DOI:10.1139/l90-020

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The 1984 edition of the Canadian Standards Association Standard 086 restricts the use of glulam rivets to Douglas-fir– larch glued-laminated timber (glulam) only. This study, undertaken in order to extend the use of glulam rivets to both spruce glulam and solid timber, presents the results from the short-term ramp testing of 33 glulam rivet connections assembled using white spruce and Douglas-fir glulam beams and Douglas-fir solid wood joists. Half of these connections were tested to failure with load applied parallel to the grain of the wood member; the other half were tested with load applied perpendicular to the grain. A species factor of 0.80 is recommended for application to the design values of Douglas-fir–larch glulam rivet connections in order to obtain values for spruce glulam rivet conne-ctions. Also, small (less than 4%) differences were found between the lateral load-carrying capacities of glulam rivet connections made with Douglas-fir glulam and connections made with Douglas-fir solid timber free from major checks and (or) splits. To provide theoretical representations of the load–slip curves of the experimental treatment groups, an exponential function was fitted to the test data.Key words: glulam rivet, timber engineering, fasteners, nails, glued-laminated, wood connectors.

ISSN:0315-1468    

DOI:10.1139/l90-021

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

When runoff begins, uplift pressures develop on the underside of the shore fast cover. Analysis shows that longitudinal cracks should form soon after runoff starts. Two cracks are normally predicted, subdividing the cover into a main central part and two side strips. Where ice thickness is large or the channel is narrow, a single mid-channel crack is predicted. Field observations support the theory. With increasing flow, the central portion of the cover may detach and become subject to transverse fractures. The latter could result from bending on vertical or horizontal planes. Vertical bending fracture requires extreme, wavelike slopes such as might prevail briefly during jam releases. Flow shear and the meandering planform of rivers cause horizontal bending manifested in commonly observed transverse crack patterns. The resulting separate ice sheets will be set in motion if there is enough room on the water surface between the river boundaries, thus initiating the breakup. This mechanism leads to a breakup forecasting criterion, called the boundary constraint, that explains past empirical findings and identifies the factors influencing various empirical coefficients. Another type of breakup is caused by ice-jam releases and formation of breaking fronts whereby the ice cover is reduced to rubble before it moves. Little is known about the motion of breaking fronts but relevant field observations are reviewed.Key words: bending, breakup, crack, cover, fracture, ice, onset, release, river, surge.

ISSN:0315-1468    

DOI:10.1139/l90-022

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Disaggregate mode choice models were calibrated for intercity passenger travel in Canada using a data base drawn from the Canadian Travel Survey. Multinomial logit models were calibrated for business and nonbusiness trips in the eastern and the western regions of Canada. The calibrated models produced reliable results in terms of goodness-of-fit measures. The likelihood ratio index, ρ2(c), varied from 0.282 to 0.436. Results obtained were comparable to those of previous studies. The research identified the significance of level-of-service factors in determining mode choice. The findings from the study indicated that the Canadian Travel Survey data could be used for developing disaggregate models for possible use in policy impact analysis. The potential for the use of this data base in the transportation planning process could be enhanced if some relatively minor modifications were made.Key words: models, disaggregate, choice, intercity, passenger, travel time, cost, frequency, service.

ISSN:0315-1468    

DOI:10.1139/l90-023

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

This paper assesses the temporal stability of trip generation, distribution, and assignment process at a state or provincial level. The assignment used data from a test study area that included the southwest part of the Province of New Brunswick with a total area of 30 000 km2. For the test year of 1979, trip generation data were developed using three models. The models were based on stepwise regression, principal components, and ridge regression. Following the trip generation phase, a gravity model was used to distribute the output of each model. Given the limited number of alternative routes, an all-or-nothing assignment was used. The stability of the models was assessed using data for 1971. Of the three models evaluated only the one based on ridge regression proved to be reasonably stable over the term period. A stepwise regression model without intercept was also developed and reasonable results were obtained for the stability of this model.Key words: planning, model, stability, trip generation, distribution, assignment, provincial.

ISSN:0315-1468    

DOI:10.1139/l90-024

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The Richter magnitude 7.1 October 17, 1989 Loma Prieta (San Francisco) earthquake is the largest to occur near a major North American urban center since the historical 1906 San Francisco magnitude 8.3 earthquake. As earthquakes of at least similar strength are expected to occur in most of eastern and western Canada, and since the amount of structural damage that occurred is considerable, the study of the effects of this earthquake is of particular significance to Canada. This paper reports on the major structures and types of structures that were most heavily damaged by this earthquake, and presents preliminary findings as to the causes of failures or collapses. The pertinence of this earthquake is reviewed in a Canadian perspective.Key words: earthquake, structures, damage, failure, collapse, buildings, bridges, heritage buildings, emergency preparedness.

ISSN:0315-1468    

DOI:10.1139/l90-025

出版商:NRC Research Press    

年代:1990

数据来源: NRC