摘要:

The Canadian Standards Association Standard CAN-CSA-S16.1-M89 “Limit states design of steel structures” assigns welded wide flange (WWF) columns to the column curve for rolled H-shaped sections. This is conservative because of differences in the production of WWF and rolled sections. The WWFs are stipulated to have flame-cut edges. The residual stress pattern, with favourable tensile stresses, results in a delayed loss of stiffness as weak axis inelastic buckling occurs. Thus the weak axis and strong axis buckling curves lie closer together for WWF shapes than they do for rolled H-shapes. Automatic cutting and welding processes result in close tolerances on out-of-straightness. As well, the statistical variations in the geometric properties are favourable. A detailed analysis of data collected from mill records and on-site measurements was made to obtain statistical parameters of relevant geometric and material properties. A finite element program modelling inelastic behaviour, residual strain patterns, out-of-straightness, and material properties was used with the test results of others to establish test-to-predicted ratios of column strengths. Parametric studies provided an assessment of the effect of varying residual strain patterns and column out-of-straightness. This formed the basis for determining the factored compressive resistance of WWF sections for three different slenderness ratios.Key words: columns, inelastic analysis, out-of-straightness, residual stresses, welded wide flange.

ISSN:0315-1468    

DOI:10.1139/l91-067

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Lagoons are the most widely used form of wastewater treatment in Canada, particularly in the western provinces and northern territories. Existing lagoon design guidelines developed for warm climates must be modified for successful use in cold climates. The use of short-detention lagoons followed either by long-detention continuous flow lagoons or by 270 – 365 d storage lagoons will be required in most situations. Under special circumstances, the conversion of small lakes to engineered lagoon – lake systems may be an acceptable option. Detailed guidelines for the planning and design of these types of lagoons are presented with emphasis on the cold regions of Canada.Key words: wastewater, treatment, cold climate, lagoon, design, guidelines.

ISSN:0315-1468    

DOI:10.1139/l91-068

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The seismic force reduction factors proposed in the seismic provisions of the National Building Code of Canada 1990 (NBCC 1990) are examined using ground motion records from two recent Canadian earthquakes. The displacement ductility demands are analyzed for structural systems with different ductility capacity. It is found that the NBCC 1990 force reduction factors, which are period independent, lead to a very high ductility demand for short-period structural systems. To avoid this, two types of period-dependent force reduction factors for short-period structures are investigated. The results show that the linearly varying period-dependent reduction factor represents a viable means to resolve the high ductility problems associated with short-period structural systems.Key words: earthquake, seismic, design, code, response, spectra, ductility, reduction factor, base shear.

ISSN:0315-1468    

DOI:10.1139/l91-069

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

This paper outlines the findings of laboratory tests to check the influence of curing and type of mould on scaling resistance of three types of concrete exposed to frost and deicing chemicals: a plain concrete and concretes with 5 and 10% silica fume (relative to total binding mass). Sodium chloride was the deicer used for the tests, which were performed according to standard ASTM C672 (Standard test method for scaling resistance of concrete surfaces exposed to deicing chemicals). The tests showed that type of mould (steel or wood) and curing (12 or 48 h) have relatively little influence on scaling resistance of concrete but that silica fume in the concrete can cause a significant drop in scaling resistance.Key words: concrete, silica fume, demolding age, formwork type, scaling resistance, freezing, deicing salt, sodium chloride. [Journal translation]

ISSN:0315-1468    

DOI:10.1139/l91-070

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

There is some controversy about freezing resistance of concrete containing superplasticizers. It has been quite convincingly demonstrated that, in some cases, such admixtures can significantly alter air-void systems in concrete. Some researchers believe, however, that concrete with superplasticizers can resist frost even when the air-void spacing factor is higher than the usual limit of 200 μm. The freeze–thaw cycle resistance tests described in this paper show that with the two types of concrete tested (a plain concrete with a water/cement ratio of 0.50 and a concrete with the same water/cement ratio but containing silica fume), the critical air-void spacing factor value is not significantly affected by the presence of a superplasticizer. When regular concrete is to be exposed to freeze–thaw conditions, the air-void system should meet the usual standards even when a superplasticizer is present.Key words: concrete, freezing and thawing, durability, superplasticizer, spacing factor, silica fume, water–cement ratio. [Journal translation]

ISSN:0315-1468    

DOI:10.1139/l91-071

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

At La Grande Complex, Quebec, Phase 1, earth and rockfill dams and dykes were constructed, in some cases, on pervious foundations and required deep impervious cutoffs (concrete cast-in-place walls) to bedrock. This paper describes the different construction phases of these concrete cast-in-place walls with emphasis on construction control and special construction problems.Key words: dam, construction, cutoff, excavation, foundations, bentonite, concrete cast-in-place wall, treatment.

ISSN:0315-1468    

DOI:10.1139/l91-072

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A new nonparametric regression model is proposed to investigate the relationship between groundwater level fluctuations and streamflow time series observations. The developed nonparametric model does not force the relationship between variables into a rigidly defined class (i.e., linear regression) and is capable of inferring complicated relationships. The results from the analysis indicate that the nonparametric method gives more accurate prediction results than those obtained from parametric regression. A split-sample experiment shows that nonparametric regression gives accurate prediction (extrapolation) results at the validation stage.Key words: nonparametric regression, cross-validation method, groundwater level, streamflow.

ISSN:0315-1468    

DOI:10.1139/l91-073

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

An analytical model of behaviour is presented, which uses one-dimensional finite element approximations to predict the short-term load – slip response of a single fastener joint. The model treats the elastoplastic behaviour of the fastener as well as the nonlinear, nonelastic properties of the wood. It accounts for some of the distinctive behaviour of timber joints such as fastener withdrawal, rotational restraint at the fastener ends, joint interface characteristics, and combined fastener bending and axial tension. Good agreement is obtained between model predictions and test behaviour for single fastener glulam rivet, nail, and bolt joints. The model can be adapted to include the variability in wood and fastener properties, and can be incorporated into a large number of computer simulations in order to predict the fifth fractiles of the populations of joint resistances, which can be used in a limit states design approach.Key words: timber structures, glulam rivet connections, nailed connections, bolted connections, mathematical model, finite element, nonlinear analysis.

ISSN:0315-1468    

DOI:10.1139/l91-074

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Timber column design methods have now to take account of a body of research work on timber properties from in-grade tests and on strength considerations using notions of stressed volume. This paper gathers results from this body of work and proposes a design formula for timber columns which is convenient to use and represents true behaviour. It includes, in particular, a material strength effect related to the length of the column. The proposed formula has been incorporated into the new Canadian code “Engineering design in wood.”Key words: timber, buckling, columns, design, size effects.

ISSN:0315-1468    

DOI:10.1139/l91-075

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The high accuracy of normal river discharge measurements is contrasted with the approximate methods used to estimate large floods. The most commonly used method, the slope–area method, is examined and it is argued that there is likely to be a strong upward bias in these flood estimates. Sources of error are subdivided into four main types: (i) error in the Manning friction coefficient, (ii) error in after-flood measurements of channel cross section, (iii) estimation of surface slope and energy grade line from high-water marks, and (iv) the effects of erosion and sediment transport. These various factors are seen to be influenced by channel curvature and meandering, floodplain flow and interaction with the main channel, and changes to channel geometry during a flood. From theoretical work on high sediment transport, it is argued that up to one third of the channel slope is required for moving the sediment, so that only two thirds of the slope is available for transporting the water.Key words: floods, river flow, channel friction, sediment transport, floodplains, meandering.

ISSN:0315-1468    

DOI:10.1139/l91-076

出版商:NRC Research Press    

年代:1991

数据来源: NRC