摘要:

Observations during many earthquakes have shown that building structures are able to sustain without damage earthquake forces considerably larger than those they were designed for. This is explained by the presence in such structures of significant reserve strength not accounted for in design. Relying on such overstrength, many seismic codes permit a reduction in design loads. The possible sources of reserve strength are outlined in this paper, and it is reasoned that a more rational basis for design would be to account for such sources in assessing the capacity rather than in reducing the design loads. As an exception, one possible source of reserve strength, the redistribution of internal forces, may be used in scaling down the design forces. This is because such scaling allows the determination of design forces through an elastic analysis rather than through a limit analysis. To assess the extent of reserve strength attributable to redistribution, steel building structures having moment-resisting frames or concentrically braced frames and from 2 to 30 storeys in height are analyzed for their response to lateral loading. A static nonlinear push-over analysis is used in which the gravity loads are held constant while the earthquake forces are gradually increased until a mechanism forms or the specified limit on interstorey drift is exceeded. It is noted that in moment-resisting frames the reserve strength reduces with an increase in the number of storeys as well as in the level of design earthquake forces. TheP→&Dgr; effect causes a further reduction. In structures having braced frames the main parameter controlling the reserve strength is the slenderness ratio of the bracing members. In these structures, reserve strength is almost independent of both the height of the structure and the effect of building sway.Key words: seismic design, overstrength factor, reserve strength owing to redistribution, steel moment-resisting frames, steel-braced frames, push-over analysis.

ISSN:0315-1468    

DOI:10.1139/l97-045

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Construction simulation is a powerful tool that can be used by a construction company for a number of tasks such as productivity measurement, risk analysis, resource planning, design and analysis of construction methods, and site planning. The success of simulation at the construction-process level has led to a natural attempt to use simulation at the construction-project level. Cyclic Operations Network (CYCLONE) and related simulation methodologies have provided the fundamental basis of these developments. This paper describes the enhancements made to the CYCLONE modeling methodology to allow simultaneous simulation of processes involved in a construction project. The objective of these enhancements is to allow development of individual models for all the processes that constitute a project and then to link them so as to simulate them simultaneously using a common resource pool. Such a simulation experiment will allow the construction manager to realistically model, analyze, and plan construction projects. This paper provides the specifications required to perform a project-level simulation using the CYCLONE modeling concepts.Key words: construction planning, construction simulation, modeling, discrete-event simulation, resource management, process interaction.

ISSN:0315-1468    

DOI:10.1139/l97-047

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Traditionally, road and lot drainage systems have been designed to convey storm runoff away as quickly as possible to reduce localized ponding. This drainage concept, using curb-gutter-sewer systems, has led to downstream flooding, erosion, water-quality degradation, reduced groundwater recharge and stream baseflow, and aquatic habitat destruction. This paper examines the pros and cons of curb-gutter-sewer systems and qualitatively compares various forms of open ditch - swale drainage alternatives with the conventional curb-gutter-sewer drainage system. These open ditch - swale drainage alternatives not only provide drainage functions but also promote infiltration, trap sediments, and reduce flow velocity along the drainage path. Thus, they can reduce erosion, enhance runoff quality, and increase groundwater recharge. However, they usually require a wider right-of-way than the conventional curb-gutter-sewer systems and may not be suitable for sites with steep topography or erosive soils. For sites that are suitable for the application of these alternative drainage systems, their environment functions make them more attractive than the conventional curb-gutter-sewer system.Key words: drainage systems, storm water, curbs, gutters, sewers, ditches, swales.

ISSN:0315-1468    

DOI:10.1139/l97-044

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The test results of an earlier experimental investigation conducted at Memorial University of Newfoundland on high-strength concrete slabs indicated that as the concrete slab strength increased from 35 to 75 MPa the shear strength increased by 7-20%, depending on the case of loading, i.e., concentric or eccentric loads. The increasing ratio of shear strength is less than half that prescribed in the Canadian code CSA-A23.3 (1994) or the ACI-318 code (1995). Hence, the significant difference between the experimental results and the predicted strength by existing North American codes tacitly means that the proportionality between the shear strength and the square root of the compressive strength is not accurate enough to predict the shear strength of high-strength concrete slabs. In the present investigation, a fracture mechanics model suitable for concrete was proposed. It was also suggested that this model might be an advantageous aid in the analysis of the shear failure of reinforced concrete slabs. In this research investigation the fracture mechanics approach utilizing finite element aided computer analysis of several reinforced slabs is briefly described, and calculated shear failure loads are given. The recommended model proves that it is necessary to consider not only the tensile strength of concrete, instead of the square root of the compressive strength, but also the tensile fracture properties of high-strength concrete. The tensile fracture properties of concrete are characterized by the parameter called characteristic length and the brittleness of concrete. The brittleness ratio of concrete slabs must be considered in any rational shear design expression to reflect the size effect factor and the aggregate type.Key words: fracture energy, uniaxial direct tension, shear strength, high-strength concrete, punching shear, slab, size effect, finite element analysis.

ISSN:0315-1468    

DOI:10.1139/l97-053

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A two-dimensional river mixing model capable of handling unsteady input conditions is evaluated in this study. The numerical model utilizes a streamtube representation of the river and a calculation grid which is optimized to eliminate errors associated with advective transport calculations. The application of the modelling procedure to natural river systems is evaluated by comparing model output with the results of tracer studies conducted on the North Saskatchewan, Peace, and Slave rivers. The study results represent a far more extensive field verification of this modelling procedure than had been previously reported by other authors.Key words: river mixing, mixing zones, tracer tests, water quality modelling, mixing coefficients.

ISSN:0315-1468    

DOI:10.1139/l97-052

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

When loads are applied to a masonry structure, viscoelastic behaviour is exhibited where the response can be divided into two distinct parts: an instantaneous elastic part and a time-dependent part. With the change in masonry construction during the last century, the latter portion of the response is becoming more important in the design of masonry structures. The effects of mortar type, stress level, age at loading, moisture condition, and masonry strength on the creep behaviour of clay masonry structures are examined. The results of a continuing experimental programme, begun in 1988, were used to evaluate the variations in specific creep of clay masonry with the different parameters considered. The test setup and the effect of moisture content on the creep behaviour of clay masonry are also described briefly.Key words: masonry, creep, specific creep, creep ratio, mortar type, moisture condition.

ISSN:0315-1468    

DOI:10.1139/l97-026

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Experimental work on prismatic concrete specimens was conducted to determine the relationship between mechanical restraint and the rate of corrosion. The current together with the changes in strain of the confining frame were monitored during the accelerated corrosion tests. The effect of mix design and cracking on the corrosion rates was also investigated. The results show that one-dimensional mechanical restraint retards the corrosion process, as indicated by the reduction in the steel loss. Improved quality of the matrix, with and without cracking, reduces the rate of steel loss. In the inferior quality concrete, the effect of cracking on the corrosion rate is minimal.Key words: corrosion, concrete, repair.

ISSN:0315-1468    

DOI:10.1139/l97-042

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The overall aim of this paper is to establish the process and amount of chlorides penetrating reinforced concrete elements when exposed to a salt-laden environment. For this purpose, a number of slabs were subjected to 70 cycles of wetting-drying regime with a 4% sodium chloride solution over a period of 2-3 years. To examine the direction of transportation of the chlorides, some of the slabs were partially coated with a surface coating system known to be highly resistant to chloride penetration. The amount and depth of penetration of chlorides in the coated and uncoated parts of the slab were then determined. The results show conclusively that, in large exposed areas of concrete, chlorides diffuse both in the direction of depth and in a direction lateral to the depth of the element. The amount of chlorides and the distance of their lateral diffusion depend on the water-to-cement (w/c) ratio of the concrete and the duration of exposure. Concrete mixes with a high w/c ratio (0.75) are highly conducive to this lateral diffusion of chlorides. Although concrete mixes of lower w/c ratios (0.45 and 0.60) are less conducive to lateral diffusion of chlorides, in practice, all concretes should be considered to be prone to chloride diffusion in both the direction of gravity and the lateral direction because of the effects of cracking. In unprotected concrete, reducing the w/c ratio from 0.60 to 0.45 is far more effective in decreasing chloride penetration than that achieved by reducing the w/c ratio from 0.75 to 0.60. The acrylic-based surface coating system is totally resistant to chloride penetration.Key words: chloride diffusion, concrete slabs, durability, water-to-cement ratio, surface coating, lateral diffusion.

ISSN:0315-1468    

DOI:10.1139/l97-046

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A full-scale laboratory test was conducted on a unique hybrid bridge girder with a reinforced concrete web and steel flanges. Half-width precast concrete deck panels were compositely attached to the top steel flange of a 17.1 m long hybrid girder to construct a "half-bridge" that was tested to study the service load behaviour and the behaviour under increasing load until failure. It was observed that the concrete web of the hybrid girder cracked because of the combination of dead weight and restrained shrinkage. Under the service loads, the concrete web had numerous closely spaced cracks that were reasonably well controlled - the maximum crack width was 0.20 mm. Although there was significant diagonal cracking in the web of the girder, the ultimate behaviour was dominated by flexure. This paper presents the methods used to construct and test the half-bridge, and a summary of the important results. A companion paper presents a detailed analysis and discussion of the test results.Key words: bridges, composite, cracking, girder, hybrid, reinforced concrete, structural design, tests.

ISSN:0315-1468    

DOI:10.1139/l97-055

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The experimental results from a full-scale test are compared with analytical predictions in order to investigate the behaviour of a hybrid bridge girder with a reinforced concrete web and steel flanges. A linear analysis indicates that restrained shrinkage had a significant influence on initial cracking of the concrete web. The longitudinal strains, predicted by a nonlinear flexural analysis accounting for shrinkage and construction stages, compare well with the strains measured during the test. The average widths of the flexural cracks at the service load level are predicted using an empirical average crack spacing approach. The modified compression field theory is used to predict the diagonal cracking of the web due to combined shear and bending moment. A rigorous nonlinear analysis indicates that the effects of creep, load-cycles, and shear deformation must be accounted for in predicting the displacement of the girder. Finally, sectional strength calculations indicate that the distributed longitudinal reinforcement in the web contributes significantly to the flexural capacity of the hybrid girder.Key words: bridges, composite, cracking, girder, hybrid, reinforced concrete, structural design, tests.

ISSN:0315-1468    

DOI:10.1139/l97-062

出版商:NRC Research Press    

年代:1998

数据来源: NRC