摘要:

The effects of silica fume on the properties of plastic and hardened concrete are now fairly well-established. If properly used, silica fume imparts significant improvement to the strength and durability of concrete; and the availability of this material together with high-range water reducers (superplasticizers) has been largely responsible for the development of high-strength and high-performance concretes. Silica fume has been used in the Canadian cement and concrete industry for over 15 years. Early use was driven by economy, since concrete of a given strength grade could be produced at lower cementitious material content (and cost) if silica fume was incorporated in the mix due to the initial low selling price of the material. The construction boom of the mid to late 1980s saw the exploitation of high-strength silica fume concrete for high-rise construction. By the 1990s, concerns over the deteriorating infrastructure had shifted the focus to concrete durability and silica fume was finding applications in high-performance concrete. Today, silica fume is perhaps the material of choice for engineers designing concrete to withstand aggressive exposure conditions. This paper documents the major developments in the use of silica fume in Canada and discusses the wide range of applications for which the product may be used to beneficial effect.Key words: blended cement, Canada, concrete, high-performance, silica fume.

ISSN:0315-1468    

DOI:10.1139/l97-105

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This paper reviews past work in construction quality management by examining its major components in the context of a study framework derived from ISO 9000. Emphasis is placed on determining the state-of-the-art and exploring the roles that information technology already plays as well as could play in improving the quality management function. The authors elaborate on several dimensions of the quality management view of a project in terms of how it would interact with the physical, process, cost, and as-built views of a project, which are essential to the quality management function as well as to other project management functions. This is done in a way that reflects the authors' vision of the kind of support that a computer system could offer for the tasks of identifying, predicting, analyzing, and solving quality problems in a preventive mode.Key words: construction quality management, ISO 9000, problem prevention, problem prediction, computer system.

ISSN:0315-1468    

DOI:10.1139/l97-098

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Tests have been conducted on wood frame shear walls to characterize the degradation of stiffness and energy dissipation that occurs under cyclic loading. A total of eight walls were tested, four sheathed in plywood and four sheathed in oriented-strand board. The tests were conducted in accordance with a draft test procedure recently proposed by the Structural Engineers Association of Southern California, which is based on a sequential phased displacement command input. The results indicate that effective stiffness decreases linearly with continued cycling at the same displacement and decreases with increasing amplitudes of displacement. Furthermore, the energy dissipation capacity of the wall decreases by 15-20% with the first cycle at a given amplitude, then decreases slightly with continued cycling at the same amplitude. The changes in effective stiffness and energy dissipation are generally independent of the type of sheathing for loads less than the wall ultimate, suggesting that the wall performance under cyclic loading is influenced more by the fastener and frame behavior. The results presented should be useful for design and for verifying hysteretic models of the shear wall behavior.Key words: cyclic, dynamic, energy dissipation, experimental, seismic, shear wall, stiffness, testing, timber, wood frame.

ISSN:0315-1468    

DOI:10.1139/l97-108

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Construction projects are commonly scheduled by the critical path method or its similar methods, with the assumption that resources are unlimited. The ranked positional weight method, which may be used for project scheduling and resource allocation for both constrained and unconstrained resource scheduling, is found to be relatively easy in application. In construction, the availability of resources is sometimes limited and this leads to an extension of project duration. The critical path method and similar approaches cannot provide an answer in this scenario. A bridge construction project is used to illustrate how the method can be applied.Key words: scheduling, resource allocation, ranked positional weight method.

ISSN:0315-1468    

DOI:10.1139/l97-100

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A review of the so-called simplified method of shear design described in CSA A23.3-94 "Design of concrete structures" shows that the method is not simple. The designer is required to check numerous equations and limits. The resulting relation between stirrup spacing and shear strength is found to be an extremely complex line resulting from the intersection of seven separate surfaces. A shear friction model has been developed which seems to predict the shear strength of beams rather well. Stirrups and longitudinal reinforcement provide a clamping force thereby increasing the friction force which can be transferred across a crack along a potential failure plane. This model is based on the shear strength after cracking so that no diagonal tension strength is included. The shear friction model has been used as the basis for determining approximate equations for maximum stirrup spacing. A comparison of these approximate shear friction predictions with those using the simplified method indicates a high degree of correlation but many important differences. It seems that shear design can be clarified as well as simplified by adoption of the shear friction approach.Key words: reinforced concrete, shear, shear friction, shear tests, stirrup spacing.

ISSN:0315-1468    

DOI:10.1139/l97-101

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The results of a test on a full-scale 5 m continuous slab are used to study the methods of analysis and calculation of deflection of reinforced concrete flat slabs. The most commonly used methods for the analysis of flat slabs, namely the equivalent frame method, the prismatic member method, the direct design method, and the finite element method, are critically compared using the results of the slab tested. Based on the comparison with the unbalanced column moments in the test, improvements for the prismatic member method are suggested. For the deflection calculations of cracked reinforced concrete flexural members, three methods are investigated: the effective moment of inertia approach, the mean curvature approach, and the bilinear method given in the CEB manual for deflections. To calculate the deflections of flat slabs as column and field strip deflections, new coefficients for distributing the bending moments between the column and middle strips are proposed.Key words: analysis, deflection, flat concrete slab, test.

ISSN:0315-1468    

DOI:10.1139/l97-102

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Turbulent rough flows in spillway chutes are considered in the first part. The drawdown curve is demonstrated to be identical with those of flows in the turbulent smooth regime. It is further shown that all drawdown curves can be expressed with a normalized streamwise coordinate that involves the bottom slope and the uniform and critical flow depths. An explicit solution is presented. The computational results are verified with model observations. Also, previous derivations are generalized and a universal drawdown curve for chute flow is introduced. The results are readily applicable for design. In the second part of this paper, incipient aeration on a spillway chute is investigated, based on the data of Bauer for the boundary-layer thickness. Predictions for the flow depth and location of incipient aeration are in agreement with observations. The effects of bottom slope and relative roughness are demonstrated to be comparably small, whereas the critical depth has a major influence on both flow depth and location of incipient aeration. Typical examples illustrate the computational procedure.Key words: aeration, chute, drawdown, spillway, supercritical flow.

ISSN:0315-1468    

DOI:10.1139/l97-103

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The purpose of this paper is to critically review the provisions of CSA A23.3-94 for the deflection calculations of normal and high strength reinforced concrete beams. Comparison is made with the provisions of CEB-FIP MC 90 and EC 2 which is similar to the MC 90. Both short- and long-term deflections are discussed. Tests from the literature are used to assess the calculation methods suggested by the codes. These methods are the effective moment of inertia approach, the mean curvature approach, and the bilinear method. A parametric study is carried out to investigate the effect of the level of loading, shape of bending moment, and reinforcement ratio on the predicted deflections.Key words: code predictions, deflections, long term, reinforced concrete beams, short term.

ISSN:0315-1468    

DOI:10.1139/l97-106

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Cable-stayed bridges are ideal for spanning natural barriers of wide rivers, deep valleys, or ravines, and for pedestrian bridges crossing wide interstate highways. Modern construction of cable-stayed bridges makes use of the segmental balanced cantilever techniques and involves many repetitive cycles of placing the concrete segments (both cast-in-place and precast) and supporting cables. It provides a fertile area for the application of computer simulation techniques for the planning and analysis of the process, particularly for studying the interaction of resources used in the construction phase and also for assessing the productivity of the construction processes. This paper employs MicroCYCLONE, a microcomputer-based simulation program, for the modeling and simulation of the construction of two cable-stayed bridges: the Dame Point Bridge in the state of Florida, U.S.A., and the Tsukuhara Bridge in Hyuougo, Japan. The paper will also provide a brief explanation of the suspended long traveler method used on the Tsukuhara Bridge, the simulation models developed to analyze the construction processes, and the results of sensitivity analyses.Key words: simulation, modeling, construction, cable-stayed bridges, resources, productivity, balanced cantilever construction.

ISSN:0315-1468    

DOI:10.1139/l97-109

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Geometric design is an important phase in the highway design process that is directly related to traffic safety. Highway elements should be jointly designed to account for such design criteria as sight distance, vehicle stability, driver comfort, drainage, and aesthetics. Intuitively, such a design should be based on a three-dimensional (3-D) analysis. This paper reviews the current practice and research work related to each design criterion with emphasis on the conformity with the 3-D nature of the highway. Current standards are based mainly on a two-dimensional (2-D) analysis that does not guarantee a satisfactory design. Recently, several research efforts have been expended in the 3-D highway analysis with sight distance being the most researched area. Analytical models and computer software have been developed to accurately model 3-D daytime and nighttime sight distances. Roads designed using current 2-D standards may compromise safety or economy. Different models are currently available to simulate the forces acting on a vehicle in 3-D. These models show that the point-mass formula for modelling vehicle dynamics in the current standards can be inaccurate. Current standards contain recommendations for drainage of surface water, but explicit quantitative coordination of combined alignments is lacking. Furthermore, research is still needed to study the effect of alignment coordination on highway aesthetics and driver's perception of information.Key words: highway geometric design, three-dimensional analysis, sight distance, vehicle dynamics, drainage, highway aesthetics.

ISSN:0315-1468    

DOI:10.1139/l97-111

出版商:NRC Research Press    

年代:1998

数据来源: NRC