摘要:

The concept of three-field displacement finite element formulations of constrained problems is explored in this paper. The approach studied uses collocation within the element domain to enforce the constraints of the problem and resembles mixed formulations because in addition to the approximation of the displacement field, all other auxiliary deformation variables that enter the constraint conditions are interpolated independently. Plate-bending as described by the Reissner–Mindlin theory is used as a model problem for the development of the approach. Two triangular plate elements are formulated based on this methodology, and their performance is investigated using several patch tests. Numerical examples are also considered to study the element behavior under locking conditions (which occur with the classical displacement approach at the thin plate limit). The ability of the elements to overcome locking is established using mathematical arguments and practical examples. The influence of the position of collocation points on the computed results is evaluated through sensitivity studies, with the aim to identify the optimal set. Results are compared with those obtained from the exact solutions and the associated classical displacement model with selective reduced integration of the constrained energy terms.Key words: finite elements, collocation, discrete constraints, mixed methods, thick plates, bending of plates, shear deformations.

ISSN:0315-1468    

DOI:10.1139/l95-001

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Alternative dispute resolution methods remain an area of interest and study because of the continued increase in the incidence of disputes, be they claims or litigation. Practice in the industry tends to stimulate litigation if negotiation of claims is unsuccessful. At variance with this is the declared preference of construction industry practitioners for mediation over arbitration and for arbitration over litigation. Mediation has had a high success rate when used in construction dispute resolution. The cost of mediation is significantly lower than litigation or arbitration. The probability of the parties to the dispute being able to work together effectively after the dispute has been resolved is higher, and the dispute can be resolved more quickly than by arbitration or litigation. This paper presents the findings of a study undertaken to identify a better process for construction contracting. An essential part of the new process is the use of proactive mediation. Proactive mediation is the use of a mediator prior to a dispute arising to help identify and address potential problems before they become difficult or unsolvable issues. The proposed methodology has been tested through a process which obtained the input of over 60 senior industry practitioners.Key words: mediation, construction management, contracts, claims, cost reduction, alternate dispute resolution, risk management.

ISSN:0315-1468    

DOI:10.1139/l95-002

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Wind interaction with flexible structures, such as air-supported structures, is different from that of the standard rigid structures. Very few experimental studies are available in the literature with regards to wind effects on such structures. This paper presents an experimental wind tunnel study on hemispherical and cylindrical models of varying ratios of height to base width. The results of the steady state pressure distribution on flexible air-supported models are compared with those of the rigid models, which are generally known. Other varying parameters are also considered, such as wind velocity and direction, internal support pressure, and the Reynolds number.Key words: structure, experimental, wind pressure distribution, flexible membrane, cylindrical, spherical.

ISSN:0315-1468    

DOI:10.1139/l95-003

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Operational experience in Canada during the early seventies showed that hovercraft can make very effective icebreakers. In a low speed mode, the hovercraft causes an air cavity to form under the sheet as it rides onto it. This causes a section of the sheet to become unsupported and fail in bending under the action of its own weight. In a high speed mode, the motion of the craft over the sheet sets up large amplitude flexural gravity waves. Research into both modes of operation has been going on at Memorial University of Newfoundland (MUN) since the mid-eighties. This paper summarizes this work. For the low speed case, scaling laws for the resistance to forward motion of two new geometries were developed and confirmed with data obtained in the ice tank at the Institute for Marine Dynamics (IMD) in Newfoundland. For the high speed case, measurements of sheet deflections in the MUN wave tank and the IMD ice tank showed that a critical speed exists for motion over a sheet. At this speed, sheet deflections are limited only by dissipation and nonlinearities. We believe this critical speed is the source of high speed mode hovercraft icebreaking.Key words: hovercraft, icebreakers, air cavity mode, wave mode.

ISSN:0315-1468    

DOI:10.1139/l95-004

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The effects of ice on the conveyance characteristics of the Mackenzie River at the outlet of Great Slave Lake are modeled on the basis of cross section surveys, discharge measurements, and water surface profiles taken during open water and ice covered conditions. The calibrated bed roughness values, expressed in terms of Manningsn, range from 0.020 to 0.030. Based on measured ice thicknesses ranging from 0.6 to 1.2 m in the study reach upstream of Providence Narrows, the calibrated roughness of the 1992 late winter ice cover is 0.015. Discharge estimates, based on this late winter ice cover calibration, measured water surface profiles, and documentation of major ice movements during April and May of 1992, show relatively good agreement with the discharge measurements taken at the same time. The analysis indicates that flow in the channel just downstream of Great Slave Lake is uniform under both open water and ice covered conditions. However, stage–discharge relationships at the Water Survey of Canada gauging station are affected by variable backwater conditions, particularly when an ice accumulation develops in Providence Rapids.Key words: ice, breakup, backwater curves, hydraulic resistance, river.

ISSN:0315-1468    

DOI:10.1139/l95-005

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A numerical study based on a two-dimensional finite element model has been conducted to analyze flow conditions associated with different possible designs for the reopening of Havre aux Basques lagoon, located in Îles de la Madeleine, in the middle of the Gulf of St. Lawrence. More specifically, the study has been done to better define the depth and geometry of the future channel as well as its orientation with regard to tidal flows within the inlet and the lagoon. Results obtained from the model have been compared and analyzed to put forward some recommendations about choice of a design insuring the stability of the inlet with tidal flows.Key words: numerical model, finite element, lagoon, reopening, Havre aux Basques, Îles de la Madeleine.

ISSN:0315-1468    

DOI:10.1139/l95-006

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

This paper, the second of a series, presents the results of a numerical study of the advection–diffusion water mixing process between the Havre aux Basques lagoon and the Gulf of St. Lawrence, after the proposed reopening of the lagoon. In this study, the reopening scheme of the inlet, which has been closed in 1957, is analyzed by using a horizontal two-dimensional numerical model. The transport model is based on the Douglas–Wang finite element formulation for a space discretization. The approximation is quadratic, using six-node triangular elements. The semi-implicit Crank–Nicholson scheme is used for a time discretization. The results show that after reopening the lagoon, mixing may take between 5 and 22 days for a diffusion coefficient considered constant throughout the region and varying from 5 to 500 m2/s.Key words: lagoon, Havre aux Basques, advection–diffusion, mixing, numerical model, finite element, Douglas–Wang.

ISSN:0315-1468    

DOI:10.1139/l95-007

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

This paper presents the test results of six full-size composite beam specimens with perfobond rib shear connectors embedded in solid concrete slab. The objective of this investigation was to study the performance of this connector in full-size composite beams and to correlate the test results with those obtained from push-out specimens. In the first three beam specimens, the amount of transverse reinforcement was varied. Two other specimens were used to investigate the effectiveness of more perfobond rib connectors of shorter length. The effect of passing transverse reinforcing bars through the connector rib holes was investigated using the last specimen. Failure of the test specimens was initiated by longitudinal splitting of the concrete slab, eventually culminating in the crushing of concrete in the bearing zone immediately in front of the end perfobond rib connectors. The test results showed that increasing the transverse reinforcement ratio, excluding the wire mesh, from 0.11% to 0.20% led to a 10% increase in the ultimate capacity. The test specimen with six 251 mm long connectors sustained 11% higher ultimate capacity compared to that with four 376 mm long connectors. An increase of 8.4% in the ultimate strength was observed when transverse reinforcing bars were passed through the perfobond rib holes while keeping the total amount of transverse reinforcement unchanged. The experimental values of the ultimate flexural capacity of the beam specimens were, on the average, approximately 1.11 times the predicted values based on push-out test results.Key words: composite beam, perfobond rib connector, push-out test, full-size test, flexural capacity.

ISSN:0315-1468    

DOI:10.1139/l95-008

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Because of their excellent torsional capacity, box girders are used extensively in modern bridge construction having curved alignments. Applications of most design codes have been limited to bridges where the radius of curvature is much greater than the span length and cross-sectional dimensions. To meet the practical requirements arising during the design process, simple design methods are needed for curved bridges. This paper presents the results of a parametric study on the relative behaviour of curved and straight box-girder bridges and on the development of a simplified design method for the combined longitudinal moment of curved bridges. The combined moment includes the effects of flexure, torsion, and distortion. Three simply supported concrete-steel composite bridge models, including single-cell, twin-cell, and three-cell box girders and subjected to loadings as specified in the Ontario Highway Bridge Design Code, were analyzed using the finite strip method. The parameters considered in the study include types of cross section; types, locations, and magnitudes of loads; span lengths; and radius of curvature. Preliminary analysis of the results suggests that the behaviour of horizontally curved box-girder bridges is dependent on a variety of parameters, but most importantly on the span-to-radius ratio. Empirical relationships for combined longitudinal moment between curved and straight box-girder bridges are also proposed.Key words: bridge, curved, composite, design, finite strip.

ISSN:0315-1468    

DOI:10.1139/l95-009

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Point-of-entry systems with granular activated carbon filters have been used extensively to provide safe water to rural homes with wells contaminated with synthetic organic chemicals. Because of the low cost of these systems, their design is generally based on the equilibrium column model, the isotherm data from the literature, and a scale-up factor. This paper analyzes the necessary scale-up factors for point-of-entry adsorbers based on fumigant adsorption data gathered through an extensive literature review. The fumigants evaluated are 1,2-dichloropropane, 1,2-dibromo-3-chloropropane, and ethylene dibromide. It was impossible to thoroughly assess the scale-up factors for 1,2-dichloropropane because of the limited data. Column data for the other two fumigants were sufficient to generate column loading lines, which can be used directly without resorting to scale-up factors. Column data showed that the scale-up factors are greatly affected by competitive adsorption with the naturally occurring background organic matter and by preloading of these organic matter. As these phenomena are not well understood, it is presently impossible to accurately predict the appropriate scale-up factors. A recommended design approach is outlined.Key words: adsorption, activated carbon, fumigants, point-of-entry.

ISSN:0315-1468    

DOI:10.1139/l95-010

出版商:NRC Research Press    

年代:1995

数据来源: NRC