摘要:

A numerical model is presented for predicting the natural frequencies of one-way stiffened plates with ribs having high ratios of flexural to shear rigidity. The model is based on the free interface modal synthesis method. Experimental validation using floors with wood I-joists and wood-based sheathing showed that the model has good numerical accuracy in the predictions of natural frequencies and mode shapes if analyses include shear deformation and rotatory inertia effects in ribs. Neglect of these effects can lead to large errors in the predicted natural frequencies for plates with ribs having high ratios of flexural to shear rigidity. Large errors can also be encountered in natural frequency prediction for plates with fairly low ratios of flexural to shear rigidity. This occurs with mode shapes that have multiple curvature along ribs if shear deformation and rotatory inertia effects are neglected.Key words: free flexural vibration, natural frequencies, ribbed plates, flexural rigidity, shear rigidity, modal synthesis.

ISSN:0315-1468    

DOI:10.1139/l93-121

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

An examination of the requirements for the design of built-up compression members in the North American and European standards and specifications reveals a great variation in the allowable maximum slenderness ratio for an individual main member, and also in the determination of an equivalent slenderness ratio. The requirements of the Canadian standard with regard to the determination of the maximum allowable slenderness ratio of a main member between points of connection can be a bit confusing.This research involved a study of model built-up members that buckled about an axis perpendicular to the plane of the connectors. Twenty-four tests were conducted on model built-up members. The theoretical analysis consisted of a finite element analysis of the model built-up struts. In addition, an equivalent slenderness ratio was calculated by several methods. These equivalent slenderness ratios were then used in conjunction with the requirements of the Canadian standard to calculate a compressive resistance, which was compared with the experimental failure load.From this research on built-up members that buckle about an axis perpendicular to the plane of the connectors it was found that at least two connectors should be used, that the slenderness ratio of the main member between points of connection has a significant effect on the compressive resistance, and that Timoshenko's equivalent slenderness ratio when used in conjunction with the Canadian standard gives results that are in the best agreement with the experimental results.Key words: battens, built-up members, compressive loads, connectors, equivalent slenderness ratio.

ISSN:0315-1468    

DOI:10.1139/l93-122

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The mechanism of oil spreading in the presence of solid ice covers had been investigated in several studies. There are good laboratory data and some field data available for the case of solid ice covers. There are, however, little data available on the subject of oil spreading in the presence of broken ice covers. The lack of data and the complexity of dealing with many different types of broken ice covers are the main reasons for the poor understanding of the oil spreading mechanism in broken ice covers. In this paper, a laboratory study is presented to investigate the behaviour of oil spreading when spilled under a broken ice cover. The experiments included different ice cover thicknesses, artificial and real ice, oils of different viscosities, and a variety of discharge and volume conditions.Laboratory observations indicate that the behaviour of oil spilled under a fragmented ice cover depends on the type of ice cover. While oil may penetrate completely through one type of cover, it may not penetrate at all in another type. In covers that allow the oil to penetrate through, initially oil spreads under the ice, with simultaneous migration through the ice cover. When the oil reaches the water surface, it starts to spread rapidly, outpacing the spreading underneath. The spreading of oil under the ice was dominated by the buoyancy and viscous forces, while oil spreading on the water surface near the top of the ice cover was dominated by interfacial and viscous forces. This paper advances the fundamental understanding of the mechanism. The data from this study can be used to develop future mathematical models on this subject.Key words: oil spreading, oil slicks, oil under ice, constant discharge, constant volume, brash ice.

ISSN:0315-1468    

DOI:10.1139/l93-123

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The semi-analytical complex finite strip method is used to study the elastic local buckling of composite tee-section beams in negative moment and shear which contain a longitudinal stiffener attached to the web. The optimum position of this stiffener for different positions of the neutral axis is calculated in order to maximize the local buckling stress. Design graphs for longitudinal stiffeners are presented. Interaction curves between shear and bending for different positions of the neutral axis in a stiffened girder are given.Key words: composite beams, elasticity, finite strips, local buckling, longitudinal stiffeners, webs.

ISSN:0315-1468    

DOI:10.1139/l93-124

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Test results are presented and discussed for 18 beam-column specimens subjected to flange local buckling resulting from applied axial and flexural forces. Flanges classified as Class 2 by CAN3-S16.1-M84 “Steel structures for buildings (limit states design)” are investigated. Three different sizes of W shape with different height and web thickness ratios within the Class 2 range were used in this investigation. The flange width-to-thickness ratio was kept constant at the current Class 2 limit. Results of this investigation show that the conventional value of plastic moment reduced in the presence of axial load, as based on studies in the late 1950s, does not apply to Class 2 sections. This discrepancy had previously been predicted by an analytical study using an extended Rayleigh–Ritz technique and presented in 1980. Experimental results presented herein verify these predictions.Key words: axial, beam-column, buckling, compact, Class 2, interaction, slenderness.

ISSN:0315-1468    

DOI:10.1139/l93-125

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Spectral analysis of surface waves (SASW) is a nondestructive and in-situ method used for determining the thickness and elastic properties of pavement and soil sites using the dispersion characteristics of surface waves. In this paper, computer simulations of actual surface wave field tests are used to clarify errors that may arise in experimental dispersion curves of pavement sites when the usual test and data analysis procedures of the SASW method are followed. Two aspects of these procedures are considered: (i) relative phase angle unwrapping and (ii) source-to-near-receiver distance. The results of these simulations reveal that the currently used procedures may lead to erroneous results for some sites; the simulations offer valuable insights on the underlying causes. An overview of the theoretical aspects and field procedures of the surface wave method is briefly presented.Key words: surface waves, nondestructive testing, pavements, soils, elastic modulus.

ISSN:0315-1468    

DOI:10.1139/l93-126

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Smooth design spectra are generally used to describe the seismic excitation provided by the maximum design earthquake for safety evaluation of critical facilities located in eastern Canada. However, a comprehensive study of the inelastic behaviour of critical structural systems requires a step-by-step inelastic analysis in the time domain. This paper presents a study of the inelastic seismic analysis of short-period structures subjected to ground motion acceleration time histories compatible with eastern Canadian conditions and defined (i) from historical records scaled to the smooth design spectrum intensity, (ii) from spectrum-compatible accelerograms generated by random vibration theory, and (iii) from the modification of the Fourier spectrum coefficients of historical records while preserving the original phase angles. The ductility demand, the input energy, the hysteretic energy, the number of yield events, and other performance indices are examined in parametric analyses to identify the type of earthquake motions that is critical for earthquake resistant design of short-period structures.Key words: earthquake resistant design, artificial accelerograms, eastern Canada.

ISSN:0315-1468    

DOI:10.1139/l93-127

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Two series of post-tensioned concrete masonry walls subjected to uniform lateral loading were tested to investigate their flexural strength behaviour. Each series of walls consisted of four full-scale prestressed specimens, with varying levels of prestressing force, and one reinforced specimen. Of particular interest were the load–deflection curves, initial cracking loads, wall stiffness, crack patterns, and ultimate failure loads. An air bag test apparatus was used for applying lateral uniform pressures to the specimens. Results of this experimental investigation showed that, for a given wall thickness, increased prestressing force increases the cracking load, initial wall stiffness, and ultimate failure load. The results have established a linear relationship between increased prestressing force and initial cracking load, initial wall stiffness, and ultimate failure load. The proposed model, which takes into account changes in wall stiffness after initial cracking of the wall, accurately predicts wall behaviour.Key words: masonry, prestressed, walls, strength, behaviour, uniform, pressure, experimental, analytical.

ISSN:0315-1468    

DOI:10.1139/l93-128

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Modifications are provided to a method previously published by the authors to determine lower fractile concrete strength from a limited number of tests. The modifications are aimed at giving estimates of the lower fractile strength that do not exceed the actual strength within a prescribed confidence limit. Another, much simpler, method is also developed to achieve the same goal. Through a large number of tests done through numerical simulations, it is demonstrated that both methods satisfy the required promise of giving safe-side results. However, the simpler method has been found to give better results, despite the simplicity of its application.Key words: compressive strength, concrete, limited test data, lower fractile strength, reliability.

ISSN:0315-1468    

DOI:10.1139/l93-129

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The 1988 Saguenay earthquake caused a large variety of geotechnical and structural damage. A total of 1927 claim files, most of which were submitted under a compensation program sponsored by the ministère de la Sécurité publique du Québec, Direction générale de la sécurité civile, have been studied. The results of this study are presented in terms of correlations between damage and geographical distribution, earthquake motion characteristics, soil conditions, and type of structures. Site effects are pointed out as one of the main causes of damage to buildings even at large distances from the epicentre.Key words: Saguenay earthquake, distribution of damage, geotechnical damage, structural damage, site effects.

ISSN:0315-1468    

DOI:10.1139/l93-130

出版商:NRC Research Press    

年代:1993

数据来源: NRC