Institute For Research In Construction Research Articles

Fiber Optics for Evaluation of Pavement Reinforcement Materials in Resisting Reflection Cracking

A major maintenance problem of pavement is the reflection cracking of pavement overlays at the location of joints and cracks in the underlayers. Pavement reinforcement materials (PRM) are used to reinforce the asphalt concrete (AC) overlay to delay reflection cracking. Assessing the effectiveness of PRM in limiting reflection cracking can be achieved by direct measurement of strain distribution within the PRM and AC overlay. A fiber-optic sensor is the only alternative that is compatible with the fiberglass structure of the PRM used in this study and, therefore, is used to measure strain within the PRM. A program of investigation, developed at the Institute for Research in Construction of the National Research Council Canada, aims at studying the state of stress leading to joint opening in pavement layers and assessing the effectiveness of PRM in reducing such cracks through monitoring the performance of PRM using embedded fiber-optic strain sensors. The investigation involves both laboratory testing and ...

Pilot study of speech quality in small rooms : Bradley, J.S. Institute for Research in Construction, National Research Council, Ottawa, Canada K1A OR6.

Pilot study of speech quality in small rooms : Bradley, J.S. Institute for Research in Construction, National Research Council, Ottawa, Canada K1A OR6.

Evaluation of the fire resistance of compression members using mathematical models

This paper deals with the research work being conducted at the Institute for Research in Construction of the National Research Council of Canada to Develop mathematical models for the calculation of the fire resistance of compression members, such as concrete walls, columns made with steel and concrete and composite steel-concrete columns. The various steps in the calculation procedure, namely the calculation of fire temperature and the thermal and structural response of the members, are discussed. Comparisons of results obtained with the models and test results are also shown for various types of columns.

Image Analysis and the Characterization of Cellular Plastics

An evaluation of sprayed polyurethane foams manufactured with alternative blowing agents is being performed under a joint research program be tween the Society of the Plastics Industry of Canada and the Institute for Research in Construction. Image analysis, or the computer-aided quantification of the cell structure of the foams is a part of this evaluation. Samples of foams prepared using the same polymer with different blowing agents were examined under a low-power microscope. The blowing agents used in prepar ing the foam samples were: CFC-11, CFC-11 + 1% water, HCFC-123, HCFC- 141b, and a blend of the two HCFCs with 0.5% water. With the aid of a computer, histograms were obtained of the distribution of areas and of aspect ratios for win dows undamaged in the sectioning process as well as for cells that were opened during the sectioning of the foams. A comparison of these histograms allows one to differentiate the foams. In addition, reasonable estimates of average cell size can be made from measurements of cross-sectional areas of cell windows and of opened cells. Thickness of struts, i.e., the edges where two cell windows intersect, were esti mated by the use of a thinning technique on strut images, and estimates of cell wall thickness were made using an optical interference technique.

Measuring degrees of combustibility using an OSU apparatus and oxygen-depletion principle

Responding to a demand from the code writing committees for a test capable of quantitatively measuring low degrees of combustibility instead of the pass/fail of the existing non-combustibility test, the Institute for Research in Construction has developed a degrees-of-combustibility test. A version of the Ohio State University (OSU) heat release rate (HRR) apparatus, with Federal Aviation Administration modifications, has been further modified by adding an oxygen-measuring system and by reducing the airflow rate. HRR values of four sample materials have been measured, the peak rates of which ranged from 8 to 300 kW/m 2. For measuring small values of HRR, an enclosed system of OSU apparatus is shown to have advantages over the open system of the cone calorimeter. In the OSU apparatus, by reducing airflow to combustion, the oxygen depletion can be increased to increase the sensitivity and accuracy of HRR measurement.

A Method To Predict the Fire Resistance of Steel Building Columns

Using the mathematical model described earlier, the temperatures of the steel of Column No. 1 were calculated. In the calculation, the thermal properties of the steel, vermiculite board insulation and the specifics of the column and furnace, given in Appendix A, were used. Because the thermal properties of the insulation of the other columns were not known, no temperature calculations were made for these columns. The results for Column No. 1 are given in Fig. 7 where the calculated average steel temperatures are compared with those measured. As also shown in previous studies, it is possible, using the mathematical model, to predict the steel temperatures with high accuracy, if the thermal properties of the insulation are known. In this case the thermal properties of the insulation were determined at the National Fire Laboratory, Institute for Research in Construction, NRCC.40 The temperatures are to some extent also dependent on the heat transfer characteristics of the furnace. If the heat transfer is high, however (which is the case for the furnace in which the column was tested), variations in heat transfer have only a small effect on the temperature of the steel.

Fire exposure to exterior walls and flame spread on combustible cladding

A segment of the on-going research program on fire spread via exterior walls conducted at the Institute for Research in Construction of the National Research Council of Canada is described. The research includes full-scale experimental studies of fire exposure to exterior walls, fire hazards associated with the use of combustible materials, and the development of new test methods for assessing the flammability of combustible cladding. Correlations between the results of a new full-scale test and standard flame spread tests (Steiner tunnel test, radiant panel test, roof deck test) were investigated. A prototype of a reduced-scale test, the vertical channel test, is described. It was found that, at present, the full-scale test is the most appropriate method to evaluate the fire hazards of combustible wall assemblies.

The strength and testing of window glass

This paper presents some of the background to the new Canadian General Standards Board (CGSB) standard on the structural design of glass for buildings. It also describes strength testing of window glass at the Institute for Research in Construction of the National Research Council of Canada using three quite different testing machines. (i) A dynamic glass testing rig, with a large 2.35 m diameter piston, applies dynamic air pressures to large panes of glass in the vertical position. Results of 107 tests to failure show the considerable effect of loading rate on strength. (ii) A loading table applies linearly increasing pressures to panes of glass in the horizontal position. Results from 47 fifteen-year-old windows confirm assumptions about the deterioration of strength with in-service use in the new CGSB standard on the structural design of glass for buildings. (iii) A ring-on-ring tester applies linearly increasing loads to small 180 × 180 mm samples; the equivalent of coupon tests for steel or cylinder tests for concrete. The resulting uniform tensile stress fields avoid failures starting at the edges of the samples. Some results are given. Testing provides the basis for the structural design of glass cladding as it does for other structural materials. A great deal more testing of window glass is required. Key words: glass strength, window strength, testing, strength deterioration, rate effect, dynamic loading.

Research institutions dealing with cold regions science and technology in Harbin, Heilongjiang province of China

Dr. Daisuke Kuroiwa (former Director of the Institute of Low Temperature Science, Hokkaido University, Japan) visited Harbin, Beijing, Lanzhou and Xian in China by invitation of the Chinese Academy of Science and the Japan Society of Promotion of Science from 4 2 0 October 1981. The major purpose of this trip was to visit research institutions dealing with cold regions sdence and technology and to attend the Second Chinese Conference on Permafrost which was held in Lanzhou, 12-18 October 1981. Since detailed information on the latter conference has been published by two attendees, J. Brown and Y.-C. Yen, as CRREL Special Report 82-3, 1982, this short note gives some information on research into frost-heaving and frozen ground which is being conducted in several institutes in Harbin, Heilongjiang Province. Harbin is the capital of the province, it is an industrial city with a population of approximately two million people. The latitude of this city is 45.5 ° North and the climate in winter is very cold. The average values of air temperature and precipitation taken over three months in mid-winter are -16.6°C and 5 mm, respectively, but the annual mean air temperature is +3.3°C because of fairly high values in summer. The severe cold and low values of precipitation in winter create seasonal freezing of soils. The permafrost in Heilongjiang province is unevenly distributed in the mountainous regions of DaHinggan Ling and near the border between the U.S.S.R. and China. In the: Harbin area, the surface soil consists of silt containing about 20% clay, but lower layers 15 m below the surface are composed of fine sand which was deposited by old floods of the Songhua Jiang. The level of ground water is usually 80-90 cm from the surface, but it descends below 1 m in depth when the surface soft begins to freeze in early November. The freezing of soil lasts until early April and the thickness of frozen ground reaches a maximum of 170-200 em depth around March 20th. The surface soil starts melting at the beginning of April and frost completely disappears around June 20th. On October 6th Dr. Kuroiwa arrived at Harbin Airport where it was sleeting slightly, but he was warmly welcomed by Mr. Xu Shaoxin, the director of the Water Conservancy Research Institute. Mr. Xu Shaoxin first took Dr. Kuroiwa to the Harbin Architectural and Civil Engineering Institute, to show research activities on frozen ground. This Institute consists of five departments: architecture, building engineering, city construction, building materials and mechanical, including electrical sections. In 1959 the institute detached from the parent institute, Harbin Institute of Technology, to become an independent organization. It has 1728 undergraduate students and 58 postgraduates, with a faculty of 560, including nearly 90 professors. Many studies on how to protect buildings from severe cold and frost-hearings of soil have been conducted in conjunction with the education and training of students and engineers. In the cold room of this institute, experiments on brittle failure, on fatigue of reinforcing steel bars and on frost-heaving force under applied pressure have been performed. There are major research institutions on cold regions sdance and technology in Harbin: the Low Temperature Construction Research Institute, the Architectural Materials Science Research Institute and the Water Conservancy Science Research Institute. These institutes are attached directly to Heilong-

A Contact Problem In Poroelasticity

The paper examines the axisymmetric problem of the indentation of poroelastic layer which rests in contact with a rough rigid and impermeable base. The indenting punch has a circular planform and the smooth contact is assumed to be either permeable or impermeable. The paper develops the integral equations governing the problem for the generalized case where the the pore-fluid is considered to be compressible. Numerical results are presented to illustrated the influence of layer thickness, drainage conditions, and the compressibility characteristics of the pore fluid on the degree of consolidation settlement of the indenting punch. INTRODUCTION The classical theory of poroelasticity which is applicable to the study of the mechanics of deformable fluid saturated porous medium was first developed by Biot [5]. This theory has been widely applied to the study of various loading and contact problems associated with halfspace and infinite space regions. A majority of these discussions have focussed on the evaluation of the response of the poroelastic medium which is saturated with an incompressible pore fluid. In this paper, attention is focussed on the problem of the indentation of a poroelastic layer by a smooth rigid circular punch. The term thin is intended to signify a layer thickness which is smaller than the diameter of the indenting circular punch. The punch is in smooth contact with the poroelastic layer which exhibits either permeable or impermeable pore pressure boundary conditions over the entire surface. The layer is underlain by an impermeable rigid base 1 Currently at The Infrastructure Laboratory, Institute for Research in Construction, National Research Council of Canada, Ottawa, Ontario, Canada K1A OR6 Transactions on Engineering Sciences vol 1, © 1993 WIT Press, www.witpress.com, ISSN 1743-3533 286 Contact Mechanics and the displacement contact conditions are considered to be adhesive (Figure 1). The paper summarizes the integral equations governing the mixed boundary value problems associated with boundary variables in the Laplace transform domain. The paper illustrates the influences of the relative thickness of the consolidating layer and the Poisson's ratios of the pore fluid on the degree of the consolidation of the poroelastic layer. A permeable or impermeable surface A rigid circular smooth indentor t A poroelastic layer saturated with a compressible pore fluid xA rough rigid and impermeable base Figure 1. An axisymmetric contact problem in poroelasticity GOVERNING EQUATIONS In the ensuing we shall present a brief account of the governing equations referred to a Cartesian tensor notation. The constitutive equations governing the quasi-static response of a poroelastic medium, which consists of an isotropic poroelastic soil skeleton saturated with a compressible pore fluid takes the forms (1) 3(1 2r/,) where cr^ is the total stress tensor, p is the pore fluid pressure, Cij are the soil skeleton strains defined by £.. = !(„..+„,.) (2) where Ui are the corresponding displacement components. In the absence of body forces, the quasi-static equations of equilibrium take the forms °ij,i = 0 (3) The equations governing quasi-static fluid flow are defined by Darcy's law which take the form %, = -/W (4) Transactions on Engineering Sciences vol 1, © 1993 WIT Press, www.witpress.com, ISSN 1743-3533 Contact Mechanics 287 and the continuity equation associated with quasi-static fluid flow is The above governing equations are characterized by the five basic material parameters which are represented by the drained and undrained Poisson's ratios v and z/% respectively, the shear modulus //, Skempton's [7] pore pressure coefficient B, and the K (=fc/7 , where k is the coefficient of permeability and 7%, is the unit weight of pore fluid). From the consideration of the positive definiteness of a strain energy potential, it can be shown that the material parameters should satisfy the following thermodynamic constraints: /j > 0, 0 0 (see. e.g., Rice and Cleary [6]). Avoiding details, it can be shown (Yue [3]) that the following sets of solution representations exist for the field variables in a linear, isotropic, poroelastic medium of layer extent saturated with a compressible pore fluid. In either the temporal domain or the Laplace transform domain and in the cylindrical coordinate systems (r, #, z) and (p, y, z), we have % roc r2ir } u(r, 0,z,t) = — I I -TlawK 27T Jo JQ p I roc /-27T ,(r, 0, z, f ) = — / / n, rA 2?r Vo Vo