Portland Cement Association Research Articles

The History of the Prestressing Strand Development Length Equation

A research study was conducted to determine the history of the strand development length equation. The strand development length equation was first introduced in the 1963 ACI Building Code and was adopted by AASHTO in 1973. The original research that formed the basis for the derivation of the strand development length equation was conducted at the Portland Cement Association (PCA) in the late 1950s and early 1960s. ACI Committee 423 derived and proposed the development length equation based on a reappraisal of the PCA results. The intent of the committee in deriving the development length equation was to provide a reasonable mean for the data points rather than a conservative estimate.

Method to Calculate the Fire Resistance of Reinforced Concrete Columns With Rectangular Cross Section

Joint studies between the National Research Council of Canada and the Portland Cement Association on reinforced concrete columns were started several years ago for the purpose of updating the information on fire resistance ratings for these columns in North American building codes. The studies include the development of mathematical models for the calculation of the fire resistance of columns of various sizes and shapes, as well as experimental studies. Among the columns examined were columns with rectangular cross section. In this paper, a method is described for the calculation of the fire resistance of reinforced concrete columns with such cross sections.

Modified moment distribution method for reinforced concrete equivalent frames

The purpose of this paper is to enhance and improve the moment distribution method used in solving reinforced concrete equivalent frame problems. In the analysis of a planar building frame which is a vertical cut from the building structure, the horizontal members are tee-sections (tee-beams) and vertical members are usually rectangular columns. When a moment is applied to the end of the tee-beam that creates compression stresses at the flange (top fibers), it can be observed that the tee-beam shows more flexural stiffness than applying the same magnitude of moment to create compression stress at the bottom fibers. In other words, its stiffness is different for applied clockwise and counterclockwise unit moments. In this study, the original moment distribution method (MDM) has been modified and the modified moment distribution method (MMDM) introduced and applied to the American Concrete Institute Equivalent Frame Method (ACI-EFM). The new technique applies different distribution factors for clockwise and counterclockwise moments at a joint and solves the problem accordingly. Several typical problems of reinforced concrete equivalent frame have been solved with the ACI-EFM, new MMDM, and also Portland Cement Association (PCA) computer software ‘Analysis and Design of Slab System’ (ADOSS). The results are found to be about 0–20% different. Considering the fact that the ACI-EFM is itself the approximate method, the results of the introduced method were observed to be close enough to use for preliminary analysis. It is also suitable for long-hand calculations.

Mechanism of plastic shrinkage cracking in portland cement and portland cement-silica fume paste and mortar

The objective of this paper is to discuss the mechanism of plastic shrinkage in portland cement and portland cement-silica fume paste and mortar. The effects of the three delivery forms of silica fume; asreceived powder, densified powder, and slurry, on plastic shrinkage are presented. In paste, plastic shrinkage is primarily related to development of tensile capillary pressure during drying. The higher the surface area of particles, the higher the tensile capillary pressure, and consequently, the more vulnerable the system would be to plastic shrinkage cracking. In mortar, plastic shrinkage is controlled by both capillary pressure in the paste and presence of fine aggregate particles. These particles serve to reduce cracking by (a) arresting cracks, and (b) refining the size and distribution of capillary pores. Data of rate of evaporation of water can only indicate degree of drying. Charts developed by Portland Cement Association to calculate the rate of evaporation can not predict whether or not plastic shrinkage cracks occur. A quantitative method could perhaps be developed to predict plastic shrinkage cracking.

Fire Resistance of Reinforced Concrete Columns: a Parametric Study

Experimental and theoretical studies were carried out to develop general methods for the prediction of the fire resistance of reinforced concrete columns. In these studies, which were carried out jointly between the National Research Council of Canada and the Portland Cement Association, 41 columns were tested. The parameters studied included load level, amount of steel reinforcement, effective length of column, concrete strength, moisture content, area and shape of cross section, aggregate type, axial restraint of ther mal expansion and load eccentricity. The experimentally discovered effects of these parameters are discussed.

Design aids for rectangular reinforced concrete sections under combined bending and axial forces

Design interaction diagrams, Pr–Mr, for rectangular reinforced concrete sections under combined bending and axial compression or tension forces in accordance with the current Canadian code are presented. The interest of the note is that the interaction diagrams eliminate the limitations of those in the Canadian Portland Cement Association Handbook. Their format can be extended to other section shapes and reinforcement layouts. Key words: Combined bending, design aids, interaction diagrams, rectangular sections, reinforced concrete, short columns, strength analysis.

The Portland Cement Association's Construction Technology Laboratories Library

The development of a special collection and the history of the organization it serves are described in this article dealing with the information facilities of a non-profit association, the Portland Cement Association/Construction Technology Laboratories. The unique classification scheme and special characteristics of the collection are discussed.

Status of Segmental Bridge Construction in Europe

Note: This paper is based on a presentation given at the Segmental Concrete Bridge Conference in Kansas City, Missouri, March 9-10, 1982. The Conference was sponsored by the Associated Reinforcing Bar Producers — CRSI, Federal Highway Administration, Portland Cement Association, Post-Tensioning Institute, and Prestressed Concrete Institute. struction methods will be discussed here: the span-by-span method (since 1960); the free cantilever method (cast in place since 1950; precast since 1962); and the incremental launching method (since 1962). Cable-stayed bridges will not be discussed here. This paper is intended to be a description of the actual situation in Europe (see Fig. 1). The survey is based upon a study of available literature and contacts with several key individuals in the European bridge industry. Where objective statistics are unavailable, the author's subjective observations and comments are offered. This review covers the situation in 18

Determination of Permissible Chloride Levels in Prestressed Concrete

NOTE: This is a Summary Report of an investigation on Research Project No. 2, Determination of Permissible Chloride Levels in Prestressed Concrete, sponsored by the Prestressed Concrete Institute. The study was carried out in the Construction Technology Laboratories, a Division of the Portland Cement Association, Skokie, Illinois. The full report (84 pp.) is available from PCI Headquarters upon request at a cost of $30 per copy; $15 to PCI members. was found that the threshold water soluble chloride limit above which corrosion of prestressed tendons occurred during and immediately after curing was between 0.11 and 0.17 percent by weight of cement. However, it was also found that under prolonged uniformly moist or dry conditions, active corrosion could not be sustained even in the presence of water soluble chloride contents as high as 0.9 to 1.0 percent by weight of cement. This study further demonstrated that, with chloride ion present, changes in exposure conditions, such as alternate drying and wetting, and differential or localized drying, can rapidly initiate corrosion. These changes had greater impact on corrosion processes than cement composition, curing method, or

Chemical Analysis of Portland Cement by Energy Dispersive X-Ray Fluorescence

Abstract X-ray fluorescence techniques have been applied for the analysis of portland cement for the past 20 or more years. During this time, applications have been developed primarily with wavelength spectrometers. In the past several years, development of solid state detectors has allowed energy dispersive X-ray fluorescence to detect and measure all the elements of interest in portland cement. Determination by energy dispersive X-ray fluorescence displays excellent precision, but a linear calibration of intensity versus concentration for many elements exhibits significant deviation from a straight line. Particle size effects that could cause errors in the calibration were minimized through fine grinding. The remaining factors responsible for nonlinear calibrations relate to interelement effects, which are usually considered as absorption and enhancement. The purpose of this investigation is to determine the interelement effects in portland cement and demonstrate the quantitative capabilities of energy dispersive X-ray fluorescence using certified National Bureau of Standards (NBS) portland cements as standard. An additional purpose is to demonstrate the application of empirical calculations for interelement effects in obtaining quantitative results utilizing Portland Cement Association check specimens as unknowns. Interelement effects in X-ray fluorescence are well documented with various techniques utilized. Many of these programs are complex and correct all elements for the presence of all other elements and require a large number of standards. The approach used by the author is an exponential model based on intensities of the interferring elements. Linear least squares fit of uncorrected intensities displayed absolute errors of 0.6% for alumina and silicon oxide to 1.0% for calcium oxide. Average deviations obtained following interelement corrections ranged from a low of 0.007% for potassium oxide to a high of 0.19% for calcium oxide. Analysis of each specimen consumed 200 s. The accuracy obtained by this method is well within the limits expected by the industry and the precision possible by alternate procedures.

Performance Approach in Determining Required Levels of Insulation in Concrete Roof Systems

S everal analytical and experimental investigations have been conducted at the Portland Cement Association and elsewherel-6 to quantify the effect of building thermal mass on heating and cooling loads. These investigations revealed that massive buildings, because of their ability to store and release large quantities of heat, require less insulation than lightweight buildings to achieve equivalent annual energy performance. Besides reducing annual energy consumption, mass was also observed to affect thermal performance in two other ways. First, peak heating and cooling loads were smaller in massive buildings than in low-mass buildings. This means that smaller heating and cooling equipment can be used. Second, peak heating and cooling loads were delayed for several hours. During summer, this means that peak loads occur in the evening when outside air can be utilized to cool the inside space instead of operating air-conditioning equipment. Most of the research done to date has dealt with the effect of thermal mass in walls. Little work has been done to determine the effect of thermal mass in roofs. If reductions in required levels of insulation can be .justified for heavy roof con-

Pavement Strength Rating Methods as Viewed by Airframes Manufacturers

The effects of allowable aircraft payload of variations in tire pressure, axle spacing, and wheel spacing were explored using four important pavement design/rating methods. The methods used were the California Bearing Ratio (CBR) (SEFL165A variation) method (flexible pavement), the Load Classification Number (LCN) method (flexible and rigid pavement) and the Portland Cement Association method (rigid pavement). The effects on payload were determined for both dual and dual tandem type loading gear on pavements of an assumed strength. This analysis was followed by a study of the payload effects of variations on pavement parameters such as subgrade strength or pavement thickness in allowable aircraft payload given a particular aircraft configuration. Based upon the foregoing analysis five airframe manufacturer's objectives for new pavement design methods were stated.

Design of Reinforced Concrete for Fatigue

An extensive experimental investigation to determine the fatigue strength of deformed reinforcing bars was recently completed by the Portland Cement Association. This work was sponsored in part by the National Cooperative Highway Research Program (NCHRP). The experimental program was carried out with each test bar embedded as the main reinforcing element within a concrete beam. Test variables included size of beam, size of bar, grade of bar, bar deformation geometry, minimum stress, and stress range. A total of 353 tests were carried out. This paper describes the test program and the design provisions developed by statistical procedures from the test data. An example of the application of the provision in bridge design is presented in an appendix.

Panorámica actual de los pavimentos de hormigón en los Estados Unidos

This article includes the most interesting developments in the field of concrete pavements in the United States, gathered during a trip by a group of Spanish engineers on the occasion of the first International Congress on Concrete Pavement Projects, held at Purdue University (Indiana). The trip was completed with a series of technical visits, among which those to the Portland Cement Association, the California Highways Laboratory and several highways, both in use as well as under construction, in that State, deserve special mention. As is well known, California has developed its own technique for hard roadbeds which has been applied in some recent works in Spain.

Computer program developments by the Portland Cement Association

At the present time less than half of the design and design/construction firms use computers. Although the cost of a terminal or even a small computer installation is within reach of every such firm, very few can afford to develop a program which will make the computer do their work. Hence, PCA decided about five years ago to undertake the programming effort needed for the design of concrete structures and pavements. A group of programs for the IBM 1130 was released in 1967-68 and included analysis and design programs for airport pavements, concrete columns, flat plates, continuous frames, bridges, shearwalls, central core and exterior column supported floor systems, and wall-beam frames. A new group of programs was released in 1971. These programs, to be discussed in more detail' include: an updated and enlarged version of the analysis and design of flat-plate floors; analysis and design of concrete columns and column stacks; quantity and cost estimating for building frames; analysis of frameshearwall structures; analysis and design of footings and foundation mats; and preliminary analysis of multi-center arch dams. All these programs were developed for the IBM 1130 and some will be converted to other machines. The provisions of the 1971 ACI Building Code were carefully followed. A comprehensive maintenance service is provided for the 1971 PCA programs, providing any assistance or information that may be needed by the users and also providing for the distribution of information obtained from users.

Some aspects of structural fire endurance of concrete

Thoroughly convinced that the fire resistance of concrete follows laws that can be expressed in terms of engineering principles, the Portland Cement Association has developed design methods that can be used to predict the fire endurance of some common structural elements. The Association feels that it is only a matter of a few years before design procedures are developed for all common structural elements.

History And Development Of Concrete Pavement Design

Concrete pavement design in the United States started with the first concrete street built in 1892, but really became a science following the Bates Road Test. Since then, Westergaard, Pickett, the Arlington tests, research at the Portland Cement Association Laboratory, field studies of pavement performance and more recently the AASHO Road Test, have all been factors in the development of current (1963) pavement design methods. The determination of pavement thickness, the proper jointing and subbase requirements must all be related to traffic, subgrade climate and local conditions to provide an adequate economical design. Continuous reinforcing and prestressing are newer design concepts being used by several states in experimental or demonstration sections. The importance of subbase design to pavement performance is related to pumping, expansive soils and frost effects. Current design recommendations are summarized.

Phase I Report on Folded Plate Construction

The various methods of analysis of folded plates, proposed to 1963, are reviewed and summarized. First consideration goes to the simple beam theories that neglect the effect of relative joint displacement, as in the original work by Ehlers and Craemer in Germany in the 1930's, that was subsequently introduced in the United States by Winter and Pei. This report then evaluates the more exact methods of analysis correcting for relative joint displacement subsequently developed by Gruber, Vlassov, Gaafar, Simpson, and Yitzhaki. Finally, the elasticity approach of Goldberg and Leve is considered. As a result of the study, the Committee recommends the use of the ordinary theory with correction for relative joint displacements. Methods in this acceptable category include those of Vlassov, Gaafar, Gaafar as modified by Simpson, Portland Cement Association Bulletin #3, and, finally, Yitzhaki. The report summarizes a method of analysis based on Gaafar's original paper and includes a numerical example for greater clarity. The Committee has also sponsored and recommends an article on folded plate analysis by Yitzhaki. A very complete Bibliography of the subject of folded plates both in English and other languages is included.

Research on Prestressed Concrete at the Portland Cement Association

Research on Prestressed Concrete at the Portland Cement Association

The determination of the compressive stress-strain properties of concrete in flexure

Summary A description is given of an apparatus for the determination of the compressive stress-strain properties of concrete in flexure, based on the principle developed by the Portland Cement Association, The apparatus can be used in a standard universal testing machine with little or no modification. The relatively small size of the test specimen is convenient and economical, especially when materials for models are being tested. A theoretical analysis is developed which enables the distribution of the stress in the concrete to be determined across the section without reference to the magnitude of the strain. If a value is assumed/or the strain at any one stage of loading, the theoretical strains at all other stages may be determined. Comparison is made between the theoretical strains and the experimental strains obtained during a test on a concrete prism.