Showing papers in "Pci Journal in 1980"

Shear and torsion design of prestressed and non prestressed concrete beams

Abstract: D esign procedures which are based on rational models rather than empirical equations enable the engineer to develop a better understanding of actual structural behavior. In this regard, the unsatisfactory nature of current shear and torsion design procedtires is evident if the ACI Code' chapter on shear and torsion is compared with the ACI chapter on flexure and axial load. In the flexure and axial load chapter a rational, simple, general method is explained in a few paragraphs of text. On the other hand, the shear and torsion chapter consists of a collection of complex, restrictive, empirical equations which, while leading to safe designs, lacks an understandable central philosophy. This lack, in the opinion of the authors, is the source of many of the complaints which arise from the engineering profession about modern design codes becoming unworkably complicated. In this paper an attempt is made to present procedures based on rational models which enable members containing web rein-

Friction Joints for Seismic Control of Large Panel Structures

Abstract: 'The research reported herein was conducted while Dr. Pall was Research Associate at Centre for Building Studies, Concordia University, Montreal, Quebec, In steelframed buildings or cast-in-place concrete structures, reliance is placed on the ductility of the structure to dissipate energy while undergoing inelastic deformations. In large panel construction, it is difficult to develop flexural ductility due to the limited continuity in the vertical steel, and although in some European systems the precast panels are jointed to give vertical continuity, the suitability in general of this type of construction for seismic regions is often questioned. The current seismic codes

Precast Concrete Connections With Embedded Steel Members

Abstract: C onnections incorporating embedded structural steel members serving as haunches or brackets have been used for many years in precast concrete construction. Fig. 1 illustrates the application of embedded structural members in a beam-column connection and in a precast panel connection. The advantages of these types of connections are listed below: (a) In contrast to corbel and headed stud precast connections, the strength of connections with embedded structural steel members is not dependent on the strength of welds.

Creep and Shrinkage Characterisation for Analyzing Prestressed Concrete Structures

Abstract: D eformations due to creep and shrinkage are normally several times larger than elastic deformations in concrete structures. Frequently, these deformations cause excessive cracking and deflections or possible failure with an inherent loss in serviceability, durability and long-time safety of concrete structures. Thus, there is an urgent need for a reliable method to predict creep and shrinkage, especially for slender prestressed concrete structure's. Recently, we have witnessed efforts to introduce creep and shrinkage into design recommendations 1,2,3 and to develop more realistic prediction formulas.4 Over the last decade, however, the subject has been plagued by persistent disagreement as to what is the proper and optimal formulation to be used.s8 Although several pertinent conclusions have been drawn from theoretical arguments, 8 we shall deliberately leave them out. The most relevant and convincing argument is, of course, the experimental evidence and how well the data correlate with the actual behavior of existing structure s. Although this has not been generally realized, vast experimental information on creep and shrinkage has already been accumulated in the literature. 4 Unfortunately, the provisions of a recent international model code were supported by very limited comparisons with test data, selected somewhat arbitrarily. This was under-

Reliability of partially prestressed beams at serviceability limit states

Abstract: A systematic investigation of the reliability of partially prestressed concrete beams at six serviceability limit states is described. The evaluation of reliability is based on the first order, second moment method. The code calibration method was used to determine the reliability index (or safety index) for 64 different beam designs. The effects of cross-sectional shape, span length, magnitude of live load and degree of partial prestressing were also determined.

Ductility of Prestressed and Partially Prestressed Concrete Beam Sections

Abstract: D analyses of structures responding elastically to ground motions recorded during severe earthquakes have shown that the theoretical response inertia loads are generally significantly greater than the static design lateral loads recommended by codes. Hence, structures designed for the lateral earthquake loads recommended by codes can only survive severe earthquakes if they have sufficient ductility to absorb and dissipate seismic energy by inelastic deformations.'-" Prestressed concrete has been widely used for structures carrying gravity loads but has not had the same acceptance for use in structural systems which resist seismic loading. Part of this caution in the use of prestressed concrete for earthquake resistant structures has been due to the paucity of experimental and theoretical studies of prestressed concrete structures subjected to seismic type loading. A survey of the research which has been conducted on the seismic resistance of prestressed concrete was published in 1970. 9 Parmeio and Hawkins" have published more recent reviews of the state of the art of seismic resistance of prestressed and precast concrete. There has been a lack of detailed building code provisions in the United States for the seismic design of prestressed and precast concrete. For example, the ACI Code,' the SEAOC recommendations, 2 the Uniform Building Code, 3 and the tentative provisions of the ATC 4 all contain special provisions for the seismic design of cast-in-place reinforced concrete structures, but do not have

Construction of Long Key Bridge

Abstract: The superstructure was erected in less than 12 months saving valuable construction time and money for all parties concerned. In the closing month of the project a record five spans of 118 ft (36 m) each, i.e., a total of 590 ft (180 m) of completed bridge deck, were erected. This rate of erection is indicative of the efficiency that can be gained using precast prestressed segmental construction and particularly span-byspan erection.

Full-Scale Tests on Horizontal Joints of Large Panel Precast Concrete Buildings

Abstract: S ince the 1968 "progressive collapse" failure of a precast concrete apartment tower at Ronan Point, England,' much attention has been given to the implementation of specific code regulations governing the construction of large panel precast concrete buildings. Many studies'' have arrived at the conclusion that the horizontal joint is the weakest link in this type of construction. The problem arises from the fact that, unlike cast-in-place concrete structures, a non-monolithic construction results from connecting precast panels at the site to form various joints. On the other hand, the reduction in time, labor and hence cost, resulting from factory controlled mass production of large panel structural components is a major factor in their steadily increasing use in residential construction. The large panel building consists basically of precast wall panels with floors and roofs of precast elements or slabs that are usually hollow and prestressed, with the walls and slabs transferring the loads directly to the foundation without intermediate frames. In some cases, the strength and safety of such structures will depend on the connections between the various precast components. The purpose of the connection is to transfer efficiently the internal forces from one element to another. Thus, the strength of adjoining elements can be fully utilized only if the efficiency of the connection, in terms of strength and ductility, is very high. Tests on horizontal joints under increasing gravity loads have been conducted in Poland,2,8,9 France,",11 and the Soviet Union. 12-" These results are, however, for joint geometries and

Developing Structural Integrity in Bearing Wall Buildings

Abstract: The prestressed concrete industry provides large volumes of precast floor and wall units for use in bearing wall buildings. In addition to the wide interest in precast panel bearing wall buildings, the industry has a vital interest in brick and concrete masonry bearing wall buildings which often utilize precast prestressed concrete floor units. For decades, relatively little engineering research and development attention was paid to bearing wall construction. It is heartening to note that the Prestressed Concrete Institute has taken a lead in this important

Efficient Splicing Technique for Precast Prestressed Concrete Piles

Abstract: F requently it is necessary, or at least desirable, to splice precast prestressed concrete piles. The advantages of reducing the lengths of long piles into shorter sections are that it. I. Results in easier handling during transportation and in the pile driver leads. 2. Minimizes the chance of cracking during handling. 3. Permits greater flexibility in determining required length of pile. 4, Allows extensions of piles when necessary. 5. Reduces cost in transportation. 6. Simplifies storage at the precasting yard and at the construction site. These advantages can only be achieved if the splice is economicaI, can develop the structural. capacity of the pile section and the connection can be made quickly and without the requirements of special trade skills in the field. This report presents the results of an extensive investigation of the structural capacity of a wedge-type splice for 12-in. (305 mm) square precast prestressed concrete piles.'

Economics and Use of Lightweight Concrete in Prestressed Structures

Abstract: •I n many structures it is economically advantageous to use lightweight concrete in place of normal weight concrete. This economy is generally reflected in the foundation design due to a 20 to 30 percent lighter dead load in the superstructure. The degree of savings varies greatly depending on: (a) Site conditions which dictate the type of superstructure design. (b) Availability and cost of lightweight aggregates. (c) Cost of high tensile steel (if the concrete is prestressed) which may be required to counteract the relatively large prestress losses in the lightweight concrete induced by creep and shrinkage. It should be noted that the properties of lightweight concrete vary significantly from place to place depending on the source and manufacture of the aggregate. However, once the design engineer is aware and familiar with the particular product, he can predict fairly accurately the creep and shrinkage characteristics of the lightweight concrete in the design of his structure. With this recognition, the design should be no more difficult than that for normal weight concrete. Therefore, it is good practice to investigate the use of lightweight concrete in the preliminary design stages of any structure. Two recent notable examples showing economy in cast-in-place structures built with lightweight concrete in America are the Napa River Bridge and the Parrotts Ferry Bridge, in California. The latter bridge has a center span of 640 11 (195 m). While lightweight concrete is often found economical in cast-in-place structures, it is found that structures employing precast elements are usually economical in lightweight concrete but for different reasons. Precast concrete structures may also

Construction techniques for segmental concrete bridges

Abstract: The author discusses the various segment casting methods and erection techniques for constructing segmental concrete bridges. Particular attention is paid to geometry control procedures.

Design features and prestressing aspects of long key bridge

Abstract: The author describes the principal design features of Long Key highway bridge in Florida together with the production and erection of precast segments and post-tensioning operations.

Prestressed concrete in transportation systems

Abstract: The authors present a literature review of the current and potential use of precast prestressed concrete for pavements, railroad track systems and transit guideways.

The Islington Avenue Bridge

Abstract: NOTE: The author was responsible for designing the Bear River Bridge, an eight-span nearly 2000-ft (610 m) long precast prestressed segmental structure completed in December 1972 near Digby, Nova Scotia. Although a few shortspan segmental bridges were built in Canada in the sixties, the Bear River Bridge was the first major bridge built in North America using the precast segmental technique. The bridge played a significant role in the introduction of segmental construction in America. In 1973, Mr. Lovell was honored by the Prestressed Concrete Institute in the PCI Awards Program for his design of the Bear River Bridge—EDITOR .that run from the shores of'Lake Ontario, right through the city, into the open country beyond (Fig. 1). The roadway differs from others in that its access to the peripheral Lakeshore Boulevard was prevented by a large railyard belonging to Canadian National Railways. Traffic predictions were sufficient to convince the planners that it would be prudent to provide this access, before the adjacent parallel streets became overloaded, and that the best route would be right across the yard at one of its widest points. This choice was not a popular one with Canadian National (CN). The railway, quite understandably, did not welcome interference with their operations in an area that was solely theirs and where there had been no road crossing

Alternate Designs for Long Span Bridges

Abstract: C urrently, American bridge engineers have been acquainting themselves with European construction methods and adapting these techniques to United States practice. Europe's dominance in the bridge field was really the result of its post World War II reconstruction efforts in which hundreds of structures had to be replaced rapidly in the face of steel shortages, scarcity of manpower and escalating costs. With Europe's reconstruction over, these construction systems are seeking new markets, and we in the United States have the good opportunity to avail ourselves of these methods if and when they fit our economy. The current interest in bridges is reminiscent of the sixties when European building systems made their entry into

Strength of Continuous Horizontally Curved Post-Tensioned Beams

Abstract: C ontinuous prestressed reinforced concrete beams curved in plan are used in highway bridges' and in elevated guideways for transit vehicles. 2 The precracking response of such beams, with particular reference to the effects of prestressing, has been studied theoretically by Campbell and Chitnuyanondh,3 but no work has been reported on their post-cracking response. However, the post-cracking response of curved non-prestressed

HRWR Admixtures in Architectural Prestressed and Precast Concrete Applications

Abstract: The term "architectural concrete" represents any concrete used to create a special visual effect.' Architectural concretes are used to create economical, visually pleasing facades, and structural elements which will require little or no maintenance. Use of high-range water-reducing admixtures (HRWR's)* in architectural prestressed and precast concretes facilitates production of complex and delicate member shapes, economic conservation of building materials, and achieving a higher quality concrete. Contemporary applications of HRWR's in architectural concretes include precast girder sections, exposed aggregate panels, and the cast-in-place Vail Pass bridges. HRWR's are highly effective chemical admixtures commonly used to reduce mix water contents and increase workability. HRWR's were first reported and used as early as 1932 2 but did not come into extensive use until about 15 years ago. The chemical characteristics of HRWR's and their use in structural concretes has been discussed in detail elsewhere, and hence will not be repeated here.3 The types and proportions of materials used in architectural concretes are closely controlled or virtually dictated by requirements for a specific, consistent concrete color and surface texture. Fortunately, therefore, pro-

Segmentally Constructed Prestressed Concrete Hyperboloid Cooling Tower

Abstract: I many large capacity power plant facilities, the natural draft cooling tower in the fonn of a thin shell of revolution is often required to di~sipate a large amount of heat. Construction of such large reinforced concrete natural draft cooling towers is expensive and time-consuming. The cost of the structure is strongly influenced by the construction technique. A possible means of reducing this cost is the technique of segmental construction in which the benefits of both precasting and post-tensioning can be combined together advantageously. This paper presents the concept of segmental construction as applied to the hyperboloid natural draft cooling tower and the method of analysis and design which have been developed in detail by Rizkalla.1 The structural behavior under gravity load, wind pressure and prestressing force is examined. The analysis is based on the finite element method using a truncated conical shell as the basic element. A numerical example is included to illustrate the design method. A conservative cost estimate indicates that there is a potential saving up to 40 percent of the cost of the tower (excluding foundations and columns) by means of segmental construction. Tower Geometry

Precast Prestressed Wall System Used for Water Storage Reservoir

Abstract: T he requirements set forth by the City of Regina for the North West Reservoir specified a desired reservoir capacity of approximately 10 million imperial gallons (45 1/2 million liters)" with a diameter not less than 220 ft (67.1 m) nor more than 230 ft (70.1 m). A further requirement was that sensitive attention be given to aesthetic treatment and landscaping so that the structure would harmonize with the existing homes and proposed freeway which border the project site. Design was started in April 1978 with a target of placing the reservoir in service before the summer of 1979.