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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-10 of 16 Abstracts search results
April 1, 1986
John G. H. Harrison
The new World Headquarters Building for Elf Aquitaine in Paris, France was designed by a Canadian architectural firm who won the commission in an invited design competition in 1979. Work on construction documents began in Paris in January 1981 and construction began early in 1982. Bouyges, the contractor for the reinforced concrete structure, undertook extensive studies to develop a special formwork system for the facade structure since there is little if any background of experience to draw on in France in the construction of high-rise buildings. At 48 stories this was a building of very significant height and would require a whole new approach. The result of these studies was a very ingenious system of facade forms, fabricated entirely in steel and consisting of column and beam forms, complete with integrated working platforms, access ladders, and 2 story high protective mesh screens. A system of alignment nibs insured faithful adherence to the allowable tolerances both vertically and horizontally. Although the research and capital costs were significant, substantial cost savings were nevertheless made in the erection of the structure both in time and labor thus confirming the validity of this formwork design.
In the last systematic review of reinforced concrete column costs in 1973, ACI Committee 439 limited its cost comparisons to concrete strengths from 4000 to 8000 psi and reinforcing steels with design yield of 60,000 psi with speculative estimates of steel with 80,000 psi yield. Design then was based upon the 1971 ACI Building Code. At that time the leading structural engineers had successfully utilized concrete with f'c = 9000 psi under the current code. A number of general conclusions on costs were presented as trends. To bring this review of reinforced concrete column costs up to date, we must consider changes in code requirements, more general availability of still higher strength concretes, superplasticizer admixtures, building code limitations and general lack of economy in a Grade 80 reinforcement, and later laboratory testing and field research on properties and performance of high-strength concretes. A recent detailed comparative cost study of reinforced concrete columns which resulted in appreciable cost savings in a Chicago high-rise building, reinforces some of the 1973 report under conditions today. As might be expected in dealing with the numerous variables involved in comparative column design costs, the detailed study was made effective only through a computer program. The essential features of this program are described in detail in the CRSI Bulletin.
Stephen Timpson and James M. Henry
The Westbury Condominium Project is a forty story reinforced concrete tower surrounded by a five-story garage. The horizontal dimensions of the tower are only 41 x 41 ft. The design and construction management team worked within rigid parking, set-back, and height restrictions to produce a marketable building design on a difficult site in a heavily developed area. The contractor used time-lapse film analysis, video observation and an ongoing work crew training and motivation program to achieve a sustained 1.25 working day per tower floor construction cycle.
James M. Shilstone, Jr..
Quality management is described as a system whereby technology is managed in such a manner as to result in concrete construction being accomplished within the minimum time. Quality is measurable and stands for conformance. Goodness does not relate. Only the contractor doing the work can manage the quality of the work. He cannot rely upon owner inspection. Quality management is performed by other than members of the operating construction team. The forces leading to current pressures for rapid construction are outlined. The sources of problems, their identification and correction procedures are traced. Findings of the National Conference on Quality Assurance in the Building Community are related to the subject. Technology of concrete is discussed and related to accelerated construction. Subjects include: contract documents, national standards, reinforcing steel, formwork, placement, compaction, testing and management techniques.
N. J. Gardner and Chi-Seng Chan
Multistory reinforced concrete structures are generally constructed using one level of shores and multiple levels of reshores. The stripping schedule is to completely strip a bay of shores before reshoring. Reshoring results in high-early-age construction loads being applied to the immature slab structures. Preshoring, or scheduled reshoring, is an attempt to reduce the adverse effects of clear bay reshoring by reducing the area stripped before reshoring. The load-strength ratio in preshored construction is little different to reshored construction but the loads are applied later which will reduce creep deflection effects. Using 2D and 3D models the slab, shore, and reshore loads were calculated for preshored construction. The advantage of preshoring is that the unsupported span lengths are reduced thus reducing slab deflections. The disadvantage of preshoring is that to realize the benefits close control of the construction process is needed.
W.. Thomas Scott
As the speed of construction of concrete frame structures has increased and the sophistication of design has improved, there has been an increased need for a more thorough understanding as to the way construction loads are disbursed into the structure. During the 60's and 70's, several designers and researchers proposed methods of analyzing the loads in multistory structures during construction. A computer program employing one of these methods has been developed. In the 1982 PCA conference the author used the results of this proqram to show how the number of levels of equipment, cycle time, and attained concrete strength affected the number of levels of reshores required. This paper describes in detail the process used to calculate the reshorinq requirements for a 35 story flat plate structure built using a three day construction cycle. The discussion includes the practical implications of providing reshorinq for a mild steel structure. The hand calculation procedure presented parallels the computer program and is sufficiently detailed to provide the reader a practical procedure that can be used on the next project.
John L. Gross and H. S. Lew
This paper describes a microcomputer-based program which can be used to assist the contractor in evaluating the safety and economy of alternate construction schemes in cast-in-place multistory concrete building construction. The program, developed at the National Bureau of Standards, assumes that the slabs are supported by evenly distributed, compressible shores or reshores. Forces on the slabs are computed by assuming that superimposed construction loads are distributed to the shoring system and interconnected floors in proportion to their relative stiffnesses. The method takes into account both the stiffness of shores and reshores and any precompression in the reshores. Slab capacity is computed from a maturity-based model of concrete strength prediction. The computed slab loads are compared with the slab capacities to determine whether the load on any slab exceeds the capacity of that slab for any stage of construction. By varying the number of shored and reshored stories, the precompression of reshores, and rate of construction, the optimum casting schedule can be determined. Examples are given which illustrate how this program can be used to assist the contractor in determining a safe casting schedule and to guide the contractor in formwork removal.
M. K. Hurd and P. D. Courtois
Presents a basic analytical method for shoring and re-shoring loads of multistory buildings. Discusses the factors that must be considered, the assumptions for simplification of the analysis and shows the method for determining the estimated loads that will be transferred to the structure. Presents the procedure required to determine the ability of the structure to resist the estimated loads with an appropriate safety factor and the adjustments to the construction procedure that must be made in the event the applied loads are in excess of the capacity of the structure.
Raymond A. Jurewicz.
Personal injury due to construction accidents inflict pain and suffering on the hapless victim and costs the construction industry billions of dollars annually. Recognizing the hazards and utilizing practical solutions can reduce this human and monetary waste. This paper deals with formwork safety from the view of working conditions and the necessary work operations that must be accomplished to install and strip formwork. It does not deal with formwork failures or the causes of these failures. The paper covers general hazards as well as the specific hazards associated with various formwork systems. Solutions to minimize risks associated with the various hazards are recommended. Various ways to develop safety awareness are also discussed.
Frank T. Connors.
Basically, the cost of concrete, steel, equipment, wages, etc., are the same for all contractors. The difference between profit and loss lies in construction procedures. One of the few items under a contractor's direct control is his method of forming concrete. The choice of the forms, themselves, may be of little significance when compared to the choice of the ties. A comparison between low-capacity and high-capacity ties indicates that the higher cost for the structural requirements of a form to be used with high-capacity ties may result in a low breakeven point in direct costs and, more importantly, may have a decided effect upon job progress.
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