shell structures constructed in light- weight concrete are the Assembly Hall at the University of Illinois, and the TWA Terminal Building at the New York International Airport.
Lightweight concrete is perhaps most suitable for bridge-deck con- struction. Besides reducing the dead load of the bridge, it improves the impact characteristics of the system. Early in 1939, expanded shale aggre- gate concrete was used for the deck of the San Francisco-Oakland Bay Bridge. "The reduction in weight materially decreased the dead load stresses in the superstructure, thus re- ducing the area and the cost of the structural members therein. reduced the direct load on the founda- tions. Of still more importance, the stresses on the foundations and, to some extent. on the superstructure due to the assumed seismic forces were materially reduced."(8)
It also
The suitability of lightweight ag- gregates for prestressed concrete has been, and still is. somewhat contro- versial. The advantages resulting from the reduction in dead load are nullified, to a certain extent, by the increased losses of prestress. In spite of this, precast prestressed roof slabs of lightweight concrete were already in mass production in the United States in the early 1950's, and later in Britain and Russia.
In addition to the manufacture of highly repetitive factory products, pre- stressed lightweight concrete has been occasionally adopted for long-span bridges in the U.S.A.
Recently, the bridge across the
Suwanee River in Florida was com- pleted, which comprises four 120 ft. spans of precast prestressed girders with a cast-in-situ deck, all of light- weight concrete. For this bridge, it was the combination of prestressing and lightweight concrete that made the present design more economical than any alternative design.
References:
(1) American Concrete Institute: ACI
Standard 318-63
"Building Code Requirements for Reinforced Con- crete"; ACI Book of Standards, 1963. (2) British Standards Institution: British Standard Code of Practice CP115:1959 "The Structural Use of Prestressed Concrete in Buildings." (3) "Tentative Specification issued by the London County Council in considering on their merits applications made to
―
the Council for modification or waiver of the relevant London Building (Con- structional) By Laws, 1952." (4) Building Research Station Digest No. 31 (Second Series) "Light-weight Aggregate Concretes 3. Structural Application"; H.M.S.O., London, 1963. (5) British Standards Institution: British Standard Code of Practice CP114: 1957 "The Structural Use of Rein- forced Concrete in Buildings" (reset and reprinted 1965). (6) British Standards Institution: British Standard Code of Practice CP11: 1965 "The Structural Use of Precast Concrete." (7) Chappell, F.W.: "High strength steel and concrete result in minimum column sizes"; Proceedings of Ameri- can Concrete Institute, Vol. 54, 1957- 58, pp. 929-938.
(8) Woodruff, G.B.: "Lightweight concrete pavement on the San-Francisco Oak- land Bay Bridge"; Proceedings of American Concrete Institute, Vol. 34, 1938, pp. 225-238.
INTERNATIONAL CONGRESS ON LIGHTWEIGHT CONCRETE
THE Concrete Society of UK. sup- ported by the Comite Europeen du Beton (CEB), The Conseil Interna- tional du Batiment (CIB), the Federa- tion Internationale de la Precontraine (FIP), and the Reunion Internationale des Laboratoires d'Essais et de Re- cherches sur les Materiaux et les Constructions (RILEM), is arranging an International Congress on light- weight concrete on 13, 14 and 15 May 1968. The congress will be held at the Europa Hotel, London W1.
The broad subjects envisaged for the first two days of the Congress. which will have a practical rather than an academic emphasis. are the properties of lightweight aggregates
and fresh concrete in relation to site operations, and in the context of aerated concrete and lightweight ag- gregate concrete: structural and ar- chitectural properties of hardened con- crete: codes of practice and regulations: general economics and applications.
The registration fee for the con- gress, including a set of the papers in English with summaries in French. German and Russian, will be £25. The detailed programme of the con- gress will be issued later this year and full information will be available from the Secretary, International Con- gress on Lighteight Concrete, Ter- minal House, Grosvenor London S.W.I.
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