STP205

    Tests of Prestressed Expanded-Shale Concrete Beams Subjected to Short-Time and Sustained Loads

    Published: Jan 1958


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    Abstract

    This paper gives the results of tests on 19 flexural members of prestressed concrete, of lengths ranging from 24 to 65 ft and including beams of doubletee section for floors and roofs, box beams for floor systems of bridges and buildings, and girders and purlins of I-section for roofs. Most of the members were composed of expanded-shale lightweight concrete, and the steel was pretensioned. Most of the tests were made under loading which would produce failure in bending; others in shear. All flexural members were loaded until first cracking was observed and then unloaded to observe recovery. Thereafter, one beam was loaded immediately until failure was produced and four beams were subjected continuously to their design loads for a period of 3 1/2 months. Observations were made on all flexural members to determine deflections and cracking, and on selected beams to determine longitudinal strains in flexure or strength in shear. Auxiliary tests were made to determine compressive strength and modulus of elasticity of concrete, creep of concrete under sustained compressive stress, and loss of tension in steel reinforcement due to creep.

    It was found that live loads required to produce first cracking in flexure ranged from 1.5 to 2.2 times the design loads. Shearing loads required to produce failure in diagonal tension ranged from 1.0 to 1.7 times those computed for conventionally reinforced-concrete beams of similar section. Live-load deflections under short-time loading were generally considerably less than was expected. When the design loads were released, elastic recovery was practically complete. When loads somewhat in excess of those required to produce flexural cracking were released, residual deflections were insignificantly small. Deflections under sustained design loads were small, and elastic-plus-creep deflections were within customary limitations except for one roof beam of very long span. Loss of tension in reinforcement under sustained loading was substantially equal to that assumed in design and was not greater for the expanded-shale aggregate than for natural aggregate. Creep under sustained load was of the same order of magnitude as that commonly observed for concrete containing natural aggregate. In general, the tests confirm the assumptions commonly made in design of prestressed concrete beams.


    Author Information:

    Davis, RE
    Professor of Civil Engineering and Director of the Engineering Materials Laboratory, Emeritus, and Professor of Civil Engineering, University of California, Berkeley, Calif.

    Troxell, GE
    Professor of Civil Engineering and Director of the Engineering Materials Laboratory, Emeritus, and Professor of Civil Engineering, University of California, Berkeley, Calif.

    McCall, DO
    Chief Engineer, and Assistant Chief Engineer, Basalt Rock Co., Inc., Napa, Calif.

    McCann, RA
    Chief Engineer, and Assistant Chief Engineer, Basalt Rock Co., Inc., Napa, Calif.


    Paper ID: STP39464S

    Committee/Subcommittee: C09.61

    DOI: 10.1520/STP39464S


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