Ten PrincipleExperimental verification of Bernoulli equation (Prof. M

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    Chapter Materials and Systems for Prestressing

    2 11 CIRCULAR PRESTRESSING

    Circular prestressing involves the development of hoop or hugging compressive stresses

    on circular or cylindrical containment vessels, including prestressed water tanks and

    pipes.

    It is

    usually accomplished by a wire-wound technique, in which the concrete pipe

    or tank is wrapped with continuous high-tensile wire tensioned to prescribed design lev

    els. Such tension results in uniform radial compression that prestresses the concrete

    cylinder or core and prevents tensile stresses from developing in the concrete wall section

    under internal fluid pressure. Figure 2.29 shows a preload circular tank being prestressed

    by the wire-wrapping process along its height.

    2 12 TEN PRINCIPLES

    The following ten principles are taken from Abeles (Ref. 2.32) and applicable not only to

    prestressing concrete but to any endeavor that the engineer is called upon to undertake:

    1. You cannot have everything. (Each solution has advantages and disadvantages that

    have to be tallied and traded off against each other.)

    2.

    You

    cannot have something for nothing. (One has to pay in one way or another for

    something which

    is

    offered as a free gift into the bargain, notwithstanding a solu

    tion's being optimal for the problem.)

    3

    It is never too late (e.g.,

    to

    alter a design, to strengthen a structure before it col

    lapses, or to adjust or even change principles previously employed in the light of in

    creased knowledge and experience).

    4 There is no progress without considered risk. (While it is important to ensure suffi

    cient safety, overconservatism can never lead to an understanding of novel struc

    tures.)

    5. The proof of the pudding is in the eating. (This is in direct connection with the pre

    vious principle indicating the necessity of tests.)

    6 Simplicity

    is

    always an advantage, but beware of oversimplification. (The latter may

    lead to theoretical calculations which are not always correct in practice, or to a fail

    ure to cover all conditions.)

    7 Do not generalize, but rather qualify the specific circumstances. (Serious misunder

    standings may be caused by unreserved generalizations.)

    8. The important question

    is

    how good, not how cheap an item

    is

    (A cheap price

    given by an inexperienced contractor usually results in bad work; similarly, cheap,

    unproved appliances may have to be replaced.)

    9. We live and learn. (It is always possible to increase one's knowledge and experi

    ence.)

    10. There

    is

    nothing completely new. (Nothing

    is

    achieved instantaneously, but only by

    step-by-step development.)

    SELE TED

    REFEREN ES

    2.1 American Society for Testing and Materials. nnual book of STM

    Standards:

    Part 14,

    Concrete

    and Mineral Aggregates. Philadelphia: ASTM, 1994.

    2.2 Popovices,

    S

    Concrete-Making Materials.

    New York: McGraw-Hill,

    1979, 1997.

    2.3 CI Committee 221. Selection and Use of Aggregate for Concrete. Journal of the American

    Concrete Institute

    Farmington Hills, MI, 1992.