CAE (Comprehensive Analytic Engineering ) , Inc.

CAE SETS (Structure Engineering Turnkey System): True #1

TRUE NON-LINEAR SAGGING CABLE FAKE NON-LINEAR SAGGING CABLE
TRUE REPRESENTATION MISREPRESENTATION or DECEPTIVE MIMICKING ?
USP, 1976 STAAD
ELEMENT BEAM,TRUSS & ONE-Way ELEMENT CABLE
  • Verification: Meaningful examples to convey the important features.
    (Most of them 3-D structures)
    		• Can or NOT STAAD provide meaningful 3-D or 2-D general non-linear sagging cable examples that are independent of given loads ? (GOOD: Load magnitudes can vary and/or load locations can vary. vs BAD: Otherwise.)
    How about independent of material and section property ? (GOOD: Cross section area can vary and/or Young's modulus can vary. vs BAD: Otherwise.)
  • A college sophomore or junior student can check, verify and be convinced.

    1. JOINT STATIC EQUILIBRIUM (From Joint(Global) Coordinate OUTPUT)
    2. STRAIN vs STRESS COMPATIBILITY of A NON-LINEAR SAGGING CABLE MEMBER
      • TENSION MAGNITUDE From Element Local Coordinate OUTPUT)
      • STRAIN: From the initial coordinate values, unstrained original length can be obtained.
      • From the output that gives final position of the sagging cable (A true non-linear sagging cable shall be able to.),
        you obtain the new strained length.
      • TENSION: It shall follow HOOK's LAW
    All in ONE INPUT and ONE OUTPUT
    (Unlimited load cases including load combinations.)
  • TRUE MEANINGFUL EXAMPLES provided with COMPLETE input and output that can be checked easily as mentioned above. VERIFICATION PROBLEM NO. 1.3.10:
    Cable Supporting Hanging Loads: 2-D beam element (cable): For the equilibrium position shown, find the horizontal and vertical reaction forces at support 1 and the maximum tension T in the cable.
    A true non-linear sagging cable gives the EQUILIBRIUM POSITION as part of final data to output rather than known data to input because it can not be known ahead of time. A FAKE non-linear sagging cable that requires you to input the EQUILIBRIUM POSITION as part of input data rather than unknown data to be obtained.
    Frequently, initial (before load) position is comparatively simple, independent of loads and known as input. (If any plain ordinary program like STAAD were to use this as input, the program would give you a simple output that would NOT meet COMPATIBILITY condition- a clear indication of NO REAL NON-LINEAR SAGGING CABLE CAPABILITY.)
    The final position (after load) is a function of loads and very different from initial position in terms of:
    • Joint equilibrium
    • Any other kinds of static equilibriums
    • Compatibility

    The real structures exist in large numbers in engineering including sagging cable net. (No such restrictions for USP as those indicated on column II.)     		The STAAD then treats it as some kind of an ordinary 2-D structure that makes no differnce between the initial (before load) and final positions (after load) for joint static equilibrium for the given load case. All plain programs can do it. Simple long hand calculations can do it. In real engineering, that kind of cable pratically does not exist because it requires:
    • Odd y-coordinate values as known positions
    • Impossibility to control and prepare the unstrained cable length, which is frequently based on a simple REAL initial position requirement GEOMETRICALLY along with/without some small pre-tension.
    • Joint loads magnitudes fixed as indicated
    • Product of Material Property and Section Properties: Constants (EA and EI)
    For a simple linear static cable with a given sagging, it has no real practical significance as verification example. You do long hand calculation faster to get answers than to prepare data to input to STAAD. See also VERIFICATION PROBLEM NO. 12
    Deflection and stress of a truss system.
    CAEinc professional opinion: Both examples were/are to confuse the public.
    A True Non-linear 2-D or 3-D Sagging Cable can not be pre-judged for a given equilibrium position.
    Conclusion: You as an end user can help police the bad apple by uncovering more of MISREPRESENTATION or DECEPTIVE MIMICKING.

    NOTE: ? mark indicates that CAEinc believes strongly with professional opinion to be correct/nearly-correct. You as a user shall find out to be 100 % absolute or not. CAEinc will verify for you without charge by analyzing your runs if you will provide the Input and Output data of the runs.

    THIS FAKE EXAMPLE BELONGS TO THE GEOMETRIC NONLINEARITY WITH BIG DISPLACEMENT: A HIGHER ORDER OF TECHNOLOGY IN FINITE ELEMENT THEORY.(BRAIN POWER vs MAN POWER) THIS IS ANOTHER DELIBERATE ACT TO MISREPRESENT. YOU ARE THE MASS PUBLIC WHO CAN EXERCISE TO POLICE. STAAD III is essentially a sub set of Hyper STRUDL. However, the public is misled to perceive the otherway around.

    STAAD III INPUT DATA AS SHOWN BELOW

    STAAD PLANE CABLE SUPPORTING HANGING LOADS
    * FILE FR2D10.STD
    *
    * REFERENCE: BEER, F.P., AND JOHNSTON, Jr. E.R.,
    * VECTOR MECHANICS FOR ENGINEERS, STATICS AND DYNAMICS,
    * McGRAW HILL BOOK CO., NEY YORK, 1962.
    *
    INPUT WIDTH 72
    UNIT FEET KIP
    JOINT COORDINATES
    1 0. 0. ; 2 20. -5.56 ; 3 30. -5. ; 4 45. 5.83 ; 5 60. 20.
    MEMBER INCIDENCES
    1 1 2; 2 2 3; 3 3 4; 4 4 5
    MEMBER CABLE
    1 TO 4
    *
    MEMBER PROPERTY
    1 TO 4 PRI AX 0.1 IZ 0.001
    CONSTANTS
    E 20000000. ALL
    *
    SUPPORTS
    1 5 PINNED
    *
    LOAD 1 GRAVITY POINT LOADS FOR EQUILIBRIUM
    JOINT LOAD
    2 FY -6.
    3 FY -12.
    4 FY -4.
    *
    PERFORM ANALYSIS
    PRINT JOINT DISPLACEMENTS ALL
    PRINT MEMBER FORCES ALL
    PRINT SUPPORT REACTIONS
    FINISH

    Structure - Programming - Vibration - Foundation - Civil

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    This page was last updated on September/20/1999 and Oct. 14, 2003     .