ML19329E161

App 5E of AR Nuclear 1 PSAR, Yield Reduction Factors. Includes Revisions 1-18

ML19329E161
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/24/1967
From:	ARKANSAS POWER & LIGHT CO.
To:
References
NUDOCS 8005300773
Download: ML19329E161 (3)

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JUSTIFICATION FOR YIELD REDUCTION FACTORS (d - FACTORS) USED IN DETERFTHH3 YIELD STRENGTH OF COICAIICENT STRUCTURE The p factors are provided to allow for variations in materials and workman-ship. In the ACI Code 318-63, y varies with the type of stress or member f

considered; that is, with flexure, bond or shear stress, or compression.

The p factor is multiplied into the basic strength equation, or, for shear, into the basic permissible unit shear, to obtain the dependable strength.

The basic strength equation gives the " ideal" strength, assuming materials are

as strong as specified, sizes are as shown on the drawings, the workmanship is excellent, and the strength equation itself is theoretically correct. The practical, dependable strength may be something less, since all these factors vary.

The ACI Code provides for these variables by using these p factors:

p = 0 90 for concrete in flexure p = 0.85 for diagonal tension, bond, and anchorage f

7 p = 0.75 for spirally reinforced, concrete compression members p = 0.70 for tied compression members p is larger for flexure because the variability of steel is less than that of concrete and the concrete in compression has a fail-safe mode of behavior; that is, material understrength without failure. The p values for coltens are lower (favoring the toughness of spiral colt =ns over tied columns) because columns fail in ecmpressicn where concrete strength is critical. Also, it is possible that the analysis might not combine the worst combination of axial lead and mcment, and since the member is critical in the g*oss collapse of the structure, a lower value is used.

Ihe additional p values used represent Bechtel's best judgment of how much understrength should be assigned to each raterial and condition not covered directly by the ACI Code. The additional p factors have been selected based on zaterial quality in relation to the existing p factors.

Conventional concrete design of beams requires that the design be controlled by yielding of the tensile reinforcing steel. This steel is generally spliced by lapping in an area of reduced tension. For members in flexure, ACI uses l 0 = 0.90. The same reasoning has been applied in assigning a value of p =

0 90 to reinforcing steel in tension, which now includes axial tension. How-ever, the code recognizes the possibility of reduced bond of bars et the laps o.3g 5-E-1

by specifying a / of 0.85 Mechanical and welded splices will develop at least 125 per cent of the yield strength of the reinforcir.g steel. Therefore,

%=090isrecommendedforthistypeofsplice.

Theonlysignificantlynewvalueintroducedis%=095forprestressedten-dons in direct tension. . A higher % value than for conventional reinforcing has been allowed because (1) during installation the tendons are each jacked to about 94 per cent of their yield strength, so in effect, each tendon has been proof tested, and (2) the method of manufacturing prestressing steel (cold drawing and stress relieving) ensures a higher quality product than conventional reinforcing steel.

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