ML19319C276

App 5D to Davis-Besse PSAR, Justification for Yield Reduction Factors (0-Factors) Used in Determining Yield Strength of Shield Bldg & Containment Internal Structures.

ML19319C276
Person / Time
Site:	Davis Besse
Issue date:	08/01/1969
From:	TOLEDO EDISON CO.
To:
References
NUDOCS 8002110755
Download: ML19319C276 (2)

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D-B APPENDIX 5D *

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JUSTIFICATION FOR YIELD REDUCTION FACTORS (9 - FACTORS) USED IN DETERMINING YIELD STRENGTH OF SHIELD BUILDING AND CONTAINMENT INTERNAL STRUCTURES The 9 factors are provided to allow for variations in materials and work =an-ship. In the ACI Code 318-63, W varies with the type of stress or member considered; that is, with flexure, bond or shear stress, or compression.

The 9 factor is multiplied into the basic strength eqaation or, for shear, into the basic permissible unit shear to obtain the dependeble strength. The basic strength equation gives the " ideal" strength assuming =aterials are as strong as specified, sizee are as shown on the drawings, the workmanship is excellent, and the strength equation itself is theoretically correct. The practical, dependable strength may be scmething less since all these factors vary.

The ACI Code provides for these variables by using these 0 factors:

0 = 0.90 for flexure.

9 = 0.85 for diagonal tension, bond, and anchorage.

@ = 0 75 for spirally reinforced compression members.

@ = 0.70 for tied compression members, b The 9 factors provide for the possibility that small adverse variations in material strengths, dimensions and work =anship occasionally may combine to resui.t in underespacity. The 9 factors for colu=ns are significantly lower since colu=n failure may cause the entire structure to collapse.

The additional $ values used represent Bechtel's best judgment of how much understrength should be assigned to each =aterial and condition not covered directly by the ACI Code. The additional 0-factors have been selected based on material quality in relation to the existing 5-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

@ = 0.90. The same reasoning has been applied in assigning a value of Q = 0.90 to reinforcing steel in tension, which now includes axial tension. However, the code recognizes the possibility of reduced bond of bars at the laps by specifying a 0 of 0.85 Mechanical and welded splices will develop at least 125 percent of the yield strength of the reinforcing steel. Therefore,

@ = 0.90 is recommended for this type of splice.

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