ML20011A483

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Procedure to Account for Out-of-Plane Interstory Drift Effects on Masonry Wall Evaluation.
ML20011A483
Person / Time
Site: Point Beach  NextEra Energy icon.png
Issue date: 09/30/1981
From:
COMPUTECH ENGINEERING SERVICES, INC.
To:
Shared Package
ML19312F019 List:
References
IEB-80-11, R553.11, TAC-42896, TAC-42897, NUDOCS 8110130469
Download: ML20011A483 (6)


Text

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PROCEDURE TO ACCOUNT FOR OUT-OF-PLANE INTERSTORY DRIFT EFFECTS ON THE MASONRY WALL EVALUATION Prepared for Point Beach Nuclear Power Plant Units 1 and 2 WISCONSIN ELECTRIC POWER COMPANY Milwaukee, Wisconsin Prepared by COMPUTECH ENGlh5ERING SERVICES, INC.

Berkeley, California September,1981 REPORT NO. R553.11 Revision 1 8110130469 81 007 PDR O

ADCCK 05000266 PDR

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TAIKE OF CONTENTS l 1

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1 INTRODUCTION . . . . . . . . . . . . ................. . . . . . 1 i 2 A NALYSIS METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 R E S U LTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 DISCUSSION OF RESULTS . . . . ...... .......... . . . . . 2 5 CONC LUSION S . . . . . . . . . . . . . . . . . . . . .......... . . . . . 2

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1 INTRODUCTION The Nuciear Regulatory Commission (NRC) staff on June 9-11, 1981 reviewed the criteria and calculations performed on IE Bulletin 80-11

  • Masonry Wall Design
  • for the Point Beach Nuclear Power Plant. Action item 11 resulting from the review meeting stated that the licensee shall provide the criteria and procedures to account for the out-of-plane Interstory drift effects in seismic analysis.

This short report is in response to that action item and includes a description of the analysis methodology, the results a discussion of the results, and the Conclusions.

2 ANALYSIS METHODOLOGY All walls were analyzed in accordance with the procedures given in

  • Criteria for the Re-evaluation of Concrete Masonry Walls for The Point Beach Nuclear Power Plant.' Specifically, to assess the out-of-plane response of the walls the boundary conditions at all supports were assumed to be pinned. This assumption was made for the following reasons.

(1) The stresses resulting from out-of-plane selsmic load are conservative.

(2) The boundary rotations required for the existence of pinned supports are very small and will exist regardless of what type of fixity is used to prevent it. A field inspection of the walls indicated this was the only reasonable assumption.

(3) The majority of the walls had no support at the top of the wall. In addition r o support was assumed around any door or other opening.

In assessing the effect of out-of-plane drift effects on the walls the same assumption of pinned boundary conditions was used for consistoney in the analytical procedures. With this assumption no forces are induced in the walls when out-of-plane interstory drift effects are assessed. The validity of this assumption I

was questioned in Action item 11 and as a result two walls (Wall Nos. 24 and 65-1) were selected to compare the results that would be obtained if fixed rather than simply supported boundary conditions had been assumed. Wall No.

24 is 164 inches long and 156 inches high and Wall No. 65-1 is 109 inches long and 176 inchos high. Each wall is double wythe and was analyzed as l a single and double wythe wall with both fixed and simply supported boundary conditions. For the fixed boundary conditions the effects of out-of-plane Interstory l drift were included in the analysis. The stresses resulting from out-of-plane l seismic load were combined absolutely with those resulting from out-of-plane l drift effects. Out-of-plane drift effects were calculated by imposing the out-of-plane displacement at the top of the wall witn the wall fixed against rotation at both the top corners and the bottom of the wall.

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3 RE3ULTS A summary of the maximum stress ratios resulting from the eight analyses perfor'aed are given in Table 1. Care must be exercised in evaluating the results becease the max! mum stresses do not fall in the same region of the wall for the different boundary conditions. In the case of the simply supported boundary conditions the maximum stress ratios are towards the center of the wall and for the fixed boundary Conditions they are close to or adjacent to the boundarles.

4 DISCUSSION OF RESULTS The results for Wall 65-1 Indicate that the maximum stress ratios of the simply supported boundary conditions for a single wythe wall are conservative when compared with those of the fixed boundary conditions that include out-of-plane Interstory drift effects. The maximum stress ratio for this wall occurred on a horizontal strip ano was reduced by almost one-half when fixed boundary conditions were used. When the same compr.rlson is made for the double wythe wall, again the maximum stress ratio, wh',ch was on a horizontal strip, was reduced by almost one-half. However, the maximum stress .atlo on the vertical strip increased from 0.n7 to 0.097. In comparing the three analyses: 1) single wythe with fixed botndarles -ad out-of-plane drift, 2) double wythe with simply supported boundaries and 3) double wythe with fixed boundaries and out-of-plane drift; the maximum stress ratlos are all less than the ratios obtained from analyzing the wall with the procedures given in the re-evaluation crite,ria.

The results for Wall 24 are similar to those of Wall 65-1 in that the maximum stress ratios on a horizontal strip decrease when fixed boundary conditions and out-of-plane drift are considered. However, on a vertical strip the maximum stress ratios increase for Wall 24. The increase for the single wythe wall is from 0.170 to 0.228 and for the double wythe wall it is from 0.075 to 0.226.

Although this increase for Wall 24 Indicates that for a vertical strip, the simply supported boundary conditions is non-conservativs the governing stress ratio on the horizontal strip is not exceeded by tha maximum stress ratlos in either direction for the other three analyses. Therefore, in this regard the assumption of simply supported boundary conc;tions used in the re-evaluation criteria can be considered conservative.

5 CONCLUSIONS The criteria and procedures used .o account for out-of-plane interstory drift effects in the re-evaluation criteria have been described and compared with results obtained from an alternate approach, in summary, the procedure used in the re-evaluation criteria assurnes the walls have pinned suppo-*- at .the boundarles because it is our opinion that this is the most realistic representation of field conditions and in addition it results in a conservative estimate of the I stresses resulting from out-of-plane selsmic load.

Two walls were selected to compare the maximum stress ratios obtained from the assumptions used in the re-evaluation criteria with those obtained from using the assumption that the top and bottom boundaries had fixed supports.

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The stresses obtained for the out-of-plane forces acting on the wall with flued boundary conditions were added absolutely to those resulting from out-of-plane drift effects.

For the two walls that were analyzed, the maximum magnitude of the stress ratio was obtained for the single wythe wall with simply supported boundary conditions. In both cases this was the stress on a horizontal strip. In th0 regard the assumptions used in the re-evaluation criteria are conservative. For Wall 65-1 the maximum stress ratio on both a horizonta! and vertical strip obtained f#om the single wythe wall with simply supported boundary conditions were consarvative. For Wall 24 the same statement is valid for the maximum stress ratio on a horizontal strip. For the maximum stress ratio on a vertical strip there was an increase when fixed boundary conditions were used but this increase did not exceed the maximum stress ratlo obtained on the horizontal strip.

From the results presented it is clear that the impact of different boundary conditions varies and is difficult to accurately assess because the region where the m'aximum stress occurs changes as the boundary condition changes. However.

for the two walls analyzed tne assumption of a single wythe wall with simply supported boundary conditions (i.e. that used in the re-evaluation criteria) produces the maximum magnitude in the stress ratio 'on either a horizontal or vertical strip. Furthermore. It is our opinion that these boundary conditions are the most realistlC for the Condillons that exist in t.9 field.

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. o TABLE 1 MAXIC4 STRESS RATIOS FOR VARYING BOU::DARY CONDITIONS tiall No. Thickness (in) Condition My /Mxa My/Mya 12 Simply Supported 0.406 0.170 12 Fixed. Drift . 0.265 0.228 24 l 25 i Simply supported 0.181 0.075 25 Fixed, Drift 0.129 0.226 6 Simply Supported 0.483 0.157 6 Fixed... Drif t 0.264 0.136 65-1 -

12 Simply Supported 0.215 0.070 12 Fixed, Drift 0.117 0.097 i<

Note: Subscripts x and y denote stress ratios on horizontal and vertical strips respectively i

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