ML20079G186
| ML20079G186 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 06/01/1982 |
| From: | CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML20079G179 | List: |
| References | |
| 17228, NUDOCS 8206080344 | |
| Download: ML20079G186 (71) | |
Text
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03072203 TECHNICAL REPORT l
STRUCTURAL STRESSES INDUCED BY DIFFERENTIAL SETTLEMENT OF THE DIESEL GENERATOR BUILDING
.. ~
CONSUMERS POWER COMPANY MIDLAND PLANT UNITS 1 AND 2 8206000344 820601 PDR ADOCK 05000329 A
MIDLAND PLANT UNITS 1 AND 2 TECHNICAL REPORT STRUCTURAL STRESSES INDUCED DY DIFFERENTIAL SETTLEMEN'I OF THE DIESEL GENERATOR BUILDI1tG TABLE OF CONTENTS 0 0,..-- ;
3 e
Page 1.0 STRUCTURAL REANALYSIS 1
1.1 STRUCTURAL ACCEPTANCE CRITERIA 1
1.1.1 Load Cases 2
1.1.2 Load Combinations 2
1.1.3 Allowable Material Limits 4
2.0 DIESEL GENERATOR BUILDING ANALYTICAL MODEL 4
2.1 APPLICATION OF LOADS TO THE BUILDING MODEL 4
2.1.1 Dead Loads 5
2.1.2 Settlement Loads 5
2.1.3 Live Loads 8
2.1.4 Wind Loads 8
2.1.5 Tornado Loads 8
2.1.6 Seismic Loads 9
2.1.7 Thermal Loads 10 3.0 ANALYSIS PROCEDURE 11 3.1 SETTLEMENT /LONG-TERM MODEL 11 3.2 SHORT-TERf" MODEL 14 3.3 ZERO-SETTLEMENT MODEL 11 3.4 STRUCTURAL ADEQUACY COMPUTATIONS 11
4.0 CONCLUSION
S 13 REFERENCES 14 APPENDIX A
OPTCON ii
Miditnd Pltnt Unita 1 cnd 2 Structural Strac033 InducId by Difforcnticl SattlcC2nt of the Diesel Generator, Building Table gr]Contentsi(yontinued)
TABLES I-l Loads and Load Combinations for Concrete Structures Other than the Containment Building From the FSAR and Question 15 of Responses to NRC Requesta Regarding Plant Fill I-2 Loads and Load Combinations for Comparison Analysis Requested in Question 26 of NRC Requests Regarding Plant Fill I-3 Soil Properties Used in the Seismic Analysis I-4 Rebar Stress Values for the Diesel Generator Building Structural Members (According to FSAR and the Responses to NRC Requests Regarding Plant Fill, Question 15)
FIGURES I-l Diesel Generator Building Dynamic Lumped Mass Model for Seismic Analysis I-2 Diesel Generator Building Finite Element Model I-3 Summary of Actual and Estimated Settlements I-3A Comparison of Measured Settlement Values (Pre-Surcharge)
With Settlement Values Resulting From a Finite-Element Analysis of the Diesel Generator Building I-3B Comparison of Measured Settlement Values (Surcharge) with Settlement Values Resulting From a Finite-Element Analysis of the Diesel Generator Building I-3C Comparison of Actual Measured Settlements (Post-Sur-charge) Plus Estimated Secondary Compression Settlement with Settlement Values Resulting From a Finite-Element Analysis of the Diesel Generator Building I-4 Basis for Calculation of Equivalent Shear Wave Velocity iii b
Midland Plcnt Units 1 cnd 2 Structural Stracess InducId by Differential Sattlem2nt of the Diesel Generator Building Cqm J
r.
Table of Contents (continued)
ATTACHMENTS I-l Diesel Generator Building Settlement Data Analysis I-2 Analyses of DGB for Zero Spring Condition iv
MIDLAND PLANT UNITS 1 AND 2 TECHNICAL REPORT STRUCTURAL. STRESSES INDUCED BY DIFFERENTIAL SETTLEMENT OF THE DIESEL GENERATOR BUILDING 1
l L3 s a m fs &
v.
-s 1.0 STRUCTURAL REANALYSIS To account for the effect of the observed and predicted settlement on the diesel generator building, a structural reanalysis was performed.
This reanalysis proceeded by. defining the acceptance criteria for the structure (see Subsection 1.1).
These acceptance criteria differ from the acceptance criteria used in the original design and analysis of the structure and set forth in the Final Safety Analysis Report (FSAR) only in the addition of four load combinations that include the effect of settlement.
These additional load combinations are described in Subsection 1.1.2, Equations 1 through 4.
To investigate the effects of the load combinations on the structure, the structural reanalysis uses two different mathematical models of the diesel generator building:
a dynamic, lumped mass model and a static, finite-element model.
The dynamic, lumped mass model (described in Subsection 2.1.6 and illustrated in Figure I-1) is used to generate seismic forces in the building, given the input ground motion from the operating basis earthquake (OBE) and safe shutdown earthquake (SSE) specified in the FSAR.
The finite-element model (described in Subsection 2.0 and illustrated in Figure I-2) is a more complex mathematical model that reduces the diesel generator building to an interrelated system of plate, beam, and boundary elements representing the walls, slabs, foundation, and soil.
Tae finite-element model is used to assess the effect on individual elements of various load combinations applied to the structure as a whole.
(These load combinations include seismic forces generated with the dynamic, lumped mass model.)
The finite-element model thereby allows the identification of those sections of the diesel generator building that will experience the greatest forces due to the postulated load combinations.
The allowable stress is then calculated and compared to the actual stress level in these sections based on the forces derived from the finite-element modol.
This comparison shows that even those sections of the building experiencing the highest forces meet the acceptance criteria.
1.1 STRUCTURAL ACCEPTANCE CRITERIA Because of the settlement problem, a structural reanalysis of the diesel generator building was performed to determine if the structure met the structural acceptance criteria which are consistent with FSAR Subsection 3.8.6.3, with settlement effects included as outlined in the response to NRC Requests Regarding Plant Fill, Question 15, Revision 3, September 1979 (Reference 1).
1
Midlend Plcnt Unita 1 and 2 Structurcl Strc2sco InducLd by Differential Settlement of the Diesel Generator. Building 1.1.1 (t.o'a il 'C a s e s 3
The following loads are considered in the reanalysis:
a.
Dead loads (D)
I b.
Effects of settlement combined with creep, shrinkage, and temperature (T) c.
Live loads (L) d.
Wind loads (W) e.
Tornado loads (W')
f.
OBE loads (E) 9 SSE loads (E')
h.
Thermal effects (To)
Thermal effects appear twice in this list (Items b and h).
For load combinations committed to in the responsa to Question 15 of the NRC Requests Regarding Plant Fill, thermal effects are contained within the settlement effects term, T.
For load combinations committed to in FSAR Subsection 3.8.6.3, thermal effects are contained in the thermal term, To (Refer to Table I-1).
All other load cases appearing in the load combinations for Seismic Category I structures listed in FSAR Subsection 3.8.6.3 (e.g.,
rupture of pipe lines) do not occur in the diesel generator building and are not addressed.
1.1.2 Load Combinations The load combinations employed for the original analysis and design of the diesel generator building are provided in FSAR Subsection 3.8.6.3.
The original FSAR load combinations did not contain a settlement effects term (T).
For the structural reanalysis performed in response to Question 15 of the NRC Requests Regarding Plant Fill (September 1979), four additional load combinations were established and committed to be considered.
These additional combinations consider the effects of differential settlement in combination with long-term operating conditions and with either wind load or OBE.
Table I-l provides the load combinations listed in FSAR Subsection 3.8.6.3 and the four additional load combinations.
These load combinations comprise the acceptance criteria for the diesel generator building and are hereinafter referred to as the Midland acceptance criteria.
2
Midlcnd Plcnt Units 1 and 2 Structural Strc cs Inducsd by Difforcntial Setticm:nt of the Diesel Generator Building By requipihg' combination of differential settlement with wind loads and OBE, the Midland acceptance critaria are more stringent than the requirements of American Concrete Institute (ACI) 318.
ACI 318 only requires combining the effects of differential settlement with the dead loads and live loads.
The Midland acceptance criteria are less stringent than ACI 349, because ACI 349 (as supplemented by Regulatory Guide 1.142) includes load combinations that combine the effects of differential settlement with extreme loads such as tornados and SSEs.
In the response to Question 26 of NRC Requests Regarding Plant Fill, a commitment was made to do a separate structural reanalysis of the diesel generator building in accordance with ACI 349, as supplemented by Regulatory Guide 1.142, for comparative purposes only.
Table I-2 provides the load combinations of ACI 349 as supplemented by Regulatory Guide 1.142.
It is unnecessary to use all Table I-1 load combinations in the structural reanalysis.
A number of combinations can be eliminated from the analysis after comparison with more severe loads or load equations.
For example, Equations 6 and 10 from Table I-1 are:
a.
U = 1.25 (D + L + Ho + E) + 1.0To (6) b.
U = 1.4 (D + L + E) + 1.0To + 1.25Ho (10)
Because there are no significant forces on the structure due to thermal expansion of pipes (Ho), these two expressions can be rewritten in simpler forms:
a.
U = 1.25 (D + L + E) + 1.0To (6) b.
U = 1.4 (D + L + E) + 1.0To (10) 6 The second expression is more critical than the first.
Therefore, Equation 10 is used in the analysis and is considered to envelop the lower force components resulting from an analysis using Equation 6.
Utilizing this approach with the entire set of load combinations eliminates the less critical equations and condenses the list to 10 load combinations.
Table I-1 Load Combinations Equation No.
a.
1.05D + 1.28L + 1.05T (1) b.
1.4D + 1.4T (2) c.
1.0D + 1.0L + 1.0W + 1.0T (3) d.
1.0D + 1.0L + 1.0E + 1.0T (4) 3
Midltnd Pltnt Unita 1 cnd 2 Structural StroccO3 Induc;d by Differential Settlement of 00072090 the Diesel Generator Building e.
1.4D + 1.7L (5) f.
1.25 (D + L + W) + 1.0To (7) 9 1.4 (D + L + E) + 1.0To (10) h.
0.9D + 1.25E + 1.0To (11) i.
1.0 (D + L + E') + 1.0To (15) j.
1.0 (D + L + W') + 1.0To (18) 1.1.3 Allowable Material Limits In accordance with regulatory requirements and the recommendations of the American Concrete Institute (ACI 318 and ACI 349), the maximun rebar tensile stress allowed in the diesel generator building rebar equals 0.90 fy (where fy equals yield stress) for computation of section capacities.
Because the diesel generator building rebar has an fy value of 60 ksi, the maximum allowable tensile rebar stress due to flexural and axial loads is 54.0 ksi.
Rebar stress values subsequently calculated for critical, reinforced concrete sections of the diesel generator building were based on this maximum allowable rebar stress value (54 ksi) and a maximum allowable concrete strain level of 0.003 in./in.
2.0 DIESEL GENERATOR BUILDING ANALYTICAL MODEL The structural reanalysis of the diesel generator building uses a finite-element model, The required load combinations were applied to this model and the resulting forces were investigated for compliance with the structural acceptance criteria.
The diesel generator building was modeled as an assemblage of plate, beam, and boundary elements.
The structure is defined by a set of 853 nodal points and 1,294 elements.
Of these elements, 901 are plate elements representing walls and slabs, 141 are beam elements, and 252 are boundary elements (translational springs, in both the vertical and horizontal directions) representing varying soil pressures.
Vertical springs were used for dead load, live load, and settlement analysis.
Sets of vertical and horizontal springs were used for other load cases.
Certain items, such as steel platforms and lightly reinforced interior secondary structural walls, have not been included in the model for the reasons listed in subsequent sections.
Figure I-2 illustrates an isometric view of the finite-element model.
2.1 APPLICATION OF LOADS TO THE BUILDING MODEL The following loads have been applied to the model in the manner noted.
4
Midltnd Plcnt Units 1 and 2 Structural Stresecs InducOd by Difforsntial Setticm:nt pf 00072090 the Diesel Generator Building 2.1.1 Dead Loads The dead load of the structure was simulated by specifying a mass acceleration value equaling that of gravity (32.2 ft/s ).
l Secondary structural walls and platforms were not included in the model because their contribution to the gross weight of the structure is minimal (less than approximately 3 percent) relative to the sum of the other loads considered.
Their exclusion does not significantly affect the magnitude or distribution of stresses.
The louvers on both the north wall and south wall, l
along with the doors on the north and south walls of the building, were modeled simply as penetrations, with dimensions equivalent to those of the doors and louvers.
This is acceptable because the doors and louvers contribute insignificantly to the building stiffness and total building weight.
The diesel generator pedestals and the ground floor slabs were omitted from the finite-element model because they were not constructed monolithically with the remainder of the structure.
Consequently, they do not add stiffness to the structure.
2.1.2 Settlement Loads The settlement effects were modeled into the structure with vertical springs as boundary elements representing varying soil conditions.
At 84 locations along the building footing, springs with varying properties were applied to represent the nonhomogenous nature of soil conditions existing beneath the diesel generator building.
Values for vertical springs were developed for two general cases:
those springs calculated for long-term loading (dead load, live load, surcharge load, and differential settlements) and those springs calculated for short-term loading (wind, tornado, and seismic).
For long-term loading, the settlement analysis addresses four distinct time periods.
A unique set of measured or estimated settlement values then corresponded to each of the following periods.
a.
July 10, 1978, to August 15, 1978:
Although construction of the diesel generator building began in spring 1978, survey data on the diesel generator building were available only as of July 10, 1978, August 15, 1978, represents the closest survey date prior to the halt of diesel generator building construction.
b.
August 15, 1978, to January 5, 1979:
Diesel generator building construction resumed and the ductbanks were separated from the structure during this period.
5
Midicnd Pltnt Units 1 and 2 Structural Stro22s3 Induend by Differential Settlement of 00072GS0 the Diesel Generator Building January 5, 1979, is the last survey date prior to the start of surcharge activities.
c.
January 5, 1979, to August 3, 1979:
Surcharge activities occurred within the structure during this period.
August 3, 1979, is the last survey date available prior to the start of surcharge removal from the diesel generator building.
d.
Forty-year Settlement Estimates:
This estimte is comprised of the following:
1)
Actual measured settlements from September 1979 to December 1981.
These settlements are small when compared with the predicted settlements and are mainly due to dewatering.
2)
Predicted secondary consolidation from December 1981 to December 2025.
These values are based on the conservative assumption that the surcharge remains in place over the 40-year life of the plant, thus exceeding the settlement which will actually occur.
To determine forces resulting from settlement, an analysis was performed separately for each of the above four cases.
Analysis results were first combined with each other to form one settlement term, then combined with other load cases (e.g.,
tornado, seismic, etc) to form the required load combinations of the Midland position, and of ACI 349, as supplemented by Regulatory Guide 1.142.
For settlement case a, a longhand analysis was performed to account for stresses in the partially completed structure.
With the actual settlement values from survey data imposed on the partially completed structure (represented as a grade beam up to el 635) this calculation indicated that the measured displacements would result in a maximum rebar stress of 2 ksi.
For the other three settlement cases, individual finite-element models were used.
For settlement case b, the finite-element model represents the structure as-built to el 662'-0".
For settlement cases c and d, the finite-element model represents a fully constructed structure.
In each of the three finite-element analyses, the diesel generator building was analyzed for "best fit" settlements resulting from a statistical analysis of the recorded or estimated settlements.
For cases b, c, and d, springs were typically calculated at each nodal point along the H
foundation by dividing the structural load represented at the selected point by the measured or predicted settlement at that point.
The' finite-element analysis of each case then involved several iterations in which the soil springs were varied until 6
Midland Plant Units 1 and 2 5tructural Stresson Inducsd by i
Differential Settlement of the Diesel Generator' Building 000720s0 l
the deflected shape of the diesel generator building, as calculated by the model, approximated the "best fit" settlements.
Figure I-3 summarizes the actual and estimated settlements employed in the finite-element settlement analyses (cases b, c, and d).
Figures 1-3A, I-3B, and I-3C give individual isometric presentations of measured and predicted settlements and also show settlement values resulting from the finite-element analysis of the diesel generator building model for cases b, c, and d.
The comparison shows good correlation between values resulting from the finite-element model and the measured values and also for the.
f predicted settlement values.
Because of the great overall stiffness of the structure (shear walls are over 50 feet high and 2-1/2 feet thick) in particular when compared with the stiffness of the underlying soil, the building will undergo mainly rigid body motion.
(For a complete discussion showing that the structure has been experiencing primarily rigid body motion, refer to Attachment I-1, Settlement Data Analysis.)
Differences between calculated and measured settlements are small and are within the accuracy of the survey.
The maximum total rebar stress resulting from all settlement analyses (cases a, b, c, and d) is on the order of 21 ksi, which occurs in the south wall in the vertical direction.
The maximum horizontal rebar stress resulting from all settlement analyses is on the order of 18 ksi, which occurs in the south shield wall.
The location of maximum settlement stresses typically does not coincide with the location of maximum seismic or tornado stresses.
Actual calculated moment and forces for settlements have been combined with other load cases and are included in Table I-4 in accordance with the governing load equations.
(A second method of addressing settlement, involving the use of zero and near zero values for soil spring constants, is discussed in Attachment I-2.)
Other springs were developed for short-term loading, in which it was assumed that the structural movement was small enough to assume the soil was linearly elastic.
The modulus of elasticity was estimated using soil density and measured shear wave velocity values.
Springs were developed for the vertical and horizontal modes.
These springs were calculated by determining the amount of force required to produce a unit displacement in the direction indicated by the particular mode.
The footings of the diesel generator building were assumed to be resting on a large mass of elastic soil for the vertical mode and-embedded within the mass of soil for the horizontal mode.
The settlement due to seismic shakedown was also identified as a possible occurrence during a seismic event.
The maximum differential settlement due to seismic shakedown, as stated in Question 27 of the NRC Requests Regarding Plant Fill, is 7
I
)
> j Midltnd Pltnt Units 1 cnd 2 tj Structural Strcssas Induc;d by li Differential Settlement of the Diesel Generator' Building 0 0 0,1 2 C L 0 approximately 1/2 inch.
The effects of seismic shakedown settlement will act to reduce the effects of differential settlement and for this reason the effect of seismic shakedown was not the governing case in tha structural reanalysis of the diesel generator building.
2.1.3 Live Loads Live loads were applied to the modeled structure by applying pressure loads on the plate elements which represent the floor slab at el 664'-0" and the roof at el 680'-0".
During the plant life, a maximum live load of 100 psf is predicted to occur on the roof slab, whereas for the floor at el 664'-0",
a maximum live load of 250 psf is postulated.
One hundred percent of the live load was used in the design of individual structural members, such as floor slab at el 664'-0" and roof slab at el 680'-0".
For overall building response, however, the live loads considered were limited to 25 percent of the above maximum loads.
This 25-percent value represents the live load expected to be present when the plant is in operation, i.e.,
100 percent of the live load will not act simultaneously on every square foot of the floor space.
2.1.4 Wind Loads Loads resulting from the design wind (100-year recurrence with a velocity of 85 mph) were applied to the modeled structure as a pressure load on the plate elements that represent the exposed walls.
Wind loads on the roof and south wall hatch covers were determined assuming the hatch covers were in place.
These loads were then distributed to the nodal points which define the perimeter of the respective hatches.
2.1.5 Tornado Loads As specified in BC-TOP-3-A (Reference 2), various combinations of velocity wind pressure, differential pressure, and local pressures were applied to the modeled structure.
The maximum wind velocity of the tornado was 360 mph.
The original structural analysis performed in accordance with the l
FSAR considered various tornado-geners"Nd nissiles.
The analysis l
considered missiles equivalent to a '".
32" by 12' wooden plank (108 pounds) traveling end-on at '93 xp. at any height; a j
4,000 pound automobile with a vric ;ty f 72 mph no higher than l
30 feet above the ground with a s.,ntos urea of 20 square feet; a 1-inch diameter, 3-foot long, 8-pound stdel bar traveling at 216 mph at any heignt in any direction, and a 35-foot long utility pole, 13-1/2 inches in diameter, weighing 1,490 pounds, traveling at 144 mph, and striking the structure not more than 8
t if Midlcnd Pltnt Units 1 cnd 2 Structural Streasts InducLd by Differential Scttlcment of 00072000 the Diesel Generator Building 30 feet above the ground.
For tornado-generated missile loads, the structure was allowed to locally exceed the yield strain.
The results of the original tornado-generated missile load analysis showed the diesel generator building was acceptable.
Results of missile impact tests conducted over the last 6 years indicate that reinforced concrete walls, thinner than the exterior walls of the diesel generator building, have a considerable margin against local damage.
The tests indicate that a wall thickness of 12 inches would sufficiently preclude unacceptable local damage (spalling) from these missiles.
(The thinnest exterior wall of the diesel generator building is 30 inches thick.)
2.1.6 Seismic Loads The seismic response of a structure depends on the stiffness prcperties and mass of the structure, the input seismic motion at the structure location, and the soil properties of the foundation medium.
Of these parrr: ters, only soil properties are affected by insufficient compa., ion of backfill.
The following paragraphs describe how the effe.c3 of insufficient compaction and eventual surcharging were accciated for in the revised diesel generator building seismic ana';fsis.
The design spectra and design time l
history as defined it FSAR Section 3.7 have been used in this reanalysis.
1 The analytical models used for the original seismic analysis and for the seismic reanalyses described in this report are one-dimensional, stick-type, lumped mass models using beam elements 1
to recresent the structural stiffness and impedence functions of the foundation medium (see Figure I-1).
The effect of soil-structural interaction is accounted for by coupling the structural model with the foundation media.
The f
foundation media are represented by impedance functions which represent the equivalent spring stiffness and radiation damping coefficients as specified in BC-TOP-4-A (Reference 3).
The structural stiffness of the lumped mass model was not revised in the new dynamic analysis.
The difference in the new model was confined to the treatment of the soil-structural interface.
The revised analysis developed the impedance functions based on the building's foundation dimensions and the modification in the soil properties described below.
In addition, for the horizontal accelerations, the weight of the soil and the concrete pedestals and diesel generator pedestals within the building were included in this revised model.
TFe original (presettlement) diesel generator building seismic analysis was based on the underlying till material, which has a 9
l
=
Midlcnd Plent Units 1 and 2 Structural Stressan Induccd by Differential Settlement-of the Diesel Generator" Building 00072000 shear wave velocity value of 1,359 ft/s (see Table I-3).
This value was not adjusted for the 30 feet of plant fill between the till and building foundation elevation.
The first seismic reanalysis accounted for the soil properties of the fill by averaging the measured shear wave velocity of the fill and underlying till (Figure I-4) over a depth of 75 feet, which is the smallest dimension of the building.
This resulted in the value of 796 ft/s, which was used in the seismic reanalysis.
However, the effect of decreasing shear wave velocity to a lower bound estimate of 500 ft/s was also analyzed.
Both the measured shear wave velocity value of 796 ft/s and the lower bound shear wave velocity value of 500 ft/s were supplied by soil consultants.
The floor spectra at all elevations of the diesel generator building were generated using a shear wave velocity value of 796 ft/s.
The resulting floor response spectra were combined in an enveloping fashion with the spectra developed in the original analysis which used a shear wave velocity value of 1,359 ft/s.
The floor response spectra were further broadened to account for a lower bound shear wave velocity of 500 ft/s.
- Thus, conservative floor response spectra were generated.
The results of the seismic reanalysis indicated that the seismic forces at all elevations of the diesel generator building were somewhat higher than the forces determined in the original analysis.
The highest seismic acceleration was derived from an analysis using a shear wave velocity value of 796 ft/s.
This increased seismic load was conservatively simulated by applying the maximum structural acceleration occurring in the dynamic model to the finite-element model in north-south, east-west, and vertical directions.
The combined effect of the three directional responses was assessed using the square-root-of-the-sum-of-the-squares method recommended in NRC Regulatory Guide 1.92.
The ability of the structure to withstand these increased seismic forces in combination with the other loads is described in Section 3.0, 2.1.7 Thermal Loads Thermal effects were included in the analysis as a linear variation of temperature across the thickness of an element.
The thermal effect due to linear variation of temperature across the thickness of an element (also called gradient) results in bending moments being applied to the element.
In general, the temperature gradient which is of most concern for the diesel generator building is that anticipated to occur in the winter.
In accordance with the Handbook of Concrete Engineering 10
l Midlcnd Pltnt Units 1 and 2 Structural Strc3cos Induc;d by Differential Satticm:nt of the Diesel Generator Building 000720L0 (Reference 4) and FSAR meteorological data, the equivalent steady-state exterior winter temperature of 14.6F was calculated.
The corresponding maximum interior ambient air temperature was 75F.
For information on how thermal effects were applied to the model, see Section 3.0.
3.0 ANALYSIS PROCEDURE To determine force components in accordance with accepted analysis techniques, the force components resulting from each load condition of Section 1.1 are calculated separately.
Applicable loads are applied to any of three models.
(The three models are identical in every aspect except for the spring elements used to represent the soil pressures.)
Various load factors are applied to the separate load conditions which are then assembled to create the required load combinations.
Using this combined response, the structure is examined to ensure that the allowable stress limit is not exceeded.
3.1 SETTLEMENT /LONG-TERM MODEL The soil moduli used to calculate the soil springs for this condition are based on the actual measured settlement data (for settlement prior to fall 1981) and estimated 40-year settlement values ( for settlement subsequent to fall 1981).
Dead load is applied to the model causing differential settlement to occur.
As detailed in Section 2.1.2, three different models (for three different time periods) are used for this purpose.
For each settlement model, an analysis iteration occurs to produce a deflected shape which best approximates the appropriate "best-fit" settlements for the particular time period being investigated.
The settlement forces corresponding to each unique time period are then obtained by imposing the calculated deflection values on a finite-elenent model and removing the dead load.
3.2 SHORT-TERM MODEL The soil moduli used to calculate soil springs for this model corresponds to short-term loads (i.e., wind, tornado, seismic).
3.3 ZERO-SETTLEMENT MODEL The dead load and live load case are constructed on the zero-settlement model.
To approximate zero settlement, large values are entered for the soil springs into this model.
3.4 STRUCTURAL ADEQUACY COMPUTATIONS The computations necessary to verify structural adequacy were performed using a computer analysis program (OPTCON) capable of 11
Midland Plcnt Units 1 cnd 2 Structural Strasgos Induced by Differential Settlement of the Diesel Generator Building 00972000 analyzing reinforced concrete sections.
This reinforced concrete analysis program models a portion of the diesel generator building and analyzes it for forces that resulted from the BSAP finite-element model analysis.
Refer to Appendix A for additional information concerning OPTCON.
To determine the structural adequacy of the diesel generator building, the modeled structure was partitioned into structural categories (i.e., north wall, center wall, roof, etc).
Critical elements from each category were then selected for further investigation based on their axial force, moment, and in-plane shear force.
Using OPTCON, rebar stress values were then calculated in these critical elements to verify that the allowable rebar tensile stress value was not exceeded.
To facilitate the calculation process, a computer program was specifically written for selecting critical elements that would undergo OPTCON investigation.
This program was written so that its selection of critical elements was based on a comparison of the axial force, bending moment, and in-plane shear force of each separate element within a structural category with all other elements of the same structural category.
Once these critical elements were selected, a thermal gradient was assigned to each element based on the location of that element within the building.
Based upon t03 procedure discussed above, all structural categories of the diesel generator building were investigated and found to meet the structural acceptance criteria.
Table I-4 shows the results of the analysis.
The left-hand column of Table I-4 describes the various structural categories of the diesel generator building.
The second column shows the load combination which produces the highest stress, i.e.,
the load combination which is critical for a particular structural category.
The third column presents the rebar stress value computed by OPTCON for the critical element within each structural category.
The highest rebar stress value (reflecting the combined effects of flexural, axial, and in-plane shear loads) exist in the south wall where the rebar stress value is 44.0 ksi.
The fourth column indicates the concrete compressive stress associated with the maximum rebar tensile stress in each structural category.
The final structural reanalysis of the diesel generator building showed that the critical load combinations (Table I-1) are those which include either the tornado load case (W'), the SSE load case (E'), or the settlement load case (T), specifically:
a.
1.0D + 1.0L + 1.0W' + 1.0To (18) b.
1.0(D) + 1.0(L) + 1.0(E') + 1.0(To)
(15) 12
Midlcnd Pltnt Units 1 cnd 2 Structurcl Strc2:as Induc;d by Differential Settlement of the Diesel Generator Building 00072Cs3 c.
1.4(D) + 1.4(T)
(2)
In approximately 70 percent of the diesel generator building, the tornado load combir.ations produce the these strecs levels.
4.0 CONCLUSION
S 1
The diesel generator building is a massive, reinforced concrete j
structure with extensive reserve strength.
The structural reanalysis performed on the diesel generator building verifies that the integrity of the structure will not be violated even under the most critical load combinations.
Based on the analysis performed, it can be stated that the settlement has had minimal effect on the structure, and there is reasonable assurance that the diesel generator building will safely perform its intended function over the operating life of the Midland plant.
13
Midltnd Pltnt Unita 1 cnd 2 Structurcl Strc22c2 Inducnd by Differential ScttlGmsnt of the Diesel Generator Building 00072090 REFERENCES 1.
Consumers Power Company, Response to NRC Requests Regarding Plant Fill, Docket 50-329, 50-330 2.
Bechtel Power Corporation, Tornado and Extreme Wind Design Criteria for Nuclear Power Plants, Revision 3, August 1974 (BC-TOP-3-A) 3.
Bechtel Power Corporation, Seismic Analyses of Structures and Equipment for Nuclear Power Plants, Revision 3, November 1974 (BC-TOP-4-A) 4.
M.
Fintel, Handbook of Concrete Engineering, Van Nostrand Reinhold Company, September 1974 1
14
Midland Plcnt Units 1 cnd 2 Structurcl Strs2=c2 Induc;d by Differenticl Satticm:nt of the Diesel Generator Building 000720aO APPENDIX A OPTCON The OPTCON computer code is a versatile and complete design and analysis program for reinforced concrete structures.
The program may be used for the investigation of an existing reinforced concrete section where the reinforcing steel area is predetermined.
Alternatively, it can be used for obtaining an optimum design by allowing the program to determine the minimum reinforcement required.
The computer program operates on the axial force / moment interaction diagram (IAD) of a section, where an IAD is a plot of the maximum allowable resistance of a section for given stress and strain limitations.
Combinations of moment (M) and axial load (P) falling within this area are acceptable.
Figure IA-1 depicts the appropriate IAD for a symmetrically reinforced, symmetrically shaped section subjected to a combination of flexural and axial loads.
The OPTCON program handles loads consisting of axial forces and corresponding bending moments due to different types of loads.
Special subroutines are provided to incorporate the thermal effects into the design and/or investigation.
The cracking effect of the concrete and the yielding effects of the reinforcement (as allowed by the appropriate stress / strain yielding criteria) are considered in the calculation of the thermal loads and moments computed by the program.
A-1
Midland Pl nt Units 1 End 2 Structural Str:sses induced by the Differential SettlIment of the Diesel Generator Building 0 0 0 7 I' U '" O Compression C(-)
Satifies Design Criteria Interaction Diagram s
Compression Failure Zone s
!!@!i li!!?N PM3 s
s ltifi m-s ga r -
ss
$i 2:N!:
\\ Balanced 39
/
Tension Failure Zone s-s Moment
/
(+)M
/
Tension T(+)
Figure IA-1 TYPICAL INTERACTION DIAGRAM (for single axis bending on a section with symmetrical reinforcement)
Midlcnd Plcnt Unit 3 1 cnd 2 Structural Stronces Induc;d by Differentici Sstticnent in the Diens1 G:ntrator Building n
r 0 0 0.. n4 ' ' " ",
TABLE I-1 LOADS AND LOAD COMBINATIONS FOR CONCRETE STRUCTURES OTHER THAN THE CONTAINVENT BUILDING FROM THE FSAR AND QUESTION 15 OF RESPONSES TO NRC REQUESTS REGARDING PLANT FILL Responses to NRC Requests Regarding Plant Fill, Question 15 a.
Service Load Condition U = 1.05D + 1.28L + 1.05T (1)
U = 1.4D + 1.41 (2) b.
Severe Environmental Condition U = 1.0D + 1.0L + 1.0W + 1.0T (3)
U = 1.0D + 1.0L + 1.0E + 1.0T (4)
FSAR Subsection 3.8.6.3 a.
Normal Load Condition U = 1.4D + 1.7L (5) b.
Severe Environmental Condition (6)
U = 1.25 (D + L + Ho + E) + 1.0To (7)
U = 1.25 (D + L + Ho + W) + 1.0To U = 0.9D + 1.25 (Ho + E) + 1.0To (8)
U = 0.9D + 1.25 (Ho + W) + 1.0To (9)
~
c.
Shear Walls and Moment Resisting Frames (10)
U = 1.4 (D + L + E) + 1.0T + 1.25Ho o
U = 0.9D + 1.25E + 1.0T + 1.25H (11) o o
d.
Structural elements carrying mainly earthquake forces, such as equipment supports U = 1.0D + 1.0L + 1.8E + 1.0To + 1.25Ho (12) 1
Midland Plant Units 1 cnd 2 Structural Strccces Inducrd by Differential Scttlement in
- o the Diesel Generator Building 000tc-Table I-1 (continued) e.
Extreme Environmental and Accident Conditions U = 1.05D + 1.05L + 1.25E + 1.0T + 1.0H + 1.OR (13) a a
U = 0.95D + 1.25E + 1.0T, + 1.0Ha + 1.OR (14)
U = 1.0D + 1.0L + 1.0E' + 1.0To + 1.25Ho + 1.OR (15)
U = 1.0D + 1.0L + 1.OE' + 1.0Ta + 1.0Ha + 1.0R (lo)
U = 1.0D + 1.0L + 1.0B + 1.0To + 1.25Ho (17)
U = 1.0D + 1.0L + 1.0To + 1.25Ho + 1.0W' (18) where B = hydrostatic forces due to the postulated maximum flood D = dead loads of structures and equipment and other permanent load contributing stress E = operating basis earthquake (OBE)
E'
= safe shutdown earthquake load (SSE)
Ho = force on structure caused by thermal expansion of pipes under operating conditions H, = force on structure caused by thermal expansion of pipes under accident conditions L = conventional floor and roof live loads (includes moveable equipment loads or other loads which very in intensity)
R = local force, pressure on structure, or penetration caused by rupture of pipe T = effects of differential settlement, creep, shrinkage, and temperature T
= thermal effects during normal operating conditions, o
including linear expansion of equipment and tempera-ture gradients T, = total thermal effects which may occur during a design accident U = required strength to resist design loads or their related internal moments and forces i
2
Midlcnd Plant Unita 1 cnd 2 l
Structural Stresacs Inducad by l
Differential Settlem;nt in i
the Diesel Generator Building 00072050 Zable I-1 (continued)
W = design wind load W' = tornado wind loads, excluding missile effects, if applicable (refer to Subsection 2.2.3.5) e 3
Midland Plant Units 1 and 2 Structural Streacca Induced by Differential Sattlem3nt in the Diesel Generator Building 0 0 0 7.0 0. 0 TABLE I-2' LOADS AND LOAD COMBINATIONS FOR COMPARISON ANALYSIS REQUESTED IN QUESTION 26 OF NRC REQUESTS REGARDING PLANT FILL ACI 349 as Supplemented by Regulatory Guide 1.142 a.
Normal Load Condition:
U = 1.4 (D + T) + 1. 7 L + 1. 7 Ro U = 0.75 [1. 4 (D + T) + 1.7L + 1.7T + 1.7Ro]
o b.
Severa Environmental Condition:
U= 1. 4 ( D + T) + 1. 4 F + 1. 7 L + 1. 7 H + 1. 9 Eo + 1.7Ro U = 1.4 (D + T) + 1.4F + 1.7L + 1.7H + 1.7W + 1.7Ro U = 0.75 11.4 (D + T) + 1.4F + 1.7L + 1.7H + 1.9Eo + 1.7To
+ 1.7Roj U i 0.75 [1.4 (D + T) + 1.4F + 1.7L + 1.7H + 1.7W + 1.7To
+ 1.7R ]
o c.
Extreme Environmental Conditions:
U=
( D + T) + F + L + H + To + Ro+Wt U=
(D + T) + F + L + 11 + T o + Ro + E.,
d.
Abnormal Load Conditions:
U=
(D + T) + F + L + 11 + T.
+ R. + 1. 5 P.
U=
( D + T) + F + L + 11 + T. + R. + 1.25P. + 1.0(Y, + Y3
+ Ym) + 1.25Eo U= (D + T) +F+L+H+T.
+ R. + 1.0P. + 1. 0 ( Yr + Yj
+ Ym) + 1. 0 E.,
1
Midltnd Plant Unita 1 End 2 Structural Stre22c3 Induc;d by Differsntini Satt1cm:nt in the Diesel Generator Building Table I-2 ( Contin ued )
where 000'!20 3
Normal loads are those loads encountered during normal plant operation and shutdown, and include:
T
= settlement loads D = dead loads or their related internal moments and forces L
= applicable live loads or their related insternal moments and forces F
= lateral and vertical pressure of liquids or their rela-ted internal moments and forces H
= lateral earth pressure or its related internal moments and forces To = thermal effects and loads during normal operating or shutdown conditions, based on the most critical transient or steady-state condition Ro = maximum pipe and equipment reactions if not included in the above loads Severe environmental loads are those loads that could infre-quently be encounter'ed during the plant life and include:
En = loads generated by the operating basis earthquake (BOE)
W = loads generated by the operating basis wind (OBU) speci-fied for the plant Extreme environmental loads are those loads which are credible but highly improbable, and include:
E.,= loads generated by the safe shutdown earthquake (SSE)
W = loads generated by the design tornado specified for the plant Abnormal loads are those loads generated by a postulated high-energy pipe break accident and include:
P.
= maximum differential pressure load generated by a postulated break T.
= thermal loads under accident conditions generated by a postulated break and including To 2
Midland Plant Units 1 cnd 2 Structural Stressos Induend by Differential Settlcm:nt in the Diesel Generator Building 0 u u~ t c " " "
e Table I-2 (Continued)
R. = pipe and equipment reactions under accident conditions generated by a postulated break and including Ro required strength to resist design loads or their U
=
related internal moments and forces loads on the structure generated by the reaction on l
Y,
=
the broken high-energy pipe during a postulated break jet impingement load on a structure generated by a Yi
=
postulated break Y
= missile impact load on a structure generated by or during a postulated break, such as pipe whipping 3
Midland Plant Units 1 and 2 Structurcl Stresses Induc:d by Differentiel Settlem nt in the Diesel Generator Building 00072GS0 TABLE I-3 SOIL PROPERTIES USED IN THE SEISMIC ANALYSIS First Second original Revised (1)
Revised (1)
Analysis Analysis Analysis Modulus of Elasticity (E) 22,000 ksf 6,598 ksf 2,609 ksf Poisson's Ratio 0.42 0.45 0.40 Unit Weight (w) 135 pcf 116 pcf 120 pc/s Shear Wave Velocity (Vs) 1,359 ft/s 796 ft/s 500 ft/s Shear Modulus 7,746 ksf 2,275 ksf 971 ksf I'I Note different shear wave velocity values.
1
Midland Pltnt Unita 1 and 2 Structural Stra2cc2 Induccd by Differential Settlement of the Diesel Generator Building 0037?UEO xx3Ls I_4 REBAR STRESS VALUES FOR THE DIESEL GENERATOR BUILDING STRUCTURAL MEMBERS (ACCORDING TO THE FSAR AND RESPON5ES TO NRC REQUESTS REGARDING PLANT FILL, QUESTION 15)
Compressive Tensile Concretet 2)
Rebar Stress Stress value (ksi)
Value (ksi)
Description of Load (11 Allowable Allowable Members / Location Combination
= 54 ksi
= 3.4 ksi Exterior - West 2'-6" thick wall Tornado 25.03 0.425 horizontal rein-forcement Exterior - South 2'-6" thick wall Seismic 44.04 0.000 0 l
horizontal rein-forcement Elevation - 664'-0" 2'-0" floor slab Tornado 39.15 0.068 N-S reinforcement Elevation - 680'-0" l'-9" floor slab Tornado 36.06 0.834 E-W reinforcement South 2'-0" missile shield Settlement 42.79 0.185 wall south, horizontal reinforcement Interior 2'-0" interior missile Tornado 28.06 0.000l20 shield wall, vertical reinforcement North 2'-0" missile shield Tornado 13.85 0.000l2h wall north, horizontal reinforcement 1
' TABLE I-4 (continued)
Compressive Tensile Concrete Rebar Stress Stress ( 2) 000'iPCC0 value (ksi) value (ksi)
Descrip'tlon of Load (1)
Allowable Allowable 3.4 ksi Members / Location Combination
= 54 ksi
=
Exterior - North 2'-6" thick wall Tornado 21.90 0.313 horizontal reinforce-ment Exterior - East 2'-6" thick wall Tornado 23.64 0.403 horizontal reinforce-ment Interior l'-6" thick wall Tornado 16.66 0.000l3) horizontal reinforce-ment South 2'-0" thick box Tornado 8.02 0.000(3) missile chield/ south, horizontal reinforce-ment Footing 2'-6" thick footing Tornado 35.22 NOTES:
(1)The tornado load combination is 1.0 (D + L) + 1.0W' + 1.0To.
The settlement combination is 1.4D + 1.4T The seismic load combination is 1.0 (D + L) + 1.OE' + 1.0To.
(2iconcrete stresses shown are associated with maximum rebar tensile stresses shown in this table.
131Section is in tension.
2
Midland Pirnt Units 1 rnd 2 Structural Stresses Induced by Differential Settlement in the Diesel Generator Building El. 680'-0" M MmW Mau Nnt) 1 (Member Number)
El. 664'-0"
'N i
2 O
El. 647'-0"
%tM
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M K
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/
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yl Horizontal Damper t
Rotational Damper
,C C,
jrK x
ri i// /// ///// / / //// /
/
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e DATA DATE DATA DERIVATION 7/10178 - 11/24/78 Measured settlements on scribe, then converted to the equivalent settlement on marker location 12/2178 - 3122179 Measured settlements directly from marker 3/30179 - 9114179 Measured settisments from substituted marker inside the building on mezzanine floor el 663' 9114179 - Now Measured settlements directly from marker CONSUMERS POWER COMPANY MIDLAND UNITS 1 AND 2 MEASUREMENT LOCATIONS FIGURE 2 i S L GENE T U LDING SETTLEMENT DATA ANALYSIS 5/6/82 G-2508-10
00072090 22 21 20 3
0.000-0.100-0.200-
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,'g.,
790914 (SUBSTITUTED MARKER) 0.600-
'790906(SUBSTITUTED MARKER) 790914 (MARKER)
CONSUMERS POWER COMPANY MIDLAND UNITS 1 AND 2 SETTLEMENT ALONG SOUTH WALL m
FIGURE 3 wouwo ums i ANo 2 DIESFL GBNERATOR BUILDWG SETTLEMENT DATA ANALYSIS 5/6/82 G 2508 09
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a FROM THE TRIANGLE RELATIONSHIP A
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IF SURVEY IS 100% ACCURATE, I DIFD" SHOULD:
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- DIFD is the deviation of the corner from a plane which induces warping.
"E DIFD is the accumulated valve of DIFD.
CONSUMERS POWER COMPANY MIDLAND UNITS 1 AND 2 WARPAGE ANALYSIS l
FIGURE 6 l
$E L GENERATO1R UILImG SETTLEMENT DATA ANALYSTS 5/6/82 Ce250848
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THE DIFFERENCE FROM 3/22179 /-
TO 6129179 CONSUMERS POWER COMPANY MIDLAND UNITS 1 AND 2 DIFFERENTIAL SETTLEMENT DETERMINATION FIGURE 8 DtES L GENE TOR BU LDING SETTLEMENT DATA ANALYSIS 5/6/82 G 250842
't I
00072050 ATTACHMENT Ir2 TO TECHNICAL REPORT STRUCTURAL STRESSES INDUCED BY DIFFERENTIAL SETTLEMENT OF THE DIESEL GENERATOR BUILDING 4
l l
00072000 MIDLAND PLANT UNITS 1 AND 2 ANALYSIS OF DIESEL GENERATOR BUILDING FOR ZERO SPRING CONDITION ANALYSIS f
CONTENTS
1.0 BACKGROUND
1 2.0 ANALYSIS PROCEDURE 1
3.0 CONCLUSION
S 2
TAELES 1
Rebar Stress Values for the Diesel Generator Building for Zero Spring Condition FIGURES 1
Diesel Generator Building Finite-Element Model for Zero Spring Condition 2
Comparison of 40-yr Estimated Settlement Values With Settlement Values Resulting From A Finite-Element Analysis of the Zero Spring Condition ii
MIDLAND PLANT UNITS 1 AND 2 g OF DIESEL GENERATOR BUILDING ZERO SPRING CONDITION ANALYSIS
1.0 BACKGROUND
During the February 23 through 26, 1982, meeting with the NRC, it was requested that a finite-element analysis of the diesel generator building (DGB) be performed for the 40-year, dead load case, modified with zero and near-zero soil spring constants in areas to represent potential bridging.
The primary purpose of this analysis would be to investigate the structure's ability to span any soft soil condition.
It was subseluently decided that, in an attempt to approximate the predicted 40-year settlement profile of the south wall (as proposed by Dr. Affifi on February 23, 1982), a soil spring value of zero would be used at the junction of the south wall and east center wall.
Soil spring values would then be linearly varied so that springs returned to their original 40-year values within a distance of approximately 15 feet from the zero spring (see Figure 1).
2.0 ANALYSIS PROCEDURE A finite-element analysis of the DGB was therefore performed using 40-year soil spring values, modified along the south wall and east center interior partition wall as described above.
Several analysis iterations were necessary to arrive at a settlement profile that approximated the desired 'best fit" settlement profile (as obtained from a statistical analysis of Dr. Affifi's estimated 40-year settlement values).
Figure 2 gives an isometric presentation of Dr. Affifi's 40-year settlement values and also the settlement values re-sulting from the finite-element analysis of the DGB for the
.zero spring condition.
Subsequent to the final analysis iteration, maximum rebar stress values were calculated for the dead load plus settle-ment case (i.e., " modified case").
These values were com-pared with the dead load plus settlement case previously calculated for the " unmodified" 40-year settlement case (see Table 1).
Such a comparison shows that, except for an increase in the south wall, the footings, the box missile shield, and the south shield wall, the maximum rebar stress values remained essentially unchanged.
Typically, stress level increases were limited to approximately 5 ksi except in the south shield wall, where the modeling technique causes the rebar stress value to increase 18 ksi, and in the footings where the nature of the analysis causes the rebar stress value to increase approximately 20 ksi.
1
Midland Plant Units 1 and 2 Diesel Generator Building 0 0 0 '.7 2 0 9 0 Zero Spring Condition Analysis As a result of this favorable comparison, it is apparent
/
that it would be unnecessary to combine the " modified" 40-year settlement case with other load cases to form the load combinations of the FSAR and the response to Question 15 of the NRC Requests Regarding Plant Fill.
g s
/
For comparative purposes, the last column of Table 1 also presents maximum rebar stress values for the governing load f
combinations of the FSAR and Question 15.
A review of this I
table indicates that settlement stress is typically only a small portion of the overall maximum rebar stress values associated with the required load combinations (FSAR and Question 15).
i Furthermore, because the maximum settlement stresses and maximum service load stresses generally do not occur at the same location, the component of settlement stress that
+
actually exists in a maximum rebar stress value would typi-y cally be less than the values of Table 1.
3.0 CONCLUSION
S As a result of the analysis performed, it can therefore be concluded that the DGB can successfully span the assumed soft soil spot introduced into the analysis without significantly increasing the rebar stress levels.
l b
/
t I
f j
I
/
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s 2
l Midland Plcnt Unit: 1 and 2
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Dieccl Guntrator Building
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Zero Spring Condition Analysis l'
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00072090
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TABLE 1 REDAR'ETRESS VALUES FOR TJIE D1ESEL GENChtATOR BUILDIMG FOR ZERO SPRING CONDITIO11
- ).
i Category '
Tensile'Rebar Stress Values (allowable = 54 ksi) t (D + T)
(D + T)
Max Rebar for for Stresses dnmo'ified Modified for'FSAR d
40-Year Case 40-Year Case and 0 15*
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Wact wall
' 2.15 2.78 25.03 s
South wall 6.82 10.98 44.04 Slab at el 664'
'16.94**
16.97**
39.15 Roof at el 680'-0" 5.61.
6.19 36.06 South missile shield 10.79 28.82 42.79 Interior missile shield
' ' 5. 51; 5.30 28.06 North missile shield 2.71 2.72 13.85 East wall 2'24' 2.80 23.64 North wall 3.85 4.26 21.90 Interi,r partition wall 3.71 4.01 16.66 Box missile shield 4.50 9.33 8.02 Footings 14.35 37.14 20.95 (longitudinal bending)
Consists of FSAR load combinations and load combinations contained in response to Question 15 of the NRC Requests Regarding Plant Fill A large portion of this value is attributable to the dead load componer.
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