Analysis and Design of Power House Structure

STRUCTURAL ANALYSIS AND DESIGN OF POWER HOUSE COMPLEX IN SAINJ H.E.P USING STAAD.Pro V8i Mr. Revanth Kantheti M.Tech – Structures, Manipal University, Jaipur, India.

Mr. Sai Krishna Seela Managing Director, AF Consult India Pvt Ltd Noida, India.

 ABSTRACT: Power House is one of the important component of hydro power projects. These comprises of surface, semi

 –  underground   underground and and underground. The current current power house which we are analysing now is an underground  power house of SAINJ hydro hydro electric-project which is located on the Sainj River which is a tributary of Beas River near village Niharni in Kullu district of Himachal Pradesh. This study gives a brief idea of methodology in analysing and designing of the power house when undergone different types of loading conditions. The critical positions, combinations and applications of loads at required particular locations in it has been highlighted which was found out after extensive study of the behaviour of structure for all possible loading cases using STAAD.Pro. This helps in the comparison of final analysed results of any other similar (geometry, geological location) projects of power houses and get an idea about the obtained results in the future.

KEYWORDS: Hydro electric project (H.E.P), STAAD.Pro, Power house, Analysis, Design, Critical combinations, Recommendations.

I. INTRODUCTION: The power house complex has installed two units of 50 MW each. The two separate Frame structure separated by EJ of plan dimensions of 18m long x 16m wide & 19m long x 16m wide as shown in Fig.1 are

 proposed to accommodate two unit’s. The power house complex two units are separated by 25mm expansion joint (EJ) with each other and also wit h erection bay & control block at the interface by 25mm EJ. The power house complex frame structure is constructed in two stages. In the first stage only the side

Page 552

column (main crane column) and crane beam along with intermediated tie beam will be constructed, while in the second stage floor slabs, connecting beam, and some additional column will be constructed.

FIG.1: Plan at elevation 1347.8m of power house

II. GEOMETRY OF THE STRUCTURE: For better understanding and realistic view the 3D rendering view of the structure from STAAD has been shown in Fig 2.As the two units of power house are symmetrical the critical unit i.e., more in length has  been considered for analysis and the same results will be applied to the other unit. The salient features of the structure has been briefed below the figure.

Page 553

FIG 2: Isometric view of the single unit of power house

III. SAILENT FEATURES: Crane column size

: 1.0m x 1.0m

Crane beam size (wide x deep)

: 1.0m x 1.2m

Floor column size

: 0.5m x 0.5m

Floor beam size (wide x deep)

: 0.5m x 0.8m

Tie beam size (wide x deep)

: 0.4m x 0.6m

Floor thickness (for all floors)

: 0.4m

IV. SCOPE: The scope of the present report is limited to the below 

Structural analysis and design of concrete elements (crane column & crane beam)



Structural analysis and design of plate elements (floor slabs)

Page 554



To check whether the deformation behaviour of frame structure are within allowable range (expansion joint limit).



To check whether the maximum foundation stresses are within the limit of safe bearing capacity.

V. MATERIAL PROPERTIES: Concrete of grade

: M30 / M25

Unit weight

: 24 kN/m3

Poissons ratio

: 0.17

Youngs modulus

: 5000 √f ck

Safe bearing capacity of rock (assumed) : 150 T/m2 Characteristic strength of steel (f y)

: 500 N/mm2

 VI. BOUNDARY CONDITIONS: Fixity boundary conditions are assumed along the interface of Turbine/Generator concrete with floor sla b as shown in Fig 3 which is a part of the methodology before analysing the structure.

FIG 3. Fixity condition assumed for the structure

Page 555

VII. DEISGN LOADS & COMBINATION: The following loads have been considered in the analysis: 

Dead Load (DL)



Crane Load (CL)



Earthquake Loads (EQ)

1. DEAD LOAD: Dead load of unit weight of RCC as 25 kN/m 3 is assumed.

2. CRANE LOAD: The load considered for EOT crane mounted at the top of the beam are following

2.1.1 EOT Crane load data (First Stage Model) Wheel load (static)-Per wheel

196 kN

Wheel load (dynamic-with impact factor)- Per wheel

245 kN

Wheel base

7.0 m

Span of EOT Crane

15.0 m

 Number of wheels at one side

4 no’s

Longitudinal force due to breaking in LT movement (Per wheel)

12 kN

Transverse force due to breaking CT movement (Per wheel)

12 kN

2.1.2 EOT Crane load data (Second Stage Model) Wheel load (static)-Per wheel

480.12 kN

Parked Wheel Load (50% static)-Per wheel

240 kN

Wheel load (dynamic-with impact factor)- Per wheel

600.7 kN

Wheel base

7.0 m

Span of EOT Crane

15.0 m

 Number of wheels at one side

4 no’s

Longitudinal force due to breaking in LT movement (Per wheel)

24 kN

Page 556

Transverse force due to breaking CT movement (Per wheel)

24 kN

Floor load at EL. 1347.80 (Operating Floor)

15 kPa

Floor load (each) at EL. 1343.43 & at EL.1339.75

15 kPa

3. EARTHQUAKE LOAD: Response spectrum of IS: 1893-2002 has been used for seismic analysis. It is assumed that the construction site falls in Zone IV of earthquake zoning map of ref [2]. As per Ref. [2], the horizontal peak ground accelerations for Zone IV (Z) is 0.24g. Further 50% reduction in horizontal spectral acceleration has been assumed, since the structure is underground with hard rock strata. Vertical seismic coefficient is taken as 2/3 of horizontal acceleration (Ref. [2]). The Importance factor (I), reduction factor (R) are taken 1.5 & 5 respectively. Further 5% damping is assumed in the structure.

4. LOAD COMBINATIONS: Following loading combinations have been considered in the analysis of power house complex for both models. 

Self-weight of structure + Crane Load (static load).



Self-weight of structure + Crane Load (dynamic load).



Self-weight of structure + 50% Crane Static (Parked crane Load) + Earthquake load (100 % x direction + 30% z direction).



Self-weight of structure + 50% Crane Static (Parked crane Load) + Earthquake load (100 % z direction + 30% x direction).

5. METHODOLOGY: The methodology adopted in the analysis and design of all the structural components of the structure has  been explained individually as shown below.

5.1 CRANE BEAM 5.1.1 MODELLING & ANALYSIS: The Crane beam is modelled as member element. Concrete properties of 1m wide & 1.1m deep have been  proposed to crane beam, whereas the remaining 0.1m depth beam dead weight together will rail dead

Page 557

weight is applied as line load of 3 kN/m. The crane beam is connected integrally with crane columns.

5.1.2 DESIGN CRITERIA: Crane beam will be designed for the load combination mentioned in sec 4, where full crane load as mentioned in sec 2.1.2 will be considered for structural design. The most critical location of the wheel loads that can induce the maximum vertical bending moment will be located by using moving load option in Staad-pro. Similarly the most critical location of wheel loads that can induce the maximum shear force will  be located. The depth of crane beam will be checked for the permissible deflection. The Crane beam will be designed for maximum bending moment, torsion & shear force. The reinforcement will also to be checked for the lateral bending moment in the crane beam. Ductile detailing will be done for beams as per IS: 13920.

5.2 CRANE COLUMNS 5.2.1 MODELLING & ANALYSIS The Crane column is modelled as member element. At bottom, the boundary condition of the column has  been proposed as fixed. At top the column is connected integrally with crane beams & other beam location as shown in above drawing.

5.2.2 DESIGN CRITERIA: Structural design of Crane column of First stage concrete model will be done for the maximum bending moments & axial force resulted from two independent analyses. In the first analysis, first stage concrete model will be analysed for the load combination mentioned in sec 4, where crane load as mentioned in sec 2.1.1 will be considered. In the second analysis, second stage concrete model will be analysed for the load combination mentioned in sec 5.4, where crane & floor load as mentioned in sec 2.1.2 will be considered. The Crane Column will be designed for biaxial bending moment & axial load induced by the most critical load combination from the two independent analyses. At the elevation of crane beam & tie beam, the crane column should have monolithical connection. Dowels will be left in column of first stage model for later stage raft & beam construction in second stage concreting. The dowels/reinforcement diameter & spacing will be done on the basis of structural analysis of second stage full model. Ductile detailing will be done for columns as per IS: 13920.

5.3 FLOOR BEAMS

Page 558

5.3.1 DESIGN CRITERIA: Intermediate floor beams will be designed for the load combination mentioned in sec 4, where full crane & floor load as mentioned in sec 2.1.2 will be considered for structural design. The second stage concrete model is considered for the structural design of intermediate floor beam to calculate the reinforcement in the beam so as to leave sufficient dowel reinforcement at Crane column interface.

5.4 TIE BEAMS 5.4.1 DESIGN CRITERIA: Tie beams will be designed for the load combination mentioned in sec 4, where full crane load as mentioned in sec 2.1.2 will be considered for structural design. The second stage concrete model is considered for the structural design of tie beam to calculate the reinforcement in the beam as this load combination will generate maximum bending moments.

5.5 INTERMEDIATE FLOOR COLUMNS 5.5.1 DESIGN CRITERIA: Intermediate floor Columns will be designed for the load combination mentioned in sec 4, where full crane & floor load as mentioned in sec 2.1.2 will be considered for structural design. The second stage concrete model is considered for the structural design of intermediate floor column to calculate the reinforcement in the column so as to leave sufficient dowel reinforcement.

6. RESULTS Structural analysis (magnitudes) of individual members are mentioned as below:

6.1 RESULTS FOR CRANE BEAMS Results of the Design moments and Shear for the Crane beams are presented below in Table 1a & Table 1b. Table 1a Design Moments & Shear for Crane Beam (Span 10m)

Factor = 1.5

END 1

END 2

SPAN

Moment type

Hogging

Hogging

Sagging

Factored Moment (kNm)

3330

2310

2895

Factored Shear (kN)

2160

2010

Page 559

Table 1b Design Moments & Shear for Crane Beam (Span 7m)

Factor = 1.5

END 1

END 2

SPAN

Moment type

Hogging

Hogging

Sagging

Factored Moment (kNm)

1650

992

1575

Factored Shear (kN)

1560

1355

6.2 RESULTS OF CRANE - COLUMNS: Results of the Analysis (factored) of Crane column are presented below in Table 2. Table 2 Design Moments & Axial force for Crane Column

Moment (My) IN PLANE kNm

Moment (Mz) OUT OF PLANE kNm

Axial Force kN

Top

2145

67.5

1935

Bottom

282

257

1934

Top

1605

69

2220

Bottom

311

242

2213

Factor = 1.5

Column D - Line

Column B - Line

6.3 Results of Floor Beams: Results of the Design moments and Shear for the floor beams are presented below in Table 3a & Table 3b. Table 3a: Summary of Design Forces in floor-Beams at EL. 1347.77 Design Moments & Shear for Floor Beam at EL Top

Factor = 1.5

END 1

END 2

SPAN

Moment type

Hogging

Hogging

Sagging

Factored Moment (kNm)

339

302

198

Factored Shear (kN)

203

123

Torsion (kN)

229.5

Page 560

Table 3b: Summary of Design Forces in floor-Beams at EL. 1343.40 Design Moments & Shear for Floor Beam at EL Bottom

Factor = 1.5

END 1

END 2

SPAN

Moment type

Hogging

Hogging

Sagging

Factored Moment (kNm)

308

123

161

Factored Shear (kN)

195

105

Torsion (kN)

124.5

6.4 Results for Tie Beams: Results of the Design moments and Shear for the t ie beams are presented below in Table 4a & Table 4b. Table 4a: Summary of Design Forces in Tie beam Design Moments & Shear for Tie Beam ( Min. Span)

Factor = 1.2

END 1

END 2

SPAN

Moment type

Hogging

Hogging

Sagging

Factored Moment (kNm)

178

156

12

Factored Shear (kN)

112

107

Table 4b: Summary of Design Forces in Tie beam Design Moments & Shear for Tie Beam (Max. Span) Factor = 1.2

END 1

END 2

SPAN

Moment type

Hogging

Hogging

Sagging

Factored Moment (kNm)

113

98

18

Factored Shear (kN)

31

16

Page 561

6.5 Results for Intermediate Columns: Results of the Design moments and Shear for the intermediate column are presented below in Table 5. Table 5: Summary of Design Forces in Intermediate Column .

Moment (My)

Moment (Mz)

IN PLANE (kNm)

OUT OF PLANE (kNm)

Top

132

111

366

Bottom

103.5

86

360

Factor = 1.5

Axial Force (kN)

7. FLOOR SLABS: 7.1 DESIGN CRITERIA: The model of the structure has been made by using STAAD Software using plate &Member elements. The sketch in figure 2 gives the brief overview of the STAAD.Pro. model. Floor slab is modelled as Elastic mat foundation feature in STAAD.Pro. Structural design of Floor slab will be done for the maximum bending moments (Mx & My). Design has been carried out as per limit state design approach. The reinforcement  provided has been as per the design calculation, but not less than the nominal reinforcement for each structural member.

7.2 LOAD COMBINATIONS: The following loading combinations in Table 6, along with load factors shown, have been Considered in the floor slab analysis: Table 6: Proposed Load Combination Load Combination

Self-Weight

Live Load

Seismic (X-direction)

Seismic (Z-direction)

LC-1

1.50

1.50

 – 

 – 

LC-2

1.20

1.20

1.20

 – 

LC-3

1.20

1.20

 –  

1.20

LC-4

1.50

 –  

1.50

 – 

LC-5

1.50

 – 

 –  

1.50

LC-6

0.90

 –  

1.50

 – 

LC-7

0.90

 – 

 –  

1.50

Page 562

7.3 SLAB ANALYSIS RESULTS: The moments obtained in the slabs at each elevation of the power house has been tabulated as shown in table 7 below: Table 7: Moments in Floor Slabs SPAN

EL.1339.75m

EL.1343.43m

EL.1347.80m

52

75

75

39

56

56

End-span negative moment (kNm/m) Mid-span positive moment (kNm/m)

7.4 DESIGN RESULTS: The reinforcement details of floor slabs after designing accordingly for the obtained moments are as shown  below: Table 8: Reinforcement details SL. No.

Description

Reinforcement

1

Floor Slab at EL. 1339.75m EL.1343.43m & EL.1347.80m

1 layer of 16mm @ 250c/c Both ways Each (Top & Bottom)

NOTE: Components are designed accordingly by the obtained magnitudes of analysis results with the help of spread sheets and sufficient reinforcement is provided and mentioned in the detailing drawings for execution in the site for future reference and usage.

8. CONCLUSIONS: Based on the analysis following conclusions can be made: 

The proposed reinforcement for various concrete elements is designed for most critical load combinations.



Continuous raft is provided at the crane column footings.



The maximum vertical deflection in the crane beam (10 m span beam centre to centre) is of 8.2mm for the critical load combination.

Page 563



The maximum horizontal deflection in the frame structure (first stage model) is of 12.5 mm for the critical load combination, which is under allowable limit of 25mm Expansion joint.



The bending moments developed at crane column footing are not significant, therefore Nominal reinforcement of 20mm dia at 250mm spacing c/c is provided.

9. SOFTWARE USED: o

STAAD.Pro

o

Microsoft Excel

10. CODES: 

IS 456:2000 ( PLAIN AND REINFORCED - CODE OF PRACTICE )



IS 1893:2002 (CRITERIA FOR EARTHQUAKE RESISTANT DESIGN OF STRUCTURES)



IS13920 (DUCTILE DETAILING OF RCC STRUCTURES SUBJECTED TO SEISMIC FORCES )



SP 16 CHART ( DESIGN AIDS FOR REINFORCED CONCRETE TO IS 456 )



IS 4247 PART  –  1 (STRUCTURAL DESIGN OF SURFACE ELECTRIC POWER STATIONS  –  DATA FOR DESIGN )



IS 4247 PART  –  2 (STRUCTURAL DESIGN OF SURFACE ELECTRIC POWER STATIONS  –  SUPER STRUCTURE )



IS 4247 PART  –  3 (STRUCTURAL DESIGN OF SURFACE ELECTRIC POWER STATIONS  –  SUB STRUCTURE

11. REFERENCES:

a) Brown, Gutherie, “Hydro Electric Engineering Practice”, Blackie & Sons Ltd., London.  b) Dandekar M.M, Sharma K.N, “Water Power Engineering”, Vikas Publishing House Pvt. Ltd. c) IS 9761: 1995 Hydropower Intakes-criteria for Hydraulic Design. d) Varshney R.S. “Hydro -Power Structures”, Nem Chand & Bros, Roorkee. e) Creager , W.P and Justin J.D, “Hydro Electric f) J.Chen,Z.Zhang, and M.Xiao, “Seismic

Hand Book”, John Wiley & Sons.

response analysis of surrounding rock of underground

 powerhouse caverns under obliquely incident seismic waves,” Disaster Advances, vol.5, no.4, pp. 1160 1166, 2012.

Page 564