seismic analysis & design of surface power house, … mohan verma.…1 shows powerhouse during...
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Seismic analysis & design of surface power house,
Rampur H.E. Project (412 MW)
Verma, L.M.
Chief General Manager (Civil Design),SJVN Limited,
Shimla-171006, Himachal Pradesh, India
Abrol, R.K.
Additional General Manager (Civil Design),SJVN Limited,
Shimla-171006, Himachal Pradesh, India
Chauhan,Manish
Manager (Civil Design),SJVN Limited,
Shimla-171006, Himachal Pradesh, India
Abstract
Rampur Hydro Electric Project 412MW (RHEP) is a tail race extension of existing Nathpa Jhakri
Hydro Electric Project (NJHEP) and runs in tandem with it. RHEP is located on river Satluj, in district
Kullu & Shimla of Himachal Pradesh, India. RHEP is designed to receive 383.88 cumecs desilted
water from tail race outfall of NJHEP with a gross head of 138.70m. The Powerhouse Complex of
RHEP is surface type, with a size of 158m x 34.5m wide x 48m high including two service bays.
This paper briefly describes loading, method of analysis and design of foundations, retaining walls,
superstructure for Surface Power House building. The analysis is based upon seismic parameters values
approved by National Committee on Seismic Design Parameters (NCSDP). Foundations of
superstructure were modelled using Modulus of Subgrade reaction for the rock beneath and analysed
accordingly. Retaining walls were designed for combination of dynamic increment on earth pressure,
active earth pressures and surcharges above. Column, Beams, Substructure and Powerhouse Steel
roofing system were designed for all load combination including seismic, using STAAD Pro &Ansys
software.The results and references obtained are being used as a reference for optimizing & improving
the engineering design & layout of upcoming Surface Power Houses.
1. Introduction :
The surface Power House of Rampur Hydro Electric Project is located on right bank
of river Satluj at EL 878.00m (Service Bay level) nearVillage Bayal, District Kullu
(Himachal Pradesh). Surface Power house complex (158m x 34.5m wide x 48m high)
consists of Unit bay having 6 units, two Service bays and a Control bay. Unit bay
(111mX24.5m wide) houses six Francis turbines each of 68.67MW capacity. Service
bay 1 is located on western side of unit bay and service bay 2 on eastern side. The
control bay is located on northern side of unit bay and gate shafts are located on
southern side. Two lifts including stair cases have been provided on western and
eastern sides of unit bay. The cross section & plan of Power House (Fig. 1 & 2) shows
the different floor elevations & lines markings such as D, E, A, F, C, G, B, H. Picture
1 shows powerhouse during construction.
Unit bay portion (24.5m wide x 111m long) consists of MIV floor at El.853.00 (MIV
floor) where Main Inlet Valves are installed, one no. for each unit. Turbine floor is at
EL861.45 where related panels (cooling water system etc.) are kept and access to
turbine block is provided. Generator floor is at EL865.45 and it houses generator
related panels like NGT, earthing transformer etc. Machine floor is at EL871m
housing UCB, excitation panels etc. For maintenance and repair of MIVs and
Journal of Engineering Geology Volume XLII, Nos. 1 & 2
A bi-annual Journal of ISEG June-December 2017
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Runners, openings are kept in turbine, generator and machine floor slabs.Service bay
1 & 2 (27m X 24.5m& 20m X 24.5m respectively)located at El.878m are beused for
erection, installation, maintenance etc. of rotor, stator, MIV, transformer etc.EOT
cranes (2 Nos.) of 150T capacity have been provided at El.890m and runs all along
Service bay 1, unit bays and service bay 2. The unit bays and service bays are covered
by a sloping lattice roof truss system.
EL 865.45
TRENCH
13200
EL. 846.50y
yEL. 846.10
yy
2000
EL.853.5
10000
BACK FILL
C/L
-OF
DR
AF
T
DT GATE HOIST
4875 4875
TRANSFORMER
EL.901.00EL.898.30
MIV
DRAINAGE GALLERY(2000 x 2500)
EL.848.452
y y y y y y y y y
G-L
INE
y
y
y
y
y
GENERATOR
EOT CRANE BEAM(1700X1500)
PANEL/CONTROL ROOM
E.O.T. CRANE(2X150 TONNES)
E-L
INE
A-L
INE
B-L
INE
H-
LIN
E
EL. 852.779
EL. 849.188
POWERHOUSE - TYPICAL CROSS - SECTION
C/L - OF PENSTOCK
EL.858.40
TRT
C/L-OF PENSTOCK
DRAFT TUBE
y
E.O.T. CRANE
CABLE
yy
TRANSFORMER
400052505250
C-L
INE
F-L
INE
D-L
INE
47508250
C/L
-OF
UN
IT
VENTILATION
24500
EL.865.45
11800
y y y y y y y y
THRUST COLLARS
(ALONG C/L OF UNIT)
EL . 878.00
EL.856.20
22000
1250
1000
SWITCHYARD
GAS INSULATED
ROOF TRUSS
DCDV / BATTERY
LINE PROTECTION
BOARD SPACE
MIVPEDESTAL
SPIRAL
CASE
ACCESS
THRUST BLOCK
FRAME FORGIS BUSHING
DT GATE SHAFT
YA
RD
FOR RAIL TRACK
EL . 853.00EL . 851.00
EL . 863.34
BUS DUCT/
GALLERY
EL . 888.00
TR
AN
SF
OR
ME
R
GENERATOR FLOOR
TURBINE FLOOR
EL.861.45
MACHINE FLOOR
EL.871
STATION SERVICE2000
EL.878
EL.883.50
EL.889
EL.867.60
EL.865.19
EL . 878.00
EL.890.00
EL.895.00EL.895
(10 TONNES)
2000
2000
2000
EL.853
MACHINE FLOOREL.871.00
GENERATOR FLOOREL.865.45
TURBINE FLOOREL.861.45
MIV FLOOREL.853.00
TU
BE
GA
TE
ROOM
Figure 2
Figure 1
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Water enters spiral case at EL858.4m and henceforth to draft tube, through penstocks
embedded in thrust block below control bay raft and main inlet valve.
The powerhouse frame consists of four longitudinal column rows (D, E, A & B lines)
with one transverse column row at beginning and end of frame block. Each frame
block consists of two units. An expansion joint has been provided after every frame
block. D-line columns are 1mX2m from EL865.45m to EL898.3m and 1mX1.1m
above EL898.3m. E-line columns are 1mX1m from EL865.45m to EL889m. A-line
columns are 1mX2m from EL853m to EL890m, 1mX0.9m from EL890m to EL895m
and 1mX0.5m above EL895m. B-line columns are 1mX2.5m from EL853m to
EL878m, 1mX2m from EL878m to EL890m and 1m X 0.9m above EL890m.
2. Geology:
In the investigation stage subsurface exploration of power house area has been done
by drilling 8 nos. holes with depth varying from 30-45m. Exploratory drill holes
established the availability of rock surface at a depth of about 4.50 m along the centre
line of the Powerhouse building. The rock encountered between depths of 4.50m to
28.00m was mainly grey - greenish Phyllite, thinly to moderately foliated and further
between 28 to 45m depth, it was mainly dark phyllite and is thinly to closely foliated.
The rock in general is soft and flaky in nature but at places it is fresh and hard in
nature.
The rock in Power house and TRT area mainly comprises of carbonaceousphyllites
and the rock quality is poor to very poor. The foliation of rock is dipping towards the
pit from river side in southern portion.The details of major joint sets are as follows:
1st set of joints are mainly foliation joints N20ºW; 40º, the whole circle
bearing works out to be 340º; 40º. These joint sets have been named as J1.
2nd set of joints are S10ºW; 55º, the whole circle bearing works out to be
190º; 55º. These joint sets have been named as J2.
3rd set of joints are N75ºW; 60º. The whole circle bearing comes to be 285º;
60º. These joint sets have been named as J3.
Picture 1 Powerhouse during construction stage
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3. Method of Frame Analysis:
The complete structure has been modelled, including column, beams and trusses to
assess the exact effect during normal and emergency conditions. Bracing for trusses
have also been modelled in the STAAD Pro model. Columns and beams have been
considered as 3-D space frame (modelled using centre lines of structural members and
offsetted where necessary) (See Picture 2). 3 D frame analysis has been carried out
using STAAD Pro Software. The columns have been considered fixed at bottom ends.
The analysis of superstructure when it is fully constructed has been called Finished
Stage analysis (Picture 2).
Moreover an intermediate stage analysis called construction stage analysis (Picture 1)
has been carried out, which represents a stage during construction that lasted for over
a year. During this stage, only A line and B line columns are to be raised so as to
install 150T EOT crane and roof truss, so that EOT crane can help in erection of spiral
case, pit liner, stay rings, lowering of rotor, stator, turbine etc. during the project
construction stage. This stage is common for all units. In this stage B-line columns
have been considered up to EL895m, laterally tied at EL865.45m on d/s side with DT
gate shaft. A-line columns have been considered up to EL895m with D & E line
columns up to EL878m along with floor slabs of EL871m & EL878m on control bay
side. However floors in unit bay portion have not been considered.In all the analyses
the structure has been considered to behave independently from the barrel and
generator foundation i.e. no load transference from the superstructure to barrel and
generator foundation has been considered. Analysis of barrel & generator foundation
was done separately using Ansys software. Load from unit bay floors (live and dead)
have been distributed directly to corresponding beams.
The seismic analysis has been done as per IS 1893 (Part 1): 2002. Response spectrum
method of analysis has been used for analysis. Base shear due to response spectrum
method was compared with static method, and whenever response spectrum base
shear was lesser all response quantities were scaled up appropriately. Spectra for
response spectrum analysis was taken as per site specific seismic parameters studies
carried out for RHEP by IIT Roorkee. STAAD Pro software has been used for seismic
as well as non-seismicanalysis.The member forces have been taken from the STAAD
Pro analysis. Based on the end forces, the critical cases for structural design have been
selected for design.
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Picture 2 3D STAADPro Model (Finished Stage)
4. Design Loads:
The following loads have been considered in Frame analysis:
4.1 Dead Loads:
Self-weight of columns, beams and roof truss has been calculated through STAAD
Pro Software (Self weight command). Dead load of floor slab of 300mm thickness
(including 50mm floor finish)has been applied through STAAD Pro software as
uniformly distributed area load.Dead load of 300mm thick RCC wallshas been
transferred as uniformly distributed load on corresponding beams at actual beam c/l
eccentricity. Dead load of roof sheeting has been considered as 0.125kN/m2 and has
been applied as uniformly distributed load on roof purlins.Same load as that of roof
sheeting has been considered for false ceiling at bottom bracing level of trusses and
applied as uniformly distributed load on bottom bracing.
4.2 Live load:
Live loads have been taken as per IS 4247 Part-1.
Floor at EL 889m (GIS floor)= 20kN/m2
Floor at EL 883.5m(Battery Room & Office area) = 10kN/m2
Floor at EL 878m(Control Room area)=10kN/m2
Floor at EL 871m(Machine floor)= 10 kN/m2
Floor at EL 865.45m(Generator Floor)= 10 kN/m2
Floor at EL 861.45m(Turbine Floor)= 15 kN/m2
False ceiling level = 0.375 kN/m2 (erection and maintenance).
Roof (Inaccessible) = 0.75kN/m2
Live load on floor slabs has been applied through STAAD Pro software as uniformly
distributed area load.
4.3 Wire Stringing Load:
A triple conductor wire with stringing tensile load of 9Tonnes at EL900.5m along D
line columns/beams has been considered at specified locations. Also shield wire
stringing load of 0.8Tonnes has been considered at EL908.5m along D line columns.
Journal of Engineering Geology Volume XLII, Nos. 1 & 2
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4.4 Seismic loads:
Project is located in the seismic zone 4 as per seismic map of India. Site specific
studies for determining seismic parameters had been carried out for RHEPby
Earthquake Engineering Department of IIT Roorkee.
The studies recommends following design earthquake parameters for the Power
House, which havebeenapproved by National Committee for Seismic Design
Parameters (NCSDP):
αh=0.14 g andαv=3
2αh=0.09g
Full seismic load in one horizontal direction only (longitudinal or transverse) has been
considered to be acting along with the full vertical seismic load simultaneously. The
response due to combined effect of the above two seismic components (vertical and
horizontal) has been evaluated.
In earthquake analysis, weight of panel walls, floor slabs and roof sheeting has been
considered as a lumped mass, distributed equally at joints. Earthquake effect on self
weight has been considered by software itself. During earthquake, only 50% live load
has been considered on floor slabs. However no live load has been considered on roof
during earthquake.
4.5 Crane loads:
Crane load corresponding to 2 Nos. 150T crane on erection bay area at EL 890m and
1 No. 10T EOT crane at EL 898.3m in control bay area has been taken both for
normal condition (fully loaded moving crane with surges) and emergency condition
(seismic condition unloaded stationary crane). Longitudinal surge has been taken as
5% of static wheel load and transverse surge has been taken as 10% of weight of
trolley and load lifted. Crane loads have been applied as concentrated loads on crane
beams in STAAD Pro-3D analysis for various load locations.
4.6 Wind loads:
The wind load has been worked out below in accordance of IS: 875 (Part III).
The reference of clauses, figures and tables given below are from IS: 875 Part III
(1987)
Design wind pressure Pz (Cl 5.4) = 0.6 x Vz2 = 1.22 kN/m2
Wind loads in horizontal directions have been applied directly on structure by
STAAD Pro commands and as uniformly distributed load vertically upwards on
purlins of trusses.
4.7 Temperature Loads:
The roof trusses have been designed for ± 280C temperature variation, which is
approximately 2/3rd of the max/min temperature difference. Temperature load has
been applied on trusses for both contraction and expansion conditions.
4.8 Snow Loads:
Snow load corresponding to a feet of snow has been considered i.e. 2.7kN/m2
Journal of Engineering Geology Volume XLII, Nos. 1 & 2
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4.9 Earth Pressure Loads:
On southern side of unit bays are the gate shaft and collection gallery. This portion
has been backfilled to EL874m after construction. Hence earth pressure on d/s side
i.e. on B line side has been considered along with water pressure corresponding to
high flood level. This pressure has been applied as uniformly distributed load (varying
trapezoidally) on B-line columns.
5. Load Combinationsfor Frame analysis:
Different load combinations have been taken as per IS 4247 Part-II:
Normal load case with fully loaded moving cranes at different locations.
Emergency load case 1 with fully loaded moving cranes at different locations
and temperature loads (contraction and expansion due to temperature load).
Emergency load case 2 with fully loaded moving cranes at different locations,
full dead loads and live loads, temperature loads (contraction and expansion
due to temperature load) and full wind load. This combination has not been
considered in construction stage analysis.
Emergency load case 3 with full earthquake forces along with unloaded
stationary cranes at different locations, full dead loads, appropriate percentage
of live loads and temperature loads (contraction and expansion due to
temperature load).
6. MaterialSpecifications
The following material properties have been adopted in design:
a) Structural Concrete
Grade M25A20, Characteristic Strength 25 N/mm2,
Modulus of Elasticity 25000 N/mm2 (MPa), Unit Weight 24.5 kN/m
3
b). Structural reinforcement
Grade Fe 415 grade, Characteristic Strength of Steel 415 N/mm2 (MPa),
Modulus of Elasticity 200,000 N/mm2 (MPa), Unit Weight 78.5 kN/m
3
c). Structural Steel
Grade Fe 250 grade, Characteristic Strength of Steel 250 N/mm2 (MPa),
Modulus of Elasticity 200,000 N/mm2 (MPa), Unit Weight 78.5 kN/m
3
7. Methodof Design:
7.1 Raft:
MIV Raft at EL853m and Control Bay Raft at EL862m have been modelled as elastic
foundation using plate elements in STAAD Pro software, using appropriate modulus
of sub grade reaction. Maximum axial loads and maximum moments from
superstructure frame(corresponding values), raft dead load,appropriate live load, MIV
pedestal loads and MIV servomotor loads have been applied on the raft model. All
conditions have been considered in evaluating critical loads to be applied on raft
model i.e. construction stage and finished stages. From output of raft model critical
bending momentsand shear forces have been obtained and design has been done
manually as per Limit state design method.
Journal of Engineering Geology Volume XLII, Nos. 1 & 2
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Picture 3 Critical Moment Contour
Picture 4 Critical Stress Contour
Modulus of subgrade reaction value has been taken as 10000T/cum (references taken
from National Building Code and “Foundation Analysis & Design” by Bowles). Main
reinforcement in each direction and shear reinforcement has been calculated. Check
for foundation punching shear and bearing pressure check has also been carried out. A
reinforcement of 32mm diameter Fe415 bars @ 150mm c/c along both directions
along with 12mm diameter stirrups @ 300mm c/c along A & B-lines and 150 c/c in
transverse direction has been proposed for MIV Raft.A reinforcement of 32mm
diameter Fe415 bars @ 200mm c/c along both directions along with 16mm diameter
stirrups @ 200mm c/c both ways has been proposed for Control Bay Raft.A safe
bearing capacity of 52T/Sqm was considered, with an increase of 50% in seismic load
conditions as per IS codes. Design was also checked manually considering imposed
loads from superstructure columns, MIV, Live Loads, Self-weight etc. and
eccentricities in either directions.
7.2 Columns:
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For column design maximum moments in Y and Z directions, maximum shears in Y
and Z directions, maximum and minimum axial forces have been considered and the
design has been performed using STAAD Pro software. Forces have been considered
at one end at a time and for one maximum value, other corresponding values have
been considered in design. Additional moment due to slenderness of columns has also
been considered in design. Design has also been checked manually.
7.3 Beams:
For beam design maximum hogging and sagging moments, maximum shears and
maximum torsion have been considered and the design has been performed using
STAAD Pro software. Forces have been considered at one end at a time and for one
maximum value, other corresponding values have been considered in design. Design
has also been checked manually.
7.4 Steel Trusses (For Machine Hall and GIS Floor):
The member forces have been taken from the STAAD Pro analysis.Based on the
member forces, the critical cases for structural design have been selected and the truss
members are designed for the same. For emergency conditions with wind and
earthquake loads, a increase of 33.33% has been considered in permissible stresses
whereas for temperature loads this increase is considered as 25%. This allowable
increase in permissible stresses for wind, temperature and earthquake loads has been
incorporated in corresponding load combinations.Overall increase of 25% has been
considered in permissible stresses in welds for design of welded connections, for all
emergency cases.
The pinned connection with RCC frame has been achieved by erecting a rocker
bearing at site, which has been designed accordingly.The bearing consists of a top
saddle arrangement and bottom saddle arrangement connected by a rocker pin on
which rotation takes place.Saddle, bearing plates, pin have been designed for bearing,
shear and bending stresses.Connection of rocker bearing to foundation plate has been
designed for shear and bending stresses.The foundation plate has been checked to
pass above load safely to concrete beneath without exceeding concrete bearing
stresses. Foundation plate has been anchored to concrete beneath by 6 nos. M33
bolts,ensuring maximum load carrying capacity of bolt is not exceeded.
Design has been done as per IS 800 using STAAD Pro software, and has also been
checked manually. Each member has been designed for axial forces, moment in either
axes or shear forces.It has been ensured that a combined ratio of axial and bending
stresses to permissible stresses is less than unity.Truss joints have been designed for
combined stresses including axial forces and bending moments, since the joints are
welded & will offer resistance to moments.
7.5 Retaining Wall:
In order to protect the power house complex from floods during high flow season,
flood protection wall has been provided towards river side with its base at El. 867.50
and top at El.880. This wall was constructed before under taking excavation of power
house pit as per opinion of experts.
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The retaining wall has been designed for a normal load condition comprising of self-
loads and earth fill loads. The wall has also been checked for earthquake load
combination comprising self-loads, earth fill loads and horizontal & vertical
earthquake loads on gravity loads& earth fill loads (dynamic increment). A high flood
condition has also been considered which considers self-loads, earth fill loads,
horizontal water pressures and uplift water pressure.
8. Permissible Deflections:
For Construction stage analysis the maximum horizontal displacement due to
earthquake forces shall not exceed 0.4% of the storey height H (H = EL895 -
EL853m). Maximum horizontal displacement is 103.91mm corresponding to
permissible limit of 168mm. (Safe)
For Finished Stage analysis the maximum horizontal displacement due to earthquake
forces shall not exceed 0.4% of the storey height H (H = EL901 - EL877.95m).
Maximum horizontal displacement is 90.3mm corresponding to permissible limit of
92.2mm. (Safe)
9. Challenges Faced:
9.1 Southern Slope Stability:
For southern slope stability, wedge analysis was carried out using Unwedge
software.Joint sets as described under para 2 “Geology”, cohesion value of 6.03KPa,
friction angle equal to 27.580 and unit weight of 2.47gm/cc was considered for wedge
/planar analysis.Since the foliation of rock is dipping towards the pit from river side in
southern portion, an unstable wedge formation was observed on southern slope.
Accordingly support consisting of 25mm dia rock bolts having alternate lengths of 7m
& 6m at spacing 1.5mx1.5m along with 100mm thick Shotcrete was proposed to
stabilize the wedge.Drainage holes of 76mm dia and 4m length have also been
proposed at a spacing of 3mx3m on southern slope.Further, for foliation angle, planer
failure analysis was done.As per provided support, anchorage force was greater than
required.
During excavation of Power House pit, rock fall was observed on southern slope.
After due discussions held between designdepartment,site, geology department. &
GSI geologist, it was proposed to increase the length of rock bolts to 9m & 7m. It was
also decided to cut the slopes, in the non-draft tube portions, at angle of about 71.5°
with respect to horizontal.Due to very poor geological conditions encountered at site
and detachment of Rock ledge in the corner portion between unit No. 2 &3, it was
decided to enhance the existing support system by providing additional beams and
columns (about 1.6m wide) in the south wall of pit. In this arrangement, beams at
three levels i.e. about EL. 868, EL. 863 & EL 858 were proposed. This arrangement
made the grid in the form of concrete beam in horizontal direction and along cut
profile in the south wall of pit. Two rows of staggered rock bolts having dia as 32mm
and about 8-9m long were to be provided through each beam.
Adequate instruments (MPBX & prism targets) were installed on southern slope. The
movements and cracks on southern slope, based on instrument data, were reported by
Journal of Engineering Geology Volume XLII, Nos. 1 & 2
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Site Engineers. Thus in consultation with site, it was decided to provide a 1m thick
slab/raft at EL 872.7m +/- along with 32 dia grouted anchor bars. 32 dia grouted
anchor bars 9m deep, 1.5m centre to centre, both ways were also proposed. The
inclination of anchor bars proposed to be about 20° with vertical, dipping towards
river side to stitch maximum foliations. The aim was to water tight and avoid the
chimney formation in the TRT area. Also further movement of cracks was expected to
be arrested.
Still due to ongoing construction work of d/s side and ingress of water from river side,
partial detachment of rock on southern slope occurred. The recommendations of
various experts viz.GSI, CWC, Advisory Board Members, World Bank etc. were
considered. Overburden was removed upto El.868m and southern slope to be
stabilized by 36 dia grouted anchor bars, 7500mm long @ spacing of 1.5m c/c.
Shotcrete of 150mm thick with wire mesh was provided (Fig. 3).
Figure 3 Southern Slope stability
9.2 Control of Differential sway & Total Sway:
During preliminary analysis it was found out that due to unsymmetrical frames(on u/s
side frame consisted of D line, E line & A line columns whereas on d/s side just B
line cantilever frame) supporting either truss ends, differential sway at EOT crane
level or total sway at top was exceeding permissible limits. In case of differential
sway it meant that there were chances that load might be transferred to the EOT crane.
Thus it was decided to tie column tops by roof trusses so as to limit differential sway
at EOT crane level and total sway at column tops. In order to keep trusses light weight
and also effective in holding together RCC frames, a rocker bearing was proposed at
column/beam & truss junction, which would eliminate moment and transfer only
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lateral force. This rocker bearing was designed accordingly as designed in section
“Method of Analysis”. Thus truss connections to superstructure (columns or beams)
have been considered as pinned. This has been achieved in STAAD Pro model by
releasing moment in plane of truss by STAAD Pro release command, thus ensuring
that the joint only transfers thrusts and the moment is not transferred at these joints.
9.3 Structural Analysis of Different Construction Stages:
During the project construction stages various analyses were carried out to finalize an
optimised structure which would be economical, safe for all loads as described earlier
and to cater Electro Mechanical requirements. Before project construction,
commencement of preliminary analysis was carried out, which helped in knowing the
general behaviour of the structure and helped in optimizing the sizes of columns and
beams. Theses analyses also brought to light the challenge to control sway (total &
differential).Afterwards the construction stage analysis was carried out, which has
been described earlier. This would be the stage during construction when only
cantilever frames would be erected so that EOT cranes could become operational and
assist in barrel erection, spiral case erection, rotor & stator lowering etc. Analysis was
also done to realise the requirement of roof trusses during construction stage. Since
erection of rotor, stator, spiral case lining, runner etc was going on in parallel with
civil structure erection, there was also need to check the safety of structure during
operation of EOT cranes for transportation of Electro – Mechanical equipments
through superstructure frames. Analyses were done for same and structure safety
ensured by setting up safety guidelines for crane operation. Analyses were also done
for erection of steel trusses using Derek structure, when approach of tower crane was
found to be limited due to construction activities. When the issue of change in layout
of control room was encountered, a complete separate analysis was carried out to
ensure safety of revised structure. Analyses were also done to check effect of
conductor stringing loads on superstructure at different elevations, so as to finalize
final conductor load location and strengthening required on that account. There were
other analyses that were carried out simultaneously which are not too significant as
far as the scope of this paper is concerned.
10. Conclusion:
This paper brings forth the methodology of seismic as well as non seismic analysis &
design, various loads considered and load combinations considered in analysis and
design of surface powerhouses. Analyses of different construction stages, based on
erection sequence of frames and loads coming over structure, have been carried to
take advantage of EOT crane for installation of heavy equipment & to facilitate the
construction process.Emphasis has been laid on foundation design based on Modulus
of Subgrade reaction, southern slope stabilization and design of retaining walls.
Overall it has been emphasized that the structural engineer has to work continuously
and has to be always ready to mould his design for changes/modifications during
construction or due to geological surprises, in a manner that the structure conforms to
Electro-Mechanical & construction requirements, is best possibly optimised and is
safe for all the loads it will be subjected to during its life time.
11. References:
Journal of Engineering Geology Volume XLII, Nos. 1 & 2
A bi-annual Journal of ISEG June-December 2017
63
In general, relevant Indian Standards (IS) have been used in the design:-
IS 456-2000 Code of Practice for Plain and Reinforced Concrete, Fourth
Revision
IS 1786-1985 Specification for High Strength Deformed Steel Bars and Wires
for Concrete Reinforcement”, Third Revision
IS 1893 (Pt-1)-2002 Criteria for Earthquake Resistant Design of Structures, Part 1 -
General Provisions and Buildings, Fifth Revision
IS 1893-1984 Criteria for Earthquake Resistant Design of Structures (Fourth
Revision)
SP 16-1978 BIS Handbook: Design Aids to IS: 456
SP 34-1987 BIS Handbook on Concrete Reinforcement and Detailing
IS 4247(Pt-1)-1993 Structural design of surface hydroelectric power
Stations, (Part-1) Data for design – Code of practice (3rd
revision)
IS 4247(Pt-2)-1992 Code of practice for Structural design of surface hydroelectric
power Stations, (Part-2) Superstructure (2nd revision)
IS 4247(Pt-3)-1998 Code of practice for Structural design of surface hydel power
Stations, (Part-3) Substructure (2nd revision)
IS 800-1984 Code of practice for general construction in steel
IS 808-1989 Dimensions for hot rolled steel beam, column, channel and
angle Sections
IS 1367(Pt-3):2002 Technical supply conditions for threaded fasteners
SP:6 (1) – 1964 ISI handbook for structural engineers (Structural Steel
Sections)
IS 816 Code of practice for use of metal arc welding for general
construction in mild steel
Report No.
EQD-3018-EQ: 2009-26 Site Specific Design Earthquake Parameters for Rampur H.E.
Project, Himachal Pradesh