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Some general view
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vikram.jeet
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PostPosted: Tue Sep 13, 2022 5:16 am    Post subject: Reply with quote

Two way shear as result of moments :

A personal perception :

Taking  a hypothetical example of a shed footing - ( wind = 100 kg/m2 )

Size of shed bay (inner) = 18.0m 4.5 m 6.0 m ht cladded shed
Uplift force = (0.8+0.5) x100 4.5x18.9/2 = 6.4 t
DL = 15 x4.5x18.9/2 = 0.6 t
Net Uplift force = 6.4 - 0.6 = 5.8 t
Wind moment on wall cladding = 100*1.2*4.5*6.0*(6/2+1.5) = 14580 kgm

Size of ftg = 3.0x3.0m 250 thk 1.5mfoundation depth
Rcc pedestal ( supporting steel col) = 600 x 450
Uniaxial Moment due to wind = 14.58 tm
Tensile force  =  6.4 t

Footing eff depth = 25 - 5- 0.6= 19.4cm

Shear two way to be chkd at d/2 from face of column pedestal
Perimeter dimensions  L=60+ 19.4 = 79.4 cm  , B= 45 + 19.4 = 64.4 cm

Area  for shear = [( 79.4) +(64.4 )]*2= 287.6 cm

Shear Stress due to uplift force =  5800 /( 287.6*19.4) = 1.04 kg/cm2
This stress is allaround

Shearstress due to Moment:

On front and back faces area = ( 64.4 )*19,4 =  1249.4 cm2
Moment balanced by shear stress s = 1294.4* ( 79.4) *s = 102775*s kgcm

On sides   area each side = 0.5*19.2 (79.4)/2*2= 770.2 cm2
Moment balanced = 770.2*s *2 * (79.4/2)*2/3 = 40769 *s  kg/cm2

Shear Stress  s = (14.58*100000 )/ (102775 +40769)= 10.15 kg/cm2

Total two way shear stress = 1.04+ 10.15= 11.19  kg/cm2
Allowable stress = 0.16* 20^0.5 = 0.715 n/mm2  ~ 7.15 kg/cm2

Hence there is need to Increase thickness of footing   / or column pedestal dimensions due to two wayshear check , even though Flexural requirements of BM and one way shear are OK for footing .


Last edited by vikram.jeet on Tue Sep 13, 2022 6:35 am; edited 1 time in total
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vikram.jeet
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PostPosted: Tue Sep 13, 2022 6:13 am    Post subject: Reply with quote

Two way Shear check as result of moments :

A personal perception :

Hypothetical Example -  A   1.75 m cantilever beam at mid landing  comming out from 200th rcc wall ( eff thk = 20 - 2.5- 0.5 = 17 cm
Stair span = 6.0m

Stairs loading  DL+LL= 1400 kg/m2

Loading on beam 230x450mm : self  = 260  kg/m
Stairs 1400x 6.0/2= 4200 kg/m
End Railing and base = say 300 kg/m

Total udl on beam = 260+4200+300= 4760 kg/m

Cantilever  BM = 4.76x 1.75^2 /2 = 7.29 tm

Two way shear area dimensions:
L= 45 + 17= 62 cm
B= 23 + 17= 40 cm

Moment resisted by top and bottom faces = 40x17 * 62*s = 42160 *s  kg cm

Moment resisted by side faces :
Area both sides = (0.5x 31x17x2 ) x2 = 1054 cm2
Moment resisted = 1054x (62/2 )x2/3 x s= 21783 *s  kgcm

Shear Stress  s = 7.27x100000 / ( 42160+21783)  = 11.37 kg/cm2

Allowable two way stress forM20 = 0.16x 20^0.5 = 0.715 n/mm2 ~7.15kg/cm2
Hence there is need to increase thickness of rcc wall / Beam size to keep two way stress within permitted limit .
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vikram.jeet
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PostPosted: Tue Sep 13, 2022 2:25 pm    Post subject: Reply with quote

Continuing posts on two way shear check :

Two way shear check :  For footing  having column under compression and moment

Generally it is seen that compressive load on column at its base is quite large compared to gravity Moment and check for Two way shear  for footing is done on compressive load only . But associated Moment will enhance the shear stress ( on front face of two way perimeter )  and  , I feel , it needs to be considered for working out gross  shear stress.

Under wind / EQ conditions , two way shear due to  the moments on Footing from columns  need to be addressed  in similar  way , but with higher permitted  stresses .


Still a learner in this vast str engg field ( A sea)   , request  experts / purists of str engg to guide regarding  this perception in all above postings on two way shear .
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vikram.jeet
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PostPosted: Sat Sep 17, 2022 3:37 am    Post subject: Reply with quote

HYDROPOWER STRUCTURES:

Structural Engineering  is inherent in Hydropower  Structures.  But knowledge of Geotechnical , Rock Mechanics  as well as Geology is also needed to understand Nature's response /  loading on Structures,  . Most of Structures in Hydropower  projects are Nature related . Geologists at field and design office provide field data values to engineers of various disciplines  viz Geotechnical / Rock Mechanics  / Structural engineers .

Engineers design the excavaton and support system for Cut slopes , tunnel excavations , Large Cavern excavations and all other structures. Geologists , Structural & Geotechnical engineers , Rock Mechanics engineers along with Hydrologists , Hydraulic design specialists , Surveyors  - all have to work as a team for mega Hydropower  Projects in Hilly terrains with project sprawled in 25 to 50km or more .

( to be continued)


Last edited by vikram.jeet on Wed Sep 21, 2022 3:28 am; edited 1 time in total
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vikram.jeet
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PostPosted: Sat Sep 17, 2022 3:14 pm    Post subject: Reply with quote

HYDROPOWER  STRUCTURES  IN HEP :



O) INFRASTRUCTURE DEVELOPMENT WORKS /STRUCTURES AT START OF PROJECT :

BRIDGES , ACCESS ROADS , RETAINING STRUCTURES , SLOPE PROTECTION , STORES , STOCKING YARDS ,WORKERS CAMPS AT VARIOUS LOCATIONS , CENTRALISED OFFICE AND CAMP , WORKSHOPS , LABORATORIES , DUMPING SITES , CRUSHING PLANT SITES , SECURITY TOWERS  

A) RIVER DIVERSION STRUCTURES

DIVERSION STRUCTURES  FACILITATING CONSTRUCTION  OF HEADWORKS-
DIVERSION TUNNEL , DIVERSION CHANNEL , UPSTREAM  COFFERDAM , DOWN STREAM COFFERDAM

B) HEAD WORKS  - DAMS , BARRAGES , WEIRS , BRIDGE , GATES

C) INTAKE & SEDIMENTATION STRUCTURES

INTAKE WORKS -  BAR SCREENS , INTAKE TUNNELS , SEDIMENTATION CHAMBERS , FLUSHING DUCTS , FLUSHING DUCT OUTFALL STRUCTURE,  GATE CHAMBER

D) .WATER CONDUCTOR SYSTEM

WATER CONVEYANCE  TUNNEL - HEAD RACE RACE TUNNEL  (CC/RCC LINED)

BALANCING STRUCTURE AS RESULT OF SURGES  WHILE OPENING & CLOSURE OF VALVES  --- UPSTREAM SURGE SHAFT (VERTICAL SHAFT)

HIGH PRESSURE CONVEYANCE - STEEL PRESSURE SHAFT WITH SURGE SHAFT (& VALVE CHAMBER ) NEAR ITS U/S AND PENSTOCKS (TO TURBINES IN PH) ON D/S ,
( PRESSURE SHAFT - IT IS GENERALLY VERTICAL BUT SOMETIMES INCLINED PRESSURE SHAFT AS PER TOPOGRAPHY )

E) POWER HOUSE STRUCTURES

UNDERGROUND DEVELOPMENTS - POWER HOUSE CAVERN (MACHINE HALL) , TRANSFORMER HALL CAVERN , BUS BAY TUNNELS , CONTROL  BLOCK (UG), ( DOWNSTREAM SURGE CHAMBER IN CASE OF FRANCIS TURBINES, FOR PELTON TURBINES THIS CHAMBER NOT REQUIRED)  , MAIN ACCESS TUNNEL (MAT) , CABLE AND VENTILATION TUNNEL ,  

OPEN PH DEVELOPMENTS -  MACHINE HALL , TRANSFORMER HALL , CONTROL BLOCK , BUS DUCTS ,

(M/C HALL - MULTI LEVEL WITH ERECTION BAY , GENERATORS   FLOOR , M/C (TURBINES) FLOOR  , UNIT TAIL RACE AT BOTTOM MOST ,GANTRY CRANE

(TRANSFORMER HALL - TWO LEVELS ,LOWER LEVEL HOUSING TRANSFORMERS ,UPPER HOUSING PANELS)

MACHINES (TURBINES) - FRANCIS LOW TO MEDIUM HEAD & HIGH DISCHARGE  ;  PELTON IS HIGH HEAD & LOW DISCHARGE TURBINE ,  

F) TAIL WORKS STRUCTURES

- TAIL RACE TUNNEL ( FOR UG PH) ,  TAIL RACE  CHANNEL( OPEN PH) . OUTFALL STRUCTURE

G)  OPEN POTHEAD YARD  (FOR UG PH)  , SWITCHYARD (FOR OPEN PH)

H) VARIOUS CONSTRUCTION TUNNELS ( ADITS)  - SOME ARE PERMANENT ACCESS , OTHERS WITH WATER CONDUCTOR SYSTEM PLUGGED  , ADIT PLUGS


J) TRANSMISSION TOWER ( LAST STRUCTURE OF HEP )  TO TRANFER POWER TO POWER GRID OF STATE GOVT


Last edited by vikram.jeet on Thu Sep 22, 2022 2:35 am; edited 6 times in total
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vikram.jeet
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PostPosted: Sat Sep 17, 2022 3:17 pm    Post subject: Reply with quote

HYDROPOWER STRUCTURES :

FOR MORE DETAILS PLEASE SEE PAGE NOS 39 TO 45 UNDER THIS POST SUBJECT ' SOME GENERAL VIEW'.
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vikram.jeet
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PostPosted: Fri Oct 14, 2022 4:31 am    Post subject: Reply with quote

PROFESSION OF STRUCTURAL ENGINEERING
(As penned by an Essay Writer )

Structural Engineering  is a field concerned with doing RESEARCH  , MAKING PLANS , DESIGNING , CONSTRUCTING ,  INSPECTING , MONITORING , REHABILITATING ,  DEMOLISHING of both Temporary and Permanent  Structures along with their COMPONENTS and  STRUCTURAL SYSTEMS.

It also considers various aspects  of Structures  like ECONOMIC , TECHNICAL ,  AESTHETIC , ENVIRONMENTAL and SOCIAL aspects.

This is an IMAGINATIVE  PPROFESSION  which makes significant contributions to  INDUSTRY ,  INFRASTRUCTURE  as well as DEVELOPMENT  of RESIDENTIAL  , BUSINESS , RECREATIONAL BUILDINGS.
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