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[vikram.jeet]

Design of staging platform :

Using Angle irons of size 75x75x8 twin angles placed back to back at 0.60m c/c for Stone slab average 32mm thick say of size 550x550mm as readily available sizel

Design of Angle Iron :
Loding on each Angle = 308 x 0.30 = 93 kg/m plus water tank loading
WT loading on Angle = 1.42 (actual water wt , not oflow) x1000 =1420 kg/m2
WT lad on each Angle = 1420x0.3 = 426 kg/m

Total load on Angle = 93 +426= 519kg/m + 10 self wt = 529kg/m
Clear span = 2.0 - 0.08 (flange of MB150) = 1.92m
BM = 529 x 1.92^2/10= 195 kgm

Z required = 195×100 / 1650 = 11.8cm3 say 11.0 cm3  OK for an gle chosen

L- - - -

Angle Iron supports are uneconomical , but still provided as these :
(i) hold the stone slab firmly and there is  no danger for Stone slab of being getting dislocated in event of EQ vibrations
(ii) these reduce the clear span of Stone slab so that these can take loading within their allowable range , though light reinforced   rcc Topping greatly reduce load on Stone slab

Alternatively T irons of required Z value can be provided but availability of such is not assured in local markets

Twin ISMC 75  can also be used but these have to be placed beneath Stone slabs and these cannot tightly hold.


To be cont'd for check of Stone slab

[vikram.jeet]

Stone slab  :
Av thickness = 3.2cm

Taking full load on Stone slab , Loading = 308 +1420= 1728 kg/m

Stone slab is one way spanning slab between Angle Iron supports
Clear span = 60 - ( 7.5 - 0.6)*2 = 46.2cm
Eff span = 46.2 +3.2 = 49.4cm

BM = 1728x 0.494^2 /8 = 52.7 kgm/m = 52.7 kgcm/cm

Tensile stress = 52.7  / ( 1*3.2^2  /6) = 30.9 kg/cm2  very high

Therefore rcc Topping taking thickness of 7.5cm and sharing full loading

Tensile stress taking pcc  :  = 52.7 / ( 1 * 7.5^2 /6) = 5.62 kg / cm2  OK for M20  ( refer IRC 21 for allowable Tensile stress)

Small reinf 8mm dia @200mm c/c bothers can be provided

[vikram.jeet]

From above illustration one thing is very clear that :

Stone slabs must be provided with rcc Topping  lightly reinforced , to transfer heavy water tank loading to Angle irons which ,in turn transfer them to wall support on one side / and steel beam support on other side ( if tank is placed by side of parapet wall ).
Otherwise tank need to be supported on staging comprising of two nos steel beams supporting Angle irons.

If two parapet walls are available ,orthogonal,  lone girder in diagonal direction can be placed to form a triangular in plan staging .

[vikram.jeet]

IS CODE ON STONE SLAB FLOORS / ROOF OVER JOISTS

IS 2792 can be referred

Salient features :

Stone wt for design = 2700  kg/m2
Stone types - Granite , sandstone , Lime Stone

Permitted stress for design :
Sandstone , limestone  = 8 kg/cm2

Topping of combined thickness of 75mm recommended in IS Code

[someshwar ganti]

All our Theories of design are GOOD on paper, but practically the structure is subjected to much more load during the construction process (and perhaps after construction due to such case of water tank load)

  
Normally (generally followed)  a water tank of 2000 lts is place on slab (perhaps near a BEAM or corner , though not in center) if the dia tank is 1.4m the load /m2 will be approx 13 kN/m2

By any design standards the SLAB SHOULD FAIL (as we normally take Max of 4.125 kN/m2 DL + 3 or 5 kN/m2 LL) DL cannot be avoided so the slab is designed for 5kN/m2 only the localized load under the tank is 13  

WOW  every building should have failed by this standard, how come they are standing for over 45 years (my own house)


There is something called the continuum effect which is never considered in the design, thanks to that ALL OUR structures are SAFELY standing even if the localised loading is far beyond the design load

Few more examples

1. Loading of SAND on slab during construction, (it is normally at the center of the slab in conical shape with a min height of 4 f (that when calculated will FAR exceed the design load,
   CHERRY ON THE SAND = CEMENT BAGS and BRICKS

I have also observed our design codes are too conservative hence the structure's actual design capacity is FAR BEYOND what actually the engineer intended for.


For example a PEB structure designed for a WIND SPEED OF 44m/s with same DL & LL


designed by ( AISC /MBMA loading) is good enough to stand all over the world where there is a wind speed of 44m/s.


but if we design the same structure as per IS code  (keeping the same wind loads and combination) the structure will fail as per IS CODE.


My question is will the structure ASK "Hey I have been designed in American Code, so the moment you put me in India  I SHOULD FAIL"


?????

[vikram.jeet]

As said earlier on sefi :

ANALYSIS IS UNIVERSAL
DESIGN IS NATIONAL
DETAILING IS PERSONAL
MODELLING HAS TO BE IDEAL ( In this age of softwares)

Structure need to be designed as per Codal provisions  of  the Nation in which it is located.
Analysis of str is irrespective of any  Country location .

Country Codes do differ in certain stipulations , primarily due to availability of materials , machinery for construction ,  quality assurance Standards and other environmental factors.