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vikram.jeet
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PostPosted: Tue Apr 06, 2021 5:10 am    Post subject: Reply with quote

In continuation to just sent post on execution friendly detailing in drawings

Slabs - It is always better to have single dia bars to be used in each direction  of a slab or slabs , spacings can be as less as 75mm if required .this will also avoid mixing of 8 dia and 10 dia bars since it the labour working in extreme weather conditions.

Reinforcements in cantilever slabs  must be provided keeping in view the practical difficulties of holding them at top face at site.

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vikram.jeet
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PostPosted: Tue Apr 06, 2021 7:33 am    Post subject: Reply with quote

Inspection by design team st site

Foundation stage
Foundation depth is very important It must be seen that Foundation depth shall be from original(virgin) GL. Reinforcement must be provided with 50mm to75 mm cover blocks as per drg.It is seen that brick bats are used which are 75 mm, even though cover shown in drgs is 50mm. This shall be asked to avoid.
In case of columns on boundary of plot, the foundation beams at found. level itself must be checked to be provided. There is tendency  not to dig at found level for found beams and these are missed in some non supervised constructions.

Floor slabs/ beams:
Shuttering must be inspected by the team and horz & x- bracings must be asked to induct. Gaps in Shuttering must be closed to avoid slurry out flow.
Slab reinf must be checked with tape for major slabs.the thickness of slab must be provided by fixing wooden bully piece of slab thickness at 3 to 5 locations in a slab panel depending on size. Top bars must be kept up in position thru chairs. Slab thickness at top bars be checked .
Beams depth must be checked by steel tape dipping in beam bottom. Extra bars at top at supports, additional bars in second layer at bottom must be seen. Stirrups spacings, any side face reinf to be checked.
Column bars going up for upper storey must be of at least Ld length, preferably Ld &2*Ld ,50 percent each.

Stair waist slab thickness must be checked.

Reinforcement must be checked for its grade and test certificate from supplier .
Many things to see but in a short visit , design team or its representative must check and report to site incharge & design office.

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vikram.jeet
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PostPosted: Tue Apr 06, 2021 7:58 am    Post subject: Reply with quote

Site inspection by design team

Missed few points
CURING must be emphasized very emphatically. Concrete & brick work must remain continuously wet/moist for at least 14 days.

Site engineers must be interacted regarding quality of coarse sand to be free from silt , stone aggregates ,conc mix ,water cement ratio must be in  accordance with mix design.( In case of site mix)
In case of RMC , the fly ash percent shall not exceed permissible.

The removal of formwork shall also needs to be discussed.

Generally Rcc columns, lintels , stair waist slabs are with site mix even if Floor slabs/ beams are with RMC in view of quantity .

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PostPosted: Tue Apr 06, 2021 8:12 am    Post subject: Reply with quote

Site inspection by design team

Few more points to add

Slabs  & beams - COVER BLOCKS of size as per clear cover given in drawings must be of precast concrete . Tendency is to put brick pieces or stone aggregate. This shall not be allowed.

Electrical conduits / fan hooks : Must be in place prior to concreting.

Plumbing - Sleeve pipes at toilet beams must be in position  before commencing concreting. Generally toilet slabs are sunk, but beams are upstand and will require pipes to pass across beams.

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PostPosted: Wed Apr 07, 2021 4:06 am    Post subject: Reply with quote

Shear force & diagonal tension

As all know, the change in BM is the cause of SF. In bending members shear stress is on x section . But due to complimentary shear in form of horizontal shear give rise to resultant shear at 45deg in form of diagonal tension.

The vertical shear is on x-sectional area but resultant shear(diagonal tension) is the force within d length of member, i e. It is a force within bxdx(d along span) volume of conc of the beam under bending as I feel by looking at formula  of strength of shear reinforcement Vs=Perm tensile stress*Total xsec area of stirrups*   d/spacing.
d/spacing is the numbers of stirrups in length d.

Request to correct me if correction is needed in my view reg physical relevance of diagonal tension quantum.

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PostPosted: Wed Apr 07, 2021 4:56 am    Post subject: Reply with quote

Shear force & Diagonal tension
Just to elaborate previous post on this subject:
The change in BM along span is the cause of SF. e.g. A simply supported Beam having equal point loads placed same distance from each support . The BM diagram indicate constant BM  in beam within span length between two point loads. The SF in this portion of span is Zero since There is no change in BM.

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PostPosted: Fri Apr 09, 2021 8:07 am    Post subject: Reply with quote

Boundary Walls

Boundary wall design must be taken seriously, as failure of  it will lead to injury or loss of life as per news reports time to time.

Boundary wall foundation is to be provided only on inside , weather it is Brick wall with brick piers at certain spacing or brick wall with rcc columns at spacing.

All brick boundary wall must be in mix 1:5 at least with brick piers at around 2.5mc/c. Ht upto 2.5 m .
For rcc columns sandwiched walls ,the spacing can be 3.0m to 3.6m generally.If wall ht is more , sandwiched beams need to be provided at PL & mid ht lvl.

Wall needs to be designed for wind loading   . Apart from that level difference between outer and inner sides must be accounted  and active earth pressure needs to be taken. In case there is no nallah / drain on outside near wall, then Passive EP relief can be taken with appropriate safety factor. Possibility of traffic parking needs to be seen in case of  GL difference, as it tend to give additional traffic LL surcharge.

Base needs to checked against overturning. Also base pressure at toe needs to be checked ..

Allowing Base upliftment is a necessity  and 25 to 30% upliftment under wind case will provide FOS against OT . But Base pressure will be high due to reduced contact area & it must be within permiied value .
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PostPosted: Fri Apr 09, 2021 8:18 am    Post subject: Reply with quote

Boundary walls

Expansion joints - in boundary walls must be provided aat about 10m for all brick and at 15 m for rcc column sandwiched walls.

Top coping needs to be in cc with minor reinf.

Damp proof to be provided above GL ( higher of inside or outside)..

Fencing post angles , concertina wire posts to be embedded at certain spacing.

Hilly areas walls can be in stone masonry but mix 1:5.
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PostPosted: Fri Apr 09, 2021 11:19 am    Post subject: Reply with quote

The roof dome of OHWater tank
Design Vs durability

The dome of OH water tank is subjected to membrane stresses and thickness to the extent of 80mm suffice as per design. Dome have edge thickenings.
But keeping in view the exposure of weather conditions, difficulty of accessibility to repairs,  it was advised by a very senior engineer of water supply Deptt, that a minimum of 125 mm thickness must be provided irrespective of design requirements in view of reasons mentioned above.
Though there is little spending at time of construction but it will have  inbuilt durability .
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PostPosted: Sun Apr 11, 2021 4:50 am    Post subject: Reply with quote

Diagonal wind force

Wind can blow in any direction. Designs are done considering wind blowing normal to structure , wind blowing transverse to structure , but sometimes wind blowing in diagonal direction  i.e. at 45deg are not carried out. Structures supporting hoardings , steel truss(lattice girder) type bridges  etc needs  check for diagonal wind.

In case a hoarding structure of column its base plate & foundation is square / circular , the effect of diagonal wind may not govern, but if dimensions are in rectangular geometrically, the diagonal wind govern.

If a hoarding area is A, p is the wind pr arrived with appropriate coeffs , The wind force for diagonal wind =pA*0.707 ( it is to be taken on projected area) acting along  45deg.
The components of this force in X &Z direction each =0.707(pA*0.707)=0.50*pA
So in rectangular configuration 0.50pA force in each direction will govern over normal wind force of 1.0pA.
Truss bridges also analysed for diagonal wind force in r/o forces on bearings and substructure.

Structures with large area in transverse direction & comparatively smaller area in longitudinal direction , check of diagonal wind critical.
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