A design engineer’s responsibility should include assuring the structural safety of the design, details , checking shop drawing.
Detailing is as important as design since proper detailing of engineering designs is an essential link in the planning and engineering process as some of the most devasting collapses in history have been caused by defective connections or DETAILING. There are many examples explained in the book" DESIGN AND CONSTRUCTION FAILURES by Dov Kaminetzky.
Detailing is very important not only for the proper execution of the structures but for the safety of the structures.
Detailing is necessary not only for the steel structures but also for the RCC members as it is the translation of all the mathematical expression’s and equation’s results.
Prepare drawings properly & accurately if possible label each bar and show its shape for clarity.
12” I ¼”dia@12”c/c Cross section of retaining wall which collapsed immediately after placing of soil backfill because ¼” rather than 1-1/4” dia. were used. Error occurred because Correct rebar dia. Was covered by a dimension line. 1- ¼”dia@12”c/c
Lap splices shall be not be used for bars larger than 36mm dia. Except where welded.
Where dowels are provided, their diameter shall not exceed the diameter of the column bars by more than 3mm.
Where bent up bars are provided, their contribution towards shear resistance shall not be more than 50% of the total shear to be resisted. USE OF SINGEL BENT UP BARS(CRANKED) ARE NOT ALLOWED IN THE CASE OF EARTHQUAKE RESISTANCE STRUCTURES.
DETAILING OF SLABS WITHOUT ANY CUT OR OPENINGS.
The building plan DX-3 shows the slabs in different levels for the purpose of eliminating the inflow of rainwater into the room from the open terrace and also the sunken slab for toilet in first floor.
The building plan DX-A3 is one in which the client asked the architect to provide opening all round.
Minimum and max.reinforcement % in beams, slabs and columns as per codal provisions should be followed.
It is better to provide a max spacing of 200mm(8”) for main bars and 250mm(10”) in order to control the crack width and spacing.
A min. of 0.24% shall be used for the roof slabs since it is subjected to higher temperature. Variations than the floor slabs. This is required to take care of temp. differences.
It is advisable to not to use 6mm bars as main bars as this size available in the local market is of inferior not only with respect to size but also the quality since like TATA and SAIL are not producing this size of bar.
A min. of 0.2% is to be provided for the compression bars in order to take care of the deflection.
CRACK CRACK INCORRECT HAUNCH BEAMS CORRECT L/8 TO L/10 L/8 TO L/10 L L Ld Ld Ld Ld
STRESSES AT CORNERS C C-COMPRESSION T-TENSION t t C RESULTANT TENSILE STRESS FOR ACROSS CORNER(ONE PLANE) t c RESULTANT TENSILE STRESS FOR ACROSS CORNER(DIFFERENT PLANE) t c CRACK CRACK
SHEAR AND TORSION REIN. IN BEAMS INCORRECT Min 0.2%bd to control deflection as well as for seismic requ. b D 100 to 200mm d D-n>500mm D/5 Skin rein.10dia is required when depth exceeds 450mm(0.1% of web area distributed equally on two faces) Stirrups taken round outermost bars spacing<=x1 <=(x1+y1)/4 <=300mm x1 y1 D-n>500mm n CORRECT
CANTILEVER BEAM WITH POINT LOAD CORRECT INCORRECT 2/3d d Shear rein. Extra ties Ld Ld
opening CORRECT OPENING IN WEB OF BEAM crack crack opening INCORRECT OPENING IN WEB OF BEAM Ld d/2 d/2 Closed stps for d/2 Closed stps for d/2
BEAM COLUMN JUNCTION-EXTERIOR COLUMN CORRECT INCORRECT CLOSED STPS 2”max IN TENSION-Ld U TYPE BARS Ld
CORRECT SPLICE DETAIL FOR COLUMN INCORRECT COVER CLOSE TIES @S/2 S-SPACING SLOPE 1:6
REDUCTION COLUMN BOTH SIDES INCORRECT CORRECT 3NO.CLOSE TIES SPLICE CLOSE STPS SPACIN <=75mm SLOPE 1:8 FROM BEAM BOTTOM 3NO.CLOSE TIES
TERMINATION OF COLUMN BARS INSIDE BEAM INCORRECT CORRECT Ld
BEAM COL. JUNCTION-EQ REGION EQ REGION -BEAM-COL JN-EXTERIOR CORRECT BEAM COL. JUNCTION-EQ REGION INCORRECT END REGION END REGION COL. CORE* SPACING OF LATERAL TIES <=100mm SPACING OF LATERAL TIES <=d/2 SPACING OF LATERAL TIES <=d/2 SPACING OF LATERAL TIES <=d/2 * COL.CORE HAS TO BE CONFINED BY CIRCULAR OR RECTANGULAR TIES IN ACCORDANCE WITH END REGION
COLUMN DETAILS IN EQ REGIONS END REGION END REGION First stirrups 50mm from beam face Spacing of shear rein. In columns incorrect Spacing of shear rein. In columns correct END REGION-h/6 or D or 450MM whichever is greater END REGION h d D b
EQ-REGION -CONTINUOUS BEAM INCORRECT Ld A=L1/3 CONTINUOUS BARS NOT LESS THAN ¼ AREA OF BARS AT COL.FACE A=L1/3 A=L1/3 2d 50mmmax Stirrup spacing=d/4 or 100mm or 8dia which ever is the least 2d 2d 2d stp@maxd/2 stp@maxd/2 CORRECT
INCORRECT FOOTING-DETAILS(INDEPENDENT) CORRECT COVER TO STARTER STARTER BARS COLUMN BARS NATURAL G.L Ldt Lb 3” SIDE COVER Ldt COVER50mm IF p.c.c below or 75mm Min.300
TYPICAL REIN DETAILS OF HAMMER FOUNDATION BLOCK INCORRECT CORRECT Ld Ld
Staircases- helical staircase, central beam type, cantilever type etc.
Different types of foundations-raft, pile foundation, strap foundation etc.
Retaining wall structures,
Liquid retaining structures.
Shear wall, walls.
Hope that I have enlighten some of the detailing technique for the most commonly encountered RCC members in buildings.
In the above statements if my senior colleagues and ACCE members can find different method or any new detailing system it will be of immense help not only for me but to other young engineers who should learn in wright ways and not wrong lessons.