COLUMN FOOTING
Column Footing is also famous as independent footing. An independent footing is one one which which is prov provide ided d unde underr a column column or either either simil similar ar membe memberr for for distri distribu butin ting g concentrated load in the form of uniformly loads on the soil below. The footing may be square, rectangular or circular in plan. Depending upon the load to be carried and the bearing capacity capacity of soil, this may be of brick masonry, stone, stone, .C.C., steel grill!age etc. "n account of low bending strength the footings constructed with brick, stone or plain concrete require require considerable depth depth to be safe to carry heavy loads. The depth of plain concrete footing can be appreciably reduced by providing reinforcements at its base to take up tensile stresses. .C.C. column footings may be circular, rectangular rectangular or square in plan. The footing is reinforced both!ways by means of mild steel ribbed bars placed at right angles to one another at equal distances apart THUMB RULES FOR DESIGNING A COLUMN LA L AYOUT THREE THUMB RULES TO BE FOLLOWED ARE AS FOLLOWS: #. $i%e $i%e of the the Col Colum umns ns &. Dista Distance nce betw between een Colu Columns mns '. Alignm Alignment ent of colu columns mns MINIMUM SIZE OF RCC COLUMNS The si%e of the columns depends on the total load on the columns. There are a(ial loads and lateral loads. )arge beam spans induce bending moment not only in the beams beams,, but also in colum columns ns which which are pulle pulled d by the the stres stresses ses in the the beams beams.. *t is important to use advanced structural design software like +Tabs or $taad pro. * highly recommend every structural designer learn these software. The thumb rules are for general designing in very small proects.
FOR THIS GENERAL THUMB RULE, WE WILL ASSUME A STRUCTURE OF G+1 FLOORS HIGH, USING STANDARD 6″ WALLS. -inimum si%e of an CC column should not be less than /( / 0&&1mm ( &&1mm2 with 3 bars of #& -- Fe144 $teel.
These days the minimum * use in my proects is 5 ( #&5 0&&1 mm ( '44mm2 with 6 bars of #& -- Fe144 steel. 7ou can never go wrong with strong columns. * also recommend use of -&4 grade concrete for the structure 0ratio # part Cement 8 #.1 parts $and 8 ' parts Aggregate with 4.1 parts water by volume2. * recommend use of 9 -- stirrups at a distance of #14 -- center to center throughout the length of column. This setup of 5 ( #&5 CC columns is safe for :;# Floors. There are a lot of other considerations, but this is ust a thumb rule. SPAN (DISTANCE) BETWEEN TWO COLUMNS
For the above column setup, a span of up to 1 meters is quite safe. "ne can use beams of si%e 5 < #&5 0&&1 -- ( '44--2 with a slab thickness of 15 0#&1 --2 cast in -&4 concrete for spans up to 1m. There are other considerations like secondary and tertiary spans, point loads and wall loads which have to be considered. *t is complicated, but thumb rules can work if the structure is simple. *t is always recommended to use structural design software like +Tabs or $taad pro for design. *n a beam of up to 1 meters length, secondary spans of up to 3 meters, wall loads of up to 9 k= per running meter, * can use steel as below. • •
•
Top $teel > & bars of #& -Crank bars > & bars of #& --, cranked at an angle of 31? at a distance of )@3 at both ends of a simply supported beam ottom $teel > ' bars of #& --.
This configuration can change depending on a lot of factors. ALIGNMENT OF COLUMNS
Blacing of columns depend completely on the plan. A planner has a very important ob. A grid column placement is always preferred in order to reduce point loads and unnecessary complications while construction. This reduces the cost of construction as well as time required for construction. eams which have continuity with other simply supported beams have reduced bending moments, and thus require less steel and concrete depth to be safe. Columns have to be connected with each other for smooth transfer of loads. An e(perienced planner will keep such things in mind when planning the structure.
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