Some useful guidelines to work out the total loads on a column & footing

This article is about calculation of loads for column and footings design.

The following types of loads operate on a column :-

1. Self weight of the column x Number of floors
2. Self weight of beams per running meter
3. Load of walls per running meter
4. Total Load of slab (Dead load + Live load + Self weight)

The columns are also susceptible to bending moments which should be included in creating the final design. There are different types of advanced structural design software like ETABS or STAAD Pro which can be applied to design a good structure efficiently. The calculation for structural loading In professional practice is based on some fundamental assumptions.

For Columns: Self weight of Concrete is approximately 2400 kg per cubic meter that is identical to 240 kN. Self weight of Steel is approximately 8000 kg per cubic meter. Suppose a large column having size of 230 mm x 600 mm with 1% steel and 3 meters standard height, the self weight of column is approximately 1000 kg per floor, that is identical to 10 kN. So, here, the self weight of column is taken as among 10 to 15 kN per floor.

For Beams: The calculation is same as above. Suppose, each meter of beam contains dimensions of 230 mm x 450 mm exclusive of slab thickness. So, the self weight is approximately 2.5 kN per running meter.

For Walls: Density of bricks differs among 1500 to 2000 kg per cubic meter. For a 6″ thick wall with 3 meter height and 1 meter length, the load can be measured per running meter equivalent to 0.150 x 1 x 3 x 2000 = 900 kg which is equivalent to 9 kN/meter. The load per running meter can be measured for any brick type by following this method.

For autoclaved, aerated concrete blocks like Aerocon or Siporex, the weight per cubic meter should remain among 550 to 700 kg per cubic meter. If these blocks are utilized for construction, the wall loads per running meter remains as low as 4 kN/meter, that leads to cutback in construction cost.

For Slab: Suppose the thickness of the slab is 125 mm. Now, each square meter of slab contains a self weight of 0.125 x 1 x 2400 = 300 kg that is similar to 3 kN. Suppose, the finishing load is 1 kN per meter and superimposed live load is 2 kN per meter. So, the slab load should remain 6 to 7 kN per square meter.

Factor of Safety: Finally, once the calculation of the entire load on a column is completed, the factor of safety should also be taken into consideration. For IS 456:2000, the factor of safety is 1.5.

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Published By
Rajib Dey
www.constructioncost.co
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The stirrups commonly found in column design

The design of stirrups for column is created on the basis of different factors like changeable cross-sections, the number of longitudinal reinforcement bars and the load bearing strength. Stirrups in column construction are generally called as vertical ties or transverse reinforcement.

The following types of stirrups or ties are found in column construction:

1. Helical Reinforcement: The helical reinforcement is different from the lateral ties since the lateral ties contain spacing among individual ties. In helical reinforcement, the quantified value is pitch, rather than spacing.

The helical reinforcement offers more ductility and flexibility to the built up column with regard to lateral ties. They can effectively support the longitudinal reinforcement. With the insertion of helical reinforcement, the resistance capacity of the column structure against buckling become superior.

a) Ambient temperature of 27 °C (80°F) or greater; and
b) Evaporation rate that surpasses 1 kg/m2/h

The helical reinforcement is also applied as spiral reinforcement. Helical bars are suitable for seismic design. By the influence of seismic loads, the concrete affixed to the helical reinforcement is stripped off preliminary. It facilitates to give a warning sign concerning the structural condition of the column.

The helical reinforcement is a perfect example in respect of uniformly distributing loads as compared to the normal rings (lateral ties).

2. Lateral Ties: The lateral ties stand for transverse reinforcement to develop a separate ring with a fixed spacing among each link. Based on the column cross-section and the number of vertical or longitudinal reinforcement bars applied, the lateral stirrups vary from two-legged stirrups, four-legged stirrups or six-legged stirrups etc.

Given below, the detail information on various lateral tie configurations for several number of vertical reinforcement bars. The configurations are dependent on the ACI 315-99 recommendations.

1. Lateral Tie Configuration for 4- Bars: The tie is configured for 4 numbers of vertical column bars. It is a standard type of configuration applied for simple column design. This configuration is known as 2 legged stirrups column type.

2. Lateral Tie Configuration for 6- Bars: The first arrangement is observed when the spacing of vertical bars are under 150mm ( below 6”). If the spacing is in excess of 150mm, the second arrangement is observed where crossties are used.

3. Lateral Tie Configuration for 8- Bars: The first arrangement is done with the standard 8 number vertical reinforcement arrangement. Here the spacing is under 6”. If the spacing is in excess of 150mm, two crossties are utilized.

The third arrangement is known as bundled bars arrangement. Under this arrangement, two bars are combined at the corners. So, no cross ties are required. Highest 4 numbers of bars are combined.

4. Lateral Tie Configuration for 10- Bars: In this case, it is required to provide cross-ties apart from the square ties. It is also organized in bundled bars. Here bundle of 2 bars is arranged at four corners and two remaining bars are supported with the help of cross ties.

5. Lateral Ties for different column cross sections: The arrangement for 16 bars employ diamond ties. The process is very complicated to fabricate diamond ties perfectly and as a result it is ignored. The process is also complicated to arrange them properly. This tie arrangement is not suggested by ACI 315 because of the complications related to it. But, in some countries, standards utilize this arrangement for simple column design.

In A 16 bars column arrangement according to ACI 315 4 bundled bars can be arranged at each corner.



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Published By

Rajib Dey

www.constructioncost.co

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Various applications of Concrete Structure Casting Remnants

The concrete applied in construction is frequently wasted in the process because of several errors in casting. The waste of ready-mix concrete is influenced by various factors like miscalculations / calculations in the jobsite, defective equipment, harmful weather, as well as inappropriate application methods resulting in wasting of materials.

Given below, some useful suggestions for utilizing the leftover concrete casting structures which can reduce the expenses of a project.

1. Applied as a practical column or lintel beam in precast.

In several enormous projects, precast methods are utilized for the wall installation work of practical columns or lintel beams. Normally, instant concrete with K-225 or K-250 is utilized. It is beneficial to utilize the structural casting residual concrete to minimize concrete waste and instant concrete purchases.

2. Applied as a cansteen

Cansteen belongs to the edge of the pedestrian, sidewalk, separator, edge of the road, park path, boulevard, and so on. It is utilized as a roadside amplifier. Normally, cansteen is measured in BQ to order the finished product. It will be better to install it in precast. Structural casting residual concrete is utilized as cansteen to reduce the budget.

3. Applied as a Car Stopper

Car stoppers belong to embankments for providing protection to the parking area to stop the moving cars. Normally, various types of materials like iron pipes, concrete and rubber are usually applied as car stoppers.

4. Applied as Paving Block

Paving blocks are mostly utilized as outdoor parking areas, jogging tracks, parks, sidewalks, home yards and pedestrians. These blocks are made precast with leftover concrete casting materials. Thus, the project costs will be curtailed significantly.



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Published By
Rajib Dey
www.constructioncost.co
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Process for creating design of Seismic Tie Beams

Tie beams are constructed to support the differential settlement among the isolated footings other than the vertical loads of the block works.

With reference to ACI 318-08 section 21.12.3.2, grade beams which are built up to function as horizontal ties among pile caps or footings should be proportioned in such a way so that the smallest cross-sectional dimension is identical to or exceeding the clear spacing among associated columns divided by 20 but should not be over 18 inches. Closed ties should be arranged at a gapping not surpassing the lesser of one half the lowest orthogonal cross-sectional dimension and 12 inches.”

But, it becomes difficult to understand that what force these tie beams are required. In this regard, IBC 2009 section plays an important role.

IBC2009 section 1809.13 for shallow foundations and 1810.3.13 for deep foundations.

For SDC C, D, E or F, ties have the capacity to bear, in tension or compression, a force similar to the smaller of the product of the larger pile cap or column design gravity load times the seismic coefficient, Sds, divided by 10, and 25 percent of the smaller pile or column design gravity load.

In brief, Tie beam force; FT = Larger of ( Pu_large x Sds /10 , Pu_small x 25%)

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Published By

Rajib Dey

www.constructioncost.co

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