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[Anupds]

An article by Anup D Shirhatti dtd. 01-09-2021

  Factor of safety is very important in civil engineering, Just like in test cricket when opposition has been wrapped up for meagre runs and the batting side is thinking about how much runs will be enough to defend and not bat again. Some say 200 runs , some say 400 runs, some go and score 1000 runs. If you score 200 runs it may not be enough, 400 runs is a psychological barrier breached seldom and 1000 runs is a drawn test. However there are many factors like boling depth, variety, batting depth weather the bowl is swinging. May be 400 runs are enough but anything more is factor of safety you don't want to lose.

  Similarly, in civil engineering the standardization of material, skillset of labours, loads are all variable. Based on studies there are are partial safety factors for soil it is 3, for concrete it is 1.5 and steel it is 1.15 and so on that means steel is highly reliable and soil is unreliable. Similarly in life also  suffer as we expect a higher factor of safety from people or organisation without analysing their  performance/ our expectation. So realistic expectations are necessary for cordial relations.

   Also, in civil engineering there are safety factors for load like wind, earthquake, live load, etc and while we take combination of loads we make   an assumption that borth earthquake and hurricane don't occur simultaneously, the stress is also on behaviour of structure should be reliable and provide ample time for people to exit. Similarly in life also for individuals and organisations extreme loads come for example COVID -19 put such a pressure on health infrastructure. So just like there is summer after rainy season. so a reasonable approach is necessary to deal with extreme events as employed in civil engineering.

[vikram.jeet]

FACTOR OF SAFETY

In Structural & Civil Engineering , FOS is not a luxury but indeed a dire necessity

Civil construction fully rely on FIVE M's.

METHODS
MODELLING (NOW IN COMPUTER AGE)   } - - - -   DESIGN STAGE

MAN
MATERIALS    - - -    CONSTRUCTION STAGE
MACHINERY

Design stage comprise of designing the structure components on basis of METHODS , THEORIES , PRINCIPLES .There are are assumptions , approximations , close relevance . Even present day softwares and modelling thereof , may not be ideal in some situations.
Construction stage with MAN performing various activities , skill , expertise all count in end product. Supervision Quality is also man dependent.
MATERIALS , difficult to test every thing before use , only some fraction to be tested. Materials production at site needs higher Factor to take care of variability. As in concrete production and CURING .
Machinery which facilitate MAN , sometimes little erroneous , but No factor is generally attributed .

APART FROM FIVE M's  , Design stage loadings are hypothetical. Floors are designed for UDL but actual loads are concentrated , small or big.  

In view of reasoning as expressed above , FOS seems necessity as one or many of above reasons if combine , FOS IS THE SAVIOUR OF STRUCTURES.
LONGEVITY// DURABILITY Is DIRECTLY RELATED TO FOS , the design life of structure is greatly reduced in case FOS is compromised , and a structure exhibits multiple maintenance issues early.
HENCE SAFETY FIRST AND ECONOMY THEREOF needs to be respected in civil structures design and construction.

[vikram.jeet]

Factor of safety also , to some extent , takes care of Overloadings , Accidental loadings , Impact load effects .

Yes , for severe Earthquake s , FOS too feels weak to protect the structure and it the ductile incorporations / detailing s which are provided in structural components to safeguard against collapse.

[vikram.jeet]

FACTOR OF SAFETY

FOS is not to be misunderstood as extra margin on strength . Field Engineers ,  Builders , other related professionals do feel that FOS is an extra safety multiplier but that is not the case  , I think.

In view of so many variables from design stage to execution and completion stage , FOS is a probability constant which balances design /idealised  assumptions vs Actual conditions/   implementation / execution  .