Reflect the relationship between design and stuctural demand. How do you determi

Question

Reflect the relationship between design and stuctural demand. How do you determine the "maximum load on a structure? Is the "maximum" load always a positive value? You might want to discuss tension vs compression axial loads or positive vs negative bending moments.
Reflect the relationship between design and stuctural demand. How do you determine the "maximum load on a structure? Is the "maximum" load always a positive value? You might want to discuss tension vs compression axial loads or positive vs negative bending moments.

Explanation / Answer

Maximum load on the structure is always defined on the basis of structural and functional requirements. Functional requirement defines the purpose(school,institution,auditorium etc.) for which the structure is being constructed, the area required, the floor space requirements etc. whereas structural requirement defines the dimensions adequate tp satisy the functional requirements of the structure. Depending on the functional requirements, we have to calculate the live loads,dead loads(only after the structure is designed),wind loads(if the structure is multi-storeyed and more than 10m height),Earthquake loads(if the structure present in earthquake prone region) and snow loads(if the structure is present in polar regions). Since live load varies with time, a standard value of live load has been given in IS:456 (code of practise in India) and considering those values, we calculate maximum live that a structure can take without failure. After finding the dimensions of structure by functional requirement, we can calculate dead load multiplying volume of buliding with unit weight of concrete(specified in IS:456). Similarly Earthquake,wind and snow loads are calculated( Provisions for calculation of all the loads are given in IS:875). After calculating all the loads individually, we go for combination of loads as all the loads are inter dependable. Using combination of loads also makes structure to take dead load efficiently once the structure is constructed since we use some multiplication factor. Maximum loads can occur by two ways, Lateral and Downward. But maximum downward loads acting on the structure is called as the maximum load on structure mostly since the effect caused by wind will be very less comparitively to the loads acting in the direction of gravity.

And the maximum value may be positive or negative and it is always the combination of loads specified which are prevalent in particular area in which the structure is being constructed. It need not be positive always. It all depends on the direction which we assume to be positive. We should be more particular about the sign we are considering before knowing the magnitude.

Some terminologies use Tension as positive and Compression as negative. Clockwise as positive bending moment and Anti clockwise as negative bending moment. But it all depends on your assumption. Before calculation of loads, you should be clear of yourself which direction you assume to be positive or negative.

I hope you understood my explanation.

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