Definition of Design Period:
Design period could be defined as the number of years in the near future in which the supply will surpass the demand. Or, It is the number of years in the near future in which the given facility is obtainable to satisfy the demand.
Why Design Period Is Provided?
The main reasons behind providing Design Periods are:
- It is prodigiously strenuous or unfeasible to produce frequent.
- It is affordable to supply one mammoth unit in lieu of constructing a variety of bijou ingredients.
Factors Affecting Design Period:
Factors affecting Design Period are given below. Following are some aspects which act on the Design Period of the structure:
- Availability of Funds.
- Life of the structure.
- Ease or Difficulty in Extension.
- Rate of Increment.
- Lead Time.
- Economy of Scale.
- Interest Rates.
- Quality of Material.
- First Cost.
#1. Availability of Funds-
- If funds are obtainable, one must hold on to a smaller design period.
#2. Life of Structure-
Life of structure is that the number of years in the near future in which the design period is physically & practically suitable to bestow the intended amenity.
So it is always ought to be less than a lifetime of structure.
- Conduits(Type of Pipes).
Factors Affecting Design Period Type of Pipe
Average Service Life
|Steel Pipes||25 – 50 Years|
|Cast Iron Pipes||100 Years|
|Concrete Pipes||75 Years|
#3. Ease or Difficulty in Extension-
For the projects whose augmentation is unquestionably feasible, it’s generally kept low. For instance, we are capable of inaugurating new tube-wells at any time since we don’t require to install all tube wells which might be required after 20
- Tubewell: Easy to drill.
- Treatment Plant: Easy to enlarge.
But for the projects whose augmentation is strenuous, their design period is kept sizeable. For instance, dams and reservoirs cannot be augmented
Adroitness and difficulty that’s likely to be faced in expansions, if undertaken at future dates. For instance, vigorous expansions mean choosing a finer value of the design period.
#4. Rate of Increment-
If the speed of growth is lofty, then for that region dwarf design period is required. Anticipated rate of population growth, including feasible shifts in communities, industries, and commercial inceptions.
For instance, if the speed of increase of population is comparatively sloth, a better figure for the design period could also be chosen.
#5. Lead Time-
It is the time from the outset of a project to its completion. Design period should be greater than the interval.
Lead Time = Time for Design of Project + Construction Time
#6. Economy of Scale-
- The decrease in monetary value parallel to the increase in a facility is thought of as an Economy of Scale.
- If the economy of scale is little, smaller design periods are used.
- It’s economical to make an oversized structure, for an extended design period.
#7. Interest Rates-
- If charge per unit is bijou, the lofty value of design period is also economically possible.
- The rate of interest depends on the borrowings and also the ancillary money which needs to be invested.
- Amount and availability of ancillary investment likely to be incurred for extra arrangements. For instance, if the funds aren’t available, one should keep a bijou design period.
#8. Performance Time-
- Structures are checked under working conditions in due course, which mustn’t be considered in the design period. During this point, it’s not providing facility to the community.
#9. Quality of Material-
- Design period mustn’t be longer than the lifetime period of the material utilized in the installation project.
- The quantity of years of which a provision is formed in designing the capacities of the varied modules of the water system scheme is recognized as design period.
#10. First Cost-
- In case of High first cost and High Rate of interest, design period should be brief, so that the aggregate cost of the project should not be disseminated to present population e.g. Houses.
Design Period Values:
Water system projects, under a standard state of affairs, could also be designed for a design period of 30 years. This 30 year period may, however, be amended in relevance to specific units of the project, depending upon:-
- The useful lifetime of the component facility.
- Ease in polishing off extensions when required.
- Rate of interest is in order that expenditure, far ahead of utility, is avoided.
The design period for designing the assorted components of a facility project is provided in the ensuing table:
Design Period in Year
|Storage by Dams||
1. Pump House
2. Electric Motors and Pumps
|Water treatment units||
|Pipe connection to the sundry treatment units and other small paraphernalia.||
|Raw water and clear water transporting units||
|Clear water reservoirs at the head works, balancing tanks, and service reservoirs||
Also, Read: What Is Limit State Method | Assumption in Limit State of Collapse | Limit State Design | What Is Working Stress Method | Assumptions in Working Stress Method | Working Stress Method of Design
What Are Design Period and Return Period for Design Conditions?
- Design life means the rock bottom span of a structure that is predicted to last.
- The longer is the design life; the further is the cost of a project.
- Therefore, in choosing the design life for a structure, engineers ought to inspect the design life which spawns an economical project without relinquishing the desired function.
- In a selection of return periods of particular design conditions, winds, waves, etc., one ought to consider the connotations of over-expenditure.
- In fact, there are ordinarily no paramount or maximum values of those design conditions, and its selection is anticipated on the probability of expenditure which is set forth to return period.
- Hence, design life might not be indistinguishable from to the return period of design conditions because their selections are succored on different considerations.