DIY Design of Rooftop Rainwater Harvesting Structure

There are hundreds of parts in a typical-sized rainwater harvesting system and with time and research most aspects of a rain water harvesting system can be figured out.

Rain water harvesting (RWH) is an excellent technique of water conservation for future needs and also to recharge groundwater. Due to the alarming population burden, climate change, uneven distribution of rainfall and abrupt variation of meteorological parameters, the surface and ground water resources are continuously depleting in India. Hence adoption of different water conservation techniques at individual, institute and community level has become imperative to cater to the needs.

The instructions on this blog help you get started. This is by no means a complete list but it will provide you a great starting place.

Determine how much you can capture –

The rooftop surface area is the catchment area that receives the incident rainfall. The rooftop area and heights of the selected building in consideration is noted

Estimation of water harvesting potential

The quantity of water that is received from rainfall over an area is called the rainwater potential of that area. And the quantity that can be effectively harvested is called the rain water harvesting potential. Rain water harvesting potential can be calculated using the following formula.

Rainwater Harvesting potential (m³) = Area of Catchment (m²) X Amount of rainfall (mm) X Runoff coefficient

Runoff coefficient

Runoff coefficient value was taken from the manual of artificial recharge of ground water, Government of Kenya Ministry of Water Resource design manual on runoff coefficient values to be adopted for design purpose.

SURFACE	RUNOFF COEFFICIENT (K)
Roof Conventional	0.7-0.8
Roof Inclined	0.85-0.95

Estimation of water demand

The Total water demand for a household is estimated considering the per capita consumption of water for domestic use as per the Kenya water design manual Per capita consumption of water for domestic use

Activities	Liters/Person
Drinking	3
Cooking	4
Bathing	20
Flushing	40
Washing Cloths	25
Washing Utensils	20
Gardening	23
Total demand of water needed	135 liters/person/day

Calculation of discharge

 To find out the required diameter of the pipe to be used for draining the rainwater down from the roof, first we need to calculate the discharge Q

i.e. given by:- Q = CIA (1)

Where,

 Q= Discharge from roofs due to rainfall in (m3 /s)

 C= Coefficient of runoff by rational method taken as 0.8 for this case

I= Intensity of rainfall i.e.20mm/hr.

A= Area of catchment,

.Calculation of number of rainwater pipes (R.W.P)

Assuming the diameter of pipe as 10 cm, the total number of required pipes was calculated in this blog. Q = C×I×A

=

/Where;

Q=Discharge

 I=Intensity of rainfall

A=Area of catchment

n=Minimum no. of pipes

d=Diameter of rainwater pipe i.e. R.W.P

 v=Velocity of water on the roof when it is at the verge of entering in the pipe due to the slope available at the roof. As the roofs are flat or having 0-2% slope so; v=0.1m/s (as per CGWB guidelines) So, no. of pipes are calculated as: n=Q / (0.785 ×v)

Importance of bar bending schedule for concrete construction

A Bar bending schedule comprises of detailed reinforcement cutting and bending lengths and sizes. If bar bending schedule is utilized together with structural reinforcement detailed drawing, the construction quality gets better and optimizes cost & time is saved significantly for developing concrete construction works.

How bar bending schedule offers huge benefits to concrete construction:-

1. By applying a bar bending schedule, cutting and bending of reinforcement is accomplished at factory and delivered to jobsite. This facilitates to perform job rapidly at construction jobsite as well as minimize time & cost for construction process as fewer workers are required for bar bending. Bar bending also avoids the wastage of steel reinforcement (5 to 10%) is reduced with bar bending. As a result the project cost is greatly decreased.

2. If bar bending schedule is applied accordance to BS 8666:2005

3. The quality control at the site gets better with bar bending because reinforcement is furnished following bar bending schedule that is developed with the provisions of relevant detailing standard codes.

4. The estimates for reinforcement steel can be done in a superior way toward a single structural member that can be utilized to workout complete reinforcement requirement for whole project.

5. It can be used for improved stock management for reinforcement. The quantity of Steel needed for next stage of construction is computed perfectly and procurement can be made. This avoids unnecessary storing of additional steel reinforcement at jobsite for prolonged period. Besides, it stops corrosion of reinforcement for coastal areas. It also checks the scarcity of reinforcement for running projects with proper estimation and thus allows the easy progression of concrete construction works.

6. Bar bending schedule is mostly suitable throughout auditing of reinforcement. It resists theft and pilferage in jobsite.

7. Bar bending schedule is essential for reinforcement cutting, bending and making skeleton of structural member prior to set them the in the necessary position. Other works like excavation, PCC etc can be carried on similarly with this activity. So, project activity management in general turns out to be smoth and minimizes construction time. It also checks any damages caused by construction time overrun.

Earthquake Resistant Structures

Earthquake means quick shaking of the ground due to the shift of rock and tectonic plates underground. The ground appears as solid, but the topmost crust of earth is deep and long periods of time produce pressure to develop among plates and fissures.

When the pressure is applied, seismic vibrations and fierce shaking reverberate to the surface which instantly impact miles of land. Once the initial quake hits, aftershocks happen to create further damage.

In areas where seismic activity is not too harsh, we can utilize these techniques to save money and complexity but make the building resistant to seismic activities.

Structure Stiffness: The most traditional way to fight quakes is to use stronger materials to construct the building. Stiffer or heavier members can be used to fight the lateral forces generated during seismic activities. While creating design for earthquake-resistant buildings, safety professionals suggest sufficient vertical and lateral stiffness and strength – specifically lateral. Structures are likely to deal with the vertical movement resulting from quakes superior to the lateral, or horizontal, movement.

Geometrical Absorption: The building can be planned in such a regular and special geometrical shape that it disperses the seismic forces evenly so that no particular member experiences excessive force. This naturally fares much better than a poorly-planned unsymmetrical building.

For existing buildings that are structurally asymmetrical, you can use seismic joints and expansion points in places where the forces are dispersed unevenly. Providing extra columns, shear walls, and framing can make the weaker section withstand the extra forces to a good level. Parking levels should have extra reinforced columns in order to negate the soft story effect.

Lateral Force Resistance: Using three types of lateral force resisting systems, we can try to negate much of the seismic forces. These are:

1. Moment Resisting Frame System: it is designed to resist all types of earthquake generated forces acting on the structure. They can be customized to fit the seismic activity scale of the region.

2. Building Frame System: these are designed to resist gravitational loads only, but they function excellently in that. A shear wall is added to resist the lateral forces acting on structure.

3. Dual Frame System: this is a combination of the above two systems. Shear walls along with moment resisting frames work excellently to fight off the vibrations and displacements from an earthquake. But, of course, they are more complex and costlier to build.

Non-Structural Parts: Much damage caused in buildings due to earthquakes comes from the collapse of non-structural elements, like walls or floors. We can negate that upto some extent if we reinforce them as well.

Building the masonry portions with hollow bricks is an excellent idea to resist seismic activity. Proper detailing and reinforcing of openings in the building will resist their collapse as well.

Base Isolation: It is a rather ambitious idea of placing the building on rollers. These rollers are as near friction-less as possible. The concept is that when the earthquake hits, the rollers will roll, but not transmit any of that energy to the structure. Therefore, the building will experience very little of the seismic forces. The base isolators, that is, the rollers or flexible pads need to be carefully placed and regularly maintained to keep them able to respond at a miliseconds notice