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

Safer and Better Roof Alternative for Low Income Families

Families from the poorest regions of the world more often than not cover their already lacking homes with corrugated metal roofs. It’s a low cost solution, but in most cases doesn’t prevent leaks, and certainly has very little insulation value. What’s more, they’re often full of toxic substances such as asbestos. To fix these shortcomings, the Indian startup ReMaterials has come up with a modular roofing system called ModRoof, which is sustainable, affordable, and everything a roof should be.

The panels for the ModRoof are made in Ahmedabad, India using recycled agricultural and packaging waste such as cardboard and coconut fibers, which are all sourced locally. The actual production process of each ModRoof panel is very simple and consists of a crushing stage, followed by a mixing stage, compression stage, drying stage and finally the waterproofing stage. The resulting roof panels are impervious to water, fire-resistant, and quiet when it rains, which is a special bonus during the monsoon period.

To assemble them into a roof, the panels are first interlocked and then a sealant is applied. ModRoof has an R-Value of 0.28 Km2/W, while tests conducted in the summer months showed that homes fitted with a ModRoof had an average interior temperature of 96 °F (36 °C), which is quite a bit lower than the 107.6 °F (42 °C) measured in homes with metal roofs. ModRoof has a lifespan of more than 20 years with next to no maintenance needed.

Cheap and Simple Way to Turn Seawater Into Drinking Water

Shortage of drinking water is being faced by more and more communities worldwide. On the other hand, the current methods of turning salt water, which is abundant, into drinking water are expensive and damaging to the environment, and therefore not a viable long-term solution. However, a team of researchers at the University of Alexandria have recently come up with a simpler, cheaper and much cleaner method of turning seawater into drinking water. Their solution could potentially bring clean drinking water to parts of the world, such as North Africa and the Middle East, which do not have sufficient access to it.

Currently, there are several large desalination plants in operation, but these work on the basis of a multi-step process. These plants utilize the process of reverse osmosis, which needs expensive infrastructure and vast amounts of electricity to function. In addition to that, such plants also pollute the oceans by releasing back into them huge quantities of highly concentrated salt water, as well as other pollutants, which adversely affects marine environments.
This is why the method developed by the University of Alexandria team is so promising. Their method involves using materials, which can be manufactured easily and cheaply in most countries worldwide, in order to purify the water. Furthermore, the method they developed does not rely on electricity overmuch.

The tech they developed is based on a method of separating liquids and solids called pervaporation. The latter is a simple process performed in two steps. The first step is filtering the seawater via a ceramic or polymeric membrane, and the second step calls for the vaporizing of, and collecting the condensed water. This final step does not depend of electrically generated heat, which makes pervaporation a lot more energy efficient, as well as cleaner and faster than currently used water desalination methods.

Pervaporation is not a new process, but until now the membrane that is needed for it to work was very expensive and difficult to make. However, the researchers have also invented a brand new, salt-attracting membrane, which is embedded with cellulose acetate powder. This membrane is used in step one of this process, while the acetate powder needed to make it is derived from wood pulp and can cheaply and easily be made in any lab.

According to the researchers, this method can be used to quickly desalinate highly concentrated seawater, while also purifying it even if it is very contaminated. The membrane they use is also capable of capturing pollutants and salt crystals and thereby greatly reducing the polluting aftereffects of using this method. Since fire can be used as a source of heat, the method is perfectly suitable to be used anywhere in the world. All in all, this looks like a very promising solution for third world countries facing drinking water shortages.

8 Famous engineering mistakes

Engineers are often prone to making mistakes. That is why we constantly have to check and double-check everything that we do. It is this type of keen focus on what we do that allowed generations of past engineers to create some of the most remarkable engineering projects.  However, details are sometimes overlooked, numbers misrepresented or even units misread.  While some of these mistakes are miniscule and can be corrected, history has witnessed some colossal oversights that led to huge disasters and in some cases, popular travel destinations.

The Leaning Tower of Pisa

One of the world’s greatest attractions is actually a result of an engineering error. For over 800 years, the leaning tower of Pisa continues to draw worldwide attention and is a popular destination for tourists. Construction began in 1173 on an unstable foundation that comprised of mud, sand and clay. When engineers got to the third floor, the tower began to sink into the soft soil and lean on one side. They tried to fix the problem by making the columns and arches of the third story on the sinking northern side slightly taller. However, construction halted due to political unrest and only resumed a century later. The tower was closed in 1990 for safety reasons and millions of dollars were poured in to stabilize the structure and set it back to the position it had in 1838. Engineers added cables to stabilize the structure, then excavated under the tower and added trusses and counterweights.

Tacoma Narrows Bridge

Known as the “Galloping Gertie”, the original Tacoma Narrows Bridge was opened in July 1940 and at the time it was the third longest suspension bridge in the world. Its nickname was derived from the bridge’s sensitivity to high winds, causing it to sway and vibrate. Just four months after opening, the structure collapsed though its only fatality was a black Cocker Spaniel. Engineers failed to account for the aerodynamic forces within the location, especially during periods of strong winds. Thus the bridge was vulnerable to vibrations generated by wind. A replacement bridge was constructed ten years later, after the end of the Second World War. The remains of the original bridge remain at the bottom of Puget Sound, where they form one of the largest man-made reefs in the world.

Chernobyl Nuclear Power Plant

On 26 April 1986, a structurally unsound reactor in the Chernobyl Nuclear Power Plant, located in Ukraine, exploded. It was the worst nuclear power plant disaster in history, resulting in a severe nuclear meltdown. Highly radioactive materials were discharged into the atmosphere and over an extensive geographical region following the explosion. It spread to as far as Italy and to date over 500,000 deaths have been linked to this catastrophe. By May, about 116,000 people that had been living within a 30-kilometre radius had been evacuated and later relocated to safer regions. The accident was caused by a flawed reactor design that was operated with inadequately trained personnel and poor safety regulations.

New Orleans Canal and Levee System

In 2005 Hurricane Katrina hit New Orleans, devastating the city and flooding about 80 percent of the region, killing thousands and displacing several families. The U.S. Army Corps of Engineers were found liable for this devastation which was compounded by an antiquated levee and canal system that protected the city. The levees failed because they were built in a disjointed fashion, were inconsistent in quality, materials and design and outdated data was used that left gaps exploited by the storm. Additionally, engineers did not take into account the poor soil quality underneath New Orleans. Since then the U.S. government has spent more than $15 billion to upgrade the system.

Deepwater Horizon Spill

One of the worst environmental disasters in U.S. history, the Deepwater Horizon occurred in April 2010 after an explosion tore through a British Petroleum drilling rig. 11 crew members were killed and it is estimated that 180 million gallons of oil was released into the gulf. Over 8,000 animals were reported dead just 6 months after the spill and 16,000 total miles of coastline were affected, including the coasts of Texas, Louisiana, Mississippi, Alabama, and Florida. Mechanical failure as well as human error led to this colossal catastrophe. The engineers repeatedly ignored the well’s orneriness and chose to take quicker, cheaper and ultimately more dangerous actions that eventually led to the total well blowout.

Space Shuttle Challenger

Just a few seconds after the space shuttle challenger was launched in January 1986, it broke apart and killed everyone aboard. It resulted due to the failure of the solid rocket booster O-rings to seal properly, allowing hot combustion gases to leak from the side of the booster and burn through the external fuel tank. Though the problems with the O-rings had been known for nine years, engineers continued to ignore it as they assumed safety was ensured with the presence of the second ring. Eager to launch the shuttle, NASA managers also ignored warnings from engineers that low temperatures could exacerbate the problem.

Banqiao Reservoir Dam

Built in the early 1950s as party of a huge project to control flooding and produce electricity in central China, the Banqiao Reservoir Dam could hold back almost 500 million cubic meters of water. A hydrologist called Chen Xing warned that overbuilding of dams (over 100 were built in that period) and reservoirs could raise the water table in Henan beyond safe levels and lead to disaster. Furthermore, the dam was only built with 5 sluice gates when Xing warned that it needed at least 12. In August 1975, Typhoon Nina dropped more than a year’s worth of rain in just 24 hours and the dam failed. It released the equivalent of 280,000 Olympic-sized swimming pools, taking with it entire towns and killing as many as 171,000.

The Boston Molasses Disaster

Towering over Boston’s North End, construction ended on a massive molasses tank that stood 50 feet tall, 90 feet in diameter, and held more than 2 million gallons of molasses. The tank would help sate the USA’s appetite for industrial alcohol, largely for use in the munitions business. However, in their haste to make a profit, the owners overlooked the wisdom in hiring skilled engineers and instead sought out a man who was unable to read blueprints or even order a simple stress test. As a result, the tank exploded without warning and caused a wave of molasses and debris to travel down the street at 35 miles per hour. At 25 feet high, it ripped buildings off their foundations, killed 21 people and injured 150 others.

PREPARATION OF BAR BENDING SCHEDULE

Bar bending schedule (or schedule of bars) is a list of reinforcement bars, a given RCC work item, and is presented in a tabular form for easy visual reference. This table summarizes all the needed particulars of bars – diameter, shape of bending, length of each bent and straight portions, angles of bending, total length of each bar, and number of each type of bar. This information is a great help in preparing an estimate of quantities.

 The below illustration depicts the shape and proportions of hooks and bends in the reinforcement bars – these are standard proportions that are adhered to:

(a) Length of one hook = (4d ) + [(4d+ d )] – where, (4d+ d ) refers to the curved portion = 9d.

(b) The additional length (la) that is introduced in the simple, straight end-to-end length of a reinforcement bar due to being bent up at say 30^o to 60^o, but it is generally 45^o) = l₁ – l₂ = l_a
Where,

Giving different values to respectively), we get different values of la, as tabulated below:
The below table presents the procedure to arrive at the length of hooks and the total length of a given steel reinforcement.