Corrosion Problem of Steel Piles

According to National Bureau of Standards ( NBS), pile driven in disturbed, or fill, soils will tend to undergo relatively more corrosion. This study is applicable for both sheet-pile and bearing pile. Undistured soils were found to be Oxygen-deficient from a few feet below the ground surface while the disturbed soil contain a high concentration.

The soil considered as corrosion  susceptible, according to NBS, is:

P^H   = 2.3 _- 8.6  
_{b)  Electrical resistivity of 300  to 50200 ohm. cm.}

Soil exposed to sea water or effluents with a PH much above 9.5 or below 4.0 will required painting or encasement in concrete to resist corrosion. This is also true for zones where the piles are subjected to water fluctuations foe several feet. A splice, increasing section slightly in the corrosive zone, may suitable alternative to the treatment stated above.


Some of the newer grades of high-strength and copper-alloy steels claim substantial corrosion resistance. The A690 high-strength low-alloy steel has approximately two to three times more corrosion resistance to sea water them ordinary carbon steel of A36 grade.

Formation of Mount Everest disappearing Tethys Sea

About 50 million years ago, the collision of the Indian subcontinent and Asia, gave a great height to Mount Everest. Although the northward drift of India slowed dramatically with initial collision, the two continents have continued to converge as India slides under Asia.


Prior to the initial collision between India and Asia, the vast Tethys Sea existed between the two. The sea disappeared, a victim of plate tectonics, but its presence before 50 million years ago is recorded by scraps of oceanic crust preserved in the southern Tibetan plateau. It is not surprising that scientists consider the Himalayan range to be one of the planet’s best natural laboratories for studying the mountain building process and associated seismic activity. Dr. Bilham, a geophysicist on the EVEREST team, is conducting research to better understand the processes that drive seismic activity in Nepal and to help assess the danger of destructive earthquakes in Nepal and northern India. In this century, four earthquakes of Richter Magnitude 8 or greater have occurred in the Himalayas. Scientists expect another of similar magnitude to occur yet this century, putting millions of lives at risk.


At 29,028 feet, Mount Everest is five miles up — about the cruising altitude of a jet airliner. Data collected by Dr. Bilham indicates the world’s highest mountain is creeping skyward 3 to 5 millimeters with every passing year. Every time a team reaches the summit, the climbers are essentially setting a new altitude record.

Loads on Helicopter Landing Area

In addition to the all loads (Rain loads, loads due to flood and surge, temperature effects, snow load, soil and hydrostatic pressure, loads due to explosions, and vertical forces on air raid shelter) that may occur in this(Helicopter Landing Area) area including dead loads, the minimum live load on helicopter Landing or touchdown Area shall be one of the loads L1, L2, L3 as given below producing the most unfavorable effect:

1. L1 = W1

2. L2 =KW2

3. L3 = w

World Highest Helipad in Burj Al Arab 

Where, W1 = Actual weight of the helicopter in KN,

W2= Fully loaded weight of the helicopter in KN,

w = A distributed load of 5.0 KN/m2,

K=0.75 for helicopters equipped with hydraulic type shock absorbers and

= 1.5 for helicopters with rigid or skid type land

Helicopter Landed on World Highest Helipad in Burj Al Arab 

The live load, L1 shall be applied over the actual of contact of landing. The load, L2 shall be a single concentrated load including impact applied over a 300 mm X 300 mm area. The loads, L1 and L2 may be applied anywhere within the landing area to produce the most unfavorable effects of loading.

Volcano-Earthquake Relationship of Philippines

The 1991 eruption of Mount Pinatubo is the world's second largest terrestrial eruption of the 20th century. Successful predictions of the onset of the climactic eruption led to the evacuation of tens of thousands of people from the surrounding areas, saving many lives, but as the surrounding areas were severely damaged by pyroclastic flows, ash deposits, and later, lahars caused by rainwater remobilising earlier volcanic deposits, thousands of houses were destroyed.


Fig: Map showing major volcanoes of the Philippines.

Mayon Volcano is the Philippines' most active volcano. The volcano has steep upper slopes that average 35–40 degrees and is capped by a small summit crater. The historical eruptions of this basaltic-andesitic volcano dates back to 1616 and ranges from Strombolian to basaltic Plinian eruptions. 

Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas.

Fig: Mayon Volcano overlooks a pastoral scene approximately five months before the volcano's violent eruption in September 1984.

Taal Volcano has had 33 recorded eruptions since 1572. A devastating eruption occurred in 1911, which claimed more than a thousand lives. The deposits of that eruption consisted of a yellowish, fairly decomposed (non-juvenile) tephra with a high sulfur content. The most recent period of activity lasted from 1965 to 1977, and was characterized by the interaction of magma with the lake water, which produced violent phreatic explosions. Although the volcano has been dormant since 1977, it has shown signs of unrest since 1991, with strong seismic activity and ground fracturing events, as well as the formation of small mud geysers on parts of the island.

Kanlaon is the most active volcano in central Philippines and has erupted 25 times since 1866. Eruptions are typically phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano. On August 10, 1996, Kanlaon erupted without warning, killing British student Julian Green and Filipinos Noel Tragico and Neil Perez, who were among 24 mountainclimbers who were trapped near the summit.

Need for Structural Safety

A structural failure, in some cases, would merely be an inconvenience. In other cases, loss of life and significant loss of property may be involved. This occurrence is considered in proportioning and designing structural member seriously. The methods of designing has been developed to have sufficient warning before failure before failure. Safety is provided to the structures to develop adequate strength against all loads that may foreseeable act on it.

If the strength of a structure, built as designed, could be predicted accurately, and if the loads and their internal effects (moments, shear, and axial forces) were known accurately, safety could be ensured by providing a carrying capacity just barely in excess of the known loads. However, there are a number of sources of uncertainty in the analysis, design and construction of reinforced concrete structures. These sources of uncertainty, which require a definite margin of safety, may be listed as follows:

1. The assumed intensity of load may not be same as that of actual intensity.

2. Actual loads may be distributed in a manner different from that assumed.

3. The assumptions and simplifications inherent in any analysis may result in calculated load effects-moments, shears etc. different from those that, in fact, act in the structures.

4. The actual structural behavior may differ from that assumed , owing to imperfect knowledge.

5. Actual member dimensions may differ from those specified.

6. Reinforcement may not be in its proper position.

7. Actual material strength may be different from that specified.

It is evident that the selection of an appropriate margin of safety is not a simple matter. But, considering the consequence of failure, the design codes are developing rational safety provisions.

Most Destructive Known Earthquake (Life loss)

The earthquake occurred near Huaxian, Shaanxi (formerly Shensi), China, about 50 miles (80 km) east-northeast of Xi'an, the capital of Shaanxi. More than 830,000 people were killed. Damage extended as far away as Taiyuan, the capital of Shanxi (formerly Shansi) and about 270 miles (430 km) northeast of the epicenter. There are felt reports as far away as Liuyang in Hunan, more than 500 miles (800 km) away. Geological effects reported with this earthquake included ground fissures, uplift, subsidence, sandblows, liquefaction and landslides. Most towns in the damage area reported city walls collapsed, most to all houses collapsed and many of the towns reported ground fissures with water gushing out (ie. liquefaction and sandblows). Gu, et.al. says that "the identified death toll of soldiers and civilians was 830,000, and the unidentified was uncountable." The earthquake was felt in all or parts of 9 provinces: Anhui, Gansu, Hebei, Hubei, Henan, Hunan, Shaanxi, Shandong and Shanxi. The maximum intensity is XI in the Huaxian-Weinan area and the estimated magnitude is 8. Additional details from Gu, et.al.:

In Huaxian, "city walls, temples, offices and civilian houses were demolished, without a single wall left standing.... The ground fissured and sunk. Water gushed out and formed canals. Sixty percent of the people (several tens of thousands were killed or injured."

In Weinan [15 miles (24 km) west of Huaxian], "city walls, temples, storehouses, offices and civilian houses collapsed totally.... In the city, the ground sunk for more than 3 meters. Fifty percent of the people were killed."

In Xi'an [one of China's major cities then as it is now], "city walls, storeyed buildings and terraces collapsed. Most temples were destroyed. More than half of the houses toppled down. Only 10-20 percent of the walls were left standing. The ground fissured crisscross. Thirty percent of the people were killed."

Even as far away as Taiyuan, "houses were destroyed in great numbers."
In many references, this earthquake is referred to as the "Shensi Province earthquake of 1556" using the old spelling for the province.

Destruction of 2004 Great Sumatra Earthquake

This is the third largest earthquake in the world since 1900 and is the largest since the 1964 Prince William Sound, Alaska earthquake. In total, 227,898 people were killed or were missing and presumed dead and about 1.7 million people were displaced by the earthquake and subsequent tsunami in 14 countries in South Asia and East Africa. (In January 2005, the death toll was 286,000. In April 2005, Indonesia reduced its estimate for the number missing by over 50,000.) The earthquake was felt (IX) at Banda Aceh, (VIII) at Meulaboh and (IV) at Medan, Sumatra and (III-V) in parts of Bangladesh, India, Malaysia, Maldives, Myanmar, Singapore, Sri Lanka and Thailand. The tsunami caused more casualties than any other in recorded history and was recorded nearly world-wide on tide gauges in the Indian, Pacific and Atlantic Oceans. Seiches were observed in India and the United States. Subsidence and landslides were observed in Sumatra. A mud volcano near Baratang, Andaman Islands became active on December 28 and gas emissions were reported in Arakan, Myanmar.

FLAT PLATE SYSTEM HAVING STEEL/ CONCRETE COLUMN

Popularity of Flate Plate

The use of flatplate appeals to designers particularly because design flexibility is possible through shifting of walls without the need for columns to be properly aligned. With increasing demand for flexibility in interior layout, the use of flat plate for landed houses is gaining much popularity amongst architects. The main and unique feature of this system is that it provides a way for the architect to achieve the concept of high and completely flat ceiling with no beam protrusion. The services can be installed within or below the slab and there are flexibilities in relocating vertical small penetrations. The soffit is often flat and high ceiling height can be achieved.

Columns Used

The columns used in this system are either cast in-situ concrete columns or circular steel hollow sections. When the columns used are steel hollow sections with concrete in-fill, the desired finish with exposed steel can be easily achieved.

Flat plate system with circular steel column

Connection & Detailing

The main consideration for steel column connection to flat plate is to ensure that the base plate for the steel columns are cast into the concrete flat plate. Hence the positioning and alignment of the base plates are of utmost importance.

If concrete in-fill and column bars are required within the steel hollow section, the starter bars for the columns have to be placed and fixed in position prior to casting of concrete flat plate (see figure 2.0 for base plate connection).

Figure 2.0 : Base plate details for column

In the concrete column with flat plate design, the connection is more simplified without the need for base plate connection. In this case, reinforcement bars should be properly detailed between the columns and slabs. Punching shear checks are critical and vertical shear reinforcement should be detailed accordingly.

Figure 3.0 : Examples of shear reinforcement

Figure 4.0 : Hidden beam within column strip

Limitation of CFRP

CFRP is used in civil engineering, automobile and other fields. But it have some drawbacks which limits its use in some fields. The first one is cost. Though CFRP is generally regarded as having superior properties, it is more costly material that its counterparts in the construction industry, glass fibre reinforced polymer (GFRP) and aramid fibre reinforced polymer (AFRP). In case of prestressing construction it cannot be used due to difficulties in anchorage of strands.

Much research continues to be done on using CFRP both for retrofitting and as an alternative to steel as a reinforcing or prestressing material. Cost remains an issue and long term durability questions still remain. Some are concerned about the brittle nature of CFRP, in contrast to the ductility of steel. Though design codes have been drawn up by institutions such as the American Concrete Institute, there remains some hesitation among the engineering community about implementing these alternative materials. In part this is due to a lack of standardisation and the proprietary nature of the fiber and resin combinations on the market, though this in itself is advantageous in that the material properties can be tailored to the desired application requirements.

It have no endurance limit when exposed to cyclic loading. In case of recycling to reclaim the carbon fibre, the milling or shredding at low temperature shortens the fibres dramatically. The shortened fibres cause the recycled material to be weaker than the original material. Other processing of reclaiming carbon fibre are costly.

In case of automative application, its use is limited for creating body-panel for some of high-end cars, hood, spoiler. However, these parts are rarely made of full carbon fibre. They are often just a single layer of carbon fiber laminated onto fiberglass for the "look" of carbon fiber. It is common for these parts to remain unpainted to accentuate the look of the carbon fiber weave.

Application of CFRP in Sports Equipments

In high-end sports equipments carbon fibre reinforced polymer has found perfect due to its light weighing property in compare to aluminium or steel. Racing bicycle is the thing where it is used widely. It produce bicycle tubing of less weight.

Fig: IVW Develops World Record Racing Bike(1).

[1. German bicycle manufacturer Canyon Bicycles GmbH, has developed a racing bike chassis of carbon fibre reinforced polymer with the Institut fuer Verbundwerkstoffe (IVW).

The lightweight Carbon Ultimate F10 bike boasts a total weight of only 1260 grams (for the frame and fork) and its high stiffness for the first time exceeded the cyclists magical limit of 100 of the stiffness to weight ratio, the so-called STW-coefficient. 

The Carbon Ultimate F10 chassis received the coveted red dot award, the international trademark for quality of design, in the red dot design award 2005, one of the largest design competitions worldwide with more than 4000 applications from 40 countries.]
The choice of weave can be carefully selected to maximize stiffness. The variety of shapes it can be built into has further increased stiffness and also allowed aerodynamic considerations into tube profiles. Carbon fiber reinforced polymer frames, forks, handlebars, seatposts and crank arms are becoming more common on medium- and higher-priced bicycles. Carbon fiber reinforced polymer forks are used on most new racing bicycles.

Other sporting goods applications include rackets, fishing rods, longboards and rowing shells. Sports shoe manufacturers may use carbon fiber as a shank plate in their basketball sneakers to keep the foot stable. It usually runs the length of the sneaker just above the sole and is left exposed in some areas, usually in the arch of the foot.

Carbon fiber reinforced polymer is used extensively in high end automobile racing. The high cost of carbon fiber is mitigated by the material's unsurpassed strength-to-weight ratio, and low weight is essential for high-performance automobile racing.

Tectonic Summary of Sumatra earthquake, 2009-09-30

The magnitude 7.6 southern Sumatra earthquake of September 30, 2009 widely felt throughout Sumatra and Java, Indonesia, Malaysia, Singapore and Thailand. A small local tsunami with wave heights of 27 centimeters (amplitude measured relative to normal sea level) was generated. This occurred as a result of oblique-thrust faulting near the subduction interface plate boundary between the Australian and Sunda plates. At the location of this earthquake, the Australian Plate moves northeast with respect to the Sunda plate at a velocity of approximately 65 mm/yr.
On the basis of the currently available fault mechanism information and earthquake depth of 80 km, it is likely that this earthquake occurred within the subducting Australian Plate rather than on the plate interface itself. The recent earthquake was deeper than typical subduction thrust earthquakes that generally occur at depths less than 50 km.
The subduction zone surrounding the immediate region of this event has not witnessed a megathrust earthquake in the recent past, rupturing last in an earthquake of M 8.5 or larger in 1797. Approximately 350 km to the south, a 250 km section of the plate boundary slipped during an Mw 8.4 earthquake in September 2007, while approximately 300 km to the north, a 350 km section slipped during the Mw 8.7 earthquake of March 2005. In early 2008, the plate boundary updip of today’s earthquake was active in a sequence of Mw 5-6 earthquakes. It is not clear how today’s earthquake is related to the sequence of megathrust subduction zone events on the shallower section of the plate boundary.

Application of CFRP in Aerodynamics

Carbon Fibre Reinforced Polymer has found a lot of use in aerodynamics. For the same strength, a carbon-fiber frame weighs less than a aircraft of any alloy. The New arrived Boeing (fuselage) 787 Dreamliner and Airbus A350 XWB will be composed of CFRP, making the aircraft lighter than a comparable aluminum fuselage, with the added benefit of less maintenance thanks to CFRP's superior fatigue resistance.

[1. Thick large-sized panel of a high-aspect swept-forward wing of the highly maneuverable aircraft made from high-modulus CFRP by automated lay-up technique with the use of special non-metallic moulding equipment.
A kit of 4 panels (two upper panels and two lower panels):

A. Mass of one panel - no more than 250 kg
B. Plan size - more than 6500x2500 mm2
C. Thickness - more than 18 mmLarge panel thickness and overall dimensions, as well as stringent requirements placed upon the accuracy of the aerodynamic surface, render this development unique. High accuracy of the aerodynamic surface has been obtained.]

Due to its high ratio of strength to weight, CFRP is widely used in micro air vehicles (MAVs). In MAVSTAR Project, the CFRP structures reduce the weight of the MAV significantly. In addition, the high stiffness of the CFRP blades overcome the problem of collision between blades under strong wind.

CFRP is used, either as standard equipment or aftermarket parts, in high performance radio controlled vehicles and aircraft, i.a. for the main rotor blades of radio controlled helicopters -- which should be light and stiff to perform 3D manoeuvres.

Fire resistance of polymers or thermoset composites is significantly improved if a thin layer of carbon fibers is molded near the surface -- dense, compact layer of carbon fibers efficiently reflects heat. This property is also make it important in this field.

Cavity Walls

Definition:
Two walls with a 5 cm to 8 cm comprise a cavity wall having cavity between them. The outer wall also known as outer leaf, consists of a 10 cm (half brick) thick wall and the inner wall is sufficiently thick and strong to carry the imposed load safety. The minimum thickness of the inner wall is restricted to 10 cm (half brick). The provision of a continuous cavity in the wall efficiently prevents prevents the transmission of dampness to the inner wall.

Advantages:

The advantages of cavity walls may be summarised as below:

1. They have good sound insulation property.

2. The layer of air in the cavity being non-conductor of heat reduces the transmission of heat from the external face to the internal one and as such cavity walls are best suitable for a tropical country like India. Tests have revealed that cavity walls have 25% greater insulating value than solid walls.

3. As there is no intimate contact between the two leaves except at the wall ties (which are of impervious material), there is no possibility of the moisture travelling from the outer leaf to the inner.

4. They are economical.

Locating Cavity:

The cavity should start near ground level and terminate near eaves level in case of sloping roof or near coping in case of flat roof with parapet wall. The cavity should preferably start 15 cm below the damp-proof course level. This has the advantage of draining any condensed moisture below the level of damp-proof course. Similarly, to prevent infiltration of moisture, the bottom of cavity should lie at least 15 cm above the out side ground level. The damp-proof course for the two leaves is laid separately, although at the same level. This is necessary to continue the cavity below damp-proof course. The cavity is kept fully ventilated by providing air bricks in the external wall immediately above damp-proof course. The air bricks should be kept 90 cm apart. Similarly, air bricks are provided near the top of the cavity.

Wall Ties:

The two walls are tied together with metallic or terra-cotta ties to obtain structural stability. They are spaced 90 cm apart horizontally and 30 to 45 cm apart vertically in staggered positions.

Quality of water in concrete Mix

Introduction

Concrete is a chemically combined mass which is manufactured from binding materials and inert materials with water. It is most popular construction material due to its unique durability and reasonable strength; more interestingly can be modified and designed for wide range of strength requirements and set under variable environmental conditions. Cement is the most important material of concrete which is produced at the cost of environmental emission of CO₂; to produce 1 tonne cement nearly 900 kg CO₂ is released in the environment. So such an energy intensive materials constitutes concrete which may be seriously affected by (both strength and durability point of view) by relatively available and cheap but essential element water; more precisely impurities in water. Quality of mixing water are mainly considered for performance of concrete in both fresh and harden state.

Impurities in mixing water intervene the setting time of the paste and may produce detrimental effect on strength and durability of concrete also. When impurities are chemically active, they may take part in the chemical reaction contributing significant change in setting, hardening and development of strength of concrete. More over health hazard during handling these water should carefully considered. In this regard past performance of a particular source of water can be used to evaluate suitability of water; if not available, some testing inevitable to evaluate water for setting time, compressive strength and durability.

Function of Water in Concrete

Three water serves the following purpose:

1. To wet the surface of aggregates to develop adhesion because the cement pastes adheres quickly and satisfactory to the wet surface of the aggregates than to a dry surface.
2. To prepare a plastic mixture of the various ingredients and to impart workability to concrete to facilitate placing in the desired position and
3. Water is also needed for the hydration of the cementing materials to set and harden during the period of curing.

The quantity of water in the mix plays a vital role on the strength of the concrete. Some water which have adverse effect on hardened concrete. Sometimes may not be harmless or even beneficial during mixing. So clear distinction should be made between the effect on hardened concrete and the quality of mixing water.

Potable water as mixing water

The common specifications regarding quality of mixing water is water should be fit for drinking. Such water should have inorganic solid less than 1000 ppm. This content lead to a solid quantity 0.05% of mass of cement when w/c ratio is provided 0.5 resulting small effect on strength.

But some water which are not potable may be used in making concrete with any significant effect. Dark color or bad smell water may be used if they do not posses deleterious substances. P^H of water to even 9 is allowed if it not tastes brackish. In coastal areas where local water is saline and have no alternate sources, the chloride concentration up to 1000 ppm is even allowed for drinking. But this excessive amount of alkali carbonates and bicarbonates, in some natural mineral water, may cause alkali-silica reaction.

Acceptable source of water

Besides potable water, various new and existing sources are available for mixing water which can be used for complete and partial replacement of valuable potable water. This includes

• Ground water

• Reclaimed water

• Treated water from municipal sewer

• Waste water of ready-mix concrete plant etc.

In many regions of the world there have scarcity of water like Dubai and Qatar and the local authorities are looking for new sources and reused water. There treated water are used for agricultural requirements and daily needs for construction industry. like washing aggregates, as concrete mixing water and curing of the same. Water from river and sometimes even sea are considered suitable if it is free from brackish matter. In arid regions, brackish groundwater is mixed with desalinated water and considered suitable for concrete production and for concrete slurry too.

Sampling guideline for mixing water

In addition to testing on constituent of concrete like aggregate cementitious materials and admixtures etc., testing of water is an important part of quality control of concrete. A systematic testing schedule for water testing yields higher efficiency of concrete and assure good performance in regard of strength and durability.

Important thing to remember is that water can be changed by chemical, physical or biological reactions; such modification may occur during sampling and at the time of analyzing. So it should be tested before using in concrete.

Collection of sample

The location of sampling should be at mid-stream and extracted from mid depth, as far as possible. When there have obstructions or major discharges are fall into river, the sample should be taken in downstream of discharges by a distance more than 100m in case of small stream; in a word, the site should be such that no change in water in the stream are seen with naked eyes. In case of wide river at least three samples should be taken along the cross section.

Sampling of waste water

When water from narrow effluent channels of treated sewers are to be tested, the sample should be taken from one third depth of water neither skimming the top surface nor scrapping the bottom. It is important to locate site having sufficient flow so that no nearby deposition is occurred. Caution should be taken during sampling to keep in-situ condition of dissolved gas i.e. must not be agitated to liberate dissolved gasses or to cause some degree if aeration.

It was observed that sewage flows are often intermittent which requires to collect samples an hour interval throughout 24 hours. At room temperature waste water generally decompose rapidly, so test set-up for certain parameter should be available at site. These are as follows:

• Dissolved oxygen
• Residual chlorine
• Sulfides
• PH
• Nitrites etc.

For some tests addition of preservatives just after collection of water will be enough.

Can ready-mix concrete washout water be used in water?

It is recommended in AS 1379 and ASTM C94, that water used in washout operation in ready-mix concrete plant can be used in concrete as mixing water. Only requirement is to store it in such a way that contamination from deleterious matters is prevented and water is collected from storage outlet. Water should conform ASTM C 1602; the sources and testing frequencies and other requirements of testing to qualify water sources. According to ASTM C94 water may be water itself or may be ice or any forms of moisture on the aggregate surface and wash water remains in the drum of truck mixer can be used for concreting next batch.

Plant washout water often called recycled ready-mix water. In 2007 experiment results were published by GL Low et al. about the requirements of recycling of cement-slurry water found from ready-mix concrete batching plant. He also examined the performance of concrete casted from reused water without any treatment. This study revealed the effects of application of such water in concrete mix on both fresh and hardened concrete based on the requirements of ASTM C94 and BS4550. The interesting thing was that they used two criteria namely specific gravity and PH; slurry water from such source can meet acceptance criteria based on concrete performance in setting time, compressive strength and drying shrinkage, when specific gravity of recycles water not exceed 1.03 and PH value of water lies between 12.3 to 13.3.

Determination of Suitability of Mixing Water

A simple way of determining the suitability of such water is to compare the setting time of cement and the strength of mortar cubes using the water in question with the corresponding results obtained using known suitable or distilled water. About 10% tolerance is generally allowed. Such tests are recommended when water for which no service record is available containing dissolved solids in excess of 2000 ppm or, in excess of 1000 ppm. When unusual solids are present a test is also advisable.

Quality Parameters	Maimum Limit (ppm)
Chlorides	500
SO3	1000
Alkali Carbonates and Bicarbonates	1000
Turbidity	2000

The effect on concreting for different types of contamination or impurities are described below:

Suspended Solids

Mixing water which high content of suspended solids should be allowed to stand in a setting basing before use as it is undesirable to introduce large quantities of clay and slit into the concrete.

Acidity and Alkalinity

Natural water that are slightly acidic are harmless, but presence of humic or other organic acids may result adverse affect over the hardening of concrete. Water which are highly alkaline should also be tested.

Algae

The presence of algae in mixing water causes air entrainments with a consequent loss of strength. The green or brown slime forming algae should be regarded with suspicion and such water should be tested carefully.

Sea Water

Sea water contains a total salinity of about 3.5%(78% of the dissolved solids being NaCl and 15% MgCl₂ and MgSO₄), which produces a slightly higher early strength but a lower long-term strength. The loss of strength is usually limited to 15% and can therefore be tolerated. Sea water reduces the initial setting time of cement but do not effect final setting time.

Chloride

Water containing large amount of chlorides tends to cause persistent dampness and surface efflorescence. The presence of chlorides in concrete containing embedded steel can lead to its corrosion.

Moisture Content of Aggregate

Aggregate usually contains some surface moisture. Coarse aggregate rearly contains more than 1% of surface moisture but fine aggregate can contain in excess of 10%. This water can represent a substantial proportion of the total mixing water indicating a significant importance in the quality of the water that contributes surface moisture in aggregate.

Effect of lead exist in mixing water

An investigation was conducted on behavior of concrete under existence of heavy metal in mixing water by Madhusudana Reddy, B and et al (2011). They examined the effect of presence of lead (Pb+) in mixing water on setting times, compressive strength, soundness and attack of sodium-sulfate on high strength cement mortar. Two types of specimens of cement mortar were used, one was casted with deionised water and others were casted with deionised water with different concentrations of lead. The lead concentration used were 10, 50, 100, 500, 1000, 2000, 3000, 4000 and 5000 mg/liter. 

The results were interesting, as compared to reference specimens, it was figured out from results that specimens having high concentration of lead lost significant strength with a significant increase in setting time of cement in mortar. However, a marginal increase in setting time and compressive strength was found at a concentration of 2000 mg/liter. 

Impurities influencing setting time of concrete 

H. Y. Ghorab and et al (1990) have studied the effect of water (from natural sources) on the setting time of cement and reported that setting time of ordinary portland cement mainly dependent on quality of water. As compared to setting time of concrete cast of tap water, a reduction of 4% was observed when used water from the Nile river and approximately 25% reduction was found in concrete cast with groundwater; same result also found for sea water. 

V. V. Red and et al. studied on the setting time and development of strength in fly ash concrete under alkaline water in laboratory condition. It was found that initial and final setting time of concrete either accelerated or retarded depending on type of alkalinity rendered by sodium carbonate or sodium bi-carbonate. When sodium carbonate exists in mixing water, both initial and final setting times are accelerated when the concentration is 6 gm/liter and 4 gm/liter respectively. In case of sodium bi-carbonate, both initial and final settinh time are retarded when its concentration in mixing water is equal to 4 gm/liter and 6 gm/liter respectively. Compressive strength and tensile strength were found reduced with increase in sodium carbonate and sodium bi-carbonate content in mixing water in excess of 6 gm/liter and 10 gm/liter respectively. 

African Plate

The earth has two kinds of crust. The continents are mostly made of thick granite. When continents pull apart, the gap is filled by thin crust made of basalt. In plate tectonics, a continent is any piece of continental crust surrounded by oceanic crust or plate boundaries. Madagascar is a continent. When Africa and eastern Gondwanaland (India, Antarctica and Australia) began to pull apart about 120 million years ago, Madagascar originally moved as part of eastern Gondwanaland. It was originally attached to Kenya, and drifted south until it reached its present location. Then the crust broke on the east side of Madagascar, leaving it attached to the African Plate.

The westerly side is a divergent boundary with the North American Plate to the north and the South American Plate to the south forming the central and southern part of the Mid-Atlantic Ridge. The African plate is bounded on the northeast by the Arabian Plate, the southeast by the Indo-Australian Plate, the north by the Eurasian Plate and the Anatolian Plate, and on the south by the Antarctic Plate. All of these are divergent or spreading boundaries with the exception of the northern boundary with the Eurasian Plate (except for a short segment near the Azores, the Terceira Rift).

Fig-2 Map of East Africa showing some of the historically active volcanoes(red triangles) and the Afar Triangle (shaded, center) -- a triple junction where three plates are pulling away from one another: the Arabian Plate, and the two parts of the African Plate (the Nubian Plate and the Somali Plate) splitting along the East African Rift Zone (USGS).

The African Plate comprises several continental blocks or cartons, stable continental blocks of old rocks, which came together to form the African continent during the assembly of the supercontinent Gondwana around 550 million years ago. These cratons are, from south to north, the Kalahari, Congo, Sahara and West African craton. Each of these cratons can further be subdivided into even smaller blocks or terranes, sutured along pre-Gondwanan orogenic belts.

The African Plate is rifting in the eastern interior along the East African Rift. This rift zone separates the Nubian Plate to the west from the Somali Plate to the east. One hypothesis proposes the existence of a mantle plume beneath the Afar region, while an opposing hypothesis asserts that the rifting is merely a zone of maximum weakness where the African Plate is deforming as plates to its east are moving rapidly northward.

The African Plate's speed is estimated at around 2.15 centimeters per year. It has been moving over the past 100 million years or so in a general northeast direction. This is drawing it closer to the Eurasian Plate, causing subduction where oceanic crust is converging with continental crust (e.g. portions of the central and eastern Mediterranean). In the western Mediterranean, the relative motions of the Eurasian and African plates produce a combination of lateral and compressive forces, concentrated in a zone known as the Azores-Gibraltar Fault Zone. Along its northeast margin, the African Plate is bounded by the Red Sea Rift where the Arabian Plate is moving away from the African Plate.

The New England hotspot in the Atlantic Ocean has probably created a short line of mid to late-Tertiary age seamounts on the African Plate but appears to be currently inactive.

The 1960 Valdivia earthquake

The Great Chilean Earthquake is also known as 1960 Valdivia earthquake. This quake was preceded by 4 foreshocks bigger than magnitude 7.0, including a magnitude 7.9 on May 21 that caused severe damage in the Concepcion area. Many aftershocks occurred, with 5 of magnitude 7.0 or greater through Nov 1. It came after a smaller earthquake in Arauco Province at 06:02 on 21 May 1960. Telecommunications to southern Chile were cut off and President Jorge Alessandri had to cancel the traditional ceremony of the Battle of Iquique memorial holiday to oversee the emergency assistance efforts. The government was just beginning to organize help to the affected region when the second earthquake occurred at 14:55 UTC on 22 May in Valdivia.

The second earthquake affected all of Chile between Talca and Chiloé Island, more than 400,000 square kilometers (154,440.9 sq mi). Coastal villages, such as Toltén, disappeared. Later studies argued that the earthquake actually had 37 epicenters through a 1,350 km (839 mi) north-south line that lasted from 22 May to 6 June. At Corral, the main port of Valdivia, the water level rose 4 m (13 ft) before it began to recede. At 16:20 UTC, an 8 m (26 ft) wave struck the Chilean coast, mainly between Concepción and Chiloe. Ten minutes later, another wave measuring 10 m (33 ft) was reported.

The Great Chilean Earthquake or Valdivian Earthquake is the most powerful earthquake ever recorded. The quake occurred in the early afternoon (19:11 UTC) of May 22, 1960, and had a 9.5 rating[1] on the Moment magnitude scale having the epicenter near Cañete (see map) some 700 km (435 miles) south of Santiago, although Valdivia, Chile was the most affected city. The rupture zone is estimated to be about 1000 km long, from Lebu to Puerto Aisen.

On May 24, Volcan Puyehue erupted, sending ash and steam as high as 6,000 m. The eruption continued for several weeks.

Severe damage from shaking occurred in the Valdivia-Puerto Montt area. Most of the casualties and much of the damage was because of large tsunamis which caused damage along the coast of Chile from Lebu to Puerto Aisen and in many areas of the Pacific Ocean. Puerto Saavedra was completely destroyed by waves which reached heights of 11.5 m (38 ft) and carried remains of houses inland as much as 3 km (2 mi). Wave heights of 8 m (26 ft) caused much damage at Corral.

Its resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, south east Australia and the Aleutian Islands in Alaska.Tsunamis caused 61 deaths and severe damage in Hawaii, mostly at Hilo, where the runup height reached 10.6 m (35 ft). Waves as high as 5.5 m (18 ft) struck northern Honshu about 1 day after the quake, where it destroyed more than 1600 homes and left 185 people dead or missing. Another 32 people were dead or missing in the Philippines after the tsunami hit those islands. Damage also occurred on Easter Island, in the Samoa Islands and in California. One to 1.5 m (3-5 ft) of subsidence occurred along the Chilean coast from the south end of the Arauco Peninsula to Quellon on Chiloe Island. As much of 3 m (10 ft) of uplift occurred on Isla Guafo. Many landslides occurred in the Chilean Lake District from Lago Villarica to Lago Todos los Santos.

Energy released by an Earthquake

Among the earthquake generated energy, traveled through the earth producing disruption, the only quantity that can be measured is that which is radiated through the earth. The total energy from an earthquake includes energy required to create new cracks in rock, energy dissipated as heat through friction, and energy elastically radiated through the earth. Of these, the radiated energy that shakes buildings and is recorded by seismographs.

The radiated energy can be obtained in various ways. Historically, the radiated energy was estimated empirically (from observations) from magnitude Ms through the Richter formula, log Es = 4.8 + 1.5Ms, where Es is seismic energy in Joules. In this formula, magnitude is measured first, after which the formula is used to obtain Es. With modern instrumentation, energy can be measured directly from velocity seismograms and converted to a magnitude. If Es is energy in joules, the energy magnitude Me is obtained by Me = (2/3) log Es -2.9. If Me is not available, the seismic moment Mo of an earthquake can provide an empirical estimate of radiated energy. After Mo is measured, it is converted to a moment magnitude Mw by Mw = (2/3) log Mo – 6.0 where Mo is in Newton-meters (Joules). Mw is then used as the magnitude in the Richter formula to obtain an estimate of radiated energy.

It should be noticed that Me and Mw do not necessarily have the same numerical value because they measure different physical quantities. Mw is a magnitude that is derived from low-frequency displacement spectra whereas Me is measured from higher frequency velocity spectra. Mw is a measure of the area of rupture and the average slip across the fault, whereas is Me is a measure of the shaking from an earthquake.

Magnitudes and corresponding energy (Joules and tons of TNT)

Magnitude	Es (from Me)	Es (from Ms or Mw)	Tons of TNT	Nuclear Bomb Equivalence (# of bombs)
4	0.22E+11	0.63E+11	15.	0.00
5	0.71E+12	0.20E+13	475.	0.02
6	0.22E+14	0.63E+14	15023.	0.79
7	0.71E+15	0.20E+16	475063.	25.0
8	0.22E+17	0.63E+17	15022833.	790.6
9	0.71E+18	0.20E+19	475063712.	25,003.3

Once the energy is known in Joules, it can be compared to the explosive energy of TNT. One ton of TNT has an energy of 4.2*10E09 Joules. In July 16, 1945 the first atomic bomb, or A-bomb, exploded on , Alamogordo, N.Mex. It produced an explosion equal to that of 19,000 short tons (17,000 metric tons) of TNT."

Critical Construction Process Requiring Good Workmanship

In reinforced concrete frame construction, it is very important to have qualified work crews with appropriate experience and competent workmanship. It is also very important to have a feasible and well-thought construction sequence to let the crews perform their tasks in a proper and timely manner. The construction crews are the last, but vital link, in the construction process.

The design engineer and the architect play important roles in ensuring that the design is feasible and can be understood by construction crews.

The design engineer should keep the structural configuration and detailing of the structural system and its sub-elements as simple and straightforward as possible. It is good practice to use standard or typical detailing as much as possible. Of course, it is the responsibility of the whole building team --from the architect and the design engineer to the field crews-- to build a good quality building.

The key processes where workmanship is critical in construction are:
1) Steelwork: the steelwork has to result in reinforcement layouts per the specifications given in the structural drawings. Reinforcing elements should be clean and
should not have any dirt or oil on them (see Figure 1).

2) Formwork: to be able to cast reinforced concrete elements properly, good quality forms need to be built. This requires use of clean, leak-proof and tightly constructed formwork systems, characterized by adequate stiffness and strength. Where necessary, proper falsework may need to be incorporated into the formwork construction to support the forms.

3) Proper placement of steelwork into the forms: reinforcing steel assemblies need to be placed and secured within the forms in such a way that the design specifications (such as minimum concrete cover thickness) have been met. This would prevent future corrosion of the reinforcement and spalling of the concrete. The steelwork should not be displaced or distorted when fresh concrete is placed into the forms.

4) Concrete work: transportation, handling, placement and consolidation of fresh concreteshould be done properly. Accumulation or loss of water, or segregation of aggregate in the concrete mix should be avoided as much as possible. If such alterations of the concrete matrix take place, the concrete mix should be reconstituted before placing the fresh concrete into forms. Fresh concrete should be poured into the forms and properly distributed (consolidated) within and around the steel reinforcing elements. Use of vibrators or other instruments that enhance consolidation of the concrete within forms is recommended. It is extremely important to have good bond

Storage of Cement

Storage of cement is a noteworthy item, because proper arrangements for storing the cement have to be made in the factories before sale or on large construction projects before use. Proper Storage preserves its quality and fitness for use. To prevent its deterioration it is necessary to protect it from rain, sun, winds and moisture.

Moisture is the first and the greatest danger to be gaurded against. Cement has great affinity for moisture and hence it should be stored well shieled from moisture laden current of air. The exposed cement is attracted by air setting which gradually spreads. It gives to the formation of lumps. If the lumps fromed are so hard that they can not be powered by passing between the fingers, it should be concluded that the cement has been rendered useless for any sound construction.

Requirement for storehouse of cement:

It is very common in construction projects, storehouses or godowns are made at site to store cement for few days. Though these storehouses are a temporary construction, they must be constructed following requirements as below:

• The walls of storehouse must be made to prevent dampness and plastered properly, 

• A proper water proofing must be applied to roof of storehouse, 

• An elevated floor of at least 300 mm above ground level must be constructed to prevent inflow of water.For economy, flooring may be constructed using two courses of bricks (150 mm thick layer of dry bricks) over a consolidated earth layer having thickness of 150 mm above a ground surface.

• For more protection cement bags are usually staked over wooden planking connected by batten. The planks are kept 100-200 mm above floor; to save timber, often concrete are used. 

• If provision for windows is kept, least number of windows having smaller size should be selected. These should be kept closed tightly to prevent moisture movement from outside of store house.

• A new storehouse is usually not used for storing cement; the exception is when structure is dried properly.

Temporary storage of cement:

It is the special case when cement is required to stored open at site for one day or two. In such situation cement bags should be staked on dry wooden platform resting on brick masonry, dry sand or may be aggregates concrete and raise 150 mm above ground surface.

This stack of cement must be covered with polythene sheet or tarpaulin completely to give protection against ambient moisture. There should have sufficient overlap of sheet on each other. But whatever the protection may be no temporary storage for cement in open condition is allowed in wet season.

Storing information:

The following information should be noted at the time of storing cement bags:

• Cement type
• Net weight of cement (approximately)
• Date of manufacture
• Manufacturer’s name or trade mark
• Certification mark of local authority.

Removal of cement from store:

While removing cement bags from storage, bags should not be removed from only one layer at the front rather two or three layer from the back should be taken off. It will produce a stepped back rows which eliminates over-turning possibility of bags.

While removing “first in, fist out” practice is followed during consumption of bags; i.e. the oldest bags are taken out first. Bags stored having separate invoice should be stacked in storehouse separately. So that one can inspect each consignment easily and can be taken out following proper sequence.

Cement should be stored in dry, leak proof and moisture proof sheds. The shed for the storage of cement should have minimum number of windows and close fitting doors. The cement bags should be stacked on wooden planks placed about 150 to 200 mm above the floor of the shed and a space of 450 to 600 mm should be kept all round between the exterior walls and the stacks.

To prevent possibilities of lumping under pressure, the maximum height of stack should not exceed 15 bags. The width of stacks should not be more than four bags or 3 m. In stacks more than 8 bags high, the cement bags should be arranged alternatively lengthwise and cross-wise so as to ensure stability of the stacks and to prevent danger of the bags in stack topping over.

In monsoon or in situations when it is necessary to store cement for unusually long periods, the cement stacks should be completely enclosed by 700 gauge polyethene sheet or some other water-proofing membrane materials.

The stack should be arranged in such a manner that cement bags can be removed on principle of first come first served i.e. oldest cement should be taken out first.