USC University Hospital, California: The Tested U.S. Base Isolated Building

The University of Southern California Teaching Hospital in east Los Angeles (1991) had a severe test in 1994, when the Northridge earthquake hit.

Though it was only 23 miles from the epicenter, the horizontal acceleration in the building was three or four times less than the peak acceleration outside: the building was effectively isolated from the motions that caused significant damage to buildings nearby.

During the 1994 Northridge earthquake, the isolators reduced the accelerations by 66% at the base and 40% at the roof.

BUILDING PROFILE
1.	LENGTH	92.35-m (303-ft)
2.	WIDTH	77.11-m (253-ft)
3.	BAY
	EAST-WEST(EW)	10
	NORTH-SOUTH (NS)	12
4.	IRREGULARITIES
	PLAN	Asymmetric with two wings, which are connected by a necked down region of the floor/base
	VERTICAL	The building has setbacks after the fifth floor
5.	STORY	Seven stories above the ground and a basement
6.	SUPERSTRUCTURE	Steel-braced framed building
7.	SUBSTRUCTURE	Reinforced concrete base slab

 

Fig. 1(a)

Fig. 1(b)

Fig. 1 shows the plan and elevation of the building. Metal decking and a grid of steel beams support all concrete floors. The superstructure bracing is located at the building perimeter. The steel superstructure is supported on a reinforced concrete base slab, which is integral with the reinforced concrete beams below, and drop panels below each column location.


 The isolators are connected between these drop panels and the footings below [Fig. 1(b)]. The footings also support a reinforced concrete pedestal provided for backup safety. The seismic isolation system consists of 68 lead-rubber isolators and 81 elastomeric isolators, as shown in Fig. 1. The building is located near the intersection of Highways 5 and 10.

The closest active faults to the site are the Raymond Fault and the Newport-Ingelwood Fault. The building was designed using spectrum compatible earthquakes—with the spectrum defined as 1.2 times the 0.4g ATC-3-06 or UBC spectrum.

Effects Of Using Polycarbonated Plastics

In today's world ‘plastic' is the substance that is being widely used by people for their daily course. Be it from carrying things in a polythene bag or store grains in plastic containers or storing water in PET bottles etc. Also in this fast pace life the stored food with preservatives is consumed widely all over the world which is mainly preserved in metal cans.

But these cans and the PET bottles is a poison for the person who uses it.

Now the question arises how it is harmful to the humans?

Many transparent 'plastic' bottles are made from polycarbonate, usually a polymer of ‘Bisphenol A'.

In this paper, mainly the harmful effects of Bisphenol A in the human life are discussed.
 

First synthesized in 1891, the chemical has become a key building block of plastics from polycarbonate to polyester; in the U.S. alone more than 2.3 billion pounds (1.04 million metric tons) of the stuff is manufactured annually. Bisphenol A also known as BPA, is used in the preparation of the polycarbonate plastic and epoxy resins, both of which are used in a wide variety of applications that make our lives better and safer.

Polycarbonate Plastic Sheet

POLYCARBONATE: A transparent thermoplastic material

Also it is an industrial chemical that has been present in many hard plastic bottles and metal based food and beverage cans since 1960. 

The polycarbonate plastics made using BPA are used in many food and drink packaging applications while the epoxy resins are commonly used as lacquers to coat the metal cans or bottle caps or water supply pipes.    

Harmful effects:

According to the scientists of University of Cincinnati (UC), the temperature of the liquid has a great impact on how much BPA is released. It is found by Schott Belcher and his team when the polycarbonate drinking bottle is exposed to boiling hot water, the amount of BPA released 55 times more rapidly than before exposure to hot water.

In Feb 2008, Belcher stated that, "There is a very strong suspicion in the scientific community, however, that this chemical has harmful effects on humans, as little clinical evidence related to humans have been found."

In another research carried out in the same University by A research team lead by Scott Belcher, PhD, Hong Sheng Wang, PhD, and Jo El Schultz, PhD, in the department of pharmacology and cell biophysics, found that exposure to BPA and/or estrogen causes' abnormal activity in hearts of female rats and mice. BPA, an environmental pollutant with estrogen activity, is used to make hard, clear plastic and is common in many food product containers. It has been linked to neurological defects, diabetes and breast and prostate cancer.

Polycarbonate Plastic Roof Panels

Belcher and team found that the presence of BPA in the cells caused an increased the release of calcium from sarcoplasmic reticulum – the part of cardiac muscle that stores and release the calcium ions indicating spontaneous release that's likely causing irregular heart beats and may have other harmful actions, especially following heart attack.

In female cardiac muscle cells, the blocking or genetic removal of estrogen receptor beta completely blocked the contractile effects of BPA and estrogen, while in males, blockade of the effects of estrogen receptor alpha caused the male heart to become more 'female-like' and become responsive to estrogen and BPA.

These studies enable us to identify the major cardiac risks after a long term exposure to BPA for a woman's health.

The U.S. Centers for Disease Control (CDC) found that traces of BPA appeared at levels ranging from 33 to 80 nanograms (a nanogram is one billionth of a gram) per kilogram of body weight in any given day levels 1,000 times lower than the 50 micrograms (one millionth of a gram) per kilogram of bodyweight per day considered safe by the U.S. Environmental Protection Agency (EPA) and the European Union's (E.U.) European Food Safety Authority (EFSA).

BPA once ingested is broken down to glucuronide a waste product that is easily excreted. Yet CDC found glucuronide in most urine samples collected in 2004, suggesting constant exposure to it glucuronide in most urine samples, suggesting constant exposure to it.

Chemist Steven Hentges, executive director of the polycarbonate / BPA global group of the American Chemistry Council states that, ‘there is a constant low-level exposure to the chemical presumably in our diet.'

Fred vom Saal, a reproductive biologist at the University of Missouri–Columbia, warns that babies likely face the "highest exposure" in human populations, because both baby bottles and infant formula cans likely leach BPA and according to him, "In animal studies, the levels that cause harm happen at 10 times below what is common in the U.S."

Tim A. Osswald, an expert in polymer engineering at the University of Wisconsin–Madison stated that during the manufacturing process, not all BPA gets locked into chemical bonds. That residual BPA can work itself free, especially when the plastic is heated, whether it's a Nalgene bottle in the dishwasher, a food container in the microwave, or a test tube being sterilized in an autoclave.

Bisphenol A is a known endocrine-active chemical. Low-level human exposure is widespread due to the chemical's presence in polycarbonate plastic and epoxy resins, but understanding long-term consequences of exposure will be challenging. According to Frederick vom Saal, it is a fundamental part of endocrinology, and it is beautifully demonstrated, that stimulation at the cerebellar cell surface receptor is able to cause effects at doses below a part per trillion. Not only are the doses many magnitudes lower than those considered in classic high-dose toxicity studies, but at extremely low dose bisphenol A demonstrate a response that disappears as the dose increases. As the dose increases there is always an increase in response, and hence it is challenging to study the effects of bisphenol A.

Bisphenol A at Low Nanomolar Doses Confers Chemoresistance in Estrogen Receptor Alpha Positive and Negative Breast Cancer Cells

Effects at even low BPA exposure include prostate cancer, breast cancer, early puberty onset, alterations in gender-specific behavior, decreased sperm count, affects on fertility, behavioral effects including hyperactivity, increased aggressiveness, impaired learning and other changes in behavior, and other problems. And, astonishingly, BPA is found everywhere making human exposure widespread.

Precautions:

Baby bottles and sippy cups:

AVOID bottles such as Dr. Brown's, Avent, clear Evenflo, FirstYears, Platex VentAire, Sassy and TupperCare as they are all contain bisphenol A. On the sippy cup side, avoid Nuby cups with handles coming up from the bottom of the cup, Gerber Soft Starter, and Gerber Suzy's Zoo & Sippy Snacker.

BPA-free bottles and sippies flagged as safe include: glass bottles, Born-Free, Medela breast milk storage bottles (made with polypropylene) and disposable bottle systems that have polyethylene plastic inserts.

If you must use a bottle/sippy made with BPA, you should NEVER store milk in a container in it, as the chemical could leach into the milk.

You should also discard any bottles that are scratched, appear cloudy or generally have an altered appearance from their "new" look.

Exposing to heat, harsh detergents (no dishwashers) and microwaving can cause leaching

It's in the lining of canned foods, where it appears to be the most common way to be exposed. BPA can leach into the food inside the can.

It's especially important to note that infants fed canned formula are at the greatest risk.

Not all the plastic food containers are made up using BPA, but care should be taken while using them so that other chemicals do not leach into the food products.

There are 7 different types of plastics out of which type 1, 2, 4 and 5 are safe fro storing food while type 3, 6, and 7 are not, with 7 being BPA.

  

Conclusion:

It is also important to note that the studies that found the harmful effects were government funded. The industry-funded studies did not find any threat to humans, so if you embark on your own search on bisphenol A, please make sure to note if the study was industry-funded. They have a way of hiding things to protect their bottom line. Searching for and manufacturing safer alternatives can be costly.

Hence, from the above discussion it can be concluded that human exposure to bisphenol A is very less but is increasing rapidly.

Scientists are looking for microbial ways to degrade it to simpler compounds so that the harmful effects can be avoided.

Thus, always heat food in a microwave safe container, glass is best bearing the pain of washing an extra dish is better than that of chemotherapy. It's your choice of selecting the pain you want to bear.

Asbestos Cancer Mesothelioma

Asbestos cancer mesothelioma.Malignant mesothelioma will be a cancer of organ linings. Two types of mesothelioma are peritoneal mesothelioma as well as pleural mesothelioma. Peritoneal mesothelioma affects the lining of the abdominal cavity as well as pleural mesothelioma affects the lining of the chest wall and lining of the lungs. Pleural mesothelioma (or lung mesothelioma) is actually a lot more popular than peritoneal mesothelioma. Mesothelioma is an asbestos cancer.

Exposure to asbestos frequently takes location at work sites. Numerous individuals who are diagnosed with mesothelioma worked utilizing asbestos containing products such brake pads, roofing shingles as well as tiles. Workers at high risk of asbestos exposure contain mechanics, electricians, plumbers and construction workers.

Mesothelioma symptoms and symptoms of other asbestos-related cancers frequently manifest decades soon after exposure to asbestos. Asbestos exposure usually occurs by inhalation of airborne asbestos fibers. Once asbestos fibers are inhaled, they become trapped within organs such because the lungs. These fibers can lead to the development of asbestos cancer decades later. Mesothelioma symptoms which the patient exhibits can vary depending on the type of mesothelioma involved. 

 

Popular mesothelioma symptoms include shortness of breath, coughing of blood, abdominal swelling, night sweats, fever and unexplained fat loss.



Mesothelioma cancer has four stages of development. Accurate identification of the stage can be important for the purpose of treatment. In the firstly stage of mesothelioma, the cancer can be local to its point of origin in the body. In the 2nd stage, the cancer has spread to regions of the system near the point of origin. Within the third stage, mesothelioma has generally spread to more distant areas. In the fourth stage, the cancer may be discovered in the most remote areas of the system.

Presently, there is actually no cure for mesothelioma. But, there are mesothelioma treatment techniques that may be efficient if applied during the early stages of mesothelioma. These treatment techniques include radiation therapy, photodynamic therapy, immunotherapy, gene therapy as well as surgical treatment. Unfortunately, not all patients benefit from these treatment techniques. Patients whose cancer is at an sophisticated stage may not be eligible for one or much more mesothelioma treatment approaches. However, there are many clinical trials underway for experimental drugs designed to treat mesothelioma. Mesothelioma patients really should speak to their doctors about participating within these clinical trials.

Limitations of Geogrid

Geogrids are planar product manufactured from polymeric material and typically placed in soil to form an integral part of a drainage, reinforcement, or stabilization system. It contains relatively high strength polymer grids consisting of longitudinal and transverse ribs connected at their intersections.


It can be either biaxial or uniaxial, depending on the size of the apertures and shape of the interconnecting ribs. As geogrids are continuous, they tend to transfer and redistribute stresses away from areas of high stress concentrations (such as beneath a wheel load). Some of the limitations of geogrid are as follows:

1. Ultraviolet Light. 
 
Even geogrids produced of carbon black (i.e., ultraviolet stabilized geogrids) can degrade when exposed to long-term ultraviolet light. It is important to protect the geogrid from sunlight and cover the geogrid with fill as soon as possible.

2. Non-uniform Tensile Strength. Geogrids often have different tensile strengths in different directions as a result of the manufacturing process.

For example, a Tensar SS-2 (BX1200) biaxial geogrid has an ultimate tensile strength of 2100 lb / ft in the main direction and only 1170 lb / ft in the minor (perpendicular) direction. It is essential that the engineer always check the manufacturer’s specifications and determine the tensile strengths in the main and minor directions.

3. Creep. Polymer material can be susceptible to creep. Thus, it is important to use an allowable tensile strength that does allow for creep of the geosynthetic. Oftentimes, this allowable tensile design strength is much less than the ultimate strength of the geogrid. For example, for a Tensar SS-2 (BX1200) biaxial geogrid, the manufacturer’s recommended tensile strength is about 300 lb / ft, which is only one-seventh the ultimate tensile strength (2100 lb / ft). The engineer should never apply an arbitrary factor of safety to the ultimate tensile strength, but rather obtain the allowable geogrid tensile design strength from the manufacturer.

Buoyancy Factor Calculation and Its Application

Buoyancy Factor is the factor that is used to compensate loss of weight due to immersion in drilling fluid. Before explaining any further, it is very important to explain the basic concept of Buoyancy. Buoyancy is the upward force that keeps things afloat. The net upward buoyancy force equals to the amount of the weight of fluid displaced by the body volume. This force will make objects lighter when it immerses in fluid. For instant, we feel ourselves lighter when we are in a swimming pool because this is the effect of Buoyancy.

How to calculate the Buoyancy Factor.

The formulas below demonstrates how to determine this factor.

Buoyancy Factor (BF) = (65.5 - m ud weight density in pound per gallon (ppg)) ÷ 65.5

 

For example, if the drilling fluid weight is 13.0 pound per gallon (ppg), as per the equation above, the factor can be calculated by simply inputting mud weight density into the equation.

BF = (65.5 - 13.0) ÷ 65.5 

BF = 0.8015

How to use the Buoyancy Factor.

In order to figure out the actual weight of drilling string in mud, the air weight of drilling string times the buoyancy factor equal to actual drill string weight, called buoyed weight, in drilling fluid. The simple equation shows the relationship of actual weight in drilling fluid.

Actual Weight = Air Weight of Drill String x BF 

If weight in the air of a drilling string is 350 kilo pound (Klb), we can use this relationship to determine the string weight in 13.0 ppg drilling fluid. The buoyed weight of drill string in 13.0 ppg mud is equal to 350 x 0.8015 (280.5 Klb).

According to the calculation, when a drill string is immersed into drilling fluid, its weight almost decreases by 20%.Therefore, it is very important that every personnel working at drilling sites should be able to calculate the buoyancy factor in order to figure out how mud weight effects the total string weight in a wellbore.

Gel Strength of Drilling Mud

Gel strength is the shear stress of drilling mud that is measured at low shear rate after the drilling mud is static for a certain period of time. The gel strength is one of the important drilling fluid properties because it demonstrates the ability of the drilling mud to suspend drill solid and weighting material when circulation is ceased.

How can we get the get strength?

We use the 3-rpm reading which will be recorded after stirring the drilling fluid at 600 rpm from a rheometer. Normally, the first reading is noted after the mud is in a static condition for 10 second. The second reading and the third reading will be 10 minuets and 30 minutes, respectively. You may wonder why we need to record the 3-rpm reading after 30 minutes. 

The reason is that the 30 minute-reading will tell us whether the mud will greatly form the gel during an extensive static period or not. If the mud has the high gel strength, it will create high pump pressure in order to break circulation after the mud is static for long time. Furthermore, increasing in a trend of 30-minute gel strength indicates a build up of ultra fine solid. Therefore, the mud must be treated by adding chemicals or diluting with fresh base fluid.

The following causes will result in the high gel strength in the water base mud.

• Bacteria

• Drill solid

• Salt

• Chemical contamination as lime, gypsum, cement, and anhydrite

• Acid gases as Carbon Dioxide, and Hydrogen Sulphide

For an oil base drilling fluid, there are several points that will cause the high gel strength in the mud system as follows.

Drilling Operation Using Drill Mud

• Over treatment with organic gelling material

• Build up of fine solid particles in the mud

Operational impacts of the gel strength are as follows:

Cutting suspension ability – Low get strength drilling mud will not be able to efficiently suspend cuttings; therefore, the cutting will quickly drop once pumps are shut down. This can lead to several problems such as stuck pipe, hole pack off, and accumulation of cutting beds.

Barite sag – The barite sag issue mostly occurred because of low gel strength drilling fluid. Hence, the mud weight in the hole will not be constant. You will see that the lower mud weight will be seen at the shallow depth but the heavier mud weight will be noticed at the deeper section of the well. This situation could possibly lead to a well control incident because of insufficient mud weight to balance formation pressure at the shallow section of the wellbore. 

 

Break circulation pressure – If you have highly progressive gel strength fluid, there will be a lot of pressure required to break circulation. Once high pumping pressure is applied, it could lead to break formation and results in lost circulation issue.

Factor Affecting the Relation Between Tensile and Compressive Strength

A number of factors affect the relation between two strengths. These are

a) Aggregate
 

The relation between the flexure strength and compressive strength depends on the type of coarse aggregate used, except in high strength concrete, because the properties of aggregate, especially its shape and surface texture, affect the ultimate strength in compression very much less than the strength in tension or cracking load in compression. The behavior was confirmed by Knab. In experimental concrete, entirely smooth coarse aggregate led to lower compressive strength, typically by 10 percent, than when roughened. It seems that the properties of fine aggregate also influence the ft/fc´ ratio. The ratio is furthermore affected by the grading of aggregate. This is probably due to the different magnitude of the wall effect in beams and in compression specimens: there surface/volume ratios are dissimilar so that different quantities of mortar are required for full compaction.

b) Age

age is also a factor in the relation between ft and fc´: beyond about one month, the tensile strength increases more slowly than the compressive strength. So the ft/fc´decreases with time. This in aggrement with the general tendency of the ratio to decrease with an increase in fc´.

c) Curing

The tensile strength of concrete is more sensitive to inadequate curing than the compressive strength, possibly because the effect of non-uniform shrinkage of flexure test beams are very serious. Thus air-cured concrete has a lower ft/fc´ ratio than concrete cured in water and tested wet.

d) Air-Entrainment

Air-entrainment affects the ft/fc´ ratio because the pressure of air lowers the compressive strength of concrete more than the tensile strength, particularly in the case of rich and strong mixes. The influence of incomplete compaction is similar to that of entrained air.

e) Light-weight concrete

Light-weight concrete conforms broadly to the pattern of the relation between the ft and fc´ for ordinary concrete. At very low strength (300psi) the ratio ft/fc´ can be as high as 0.3, but at higher strengths it is the same as ordinary concrete. However, drying reduces the ratio by some 20% so that in the design of light-weight concrete a reduced value of ft/fc´ is used.

f) Method of Test

As stated above, the tensile strengths of concrete measured by different tests, produce results of varying value. Incidentally, the value of the compressive strength is also not unique but is affected by the shape of the test specimen. So the numerical value of the ratio of the tensile strength to the compressive strength is not the same. For these reasons, in expressing the ratio of the tensile to compressive strengths, the test method must be explicitly stated. If the value of flexural strength is of interest, a factor relating the splitting strength to flexural strength needs to be applied.

Codes Requirements in Execution of Wind-Tunnel Tests

Wind-tunnel tests are used in determining design wind loads for structures with unusual shapes, unusual response to lateral loading, or location where channeling effects or buffeting in the wake of upwind obstructions are likely to occur. Tests also are desirable where wind records are not available or when more accurate information is needed. Codes often require that the following conditions be met in execution of wind-tunnel tests:

1. Air motion should be modeled to account for variation of wind speed with elevation and the intensity of the longitudinal component of turbulence.

2. The geometric scale of the model should not be greater than 3 times that of the longitudinal component of turbulence. 

Burj Dubai: Wind Tunnel Model-Aeroelastic Model at 1:500 scale

3. Instruments used should have response characteristics consistent with the required accuracy of measurements to be recorded.

4. Account should be taken of the dependence of forces and pressures on the Reynolds number of the air motion.

5. Tests for determining the dynamic response of a structure should be conducted on a model scaled with respect to dimensions, mass distribution, stiffness, and damping of the proposed structure.

Properties of Tsunami Waves

Properties of tsunami waves 

a) Speed

i) Open ocean

The waves propagate across the deep ocean at jetliner speeds. The speed is of the order of 450~600 miles per hour in open ocean.

ii) Near coast

The wave slows down to highway speeds as it enters shallow water, and it sometimes runs ashore as a tide like flood.

b) Wave Length

Tsunami would not be felt by ships. This is due to large wave length of its propagation. This length may be hundreds of miles long.

c) Amplitude

i) Open ocean

The amplitude of waves in open ocean is only few feet. As the length of waves is large a sea surface slope of gentle value occurs.

ii) Near coast

As the waves approach the coast, their speed decrease and their amplitude increase. These unusual wave heights have been known to be over 100feet height.

Protection for Properties Against Tsunami

Protection for properties can be made by taking following steps:

a) Avoid building or living in building within several hundred feet of the coastline. These areas are more likely to suffer damage from tsunamis, strong winds, or coastal storms.

b) Make a list of items to bring inside in the event of a tsunami. This list help you remember anything missing that can be swept away by tsunami waters.

c) Most tsunami waves are less than 10 feet. So elevating house will help reduce damage to your property from most tsunamis.

d) Consult with a professional for advice to derive waves away from your property.

e) Take help from engineers to check your home and make it more resistant to tsunami water. Improperly built walls may make situation worse.

Properties of Black Cotton Soil

Rich proportion of  montmorillonite is found in Black cotton soil from mineralogical analysis. High percentage of montomonillonite renders high degree of expansiveness. These property results cracks in soil without any warning. These cracks may sometimes extent to severe limit like ½” wide and 12” deep. So building to be founded on this soil may suffer severe damage with the change of  atmospheric conditions. 

As plasticity index and linear shrinkage decreased with the increase of lime content, a mixture of both lime and cement is necessary for adequate stabilization of road bases for heavy wheel loads on the black cotton soils. Previously derived results from African and Indian black cotton soils are also matched with these results.

SI No.	Description of properties	Value
1	Shear strength	soaked CBR of only 1.5%,
2.	residual strength parameter Φr	12°
3.	permeability	10−10 cm/sec
4.	Liquid limit (Indian subcontinent)	40% ~ 100%.
5.	Free Swell index	Sometimes > 50%
An increase in lime content of 0 to 9% results in plasticity index to decreases from 47% to 5% and linear shrinkage to decreases from 11 to 3.6%  respectively.

Structure:

we have already noticed that black cotton soils of different region show considerable variation of properties. So while explaining any property, we will try to mention region where the tests were conducted.

In Hyderabad, the formation of this soil is similar to lentil seed; their subsurface structure takes shape like double-convex lens.A study on African soil (Sudan) shows such aggregated structure is a consequence of variation of pressure exerted under swelling shrinkage process due to seasonal change.

Infiltration rate:

At the beginning of wet season, black cotton soil shows high initial infiltration,but this rate decreases drastically when water content is increased. Infiltration rate decrease during first on hour from 34 mm/h to 45 mm/h. The decreasing rates are:

Elapse time	Decreasing rate(mm/hr)
After 1 hr	34 to 45
>1hr and ≤2 hr	4
>144h	0.2
Krantz et al. (1978)

 
Jewitt et al. tested some African soils and found infiltration rate ranging from 0.2 mm/h ~ 0.5 mm/day when cracks in soil are sealed and profile becomes thoroughly wet. In such extremely low infiltration rate, surface runoff is occurred.

Bulk density:

Black cotton soil shows high bulk density in dry condition and low value at swollen stage. Depending on moisture condition bulk density of these soils may be (1~2) gm/cm³ (Jewitt et al.) 

Black cotton soil of American origin have bulk density ranging from (1.81~2.08) gm/cm³. Huston clay has bulk density (1.59~2.1) gm/cm³. 

Indian black cotton soil (Hyderabad) was found to swell up to 60% when get saturated from dry state.

Again some researchers recommended to correct bulk density of black cotton soil for particular moisture content [25% w/w]. It facilitates to reduce errors observed due to initial moisture content in these soils. Following table helps us to realize this fact.

Adsorption:

We know water molecule behaves as electrical dipoles, of which positive charge is situated near atoms two hydrogen and have negative charge near oxygen atom. This enables water molecules to interact/attract neighbor charged particles. The mechanism of adjoining water molecules with clay crystals is termed as adsorption. 

Montmorillonite is the key compound of black cotton soil which can absorb large amount of water molecules. The adsorbed water takes place their position between crystal sheets of montmorillonite which yields large volume change due to absence and presence of water.

Shrinkage

Black cotton soil is usually known as expansive soil; but the mass that expand under wetting will shrink after drying. The shrinkage process often associated with cracking. When structural issue is concerned shrinkage is more destructive than swelling.

Swelling process affects to lighter building than heavier one. As vertical expansion may be mitigated by mass of structure. But shrinkage is harmful to all type of structures and careful design and sometimes limitation of loading may be needed to be imposed.

Depending on moisture-volume relation, three stages shrinkage are defined (Ritchie & Yule, 1980); these are:

a. Structural shrinkage; in this stage, water is lost due to air drying from large pores in soil i.e. no volume change is occurred.

b. Normal shrinkage, this shrinkage facilitates us to determine COLE (coefficient of linear expansion). Water is lost due to matric potentials of (-0.3~ -15) bars.

c. Residual shrinkage, matric shrinkage potential also responsible for this shrinkage but range is -15 bars to -20 bars. Water is lost from crystal of montmorillonite. No significant change in volume is occurred as air fills inter-crystalline spaces.

That is, first and last stage of moisture loss doesn’t contribute to significant volume change. Other structural volume changes in these soils are slickensides, gilgais etc. 

P^H: 

Black cotton soils have consistent chemical properties and which are not much influenced by their formation. The chemical tests on these soils of Sudan, Ethiopia, India and many other regions of Australia and Africa show that their P^H varies within ranges of 7.5 ~ 8.5 (variation may be region to region or within profiles with increase in depth). 

P^H is attributed to soil profile due to presence of CaCo3; calcium and magnesium bases dominate in these soils.

In some tropical areas exchangeable sodium, due to irrigation or under natural gravity flow (area located at valleys), may be accumulated over top surface of soil. When underlying soil is black cotton soil containing high percentage of montmorillonite PH may reach to 9.5 which may destroy soil structure.

Material Hoists for Construction Site

Hoists are designed for the vertical transportation of materials, passengers or materials and passengers. Materials hoists are designed for one specific use (i.e. the vertical transportation of materials) and under no circumstances should they be used to transport passengers. 

Most material hoists are of a mobile format which can be dismantled, folded onto the chassis and moved to another position or site under their own power or towed by a haulage vehicle. 

When in use material hoists need to be stabilized and/or tied to the structure and enclosed with a protective screen.

What is Seismic Surface Waves

Whenever the earth is suddenly struck or disturbed  due to earthquake vibration are produced. These vibrations are setup or start from a limited area and are propagated outward in all directions. Thus an earthquake may be defined as the passage of these vibrations in the earth.

Surface Waves

These waves travel along the earth's surface having similarity in behavior with sea waves.These waves also known as Long waves (L-waves).

Surface waves consist of two waves. These are

a) Love Waves

b) Rayleigh Waves

a) Love Waves

Love waves cause surface motions similar to that by S-waves, but with no vertical component. S-waves in associated with effects of Love waves cause maximum damage to structure by their racking motion on the surface in both vertical and horizontal directions.


 


b) Rayleigh Waves

Rayleigh Wave makes a material particle oscillate in an elliptic path in the vertical plane (with horizontal motion along direction of energy transmission).