Earth Quake Proof Buildings Possible?

Is it possible to construct Earthquake-proof buildings?

 Maybe it is, but the costs can be huge. So, only Nuclear Power Plants can afford to be Earthquake Proof. For the rest of us, its earthquake resistant buildings, so that we can minimize the loss of life and property,

Earthquakes do not kill people, but actually people are killed by the collapse of badly designed and constructed buildings. But, with the different types of new materials available in our inventory, it is feasible to construct an earthquake-resistant building.

Earthquakes can be disastrous...

Some care should be taken while constructing a building in earthquake prone areas. Special attention should be given to Structural Design of the structure. Here are some tips for designing safer structures.

1. Building should be of regular shapes. Cylindrical structures perform better in high-wind areas.

2.Architect should try to design the building as aerodynamic as possible. This reduces the effect of Wind load on tall structures.

3.There should no odd shapes in elevation and the whole building should be in balance. The center of gravity of building should not move.

4. Cantilever projections should be minimum and their length should not be more than 3 to 4 feet.

5.The span between the columns should be as small as possible.

6. Point loads on load-carrying beams should be avoided.

7. The dead loads on the cottage-building should not be increased unnecessarily. For Example, Terrace garden or terrace swimming pools should be avoided, if possible.

8. The sunk portions of WC and bath should be minimum.

9. Building should be a Reinforced Concrete framed structure. It provides better stability and reliability in Earthquake-prone areas.

10. Cottage-building's foundation should be placed on hard and level ground.

11. There should not be very large overhead water tanks than are required. If it has to have larger capacity, then it should be divided into two three smaller tanks and should be kept at different locations to maintain balance of cottage-building.

12. If the column length is more than 12 feet, then bracing beams should be provided in between the column at regular intervals. Bracing beams strengthen a column, and allow construction of multistoried buildings.

13. The columns should be connected at each level.

14. For strengthening the brickwork, a sill or a lintel should be provided at every 3 feet level, and R.C.C. wall should be taken where it is possible.

15.Cottage- building should not contain very large and heavy windows. They are bound to weaken the structure.

16. The cottage- building's electrification should contain a main switch and circuit breakers so as to avoid fire hazards because of short circuit in the earthquake.

17. The glass used any structure should be fiber-reinforced glass or wire glass.

18.Use of new and better materials like Fiber-reinforced Concrete and fiber-glass should be recommended. These new materials decrease dead load and increase the structure's strength.

What do you mean by Reinforced cement concrete (RCC)

 

Reinforced concrete is concrete in which reinforcement bars ("rebars"), reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. The term Ferro Concrete refers only to concrete that is reinforced with iron or steel. Other materials to reinforce concrete can be organic and inorganic fibres as well as composites in different forms. Concrete is strong in compression, but weak in tension, thus adding reinforcement increases the strength in tension. In addition the failure strain of concrete in tension is such low that the reinforcement has to hold the cracked sections together. For a strong, ductile and durable construction the reinforcement shall have the following properties:

 

* High strength

* High tensile strain

* Good bond to the concrete

* Thermal compatibility

* Durability in the concrete environment

 

Use in construction

 

Concrete is reinforced to give it extra tensile strength; without reinforcement, many concrete buildings would not have been possible.

 

Reinforced concrete can encompass many types of structures and components, including slabs, walls, beams, columns, foundations, frames and more.

 

Reinforced concrete can be classified as precast or cast in-situ concrete.

 

Much of the focus on reinforcing concrete is placed on floor systems. Designing and implementing the most efficient floor system is key to creating optimal building structures. Small changes in the design of a floor system can have significant impact on material costs, construction schedule, ultimate strength, operating costs, occupancy levels and end use of a building.

 

Materials

 

Concrete is a mixture of cement (usually Portland cement) and stone aggregate. When mixed with a small amount of water, the cement hydrates form microscopic opaque crystal lattices encapsulating and locking the aggregate into a rigid structure. Typical concrete mixes have high resistance to compressive stresses (about 4,000 psi (28 MPa)); however, any appreciable tension (e.g. due to bending) will break the microscopic rigid lattice resulting in cracking and separation of the concrete. For this reason, typical non-reinforced concrete must be well supported to prevent the development of tension.

 

If a material with high strength in tension, such as steel, is placed in concrete, then the composite material, reinforced concrete, resists compression but also bending, and other direct tensile actions. A reinforced concrete section where the concrete resists the compression and steel resists the tension can be made into almost any shape and size for the construction industry.

Key characteristics

 

Three physical characteristics give reinforced concrete its special properties. First, the coefficient of thermal expansion of concrete is similar to that of steel, eliminating internal stresses due to differences in thermal expansion or contraction. Second, when the cement paste within the concrete hardens this conforms to the surface details of the steel, permitting any stress to be transmitted efficiently between the different materials. Usually steel bars are roughened or corrugated to further improve the bond or cohesion between the concrete and steel. Third, the alkaline chemical environment provided by calcium carbonate (lime) causes a passivating film to form on the surface of the steel, making it much more resistant to corrosion than it would be in neutral or acidic conditions.

 

The relative cross-sectional area of steel required for typical reinforced concrete is usually quite small and varies from 1% for most beams and slabs to 6% for some columns. Reinforcing bars are normally round in cross-section and vary in diameter. Reinforced concrete structures sometimes have provisions such as ventilated hollow cores to control their moisture & humidity.

Anti-corrosion measures

 

In wet and cold climates, reinforced concrete for roads, bridges, parking structures and other structures that may be exposed to dicing salt may benefit from use of epoxy-coated, hot dip galvanised or stainless steel rebar, although good design and a well-chosen cement mix may provide sufficient protection for many applications. Epoxy coated rebar can easily be identified by the light green colour of its epoxy coating. Hot dip galvanized rebar may be bright or dull grey depending on length of exposure, and stainless rebar exhibits a typical white metallic sheen that is readily distinguishable from carbon steel reinforcing bar. Reference ASTM standard specifications A767 Standard Specification for Hot Dip Galvanised Reinforcing Bars, A775 Standard Specification for Epoxy Coated Steel Reinforcing Bars and A955 Standard Specification for Deformed and Plain Stainless Bars for Concrete Reinforcement

 

Another, cheaper way or protecting rebars is coating them with zinc phosphate.[1] Zinc phosphate slowly reacts with the corroding agent (e.g., alkali) forming a stable hydroxyapatite layer.

 

Penetrating sealants typically must be applied sometime after curing. Sealants include paint, plastic foams, films and aluminium foil, felts or fabric mats sealed with tar, and layers of bentonite clay, sometimes used to seal roadbeds.

Reinforcement and terminology

 

A beam bends under bending moment resulting in a small curvature. At the outer face (tensile face) of the curvature the concrete experiences tensile stress while at the inner face (compressive face) it experiences compressive stress.

 

A "singly-reinforced" concrete means that the concrete element is only reinforced near the tensile face and the reinforcement, called tension steel, is designed to resist the tension.

 

A "doubly-reinforced" concrete means that beside the tensile reinforcement the concrete element is also reinforced near the compressive face for assisting the concrete to resist compression. The latter reinforcement is called compression steel.

 

An "under-reinforced" concrete means that the tension capacity of the tensile reinforcement is smaller than the combined compression capacity of the concrete and the compression steel (under-reinforced at tensile face). When the reinforced concrete element is subject to increasing bending moment, the tension steel yields while the concrete does not reach its ultimate failure condition. As the tension steel yields and stretches, an "under-reinforced" concrete also yields in a ductile manner, exhibiting a large deformation and warning before its ultimate failure.

 

An "over-reinforced" concrete means that the tension capacity of the tension steel is greater than the combined compression capacity of the concrete and the compression steel (over-reinforced at tensile face). An "over-reinforced" element will fail suddenly, when the concrete fails brittle and crashes before yielding of the tension steel. It is however possible to push the design of an "over-reinforced" concrete element to "under-reinforced" concrete element by adding sufficient compression steel. There is however a limit in the quantity of both tension and compression steel for practicality of placement of reinforcement.

 

Steel reinforced concrete elements should normally be designed to be under-reinforced so users of the structure will receive warning of impending collapse.

 

Characteristic strength of a material where less than 5% of the specimen show lower strength.

 

Design strength of a material including a material safety factor.

 

Ultimate limit state theoretical failure point with a certain probability. State under factored loads and factored resistances.

 

Nominal strength actual strength from the material properties is called the nominal strength . Its relation with design strength can be represented as:

 

Nominal x Ø = Design strength

Common failure modes of steel reinforced concrete

 

Reinforced concrete can fail due to inadequate strength, leading to mechanical failure, or due to a reduction in its durability. Corrosion and freeze/thaw cycles may damage poorly designed or constructed reinforced concrete. When rebar corrodes, the oxidation products (rust) expand and tends to flake, cracking the concrete and unbonding the rebar from the concrete. Typical mechanisms leading to durability problems are discussed below.

Mechanical failure

 

Reinforced concrete can be considered to have failed when significant cracks occur. Cracking of the concrete section can not be prevented; however, the size of and location of the cracks can be limited and controlled by reinforcement, placement of control joints, the curing methodology and the mix design of the concrete. Cracking defects can allow moisture to penetrate and corrode the reinforcement. This is a serviceability failure in limit state design. Cracking is normally the result of an inadequate quantity of rebar, or rebar spaced at too great a distance. The concrete then cracks either under excess loading, or due to internal effects such as early thermal shrinkage when it cures.

 

Ultimate failure leading to collapse can be caused by crushing of the concrete matrix, when stresses exceed its strength; by yielding of the rebar; or by bond failure between the concrete and the rebar.

Carbonation

Rebar for foundations and walls of sewage pump station.

 

Carbonation, or neutralisation, is a chemical reaction between carbon dioxide in the air with calcium hydroxide and hydrated calcium silicate in the concrete. The water in the pores of Portland cement concrete is normally alkaline with a pH in the range of 12.5 to 13.5. This highly alkaline environment is one in which the embedded steel is passivated and is protected from corrosion. According to the Pourbaix diagram for iron, the metal is passive when the pH is above 9.5.[3] The carbon dioxide in the air reacts with the alkali in the cement and makes the pore water more acidic, thus lowering the pH. Carbon dioxide will start to carbonate the cement in the concrete from the moment the object is made. This carbonation process will start at the surface, then slowly move deeper and deeper into the concrete. The rate of carbonation is dependent on the relative humidity of the concrete - a 50% relative humidity being optimal. If the object is cracked, the carbon dioxide in the air will be better able to penetrate into the concrete. When designing a concrete structure, it is normal to state the concrete cover for the rebar (the depth within the object that the rebar will be). The minimum concrete cover is normally regulated by design or building codes. If the reinforcement is too close to the surface, early failure due to corrosion may occur. The concrete cover depth can be measured with a cover meter. However, carbonated concrete only becomes a durability problem when there is also sufficient moisture and oxygen to cause electro-potential corrosion of the reinforcing steel.

 

One method of testing a structure for carbonation is to drill a fresh hole in the surface and then treat the cut surface with phenolphthalein indicator solution. This solution will turn [pink] when in contact with alkaline concrete, making it possible to see the depth of carbonation. An existing hole is no good because the exposed surface will already be carbonated.

Chlorides

The Paulins Kill Viaduct, Hainesburg, New Jersey, is 115 feet (35 m) tall and 1,100 feet (335 m) long, and was heralded as the largest reinforced concrete structure in the world when it was completed in 1910 as part of the Lackawanna Cut-Off rail line project. The Lackawanna Railroad was a pioneer in the use of reinforced concrete.

 

Chlorides, including sodium chloride, can promote the corrosion of embedded steel rebar if present in sufficient concentration. For this reason, only use fresh raw water or potable water for mixing concrete. Insure that the coarse and fine aggregates do not contain chlorides. Do not use admixtures that contain chlorides.

 

It was once common for calcium chloride to be used as an admixture to promote rapid set-up of the concrete. It was also mistakenly believed that it would prevent freezing. However, this practice has fallen into disfavor once the deleterious effects of chlorides became known. It should be avoided when ever possible.

 

The use of de-icing salts on roadways, used to reduce the freezing point of water, is probably one of the primary causes of premature failure of reinforced or prestressed concrete bridge decks, roadways, and parking garages. The use of epoxy-coated reinforcing bars and the application of cathodic protecton has mitigated this problem to some extent. Properly designed concrete mixtures that have been allowed to cure properly are effectively impervious to the effects of de-icers. (One common problem today is that concrete is allowed to "dry" (dries out) in two to three days by contractors before it cures and thus ultimately develops less than 10% of its design strength).

 

Another important source of chloride ions is from sea water. Sea water contains by weight approximately 3.5% salts. These salts include sodium chloride, magnesium sulphate, calcium sulphate and bicarbonates. In water these salts dissociate and migrate with the water into the capillaries of the concrete. Chloride ions are particularly aggressive and make up about 50% of these ions.

[edit] Alkali silica reaction

Main article: Alkali Silica Reaction

 

This a reaction of the amorphous silica sometimes present in the aggregates with alkalies, for example from the cement pore solution. The silica (SiO2) reacts with the alkali to form a silicate in the Alkali silica reaction (ASR), this causes localised swelling which causes cracking. The conditions for alkali silica reaction are: (1) aggregate containing an alkali reactive constituent, (2) sufficiently availability of alkali ions, and (3) sufficient moisture, above 75%RH within the concrete.[4][5] This phenomenon has been popularly referred to as "concrete cancer". This reaction occurs independently of the presence of rebars: massive concrete structures such as dams can be affected.

Conversion of high alumina cement

 

Resistant to weak acids and especially sulfates, this cement cures quickly and reaches very high durability and strength. It was greatly used after World War II for making precast concrete objects. However, it can lose strength with heat or time (conversion), especially when not properly cured. With the collapse of three roofs made of prestressed concrete beams using high alumina cement, this cement was banned in the UK in 1976. Subsequent inquiries into the matter showed that the beams were improperly manufactured, but the ban remained.

Sulfates

 

Sulfates (SO4) in the soil or in groundwater, in sufficient concentration, can react with the Portland cement in concrete causing the formation of expansive products, e.g. ettringite or thaumasite, which can lead to early failure of the structure. The most typical attack of this type is on concrete slabs and foundation walls at grade where the sulfate ion, via alternate wetting and drying, can increase in concentration. As the concentration increases, the attack on the Portland cement can begin. For buried structures such as pipe, this type of attack is much rarer especially in the Eastern half of the United States. The sulfate ion concentration increases much slower in the soil mass and is especially dependent upon the initial amount of sulfates in the native soil. The chemical analysis of soil borings should be done during the design phase of any project involving concrete in contact with the native soil to check for the presence of sulfates. If the concentrations are found to be aggressive, various protective coatings can be used. Also, in the US ASTM C150 Type 5 Portland cement can be used in the mix. This type of cement is designed to be particularly resistant to a sulfate attack.

What is Prestressed concrete(PCC) in construction?

Prestressed concrete is a method for overcoming the concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the concrete compression member would otherwise experience due to a bending load. Traditional reinforced concrete is based on the use of steel reinforcement bars, rebars, inside poured concrete.

Prestressing can be accomplished in three ways: pre-tensioned concrete, and bonded or unbonded post-tensioned concrete.


Pre-tensioned concrete is cast around already tensioned tendons. This method produces a good bond between the tendon and concrete, which both protects the tendon from corrosion and allows for direct transfer of tension. The cured concrete adheres and bonds to the bars and when the tension is released it is transferred to the concrete as compression by static friction. However, it requires stout anchoring points between which the tendon is to be stretched and the tendons are usually in a straight line. Thus, most pretensioned concrete elements are prefabricated in a factory and must be transported to the construction site, which limits their size. Pre-tensioned elements may be balcony elements, lintels, floor slabs, beams or foundation piles. An innovative bridge construction method using pre-stressing is described in Stressed ribbon bridge.

Bonded post-tensioned concrete

Bonded post-tensioned concrete is the descriptive term for a method of applying compression after pouring concrete and the curing process (in situ). The concrete is cast around a plastic, steel or aluminium curved duct, to follow the area where otherwise tension would occur in the concrete element. A set of tendons are fished through the duct and the concrete is poured. Once the concrete has hardened, the tendons are tensioned by hydraulic jacks that react against the concrete member itself. When the tendons have stretched sufficiently, according to the design specifications (see Hooke's law), they are wedged in position and maintain tension after the jacks are removed, transferring pressure to the concrete. The duct is then grouted to protect the tendons from corrosion. This method is commonly used to create monolithic slabs for house construction in locations where expansive soils (such as adobe clay) create problems for the typical perimeter foundation. All stresses from seasonal expansion and contraction of the underlying soil are taken into the entire tensioned slab, which supports the building without significant flexure. Post-tensioning is also used in the construction of various bridges, both after concrete is cured after support by falsework and by the assembly of prefabricated sections, as in the segmental bridge.The advantages of this system over unbonded post-tensioning are:

1. Large reduction in traditional reinforcement requirements as tendons cannot destress in accidents.
2. Tendons can be easily 'weaved' allowing a more efficient design approach.
3. Higher ultimate strength due to bond generated between the strand and concrete.
4. No long term issues with maintaining the integrity of the anchor/dead end.


Unbonded post-tensioned concrete

Unbonded post-tensioned concrete differs from bonded post-tensioning by providing each individual cable permanent freedom of movement relative to the concrete. To achieve this, each individual tendon is coated with a grease (generally lithium based) and covered by a plastic sheathing formed in an extrusion process. The transfer of tension to the concrete is achieved by the steel cable acting against steel anchors embedded in the perimeter of the slab. The main disadvantage over bonded post-tensioning is the fact that a cable can destress itself and burst out of the slab if damaged (such as during repair on the slab). The advantages of this system over bonded post-tensioning are:

1. The ability to individually adjust cables based on poor field conditions (For example: shifting a group of 4 cables around an opening by placing 2 to either side).
2. The procedure of post-stress grouting is eliminated.
3. The ability to de-stress the tendons before attempting repair work.

Picture number one (below) shows rolls of post-tensioning (PT) cables with the holding end anchors displayed. The holding end anchors are fastened to rebar placed above and below the cable and buried in the concrete locking that end. Pictures numbered two, three and four shows a series of black pulling end anchors from the rear along the floor edge form. Rebar is placed above and below the cable both in front and behind the face of the pulling end anchor. The above and below placement of the rebar can be seen in picture number three and the placement of the rebar in front and behind can be seen in picture number four. The blue cable seen in picture number four is electrical conduit. Picture number five shows the plastic sheathing stripped from the ends of the post-tensioning cables before placement through the pulling end anchors. Picture number six shows the post-tensioning cables in place for concrete pouring. The plastic sheathing has been removed from the end of the cable and the cable has been pushed through the black pulling end anchor attached to the inside of the concrete floor side form. The greased cable can be seen protruding from the concrete floor side form. Pictures seven and eight show the post-tensioning cables protruding from the poured concrete floor. After the concrete floor has been poured and has set for about a week, the cable ends will be pulled with a hydraulic jack, shown in picture number nine, until it is stretched to achieve the specified tension.

What is Structural engineering?

Structural engineering is a field of engineering dealing with the analysis and design of structures that support or resist loads. Structural engineering is usually considered a specialty within civil engineering, but it can also be studied in its own right.  Structural engineers are most commonly involved in the design of buildings and large nonbuilding structures but they can also be involved in the design of machinery, medical equipment, vehicles or any item where structural integrity affects the item's function or safety. Structural engineers must ensure their designs satisfy given design criteria, predicated on safety (e.g. structures must not collapse without due warning) or serviceability and performance (e.g. building sway must not cause discomfort to the occupants).

Structural engineering theory is based upon physical laws and empirical knowledge of the structural performance of different landscapes and materials. Structural engineering design utilizes a relatively small number of basic structural elements to build up structural systems that can be very complex. Structural engineers are responsible for making creative and efficient use of funds, structural elements and materials to achieve these goals. 

Structural engineering has existed since humans first started to construct their own structures. It became a more defined and formalized profession with the emergence of the architecture profession as distinct from the engineering profession during the industrial revolution in the late 19th Century. Until then, the architect and the structural engineer were often one and the same - the master builder. Only with the understanding of structural theories that emerged during the 19th and 20th century did the professional structural engineer come into existence.

The role of a structural engineer today involves a significant understanding of both static and dynamic loading, and the structures that are available to resist them. The complexity of modern structures often requires a great deal of creativity from the engineer in order to ensure the structures support and resist the loads they are subjected to. A structural engineer will typically have a four or five year undergraduate degree, followed by a minimum of three years of professional practice before being considered fully qualified.

Structural engineers are licensed or accredited by different learned societies and regulatory bodies around the world (for example, the Institution of Structural Engineers in the UK)[3]. Depending on the degree course they have studied and/or the jurisdiction they are seeking licensure in, they may be accredited (or licensed) as just structural engineers, or as civil engineers, or as both civil and structural engineers.

Structural engineering dates back to at least 2700 BC when the step pyramid for Pharaoh Djoser was built by Imhotep, the first engineer in history known by name. Pyramids were the most common major structures built by ancient civilizations because the structural form of a pyramid is inherently stable and can be almost infinitely scaled (as opposed to most other structural forms, which cannot be linearly increased in size in proportion to increased loads).

Throughout ancient and medieval history most architectural design and construction was carried out by artisans, such as stone masons and carpenters, rising to the role of master builder. No theory of structures existed, and understanding of how structures stood up was extremely limited, and based almost entirely on empirical evidence of 'what had worked before'. Knowledge was retained by guilds and seldom supplanted by advances. Structures were repetitive, and increases in scale were incremental.

No record exists of the first calculations of the strength of structural members or the behavior of structural material, but the profession of structural engineer only really took shape with the industrial revolution and the re-invention of concrete (see History of concrete). The physical sciences underlying structural engineering began to be understood in the Renaissance and have been developing ever since.
Structural failure
Main articles: Structural failure and List of structural failures and collapses

The history of structural engineering contains many collapses and failures. Sometimes this is due to obvious negligence, as in the case of the Pétionville school collapse, in which Rev. Fortin Augustin said that "he constructed the building all by himself, saying he didn't need an engineer as he had good knowledge of construction" following a partial collapse of the three-story schoolhouse that sent neighbors fleeing.[5] The final collapse killed at least 94 people, mostly children.

In other cases structural failures require careful study, and the results of these inquiries have resulted in improved practices and greater understanding of the science of structural engineering. Some such studies are the result of Forensic engineering investigations where the original engineer seems to have done everything in accordance with the state of the profession and acceptable practice yet a failure still eventuated. A famous case of structural knowledge and practice being advanced in this manner can be found in a series of failures involving Box girders which collapsed in Australia during the 1970s.

Structural building engineering includes all structural engineering related to the design of buildings. It is the branch of structural engineering that is close to architecture.

Structural building engineering is primarily driven by the creative manipulation of materials and forms and the underlying mathematical and scientific ideas to achieve an end which fulfills its functional requirements and is structurally safe when subjected to all the loads it could reasonably be expected to experience. This is subtly different from architectural design, which is driven by the creative manipulation of materials and forms, mass, space, volume, texture and light to achieve an end which is aesthetic, functional and often artistic.

The architect is usually the lead designer on buildings, with a structural engineer employed as a sub-consultant. The degree to which each discipline actually leads the design depends heavily on the type of structure. Many structures are structurally simple and led by architecture, such as multi-storey office buildings and housing, while other structures, such as tensile structures, shells and grid shells are heavily dependent on their form for their strength, and the engineer may have a more significant influence on the form, and hence much of the aesthetic, than the architect.

The structural design for a building must ensure that the building is able to stand up safely, able to function without excessive deflections or movements which may cause fatigue of structural elements, cracking or failure of fixtures, fittings or partitions, or discomfort for occupants. It must account for movements and forces due to temperature, creep, cracking and imposed loads. It must also ensure that the design is practically buildable within acceptable manufacturing tolerances of the materials. It must allow the architecture to work, and the building services to fit within the building and function (air conditioning, ventilation, smoke extract, electrics, lighting etc). The structural design of a modern building can be extremely complex, and often requires a large team to complete.

Structural engineering specialties for buildings include:

* Earthquake engineering
* Façade engineering
* Fire engineering
* Roof engineering
* Tower engineering
* Wind engineering

What is a Highway Culvert?

A highway culvert is a drainage facility that allows water to flow under the road without causing any traffic disruption. Corrugated and spiral steel pipe are popular for culverts because they can be installed quickly, have long life, are low in cost, and require little maintenance. With corrugated steel pipe, the seam strength must be adequate to withstand the ring-compression thrust from the total load supported by the pipe. This thrust C, lb/ft (N/m), of structure is

C=(LL+DL)S/2

where
LL= live-load pressure, lb/ft2 (N/m2)
DL= dead-load pressure, lb/ft2 (N/m2)
S= span (or diameter), ft (m)

The pipe should have sufficient handling and installation strength so as to withstand stresses due to shipping and placing of the pipe in the desired position. The handling strength is measured by a flexibility factor which is:

FF=D2/EI

where
D =pipe diameter or maximum span, in (mm)

E= modulus of elasticity of the pipe material, lb/in2
(MPa)

I =moment of inertia per unit length of cross section of the pipe wall, in4/in (mm4/mm)

Civil Engineering Disasters – Collapse Of Bridges

This is not the first destruction of the bridge. The first time tragedy occurred in 1907.
About first collapse of the bridge
The bridge was nearing completion, when the local engineering began noticing increasing distortions of key structural members already in place. After four years of construction, the south arm and part of the central section of the bridge collapsed into the St. Lawrence River in just 15 seconds. Of the 86 workers on the bridge that day near quitting time, 75 were killed and the rest were injured.
About second collapse of the bridge After a Royal Commission of Inquiry into the collapse, construction started on a second bridge, but September 11, 1916, when the central span was being raised into position, it fell into the river, killing 13 workers.

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December 15, 1967. Silver Bridge (USA)
On December 15, 1967, the Silver Bridge collapsed while it was choked with rush hour traffic, resulting in the deaths of 46 people. Investigation of the wreckage pointed to the cause of the collapse being the failure of a single eye-bar in a suspension chain, due to a small defect only 0.1 inches (2.54 mm) deep. It was also noted that the bridge was carrying much heavier loads than it was originally designed for and was poorly maintained.The new bridge that replaced the Silver Bridge was named the Silver Memorial Bridge.

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March 17, 1945. Ludendorff Bridge (Remagen, Germany)
28 U.S. army engineers were killed while working to strengthen the bridge, and 93 others were wounded.

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May 9, 1980. Sunshine Skyway Bridge (Florida, USA)
The Sunshine Skyway Bridge was collapsed on May 9, 1980, when the freighter SS Summit Venture collided with a pier (support column) during a storm , sending over 1200 feet of the bridge plummeting into Tampa Bay. The collision caused six automobiles and a bus to fall 150 feet, killing 35 people.

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June 28, 1983. Mianus River Bridge (Connecticut, USA)
Three people were killed when their vehicles fell with the bridge into the Mianus River 70 feet below, and three were seriously injured. Collapse due to failure of the Pin and Hanger assembly supporting the span.

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October 21, 1994. Seongsu Bridge (Seoul, South Korea)
On October 21, 1994, Seongsu Bridge connecting Seongsu-dong and Apgujeong-dong of Gangnam-gu, Seoul, collapsed. The slab (48 m) between the fifth and the sixth leg of the Bridge collapsed so 32 people died and 17 people were injured. One of its concrete slabs fell due to a failure of the suspension structure. This structural failure was caused by joints of trusses (steel structures) supporting the bridge slab were not welded to the full; the welding thickness, which should be over 10mm, was only 8mm; and further, connecting pins for steel bolts were poor.

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January 4, 1999. Rainbow bridge (China)
In January 4, 1999, a pedestrian Rainbow bridge across the Qi River in the Sichuan province collapsed three years after it was built. The collapse of the Rainbow bridge led to 40 deaths and 14 injuries. Parts of the bridge were rusty, concrete used in its construction was too weak and there were serious welding problems.

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March 4 , 2001. Hintze Ribeiro Bridge (Castelo de Paiva, Portugal)
On March 4, 2001, the Hintze Ribeiro Bridge, made of steel and concrete, collapsed in Entre-os-Rios, Castelo de Paiva, Portugal, killing to 70 people, including those in a bus and three cars that were attempting to get to the other side of the river.

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August 28, 2003. Bridge Daman (Daman, India)
At least 25 people, including 23 children, die when a bridge in the western coastal area of Daman collapsed into a muddy river, throwing a school bus, 10 vehicles and pedestrians into the swirling waters due to heavy rains.

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November 7, 2005. (Almunecar, Spain)
Five Portuguese and one Spanish national died near Almunecar on Spain’s, after a 20-ton section of motorway viaduct fell from 80 meters onto workers below.

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December 2, 2006. (Bihar, India)
Thirty-three people are killed when a 150-year-old bridge, being dismantled, crashed on the train near the Bhagalpur railway station in the state of Bihar.

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August 1, 2007. Minneapolis I-35W bridge (Minneapolis, USA)
On August 1, 2007, during the evening rush hour, the main spans of the bridge collapsed, falling into the river and onto its banks. Thirteen people died and approximately one hundred more were injured. The 1,907-foot bridge fell into the Mississippi River. Currently under investigation.

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August 13, 2007. Tuo River bridge (Hunan, China)
The 140-foot-high bridge spanning the Tuo River in the central Hunan city of Fenghuang collapsed as workers removed scaffolding from its facade. Investigation underway.

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In case we missed some please feel free to write about it in the comment box and we will update it as soon as possible

What is Biocement?

It’s safe to say that without microbes, biotechnology would be an extremely limited science. Microbes are microscopic organisms such as fungi (which include yeasts), bacteria and viruses. They not only provide the foundation for much of the basic research involved in biotechnology, they help to create durable building materials and structures.

The early scientific study of microbes concentrated on their effects, such as causing disease. Eventually, scientists discovered microbes could be used for the study of processes which are common to all living organisms. An innovative alternative approach lies in the combined use of microorganisms, nutrients and biological processes naturally present in the subsurface soils to effectively improve their engineering properties. Considerable research on carbonate precipitation by bacteria has been performed using ureolytic bacteria. These bacteria are able to influence the precipitation of calcium carbonate by the production of an enzyme, urease (urea amidohydrolase, EC 3.5.1.5). Calcium carbonate precipitation occurs as a consequence of bacterial metabolic activity that raises the pH of the proximal environment.

Recently I discovered and improved few bacterial species which were able to precipitate calcite at higher rate and eventually this process lead to improved compressive strength, reduced permeability and low corrosion rate of reinforcement.

Biocement, a self-healing material to enhance durability of building structures and conservation of cultural heritages

Although hundreds of thousands of successful concrete and buildings are annually constructed worldwide, there are large numbers of concrete structures (including historical monuments) that deteriorate or become unsafe due to changes in loading, changes in use or changes in configuration. The constant developments in the field of civil engineering and the growth of industrial activity have created a growing demand for materials for the construction industry that do more and more to comply with structural requirements and meet stricter demands for working conditions and environment. Traditionally, mechanical strength has been the main criterion used when choosing building materials such as cement, concrete or bricks. Compressive strength, permeability and corrosion analysis are the most common used measures in designing of buildings structures. Considerable effort has been devoted to develop high-strength materials. However, with increasing volumes of constricted facilities that need to be maintained the focus is shifting towards durability.

Besides building materials preservation of the cultural heritage, socioeconomic growth and sustainable development is finding considerable resonance amongst specialists in the field. It calls for an innovative strategy for the maintenance of our cultural heritage. This strategy implies that the protection of historical buildings represents an important prerequisite for peace and stability and provides social and economic opportunities at the same time. The preservation of culture contributes to the identity of the citizens, creates jobs, supports the economy and promotes the responsible handling of societal resources. Although there is a great deal of knowledge and information on world heritage monuments, this is lacking in respect of standard monuments both at national level and international level. There is a need for research at this level into the number and quality of monuments and historical sites. Large sums of money are being spent worldwide on measures for the preservation of monuments and historical buildings. The economic and ecological commitment to the preservation of monuments and historical buildings requires, however, a prudent handling of the appropriate funds. This demands an optimization of damage analysis procedures and damage process controls as well as the development of monitoring and early warning systems for damage prevention. Therefore, the goal needs to be the implementation of permanent preservation measures, which requires long-term maintenance.

All building materials are porous. This porosity of building material along with ingress of moisture and other harmful chemicals such as acids, chlorides and sulfates affect the material and seriously reduce their strength and life. An additive that seals the pores and cracks and thus reduces the permeability of the structure would immensely improve its life. Conventionally, a variety of sealing agents such as latex emulsions and epoxies etc.; and surface treatments with water repellents such as silanes or siloxanes are used to enhance the durability of the concrete structures. However, they suffer from serious limitations of incompatible interfaces, susceptibility to ultraviolet radiations, unstable molecular structure and high cost. They also emanate toxic gases.
In order to overcome the shortcomings of conventional sealing agents, materials with self-healing capability can be used effectively. Use of urease producing microbes addresses these problems effectively, as these continue to survive and grow within the concrete structure after the initial use. Urease helps in mineralization of calcium carbonate, by hydrolyzing urea present in the environment. It releases carbon dioxide from urea that combines with calcium ions resulting in deposition of calcium carbonate in the form of calcite. Due to urease activity, bacteria are able to use urea as a sole nitrogen source and produce ammonia, which increases the pH in the proximal environment, causing Ca2+ and CO32- to precipitate as CaCO3. These unique properties make it particularly suitable for many applications in civil engineering (concrete structures, plasters, mortars, prefabricated elements, refractory elements, bricks, natural stones, etc.)

A microbial additive that helps in calcite precipitation with urease would enhance durability of building materials as well preserve the cultural heritage.

I am pleased to present herewith my preliminary findings of the effects of microbial additives (where I used Sporosarcina pasteurii, previously known as Bacillus pasteurii, a facultative anaerobic Gram-positive soil bacterium) to enhance the durability of building materials. The significant amount of data, some of which are attached hereto, accumulated to date leads us to the preliminary findings:

1. Microbial additive resulted in improvement in compressive strength of mortar by up to 38%.

2.Microbial additive can remediate cracks in building materials and monumental stones and regain strength within 28 days.

3. To make the process economic, microbial additive can be prepared by growing cells using industrial by products such as lactose mother liquor, corn steep liquor as nutrient sources.

4.Microbial additive can enhance the durability of bricks by reducing their permeability and increasing compressive strength.

5.The reduced permeability rates resulting from the microbial additive will increase the concrete structures’ useful life.

The data accumulated to date are, in my opinion, sufficient in quantity and trend to allow me to draw some preliminary conclusions with a reasonable confidence that in future it will further support the preliminary findings. As previously stated though the study period has not yet run the full course, the data and trends indicate the microbial additive is having the beneficial effect of enhancing the durability of building materials and preservation of cultural heritage.

Concrete Mix Design Calculations

Concrete Mix Design Calculations

The concrete mix design available on this site are for reference purpose only. Actual site conditions vary and thus this should be adjusted as per the location and other factors. These are just to show you how to calculate and we are thankful to all the members who have emailed us these mix designs so that these could be shared with civil engineers worldwide.

If you also have any mix design and want to share it with us, just comment on this post and we will be in touch with you.

Here is the summary of links of all the mix designs we have till date:-

Mix Design For M20 Grade Of Concrete

Mix Design For M35 Grade Of Concrete

Mix Design For M40 Grade Of Concrete

Mix Design For M50 Grade Of Concrete

Mix Design For M60 Grade Of Concrete

In case you want the complete theory of Mix Design, Go here What is Concrete Mix Design

We will add more soon. You can help us do this fast, just email us any mix design you have.

The mix design M-50 grade (Using Admixture –Sikament) provided here is for reference purpose only. Actual site conditions vary and thus this should be adjusted as per the location and other factors.

Parameters for mix design M50

Grade Designation = M-50
Type of cement = O.P.C-43 grade
Brand of cement = Vikram ( Grasim )
Admixture = Sika [Sikament 170 ( H ) ]
Fine Aggregate = Zone-II

Sp. Gravity
Cement = 3.15
Fine Aggregate = 2.61
Coarse Aggregate (20mm) = 2.65
Coarse Aggregate (10mm) = 2.66

Minimum Cement (As per contract) =400 kg / m3
Maximum water cement ratio (As per contract) = 0.45

Mix Calculation: -

1. Target Mean Strength = 50 + ( 5 X 1.65 ) = 58.25 Mpa

2. Selection of water cement ratio:-
Assume water cement ratio = 0.35

3. Calculation of water: -
Approximate water content for 20mm max. Size of aggregate = 180 kg /m3 (As per Table No. 5 , IS : 10262 ). As plasticizer is proposed we can reduce water content by 20%.

Now water content = 180 X 0.8 = 144 kg /m3

4. Calculation of cement content:-
Water cement ratio = 0.35
Water content per cum of concrete = 144 kg
Cement content = 144/0.35 = 411.4 kg / m3
Say cement content = 412 kg / m3 (As per contract Minimum cement content 400 kg / m3 )
Hence O.K.

5. Calculation for C.A. & F.A.: [ Formula's can be seen in earlier posts]-

Volume of concrete = 1 m3
Volume of cement = 412 / ( 3.15 X 1000 ) = 0.1308 m3
Volume of water = 144 / ( 1 X 1000 ) = 0.1440 m3
Volume of Admixture = 4.994 / (1.145 X 1000 ) = 0.0043 m3
Total weight of other materials except coarse aggregate = 0.1308 + 0.1440 +0.0043 = 0.2791 m3

Volume of coarse and fine aggregate = 1 – 0.2791 = 0.7209 m3
Volume of F.A. = 0.7209 X 0.33 = 0.2379 m3 (Assuming 33% by volume of total aggregate )

Volume of C.A. = 0.7209 – 0.2379 = 0.4830 m3

Therefore weight of F.A. = 0.2379 X 2.61 X 1000 = 620.919 kg/ m3

Say weight of F.A. = 621 kg/ m3

Therefore weight of C.A. = 0.4830 X 2.655 X 1000 = 1282.365 kg/ m3

Say weight of C.A. = 1284 kg/ m3

Considering 20 mm: 10mm = 0.55: 0.45
20mm = 706 kg .
10mm = 578 kg .
Hence Mix details per m3
Increasing cement, water, admixture by 2.5% for this trial

Cement = 412 X 1.025 = 422 kg
Water = 144 X 1.025 = 147.6 kg
Fine aggregate = 621 kg
Coarse aggregate 20 mm = 706 kg
Coarse aggregate 10 mm = 578 kg
Admixture = 1.2 % by weight of cement = 5.064 kg.

Water: cement: F.A.: C.A. = 0.35: 1: 1.472: 3.043

Observation: -
A. Mix was cohesive and homogeneous.
B. Slump = 120 mm
C. No. of cube casted = 9 Nos.
7 days average compressive strength = 52.07 MPa.
28 days average compressive strength = 62.52 MPa which is greater than 58.25MPa
Hence the mix accepted.



Mix Design M-40 Grade

The mix design M-40 grade for Pier (Using Admixture – Fosroc) provided here is for reference purpose only. Actual site conditions vary and thus this should be adjusted as per the location and other factors.

Parameters for mix design M40

Grade Designation = M-40
Type of cement = O.P.C-43 grade
Brand of cement = Vikram ( Grasim )
Admixture = Fosroc ( Conplast SP 430 G8M )
Fine Aggregate = Zone-II
Sp. Gravity Cement = 3.15
Fine Aggregate = 2.61
Coarse Aggregate (20mm) = 2.65
Coarse Aggregate (10mm) = 2.66
Minimum Cement (As per contract) = 400 kg / m3
Maximum water cement ratio (As per contract) = 0.45

Mix Calculation: -

1. Target Mean Strength = 40 + (5 X 1.65) = 48.25 Mpa

2. Selection of water cement ratio:-
Assume water cement ratio = 0.4

3. Calculation of cement content: -
Assume cement content 400 kg / m3
(As per contract Minimum cement content 400 kg / m3)

4. Calculation of water: -
400 X 0.4 = 160 kg Which is less than 186 kg (As per Table No. 4, IS: 10262)
Hence o.k.

5. Calculation for C.A. & F.A.: – As per IS : 10262 , Cl. No. 3.5.1

V = [ W + (C/Sc) + (1/p) . (fa/Sfa) ] x (1/1000)

V = [ W + (C/Sc) + {1/(1-p)} . (ca/Sca) ] x (1/1000)

Where

V = absolute volume of fresh concrete, which is equal to gross volume (m3) minus the volume of entrapped air ,

W = mass of water ( kg ) per m3 of concrete ,

C = mass of cement ( kg ) per m3 of concrete ,

Sc = specific gravity of cement,

(p) = Ratio of fine aggregate to total aggregate by absolute volume ,

(fa) , (ca) = total mass of fine aggregate and coarse aggregate (kg) per m3 of
Concrete respectively, and

Sfa , Sca = specific gravities of saturated surface dry fine aggregate and Coarse aggregate respectively.

As per Table No. 3 , IS-10262, for 20mm maximum size entrapped air is 2% .

Assume F.A. by % of volume of total aggregate = 36.5 %

0.98 = [ 160 + ( 400 / 3.15 ) + ( 1 / 0.365 ) ( Fa / 2.61 )] ( 1 /1000 )

=> Fa = 660.2 kg

Say Fa = 660 kg.

0.98 = [ 160 + ( 400 / 3.15 ) + ( 1 / 0.635 ) ( Ca / 2.655 )] ( 1 /1000 )

=> Ca = 1168.37 kg.

Say Ca = 1168 kg.

Considering 20 mm : 10mm = 0.6 : 0.4

20mm = 701 kg .
10mm = 467 kg .

Hence Mix details per m3

Cement = 400 kg
Water = 160 kg
Fine aggregate = 660 kg
Coarse aggregate 20 mm = 701 kg
Coarse aggregate 10 mm = 467 kg
Admixture = 0.6 % by weight of cement = 2.4 kg.
Recron 3S = 900 gm

Water: cement: F.A.: C.A. = 0.4: 1: 1.65: 2.92

Observation: -
A. Mix was cohesive and homogeneous.
B. Slump = 110mm
C. No. of cube casted = 12 Nos.
7 days average compressive strength = 51.26 MPa.
28 days average compressive strength = 62.96 MPa which is greater than 48.25MPa

Hence the mix is accepted.

We are thankful to Er Gurjeet Singh for this valuable information.

Concrete Mix Design – M 20 Grade Of Concrete

1. REQUIREMENTS
a) Specified minimum strength = 20 N/Sq mm

b) Durability requirements
i) Exposure Moderate
ii) Minimum Cement Content = 300 Kgs/cum

c) Cement
(Refer Table No. 5 of IS:456-2000)
i) Make Chetak (Birla)
ii) Type OPC
iii) Grade 43

d) Workability
i) compacting factor = 0.7

e) Degree of quality control Good
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Concrete Mix Design M-60

CONCRETE MIX DESIGN (GRADE M60)


(a) DESIGN STIPULATION:-
Target strength = 60Mpa
Max size of aggregate used = 12.5 mm
Specific gravity of cement = 3.15
Specific gravity of fine aggregate (F.A) = 2.6
Specific gravity of Coarse aggregate (C.A) = 2.64
Dry Rodded Bulk Density of fine aggregate = 1726 Kg/m3
Dry Rodded Bulk Density of coarse aggregate = 1638 Kg/m3
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