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CONCRETING OPERATIONS

Operations followed in the making of concrete in compliance with the safety and quality requirements are known as concreting operations. Concreting operations include:

PURPOSE

Concreting operations are vulnerable to safety and health hazards. This method statement describes the safety requirements and safe work procedure for concreting operations to:

  1. Prevent improper carrying out of concreting works;
  2. Carry works in a manner that’s safe at all times;
  3. Know the hazards involved in performing the activity;
  4. Ensure controls are in place to steer clear of hazard exposure.

Use any other resources and methods not referred to in this method statement to suit the project requirement. Execute the work safely complying with the required standard.

The sequence of activities is a repetitive process and many hazards are common to distinct sites. Include with detail, any crucial information specific to the project. Follow the approved checklists prior to the start of the activity.

PROCEDURES IN CONCRETING OPERATIONS

STORAGE OF CONCRETE MATERIALS

STORAGE OF CEMENT:

  • Store cement in a weatherproof shed to keep it dry,
  • Make proper arrangements to prevent rain penetration,
  • Store cement on a platform raised above ground level.

STORAGE OF AGGREGATES

  • Keep aggregates in a clean condition. Take necessary measures to prevent contamination with undesirable substances,
  • Make floor of the storage bins with plain cement concrete,
  • Separate storage bins with partitions to prevent mixing of different aggregate sizes.

BATCHING AND MIXING OF MATERIALS

  • Inspect and check the batching equipment including equipment calibration before the operation begins.
  • Weigh the cementitious materials and aggregates independently in separate compartments.
  • Ensure that the weigh hopper charging and discharging gates close tightly when producing concrete.
  • Make sure that the equipment allows to control the material flow rate and stop the flow within the specified weighing tolerance.
  • Make sure that the measuring accuracy of batch materials weighing scales, and the water measuring equipment meets accuracy requirements before the work begins.  

CONCRETE MIX TRANSPORTATION

The operation of moving concrete mix from the concrete batching plant to the concrete pour location is known as concrete mix transportation.

Ensure that the water-cement ratio and slump are maintained as per concrete design mix before placing of concrete. During transportation, the concrete mix shall maintain its cohesiveness and workability.  

PLACING OF CONCRETE

  • Check the formwork and reinforcement before placing the concrete to ensure that they are clean and free of any debris.
  • Deposit the concrete as close as possible to its final position. Make sure that reinforcement dislodging or overfilling of formwork doesn’t occur during concrete discharge.  
  • When filling columns and walls, take care that the concrete does not strike the formwork face, which might impact the surface finish.
  • For deep sections place the concrete in layers that are uniform, generally not exceeding 500 mm thick, each layer being fully compacted.

COMPACTION OF CONCRETE

After the concrete is placed, it contains entrapped air voids. Compaction is the process to expel entrapped air from concrete. Consequently, compaction increases the density of concrete.

Three types of vibrators are available to achieve the desired compaction:

  1. Immersion vibrators or needle vibrators: appropriate for all sorts of sections. As per IS: 3558 [Code of practice for use of immersion vibrators for consolidating concrete],  “the vibrating needle should preferably be inserted vertically. The insertion at an angle, in thick layers, may leave concrete unconsolidated without any indication at the surface.” 
  2. Surface vibrators:  They are appropriate for compacting slabs, industrial floors, road pavements, and similar flat surfaces. Furthermore, they also aid in surface leveling and finishing.
  3. Table vibrators: Vibrating tables are used for the consolidation of concrete in moulds for the manufacture of plain and reinforced concrete or prestressed concrete elements. IS 7246 [Recommendations for use of table vibrators for consolidating concrete.]
  4. Form vibrators: For complex members or members with higher reinforcement congestion, form vibrators are appropriate. They are fixed to the exterior of the formwork. Therefore,  these are also called external vibrators. The formwork needs to be designed to resist the forces imposed on it by form vibrators.

CONCRETE SURFACE FINISHING

Finishing is the operation of attaining a concrete surface of desired texture and pattern. Functional and decorative requirements determine the finish of a concrete surface.

As per IS 2571 [Code of practice for laying of in-situ cement concrete flooring]:

The floor finishes shall be laid depending upon the expected load and wear on the floor and the fact whether the topping is to be laid monolithic with the base or separately on a set and hardened base. In either case, special precautions are necessary to ensure a good bond between the topping and the base.”

Finishing makes concrete more functional and aesthetic. Concrete that will be visible, such as driveways, highways, or patios, often needs finishing. Concrete’s end use usually determines the final surface texture and patterns.

Finishing of concrete surface requires one, or many of the following operations:

  1. Level the surface
  2. Edge the concrete
  3. Joint the concrete
  4. Float the concrete
  5. Trowel the concrete
  6. Texture the concrete surface
  7. Cure the concrete

Never add cement or sprinkle water on concrete while finishing it.


    👉What is batching of concrete? 

Batching of concrete means measuring different ingredients of concrete (i.e. cement, sand, coarse aggregate and water) before mixing it. When this measurement is done on the basis of volume, we call it Volume Batching.

    👉What is a small batching plant?

Small batching plant is suitable for places that require extreme mobility. There are two models available which are powered by electric motors and there is one model powered by diesel engine. There are total of three bins for addition of sand, cement and aggregates. All the bins are with individual load cells for accurate weighing.

Methods of Batching Concrete

1. Volume Batching

  • In volume batching, materials are measured on the basis of volume. It is less precise method of batching
  • Measurement boxes or gauge boxes of known volume are used to measure materials.
  • Cement is taken in the form of bags, where volume of one bag of cement (50 kg) is taken as 35 liters.
  • Volume of Gauge box used is made equal to the volume of one bag of cement which is 35 liters or multiple thereof.
  • Gauge boxes are generally deeper and contains narrow top surface and they are made of timber or steel or iron.
  • Volumes of different sized fine aggregate and coarse aggregate are measured individually by these gauge boxes.
  • Water is measured using water meter or water cans of known volume are used.
  • To make 1:1:2 ratio concrete mix according to volume batching, one should take one bag of cement (35 liters) , 1 gauge box of fine aggregate (35 liters) and 2 gauge boxes of fine aggregate (70 liters). If the water-cement ratio is 0.5, then half of the volume of cement which is 25 liters of water should be taken.

 

2. Weight Batching

  • In this method, Materials are measured on the basis of weight. It is accurate method of batching.
  • Weigh batchers or other types of weighing equipment are used to measure weight of materials.
  • Cement, fine aggregate, coarse aggregate and water are taken by weighing.
  • Weigh batchers used are available in two types namely mechanical weigh batcher and electronic weigh batchers.
  • In mechanical weigh batchers, weights are measured using spring and dial gauge arrangement and it is widely used equipment in weigh batching.
  • In electronic weigh batchers, electronic scales and load cells supported by hoppers are used to measure the weight of ingredients of concrete.
  • Weigh batchers available are may be Manual or semi-automatic or fully automatic . Manual type is used for small concrete production job while other two types are used for large concrete production.
  • In case of semi-automatic weigh batching, aggregate container gates are lifted manually and it is automatically closed after reaching required quantity in the weighing machine.
  • In fully automatic weigh batcher, all the process will be done automatically. The benefit of this type equipment is, it also measures the moisture content present in the aggregate and corrects the required quantity of water-cement with respect to moisture content of aggregates.
  • To prepare 1:1:2 concrete mix using weigh batching, measured quantity of materials are 50 kg of cement, 50 kg of fine aggregate and 100 kg of coarse aggregate.

What is the maximum height limit for concrete construction for 1 day?                                

    Sometimes specifiers and inspectors dictate the maximum free-fall distance of concrete because they believe limiting free fall is necessary to minimize concrete segregation. 

    Usually they limit the free-fall distance to 3 to 5 ft (0.9 to 1.5 m), but occasionally the limit is as little as 2 ft (0.6 m). Neither ACI 301- 99, “Specifications for Structural Concrete,” nor ACI 318-02, “Building Code Requirements for Structural Concrete,” limit the maximum distance concrete can free fall. ACI 304R-00, “Guide for Measuring, Mixing, Transporting, and Placing Concrete,” states that “if forms are sufficiently open and clear so that the concrete is not disturbed in a vertical fall into place, direct discharge without the use of hoppers, trunks, or chutes is favorable.” ACI 301, 304, and 318, however, all require placing the concrete at or near its final position to avoid segregation due to flowing. 

At least four field studies have shown that free fall from great distances doesn’t reduce concrete quality.

                                                                    Download IS-CODE 




👉 Why is only concrete used for construction but not only cement?

Understanding the fundamental differences of cement and concrete is important. Cement is an ingredient in concrete, and concrete is the finished product used in building foundations, driveways, roads, homes, and the infrastructure around you.[0]

Among all the construction materials used in the world, concrete is most widely used due to its unique advantages compared to other materials.

  • Concrete Hardens at Ambient Temperature. Concrete sets, hardens, gain its strength at regular room temperature or ambient temperature.
  • Ability to be Cast into Shape. Fresh concrete is flowable and is in liquid state.
  • Energy Efficiency in Production. The amount of energy required for production of concrete is low compared with steel.
  • Excellent Water Resistance Characteristics. Though chemical in water can induce corrosion in concrete and reinforced concrete.
  • High-temperature resistance. Concrete can withstand high temperatures better than wood and steel.
  • Ability to Consume and Recycle Waste. Many industrial wastes can be recycled as a substitute for cement or aggregate.
  • Application in Reinforced Concrete. Concrete has comparable coefficient of thermal expansion to steel.
  • Low or Zero Maintenance Required. Concrete structures do not require coating or painting for regular applications as protection for weathering compared to steel or wooden structures where it is inevitable.
  • Multi-Mode Application. One of the major advantage of concrete is its ability to be used in different application methodologies.
  • Concrete is Economical. Compared to engineered cementitious materials used for construction, the production cost of cement concrete is very low.[1]
        Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. 
                                        In the past limebased cement binders were often used, such as lime putty, but sometimes with other hydraulic cements, such as a calcium aluminate cement or with Portland cement to form Portland cement concrete (named for its visual resemblance to Portland stone).[2]


        



Table of Contents

 1. Watch out for inexperienced workers
 2. Provide clear instructions to workers
 3. Keep a close tab on faulty machinery and tools
 4. Climb on and off equipment safely
 5. Use a high quality adjustable ladder
 6. Maintain a safe distance from operating machinery
 7. Have a first aid kit
 8. Be weary of fall hazards
 9. Always plug tools out of the outlet
 10. Reduce or ban the use intoxicating substances
 11. Final Thoughts: Safety Tips for Construction Sites
 


1. Watch out for inexperienced workers

Allowing a guy who only has a few months of construction work under his belt to operate an excavator in a tight space is not the smartest idea. In fact, allowing him to operate an excavator or any other dangerous equipment with people in close proximity is foolish.

Let the less experienced workers build up their skills by operating excavators, cranes and other dangerous machinery by doing work away from others first.

For example, digging a hole while there’s no one around and filling it up again is the best way to learn how to operate an excavator. Use the same educational tactic for other machines until the person develops decent skills and spacial awareness.

2. Provide clear instructions to workers

Construction work can become dangerous if the site operative doesn’t provide clear instructions to his workers. Imagine a scenario where a bunch of workers are fixing a roof while others aren’t aware of this. Another worker could be moving around carelessly and have a bucket or an AC conditioner drop on his head.

Such a stupidly occurring event can be devastating, and it’s usually the easily avoidable lack of awareness that leads to such accidents. Each person on the site should know what their objectives are, what others are doing and what he/she should be doing. Otherwise chaos ensues and people walk around mindlessly with things falling on their heads.

As a construction site operative or a regular worker, it’s important that everyone knows the main objective of the job at hand and that the work involved is delegated at the beginning of the day with everyone present at the meeting to hear about it.

If someone isn’t present, they should be made fully aware of the situation when they arrive, along with letting others (at least in passing) of what that person will be doing.

Naturally, this isn’t always a realistic proposal on a large construction site. In that case, be aware of how many safety zones there are on the site. This will mean that the work of one group is separate from the work of another group.

If they don’t intermingle, it makes it easier to explain the safety precautions to one group of workers that is important to them and making sure that they don’t go to the safety zones of the site that have a different objective.

3. Keep a close tab on faulty machinery and tools

A story from my father will serve as an example of why this is important:

They had an excavator on the site and the arm got completely out of whack. If someone touched the controls in the excavator, it would fall in full speed, and it couldn’t be controlled.

They had this old guy who operated excavators all his life. Despite of being told of the malfunction he got in and started picking on the controls for whatever reason.

The arm moved in full speed and the bucket fell only a few inches by the truck while my father and 2 other workers were in the cabin. If they were only a few inches closer it would’ve killed them.

Now, this old dude was obviously determined not to listen to reason. But if there is any malfunctioning machinery, it’s important to make everyone aware of its faults in order to minimize the risks as much as possible.

It could be a faulty ladder, a drill or whatever. I’m not going to say you should replace the tool or not use it entirely. Because in some situations it might only be a minor issue that can be fixed eventually, but in the meanwhile the tool is usable as long as the person is aware of the fault.

But regardless of the state of the tool, make sure that everyone operating it or working near it is aware of the malfunction first and knows how to avoid it.

4. Climb on and off equipment safely

Climbing on and off different objects is where most construction site accidents happen. One of the main reasons is slipping due to muddy boots, so make sure to clean any mud or slippery material from the bottoms before climbing.

Some workers will also tend to jump from a machine instead of climbing down in a safe way, especially younger workers. This is also a very common reason for injury.

Wearing gloves is also recommended because it can help in ensuring a decent grip, although the necessity of gloves will depend on the situation. Having a three-point stance, in other words not having to stretch too much to reach a handle is also important.

Lastly, no one climbing up or down in a difficult situation should be carrying anything. Perhaps in a backpack, but not if heavy equipment is involved.

5. Use a high quality adjustable ladder

The length of the ladder is very important in preventing accidents. If a worker has to stretch beyond a certain point to reach an object or climb off the ladder they can tip over or fall.

A ladder that’s too tall can also be dangerous because it’s not placed properly on an object or it simply takes away too much space.

A ladder should also have a fully functioning locking mechanism, so that it stays firmly in place and doesn’t extend or retract by accident.

I’ve been using this telescoping ladder from Amazon at home and it’s pretty great because it easily extends or retracts but the locking mechanism is also well designed.

6. Maintain a safe distance from operating machinery

Seinfeld has a great line about men just loving to watch other men work. This is especially true at construction sites, where workers typically gather around and watch as someone is getting the job done.

Unfortunately, the machinery can go berserk or the working handling it can lose concentration for a moment. To avoid accidents you can still be an observer, but maintain a safe distance.

7. Have a first aid kit

Minor or serious accidents can happen at any time, and it can be very helpful to have the right medication at hand to help straight away instead of having to wait for a doctor for basic help. Having bandages, a disinfectant for cuts and wounds, painkillers… these should be part of your first aid kit.

I suggesting getting a waterproof first aid bag (link to Amazon) and filling it up with basic medication and other necessary stuff for helping an injured person.

You probably already have one of these in your vehicle. But it’s best to use a different one instead of sharing it for both situations and then not having the necessary medicine in case of a car accident.

8. Be weary of fall hazards

If there are workers on the upper floors, make sure to place warning signs so that people can safely avoid any falling objects. Warning signs should also be placed on these upper areas if there’s an increased risk of falling down.

Other than warning signs, other safety measures should be taken,  such as guardrails, safety nets, safety cords, and personal fall arrest systems, depending on the nature of the job.

As far as personal fall arrest systems, I do know a bit about them. I’ve had experience using the Guardian Fall Protection gear for doing home improvement projects. It’s got a 50-foot vertical lifeline assembly and HUV, and I’ve found it to be quite comfortable.

9. Always plug tools out of the outlet

Never plug tools by the cord, by simply yanking it. It can be tempting after a long day to do this instead of walking to the power outlet. While I agree that it may be convenient in the moment, it can also damage the tool over time.

The cord can also be pulled over liquids which combined with electricity at a later time can cause a major accident. Yanking the cord is simply not worth the risk.

10. Reduce or ban the use intoxicating substances

No worker should be on a construction site drunk or under the influence of drugs. And yet this is almost a common occurrence due to the difficult nature of the job.

Construction workers get tired and simply need to relax more than an office worker. Over time the stressful nature of the job can lead to the abuse of various substances, usually alcohol.

But with so many dangers of injury or even death present on a construction site, this is a huge risk for the person and everyone around. A beer or two has rarely hurt anyone, but it’s best to avoid working with drunkards on any project, especially ones that involve climbing or operating heavy machinery.

Some workers have a reputation for being drunkards but they have so much experience in construction that people let it slide. But these are the types that are really an accident waiting to happen because their experience gives them a false sense of safety, which allows them to pay even less attention to the job at hand. Stick to sober colleagues even if they have less experience and you’ll generally be much safer.

Final Thoughts: Safety Tips for Construction Sites

Construction is a difficult job by it’s very nature. Even with all safety precautions there’s no 100% guarantee that you’ll manage to avoid all accidents.

But you can drastically minimize them or their impact in case they happen. In other words, it’s impossible to prevent a worker from falling off of a building entirely. For example, with a safety net and personal fall arrest system in place a serious tragedy can be avoided.

It’s important to use common sense and not fool around. Workers with experience are the ones that usually take things for granted because they feel like their superior skill levels can save them from any harm. The less experienced workers are usually more cautious, but they lack in skill levels necessary to operate heavier machinery and deal with more complex situations.

 →Definitions of Earthquake: - 

Earthquake is defined as the shaking of earth’s surface due to any reason which, result in 

release of large amount of energy.

For example-: The energy released in during 2001 Bhuj Earthquake (Gujrat, india) was 

about 200 times that of energy released by Atom bomb dropped on Hiroshima 

(Japan) In the year of 1945.

 Or

* The ground vibrations, both feeble and strong, produced on the surface of earth due to any 

reason what so ever are described as earthquake.

* Define Earthquake Engineering/Seismology-:

The branch of science which deals with the study of earthquakes.

It includes causes and types of earthquake, Study of origin, Propagation, Recording and 

analyzing seismic waves that occur inside the earth along with the source that produce them 

is known as Earthquake Engineering or Seismology.

* Important Terminology related with Earthquake Engineering 

Seismology-:

1. Hypocenter or focus or seismic center-: The exact point or place inside the surface of 

earth at which an earthquake originates is termed as focus or seismic centre. It is also 

known as Hypocenter. Most of the damaging earthquakes have shallow focus with 

focal depth less than 70 K.M its position is determine with the help of seismograph 

records.

2. Epicenter-: The point on the earth's surface vertically above the focus of an earthquake

known as Epicenter or Epicentral line.

3. Focal depth-: The depth of focus from the Epicenter is called as focal depth. Or the

vertical distance between Epicenter and Hypocenter/focus.

4. Epicenter distance or depth-: The horizontal distance from epicenter to any place or 

discussion is known as epicentral distance. As the Epicentral Distance is increased, the 

effect of earthquake becomes less.

5. Anti center-: The point on the surface of earth diametrically opposite to the epicenter is 

called as anti center.

6. Seismic waves: - The wave transmitted in all the directions due to large strain energy 

released from the focus during an earthquake are known as seismic waves. These are two 

types Body waves and Surface waves.

7. Seismograph-: An instrument which is used to record ground vibration or surface 

displacements known as seismograph.

Seismographs are used only to record weak motion. For recording higher intensities, special 

strong motion instrument called accelerographs are used.

8. Isoseismal-: An imaginary line on the surface of the earth along which the intensity of 

measured seismic shock is equal at every point is termed as Isoseismal. It is just like a 

contour line which joins points of same elevation.

9. Isoseismal Map-: A map showing different Isoseismal for a particular earthquake is 

termed as isoseismal map. Such a maps is quiet helpful to scientists and engineers in the 

development of seismic zones.

10. Seismic Zone & Seismic Belt-: The region of earth’s crust where earthquake occur 

frequently and repeatedly are known as seismic zone & seismic Belt. Depending upon the 

intensity of seismic activity, these zone are further divided into Highly Seismic, Moderately 

Seismic, and Poorly Seismic zone.

11. Fault-: A fracture or a crack along which blocks of earth’s mass move relatively on either 

side parallel to the fracture is termed as a fault. This sliding of earth’s mass takes place in 

pieces called “tectonic Plates”

12. Tsunamis-: Tsunami is a series of large sea waves caused by earthquake or seismic 

activity near the coastal regions or at the ocean floor.

Necessity of Earthquake engineering:-

1. To carry out advance research and development for effective earthquake management.

2. for earthquake preparedness that is to learn how to prepare facing earthquake.

3. for seismic evaluation and retro fitting.

 Causes of Earthquakes: -The important causes of the earthquake are-: 

A. Natural Causes of Earthquake.

B. Artificial Causes of Earthquake.

C. Superficial Causes

A. Natural Causes of Earthquake:-

1. Tectonic Movement: This particularly happens when the continental plate collides 

against the oceanic plate. The oceanic plate is overridden by the continental plate. By a 

process called subduction jerky movements are caused along the inclined surface. Tectonic 

earthquakes have occurred in Assam in 1950.

2 Volcanic Activity: Earthquakes may also be caused by the movement of lava beneath the 

surface of the earth during volcanic activity. The earthquakes due to Krakatoa volcanic 

eruption in 1883 is a good example of volcanic eruption.

3. Dislocation of the Earth’s crust: Earthquakes may be caused by the dislocation of the 

crust beneath the surface of the Earth.

4. Adjustment in inner Rock Beds: Earthquakes are also caused where is an adjustment 

between Sima [i.e., beneath the ocean is formed by Silica and Magnesium = Si + ma =

Sima] and Sial (i.e., Continent is formed by Silica and Aluminum = Si + al = Sial) in the 

interior of the Earth’s Crust. This Earthquake may be called as a Plutonic Earthquake.

5. Pressure of gases in the interior: The expansion and contraction of gases in the interior 

of the Earth sometimes cause a sudden shake on the Earth’s surface.

B. Artificial Causes of Earthquake:-

Man-made Earthquakes:-

1. The impounding of large quantities of water behind dams disturbs the crustal balance. 

This causes earthquakes such as the Koyna earthquake in Maharashtra.

2. The shock waves through rocks set up by the underground testing of Atom bombs or 

Hydrogen bombs may be severe to cause earthquake.

C. Superficial Causes:-

1. Landslides and avalanches,

2. Denudation of the Landmasses and depositions of materials,

3. Faulting and folding in the rock beds are responsible for causing minor earthquakes.

4. Mining blasts in mining areas.


* Effects of Earthquake-

A. Destructive Effects:-

1. Earthquake causes dismantling of buildings, bridge and other structures at or near 

epicenter. Many men and animals are killed or buried under collapsed houses.

2. Rails are folded, underground wires broken. Fire breaks out inevitably in large towns.

3. Earthquakes originate sea waves called Tsunamis.

4. Earthquakes result in the formation of cracks and fissures on the ground formation.

5. The earthquakes cause landslides and disturb the isostatic equilibrium.

6. Landslide due to earthquake may block valleys to form lakes.

7. Earthquake causes damage to the building, bridges and dams.

8. Earthquake in many cases can cause great loss of life.

9. Earthquake can also cause floods and landslides. Landslides, triggered by earthquake, 

often cause more destruction than the earthquake themselves.

10.If the earthquake happens to be beneath the ocean floor, they can lead to a tsunami.

B. Constructive Effects:-

1. Sometimes the earthquakes cause formation of hot springs which are very useful to 

people.

2. The earthquakes sometimes cause submergence in coastal land, and result in formation 

of inlets, bays and gulfs which help to develop of fishing and shipping etc.

3. Sometimes, the earthquakes cause emergence of costs and bring fertile shore out of 

water to give chance to develop crop production.

 Seismic waves: - 

The wave transmitted in all the direction due to large strain energy released from the focus 

during an earthquake is known as seismic waves. These are two types Body waves and 

Surface waves.

* There are two type of seismic wave:

1. Body Waves: - 1.1 Primary waves or p waves, 1.2 Secondary waves or s waves 

2. Surface Waves: - 2.1 Rayleigh waves (LR-waves), 2.2 Love wave (LL- wave).

1. Body waves: - The wave which travels through the earth layer in all directions and are 

not restricted to any depth is known as body wave.

Body wave are of two types: - 1.1 Primary waves or p waves

 1.2 Secondary waves or s waves

1.1 Primary waves or p waves: The waves in which material particles vibrate in the 

direction of propagation of the wave with a push and pull effect are known as primary wave.

These are also called as longitudinal wave or compressional waves. 

Due to effect of "P" wave the particle undergo extensional strain (Pull effect) and 

compression strain (push effect)

 Characteristics of primary waves/ p-waves: - P wave have the following important 

characteristics.

1. These wave are fastest to travel (hence are first to be recorded). At the recording station.

2. In granite rock P waves have the velocity of 5 km/sec.

3. These wave are capable of passing through the solid as well as liquid.

4. These waves are responsible for preliminary shocks upon the earth surface.

5. These are longitudinal and compressional in nature like sound waves.

6. These waves cause volumetric change in the material through which they pass.

Secondary waves/S-waves:- The wave in which material partial vibrate at right 

angle to the direction of propagation i.e. secondary wave. These are also called as 

shear waves shake waves.

 Characteristic of Secondary waves/ S-waves:-

1. These wave slower to p wave slower at the recording station in same material.

2. In granite rock velocity of S wave is approximate 3 km/sec.

3. These waves are capable of passing through the solid but are unable to propagate 

through fluid as they do not have any shear strength.

4. These wave are transverse in nature like light waves.

5. These wave unlike P wave don't change the volume of the material through which they 

pass.

6. Vertically polarized S waves are known as SV waves on other hand

Horizontally polarized s waves are called as SH waves.

2. Surface waves or Long waves: - The wave which travels along the surface 

of the earth in a circumferential path is known as surface wave or long wave. These 

waves do not propagate deal inside of the surface of the earth.

 Characteristics of surface or long wave :-

1. These waves are the slowest to travel and therefore last to be recorded at the recording 

station.

2. These waves are also transverse in nature.

3. Behaviour of surface wave is similar to that of sea waves.

4. These waves are most destructive in nature.

5. Surface wave or long waves are responsible for all the damage on the surface on the 

earth during earthquakes.

Types of surface wave or long waves:-

1. Rayleigh waves (LR-waves)

2. Love wave (LL- waves)

1. Rayleigh waves/ (LR-waves):-These waves are first discovered by Lord Rayleigh in 

the year 1885 the major axis is along vertical direction and minor axis is in the direction of 

wave propagation. Thus resulting elliptical particle motion can be described as a 

combination of P and SV motion. Rayleigh wave is the part of surface wave in which 

material particle vibrate in an elliptical path in the vertical plane i.e. Rayleigh wave.

 Characteristics of Rayleigh waves :-

1. The shacking produced by Rayleigh waves causes both vertical and horizontal

movement.

 2. They advance in a backward rotative elliptical motion 

2. Love waves/ (LL- waves):-

It is the part of surface wave in which practical motion is in the horizontal plane and 

vibrates in right angle and to the direction of propagation i.e. love wave.

Love wave is similar to that of sec. Wave but with no vertical component.

History: - 

These waves are first described as seismologist AEH in the year 1911 in which the 

particle motion can be described as Sh vibration.

 Characteristics of love waves:-

1. Love wave cause surface motion. Similar to secondary waves, but with no vertical 

component.

2. Love wave motion is from side to side in a horizontal plan roughly ||el to the earth 

surface.

3. Love waves travel faster than Rayleigh eave.

4. Love wave do not move through liquid or air.

5. Love wave along with secondary wave cause max. Damage to the structures.

Earthquake size: -

Earthquake size is measured of the quantitative and qualitative effects of the vibration 

produced by the earthquake.

It is defined as in terms of two things:-

1. Earthquake Magnitude. 2. Earthquake Intensity.

1. Earthquake magnitude: - 

Earthquake magnitude is a quantitative estimate of the earthquake size.

It is measures of amount of energy release during the earthquake.

The magnitude of an earthquake is generally measured on Richter scale.

 Explanation:-

Richter magnitude scale is the most globally accepted scale which is used to define 

size of an earthquake according to Richter scale magnitude can be defined as 

logarithm (base 10) of the maximum amplitude A (in micron = 1/1000 mm) of the 

ground motion on a standard Seismograph at a distance of 100 km from the epicenter.

Richter gave a relationship between strain energy released by an earthquake and its 

magnitude.

It is given by ( log10E

= 11.4 + 1.5 M )

M = magnitude of an earthquake

E = energy in earg.

For Example: - 

As per table energy release in magnitude 7 earthquake is 80×1020 and energy released in 

a magnitude 8 earthquake is 2500×1020 ergs which is approximately 31 time of M 7.0 

earthquake. or it should be note that M less than 5 on Richter scale is of no Engineering 

Significance.

2. Earthquake intensity:-

Intensity of an earthquake may be defined as qualitative measures of actual vibration set 

up on the earth’s surface due to seismic shock.

 OR

It may also be state as measures of the degree of destruction caused by an earthquake.

Intensity of an earthquake decrease with distance from the epicenter.

Question:-What factors earthquake intensity depends: -

1. Earthquake magnitude

2. Distance from hypocenter and epicenter

3. Type of foundation material

4. Buildings style

5. Duration of shaking

 Compression b/w magnitude and intensity :-

MAGNITUDE INTENSITY

1. Magnitude is a quantitative estimate of 

Earthquake.

Intensity is a qualitative estimate of 

Earthquake

2. Measured on Richter scale. Intensity scale

3. Magnitude of an earthquake is 

measured of its size in the form of amount 

of strain energy released by the fault 

rupture.

Intensity is an indicator of the severity of 

the earthquake caused due to shacking of 

ground at the given location.

4. Magnitude on an earthquake is a single 

value.

--------------–--------

Intensity is different at different Location, 

thus many value.

 Based on the above factors two scales are commonly used:-

1. MSK Intensity Scale.

2. Modified Mercalli Intensity (MMI) Scale.

Both Scale is quite similar and range from I (least Severity) to XII (Most Sever).

 The intensity scale are developed keeping in view the following 

things:-

1. The experience of people.

2. Performance of Building.

3. Changes in natural Surroundings.



 INTRODUCTION


When a tension member is subjected to axial tensile force, then the distribution of stress over the cross-section is uniform. The complete net area of a member is effectively used at the maximum permissible uniform stress. Therefore, a tensile member subjected to axial tensile force is used to be efficient and economical member. The procedure of the design of a tension member is explained below with help of example problems.

Tension members :- Are structural elements that are subjected to axial tensile forces. Examples of tension members are bracing for buildings and bridges, truss members, and cables in suspended roof systems.

When things feel so tight they might snap, that's tension. The noun tension has its Latin roots in tendere, which means to stretch, and tension occurs when something is stretched either physically or emotionally. ... Strained relations between countries can cause political tensions to rise.

Types of Tension Members

i)Wires and cables,

ii)Rods and bars.

iii)Single structural shapes and plates.

iv)Built-up members.


i)Wires and Cables

The wire types are used for hoists, derricks, rigging slings, guy wires and hangers for suspension bridges.


(ii) Rods and Bars

The square and round bars are shown in figures are quite often used for small tension members. The round bars with threaded ends are used with pin-connections at the ends instead of threads.

The ends of rectangular bars or plates are enlarged by forging and bored to form eye bars. The eye bars are used with pin connections. The rods and bars have the disadvantage of inadequate stiffness resulting in noticeable sag under the self weight.


iii) Single Structural Shapes and Plates

The single structural shapes, i.e. angle sections and tee-sections as shown in figures are used as tension members. The angle sections are considerably more rigid than the wire ropes, rods and bars. When the length of tension member is too ling, then the single angle section also becomes flexible.

The single angle sections have the disadvantage of eccentricity in both planes in a riveted connection.

The channel section has eccentricity in one axis only. Single channel sections have high rigidity in the direction of web and low rigidity in the direction of flange.

Occasionally, I-sections are sued as tension members. The I-sections have more rigidity, and single I-sections are more economical than built up sections.


(iv) Built-up Sections

Two or more than two members are used to form built up members. When the single rolled steel section can not furnish the required area, then built-up sections are used.

The double angle sections of unequal legs shown in the figure are extensively used as tension members in the roof trusses. The angle sections are placed back to back on two sides of a gusset plate. When both the angle sections are attached on the same side of the gusset, then built-up section has eccentricity in one plane and is subjected to tension and bending simultaneously. The two angle sections may be arranged in the star shape (i.e. the angles are placed diagonally opposite to each other with leg on outer sides). The star shape angle sections may be connected by batten plates. The batten plates are alternatively placed in two perpendicular directions.

The star arrangement provides a symmetrical and concentric connection.

Two angle sections as shown in the figure (a) are used in the two-plane trusses where two parallel gussets are used at each connection. Two angle sections as shown in figure (b) have the advantage that the distance between them could be adjusted to suit connecting members at their ends.

STEPS TO(c) are also used in the two-plane trusses. The angles are connected to two parallel gussets. For angle sections connected by plates as shown in figure (d) are used as tension members in bridge girders.

A built-up section may be made of two channels placed back to back with a gusset in between them. Such sections are used for medium loads in a single plane-truss. In two-plane trusses, two channels are arranged at a distance with their flange turned inward. It simplifies the transverse connections and also minimizes lacing. The flanges of two channels are kept outwards, as in the case of chord members or long span girders, in order to have greater lateral rigidity.



The heavy built-up tension members in the bridge girder trusses are made of angles and plates. Such members can resist compression in reversal of stress takes place.


 BE FOLLOWED IN THE DESIGN OF A TENSION MEMBER

The following steps may be followed in the design of axially loaded tension members.

Corresponding to the loading on the structure of which the tension member is a part, the tensile force in the member is first computed.

The net area required for the member is determined by dividing the tensile force in the member by the permissible tensile stress.

Now, a suitable section having gross area about 20 per cent to 25 per cent greater than the estimated area is selected. For the member selected deductions are made for the area of rivet holes and the net effective area of the section is determined. If the net area of the section of the member so determined is greater than the net area requirement estimated in step i, the design is considered safe.

The slenderness ratio of a tension member shall not exceed 400. In the case of a tension member liable to reversal of stress due to the action of wind or earthquake, slenderness ratio shall not exceed 350. If the reversal of stress is due to loads others than wind or earthquake, the slenderness ratio shall not exceed 180.

Example 1: Determine the tensile strength of the 12 mm thick plate shown in Fig 9.1. Rivets used for the connection are 20 mm diameter. Allowable tensile stress is 150 N/mm2.

Solution

Diameter of the rivet hole       = 20 + 1.5 = 21.5 mm

The critical section to be considered is a section like ABCDE.

Effective width at critical section           = b – nd = 180 – (3 x 21.5) = 115.5 mm

Effective net area                                 = 115.5 x 12 mm2              = 1386 mm2

Strength of plate                                  = 1386 x 150                      = 207900 N     = 207.9 kN.



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