Builtconstruct

Saturday, August 4, 2018

Roles and Responsibilities of Architect in Construction

Architects in construction plays an important role and they are responsible for visual appearance of the buildings and structures before final structural design.

Architect is a person appointed by the client, who develops a facility as per the design concept and the requirements specified by the client. The architects develop design that are more creative in aesthetics.

The architect makes use of vision and creative ideas to satisfy the client. But the design evolved by the architects have to satisfy with the building laws and the regulations of the state.

Roles and Responsibilities of Architect in Construction

Role of Architects in Construction

An architect both artistic and functional mind for the design of structures. Once an architect is approached by a client or a sponsor, he calls a meeting to know the needs and the wants of the construction work or project.

An edifice is designed by the architect that will satisfy the client. The architect brings more of creativity and artistic elements on the building. This creation of design will be repeated till both the parties i.e. the client and the designer are satisfied.

Responsibilities of Architects in Construction

The work carried out by the architect have to be properly organized. This demands to keep the records of different contracts, the details of the project, the cost and the budget details, the time limit and the day by day progress report.

Most of the cases the architects have to work with the civil or structural engineers for communication and discussion relating the technical issues faced in the design and the implementation.

The key responsibilities of an architect in construction projects are mentioned below:

Role of Architects in Project Discussion

Meeting and discussions have to be kept with different members and professionals of the organization before approval of the project design. This helps in realizing different technical difficulties that would be faced, opinions and economical ideas. This can help in moving the team together for the completion of the project.

The project discussion carried out by the architect includes the following works:

The initial step involves understanding the client’s requirement through a detailed discussion. A careful note on his/her objectives and the expectations are taken.
Quantifying and qualifying the project will involve the discussion about the expected budget, the characteristics of the site and other planning regulation of the area under consideration.
Next is the difference sequence of operations, guarantees, and responsibilities offered by the architect. This will include:
- Understanding the limitations and potential of the site.
- Discussing about the financial targets
- Suggesting and studying all possible solutions if the work is renovation or rehabilitation or a new construction
- Bringing and presenting the feasibility study
- Different choice of site or building based on the requirement
- Provision of different options to overcome different administrative procedures
- Procedures planned and prepared are kept in line to make communication easier.

Role of Architects in Preparation of Drawings

A construction project has enormous design drawings that have to be prepared all before the execution of the work on site. Any errors have to be pre-checked before implementing it.

This early submission of drawings helps in avoiding the delaying of the project. The drawings are the basis on which detailed estimation, material procurement and work at site is carried out.

Initially, the sketch designs are prepared which will shows the building location. This gives an idea about the layout of different spaces within and nearby as well as different links to the sit. The overall massing and the appearance of the project too is reflected on the sketch design.

The sketch design is the basis on which the client agrees to certain principles and agreements. The end of sketch design will follow the contract proposal that will move to the next phase of cost estimation and the timescale of the project.

The construction of a building or a structure is now performed by both the architect and a civil engineer provided they have adequate experience and skill. The different drawings an architect can render will include the floor plan, the site plan, the elevation and the isometric vies, Other detailed structural drawings, 3D models and 3D views.

Mainly these works or details provided by the architect will depend on the work provided to him. Sometimes there comes situations where we have a structural designer to design the plan and the structural building.

We need to have a good elevation for the given plan. Here, we will approach the architect to deal with the front elevation and the landscaping details. This will hence ask for cooperation and discussion between the engineer and the architect.

Role of Architects in Cost Estimation of Construction Project

The estimation of the costs at different stages of the project progress helps in having a control over the budget. This keeps the client and the project team alert before a bigger budget issue is faced.

The architects do have an important role in visualizing top to down of the whole building structure, that results in emerging with new ideas and designs. This brings difficulty in their implementation without the help of engineers and without understanding the practicality of construction.

Hence, the greatest challenge or the responsibility of the architect is not to underestimate the cost of materials and the construction time. This point helps in bringing out effective cost estimation.

The extent and details of cost estimation conducted by the architect too is dependent on the extent of work is carrying out. If the client is completely providing the project over to him, where the engineers comes later or under, the complete construction estimation is performed by the architect.

Now, if the architect is placed only for the façade improvement or for landscaping modeling and implementation, he brings a cost estimation for the same.

Role of Architects in Construction Contracts

If the whole size of the project is known, it is able to understand the different sectors of the project that can be divided and provided to the contractors. Contractors take over the project and implement it with their labors as instructed by the architects/engineers.

The bidding of the tender and allowing the building contract can be carried out with the architect’s assistance. This helps the client to choose the correct procurement form. This way the whole contract procedure is well coordinated.

The activity of contract agreement must be transparent and fair. The architects have role in suggesting and choosing the contractors for different activities of construction.

After receiving the tender, the architect carries out a tender analysis report. These results are compared with the client’s expectations and budget.

What type of work the architect is engaged is based on the contract agreement. Most of the project, the architect takes in hand with civil structural engineers is to move the construction. Huge construction will of course demand somebody with huge technical knowledge to know about the stability and strength factors.

The contract with the architect by the client will decide what trade the architect must focus on. Based on the demand the architect will coordinate the construction activity as per the standard codes and regulations.

The architect has the role of checking the invoices at the month end to check the payment requested is corresponding to the completed works at the site.

Role of Architects in Marketing

Architects gain popularity through marketing their works to the public. They bid new works and designs based on the creativity developed in the form of buildings. This helps in developing their career.

The design to the construction process also includes the following responsibilities for the architect:

Clarification of the details of design with the construction team
The design can be redesigned if necessary. This can also bring change to the scope in order to satisfy any rules or regulations
Certification to know that the work has been completed in the correct manner

The role of architect from the construction process to the maintenance will insist the architect to handover an owner’s manual that will have recommendations for the future maintenance and repairs.

It is not a practice everywhere, but there are architects who offers such a facility. The architect has to be contacted in future if any issues arise, and it’s the duty of the architect to be available when needed.

The responsibilities of the architectural engineer are somewhat similar to that of structural engineer. The difference is that the architects take more effort on how the building looks and its aesthetics, while the structural engineer focus on the construction type and durability of the structure. But both have a common goal of bringing a well-structured building.

Wednesday, August 1, 2018

Ventilation in Tunnels -Types of Ventilation Systems in Tunnel Construction

There are various types of ventilation systems in tunnel construction provided to remove dust and poisonous gas during its construction and operation. These ventilation systems in tunnel construction are discussed in this article.

The tunnel construction works are mainly carried out by drill and blast method, which have many safety and health issues due to the emission of dust and many poisonous gasses. Hence it is essential to provide ventilation systems in in tunnel during construction.

The main objectives of providing ventilation systems in tunnel are:

To provide the working crew an environment of fresh air.
To exhaust out fumes and gasses, that is injurious to health and explosive in nature.
To remove the drilling, mucking and blasting gasses emitted.

Ventilation during construction and after completion of tunnel construction is an essential feature that a tunnel should own to facilitate functional, comfortable and a safe tunnel environment for both the road and railway tunnels.

Types of Ventilation Systems in Tunnel Construction

Why Ventilation Systems in Tunnel Construction Required?

When the work is being carried out within the tunnel, each worker has to be supplied with 200 c. ft to 500 c. ft of fresh air constantly. The consideration of compressed air emitted during drilling purpose is contaminated with oil and dust. So this should not be taken as a source of air to play the role of ventilation.

After each explosion, the face is completely covered with air that is full of fumes and dust, which is unfit for breathing. Before he starts to remove the debris of the explosion, the foul air surrounding him must be removed out by any source of exhaustion and get him fresh air.

There exist 30 minutes between the explosion and mucking process, within which the ventilation system installed should clear the tunnel contaminated with poisonous gas and dust and refill with fresh air.

There are mainly three factors, based on which the form and capacity of the ventilation system are dependent:

The length of the tunnel and its size.
The amount of explosives used for blasting and their respective frequencies
The condition and rate of temperature and humidity inside the tunnel

Working Environment inside a Tunnel

The working environment inside a tunnel is contributed by the following factors:

The dust and the gasses emitted by the tunneling operations
Exhaust gasses emitted by the diesel operations
Explosive or organic solvent emitted poisonous gasses. For example Nitrogen oxide, hydrogen sulfide, sulfurous acid gas, carbon monoxide
Flammable gasses or oxygen shortage gas in the ground. For example, methane, carbon monoxide and hydrogen sulfide
High temperature and humidity factors

Table-1: Density of Dust Emitted due to Tunneling Works

Tunneling Works	The Density of Dust Formed in mg/m3
Excavation	10 -1000
Loading of materials that are excavated	10 – 1000
Mucking	10 – 100
Drilling	1-50
Blasting	100 – 300
Shotcreting	10 – 200

Table-2: Volume of Generated Poisonous Gas in Tunnels

The table below shows the allowable density of dust poisonous gas to control the standard values.

Table.3: Allowable Density Value of Dust inside Tunnel

Table.4: Allowable Density of Poisonous Gas in Tunnels

Tunneling Works Safety and Health

To secure safer and healthier environment during the tunneling works, it is necessary to take absolute measures while carrying out the operations of drilling, blasting, excavation, Shotcreting and mucking. Dust, smoke and poisonous gasses inside tunnel can be removed efficiently with the help of a proper ventilation. The government has considered this step to safeguard the health and safety of the labors working in the tunnel.

Types of Ventilation Systems in Tunnel Construction

The methods employed for tunnel ventilation generally depends upon the normal, emergency or congested operation that will be dependent on the actual conditions of the size, cross section, traffic conditions, intermediate ventilation shafts etc.

Types of Ventilation Airflow Systems in Tunnels

Longitudinal Ventilation Airflow Systems in Tunnels

Here the direction of airflow is longitudinal in nature. At the beginning of the tunnel or the tunnel section starting, these moves the pollutant gasses and effluents, that is followed by the fresh air. Then at the end of the tunnel portal or at the tunnel section end, the polluted air is discharged. This is shown in the figure-1.

The configuration of longitudinal ventilation can be either portal to portal, shaft to shaft or from portal to shaft. For transit and railway tunnel, the longitudinal airflow system is used.

Fig.1: Configuration of Longitudinal Ventilation in Tunnels

Transverse Airflow Ventilation Systems in Tunnel

Here uniform distribution of fresh air is created along the length of the tunnel. It is mainly employed in road tunnels. Occasionally it is used for transit tunnels. A consistent level of temperature and the pollutants will be maintained if this system is employed. The system can be either fully or semi-transverse.

Transverse or semi-transverse ventilation tunnel is better than a longitudinal one for the tunnels that are longer than 4 to 5 km.

The ventilation system capability and their choice will depend on the air considerations, the amount of air within the tunnel that too must be calculated based on the traffic conditions, the rate of emission of gases within the tunnel, standards of pollution level, the local standard conditions so that the neighboring environment too is not polluted and harmed.

In the case of railway tunnels, the emergency scenarios of smoke or fire cause is a major concern behind the choice of ventilation. Here mainly longitudinal ventilation is used- that uses ventilation plants at intermediate shafts or at the station adjacent. These may be either combined with exhaust from large caverns.

The ventilation provided can be either Natural or Mechanical ventilation.

Natural Ventilation Systems in Tunnel

When from one portal to next portal of the tunnel, there is a provision of drift, it forms a fair ventilation during the operations involving enlarging. This is when the tunnel length is short. In the case of long tunnels, such natural ventilation will be inadequate and we must design separate mechanical ventilation system.

Fig.2: Natural Ventilation Configuration in Tunnels

The natural ventilation can be configured from portal to portal, shaft to shaft or from portal to shaft. As shown in figure.5. the roadway has an air velocity that is uniform. The temperature and the pollutant level increases at the exit portal or the section end.

If the meteorological conditions of the tunnel go adverse, the velocity, the temperature, and the pollutant level get increased. The pressure differential between the two tunnel portals, that is formed by the differences in the elevation and the ambient temperatures of wind are the chief meteorological conditions.

A sudden change in wind direction or the wind velocity will affect the natural effects along with the vehicle generated piston effect.

Fig.3: Airflow Characteristics in Natural Ventilation System in Tunnels

Mechanical Ventilation System in Tunnels

Mechanical ventilation system employs mechanical devices like electric fans, exhaust, and blowers, which serves the function of removing the exhaust gasses within the tunnel and help in blowing fresh air into the tunnel. Now, whatever be the device employed, there are three main services they can provide:

Blowing
Exhausting
Combination of blowing and exhausting

Blowing Ventilation Systems in Tunnel

As the name tell, fresh clean air is blown to the working face, with the help of pipes. When it flows back to the portal, it takes the dust and gasses with it. This system of ventilation help providing fresh air near the working face with ease. But in long tunnels, these systems have a disadvantage of fogging the atmosphere inside the tunnel when the smoke, dust and foul air move out.

Exhausting Ventilation Systems in Tunnel

The system incorporates an exhausting duct near the working face, into which, the foul air and the dust are let. By this fresh air is maintained within the tunnel, through the entrance. Quick removal of dust and smoke is one advantage of the exhausting system.

The combination of Blowing and Exhausting

The figure below shows a schematic figure of a blowing and exhausting system applied in a combination. This concept is developed, so that the advantage of each system can be combined, bringing a ventilation system of higher performance.

Combination of a Blowing and Exhausting Ventilation System in Tunnel Construction

Fig.4: Schematic Representation of Combination of a Blowing and Exhausting Ventilation System in Tunnels

Working: After the explosion or blasting, the exhausting system will operate for a period of 15 to 30 minutes. This will remove harmful air immediately. After this, the blowing system works continuously to supply the fresh air till the next blasting.

From the figure-4, D is the fan and it is supposed to rotate only in one direction. Now the valves A, B, and C are valves that are manipulated either to exhaust from or blow into the tunnel.

Dust Prevention in Tunnel Construction

The dust accumulation within the tunnel is the after effect of conduction the blasting, drilling mucking operations. If the dust accumulated amount is beyond the permissible limit, it creates harmful effects for the people working and to the surrounding environment.

The blasting of rocks as a part of tunneling operation will emit a high amount of silica in the environment. The intake of same will cause a disease called the “silicosis” which is fatal.

Dust Control Methods in Tunnels

The methods used to control dust accumulation are:

Wet drilling
Use of vacuum hood
Use of respirators

Now modern drilling machines are available, that make use of water to drill. Here the area that is to be bored is made wet, resulting in a reduction of dust emission.

The figure below shows a vacuum hood that is used in tunneling work. A hood is fitted to a drill face. This is at the rock face. This is connected to an exhaust pipe. The exhaust pipe takes in the dust formed by the drilling process and that is taken safely out of the tunnel. This reduces no flying of dust to outside.

Another common and efficient method to prevent dust inhalation is using respirators. These are well designed units that are worn by the miners and workers, who are highly exposed to the dusty environment.

Tunnel Engineering -Features, Advantages and Methods of Tunneling in Construction

Tunnels are underground constructions used for transportations. The features, advantages, disadvantage and methods of tunneling in construction is discussed.

The tunnel engineering is one of the most interesting disciplines in engineering. The work is complex and difficult throughout its course, even though it is interesting.

The tunnels are defined as the underground passages that are used for the transportation purposes. These permit the transmission of passengers and freights, or it may be for the transportation of utilities like water, sewage or gas etc.

The operations and the constructions are carried out underground without disturbing the ground surface. This operation is called as the tunneling.

Construction of First Tunnel

It is found that the first tunnel was made by the Egyptians and the Babylonians, 4000 years ago. This tunnel served the purpose of connecting two buildings in Babylon. The connection was from the royal palace to the temple. The length of this tunnel was found to be 910m, which was brick lined.

Construction of Largest Ancient Tunnel

The largest tunnel in ancient times was constructed between Naples and Pozzuoli, in 36.B.C. This tunnel was 4800-foot-long, 25-foot-wide and 30 foot in height. It was a road tunnel.

During the second half of the twentieth century, the development and progress of explosives and sophisticated equipment were flourished, that made the tunneling process more feasible.

The tunneling, work better for different approaches under different circumstances. It is hence dependent on the experience and the knowledge of the engineer. Mainly the tunneling works are carried out by the civil engineers.

This discipline will let us know, that the knowledge on structural and concrete technology is not sufficient. An equal and thorough skill and knowledge on geology, mechanical engineering, geomechanics and the new construction technologies are also essential.

Selection of Tunneling Route

The two main factors that help in the efficient route of the tunnel are the alignment restraints and the environmental considerations. The underground, as we know is heterogeneous in nature. A proper inspection on the nature of soil, rock, the water table level, and all the alignment restraints had to be made before fixing the route.

The site chosen for tunneling is such a way that the inconvenience and difficulty that is caused to the environment in that area including living is minimum.

The tunneling method chosen depends on the ground conditions, the water table level, the tunnel drive length and the diameter, the tunnel depth, final utility requirements, the shape of the tunnel and the risk of construction.

Advantages of Tunneling

The tunneling method gain certain advantages compared with other methods, which are mentioned below:

The tunneling procedure is more economical in nature, compared to open cut trench method when the depth is beyond a limit
The surface life or ground activities like transportation are not disturbed when tunneling is undergone.
The method ensures high-speed construction with low power consumption
Reduces Noise Pollution
These methods have freedom from snow and iceberg hazards, in areas of high altitudes
Surface and air interference is restricted for tunnels
Provision of tunnels with easy gradients, help in reducing the cost of hauling
For the transportation of public utilities, tunneling method has a remarkable advantage compared to the bridge.
The dangerous open cut to a nearby structure, when it is needed, is solved by the tunneling method
The tunneling grant greater protection in aerial warfare and bombing conditions

Tunneling Disadvantages

The tunneling method gains certain disadvantages, which is due to its complexity and difficulty. Some of them are:

The initial investment cost for commencing the tunnel is high compared to the open cut method.
Highly skilled and experienced designers and engineer team only will work best for this operation.
Higher and constant supervision from the start to the end of the tunneling project is necessary without any compromise
Highly sophisticated and specialized equipment are necessary to perform the tunneling operations.

Comparison between Open Cuts and Tunneling

There are always debate arising on the cost that is consumed between the open cuts and the tunneling techniques, to conclude which is more economical. Consider the following factors:

a) Open cuts are found very costly at deep cutting for soil with varying nature and slopes. This method will account for the large volume of excavation, which is costly. At this situation, tunneling method will bring more economy than the open cuts.

b) When the material of drilling is rock, open cut performs well with less amount of excavation and finds cheaper. While tunneling method is found difficult to show its activity.

c) Based on the requirement of material for nearby filling, an open cut method can be suggested, but the tunneling is found comparatively economical in working. For depth of cutting greater than 60 feet, the method of tunneling is always recommended.

Approaches in Tunneling Method

There are two approaches based on the open cuts on the either ends of a slope. They are short approach and long approach. The approach is said to be short, when the hill slope is very steep in nature, as shown in figure.1.

The approach is said to be very long, when the slope of the hill is very flat, as shown in figure.2. The cost of this mainly depends upon the topography of the considered area. In high altitudes, these approaches will be bounded with snow or may be blocked by the heavy landslides. These are the factors that would cause the decision of open cut or tunnel method.

Fig.1: Short Approach in Tunneling

Fig.2: Long Approach in Tunneling

Alignment and Grade in Tunneling Process

Certain factors that must kept in mind in the tunneling procedures are:

The best and economical alignment was chosen must be straight in nature
Tunnel should have a grade, which is less than the outside. It is observed that in the railway tunnels, constant slipping of the wheels takes place due to the wetness of the rails. This reduces the hauling capacity of the locomotives.
0.2% gradient must be provided to ensure proper drainage.
When it comes to long tunnels, two grades at the either ends must be provided (That rise from each end then towards the center as shown in figure-3).

Fig.3: Surface Alignment and the provision of grade for the tunnel

If the grade is provided on one side, instead of either side, the effectiveness of ventilation can be increased.

Roles and Work of Surveyor in Construction

The surveyor is the person who is supposed to make precise measurement that will identify the boundary. Surveyors help in providing unique contours on the surface of the earth which will let the engineers to make maps and construction projects.

What are the Duties of a Surveyor?

The following are the duties of a surveyor.

The surveyors have to measure the distance and the angles between specific points on the earth surface.
Based on reference points, certain important features points are located by traveling.
Detailed research is carried out on the records related to the land, survey, and the titles of the land.
The boundary lines are to be located by searching for the past boundary present in the site.
The surveying is conducted and the obtained results are recorded. Later they are verified for accuracy and corrections.
Based on the surveyed records plots, maps, the respective reports of the surveyed site is prepared.
The findings obtained from the surveying is presented to the clients and the respective government agencies.
The official land needs and water boundaries are established. These are established either for lease or deeds.

Work Characteristics of Surveyor

The works performed by the surveyor can be divided into three different parts. They are:

Field Work
Office Work
Instruments Care and Adjustments

Field Work Conducted by Surveyors

As mentioned in the duties of surveyor, he has to determine the points and their respective distances and angles which have to be recorded in the form of field notes.

The operations involved in the field works are:

Initial establishment of benchmarks and all the stations as the reference. Based on these operations the horizontal and the vertical control is established.
The angles between the survey lines created have to be measured.
All the details of the survey are explained and located based on the stations and the lines between the stations. The details are the streams, buildings, milestones, streets and any other natural or man-made features present in the area surveyed.
For the constructions works related to buildings, culverts, sewers, bridges, and water supply schemes the lines have to set out and the grades are established by the surveyors.
Height or the elevation of certain points are determined by surveying by the surveyor. Or in either case, specific points have to be established in required elevations.
Carrying out topographic surveying. This is the surveying of contour of the given land which involves both vertical and horizontal controls.
Parallel lines and perpendicular lines have to be established.
The inaccessible points have to be measured.
To conduct survey past the obstacles. Many miscellaneous field works based on the trigonometric and the geometric principles have to be conducted.
Determination of the meridian, latitude, and longitude or to determine the local time by carrying out observations on the sun or a star.

When dealing with field works, it is very important to understand the importance and the features of Field Notes.

Field notes are written notes that are prepared when the field work is carried out. There are situations when the whole precision of the survey and the field work becomes futile if the value recorded is wrong.

Hence the quality and competency of a surveyor’s work is more reflected in the field record when compared to the basic elements of surveying he performed.

The prepared field notes must be eligible, comprehensive, and Concise. The values and remarks have to be written in clean, clear plain letters and figures. There are certain basic rules to be keep while maintain a field note. They are:

As soon as the observations are made, the values are recorded in the field book
The pencil used must be sharp 2H or 3H. Never make use of a soft or ink pencil
It is recommended to have simple style of writing that must be consistent
Try to use liberal number of sketches
Each day of survey work must end up with a brief note. This must have the title of the work, the date of survey, the conditions of weather, the personnel involved, the list of the instruments and the equipment used.
It is recommended not to erase. If a mistake is made, rule through the mistake and the corrected value is marked above it.
The daily notes created must be signed.

The filed note consists of three parts:

1. Numerical Values

All the recorded measurements like length, angles, staff readings, offsets are recorded in this column on the field book. All the figures that are significant must be recorded correctly. Values nearest to 0.01 must be recorded. A value observed as 342.30 must be written as same and not as 343.3.

2. Sketches

The sketches will resemble the outlines, the topographic features, and the locations relative to each other. These are not made to the scale. If we plan to place the measurements on the sketches, correct belongings must be made while marking it. Always make a sketch which makes the interpretation easier. This must avoid maximum confusion. The sketches must be large, open as well as clear.

3. Explanatory Notes

All those that cannot be conveyed through the values and the remarks must be written in the explanatory note section. These remarks will help to proceed the later works.

Office Works Done By surveyor

Drafting, computing, and designing are the office works that have to be performed by the surveyor.

The drafting performed consists of the preparation of plans and the sections. These must be plotted to the measurement and to scale and prepare the topographic maps.

The computing process is done in two cases. Initially, it can be done for the plotting. Secondly, it can be constructed for the determination of the areas and the volumes.

Instruments Care and Adjustments by Surveyors

If there is good experience in handling the equipment, the works can be carried out with great experience and precision. This knowledge on handling will make us understand the limitations of the instrument and can take proper care of these equipment.

There are many instruments like the level, theodolite, etc. that requires great care with delicate handling. There are many delicate parts in the instruments, if any of the parts get affected, it will bring total complaint and total loss.

The relative positions of the instruments must be checked while taking out the instrument and during its placement back after the use. Straining the parts of the instrument will result in the incorrect measurements.

The precautions that must be taken are:

The instrument must not be lifted by holding the telescope or the circular plate. We must hold the foot plate or the leveling base.
The movement of the instrument from one place to another must be carried out by placing it on the shoulder. All the clamps are set tightly.
When not in use, the lens must be covered.
Setting up the instrument on a smooth floor without any kind of precautions must be avoided.
The instrument must not be exposed to dust and dampness or direct sun rays. A waterproof cover can be used to cover and protect it.
Not leave the instrument without any guard.
The steel tape after use must be cleaned and kept dry. While measuring, vehicles are not allowed to move over it.
In case of compass instrument, the compass must not be allowed to swing without any need. This is lifted off the pivot when not in use.