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Advantages of composite construction

Advantages of composite construction

Composite construction basically refers to the use of steel and concrete formed so that the resulting component behaves as a single element. The objective of the composite construction is to use the best properties of the different materials and offer a performance that is greater than individual components had been used together but not unified. In the case of steel and concrete, the best properties would be the tensile strength of the steel and the compression capacity of the concrete. The composite construction dominates the multi-storey non-residential construction sector. This has been the case for more than twenty years. Its success is due to the resistance and rigidity that can be achieved with the minimum use of materials. The reason why the composite construction is often so good can be expressed in a simple way, concrete is good at compression and steel is good at tension. By structurally joining the two materials, these strengths can be used to obtain a highly efficient and light weight.

 

Composite construction is an effective method of construction and delivers good performance. The methodology for designing composite structures has been researched in great detail. Composite construction is a very popular method of construction around the world.

 

 

 

Advantages of Composite Construction

 

1: The significant feature of a composite system is a stiffer and stronger structure that can be obtained from the same beam and slab acting no compositely. In this sort of construction smaller and shallower beams may be used.

 

2: The benefits of composite construction include speed of construction performance and value. Steel framing for a structure can be erected quickly and the pre-fabricated steel floor decks can be put in place immediately. When cured the concrete provides additional stiffness to the structure.

 

3: The concrete encasement protects the steel from buckling, corrosion and fire, service integration with in the channels on the composite decks is another advantage to composite construction.

 

4: Building quality standards can be adhered to easily by the use of pre-fabricated decks. Excessive deflections can be controlled by cambering the beams or by shoring the metal decks to limit deflection when concrete is poured. It also helps in longer spans without deflection problems.

 

What is pile foundation?

What is pile foundation?

A concrete pile is basically a long cylinder in reinforced concrete that is buried in the ground to act as a stable support for the structures that will be built on top of a platform supported by one or more of said cylinders. The set is known as foundation piles or deep foundations.

Pile foundations are mainly required for tall buildings as the design loads are too large to be supported on spread footings. Sometimes, when soil has low SBC or the soil is clayey, a raft or a pile foundation may be the solution.

 Piles can by classified in 3 ways:

  1. The way in which the load is transferred on to the soil.
  2. Method of Installation.
  3. Material of construction.

 

Classification of Piles based on load transfer

 

Point Bearing Piles

 

If bedrock or hard strata is present within reasonable depth, piles can be extended to rest on the bedrock or penetrate required depth into the hard strata. In this case, the ultimate bearing capacity of the pile depends entirely on the underlying rock/strata.

 

Friction Piles

 

In a friction pile, the load on pile is resisted mainly by skin friction along the pile shaft. Pure friction piles tend to be longer than point bearing piles. Resistance is a function of the shaft area in contact with the soil. In cohesion-less soils, such as sands of medium to low density, friction piles are often used to increase soil density. When hard strata are not available at reasonable depth, end bearing piles are uneconomical. For this type of subsoil condition, piles are driven through the softer material to required depth.

 

Classification of Piles based on Method of Installation

 

Driven or displacement piles

 

 

They are usually pre-cast before being driven or hammered into the ground. This category consists of driven piles of steel or concrete and piles formed by driving tubes or shells which are fitted with a drive shoe.

 

Bored piles

 

 

These piles require a hole to be drilled first and into which the pile is then formed usually of reinforced concrete.

 

Types of Piles based on Materials

 

Timber piles

 

 

  • Timber piles are made of tree trunks that are driven with narrow end as a point
  • Maximum length: 30~40m; Optimum length: 10-20m
  • Max load for usual conditions: 40 MT

 

Advantages

 

Low initial cost compared to concrete piles, permanently submerged piles are resistant to rot/decay, handling is easier, these are best suited as friction piles.

 

Disadvantages

 

Splicing is difficult, piles are vulnerable to damage especially while hard driving, piles are vulnerable to decay unless it is below permanent water table as is usually the case. if subjected to alternate wetting & drying, life can be short.

 

 

Steel piles

 

 

These are commonly used in marine and other structures. Maximum length is practically unlimited. They have a comparatively larger load capacity.

 
Advantages 

 

Larger capacity, best suited for end bearing, easy to splice, small displacement, able to penetrate through light obstructions

 
Disadvantages

 

  • Required corrosion protection to the metal.
  • May be damaged/deflected by major obstruction

 

Concrete Piles

 

 

  • Concrete piles may be precast, prestressed, cast in place, or composite construction.
  • Precast concrete piles may be made using ordinary reinforcement or prestressed steel.
  • Precast piles using ordinary reinforcement are designed to resist bending stresses during transport & bending moments from lateral loads and to provide sufficient resistance to vertical loads and any tension forces developed during driving.
  • Prestressed piles are formed by tensioning high strength steel prestressed cables. It is common to have higher-strength concrete (M35 to M55) in prestressed piles because of the large initial compressive stresses induced by pre-stressing. Pre-stressing the piles, tend to counteract any tensile stresses during handling or driving.
  • Max length: 10 - 15 m for precast, 20 - 30 m for prestressed
  • Optimum length 10 - 12 m for precast. 18 - 25m prestressed

 

Advantages

 

  1. High load capacities.
  2. Corrosion resistance can be achieved by cathodic protection…sacrificial anodes or impressed current method.
  3. Hard driving possible
  4. Cast in place concrete piles are formed by drilling a hole in the ground & filling it with concrete. The hole may be drilled or formed by driving a shell or casing into the ground.

 

Disadvantages

 

  1. Certain organic soils contain materials that may form acids that can damage the concrete.
  2. Salt water may adversely react with the concrete.
  3. Concrete piles used for marine structures may undergo abrasion from wave action and alternate wetting and drying, especially in the splash zone.
  4. Difficult to handle unless prestressed.
  5. High initial cost, considerable displacement.
  6. Prestressed piles are difficult to splice.
  7. Alternate freezing thawing can cause concrete damage in any exposed situation.

 

What is an underground water tank?

What is an underground water tank?

An underground (U/G) tank is a container that can be used for storing a liquid without appreciable loss by leakage through its walls or base. Various underground water tanks are U/G components of a sewage treatment plant, swimming pools, sumps, oily water sewers, sulphur pits, manholes and catch basins.

 

Water tanks are used to provide storage of water for use in a number of applications. Structural design of a water tank includes design parameters such as concrete grade, reinforcement grade, soil parameters, water table and edge support conditions of the tank walls. The tank slab and wall thicknesses mainly are decided based upon the edge shears and bending moments. Generally, reinforcement consists of 2 orthogonal layers on each face with adequate concrete covers. Crack control check is a necessary check in u/g tank design. Testing for leakage is an obligatory test is u/g tank design.

 

In general, underground water tanks are used for various purposes such as storage of potable drinking water, waste water, rainwater collection, housing underground tanks and vessels etc. The outer walls generally are required to retain outer soil and ground water and sometimes a surcharge load that may come from construction vehicles moving in the vicinity of the u/g tank.

 

 

 

Filling a newly constructed underground water tank while backfilling on the outer side reduces the differential pressure between the outside and the inside of the tank, thus, minimizing any possible damage to the tank. U/G tanks required to store hot fluids such as those collecting sulphur in Oil and Gas plants, are constructed in special thermal insulation material/ refractory lining so as not to damage the concrete.

 What exactly infrastructure engineers do?

 What exactly infrastructure engineers do?

Civil infrastructure engineers are required to work with various types of client including private individuals, architects, land developers, master planners and housing developers from one off projects to more regular ongoing assistance and support. They are experienced in developments across sectors including residential, housing, commercial and industrial. Civil infrastructure systems involve design, analysis, and management of infrastructure supporting activities including electric power, oil and gas, water and waste water, communications, transportation and collections of buildings for urban and rural communities. These networks deliver essential services, provide shelter, and support social interactions and economic development. In one line,  they are the lifeline of any society. 

 

Infrastructure engineer

 

Civil infrastructure systems builds on and extends traditional civil engineering areas. Rather than focus on individual structural components or structures, it emphasizes on how different structures behave together as a system that serves a community's common needs. Risks in this field are problems that typically involve a great deal of uncertainty, multiple and competing objectives. The technical aspects of infrastructure engineering needs to be understood in social, economic, cultural and political context in which they exist. And this must be considered over a long term horizon that includes not just design and construction, but maintenance, operation and performance in natural disasters and other extreme events and sometimes in destruction as well.

 

The services of a civil infrastructure engineer include:

 

Flood risk assessment

 

  • Flood risks and mitigation measures.
  • Drainage planning.
  • Sustainable Drainage Systems.

 

Highways

 

  • Highways design.
  • Pedestrian footpath design.
  • Setting out reports.
  • Street lighting.
  • Parking design.

 

Drainage

 

  • Foul and surface water drainage systems.
  • Site surface water management.
  • Ponds & soakaway pits.
  • Sewer design.
  • Pump stations.
  • Water authority approvals.
  • Plot drainage system.

 

External Works

 

  • Cut and fill analysis.
  • Retaining wall requirements.

 

Utilities

 

    • Diversion requirements.
    • Existing utility assessment.
    • Proposed utility layouts.

What is meant by RCC structure?

What is meant by RCC structure?

Reinforced Cement Concrete

 

The acronym RCC stands for Reinforced Cement Concrete. An RCC framed structure is essentially a set of slabs, beams, columns and foundations which are interconnected together to form a stable configuration. The transfer of load in such structure takes place from the slabs to the beams, and from the beams to the columns and finally to the foundation which in turn transfers it to the underlying soil.

 

 The floor area of ​​a RCC framed structure is 10 to 12 percent more than that of a load bearing structure because of the load bearing walls that have a relatively large base area compared with footings for a framed structure. Therefore, there is a real economy in case of an RCC framed structure especially where the cost of the land is very high. Most importantly, in case of RCC framed structures, the internal planning of the rooms, bathrooms, W/Cs etc. can be altered by changing the position of the non-loaded partition walls, thus providing greater flexibility in planning and subsequent modifications.

 

 

RCC

 

 

Reinforced concrete is one of the widely used modern building materials. Concrete is an artificially made construction material that is obtained by mixing cement, sand and aggregates with water. Cool concrete can be moulded into almost any shape, which is an inherent advantage over other materials. Concrete became immensely popular after the invention of Portland cement in the 19th century. However, its limited tensile resistance prevented its wide use in the construction. To overcome this weakness in tension, the steel bars are embedded in the concrete to form a composite material called reinforced concrete.

 

 Reinforced concrete is widely used in a wide variety of engineering applications. The worldwide use of reinforced concrete construction is due to the wide availability of reinforcing steel, as well as concrete ingredients. Concrete Production does not require expensive manufacturing factories. However, concrete construction requires a certain level of technology, experience andmanpower particularly in the archive during constructions. In some cases, single-family houses or simple low-rise residential buildings are built without any engineering assistance.

 

 To conclude, RCC is mainly used for buildings, bridges, culverts, concrete pavements, roads, drain trenches, retaining walls etc to name a few. Most of the reinforced concrete structures show great strength, excellent durability, better fire resistance and good performance. Adverse environments or poor construction the practice can lead to corrosion of the reinforcing steel in the concrete. The main mechanisms for corrosion are the atmospheric oxygen and chlorides and sulphates in water. The corrosion and deterioration mechanisms are essentially the same for both carbonation and chloride attack. The right choice of suitable materials, adequate cover to reinforcement and good quality concrete and attention to the environment during construction will improve the durability of reinforced concrete structures.

How to select a suitable type of foundation?

How to select a suitable type of foundation?

There are different types of foundations for building construction and the selection of a particular type depends on soil conditions and loads from the structure. It is advisable to know the suitability of the chosen type of foundation before making any decision on its selection. The selection of a particular type of foundation is often based on a number of factors, such as:

 

ADEQUATE DEPTH

 

The foundation depth depends on the following factors:

  • Getting an adequate allowable bearing capacity of subsoil.
  • For clayey soils, depth should be below the zone where shrinkage and swelling due to seasonal weather changes are likely to cause appreciable soil movements.
  • For fine sands and silts, founding depth should be below the frost zone.
  • For bridge piers, the maximum depth of scour should be considered with the foundation located sufficiently below this depth.
  • Depth of foundation shall be at least below the top soil, miscellaneous fill, vegetation i.e approximately 300 mm below NGL.

All foundations should be taken down to a minimum depth of 0.5 m below natural ground level as a matter of sound engineering practice. In filled-up ground it may be necessary to go beyond the depth of fill or take special precautions to avoid settlement issues for the structure. In such cases, it may be necessary to have a shallow foundation i.e. at a higher level, and replace the soil in between the base of foundation and the level of excavation either by:

(a) Lean concrete, 

(b) Well compacted structural fill to required specifications. The width of fill should not be less than the width of foundation. This is necessary for dispersion of load on either side of the foundation.

In sloping grounds, the horizontal distance from the footing edge (shallow side) to ground surface shall not be less than 60 cm for rock sub-base, and 90 cm for soil. In addition, a line drawn at 30 degrees to the base from the outer edge should not intersect the sloping surface of the ground.

 

For foundations near existing structures, the minimum horizontal distance between existing and new footings shall not be less than the width of the wider footing. An analysis of bearing capacity and settlement may be required to study pressure bulb overlaps and the likely impact on the foundations.

 

 BEARING CAPACITY FAILURE

 

Bearing capacity of the soil is its capacity to support the structure loads. It is the maximum pressure the soil can without failure.

 TYPES OF BEARING CAPACITY FAILURES

Bearing capacity failures of foundations can be grouped into three categories:

(a) GENERAL SHEAR

This involves total rupture of the underlying soil. There is a continuous shear failure of the soil from below the footing.

General shear failure ruptures and pushes up the soil on one or both sides of the footing, often resulting in a subsequent tilt in the structure.

(b) LOCAL SHEAR

Local shear failures involve soil rupture immediately below the footing. There is soil bulging on both sides of the footing, but the bulging is small when compared to that in general shear. This mode of failure is characteristic of medium dense or firm soils.

(c) PUNCHING SHEAR

In punching shear, the soil outside the loaded area remains relatively uninvolved and there is hardly any movement of soil on the sides of the footing. This is associated with compression of the soil directly below the footing and vertical shearing of soil around the footing perimeter. A punching shear failure is characteristic of loose or soft soils.

Any foundation must be safe against all of the above 3 types of bearing capacity failures.

 

SETTLEMENT

 

All foundations settle to varying extents as the soil beneath them adjusts to the building loads. Foundations on rock bed settle by an insignificant amount, if any. Foundations on other soils, such as clay, may settle more. Where all the foundation elements settle at the same rate, it is termed as ‘uniform’ settlement. Settlement that occurs at differing rates between the various elements of building foundation system, it is termed ‘differential’ settlement.

When all parts of a building rest on one type of soil, and the soil pressures are uniform, differential settlement is usually not a concern. However, where soil pressures between the various areas of a building support system are different, differential settlements are likely. This may result in a tilt or distortion of the building frame and may cause ‘structural’ or ‘non-structural’ damage to it.

 

QUALITY

 

The foundation must be of an adequate quality so that it is not subjected to deterioration, for example, by chloride or sulfate attack.

 

STRENGTH

 

The foundation must be designed with sufficient strength that it does not fracture or break apart under the applied structure loading. The foundation must also be properly constructed in accordance with the design code and project specifications.

 

ADVERSE SOIL CHANGES

 

The foundation must be able to resist long term adverse soil changes. Expansive soils, that expand or shrink with moisture content, thereby causing movement of the foundation, may severely damage the structure. In such cases, the foundation level may be considered below such soils.

 

SEISMIC FORCES

 

A foundation must be able to resist excessive settlement or lateral movement in case of an earthquake.

 

Conclusion 

 

Based on an analysis of all of the factors listed above, a specific type of foundation, for example, isolated footing, combined footing, mat foundation, piled foundation etc may be recommended by the geotechnical engineer.

What do Civil engineers do ?

What do Civil engineers do ?

Civil Engineering

 

Civil engineers create, improve and preserve the environment we live. They do the planning, designing and overseeing of construction and maintenance of building structures and infrastructure including roads, bridges, railways, airports, harbours, dams, irrigation projects, power plants, and sewerage systems. They also design and build houses, buildings and large structures that can withstand all weather conditions.

 

 

Civil engineers can be broadly categorised into consulting engineers and contracting engineers. Consultants are responsible for the design work of projects and work mainly in offices. Contractors, on the other hand, take the designs and implement them during construction. Contractors work on site, managing the construction of the structure. Depending on whether the civil engineer is a consultant or a contracting engineer, work activities can differ. A consulting civil engineer may be required to:

 

  • Undertake technical studies, feasibility studies, geotechnical investigations.
  • Develop detailed designs.
  • Assess, study, mitigate/eliminate the potential risks of specific projects, as well as undertake risk management in specialist roles.
  • Supervise tendering procedures and prepare bids.
  • Manage, supervise and visit contractors on site and advise on civil engineering issues.
  • Oversee works of junior staff, mentor young civil engineers.
  • Liaise with colleagues and architects, subcontractors, contracting civil engineers, consultants, co-workers and clients.
  • Resolve design and development problems.
  • Manage budgets and other project resources.
  • Manage change request from clients and ensure relevant parties are notified of changes in the project.
  • Lead teams of other engineers, sometimes from other organisations or firms.
  • Compile, check and approve reports.
  • Review and approve project drawings.
  • Use computer-aided design (CAD) packages for designing/drafting projects.
  • Undertake design calculations.
  • Schedule material and equipment purchases and delivery.
  • Attend public meetings to discuss projects, especially in a senior role.
  • Ensure smooth running of projects, timely completion of projects and completion within budget.

 

 Typical employers of civil engineers

 

  •  Consulting firms
  • Construction firms
  • Local authorities and government departments
  • Rail companies
  • Utility companies

 Working hours for consultants are generally 40 hours a week, with some extra hours and weekend work close to project deadlines. Contractors, on the other hand, often work shifts and weekends and are outside for most of their time. Civil engineers often specialise in a particular type of project or discipline such as buildings, road works, industrial projects, bridges, dams, tunnels, marine, power, water and transport. They may work on projects involving

  •  Buildings
  • Coastal development
  • Construction of dams and canals
  • Geotechnical engineering
  • Highway construction
  • Waste management