Pre Engineered Buildings (PEB)

Pre Engineered Buildings (PEB) are the buildings which are engineered at a factory and assembled at site. Typically PEBs are steel structures. Developed segments are manufactured at the factory to correct size, moved to site and assembled at site with catapulted associations. This sort of Structural Concept is commonly used to manufacture Industrial Buildings, Metro Stations, Warehouses and so on.

The adaptability of PEB in the spot of Conventional Steel Building plan ideas brought about numerous favorable circumstances, including economy and simpler manufacture.

These sort of building structures can be done inside to serve any capacities that are really helpful in a low ascent building plan. Instances of Pre-Engineered Buildings are distribution centers, Canopies, Factories, Bridges and so on.

Segments of PEB: Pre Engineered Buildings comprise diverse steel structural part which are as per the following,

1. Primary Frame: Primary surrounding of a PEB is a gathering of built up I-Shaped steel individuals and encircling brackets or castellated beams and so forth.
2. Secondary Structural Elements: It is really Cold Formed Members, which can be in diff. shapes like "Z", "C" and so forth. As a rule known as "Purlins".
3. Roof and Wall Panels : Tin conceals and Curtain Wall made of Glass and Roll-shaped steel sheets typically comes in this class.
4. Sandwich Panels: Sandwich Panel is made of three layers , in which a non-Aluminum Core is embedded b/w two aluminum sheet.
5. Different Accessories: Mezzanine floors, Bolts, Insulation, and so on.



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Published By
Rajib Dey
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Advantages and Disadvantages of On-site and Off-site Construction

The needs and restrictions at your construction project may make you choose between one of the two main methods of construction: on-site and off-site. Both are widely used in today’s construction industry, depending upon the requirements at the site and according to design.

What is On-Site Construction?
On-site construction is the more traditional method. Here, structures are assembled from raw materials at the site itself, hence the name. The method has to be carried out sequentially and materials needs to be stored and used at the site.

What is Off-Site Construction?
With modern technologies, off-site method of construction has become possible. In this, parts or blocks of the structure are constructed in a designated factory or yard in standardized process. Then, these pre-built blocks are carried to the project site where they are assembled together to form the structure.

Both of the above methods have their own advantages and disadvantages, which make them suitable to different scenarios. Let’s discuss them below.

On-Site Construction

Advantages:

1. Customized Design: Since there is no restriction on what shape of objects are available of construction, there are limitless customization options in this manner. In fact most non-standard designs have to rely upon the on-site method just for this.
2. Alteration: After the construction you can easily modify the structure with this method. It doesn’t require you to depend upon third-party construction factories to add or change a room in your house that has been constructed in the traditional method.
3. Space-friendly: Transporting precast blocks in tight urban areas can get simply impossible. More often, it’s prohibitively expensive. In these scenarios you have no choice but to construct everything on-site.

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Rajib Dey

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Construct Earthquake Resistant Buildings by Simple Means

The engineering science is continuing to advance in response to seismic threats. There have been significant breakthroughs in the field. However, most of them are very complex and require exceptional machinery. Not to mention, expensive as well. However, there are some simple ways to build a structure that will be resistant to earthquake damages up to a certain level.

In areas where seismic activity is not too harsh, we can utilize these techniques to same money and complexity but make the building resistant to seismic activities.

Structure Stiffness: The most traditional way to fight quakes is to use stronger materials to construct the building. Stiffer or heavier members can be used to fight the lateral forces generated during seismic activities. For special quake-proof structures, ACI codes prescribe at least 10” thick members.

Geometrical Absorption: The building can be planned in such a regular and special geometrical shape that it disperses the seismic forces evenly so that no particular member experiences excessive force. This naturally fares much better than a poorly-planned unsymmetrical building.

For existing buildings that are structurally asymmetrical, you can use seismic joints and expansion points in places where the forces are dispersed unevenly. Providing extra columns, shear walls, and framing can make the weaker section withstand the extra forces to a good level. Parking levels should have extra reinforced columns in order to negate the soft story effect.

Lateral Force Resistance: Using three types of lateral force resisting systems, we can try to negate much of the seismic forces. These are:

1. Moment Resisting Frame System: it is designed to resist all types of earthquake generated forces acting on the structure. They can be customized to fit the seismic activity scale of the region.

2. Building Frame System: these are designed to resist gravitational loads only, but they function excellently in that. A shear wall is added to resist the lateral forces acting on structure.

3. Dual Frame System: this is a combination of the above two systems. Shear walls along with moment resisting frames work excellently to fight off the vibrations and displacements from an earthquake. But, of course, they are more complex and costlier to build.

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Types of Foundations in Construction Industry

Today, we shall talk about the common sorts of foundations in buildings. Generally, all foundations are divided into 2 categories: shallow and deep. The words ‘shallow’ and ‘deep’ check with the depth of soil during which the inspiration is created.

Shallow foundations may be created in depths of as very little as 3 feet, whereas deep foundations may be created at depths of sixty – 200 feet. Shallow foundations are used for little, lightweight buildings, while deep ones are for giant, serious buildings. The following sorts of Foundations In Building Construction may be elaborated below.

Raft or Mat Foundations: Raft Foundations, conjointly referred to as Mat Foundations, are most frequently used once basements are to be made. In a raft, the complete basement floor block serves as the foundation; the burden of the building is unfold equally over the entire footprint of the building. it's referred to as a raft as a result of the building is sort of a vessel that ‘floats’ in an exceedingly ocean of soil.

Mat Foundations are used wherever the soil is weak, and thus building hundreds have to be compelled to meet an oversized space, or wherever columns are closely spaced, which suggests that if individual footings were used, they might hit one another.

Shallow Foundations: Shallow foundations are referred to as unfold footings or open footings. The ‘open’ refers to the very fact that the foundations are created by 1st excavating all the planet until all-time low of the footing, so constructing the footing. Throughout the first stages of labor, the complete footing is visible to the attention, associated is so referred to as an open foundation.

The concept is that every footing takes the focused load of the column and spreads it out over an oversized space,so that the particular weight on the soil doesn't exceed the safe bearing capability of the soil.

There are many forms of shallow footings: individual footings, strip footings and raft foundations.

In cold climates, shallow foundations should be protected against freezing. This can be as a result of water within the soil round the foundation can freeze and expand, thereby damaging the inspiration. These foundations ought to be engineered below the frost line, that is that the level within the ground higher than which freeze happens.

If they can't be engineered below the frost line, they must be protected by insulation: commonly a touch heat from the building can permeate into the soil and forestall freeze.

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Industrial Roof Trusses: Understanding and Designing

The industrial buildings such as godowns and factory floors are often low rise structures with few or none internal walls. In such buildings, special Care needs to be taken while designing industrial roof trusses, since large spans need to support the entire roofing system without intermittent support. Trusses with roof covering materials make up of the entire roofing assembly here.

What are Trusses?
Trusses are triangular formation of metal sections, usually used to span large lengths in space instead of solid girders. The external load apply mostly axial forces on the members in a truss. Depending upon how the force is applied, trusses can be designed in the following two ways:

Plane Trusses: where the external load is placed on the plane of the truss.

Space Trusses: where the external load can be applied to any three-dimensional space within.

How are Trusses Built?
Trusses mostly consist of axially loaded members to support loads. The reason for this that when steel members are subjected to axial forces, they perform better in bearing that load, than members that are in flexure. This is because the cross-section of such a system is uniformly stressed under axial forces.

Trusses are very common in most architecture. Mostly used to span long distances, they are well suited to bear the load of single-storey industrial buildings. They can also be designed to bear gravity loads in long span floors. For the same reason they are also mounted to bear loads of long span bridges.

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Case Study: Vista Tower, Chicago

The construction business in Chicago has always been successful, to say the least. The city hosts major buildings and modern landmarks, as well as widespread infrastructure expansions and land developments in the outskirts of the prestigious city. By analyzing and understanding some of the biggest projects in the city, completed or ongoing, we can realize the technology and the efforts that went into developing them. This is called case studies, which are one of the best ways to understand the construction industry overall.

Today we will look into the construction of the Vista Tower in Chicago. Located at 363 East Wacker Drive, Chicago, Illinois, the construction of this megaproject is still going on and is scheduled to finish by 2020. This is going to be the third tallest building in Chicago after the Willis and Trump Towers.

The official name of the complex is Lakeshore East, and it will host a mixed-use building with both residential and hotel usage. The Vista Tower is supposed to be 101 stories tall at 1198 feet (365 meters), and it will be divided into three buildings respectively of 47, 71, and 93 stories. The building was designed to contain 406 condos and 210 hotel rooms under the Wanda Vista five-star hotel.

Designed by Jeanne Gang, the Vista Tower is being constructed by the Magellan Development Group and the Wanda Group, who are going to pump in nearly a billion dollars into the project. Point to note here that when completed, the Vista Tower will become the world's tallest structure designed by a female architect.

The Tower's proximity to the Chicago River and Lake Michigan's lakefront park system will allow the building to define the skyline with a high level of prominence. The brilliantly imagined vertically stacked frustums (pyramids with the tops cut off) made of reinforced concrete will be adorned with a flowing glass facade, colored in gradients. The building will have 19 such frustums (at most) with spandrel covered floor slab edges, which is expected to create a unique visual texture for the outer skin.

The tower being so tall, may fall victim to wind-induced swaying. To prevent this, seven water-filled tanks are placed atop the tower. When the building is pressed by the wind to sway is a certain direction, the water in the tanks will slosh in the opposite direction which in turn will offset the swaying effect. Also, since this is not enough to prevent high powerful winds exerting more power on the building sides, there will be a large "blow-through floor", the first of its kind in Chicago, near the top of the tower which will let these winds through.

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Details about structural and non structural defects in buildings

Concrete has diversified nature. It casts in place by including or excluding reinforcement. It is also precast or pre-stressed to attain necessary strength. For this purpose, there should be adequate knowledge on the behavior and constituents based on which the concrete is produced.

There should not be any type of laxity in any of its phase like placement, design & maintenance as these can create deterioration and resist concrete to accomplish its proposed functions. Given below, some vital factors which can weaken the quality of concrete:

1. Accidental loading
2. Chemical reaction like sulfate attack, alkali carbonate reactions, alkali silica reactions etc
3. Erosion of steel reinforcement
4. Inferior construction detailing

5. Erosion
6. Freezing and Thawing
7. Shrinkage
8. Settlement
9. Fire and weathering

Flaws in Building Design: Due to deficient structural design, the concrete is uncovered to flexural and shearing stresses and as a result spalling and cracking of concrete are developed. Any sudden modification in cross section of any member can result in raising the stress concentration in that member that leads to cracking of concrete.

Deflection is considered as one of the significant part in structural design. If there exist any issue in its consideration throughout design, that can produce cracking of concrete. Insufficient arrangement of drainage and expansion joints throughout the design also leads to deterioration and spalling of concrete.

Flaws During Construction: Flaws throughout building construction vary from inappropriate mixing, placing and curing of concrete. Detachment of shoring & formwork can also produces cracks in concrete.

When extra water is provided in concrete to enhance the workability of concrete, the water cement ratio is raised significantly and it can reduce the strength of concrete. Inappropriate alignment of formwork produces corrosion in concrete.

Structural Defects in Building Construction - The following structural defects are found in buildings:

1. Cracks in foundation (substructure)
2. Cracks in floors and slabs (superstructure)
3. Cracks in Walls (superstructure)

These above defects are occurred due to the following factors:

1. Inappropriate soil analysis
2. Inappropriate site selection
3. Application of defective materials
4. Inferior work

These structural issues can be resolved with perfect design and planning.

Non Structural Defects in Building Construction - The following non structural defects are common in buildings:

1. Defects in brick work
2. Dampness in old structures
3. Defects in plaster works

So, it is found that minimum design and construction defects lead to minor cracking or spalling which can weaken the concrete and result in collapsing of the structure. To get rid of these issues, proper care and attention should be taken in designing, detailing and construction of concrete structure.

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Commonly used Indian Standard Codes (IS codes) for civil engineers

IS stands for Indian standard. Each country possesses their own code book identical to that India contains IS code book for RCC, steel structure. The IS codes includes numerous standards and methodology for construction, raw material used, structural analaysis and other provisions.

It comprises of some data based on which a civil engineer design the structure. It contains some pre defined formulae and data.

Civil engineers who perform construction activities of big projects generally should be well versed with a wide array of IS codes since such projects require different types of construction materials in several structures like buildings, roads, steel structures, all sorts of foundations etc.

Given below, detailed lists of some IS codes which are extensively used by construction engineers.

IS 456:2000: Plain and Reinforced Concrete - Code of Practice (Download link bit.ly)

IS 383:1970: Specifications for fine & coarse aggregate from natural sources for concrete (Download link drive.google.com)

IS 2386 (Part I) 1963: Methods of Test for Aggregates for Concrete, Part I: Particle Size and Shape (Download link drive.google.com)

IS 2386 (Part II) 1963: Methods of test for aggregates for concrete, Part II: Estimation of deleterious materials and organic impurities (Download link drive.google.com)

IS 2386 (Part III) 1963: Methods of test for aggregates for concrete, Part 3: Specific gravity, density, voids, absorption and bulking (Download link drive.google.com)

IS 2386 (Part IV) 1963: Methods of test for aggregates for concrete, Part 4: Mechanical properties (Download link drive.google.com)

IS 2386 (Part V) 1963: Methods of Test for Aggregates for Concrete, Part V: Soundness (Download link drive.google.com)

IS 2386 (Part VI) 1963: Methods of test for aggregates for concrete, Part 6: Measuring mortar making properties of fine aggregates (Download link drive.google.com)

IS 2386 (Part VII) 1963: Methods of Test for Aggregates for Concrete, Part VII: Alkali Aggregate Reactivity (Download link drive.google.com

IS 2386 (Part VIII) 1963: Methods of Test for Aggregates for Concrete, Part VIII: Petrographic Examination (Download link drive.google.com)

IS 2430-1986: Methods for Sampling of Aggregates for Concrete (Download link drive.google.com)

IS 4082-1996: Recommendations on stacking and storage of construction materials and components at site (Download link drive.google.com/)

IS 2116-1980: Sand for masonry mortars – Specifications (Download link drive.google.com)

IS 269-1989: Specification for Ordinary Portland Cement, 33 Grade (Download link drive.google.com)

IS 8112-2013: Specification for 43 grade ordinary Portland cement (Download link drive.google.com)

IS 12269-1987: Specification for 53 grade ordinary Portland cement (BI-LINGUAL) (Download link drive.google.com)

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Some vital guidelines for measuring staircase dimensions and designs

A staircase mainly includes a series of steps which involve a tread (the horizontal portion, where the foot stands) and a riser (the vertical portion).

In every step, there are one or more landings, handrails, and a small nosing. The latter obtrudes from the tread over the lower step, facilitating to raise its size devoid of inclusion of centimeters to the overall dimensions of the staircase.

By using the following formula, find out the exact dimensions of a convenient and efficient staircase in accordance with its use.

2 Risers + 1 Tread = 63-65 cm

The required space to attain these optimal dimensions is unavailable sometimes, but it's suggested to approach them as much as possible.

A schematic illustration of a steep and low-transit staircase.

(2 x 21) + (1 x 21) = 63 cm

A schematic illustration of an optimal staircase.
(2 x 18) + (1 x 28) = 64 cm

A schematic illustration of a loose staircase, desirably for exterior application.
(2 x 13) + (1 x 39) = 65 cm

Sample measurement of a staircase that should be 2.60 meters high.

1. Workout the required number of steps - Assume an ideal riser of 18 cm, the height of the space is divided with the height of each step. The result should always be rounded up:
260/18 = 14.44 = 15 steps

2. Workout the height of every riser - The height of the space is divided with the number of steps already acquired:
260/15 = 17.33 cm height for each riser.

3. Workout the width of the tread - It can be calculated with the following formula:
(2 x 17.33 cm) + (1 x tread) = 64

Each tread will be computed as 29.34 cm

The consequential staircase will contain 15 steps of 29.34 cm of tread and 17.33 cm of riser.

Based on the use and local regulations, there should be a minimum width of 80 cm for stairs in single-family homes, and more than 1.00 meters in public buildings.

Preferably, a stairway shouldn't contain in excess of 15 steps in a row. After 15 steps, a landing should be arranged. It's suggested that a landing is calculated minimum the same as 3 treads.

The height among the steps and the ceiling should remain 2.15 meters at minimum. The height of the handrail differs among 80 and 90 cm from each step.

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Common thumb rules for civil engineering works

Thumb Rules is very important for any civil engineer, Site engineer or civil supervisor to obtain instant decisions on the construction site. By applying thumb, the engineers can get the solution with a simple mathematical formula and take proper decisions wherever required. Before applying these thumb rules, it should be kept in mind that the thumb rule can only provide fairly accurate results never the correct results.

The following types of thumb rules for civil engineers are commonly used in construction work :-

Thumb rule for measuring the Concrete Volume relating to the area:
The volume of concrete necessary = 0.038 m3/square feet area.

As for instance, if Plan Area = 40 x 20 = 800 Sq. m., total necessary volume of concrete will be as follow :-
= 800 x 0.038m3 = 30.4m3

Thumb rule for Steel quantity necessary for Slab, Beams, Footings & Columns:
Essential quantity of steel in residential buildings = 4.5 Kgs – 4.75 Kgs / Sq. Ft.
Essential quantity of steel in commercial buildings = 5.0 Kgs-5.50 Kgs/Sq. Ft.

Thumb Rules For Civil Engineers recommended by B N Datta for the Steel quantity that will be applied for several members of the building :-

Proportions of Steel in Structural Members:

1) Slab – 1% of the total volume of concrete
2) Beam – 2% of the total volume of concrete
3) Column – 2.5% of total volume of concrete
4) Footings – 0.8% of the total volume of concrete

As for instance, suppose the length, width and depth of the slab are 5m, 4m and 0.15m. Now, the quantity of steel for the slab will be computed as follow :-

Initially, it is required to work out the concrete volume.
The total volume of concrete for the slab = 5x4x0.15 = 3m3

Secondly, work out the quantity of steel with formula as follow :-
Based on the guidelines provided in B. N. Dutta reference book, the quantity of steel in slab is 1% of the total volume of concrete used.
Thumb rule to work out the quantity of steel in above slab = Volume of concrete x density of steel x % of steel member.

The weight of steel necessary for above slab = 3x7850x0.01 = 235 kgs

To make perfect calculation, use bar bending schedule.

To learn how thumb rules are applied to calculate the shuttering area and the quantity of cement, sand, course aggregate in several grades of concrete, click on the following link civiconcepts.com

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Benefits of I-beams in construction

Hot-rolled steel beam having I-shaped cross section, and tapered flanges closer than wide flanged beam is known as I-beam.

I Beam contains one vertical plane and two horizontal planes or flanges which develop 'I' or 'H' structure. The vertical plane withstands the shear stress , whereas horizontal planes withstand the bending movement. I Beam is majorly utilized in construction industry like construction of manufacturing plants, multi-story buildings etc.

I-beam is frequently applied as important support trusses, or the primary framework, in buildings. Steel I beams retain structure’s integrity with persistent strength and support. The extreme power of I beams minimizes the requirement for several support structures and as a result huge time and money is saved. The stability of the structure is improved considerably.

Some vital jargons of I-Beam:

1. Flange thickness: Top and bottom horizontal plate-like segments of an I-beam are known as flange. The density of the flanges is defined as the flange thickness.

2. Flange width: The width of the flanges is known as flange width.
3. Beam depth: The height among the top and bottom surface of the steel I beam is termed as beam depth.
4. Web thickness: The vertical segment of steel I beam is known as web, and the thickness of the web is termed as web thickness.
5. Fillet radius: The curved section, where the changeover among the web and flange occurs is known as a fillet. The radius of the fillet is defined as the fillet radius.

A properly sized I Beam can be chosen on the basis of the following criterion :-

The entire method of choosing the proper size of the I beam is dependent on the basic mechanical design calculations as given below:

1. The first input necessary belongs to the steel I beam load specifications or loading details on the steel I beam.
2. Draw bending moment diagram for the specified loads and get the value of maximum bending moments (suppose M) that the steel I beam is likely to experience.
3. Select an exact size of steel I beam from a standard I beam table.
4. Determine the area moment of inertia (suppose I) of the selected steel I beam.
5. Obtain the beam depth (suppose d) of the selected steel I beam.
6. The stress developed (f) in the beam can be measured with the formula given below :

f/(d/2)=M/ I

f denotes the bending stress.
M denotes the moment at the neutral axis.
y denotes the perpendicular distance to the neutral axis.
I denotes the area moment of inertia about the neutral axis x.

7. Compare the calculated value of the bending stress with the yield stress of the steel with the purpose of verifying the safety factor of your design.

The structural design will be perfect when the size of the I-beam is accurate. The method described above is dependent on static I beam load specifications. In case where dynamic loads are concerned, it is necessary to apply FEA tools like ANSYS, Pro Mechanica, etc.

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Impacts of earthquake on structures

Earthquake produces severe damages to the structures. For this purpose, thorough knowledge about the seismic effects on a structure is required. The designers and contractors should be capable of analyzing the effect of seismic forces on buildings to adopt protective measures against failures and collapses.

When earthquake strikes on structures, it develops damaging inertia forces which lead to deformations as well as horizontal and vertical shaking.

Given below, detail explanation about these effects :-

Impacts of Earthquake on Structures

1. Inertia Forces in Structures: The formation of inertia forces in a structure refers to one of the seismic influences that adversely damage the structure. When ground shaking occurs due to earthquake, the base of the building proceeds but the roof remains motionless. As the walls and columns are connected with it, the roof is pulled by the base of the building.

The susceptibility of the roof structure to stand at its original position is known as inertia. The inertia forces lead to shearing of the structure that can consolidate stresses on the fragile walls or joints in the structure causing failure or perhaps total collapse. Lastly, more mass signifies greater inertia force and due to this lighter buildings can resist the earthquake shaking efficiently.

2. Impact of Deformations in Structures: When a building undergoes earthquake along with ground shaking, the base of the building proceeds with the ground shaking. But, the roof movement varies from that of the base of the structure. This variation in the movement produces internal forces in columns and as a result the column goes back to its original position.

These internal forces are known as stiffness forces. The stiffness forces become greater when the sizes of columns are raised. The stiffness force in a column belongs to the column stiffness times the relative displacement among its ends.

3. Horizontal and Vertical Shaking: Earthquake contributes to shaking of the ground in all the three directions X, Y and Z, and the ground shakes indiscriminately from side to side along each of these axis directions. Normally, the purpose of designing the structures is to resist the vertical loads in order that the vertical shaking resulting from earthquakes (either adds or subtracts vertical loads) is controlled through safety factors provided in the design to sustain vertical loads.

However, horizontal shaking along X and Y directions is dangerous for the operation of the structure as it develops inertia forces and lateral displacement and consequently sufficient load transfer path should be arranged to resist its detrimental influences on the structure.

Exact inertia force transfer path is formed through adequate design of floor slab, walls or columns, and connections among these structural components. It should be noted that the walls and columns are vital structural components in transmitting the inertial forces. The masonry walls and thin reinforce concrete columns create weak points in the inertia force transfer path.

4. Other Effects: Due to earthquake various other effects may occur which range from liquefaction, tsunami, and landslides. These belong to the indirect effects of strong earthquakes that can lead to significant devastation.

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Some useful tips to eliminate the deficiencies of the reinforced concrete shear walls

Reinforced concrete shear walls are considered as perfect structural systems for a long time which offer both lateral resistance and drift control in RC buildings.

However these aging shear walls were normally designed for combined actions against gravity loads and wind loading. Seismic loading and design were not taken into consideration for day to day mid-height building structures.

There are lots of shortcomings in design and detailing of these shear walls and because of these, the shear walls become susceptible to seismic hazard.

General shortcomings of Thin Reinforced Concrete Shear Walls :-

The following shortcomings are mostly found in several existing buildings:

• Deficient wall thickness containing only one curtain of distributed horizontal and vertical reinforcement;
• Deficient lap splice lengths of the longitudinal reinforcement;
• lap splices are situated in the zones of potential plastic hinging;
• Insufficient confinement of the end regions of the walls;
• Deficiency in controlling the buckling of the flexural reinforcement;
• Inadequate amounts and defectively detailed transverse (shear) reinforcement.

Points to be followed for improvements:

To improve the condition of these defective walls, various repair and retrofit schemes should be undertaken.

The details of these schemes are given below:

Carbon-Fiber Reinforced Polymer (CFRP) wraps:

Under this method, the shear wall is covered with a layer of CFRP sheet. This layer makes the confinement better around the boundary elements to some extent. As this confinement effect is nominal, it enhances the ductility of the section, and prevents brittle failure of lap splices.

Fibre-Reinforced Self Consolidating Concrete Jacketing

A combination of steel fibers and reinforcement are applied to enhance the flexural strength of concrete section, and the simultaneously, increases the ductility of the wall to the new plastic hinge location.



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