The fundamentals of setting up Post-Tensioning Slabs

Construction of post-tensioned slabs on grade is equivalent to apply reinforcing steel, devoid of the tensioning step.

Cables are set up as per instructions of the engineer and placed to go over the center of the slab. For residential construction, tendons at 48 inches on center are generally accepted. Commercial foundations will contain much more steel. Tendons are routed around obstructions smoothly.

Generally, a residential post-tensioned concrete slab should have been 8 inches thick with 3000 psi concrete. As soon as the concrete achieves strength to 2000 psi, normally within the 3 to 10 days as suggested by PTI, the tendons are stressed.

Now-a-days, tendons are seven high-strength steel wires wound together and arranged inside a plastic duct. A PT anchor is situated at each end and these are found in pockets which are implanted into the slab edge. As soon as the strands are stressed, the wires are expanded —about 4 inches for a 50 foot strand—to employ 33,000 pounds of load.

The qualified workers should be appointed for doing stressing. Once the stressing is completed, the tendon is cut off and the pocket in which the anchors are situated is filled with grout to defend then against corrosion.

Bigger structural concrete members may also be post-tensioned, particularly in bridges and floors and beams in parking structures. The process is equivalent to that applied for slabs, with the exception of a bigger scale. The tendons will frequently be “draped” in order that they are low at the midpoint of a beam and high at the supports—this arranges the steel at the point of highest tension where it can retain the concrete to be remained together firmly.

With structural members the duct is frequently grouted full following stressing to tie the strand to the concrete along its entire length—these are known as bonded tendons. Unbonded tendons are mostly found in residential slabs and stay free to progress within the duct and are safeguarded from corrosion with grease.

The position of PT tendon and stressing is normally performed with companies with certified workers having expertise in this type of work.

For more information, read the following construction article concretenetwork.com

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Published By
Arka Roy
http://www.constructioncost.co
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Variations among Plinth Area and Carpet Area

In this construction video tutorial, you will come to know the variation among carpet area and plinth area as well as types of area included and excluded in carpet and plinth area.

Carpet area means the actual utilized area of a building. Floor area is similar to carpet area. Built up Area is the carpet area along with the width of outer walls and the balcony.

Super Built Up Area means the built up area along with the proportional area of common areas like the lobby, lifts shaft, stairs, etc. Generally, carpet area is 75% of super built up area.

Plinth Area or Built-Up Area means total covered area of the building unit. It is measured by adding areas of utility ducts surrounded by property unit, internal and external walls to the carpet are. It covers 10 to 20% more area from carpet area.

In carpet area, included items are all rooms, kitchen and bathrooms, store and balconies and excluded items are porch, lift, corridor etc.

In plinth area, included items are carpet area, internal & external walls, cover of stairs, porch excluding cantilever and excluded items are balconies, curvature of building (curves & sheds to enhance the look of the buildings) etc.

To get more clear ideas, go through the following construction video tutorial.

Read more

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Published By
Arka Roy
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Some useful points to consider for choosing a career in quantity surveying profession

The Quantity Surveyors are employed to manage the finances and contractual administration of Construction projects. Given below, some useful points which should be considered to make a good career in quantity surveying profession.

The Quantity Surveyors provide significant contribution for the successful completion of projects from one small project to multi billion euro capital projects.

They possess sound knowledge regarding the contract and project cost, right from the preliminary sketch design proposal in order that the clients can obtain the best possible end product for their budget.

Quantity surveyors can render their specialized services for both the clients and the contractors meaning so it is possible to manage the office based work and construction site based work simultaneously. In either career path each day makes a new challenge and the job satisfaction that comes by involving in a project right from its setting up through to a happy client taking the possession of the building over on execution.

In the Quantity Surveying profession, one can get a good salary as compared to the average industrial wage (check average national wage for a Chartered Surveyor published by the SCSI)( www.scsi.ie). Besides, there are exciting commensurate perks which fluctuate on the basis of the employer. It also contains company cars, group pension schemes, performance based incentives etc.

The profession of Quantity Surveying is acknowledged globally and is in high demand. You can make yourself prepared to work for the larger consultancies and contractors who have offices in the UK, Europe, the Middle East and the Americas. Here, the staff can easily take transfer and obtain the most of the perks and life experience that coincide with travel (you can of course just join companies in these countries directly too). It provides a healthy salary that goes with the cost of living in every one of these countries facilitating the graduates to keep up the standard of living they generally maintain. This capability to travel also makes sure that there are sufficient works for these construction professionals.

Besides men, women can also make a sound career in quantity surveying profession. Quantity Surveyors are professionals first and foremost and, specifically for those who perform on the client side, holds much similarity to the office based 9 – 5 career you should anticipate in other disciplines like finance and business but with the additional perk of working on physical projects with long-term and profound effect on the landscape of the country.

For more information, go through the following article www.wit.ie

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Published By
Arka Roy
http://www.constructioncost.co
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Tips to compute the quantity of cement, sand and aggregate in concrete & water cement ratio

In this construction video tutorial you will learn how to work out the quantity of cement, sand and aggregate in concrete and water cement ratio.

To do it, you should have clear conceptions on the following items :-

Grades of concrete Mix Ratio

M10 – 1:8:6
M15 – 1:2:4
M20 – 1:1.5:3
M25 – 1:1:2

Here, M means Mix and number means the compressive characteristics strength of concrete in 28 days.

Water Cement Ratio :- Grade of cement Water per bag (50 kg) cement (weight of 1 bag cement is 50 kg)

M5 – 60 litre
M7.5 – 45 litre
M10 – 34 litre
M15 – 32 litre
M20 – 30 litre

For calculation purpose, wet volume of concrete = 1 m3

Dry volume = 54% increase by weight volume
Wet volume = 100% + 54% = 154%
In order to covert it to numbers, just divide by 100
154/100 = 1.54

So, dry volume is 1.54 x wet volume
Now, you have to provide the density of cement, fine aggregates and course aggregates as follow :-
Cement = 1440 Kg
Fine Aggregate = 1450 to 1600 Kg/m3
Course Aggregate = 1450 to 1500 Kg/m3

Now, on the basis of the above dimensions, you can start calculation for the different grades of concrete. To know the detailed calculation process, watch the following video tutorial.

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Published By
Arka Roy
http://www.constructioncost.co
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Prestressed Girder SUPERstructure design and analysis

It is powerful open source software that is used for designing and analyzing of precast-stress free girder bridges and can handle easily. It allows creating models in a simple way and continuously stretches structures and designs as per with the AASHTO LRFD Bridge Design Specifications.

It also has advanced Bridge Information Modeling or BrIM capabilities that help users to keep focused continuously on modeling, designing and analyzing real bridges.

PGSuper examines and designs formed girders for every critical stage such as: casting, lifting, carrying, building, service and final conditions. The automatic designer fixes the prestressing, solid strength, lifting, transportation and slab side requirements and this software has the broadest and detailed reports and every detailed calculation can be reviewed.

PGSuper 2.8.2 is created by the Washington State Department of Transportation’s Bridge and Structures Office and licensed under the Alternate Route Open Source License. The software file size is about 24.09 MB and works with the Windows only and is free to be used and can be modified by all; but it is not the most capable precast girder bridge design program. This software is mainly designed by Bridge Engineers to use n high-production design environments and supports a huge order of parametric shapes and has user defined filament, reinforment and stirrup layouts.

Here are some design specifications of PGSuper, such as:

• Has AASHTO LRFD 1998-2008
• It rectify all suitable specifications
• It is very much configurable

• Comes with User Input Stress Limits
• Can computed and has User-Input Distribution Factors
• Also has User-Input LRFD Load Modifiers
• Have five methods of Loss Calculations.

There is some other software that has the same features like PGSuper and here are some descriptions about them:

1. PGSPLIC 1.0: It is joined girder analysis software of Washington State Department of Transportation and has been developed for the Alternate Route Project.
2. BRIDGELINK 3.0: BridgeLink is an integrated bridge engineering software tool for analysis, design and load rating.
3. RSPBR2 1.3: It is a plane frame structural analysis program for supporting bridge engineers in design and checking beam bridges.

4. QCONBRIDGE 4.3.2: it is a live road analysis program to continuous bridge frames.
5. BARLIST: This program is used for calculating the weight of steel reinforcement bars which is used in a bridge structure and for assisting in the creation of barlist drawings for bridge project contract plans.
6. PSGSIMPLE: it is a spreadsheet that performs prior analysis of a precast prestressed bridge girder at the prestress transfer and service stages.

To gather more information, go through the following construction article pgsuper.com

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Published By
Arka Roy
http://www.constructioncost.co
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Brief information on Project Cost System

If the design is modified at the design stage of a construction project, the project costs are constantly estimated and evaluated to keep the project costs within the budget of the owners. This working budget is normally known as the engineers or architects estimate. As soon as the design is completed, the field cost-control system is prepared with a final, detailed cost estimate of the total work.

This type of cost estimate is generally created by the construction contractor or another party who will be directly associated with the field operations. The contractor estimate is then abridged to a working construction budget and develop the foundation of the construction cost control system.

While the construction process is going on, cost accounting methods are utilized to recover actual construction expenses from current construction operations. This information is then applied for the purpose of controlling the cost on the current project and for working out the cost of future projects. Besides, the cost system offers significant information related to project financial control.

Preliminary Cost Estimates: Preliminary estimates of future construction expenses, are prepared throughout the project planning and design stages on the basis of approximation because these are accumulated prior to define the project entirely. This type of conceptual estimates differs from ascertaining the final detailed estimate of construction costs.

Basically, all conceptual price estimates are prepared on the basis of some system of gross unit costs which are acquired from earlier construction work. These unit costs are guessed forward in due course to focus on present market conditions, project location as well as the specific character of the job currently being considered. The following methods are followed to make preliminary estimates.

Cost per Function Estimate: This analysis is produced on the basis of the estimated expense per unit of use, like cost per patient, student, seat, or car space.

Construction expense may also be guessed like the average outlay per unit of a plants manufacturing or production capacity. These factors are normally applied as a method of instantly characterizing facilities costs at the setting up of a project when there is only raw marketing information, like the number of patients retained by a planned hospital. This extensive method of producing costs can also provide a powerful control on more detailed estimates as soon as they are created.

Index Number Estimate: This method is applicable for working out the price of a projected structure by upgrading the construction cost of the same type of current facility. It is performed by multiplying the original construction cost of the current structure with a national price index that is modified as per local conditions, like weather, labor expense, materials costs, transportation, and site location. A price index refers to the ratio of current construction cost to the original construction outlay for the type of structure concerned. Various types of price indexes are available in different trade publications.

Unit Area Cost Estimate: Under this type of method an approximate cost is selected with an estimated price for each unit of gross floor area. The method is found extensively in building and residential home construction. It offers a perfect rough calculation of costs for structures which are standardized or contain a large sampling of historical cost information from equivalent structures. This type of estimate is frequently applied in the industry to tally the relative value of different facilities.

To gather more information, go through the following construction article onlinecivilforum.com

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Published By
Arka Roy
http://www.constructioncost.co
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Use and benefits of self compacting concrete

Self-consolidating concrete alias self-compacting concrete (SCC) is a concrete mixture that can flow into very complex forms with various reinforcing bars (rebar congestion) and leaves no voids.

It can be arranged with its own weight devoid of any mechanical vibration. SCC retains all the conventional mechanical and durability characteristics of concrete.

With extremely fluid nature of SCC, it becomes possible to arrange it in complicated conditions and in sections with congested reinforcement. It can also reduce hearing-related damages on the worksite due to vibration of concrete. In SSC, the required time is curtailed significantly for arranging bigger sections.

In some cases, the superplasticizers and viscosity modifier are provided to the mix to minimize bleeding and segregation.

A well designed SCC mix never segregates because it contains extreme deformability and outstanding stability characteristics.

Self-Compacting Concrete Properties: Self-compacting concrete has good resistance capacity against segregation as it applies mineral fillers or fines as well as special admixtures. Self-consolidating concrete is essential to flow and fill special forms under its own weight. It is flown adequately to travel over extremely reinforced areas, and should have capability to circumvent segregation of aggregate.

Self-compacting concrete contains an equivalent water cement or cement binder ratio that provides normally a slightly higher strength with regards to conventional vibrated concrete and because of non-existence of vibration, a better interface among the aggregate and hardened paste is created.

The concrete mix of SCC should be arranged at a comparatively greater velocity as compared to regular concrete. Self-compacting concrete is placed from heights longer than 5 meters exclusive of aggregate segregation. It is also useful for areas having normal and congested reinforcement, with aggregates as large as 2 inches.

Self-Compacting Concrete Uses – Self-compacting concrete is mostly utilized in bridges and even on pre-cast sections. This type of concrete is suitable for the following:

• Drilled shafts
• Columns
• Earth retaining systems
• Areas with high concentration of rebar and pipes/conduits

To know about the benefits of self consolidating concrete, go through the following link thebalance.com

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Published By
Arka Roy
http://www.constructioncost.co
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Benefits and drawbacks of steel members

Steel is formed by mixing iron, carbon and other components. Due to its extreme tensile strength and low cost, it is considered as a most vital component that is extensively utilized in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons.

The steel provides lots of benefits as follows:

1. The steel members contain high strength. So, the steel members have the ability to withstand extreme loads with relatively light weight and small size of members.
Due to their small size, it becomes easier to deal with and transport steel members.
2. The steel members have strong resistance capacity against gas and water due to their high density power (the unit weight of steel is 7.85kN/m3).
3. The steel members last for prolonged periods due to great and standardized strength and density properties of steel.
4. The steel members are utilized as pre-fabricated members as they can be easily managed, fabricated and constructed.
5. The steel members can be easily disassembled or substituted.
6. The supplementary sections or plates can be added with the existing steel structure and structural components to improve the strength significantly.
7. The steel structures can be examined rapidly and smoothly.

8. It may be reprocessed / recycled in furnaces.
9. This material contains high ductility and it is very effective for earthquake resistance structures.

The drawbacks of steel members are as follows:

1. The steel members are vulnerable to corrosion. To get rid of corrosion, apply painting or other methods.
2. The steel members are expensive.

Source: civilsnapshot.com

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Published By
Arka Roy
http://www.constructioncost.co
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Post Tension Slab and its benefits

Generally, post-tensioned (PT) slabs belong to flat slabs, band beam and slabs or ribbed slabs. PT slabs provide the leaner slab type, as concrete functions to its strengths, mostly being maintained in compression. Longer spans are obtained because of pre-stress, which are also utilized to resist deflections.

Post-tensioned slabs employ high-strength tensioned steel strands to compress the slabs to retain most of the concrete in compression. Reinforcement is arranged to control the compression.

In Post tension slab, the cables/steel tendons are applied to replace the reinforcement. It develops a very well-organized structure to reduce material usages as well as economic span range with regard to reinforced concrete.

Post-tensioning is very useful to defeat the natural weakness of concrete in tension and to optimize its strength in compression. In concrete structures, high-tensile steel tendons/cables are placed in the element prior to casting.

If the concrete attains the preferred strength the special hydraulic jacks are used to drag tendons and retain them in tension with specially designed anchorages fixed at each end of the tendon. It offers compression at the edge of the structural member that enhances the strength of the concrete for withstanding tension stresses.

If tendons are properly curved to a specific profile, they will employ, besides compression at the perimeter, a beneficial upward set of forces (load balancing forces) that will resist applied loads, alleviating the structure from a portion of gravity effects.

In this type of slab, cables are attached in spite of reinforcement. In Steel reinforcement the gapping among bars is 4 inch to 6 inch while in Post tension slab the gapping is over 2m.

Benefits:

• It facilitates slabs and other structural members to be slimmer
• It facilitates us to develop slabs on expansive or soft soils
• The produced Cracks are retained firmly mutually
• Post tension slabs are useful for building up stronger structures economically.
• It minimizes or removes shrinkage cracking. So, no joints, or fewer joints, are essential
• It allows us to design longer spans in elevated members, like floors or beams

Drawbacks:
• Only experienced professionals can construct post tension slabs.
• If precaution is not undertaken at the time of making it, it can cause future mishaps. In various situations, untaught workers become unable fill the gaps of the tendons and wiring entirely. These gaps lead to decay of the wires which become breakable quickly and unexpected collapsing may occur.

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Published By
Arka Roy
http://www.constructioncost.co
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Some practical issue prior to start foundation design

In foundation design, there may occur different types of issues associated with construction and costs.

Given below, the details of main issues :-

1. The foundations should be retained as shallow as possible, suitable for coping up with climatic effect, and strength of the surface soil; particularly in waterlogged ground. Excavation in severely waterlogged ground is extravagant and time consuming.

2. Expensive and complicated shuttering details should be bypassed specifically in stiffened rafts. Proper care should be taken with buildability.

3. Curtailment in the costs of piling, betterment in ground treatment, improvements in soil mechanics, etc. have significantly impacted the economics of design, and various standard solutions becomes obsolete. So, it is very much important to evaluate construction costs and methods on a regular basis.

4. Designers should have clear ideas on the assumptions which are provided in design. These range from the inconsistencies of ground conditions, the infrequent unsuitability of refined soil analyses and the feasibility of construction.

5. The authenticity of the soil analysis, through vital evaluation.

6. Impact of construction on ground properties that range from vibration from piling, degradation of ground uncovered with excavation in unfavorable weather conditions, exclusion of overburden, seasonal disparity in the water-table, compaction of the ground by construction plant.

7. Impact of changeable shape, length and inflexibility of the foundation, and the requirement for movement and settlement joints.

8. Consequences on finished foundations of sulfate attack on concrete, ground movements because of frost heave, shrinkable clays, and the impacts of trees; also modifications in local environment due to new construction, re-orientations of heavy traffic, setting up of plant in adjacent factories inducing impact and vibration.

9. Rapid but invaluable construction is more cost-effective as compared to low-cost but slow construction to clients to bring quick return on capital investment.

10. Impact of new foundation loading on obtainable adjacent structures.

For more information, go through the following construction article civilblog.org

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Published By
Arka Roy
http://www.constructioncost.co
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