Types of construction contracts

Types of construction contracts/The Nature of Construction Contracts

A contract is an understanding made between two or more persons, by which rights are acquired on the one side to acts or forbearances on the other. To make an agreement which results in a contract, there must be an offer and acceptance which leads to a binding force of obligation.

Lump sum contract

A lump sum contract is an agreement pursuant to which one party consents to pay another party a set dollar amount for completing the work or providing the goods described in the agreement. Typically, lump sum contracts do not require contractors to provide a detailed breakdown of costs. Rather, the payment of the total contract price is linked to the contractor completing all of the work specified in the contract.

Cost-Plus

Under this arrangement the contractor is reimbursed for the actual cost of labor and materials, plus charges a fee (typically an agreed-upon lump or percentage of the total costs) for overhead and profit.  This arrangement seldom begins with a blank slate regarding specifications and costs. Rather, the consumer and contractor will create a list of specifications and an estimated budget to match to those specifications.  Although the contractor under this arrangement will have to keep copious records of its costs, most residential consumers in a cost-plus arrangement suffer from kid-in-a-candy storeitis and overspend. One way to prevent breaking the budget is to set a guaranteed maximum price.  However, even a maximum price will not alleviate problems.

Unit Price Contract

In a unit price contract, the risk of inaccurate estimation of uncertain quantities for some key tasks has been removed from the contractor. However, some contractors may submit an “unbalanced bid” when it discovers large discrepancies between its estimates and the owner’s estimates of these quantities. Depending on the confidence of the contractor on its own estimates and its propensity on risk, a contractor can slightly raise the unit prices on the underestimated tasks while lowering the unit prices on other tasks. If the contractor is correct in its assessment, it can increase its profit substantially since the payment is made on the actual quantities of tasks; and if the reverse is true, it can lose on this basis. Furthermore, the owner may disqualify a contractor if the bid appears to be heavily unbalanced. To the extent that an underestimate or overestimate is caused by changes in the quantities of work, neither error will effect the contractor’s profit beyond the markup in the unit prices.

Target Estimate Contract

This is another form of contract which specifies a penalty or reward to a contractor, depending on whether the actual cost is greater than or less than the contractor’s estimated direct job cost. Usually, the percentages of savings or overrun to be shared by the owner and the contractor are predetermined and the project duration is specified in the contract. Bonuses or penalties may be stipulated for different project completion dates.

Guaranteed Maximum Cost Contract

When the project scope is well defined, an owner may choose to ask the contractor to take all the risks, both in terms of actual project cost and project time. Any work change orders from the owner must be extremely minor if at all, since performance specifications are provided to the owner at the outset of construction. The owner and the contractor agree to a project cost guaranteed by the contractor as maximum. There may be or may not be additional provisions to share any savings if any in the contract. This type of contract is particularly suitable for turnkey operation.

Advantages of Suspension Bridges

Suspension bridges are adopted in places where it is difficult to construct other type of bridges. For very large spans, they can be adopted economically.

·         In a suspension bridge, tensile stresses are predominant. Thus it requires high tensile ropes, which are economical than mild steel trusses etc.

·         During construction, temporary central supports do not need to be built, and access to the construction is not required from beneath. This means busy roadways and waterways do not need to be disrupted.

·         The stresses are directly passed to the supports through cables and suspenders, hence slender sections are required effecting overall economy.

·         The area spanned by a suspension bridge is very long in proportion to the amount of materials required to construct bridges.

·         They are light and require no false work.

·         The material of construction can be transported easily.

·         The time of construction is less.

·         They provide the roadway at a low elevation and have low centre of wind pressure.

·         They give good aesthetic appearance.

·         They require no centering for construction.

·         There is no likely hood of failure during erection and after construction.

·         It is the safest structure as cables have vast reserve strength.

·         The chords of the stiffening truss can be repaired without interruption to traffic, while in other bridges the failure of a single truss member causes collapse of the bridge.

  What are the advantages/disadvantages of beam,arch, and suspension bridges?

Construction Ecology Nature as a basis for green buildings free download

Industrial ecology provides a sound means of systemizing the various ideas which come under the banner of sustainable construction. As designers of built environments focus increasingly on green and sustainable construction they will be able to learn much from the field of industrial ecology.
Construction Ecology Nature as a basis for green buildings free download 






LIST OF CONTENT


1 Defining an ecology of construction 7
2 Material circulation, energy hierarchy, and building construction 37
3 On complexity theory, exergy, and industrial ecology 72
4 Applying the principles of ecological emergence to building design and construction 108
5 Using ecological dynamics to move toward an adaptive architecture 127
6 Minimizing waste emissions from the built environment 159
7 Industrial ecology and the built environment 177
8 Construction ecology and metabolism 196
9 Construction ecology 220
10 Ecologic analogues and architecture 231
11 Natural metabolism as the basis for “intelligent” architecture 248
12 Green architecture 269


Construction Ecology Nature as a basis for green buildings free download 

Download 

Methods of reducing corrosion for structural Reinforcement

Better grade of concrete with lower w/c ratio and well compacted.

A polymeric coating is applied to the concrete member to keep out aggressive agents. A polymeric coating is applied to the reinforcing bars to protect them from moisture and aggressive agents.

Fly Ash -  Using a Fly Ash concrete with very low permeability, which will delay the arrival of carbonation and chlorides at the level of the steel reinforcement. Fly Ash is a finely divided silica rich powder that, in itself, gives no benefit when added to a concrete mixture, unless it can react with the calcium hydroxide formed in the first few days of hydration. Together they form a calcium silica hydrate (CSH) compound that over time effectively reduces concrete diffusivity to oxygen, carbon dioxide, water and chloride ions. 

Modified quality of steel reinforcement which are less susceptible to corrosion such as special grade of stainless steel, CRS (Corrosion Resistant Steel),TMT steel etc.

Pre-applied impermeable coating (Epoxy, CECRI & CBRI coating)

Stainless steel or cladded stainless steel is used in lieu of conventional black bars

Admixtures (Nitrites and Nitrates) for concreting, which are to be added in the green concrete.

Electrochemical injection of the organic base corrosion inhibitors, ethanolamine and guanidine, into carbonated concrete.

Other inorganic inhibitors, which are known to be migratory in nature. The migration process is diffusion through water and diffusion through vapour phase.

Structural design aspects of corrosion control involve factors such as configurational (geometrical) considerations that minimize or, if possible, eliminate exposure to corrosives

The contract documents

The contract documents in order of importance are follows

Form of contract

This is the principal document and will often be a printed standard form, such as one of the variants of the JCT Form.

The Articles of Agreement

The Conditions

Total contract sum

Condition of contracts

The condition of contract is represent the legally binding agreement between the parties and cover such important as expected completion date of the work, methods and timing of payments, access to the works etc.

Specification

The specification may describe the method of working and quality required in the works, to assist the contractor in preparing the tender. Specification is used during.

Tendering, to help the estimator to price the work that is required to be carried out

Construction by the designer in order to determine the requirements of the contract, legally technically and financially, and by the building contractor to determine the work to be carried out on site.

Bill of Quantities

When tendering, the bill of quantities is sent out as part of the package of contract documents for the contractor to price. The  enters a unit price or rate against each item of work, the quantities are then multiplied by the rate and the price for the item of work established all the item prices are then added up to give the contract price. Provision may be made for variation and additional work within the bill of quantities by including provisional sums.

Contract drawings

The drawings should be indicate the location, scope and design complexity of the works and show graphically the full extent of what is required to be constructed.

What Is Construction Economics?

“Construction Economics is the construction Project to study of how individuals and groups make decisions with limited resources as to best satisfy client’s wants, needs, and desires".  Resources available to the construction industry may be appropriately allocated and optimally used to products and services.

Evaluation of the total (life cycle) costs of alternative solutions to the problem of meeting the requirements of a particular client and choice of the best solution.

Assessment of the determinants of demand for construction activity and study of the effect on the industry of different volumes and mixes of total demand.

Consideration of the nature of the construction industry and its needs, strengths and weakness.

Shovel loader

These are used primarily to excavate earth and load into hauling units such as trucks or tractor pulled wagons or in conveyer belt etc. Shovels can be used to excavate all type of soils except hard rocks without prior loosening.

The quantity of materials that can be hauled by the loader depends upon its bucket capacity. Loader bucket capacities are specified by the manufacturer either in terms of heaped capacity or struck capacity. However, planning can be based on the loose soil struck capacity of the bucket, and the heaped capacity (loose soil) can be converted into struck capacity (loose soil) as under:

Bucket struck capacity = bucket heaped capacity X fill-factor

Type of shovels  

Shovels can be divided into the following groups:

1. Crawler mounted shovels

2. Tyred mounted shovels

3. Self-propelled shovels

4. Non self-propelled shovels.

batteries Shovel loader

Preparation of a Cost Analysis

         

Preparation of a cost analysis

The primary purpose for using cost analysis of construction project provides useful source of cost information.  Any form of cost analysis should be provided in standard way with the following.

Information on the total project

Summary of element costs with preliminaries shown separately and also apportioned among the elements

A brief specification in element form

Sketch plans and elevations for the project

The amplified analysis

Information of the total project is important as it includes the building type which is necessary for future analytical purpose of a similar type of project. In addition, the client, location, tender date, contract particulars, market conditions, competitive tender list, project details, and brief cost information are provided under project information section of the cost analysis.

The following  basic principles  need to be followed in preparing the cost analysis

The qualitative aspects of the project should be expressed by reference to accompanying specification notes

An element should be of cost significance

The analysis should consider the features in different building which have heavy bearing on cost.

An element should be easily definable and capable of having the appropriate costs allocated against it with a minimum of effort on the part user

Other information relevant to the costs in the analysis should be provided as a background to these data

Construction of Cofferdams

 Cofferdam is a temporary structure built for the purpose of excluding or soil sufficiently to permit construction to proceed without excessive pumping, and to support the surrounding ground.

Construction of foundation is most important in a structure, so all the correct and safe actions should be taken while doing a foundation.

Cofferdam is commonly used for oil rig construction and repair, bridge and dam work, the cofferdam is usually a welded steel structure that is temporary and is typically dismantled after work is completed.

Cofferdams is used to provide a safe working space at foundation level

It’s difficult to handle deep foundations under water or ground in deep

Safety in construction of cofferdams

Construction of cofferdam presents safety problems unique to this type of construction.

They will be limited access, limited work areas, damp or wet footing, and deep excavations.

Provisions must be made for safe access in terms of adequate walkways, rails, ladders, or stairs into and out the lower levels.

The work may be within a waterway, in which case additional safety regulations may apply. These would include provisions for flotation devices, boats, warning singles, and suitable means for a rapid exit.

 

    Inside the Barge Gate Cofferdam

Inspection and Maintenance

Dams should be inspected regularly and immediately repaired if required.  A through inspection should be conducted following flood events.

Water removed from work area may be silty and should be discharged to a

vegetated area at least 30 m from the watercourse, or pumped through a filter bag

The weather forecast should be monitored to anticipate the occurrence of high flow

events.  Work operations should be adjusted to accumulate possible overtopping of

the coffer dams

       Barge Gate Cofferdam

Consideration of Selection of a cofferdam

Soil conditions

Location of the coffer dam (land/water)

Plan size of working area

Maximum depth of soil or water to be retained.

Nature of the permanent or floating structure

Effects on excising adjacent structures

Ground water level & their fluctuation

Construction time

Availability of equipment and material

Possible construction method & dismantling

Effects of noise, vibration and fumes, & fire risk.

It water cofferdam behavior of water.

Cofferdams is mainly of two types

Gravity coffer dam :-

Sheeting cofferdam 

Steel Structure Design methods

Steel structure may be design three methods.

Elastic design

Plastic design

Limit sate design

Elastic design is the traditional method. Steel is almost perfectly elastic up to the yield point and elastic theory is a very good method on which ton base design. Structures are anayesed by elastic theory and sections are sized so that permissible stresses are not exceed. Design is in accordance with BS 449: plastic theory developed to take account of behavior past the yield point based on finding the load that cases the structure to collapse. Then working load is the collapse load divided by a load factor. This too is permitted under BS449.

Plastic design

In plastic analysis and design of a structure, the ultimate load of the  structure as a whole is regarded as the design criterion. The term  plastic has occurred due to the fact that the ultimate load is found from the strength of steel  in the plastic range. 

This method is rapid and provides a rational approach for the analysis of the structure. It also provides striking economy as regards the weight  of steel since the sections required by this method are smaller in size than those  required by the method of elastic analysis. Plastic analysis and design has its  -main application in the analysis and design of statically indeterminate framed  structures.

Limit sate design

A Civil Engineering Designer has to ensure that the structures and facilities he designs are (i) fit for their purpose (ii) safe and (iii) economical and durable. Thus safety is one of the paramount responsibilities of the designer. However, it is difficult to assess at the design stage how safe a proposed design will actually be. There is, in fact, a great deal of uncertainty about the many factors, which influence both safety and economy. The uncertainties affecting the safety of a structure are due to 

 · Uncertainty about loading

 · Uncertainty about material strength and 

 · Uncertainty about structural dimensions and behaviour.

These uncertainties together make it impossible for a designer to guarantee that a structure will be absolutely safe. All that  the designer can ensure  is that the risk of failure is extremely small, despite the uncertainties. 

Aluminium Formwork for High Rise Buildings

Now a day’s Aluminium formworks used to construction for High Rise Buildings. Probably the most versatile modern construction system, aluminium formwork system, which has created new benchmarks in construction.  This produces a lightweight panel with an excellent stiffness to weight ratio, yielding minimal deflections under concrete loading. Once erected, these panels are subjected to a trial erection in order to eliminate any dimensional or on-site problems.

 Aluminium formwork  High Rise Buildings video 

Aluminium formwork can be used reused  more times  with careful handling and good maintenance. One of the biggest advantage of aluminium formworks has its unsur- passed construction speed. Compared to conventional construction procedures, use of aluminium formworks reduces floor completion cycle from 15 days to 4 to 5 days, primarily because of light weight nature enables fast erection and dismantling and simple system of pin & wedge makes the assembly easier. Pouring concrete together for walls, beams and floors and System ensures accuracy of dimensions without need for re-work and uncomplicated system  requiring use of minimum skilled labour.

But, over and above its strong advantages of speed, economy, re-usages and no extra cost, Aluminium Formworks give your construction structure a very high quality finish. High quality finish is possible due to uniformity of panels and precise joints, as it leaves no deflection, creating evenness, eventually adding style and stability.

Strength of Concrete

Strength of concrete depends upon amount of cement content, quality and grading of aggregates, water of concrete ratio, compaction and curing Strength of concrete increase very fast in the initial stage.

In the 7 days the strength gained is as much as 60 to 65 present of 25 days strength it is customary to assume the 28 days strength as the full strength of concrete however concrete gains strength beyond 28 days also.

The strength/grade of concrete is specified and measured in newtons/sq. mm., meganewtons/sq. meter or even megapascals, in fact the numerical figure will be the same in each case. 

E.g. a strength of 20 newtons/sq.mm. is the same as 20 meganewtons/sq.metre

Compressive strength of concrete

The characterize strength of concrete is defined. As compressive strength of 150mm size cubes after 28 days. Concrete mixtures can be designed to provide a wide range of mechanical and durability properties to meet the design requirements of a structure. The compressive strength of  concrete is the most common performance measure used by the engineer in designing building and other structures.

The compressive strength is measured by cylindrical concrete specimens in a compression-testing machine. The compressive strength is calculated from  

Tensile Strength

The tensile strength of concrete is usually considered about one-tenth of the compressive strength; that is, concrete which has a compressive value of 2,000 pounds per square inch should have a tensile strength of about 200 pounds per square inch. Although there is no fixed relation between the two values, the general law of increase in strength due to increasing the percentage of cement and the density, seems to hold in both cases.

The characteristics of good building stones

 Stone is a naturally available building material, which has been form the early age of civilization.  It is available in from in the form of rock, which is cut to the required size and shape and used as building block. Stone has been used to build small residential building to large places and temples.

Stones should possess fine – grained texture. It should be free from soft patches, flows and cracks

The strength of stone should be ascertained if it is to be subjected to any excessive or unusual stresses.

Shade of the stone should be uniform and pleasing.  Freshly broken surface should be bright and cracks

The stone should be strong, hard and durable. the hardness of stone is often of importance, especially if it is to be subjected to a considerable amount of wear and friction, as in pavements. 

The specific gravity should not be less than 2.5

It should possess good resistance to weathering

It should be easily workable before seasoning.the appearance of stone is often a matter of importance, especially in the face work of conspicuous buildings.In order that the appearance may be preserved, a good weathering stone should of course be selected, free from flaws, clayholes, etc.

It should have good resistance to smoke, fire and acidic atmosphere

It  should not absorb more than 5% of water by weight, when kept immersed in water for 24 hrs.

In attrition test, the stone should not show wear of more 2%

The weight of a stone for building has occasionally to be considered. In marine engineering works it is often advisable to use heavy stones to resist the force of the sea. A light stone would be best adapted for arches, while heavy stones would add to the stability of retaining walls.

It should become hard after seasoning. This seasoning gets rid of the moisture, sometimes called "quarry sap," which is to be found in all stone when freshly quarried.

Toughness index should be more than 19

Industrial Building Floor Construction

Industrial Building Floor Construction

Generally concrete slabs are used for industrial constructions.  They can be used below a layer of flooring material or are exposed; slabs on grade provide foundation for all building foundations. 

Also generally super-flat industrial floors are installed with laser-guided screeds and power trowels.  Quality material combined with good design and expert workmanship only yield the best concrete slabs.

Importantly the slabs are supported on the intermediate rolled steel joists.  The intermediate rolled steel joists are supported on columns spacing into two or more panels.

Floors in heavy engineering factories, workshops and garages should be resistant to impact, abrasion and attack by lubricating oils. The epoxy resin floor topping is suitable for heavy industrial floors. 

The extent to which the floors will be subjected to heavy wear and impact will often vary widely in different parts and since the more important type of finishes are more expensive it is advisable to ascertain as far as possible, before laying the finishes, where trucking gangways or process involving impact will be located and to provide accordingly.

Steel or cast iron tiles or plates, embedded in granolithic concrete may be used for areas of heavy abrasion by steel-tyred trucks or where a high resistance to impact is required. Granolithic concrete with suitable materials and good workmanship will provide in light industrial workshops and garages a floor finish of reasonable durability.

Special aggregates and metallic floor hardeners may be added to the granolithic concrete where heavy impact and wear is expected. Your factory will be invariably having a loading and unloading platforms. The requirements of the floor of loading and unloading platforms and industrial loading bays are primarily high resistance to impact and abrasion and non-slipperiness. Steel tiles or ‘anchor-plates’ or metal grids embedded in granolithic concrete are suitable for loading and unloading platforms subjected to heavy impact.

Comparison between stone masonry and brick masonry

Comparison  stone masonry and brick masonry

Construction of brick masonry is quick as the uniform size and regular shape of bricks facilitates in maintaining proper alignment. Whereas, the dressing and handling of stone need more time and extra labour in the construction of stone masonry.

Stone masonry possesses higher strength, durability and weather resisting quantities than brick masonry

Brick masonry has cost of construction is less than stone masonry

Stone has higher crushing strength than brick .this makes stone suitable for the construction of dams, piers, docks and other marine structures.

Skilled labour need to stone masaonry than brick masonry.

 In monumental buildings which require heavy molding with large projections and carving, stone is suitable whereas brick can be used only for light ornamental work of lesser importance.

Stone masonry is more water-tight than the brick masonry.


Stone masonry gives a massive appearance and hence used for monumental works

Well textured stone masonry of superior quality needs no treatment to improve its appearance. The apparent defects of brick masonry can be only concealed by plastering.

Generally stone masonry is not damaged by chemicals present in the environment and salts present in water or sewage whereas expected brick masonry reacts and gets disintegrated.

The use of stone masonry is only appliance are restricted to handle the stone blocks and bricks can be conveniently moved by manual labour.

The brick masonry is more fire-resisting than stone masonry.

Type of CAD software used in construction Field

list of Computer-aided design

AutoCAD -  AutoCAD is probably the most popular commercial CAD software today. This software was developed by Autodesk, and the first version was made back in 1982. AutoCAD is one of the first CAD software programs to run on personal computers, because during that time, CAD software had to run on specialized computers like mainframes. Today, AutoCAD is capable of creating full plans like blueprints or even models of other objects. It is capable of either 2D or 3D designs that are very detailed. Professionals and amateurs alike often use this software.

http://www.autodesk.com/autocad

ArchiCAD - ArchiCAD is a complete design suite with 2D and 3D drafting, visualization and other functions for architects, designers and planners. A wide range of software applications are integrated in ArchiCAD to cover most of the design needs of an architectural office:

http://www.graphisoft.com/

3D Max - Autodesk 3ds Max, formerly 3D Studio MAX, is a modeling, animation and rendering package developed by Autodesk Media and Entertainment. It has modeling capabilities, a flexible plugin architecture and is able to be used on the Microsoft Windows platform www.autodesk.com/3dsmax

MicroStation - MicroStation is a CAD software product for 2- and 3-dimensional design and drafting, developed and sold by Bentley Systems. it generates 2D/3D vector graphic objects and elements. Current version is MicroStation V8i.

http://www.bentley.com/en-US/Products/MicroStation/

Chief Architect - Chief Architect is a professional 3D architectural home design software. Automated building tools make home design, remodeling, interior design and kitchen & bath design easy. Discover why Chief Architect is the home design software product of choice for 2D and 3D design. 

http://www.chiefarchitect.com/

TurboCAD - TurboCAD is a CAD software application for 2D and 3D design and drafting running on the Macintosh and Microsoft Windows operating systems.

http://www.turbocad.com/