biosamnewbcropdic.ga Key Terms Section , for guidance on estimating construction contingency. construction cost estimating from planning phases through modification of Construction Cost Estimate - The independent review processes. Estimating Building Costs Calin M. Popescu University of Texas at Austin Austin, Texas, U.S.A.. Kan Phaobunjong Turner Construction Company Houston.
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Building Materials & Construction Planning Textbook free. Pages·· MB·19, CONSTRUCTION COST ESTIMATING GUIDE for CIVIL WORKS. approximately estimate construction costs of future residential-commercial buildings. An estimate model consists of the cost analysis of completed construction. PDF | Building actors need accurate estimates in order to efficiently undertake the construction of buildings. The knowledge of real expected costs of construction.
The owner generally is interested in the cost of major components of the project, rather than the cost of construction materials. For example, if the estimated cost exceeds the owner's permissible budget, cuts must be made by eliminating a building, or parts of a building, rather than merely reducing the cubic yards of concrete or pounds of steel. During negotiations, the contractor will likely have to reformat the estimate to enable the owner to make decisions on how to derive a contract amount that matches available funds.
The contractor may unbalance the bid by decreasing the unit price of the under estimated quantity and increasing the cost of another bid item, resulting in increased cost to the owner.
The contractor may underbid the job to win the contract, then look for change orders during construction to obtain additional money. The reduced quantity of work may result in reduced profit for the contractor. The contactor may have an excessive number of over-sized equipment on the job, resulting in reduced profit.
The contractor may file a claim against the owner, which will cause legal expenses. Prepare a list of methods a contactor may use to obtain costs above the bid amount. This has become even more important in countries which have experienced social unrest and protests during and The advantages of community prequalification include: There is also an interesting argument that the developed economies in Europe and North America may take up some of the in-country value policies in order to help in the recovery from the sovereign financial crises in and Because of the size and complexity of international airports.
It is also an option to open the bids the other way round. If a particular technical proposal is rejected for any reason. The contents of this report would include the following: The sour taste of poor quality lingers long after the sweet smell of cheap price has gone. This would also apply if there is a significant value engineering requirement at this pre-construction stage.
It is relatively easy to imagine that a company who puts in a poor technical proposal may well be able to submit a much-reduced commercial and financial bid and thereby have Downloaded by Introduction to estimating construction work 11 has been completed and the contractor is required to contribute to the design. See sections 3. Of course. Each tenderer may propose something slightly different and the client team must be able to assess whether the various proposed solutions meet their necessary functional requirements as well as ensuring that they do not cause coordination or interface problems with other packages.
For further discussion in this area. C Technical evaluation C1 Evaluation of technical submittals by individual tenderers C2 Post-tender technical clarification meetings if any Downloaded by Although the tender committee would approve or endorse the placing of capital projects.
D6 Submission of bid bond D7 Total value of bid E Conclusions and recommendations Tender committees are often very powerful within the client organisation.
The bid manage- ment department would take the leadership of the initial stage including a detailed. This procedure is generally known as the bid management process and would cover the following areas: The terms of reference of the tender committees are normally to approve or endorse recommendations for contract award and at other major milestones within the procurement process.
A schedule of what has to be provided and returned with the tender. The more sophisticated clients may also contract with specialist firms themselves. Tendering is an expensive business for contractors and the costs of tendering rise in proportion to the requirements of the tender documents.
Additional material for bid submissions. Another aspect of seeking best value rather than lowest price is an increase in the attention paid to the supply chain involved in tendering and delivering contracts.
Tender performance and bidding strategy will be discussed more fully in Chapter 7 but the. HVAC and telecommunications services together with more rigorous environmental and low carbon regulations means that the actual building is often seen as a mere envelope for the complex technology inside.
Scheduling and managing the internal bid progress and Downloaded by This may have an effect on the procurement approach for client organisations. Analysis of subcontractor bids to ensure coordination with the main contract. The need for assurance of high-quality delivery from subcontractors has encouraged many main contractors to enter into formal and informal partnering arrangements with specialist contractors who can demonstrate a good track record. Coordination of the bid response: Specialist subcontractors have a critical role in the modern hi-tech industry where client requirements for specialist MEP.
Introduction to estimating construction work 13 RFP analysis and assessment of client requirements. The need to work in this way will also impose some restrictions on the way in which some estimators have. European or International Standards documents. Information available at this stage should be used to make allowance for the time and resources required to deal with particular problems during construction. In a competitive tendering environment. Particular attention must be paid to contaminated land or dangerous materials such as asbestos.
Sources of information would include the client. During the estimating and tendering stage. A well-produced risk and opportunity register will carry forward into the construction phase and will become a key tool for the project manager. Mistakes and errors are also possible either through the use of incorrect data or just basic arithmetical errors in adding up the totals.
This is clearly a cynical view. There is always an element of risk in anticipating the future and nobody can be entirely sure that the decisions and judgements that are made at the estimating stage Downloaded by The tenderer should find out about the history of the site and its surroundings. The project will run much more smoothly. When materials are bought. Introduction to estimating construction work 15 In the UK. The construction programme should also ensure that everyone who needs to use an item of general plant has sufficient time allocated to do so.
Obtaining health and safety risk assessments and method statements will help to decide what plant and equipment will be required and check that it will be suitable. The tendering contractor must decide what equipment will be required. Having to stop or reschedule work to deal Downloaded by When estimating costs and preparing the programme schedule. If it is a particularly important potential hazard. It hopefully goes without saying that the access to the item of plant must be safe and suitable for their use.
All tenderers must ensure its contents have been taken into account before tenders are submitted. For example. The main contractor should find out how they are going to work. When tender programmes are being prepared.
Where CDM does not apply. They must also identify any health or safety risks that their operations may create for others working at the site and agree appropriate control measures. Main contractors should always discuss any proposed working methods and method statements with subcontractors before letting those subcontracts. If there are significant hazards.
Estimators should ensure that this is obtained and taken into account. The supplier is required to deliver the specified product or service as cheaply as possible. All project participants.
According to Constructing Excellence. In traditional contractual relationships. To fully realise the potential of SCM. This in turn creates higher customer satisfaction levels and. Each company in the supply chain therefore has their own internal customer. Construction companies that work in this way have been seeing the benefits both for themselves and their clients.
All construction companies have lists of preferred subcontractors and preferred suppliers. The benefits for end-users and project clients will include a more responsive industry able to deliver facilities that meet user needs in a better way.
The way in which these products and services are procured and managed may have a considerable effect on the outcome of the project. Having established relationships will mean that all parties will better understand the processes with reduced opportunities for ambiguities and disputes.
A successful partnership will deliver mutual commercial benefit through greater success in the market. Involve the designers Early involvement of the contractor requires a design input to the project. These are the strategic supply chain partners Downloaded by It is vital that time and care is taken to establish which companies fulfil the criteria of strategic partners and that they have similar serious interests in developing long-term relations.
Start by establishing relationships with those suppliers and subcontractors who are critical to the delivery to the client or project. Whether the supply chain is being established for a single project or by a group of companies as a marketing tool.
If anyone is inclined to quit when the going gets tough. In particular. What is being sought is a partner capable of reliably supplying quality products and services at competitive prices on a long-term basis. In either case.
All parties in the supply chain must be committed to working for the long term on the basis of continuous improvement and innovation.
A successful supply chain of first tier suppliers is a manageable objective and in time each of these suppliers will have similar chains. In summary. If the design is completed and the specification of materials decided. By this recognition. The costs of plant and equipment will certainly vary according to the method of construction adopted by the contractor.
Labour productivity see section 2. The all-in rate for labour see Chapter 2 for a detailed explanation of this calculation should again be broadly similar for companies in a competitive environment. Considering the different components of the tender price: Passing all risk down the supply chain is an easy option and will not lead to the lowest cost and certainly will not lead to best value for the client in the final analysis.
Therefore the actual labour costs should also not create a large differential in the tender costs. The principle of sharing risk and reward underpins the whole process of collaborating for mutual benefit. Even where the supply chain cannot get such agreements from a client. There are a considerable number of ways that a construction process can be carried out. Therefore the material costs should not create a large differential in the tender costs.
Figure 1. This will reduce the labour costs. This tender programme will also be used by the contractor to show how they had originally intended to sequence the work and consequently. Introduction to estimating construction work 19 example. This is a very important tool in establishing any claims for loss and expense due to delay and disrup- tion to the works or for attempting to prove an extension of time or acceleration claim. Very confusing until you are used to it! During the tender process.
This will not usually form part of the contract documents. It will mainly be concerned with potential hazards and safety. This is a North American term and merely refers to the project programme and its revisions. The tender programme and the tender stage method statement should be developed concurrently and taken together. The accuracy of the tender programme very much depends on the effort which was put into it at tender stage and the skill of the planner and estimator.
In this North American terminology. If the programme is sufficiently detailed with reference to the contract scope. See section 6. In many international projects. The contractor will naturally wish to use the most cost-effective method of construction. Under UK health and safety legislation. A pre-tender method statement will be submitted with a tender bid and a detailed method statement is required to be produced before construction begins and should be prepared with the same care and thoroughness required for any other contract documents.
As mentioned earlier in the chapter. In terms of the estimating function. At each of these stages. Introduction to estimating construction work 21 the logistics of the programming and sequencing decisions.
All contractors are under a legal requirement to conduct a risk assessment of work procedures to be carried out prior to commencement of work. See Figure 1.
If yes. Safe systems of work and lifting plans within a detailed method statement are a good way of doing this. It would be useful at this point to summarise some of the different types of estimates used in the pre-contract design stage. From Pre.
1. Easy-Pro Builders Estimator
It all adds to the rich confusion of modern construction procurement! A higher-quality building will increase the cost. See Chapter 4 for a more detailed discussion of these different types of estimates. The detailed estimate is more definitive and is made when the scope of work is clearly defined and the design is sufficiently progressed so that the essential features of the project are clearly identifiable.
The final pre-tender estimate is based on the completed plans and specifications. In the planning and design stages of a project. The direct cost of construction for bid estimates is usually derived from a combination of the following: When the detailed design has progressed to a point when the essential details are known.
At the very early stage. For conceptual estimates. The costs associated with a project may be disaggregated into a hierarchy of levels which is appropriate for the purpose of cost estimation roughly equating to a work breakdown structure — WBS.
In preparing these estimates. A feasibility estimate is made for each of the potential alternatives. Introduction to estimating construction work 23 Design estimates For the client and their design professionals. Tender or bid estimates For the bidding contractors who are pricing on full design information. As mentioned. The level of detail of the WBS depends on the type of cost estimate to be prepared. A preliminary estimate or conceptual estimate is based on the concept design of the project at the stage when the basic layouts for the design are known.
When the detailed plans and specifications are completed. As the bridge type is selected depending on span.
A revised estimated cost is necessary either because of change orders initiated by the owner or due to unexpected cost overruns or savings. If a tendering contractor intends to subcontract parts of the project. The larger contractors have well- established cost-estimating procedures while others do not and rely on publicly available pricing information or a rough estimate of their time and resources.
For the contractor. For the client. Since only one tendering contractor will be successful. The budgeted cost should also be updated periodically to reflect the estimated cost to completion as well as to ensure adequate cash flows for the completion of the project. As the work progresses. Both the client and the contractor must adopt some baseline for cost control during the construction.
Control estimates For the purpose of monitoring the project during construction. If all or part of the construction is to be undertaken by the main contractor themselves.
Introduction to estimating construction work 25 1. Fixed costs are those which do not change irrespective of the amount of work that is carried out Figure 2. Direct costs consist of those costs incurred on site and directly related to the work being carried out and indirect costs consist mainly of head office overheads and non-site-located service provisions.
Fixed costs are the same irrespective of turnover and variable costs will increase in direct proportion to turnover. This would include the head office overheads and other common costs or non-project-specific costs. This would include the labour.
HR and finance. A particular cost may be direct or indirect. An indirect cost is a cost that cannot be easily and conveniently traced to a particular project. A direct cost is a cost that is incorporated into the finished work. In construction. If the company did Downloaded by This would include the costs of actually doing the work.
The various direct costs of labour. So a large project will have much greater variable costs than a small project. We will first look at what primarily affects costs in construction. Variable costs. Notice that we have established two different types of fixed or overhead costs related to construction projects — head office overheads are a fixed cost to the company and must be spread over all the projects that the company is engaged in.
Let us now consider the various costs associated with construction projects. Very confusing — and each company may account for these costs in slightly different ways. The nature of costs in construction 27 example. Improvement of labour productivity should be a major and continual concern of those who are res- ponsible for cost control of construction.
It should go without saying that good project management in construction must address the efficient utilisation of labour. Organisations which do not recognise the impact of the various modern innovations and have not adapted to changing environments will find this reflected in their tender prices and will therefore find it difficult to remain competitive in mainstream construction activities.
The chapter is completed by a discussion of profit and risk costs. The trends in construction technology can present a very mixed and ambiguous picture. On the one hand. No motor trucks were used in the digging of the canal. These include HSE requirements. Simon and Schuster. What is needed now is strategic planning to usher in a revolution which can improve productivity by an order of magnitude.
This strategic planning should look at opportunities and ask whether there are potential options which will give better outputs by the use of existing resources. The construction industry often points to factors which cannot be controlled by the industry as an explanation of cost increases and the lack of technical innovation. Money spent on development is an investment and therefore should generate additional revenue or savings in the future. The nature of costs in construction 29 The work could not have been done any faster or more efficiently in our day.
Technological change is certainly occurring in construction. The specious argument is usually dragged out that the industry cannot afford to invest in research and development because all projects are won by intense cost-based competition. And because of the mud and rain. The Path Between the Seas.
Labour characteristics Performance analysis is a common tool for assessing the quality of individuals or teams and their contribution to the project completion. Since labour constitutes a large part of the construction cost and the quantity of labour hours in performing a task in construction is more susceptible to the influence of management than are materials or capital.
Construction output may be expressed in terms of functional units or financially. Labour productivity measured in this way requires considerable care in interpretation. Each category of factors affects the productive labour available to a project in addition to the on-site labour efficiency.
Productivity of construction labour is often broadly defined as output per man-hour. In the former case. The non-productive activities associated with a project may or may not be paid for by the client. In the latter case. The value of construction in this regard is not measured by the benefit of constructed facilities. Factors that might be evaluated in such a performance analysis may include: For this purpose. These different factors could each be assessed on a three point scale: Examples of work performance in these areas might also be provided.
More detailed measures are more useful for monitoring individual activities and personal performance. Both contractors and clients will be concerned with the labour activity and produc- tivity at project sites. In this way. A base labour productivity may then be defined for a set of work conditions specified by the client or contractor who wishes to observe and measure the labour performance over a period of time under such conditions.
The productivity indices compiled from statistical data should include parameters such as the performance of the major trades. A labour productivity index may then be defined as the ratio of the project labour productivity under a different set of work conditions to the base labour productivity. This process is known as benchmarking. The degree of equipment utilisation on a construction project will clearly have a further direct bearing on site labour productivity.
The effects of various factors related to work conditions on a new project can be estimated in advance. In order to develop industry-wide standards of performance which are published in the public domain in the standard pricing books.
The Choice: Embrace the Possible
Site acces- sibility may also reduce the labour productivity index if the workers are constrained in how they can perform their jobs. Since the file is updated throughout the construction, it contains all the elements that have been used in the actual project rather than the originally designed elements that might be modified during construction.
BIM provides reliable features to architects, owners, engineers, contractors, and all participants involved in the project Alkas and Jrade, It uses a single outlet to store all information about the building Cyon Research Website, It is a system that creates a single building model as a repository for all elements of a building Levy, The development of a digital database enables collaboration among participants in the construction project Smith and Tardif, , thus documents can be kept consistent with one another Cyon Research Website, Review and changes can be recommended from every party involve in the project.
These documents are created separately and have no intelligent connection between them. The possibility of uncoordinated data is very high. The change management created by CAD is a tedious and error-prone process. By and large, CAD is strictly a 2D technology with a specific need to output a collection of lines and text on a page. These lines have no meanings, whether inside the computer or on the printed sheet.
CAD drafting has its efficiencies and advantages over pen and paper, but is really just a simulation of the act of drafting. Historically, the designer drew a set of plans and then used those plans to manually derive sections, elevations, and details.
During the development of a project, if any of those items changed, the designer had to modify each of the other drawings that were affected to take the change into account. The beauty of BIM is that it manages change without having to change all drawings.
Unlike CAD, the intent of BIM is to let the computer take responsibility for redundant interactions and calculations, providing the designer with more time to design and evaluate decisions. A core feature of BIM allows users to create and modify everything in one design context.
The system will propagate changes to all relevant views in the project. As the designer models in plan, the elevations, sections, and details are also being generated. For example, if a change is made to the size of a window opening in elevation, this change is made throughout the entire model. An additional advantage of a BIM methodology is that the design cannot be cheated.
In CAD system, this can be easy to overlook, because the door has to be manually transcribed from plan to section and elevation. CAD files are created individually and have no intelligent connection between them. Each drawing represents a separate piece of work to be managed and updated throughout the design process. The possibility of uncoordinated data between drawings is therefore very high.
BIM takes a different approach by combining all the information and relating it to a single file, thus guaranteeing a consistent model Dzambazova, Demchak, and Krygiel, ; Dzambazova, Demchak, and Krygiel, Interference checking in BIM also permits the user to immediately see conflicts among architectural, structural, and mechanical elements in 3D. Because a building model is an assembly of meaningful, to-be-built objects, the user controls visibility and graphics of objects using a rational list of well understood categories.
This is different from CAD, where every line belongs to a layer, and it is up to the user to manage all layers. Traditional CAD files need to be annotated before they are sent to the fabricator. Models from BIM can be sent directly to fabrication machines without the need of traditional shop drawings Dzambazova, Demchak, and Krygiel, Data exchange between various parties involved in the project is also critical Day, Interoperability depicts the need to pass data between applications, allowing multiple types of experts and applications to contribute to the work at hand.
Interoperability is defined as the ability to exchange and use information. It is also the capability of different software to communicate and work together seamlessly. The standard and compatibility between different applications have to be realized. The design and construction of a building is a team activity, and increasingly each activity and each type of specialty is supported and augmented by its own computer applications.
Interoperability identifies the need to pass data between applications, and for multiple applications to jointly contribute to the work at hand.
Interoperability eliminates the need to replicate data input that has already been generated, and facilitates smooth workflows and automation. Data exchanges between two applications are typically carried out in one of the four main ways listed below: Direct, proprietary links between specific BIM tools 2. Proprietary file exchange formats, primarily dealing with geometry 3.
Public product data model exchange formats 4. XML-based exchange format Direct links provide an integrated connection between two applications, usually called from one or both application user interfaces.
While a direct linking of application is a runtime and binary interface, and exchange format is implemented as a file of human readable text format. In , an industry consortium was initiated to develop a class library for representing construction project information and facilitating project data exchange among software serving the AEC industry. The consortium was initially called Industry Alliance for Interoperability.
In , the Alliance was renamed to International Alliance for Interoperability IAI and became a global standards-setting organization representing diverse constituencies including architects and engineers, software manufacturers, government agencies, contractors, building owners and product manufacturers IAI Website, IFC is a comprehensive data representation of the building model. The IFC object descriptions deal with not only full 3D geometry but also relationships, process, material properties, cost, and other behavior data Hamilton et al.
Integrating a CAD model with IFC enables the accurate geometric representation to be integrated with structural and behavior elements and facilitates linking with external applications. According to Khemlani AECbytes Website, , the IFC data model is likely to become the international standard for data exchange and integration within the building construction industries. XML allows definition of the structure and meaning of some data of interest; that structure is called a schema.
The different XML schemas support exchange of many types of data between applications. This creates more possibilities for BIM to be used by different participants during a construction project. Applications associated with BIM are discussed in section 3. It is useful during the design phase, during actual construction and after the construction has been completed.
BIM uses interoperability to enable the exchanging of information between different applications. Interoperability, as discussed in section 3. Therefore, BIM could be used as a tool to help improve not only the construction process but it also helps to manage the facility after the construction is completed.
Concept and Feasibility Study Before the owner approaches an architect, it is necessary to determine the size of the building, its functionalities and features that can be built within the budget and time constraints. The goals and expectations could be achieved if the concept and feasibility study of the project are within the acceptable limitations.
A rough sketch of building model built and linked to a cost database can be a tremendous assistance to an owner. BIM could be used as an application to help owner during the concept and feasibility study. This reduces the amount of time and number of errors, while generating project drawings. Also, when changes are made to a model, the drawings are updated and may be regenerated as soon as the modifications are made.
The coordination of mechanical, electrical and plumbing MEP , architectural, and structural systems can be achieved through the fully integrated 3D models that BIM provide. Design time could be shortened and design errors and omissions can be reduced. Rework due to the design flaws could be avoided with this coordination of work. It also gives an earlier insight into the design problems and provides an opportunity for a design to be improved continuously.
5 Free Construction Estimating & Takeoff Products to Cut Turnaround Time and Win More Bids
It allows the designer to see if the design intent of the project has been achieved. The intent of the design is the arrangement of features and dimensions that has been specified at the conceptual design of the project. Purposes of spaces and rooms can be visualized at an earlier stage of construction where changes can be made with little to no addition cost.
Estimates that use conceptual BIM consisting of components can provide owners with quick feedback on various design scenarios. BIM provides quantity takeoff tools to create faster, better detailed, and more accurate estimates. During the construction of a project, owners and estimators struggle with the ability to respond to design and requirement changes and to understand the impact of those changes on the overall project budget.
By linking the design model to an estimating application, the project team can speed up the quantity takeoff and overall estimating process to get faster feedback on proposed design changes.
Improve Energy Efficiency and Sustainability The green building trend is leading many owners to consider the energy efficiency of their facilities and the overall environmental impact of their projects. Sustainable building is good business practice and can lead to greater marketability of a facility.
Building models provide several advantages over traditional 2D models due to the richness of object information needed to perform energy or other environmental analyses.
Daylight analysis, glare, and solar heat gain are a few scenarios that help reduce the cost of operation for the facility. The parametric nature of the BIM model makes design changes easier and it automatically updates the necessary documentations.
Owners also pay the cost for construction delays or lengthy project durations, either in interest payments on loan, delayed rental income, or other income from sales of goods or products.
The application of BIM to support coordination and prefabrication can result in improved field productivity, reduced field effort, and reductions in the overall construction schedule, which results in on-time delivery for the owner. BIM models can also be used to create a 4D model by adding the time dimension. Owners and their service providers often encounter unforeseen conditions that even the best digital models cannot foresee.
Teams using digital models are often in a better position to respond to unforeseen conditions. Local Code Compliance Owners and their design teams must work with a variety of jurisdictions to ensure their facilities meet design, performance, and work place safety codes.
Regulatory personnel also face challenges for ensuring compliance and conformance during design and construction.
A potential benefit of a building information model is the ability to automatically analyze and check the model for code compliance.
These errors are eliminated with the adaptation of virtual 3D model. Clashes can be identified before the construction in the field begins. BIM shows exactly how the component will fit into the project. Necessary information for the component is provided within the model. Fabrication of components on site would be faster through better coordination, better connections, better assembly planning and training.
Lean Construction Lean construction is a way to design production systems to minimize waste of materials, time, and effort in order to generate the maximum possible amount of value Koskela et al. BIM maximizes the efficiencies by providing accurate model information and the material resources needed for the different stages of construction. It provides the basis for better planning and scheduling. This helps ensure that labor, equipment, and material are ready at the job site when they are needed.
Facility Operation and Management Systems BIM helps produce higher quality and maintainable infrastructure through interactive review of coordinated models.
Interactive review of the model allows owners to virtually access and simulates maintenance procedures. BIM could be used to quickly populate a facility management database. Since BIM is updated throughout the construction of the project, it can also be used as the as- built plans that are used to manage the facility.
Maintenance work and impact to retrofits could be evaluated by using the visual and intelligent models to help facility managers. A model, which has been updated throughout the construction, is a tool with great accuracy for operating and managing the completed building.
BIM can be used as an advanced facilities management tool. It could be used for an evacuation plan, fire protection simulation, thermal calculation and air-conditioning analysis Eastman et al.
The transition from early adoption of technology to the mainstream practice is expected in the near future. The future impact of BIM can be separated into different parties and participants. Architects and engineers will be able to explore different designs while keeping the cost and schedule of the project in check. Virtual reality will enable exploration of different environmental impact scenarios such as sun studies, wind analysis, and energy efficiency.
Engineers will also be able to do the structural analysis aspect of the model. Owners will be able to see 3D visualization of the project at an earlier stage. Change orders and material changes will be instantaneously updated throughout the model. BIM will allow faster and easier calculation of the construction cost.
The collaboration of both designers and the contractors can help minimize delays during construction. Estimators are able to use the properties provided in the model to estimate the cost of construction. Labor intensive tasks during estimating process can be simplified. BIM facilitates collaboration between project participants. Interoperability also enables different applications to be developed.
BIM delivers many significant benefits and tools for all participants during various phases of the project. This thesis will utilize BIM as a technology to develop a visual approach to construction cost estimating. Although there are technologies to assist with the cost estimating process, inefficiencies still abound. During the process of construction cost estimating, the estimator must learn about the design and conditions of the project.
A lot of data are needed to prepare an estimate. Reviewing drawings, extracting information for quantity takeoff and looking up the latest cost information from the cost databases are tasks that estimators must accomplish. The latest findings in cognitive psychology, a branch of science that relates to how humans process information, will be examined for this purpose. In addition to cognitive psychology, visualization technology can also help improve how humans understand and process information.
Computer aided design CAD and building information modeling BIM , which have been discussed in Chapter 3, are two examples of how visualization is currently used in the construction industry. Visualization is useful not only in the design process but also during the construction. This chapter will discuss cognitive theory along with virtual reality. According to visual computing theorists and dual processing theory, a basic way to effectively facilitate the connection between internal mind and external environment is to improve the visibility of the information embedded in the data.
Introduction to Estimating for Construction.pdf
A good external representation will be one that links naturally to the internal representations that people are capable of forming, thereby supporting their overall cognitive process. Using lines and symbols to represent the thoughts and ideas of engineers and designers often provides a more effective means of communicating these concepts than verbal descriptions Scribner and Anderson, According to Bertoline et al.
There are three types of processors: Attention is needed to facilitate and control this cognitive system.
Each processor has specific functions. The perceptual processor senses, detects, and accepts inputs from the external world and stores parts of the input in the working memory. The cognitive processor interprets, manipulates and makes decisions about the inputs.
Estimating in Building Construction
The motor processor is responsible for interpreting cognitive decisions into physical actions. As stated earlier, the processors work with memory in order to process information. Capacity to store data is differed in two types of memory. A chunk of data is a unit of information such as name. The capacity and retention of long-term memory is practically unlimited, however, retrieval of information can be difficult.
It is very important to understand how the processors and memories work together. Research in the field of cognitive science and human-computer interaction has shown limitations of human brain during the information-processing task. First, the user will not notice screen changes that fall within an interval of milliseconds.
Second, the user cannot be expected to work with more than seven chunks of information simultaneously; displaying more chunks means the user will concentrate on some parts of the screen, ignoring other parts. Third, retrieval of information that is not expected to be in working memory will probably degrade both speed and accuracy during information processing.
This is very important for software developers to keep in mind during design of software such as an estimating program. According to Gardiner and Christie , realizing that designing for human- machine cognitive compatibility can help make a machine more acceptable and more useful to its intended user.
The benefits of realizing the use of cognitive science in developing software are many. Less training is needed to use the software, errors in using it are less likely, more complex operations can be carried out by more people, work can be done faster, and more interesting work can be done with little or no undesirable stress on the user Gardiner and Christie, The knowledge that users bring to the interaction and the way in which they develop their understanding will influence the ease of use of the software Hammond et al.
Whether it is to see if the designed building would fit in the surrounding environment or owner requirements have been fulfilled. One way to view a project during the design is by using virtual reality. Virtual reality is about creating acceptable substitutes for real objects or environments for training, entertainment, or design purposes Vince, ; Gutierrez, Vexo, and Thalmann, Virtual reality is about using computers to create images of 3D environments within which one can participate in real time and experience a sensation of being there Vince, ; McMenemy and Ferguson, ; Gutierrez, Vexo, and Thalmann, The presence could be found in the form of navigation and interaction.
The use of virtual reality is to immerse the user in the display Richards, Virtual reality requires real time graphics and a stereoscopic display that is used for producing the depth for 3D images. Commonly used technologies include but are not limited to head-mounted displays HMD , personal computers PC , workstations, cave automation virtual environments CAVE , large screen systems, and virtual tablets. Interaction can be achieved using a tracking device, which may be integrated in the HMD itself, for tracking head and body movement.
Data gloves can be used to track hand movements. Computer mice can be used to navigate and interact on the personal computer level.
These devices let the user point to and manipulate objects in the virtual scene Vince, ; Gutierrez, Vexo, and Thalmann, According to Richards and Vince , Virtual reality can be a model for other types of visualization systems and a test system for display and interactive techniques. The benefits of seeing a product as a true 3D object is immense, and the ability to explore different perspectives of the project before anything is built are immeasurable.
Designers will be able to explore different design alternatives to maximize value.
One advantage of using virtual reality in construction industry is its capability to represent complex building components as a three dimensional graphical object. This helps user to visualize a project better than with 2D drawings.
Since virtual reality could be used to explore designs before they are built, engineers and designers can use the technology to visualize structures before actually building them McMenemy and Ferguson, In addition to visualizing buildings and structures, designers and engineers are also able to interact with them.
Engineers can use virtual reality in many applications, such as structural analysis and construction cost estimating. In this study, a virtual model of a project is created by extracting the geometry and material properties from each element in a CAD model.
Microsoft DirectX Library is used to create a virtual environment using the extracted information. Construction cost estimating can then be done by walking in the building and selecting elements in the virtual model for estimating. Next section will discuss interactive visualization in more detail.
Virtual reality and interactive visualization can be used to perform estimating while navigate in a virtual model f the building. Information could be extracted from the model during navigation. A cost estimating application is needed in order to use extracted information. The next chapter will discuss computer database technology and how a cost estimating database can be developed for an estimating application.
These data need to be organized in a way that they can be easily accessed. One way to solve the problem is to use a database for storage of the data. A database is a storage facility or a collection of related records or documents.
Databases are designed, built, and populated with data for a specific purpose and has an intended group of users and some applications in which these users are interested Retik and Langford, The estimating software designed for visual estimating adopts database technology to store all the information necessary for estimating.
The cost estimating database will also be used to store new estimate information. This chapter will discuss why databases are used, database models especially the relational model, and how the estimating database used in this study was designed. A database is an organization or a collection of related data. It is designed specifically to manage large bodies of information, and store data in an organized and structured manner that makes it easy for users to manage and retrieve data when required Agarwal et al.
It is very much like a spreadsheet. However, a database is designed to perform some very specific tasks which a spreadsheet is not able to do effectively.
These are some of the reasons why databases are used Agarwal et al. Databases help in maintaining large amounts of data, and thus completely replace voluminous paper files. Searches for a particular piece of data or information in a database are much faster than sorting through piles of paper. It is a dull work to maintain files by hand; using a database completely eliminates such maintenance. Database systems can easily be updated and so provide accurate information all the time and on demand.
These models present three ways of logically perceiving the arrangement of data in the file structure Bagui and Earp, Following is a brief description of each database model. Hierarchical Database Model The hierarchical model represents data using hierarchical tree structures.
Each hierarchy represents a number of related records, arranged in multi-level structures, consisting of one root record and any number of subordinate levels Retik and Langford, This can be seen in Figure Hierarchical Database Model Network Database Model The network model was developed as a successor to the hierarchical model. The network model represents data as record types with more complex many-to-many relationships.
This allows flexibility in describing different structures and relationships. Figure shows how network model is arranged. Tables consist of a number of rows, each row containing the same number of columns Carter, A database based on the relational model was developed by E. Codd during the s. A relational database allows the definition of data structures, storage, and retrieval operations and integrity constraints.
Figure shows how data is viewed in the relational model. This is where data is kept within the database. System tables are special tables that SQL Server uses to help it work with the database. These tables contain information within rows and columns. These provide a definition of each single item of information that builds up to a table definition. A column is made up of cells that all hold data. Each cell can hold a different type of data.
Although they are restricted to what the data within it relates to, the type of data it will hold, and how much information can be stored in it. Each table must have at least one column. A row is made up of one cell from every column defined for the table.
There can be any number of rows in a table; the limitation is set by the disk space, the amount of disk space that was defined as the maximum in database creation definition, or the amount of disk space in the server. A row will define a single unit of information, such as, a person name, address, phone number, etc.
Rows are also called records. SQL or structured query language is database computer language designed for managing data in the relational database management systems. Stored procedures are permanently stored in the database, ready for use at any time. These can be regarded as predefined lists of information that can inform the database how the data is physically sorted and stored, or they can be used to find rows of data quickly using information supplied by a SQL query and matching this information to data within columns.
An index consists of one or more columns from the table it is defined for, but it is not possible for an index to cover more than one table.
Index is very much like the index of a book, which is used to locate a piece of information faster than looking through the book page by page.
These can be thought of as virtual tables. Views can contain information combined from several tables and can present a more user- friendly interface to the data. Views can also add a great deal of security to an application, but they do give reduced functionality over the use of stored procedures or direct access to the tables.
Views can also be indexed to speed processing of data within. Since in this study a relational database is used for keeping data for cost estimating purposes, it would not be a relational database at all if database relationship is not discussed. The following section will provide the definition of relationship in the relational database model and how it works with data. It is impossible to have a physical link, although a physical line is drawn between two database tables when graphically illustrating the structure of a database.
The following sections present specific details about relationships, starting with a look at cardinalities. Cardinalities Cardinality is a description of how many of one record type relate to the other, and vice versa. Mapping cardinalities, or cardinality ratios, express the number of entities to which another entity can be associated via a relationship set.
Three main types of cardinality can exist in a database, these are; One-to-one, One-to-Many, and Many-to- Many. For each row in Table A, there is at most only one related row in Table B, and vice versa. This relationship is typically used to separate data by frequency of use to optimally organize data physically.
Typically, there is no real reason for one record in one table to match just one record in another. For example, one department can have only one department head. For example, a customer can have many orders, but an order can only belong to one customer.
For each row in Table A, there are zero, one, or more related rows in Table B, and vice versa. Although it can happen relatively frequently, many-to-many relationship is not so easy to achieve. It also requires a special technique to implement. This relationship is actually implemented in a one-many-one format, so it requires a third table often referred to as a junction table to be introduced in between that serves as the path between the related tables.
An example of a many-to- man relationship might be where an order can have many products and a product can belong to many orders. Now that all the cardinalities have been explained, keys will be discussed next. Keys Relationships are represented by data in tables. To establish a relationship between two tables, data in one table must be related to rows of data in another table. A key is one or more columns of a relation that is used to identify a row.
In relational database management system, it mainly works with two types of keys: Primary Keys A primary key is an attribute column or combination of attributes columns whose values uniquely identify records in an entity.
Before choosing a primary key for an entity, an attribute must have the following properties: Besides helping in uniquely identifying a record, the primary key also helps in searching records as an index automatically gets generated when assigning a primary key to an attribute.
Foreign Keys A foreign key is an attribute that completes a relationship by identifying the parent entity. Foreign keys provide a method for maintaining integrity in the data called referential integrity, this will be discussed in the following section and for navigating between different instances of an entity.
Every relationship in the model must be supported by a foreign key. Data Integrity Data integrity means that data values in a database are correct and consistent. There are two aspects to data integrity: This is to guarantee that primary key values exist for all rows. The requirement that primary key values exist and that they are unique is known as entity integrity. Once a relationship is defined between tables with foreign keys, they key data must be managed to maintain the correct relationships to enforce referential integrity.
Referential integrity requires that all foreign key values in a child table either match primary key values in a parent table or, if permitted, be null. This is also known as satisfying a foreign key constraint. Normalization Normalization is a technique for avoiding potential update anomalies, basically by minimizing redundant data in a logical database design. Normalized database designs usually reduce update processing costs but can make query processing more complicated.
These trade-offs must be carefully evaluated in terms of the required performance profile of a database. Often, a database design needs to be denormalized to adequately meet operational needs.
Normalizing a logical database design involves a set of formal processes to separate the data into multiple, related tables. The result of each process is referred to as a normal form. Five normal forms have been identified in theory, but most of the time third normal form 3NF is as far as needed in practice. This thesis will not get into detail about normal form.
The cost estimating database will use 3NF. Now that all the necessary components of relational database have been described, cost estimating database will be described in the following section. The ability to integrate this data into the estimating process would be beneficial during an estimate. A cost estimating database was developed to store all the data required for the estimating application developed in this study.
The application is named Visual Estimating Application. This section will present what should be stored in the cost estimating database, how the database was designed using the relational database model, and how the estimating data are related to each other. The cost of a building element is the sum of the costs of the work items necessary for the construction of the element. The data needed for estimating include labor, equipment, material costs and productivities.
Figure shows the schema of the database developed for storing the necessary data. The following will discuss each table in the cost estimating database. Labor Table: The labor table is used to keep data for each labor trade.
A code is assigned to each labor trade because it is easier to find a labor trade by code rather than searching by its description. Description attribute is used to store the name of the labor trade, and BaseHourlyRate attribute keeps the cost for each labor in the database. Figure shows a sample list of labor trades stored in the Labor table.
Labor Table Equipment Table: Equipment table is used to store equipment-related data. Equipment data that is required to be stored in the equipment table include equipment code, equipment description, and equipment cost per day.
Similar to labor code, equipment code is uniquely assigned to each piece of equipment.There are three general categories the data fall under: material, labor, and tax and insurance.
Each drawing represents a separate piece of work to be managed and updated throughout the design process. Cost Studies of Buildings. The knowledge that users bring to the interaction and the way in which they develop their understanding will influence the ease of use of the software Hammond et al.
Pratt, David. The network model represents data as record types with more complex many-to-many relationships. Since the file is updated throughout the construction, it contains all the elements that have been used in the actual project rather than the originally designed elements that might be modified during construction.
Without their love and support, this work would not have been developed, progress, or completed. Wages include six trades plus common labor.
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