This paragraph describes the scientific literature regarding detailed estimation methods that used a building information model. The studies did not compare the estimation methods, but solely applied the methods. To estimate the costs of the construction of a bridge, Marzouk and Hisham (2012) used a program
developed by C# programming language that extracts the quantities of the building information model. The quantities are exported to an Excel file and BOQ numbering is added to the file. The BOQ numbering has been used to connect the quantities with the unit prices and is a codification method. The function
VLOOKUP in Excel was used to find the corresponding unit prices for the quantities. The method of Marzouk and Hisham (2012) comprises of five steps: (1) development of the 3D information model of the bridge, (2) visualization of the construction steps, (3) add additional information required for the cost estimation to the bridge information model, (4) export all information, e.g. volume, casting type, length, ID and material type to an Excel spreadsheet and step 5 is estimating the costs automatically by using the program developed by C# language. Marzouk and Hisham (2012) only proposed the method and did not evaluate it.
Vitásek and Matějka (2017) researched how to utilize BIM to estimate the costs of transport infrastructure projects by using QTO. To estimate the costs of an infrastructure project during preliminary stage, the complete design is not required. A schematic design is often incomplete. Therefore, a list of the requirements for the information needed should be created (Vitásek and Matějka, 2017). Vitásek and Matějka (2017) use two case studies of the construction of a motorway in Czech Republic. Vitásek and Matějka (2017) mention that to automatically extract the quantities of building information models, three phases need to be
performed: (1) the requirements for the designers should be specified, (2) price databases should be created and implemented in BIM and (3) a software extension is required for the conversion of data from the building information model to the price database.
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Summary
Several studies have been performed regarding quantity- and cost estimation. The literature that has been described in this section is mainly focused on BIM and early-stage designs. Most studies focused on cost estimation and to estimate the costs, the construction material quantities are required. Those quantities are multiplied with the corresponding unit prices. To determine the corresponding unit prices information of the construction object is required. This can be done by either a code that was added to the object or by using multiple entries, e.g. element type, element name etc.
Based on the studies, several possible criteria can be used for this research to compare the early-stage quantity estimation methods. Most studies mention accuracy and/or efficiency as advantages of BIM-based QTO. However, other criteria can be used as well, e.g. flexibility and generality.
Literature also mentioned disadvantages and problems of implementing BIM to estimate quantities. For example, earthwork is inadequately represented for BIM-based QTO. Therefore, using BIM-based QTO to estimate quantities and costs of earthwork will create problems. Furthermore, there was mentioned that often only 50% of the required data for automatic quantity extraction is available in the building information model. Therefore, there should be verified that all required data to estimate the costs are available.
To estimate the costs of an early-stage design, the quantities of cost determining objects were used in the research. Only using costs of the cost determining objects leads to an underestimation of the costs and therefore a percentage over the costs of the cost determining objects should be used to estimate the total costs. Nesticò et al. (2017) used an additional percentage of 10% over the costs of the cost determining objects, where cost determining objects are 30% of the quantities. If only 10% of the quantities of a
construction project are used to estimate the costs, an additional 30% over the costs of the cost determining objects should be used to estimate the costs.
Vitásek and Matějka (2017) mention three phases must be performed to automatically extract quantities and costs using a building information model, namely: (1) specify the requirements for the designers, (2) create price databases and (3) a software extension is required for the conversion of data from the building
information model to the price database. Marzouk and Hisham (2012) mention five steps that are required to automatically estimate the quantities and costs of a construction project using a building information model, namely: (1) developing a 3D information model, (2) visualizing the construction steps, (3) adding additional information required for the cost estimation to the bridge information model, (4) exporting all information, e.g. volume, casting type, length, ID and material type to an Excel spreadsheet and (5) estimating the costs automatically by using a cost database and software. Vitásek and Matějka (2017) and Marzouk and Hisham (2012) both mention developing a building information model and using a cost database and software. Those are the most important steps required to estimate costs of a construction project.
Cheung et al. (2012) mention the information entries that can be used to connect quantities with its corresponding unit price. Fourteen entries were mentioned that belong to the objects and can be used to determine the unit prices, differing from element name to data source reference.
Nesticò et al. (2017) decomposed the construction objects using levels of breakdown. Five levels of
breakdown were used: (1) class of technological units, (2) technological units, (3) class of technical elements (4) technical elements and (5) work items. This decomposition structure could be of use for this research.