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RESEARCH REPORT

Paper Study: A survey on modeling guidelines for quantity takeoff-

oriented BIM-based designAndre Monteiro, Joao Pocas Martins

Advisor: Professor Wei-Chi WangStudent: Abdoul-Aziz GANSONRE

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ACRONYMS BIM: Building Information Modeling

QTO: Quantity TakeOff

SIGABIM: A research project for application and implementation of BIM.

CRMC: Curso Sobre Regras de Medição na Construção” (Course on Measurement Rules in Construction)

LOD: Level Of Development

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CONTENT

Introduction

Study outline

Research findings

Conclusion

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INTRODUCTION Quantity TakeOff (QTO) is one of the potentially most

important applications of BIM.

Traditionally, quantity takeoff is a manual process that involves measuring the different design elements, namely, floor plans, elevations, cross sections and other similar documents. (error prone: e.g. a cross section of the connection of a beam, a column, a wall and a slab).

This type of survey also aims to highlight the potential benefits of using BIM for QTO.

The following presentation will be divided will show the applications of BIM-based QTO, its problems and recommandations. 1/7/2014

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STUDY OUTLINE

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OVERVIEW OF QUANTITY TAKEOFF (1/2)

QTO is one of the key tasks in the construction process.

QTO is the measurement of the building's schematics or of the work done on site which is assembled in a Bill of Quantities.

QTO should be accurate because the budget of the whole construction process depends on it.

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OVERVIEW OF QUANTITY TAKEOFF (2/2)

Relation of quantity takeoff with the other major tasks in the project life-cycle.(A. Monteiro, J. Poças Martins / Automation in Construction 35 (2013) 238–253)

QTO applications

•Early stage: it provides the base for a preliminary cost estimate for the project.

• Tendering stage: it is used to assist in the estimation of the project's cost and duration of the construction activities.

•Construction stage: it is used for the economic control of the project.

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BIM-BASED APPROACH

BIM-based QTO provides simpler and yet more detailed and accurate cost estimates of the project.

Although capable of providing QTO tables, popular BIM tools cannot manipulate that data.

Information is usually exchanged between the BIM and cost estimation software in one of two ways:

• Both systems use the same proprietary format for product data definition and the exchange is done smoothly without loss of data.

• The systems use different proprietary formats and the exchange is done by converting the data to a third, common format, usually the Industry Foundation Classes (IFC).

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SOFTWARE ANALYSIS (1/2) ArchiCAD and Revit Architecture are the two most widely

used BIM tools for architectural design.

Revit's QTO feature is simpler and not as powerful as ArchiCAD's.

ArchiCAD provides a larger choice of pre-defined parameters, while Revit has fewer predefined measurement parameters.

Autodesk Revit Architecture (left panel) and Graphisoft ArchiCAD (right panel) QTO parameterization interface.(A. Monteiro, J. Poças Martins / Automation in Construction 35 (2013) 238–253)

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SOFTWARE ANALYSIS (2/2) ArchiCAD allows the user to edit some of the fields through the

definition of new configurations directly on the takeoff sheet, with such changes being then automatically processed in the building model.

ArchiCAD can save the tables in various formats, including Excel, PDF and DWF. Revit only exports tables in TXT format, which often requires further processing in order to handle the data in subsequent phases.

There is also a number of different applications that allow the user to perform QTO on a BIM model Vico Office, Solibri Model Checker, Autodesk Navisworks etc.

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PROCESS OUTLINE (1/3)

This study was conducted under the SIGABIM project.

ArchiCAD was adopted as the BIM tool.

The CRMC as the criteria to be surveyed.

As for modeling detail, the most used level was the LOD 300.

SIGABIM ArchiCAD

CRMC LOD 300

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PROCESS OUTLINE (2/3)

BIM-based QTO according to the CRMC criteria survey — conceptual workflow.(A. Monteiro, J. Poças Martins / Automation in Construction 35 (2013) 238–253)

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PROCESS OUTLINE (3/3) Export to Vico Office was also taken into account in the modeling

process, meaning that no specific functions of ArchiCAD were used, thereby preventing conflicts. The goal in SIGABIM is to use Vico Office as a tool to extract quantities.

Vico Office uses the same extracting engine as ArchiCAD's, which means it will recognize the object's takeoff parameters.

Certain CRMC criteria require greater detail in the modeling. An example of this is would be the modeling of waterproofing finishes in roofs, where LOD 500.

For the purpose of this article and for the sake of simplicity, the BIM design is considered “automatic” when the element ismodeled using the same ArchiCAD element type.

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RESEARCH FINDINGS

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EARTHWORK

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COATINGS

For QTO in BIM, the coating quantities can be obtained in 2 ways:

It can be modeled to obtain the exact quantity. (overloaded)

It can be taken from the structural elements with a margin of error being assumed. (errors)

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FORMWORK (1/2)

The formwork is not created directly from the model and there is not even a tool for modeling formwork.

In the IFC format, no entity is defined for formwork. In terms of QTO, it is not possible to obtain systematic,

complete and consistent results. The formwork can be measured based on the surface of the

elements involved, but this does not work where elements intersect.

The only solution for a full and effective system is to explicitly model the formwork, but this is extremely time consuming.

Issues in extracting formwork quantities from a BIM model.(A. Monteiro, J. Poças Martins / Automation in Construction 35 (2013) 238–253)

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FORMWORK (2/2) The solution found involved creating an add-on for

ArchiCAD that would automatically provide a formwork model based on the structural model of the building.

The add-on would use the standard ArchiCAD tools, Wall, Slab and Roof, respectively for vertical, horizontal and sloping formwork, to assemble the formwork model and the QTO process would develop from there over the formwork model obtained.

Formwork model.(A. Monteiro, J. Poças Martins / Automation in Construction 35 (2013) 238–253)

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REINFORCEMENTS

ArchiCAD can be used to design a structural model but it is not possible to represent the reinforced concrete elements' rebars.

Process: build building structure elements in a low LOD and then export the model in a structural analysis applicaton where the cross sections are designed and the elements' connections detailed.

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REINFORCED CONCRETE ELEMENTSMeasuring the volume of concrete is easy because it is automatically extracted, but grooves/recesses is difficult.

All the grooves/recesses should be modeled manually.

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FOUNDATIONS Footings, piles, beams or foundation walls, are different types of

Foundations.

Foundations are an example of building elements which do not have a specific modeling tool.

Foundation elements have to be modeled using other types of elements such as the Slab, Beam, Column, Wall.

Each object is then associated with a specific Layer or ID in order to be possible to isolate it from other building element types.

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STAIRS

Stairs are rather problematic elements in that they are hard to model and to measure.

The ArchiCAD Stair object is quite limited in terms of QTO; their measurement parameters are applied to the staircase object as a whole, not to the sum of its component parts.

The good point is that it is possible to automatically extract quantities of the staircase.

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OPENINGS (1/2) To obtain an accurate QTO for the windows and doors, we

use the following steps:.

1. Define and model the opening's configurations manually, usingother ArchiCAD tools such as Wall or Beam.

2. Model the opening using the Window/Wall tool in ArchiCAD

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OPENINGS (2/2)

3.Calculate the values manually and add them to the element as a label.

4. Classify the openings in accordance with their dimensions and other configurations, then model and provide each opening with a specific ID in accordance to its classification.

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MEP ELEMENTS

The measurement of MEP elements – pipes, ducts and cableways –cannot be achieved directly by the assessed tools.

The average length can be taken for straight elements but not for curved ones. In these cases, their radius and the angle of curve should be extracted and then applied in a formula to arrive at the average length.

IDs and Layers should be assigned to enable the identification and separation of the elements belonging to each continuous structure.

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CASE STUDY 1/2

The SIGABIM methods presented in this article were applied, specifically, in three projects — a hospital, an office building and a research center.

The overall modeling LOD 300 used in most cases proved to be enough to satisfy the modeling and QTO needs.

The quantities taken from ArchiCAD directly generally meet the measurement requirements according to the demands of traditional processes.

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CASE STUDY 2/2Using BIM compared to traditional approach gives the following benefits:

Increased accuracy in most measurements.Direct linkage of the model extracted quantities to planning Software.

Comparison of measurements for different phases of the building.

Life-cycle becomes available.Possibility of extracting partial or total quantities relating to a given spatial area.

Margins of error often below 1% Possibility of extracting information beyond typical measurements, such as the number of openings or number of beams with a particular material characteristic, among others.

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SURVEY CONCLUSIONS (1/2)

The modeling is somewhat limited by the tools available. When it comes to modeling — a staircase, for instance.

As an alternative, users can configure a staircase according to their requirements through the GDL programming function in ArchiCAD.

Another solution would be to use elements other than the Stair tool and assemble a staircase using Walls, Slabs and Beams.

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SURVEY CONCLUSIONS (2/2)

Modeling elements for QTO purposes — conceptual workflow.(A. Monteiro, J. Poças Martins / Automation in Construction 35 (2013) 238–253)

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PERSONAL REFLEXIONS

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PROBLEMS (1/2)

The BIM based-estimation process is not completely automatic.

There is not a specific standard of parameterization of objects.

Because the case study focuses on ArchiCAD, it cannot be regarded as representative for all BIM applications.

A quick analysis of Revit's QTO parameters and mechanics shows that the same problems experienced with ArchiCAD are likely to occur with Revit.?

ArchiCAD's specific or proprietary functions often lead to errors both in the IFC translation and in the Vico Office QTO.

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PROBLEMS (2/2)

About coating in the BIM tools, it is difficult to perform QTO with exact accuracy.

One major disadvantage of the BIM tools that were evaluated is their inability to work with formwork in the model.

For simplicity in this research, the BIM design is considered “automatic”. For manual design, the results of the present research may not be totally relevant.

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RECOMMANDATIONS Use ArchiCAD’ GDL Programming functions to configure better

modeling and QTO parameters. (Difficult)

Perform a survey on BIM-based QTO using Revit and see if we encounter the same problems. Then, compare with ArchiCAD and use some ArchiCAD QTO positive aspects to improve the QTO on Revit.

A study on how to improve the accuracy of quantities extracted including:

• the standardization of QTO parameters,

• the adequate BIM software and cost estimation software to use depending on the project.

• The best ways of obtaining perfect interoperability during the extracting process

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REFERENCES

Monteiro, A., and Martins, J. P., (2013), “A survey on modeling guidelines for quantity takeoff-oriented BIM-based design,” Automation in construction, Vol. 35, pp. 238-253.

http://www.archicadwiki.com/MEP/FAQ

http://www.abvent.com/softwares/archicad/

http://fr.wikipedia.org/wiki/ArchiCAD

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