BIM and advanced post-tensioning design methods

Jyrki JAUHIAINEN

Head of Department, Advanced Concrete Structures

Civil Engineer , M.Sc.Finnmap Consulting Oy Helsinki, FinlandJyrki.Jauhiainen@finnmapcons.fi

Jyrki Jauhiainen, born 1973, received his civil engineering degree from the University of Oulu, Finland.

Summary

The goal of this paper is to describe one process for developing advanced design techniques for post-tensioned concrete structures. The integration between finite element calculation softwares and different 3D modelling softwares has become more and more important in everyday engineering work. The design of the post-tensioned structures has been a well specialized field in construction business. Different 3D and FEM programmes have been developed in order to enhance the effectiveness of design process. Yet, no practical solution for BIM and post-tension design has been presented. The methods and results of BIM; its advantages, problems encountered, solutions and future prospects will be presented in this paper. The author presents observations gathered during this hectic development process.

Keywords: post-tensioning; anchors; slabs; beams; BIM; FEM; advanced design methods; VBC

1. Introduction

All data needed for the design, construction, use and maintenance of buildings is easier to manage – quickly, in real time, graphically and in digital form – when using the help of a product model. With the help of the product model you can exchange and manage a huge quantity of information more reliably and efficiently than before.

The design of post-tensioned concrete structures is a specialized field in construction business. Structural engineer provides the calculations while draftsmen are preparing drawings and site personnel are executing the actual work. As a result of this, customer will receive durable and good product, concrete structure by means of reliable and cost-effective plans as well as state of the art site production. The increasing use of BIM technology has forced us to take a closer look on this procedure as a whole, how to maximize the effectiveness and how to minimize errors and miss-information. And of most importance, how to maximize the benefits for our customer.

Linking the design and drafting capabilities of various software gives the engineer a completely new set of tools. The design process can be accessed in each phase and the iterative nature of prestressed structure design will show its strength.

Fig 1 Created data link between BIM and FEM

2. Requirements

After earlier mentioned input data processing, the engineer has normally conducted structural calculations manually or by using in-house developed spreadsheets. If results were shown to be not satisfying, the input data had to be modified.[1] In our project we wanted to enhance the effectiveness of this phase. Post-tensioning calculation is an iterative process and by combining the experience of the engineer with computer calculation power, iteration can be made faster and more effective. Our idea was to create/write a link between input source, static software and BIM environment so that all information could be transferred as automatically as possible and yet the engineer would have possibilities to intervene and control the process. One crucial point for us was of course that this data transfer should work in both directions, a bi-directional data transfer. Of an importance was to notice that if changes in dimensions occurred,

these also needed to be included directly in BIM environment.[2] Accordingly also update in input data source had to be done.

3. Discussion, Conclusions and Acknowledgements

This developed new tool and way of working has already proven its effectiveness in everyday design work. Both time consumption and numbers of design errors have been decreased. The quality of design has improved. It enables faster information flow from designer to draftsmen or modeller and it also opens possibilities for further development within BIM.

Virtual building concept

In the future the VBC Virtual Building Concept will become an everyday issue for engineers.[3] The tools developed will offer a powerful way to implement also post-tensioned structures as a vital part of the whole construction process. VBC model can also contain information of structures life-cycle design. Tendons can be measured after laying them on site and this information can be stored in the model and used later for repairs or new openings etc. The VBC can work as data storage for everybody involved in the project, including future users.

4. References

[1] AALAMI, BIJAN, Guidelines for the design of Post-tensioned Floors, Concrete International, March 2003

[2] CHUCK EASTMAN, PAUL TEICHOLZ, RAFAEL SACKS, KATHLEEN LISTON BIM Handbook: A Guide to Building Information Modeling for Owners, Managers, Designers, Engineers and Contractors, 2008

[3] CONFEDERATION OF FINNISH CONSTRUCTION INDUSTRIES, ProIt, Product Model Data in the Construction Business, 2006

BIM and advanced post-tensioning design methods

Jyrki JAUHIAINEN

Head of Department, Advanced Concrete Structures

Civil Engineer , M.Sc.Finnmap Consulting Oy Helsinki, FinlandJyrki.Jauhiainen@finnmapcons.fi

Jyrki Jauhiainen, born 1973, received his civil engineering degree from the University of Oulu, Finland.

Summary

The goal of this paper is to describe one process for developing advanced design techniques for post-tensioned concrete structures. The integration between finite element calculation softwares and different 3D modelling softwares has become more and more important in everyday engineering work. The design of the post-tensioned structures has been a well specialized field in construction business. Different 3D and FEM programmes have been developed in order to enhance the effectiveness of design process. Yet, no practical solution for BIM and post-tension design has been presented. The methods and results of BIM; its advantages, problems encountered, solutions and future prospects will be presented in this paper. The author presents observations gathered during this hectic development process.

Keywords: post-tensioning; anchors; slabs; beams; BIM; FEM; advanced design methods; VBC

1. Introduction

All data needed for the design, construction, use and maintenance of buildings is easier to manage – quickly, in real time, graphically and in digital form – when using the help of a product model. With the help of the product model you can exchange and manage a huge quantity of information more reliably and efficiently than before.

The design of post-tensioned concrete structures is a specialized field in construction business. Structural engineer provides the calculations while draftsmen are preparing drawings and site personnel are executing the actual work. As a result of this, customer will receive durable and good product, concrete structure by means of reliable and cost-effective plans as well as state of the art site production. The increasing use of BIM technology has forced us to take a closer look on this procedure as a whole, how to maximize the effectiveness and how to minimize errors and miss-information. And of most importance, how to maximize the benefits for our customer.

Traditionally more advanced calculation methods have been considered to be separate software from drafting tools. Like various FEM tools and CAD based drafting tools. But we wanted to find out a way to link FEM programmes with our modelling tools and make this link usable for group of programmes, not just one particular.

Linking the design and drafting capabilities of various software gives the engineer a completely new set of tools. The design process can be accessed in each phase and the iterative nature of prestressed structure design will show its strength. As shown on Figure 1. The BIM design path can be edited or accessed in various phases.

Fig. 1: PT design workflow

Product model-based data management in a construction project connects the information needed for design, product manufacturing, construction, and the use and maintenance of the building. Product modelling transforms building design from traditional line-drawing to 3-D design combined with other product information. Design is done with the help of product structures and components. The spatial model contains information about the spaces, their location, area, and other desired characteristics of the spaces. Product structures such as walls and slabs contain information about, for example, materials, measurements, thermal insulation, strength and environmental qualities. When the schedules are linked with product structures, the result is 4-D design.

2. Project

2.1 Details

First we had to define carefully our needs, our capabilities to do the work, time schedule and budget. Of course the main idea was that our tools must be in everyday use all the time and development should always supplement our work. Alternatives for our solution considered were:

a) More manual editing, simply using BIM as a helping tool. Simply printing out results from FEM programme and preparing manually the input data for modelling. The tender model is not used in calculation process. Calculation model is prepared separately

b) More automated data transfer through manual editing in Excel etc. The results are taken automatically from FEM programme and post-processed in Excel. The tendon coordinates are then manually transferred to BIM software.

c) Fully automated data processing between calculation and modelling software, editing is done in BIM environment. This involves the use of tender model as a source of input for calculation. All editing is done either in FEM environment or in BIM environment. The connection works in both directions.

After carefully examining these alternatives, we decided to go further with the alternative c. It is most advantageous and completes our needs for BIM. It will also produce most added value for the project and for the customer.

INPUT DATA

STRUCTURALCALCULATION

DRAFTINGCAD

BIM3D

OUTPUTDRAWINGS, LISTS

OUTPUTDRAWINGS, LISTS, MODEL

Fig 3 Created data link between BIM and FEM

2.2 Requirements

Basically post-tensioning projects consist of few major parts [1]. Fist can be described as input data processing. Engineer traditionally receives input data – developed by means of CAD- or pdf-file - for calculation from client or other designer. The engineer uses this information stated in these documents as the basis for ones calculations and takes into account also other design requirements. Now, however, we desired to use geometrical model, modelled already at tender phase of the project as input data source. This geometrical data could include also loading, material information etc, vital information for PT designs.

Fig. 2: Yesterday: Manual calculation by Excel or MathCAD sheets

After earlier mentioned input data processing, the engineer has normally conducted structural calculations manually or by using in-house developed spreadsheets. If results were shown to be not satisfying, the input data had to be modified. In our project we wanted to enhance the effectiveness of this phase. Post-tensioning calculation is an iterative process and by combining the experience of the engineer with computer calculation power, iteration can be made faster and more effective. Our idea was to create/write a link between input source, static software and BIM environment so that all information could be transferred as automatically as possible and yet the engineer would have possibilities to intervene and control the process. One crucial point for us was of course that this data transfer should work in both directions, a bi-

directional data transfer. Of an importance was to notice that if changes in dimensions occurred, these also needed to be included directly in BIM environment. Accordingly also update in input data source had to be done.

The programme we wrote automatically reads the needed tendon information from calculation software. After this, the engineer can define anchors and required reinforcement etc. The BIM software will model the tendons with designed heights and other parameters. The modelled tendon will have some user defined parameters such as elongation, tendon ID, material features. This information can be used to produce traditional tendon lists with elongations and all the information needed for the quantity engineer and for the site traditionally or Virtual Building Concept, the site and manufacturer can obtain this information automatically.

Fig. 4: Geometrical model

3. Problems encountered

3.1 Software

The development of an in-house, non-commercial solution faces many problems. First and not least is the programmes capability to communicate with other types of programmes. Application Programming Interfaces (API) enables, if released for users, writing codes to switch information. Our requirements were naturally to transfer adequate amount of tendon and geometrical information from calculation software to the used BIM software. To meet our demand, we had to develop as open system as possible to be able to use various programmes, and not to limit only one software provider. [2]

However, we encountered some problems, described below. Some programmes are partly not ready yet for use. They are still in beta-testing phase or there simply is no suitable software available. The use of these programmes can be more challenging than normal CAD based programmes. The user interface might be unfamiliar and new. Cost for software licences can be substantial. More advanced FEM programmes, which can handle tendon design to some level, are expensive. The choice of programme for structural engineer is limited at least for now. At some special areas, traditional 2D design can still prove to be more efficient, not forgetting paper and pencil. Quality printouts may be a problem if not taken into account. Resources must be focused more in the beginning of the projects. This is very important point and to be considered by all parties involved in the project. Although these obstacles created a problem, we did find a way to overcome these. The application interface should be kept as simple as possible and yet it should provide to engineer

adequate level of control of the data transfer procedure.

4. Benefits

4.1 Designer

The use of advanced BIM tools both in design and calculation operations can greatly decrease errors made by design team by allowing the use of conflict detection where the computer actually informs team members about parts of the building in conflict or clashing, and through detailed computer visualization of each part in relation to the total building [3]. It improves design, avoids spatial interferences, and reduces RFIs (requests for information). The new tools also make design work faster and more cost effective. The information which designing engineer creates with various calculation software can now easily and error free manner be transferred for modellers use. Enhance and speed up design by generating more precise information and by reducing design errors, by improving the plans compatibility and by promoting collaboration between various designers. Total execution time for whole project will actualize only after all parties have implemented BIM techniques and test period has been successful. For smaller only PT projects and for PT parts of larger projects, this technique is already a powerful tool.

4.2 Customer

The benefits for customer are following:

Of most importance is that total time used for design can be decreased when all parties use the same model - BIM – simultaneously. One other big benefit refers to BIM requiring update of information for all parties; the information will in this way always be accurate. Customer service will be improved by generating useful information to support decision-making and by visualizing and comparing alternatives functionally and in terms of costs. The cross-checking of designs is easy and fast, mistakes can located easily; model check. The complexity and challenging features of the project can be easily visualized, efficiency in tender phase.

Fig. 5: Present information flow Fig. 6: Future information flow

The flexibility of designs will be enhanced and documents will be updated automatically. The control of design information in large projects can be optimized. Using BIM will give the competitive advantage and time schedule in 4D. The whole construction sequence can be modelled and material flows can easily be controlled. Overall information flow will be better.

4.3 Site

From the sites point of view, modelling offers some clear advantages and of course in the future even more possibilities. It enables the transfer to completely paperless site. The site personnel can quickly check directly from the model all the information needed to execute their work.

Fig. 7: Connecting design with execution

All geometrical data can be transferred directly from the model without any manual editing. Material lists and structural dimensions can be produced automatically. And in the model all reinforcement is shown in 3D as it would appear on site and collision risks can be detected and avoided in time. This will save time and costs on site. To improve construction work quality and productivity by generating more practically usable information for production planning, cost management and scheduling, and the manufacture and procurement of building products are also our goals. This technique also - if not guarantees - but makes it easier to check HVAC and other installations before noticing costly collision with structures on site.

Fig. 8: Tendon plan (CAD) Fig. 9: Finite element model, tendons (FEM)

5. Discussion, Conclusions and Acknowledgements

This developed new tool and way of working has already proven its effectiveness in everyday design work. Both time consumption and numbers of design errors have been decreased. The quality of design has improved. It enables faster information flow from designer to draftsmen or modeller and it also opens possibilities for further development within BIM.

The site and customer can also take a closer look on model in earlier stage and procurement can be started in earlier stage. Demanding structures can be visible to all parties of the project and all have access to same information.

Virtual building concept

In the future the VBC Virtual Building Concept will become an everyday issue for engineers. The tools developed will offer a powerful way to implement also post-tensioned structures as a vital part of the whole construction process. VBC model can also contain information of structures life-cycle design. Tendons can be measured after laying them on site and this information can be stored in the model and used later for repairs or new openings etc. The VBC can work as data storage for everybody involved in the project, including future users.

6. References

[1] AALAMI, BIJAN, Guidelines for the design of Post-tensioned Floors, Concrete International, March 2003

[2] CHUCK EASTMAN, PAUL TEICHOLZ, RAFAEL SACKS, KATHLEEN LISTON BIM Handbook: A Guide to Building Information Modeling for Owners, Managers, Designers, Engineers and Contractors, 2008

[3] CONFEDERATION OF FINNISH CONSTRUCTION INDUSTRIES, ProIt, Product Model Data in the Construction Business, 2006