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The Big 5

The next level

Stephan Langhans* of Germany-based IDAT elaborates on the advantages of using modern CAD software for concrete precasting plants.

01 November 2010

PRE-production planning of concrete precasting plants is almost always done with computers today. With the availability of CAD (computer-aided design) software and the rapidly progressing development of computer technology, conventional manual planning no longer makes sense from an economic perspective.

For the single family house project, the wall shown was changed from original model (upper pictures) to meet the new requirements (lower pictures). On the left, the whole building model is shown in 3D.

With the growing market for CAD software, a number of manufacturers have begun offering solutions. However, AutoCAD software from Autodesk has established itself as the clear market leader – and this is not just because of the large number of installed licences. AutoCAD has set the industry standard with its DWG and DXF data formats, which still remain the standard format for CAD data exchange.

AutoCAD is a vector-oriented drawing programme that works with the aid of simple objects such as lines, circles and arcs, enabling the user to create the required element and layout plans, which contain necessary information such as component geometries, reinforcements and mounting parts. Functions such as copy, mirror, dimensioning and labelling make work easier and faster. The results can then be assembled and printed out as needed so that planning information is available on paper.

The programmer interfaces in AutoCAD also offer the option of integrating macros and functions that are specially designed for the planning of precast concrete elements.

However, there are still problems that cannot be solved, and may even be aggravated, by using 2D CAD software. As is the case for drawing, the user alone is responsible for the results from their 2D CAD software. The software doesn’t logically evaluate the draftsman’s work, and the user must manually calculate quantities and weights, with all of the errors that this may involve. CAD software functions such as copy and mirror often tempt the user to skip a careful check of the details but if a draftsman overlooks a planning error, then there is a good chance that this will first show up at the construction site, where the error will have to be corrected and paid for.

Within the last 20 to 25 years since the CAD software kicked off the first revolution in engineering offices, CAD developers and computer technology have made enormous progress. Today, we have software solutions that can eliminate or minimise the aforementioned errors while simultaneously increasing drafting speed and certainty. The CAD industry is about to introduce another revolution, the advantages of which are even more significant and far-reaching than the first.

3D and BIM replace 2D
BIM (building information modelling) is the optimised planning, execution and management of construction projects using specialised software. In BIM-supported planning, all of the involved trades perform their services on the basis of a networked building model. The advantage for the planning process lies primarily in the fact that the building data and quantity lists are always current and available, and changes are directly visible for every specialist engineer.

In the building with columnal elements, the intermediate ceiling in the original model (upper pictures) was moved up 1,000mm up just by changing the position of the affected beams. The changes to all other affected parts was done automatically by the 3D software.

By bundling the data flow in construction projects into a shared data source, the BIM process eliminates sources of error and significantly accelerates the entire process. An additional advantage of this method is that it provides the option of linking or coordinating objects contained within the building model. This allows many work and planning processes to be automated and subjected to plausibility checks, which actively contributes to quality improvement and productivity gains throughout the entire planning process.

Let’s look at a real world example of a building model of a single-family house project, the planning of which was officially concluded. Shortly before approving the plan for production, the builder requested that the four windows in the front of the building be replaced by two larger windows – a small change, but one that requires the intervention of a number of specialists. It required a change in structurally-relevant reinforcements in the wall or wall element. The quantity lists will change (reinforcement positions, concrete volumes, and maybe a change in the number and type of lifting anchors due to weight changes) and the production documents (construction and layout plans) will also have to be modified. Conventional methods would require two things to be done manually: every affected specialist area to be notified of the change and given the information that they require; and secondly, all of the given changes must be manually implemented by the specialist departments and checked against the plans and lists. When using the BIM method, the necessary changes are entered directly into the 3D building model and are available directly for every specialist department. All of the necessary changes are then entered either by an engineer into the building model or are done by specialised programs for precast concrete unit planning in a fully automated manner. Some of these programs are so highly automated that the software can automatically perform all of the changes in the construction plans with 100-per-cent accuracy, without user-intervention. The equally automatic adjustment of quantity lists constantly guarantees that the latest valid quantities are used for purchasing, inventory and accounting.

On larger and more complex construction projects, BIM has even more significant advantages. For example in a building with columnar elements (columns, beams, trusses), all of the details regarding element connections need to be measured and reinforced – requiring a total of more than 120 different construction plans, as well as additional elevations and cross-sections.

Now if the entire middle floor, with its hollowcore ceiling, is to be raised by 1,000 mm, the position of the weight-bearing beams, and most importantly the position of the brackets in the columns, must be changed. While this change in position doesn’t influence the data for the ceiling and the beams, all of the construction drawings for the columns have to be adjusted to the new position of the brackets. In the conventional scenario, the 120 construction drawings would to be adjusted by hand and under time pressures, creating the risk of individual errors. In the BIM building model, only the height of the beams need be adjusted – the attached ceiling and the affected brackets are automatically adjusted to the new position of the beams. All of the construction drawings are immediately updated, as well as the cross-sections and elevations on the layout and placement plans. Days of work are reduced to seconds, performed with greater accuracy.

Precast concrete unit planning
Transitioning from a conventional planning process, with 2D CAD software and manual or partially-automated calculation processes, to a BIM system makes sense for every precast concrete manufacturer. However, there are a few important points to keep in mind in order to guarantee long-term success. First, the prospective user must understand that this conversion will necessitate a complete reorganisation of internal project handling. Furthermore, while there are costs involved, the investment must always be considered in the context of significant increases in productivity. By using an optimised, customised BIM software, a 30 per cent increase in productivity compared to conventional 2D planning is possible, and in most cases the gains will be even higher; and this is coupled with 30 per cent lower engineering office operating costs.

The following points should be kept in mind when converting to a BIM system:

• Involve, motivate and educate employees. Without the active support of employees, converting to new software won’t work.
• Bring IT up to the latest standards – the range of functions offered in modern 3D planning software requires modern hardware and a stable and fast network.

Selecting the right software
Even for a relatively straightforward market such as the precast concrete unit industry, there are a number of software solutions available. Some of these have been developed for special types of units and others have functionality that covers all possible unit types.

Not every software program that describes itself as 3D actually has all of the features and functions of a true 3D program. There are two points that are fundamentally important and that should be explained or guaranteed beforehand.
First of all, the software specialist should be able to explain how the software’s functionality meets your company’s requirements. Does the software’s range of functions include all of the required features? Software that can only be used to work with ceilings shouldn’t even be considered by precast concrete unit manufacturers whose scope of delivery includes also other elements like precast concrete walls.

Another immensely important factor is the software’s user-friendliness and connectivity. Although the choice of software depends on several other factors, such as functionality and price, nothing is more important than whether the new software builds on AutoCAD.

Furthermore, data must be exchanged constantly with external people, such as builders, structural engineers and architects. These people most likely work with AutoCAD. Data are typically exchanged in the DWG and DXF AutoCAD formats. Autodesk’s AutoCAD Architecture programme offers a platform with full AutoCAD functionality and is completely based on 3D. A programme based on AutoCAD Architecture should be the automatic choice to keep cost of BIM software as low as possible and guarantee the greatest possible certainty of seamless operation.

*Stephan Langhans, will be present at IDAT’s stand (Zabeel E113) at The Big 5.