Attention to detail

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In the last issue of AEC Magazine we looked at Nemetschek’s Allplan product portfolio, and its architectural design solution. This month it’s the turn of Allplot, which among other things, makes the RC detailing process a whole lot more efficient.

Nemetschek has been active in the UK AEC market for some two years now, and in our October issue we ran through the German company’s extensive portfolio (you can find the article elsewhere at www.cadserver.co.uk). Within the scope of the feature we saw how the Allplan suite provides a wide range of modules to cater for the variety of disciplines involved in the construction process, from architecture and structural engineering, to HVAC and urban planning. We also took a more in-depth look at the core architectural design tools, and the single building model approach that Nemetschek adopts. Now – moving from architectural design into hardcore engineering within the space of a month – it’s the turn of Allplot, Nemetschek’s structural and civil engineering design solution. However, with the wide range of tools available in the Allplot product range including digital terrain modelling and site design, for the purpose of this review we’re going to focus on the structural side of things, with a specific focus on Reinforced Concrete detailing, and those that battle with bar marks and reinforcement schedules on a daily basis will know you can’t get much more hardcore than that.

RC Detailing

Advantages of working in 3D

From drawing board to CAD, reinforced concrete detailing involving bar and mesh reinforcement has come along way in its hundred or so years. While the introduction of 2D CAD has provided RC detailers with a range of productivity enhancing tools, the working method still pretty much mimics the drawing board process, albeit with some automated routines. Of course, working in this way requires the RC detailer to be entirely responsible for the consistency of data between views, and as a result can be susceptible to errors. In addition, the process often requires numerous written notations to make the drawings clear.

The advantages of working in 3D: since the drawing is generated from a central three-dimensional model, the plan views, elevations and sections are interdependent. This means that any changes made to the central model are automatically reflected in each view, and of course in the reinforcement and bending schedule.

For example, a construction group consisting of bar reinforcement, fixtures and void formers — a dynamic macro commonly found in pre-fabricated units — can be pulled from a catalogue and placed in or on top of a column. The user then immed-iately sees the steel correctly represented in all views and sections. The creation of this 3D macro alone is a simpler process than fashioning several 2D symbols, and that’s even before you take into account that placement can be made at a single location. Perhaps of more importance though, is the fact that you can be confident that the views and sections derived from the 3D macro are auto-matically correct. What’s more, you can carry out collision control during reinforcement design, with any clashes highlighted in the animation window.

As a result, you could think of 3D programs such as Allplot as more than just a ‘drawing and design’ tool, as it could be used consistently for quality assurance during all phases of the building process.

To the untrained eye, a reinforced concrete detailing drawing is just a mess of lines, tags, and schedules, and even to the trained eye it takes a great deal of concentration to fully understand the positioning, type and quantities of bars within the structural concrete element. Therefore, it’s of the utmost importance that any drawings created are clear and perhaps more critically, accurate in terms of their depiction of steel reinforcement in all views, plans, sections, and elevations.

As with its parent application, Allplot addresses the design process from a 3D perspective. That is, you build a 3D model, which is then used to produce all your plans, elevations, sections, and indeed bar schedules automatically. If you want, you can also work in a semi-automatic 2D mode, but while applicable in some scenarios, this fails to take advantage of Allplot’s powerful functionality. It’s a bit like buying a Porsche and never getting out of first gear.

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Whether you’re creating pad or continuous foundations, door recesses, stairs or simply a slab, the starting point for RC detailing in Allplot is always the shell. The easiest way to think of a shell is the concrete element in its entirety, and this can be produced in a number of ways. You can either take architectural elements direct from Allplan, convert 3D geometry imported from another CAD program (such as AutoCAD DWG, DXF, or IFC), use imported 2D data as the basis to build up a 3D model, or use Allplan’s 3D modeller to start from scratch.

Once you have your structural shell, you can start detailing. Here, Allplot provides a range of tools to help automate the process, at the same time as building up a central database of all the steel used. From Allplot’s bending shape catalogue you need to select shape, diameter/steel grade, concrete cover, number of bars/spacing and away you go. Because you are working within the confines of a shell, the product’s in-built intelligence helps ensure all the steel is automatically placed in the correct place, so you don’t have to work out exact lengths etc. Bar marks are also placed automatically, which of course link into the central steel database to enable automatic scheduling, and any reinforcement elements with the same characteristics are automatically assigned the same mark number. In addition, as well as providing the full range of standard bar shapes, you can also design non-standard shapes.

Bamtec – a revolution in slab reinforcement?

Bamtec is a relatively new economical method of creating concrete slab reinforcement. Instead of conventional steel mesh or cut and bent bar, Bamtec uses pre-fabricated reinforcement carpets produced using an automated engineering process and rolled out on site just like a carpet.

With Bamtec you can automatically reinforce plate structures optimally designed by finite element analysis using the minimum amount of steel. The round steel bars are used in carpet production with different diameter and lengths, allowing carpets to fit slab layouts precisely and cope with varying load requirements.

Of course one of the main principles behind Bamtec is one of saving – both time-wise (during the construction process) and in terms of cost (as Bamtec is designed to make significant savings on the amount of steel used). The figures quoted claim on-site fixing cost savings of up to 80%, materials savings of 20-40% and shorter and more automated design and detailing time. So how does this revolutionary system work?

Starting with a slab model or plan, structural calculations are carried out using a finite element analysis system such as Staad.Pro. This determines the reinforcement required in the X and Y directions in both the top and bottom of the section. After dividing up the floor surface into the minimum number of carpets, the Bamtec software automatically determines the make up of the carpets, as well as the position, length and diameter of all its bars. Four carpet positions are required per floor — two at the bottom (in X and Y), and two at the top. The engineer can also select parameters himself — for example, the bar diameter and spacing of the main reinforcement can be individually set.

The end result of this process is a number of assembly and production drawings, which are automatically created and then used in the Bamtec manufacturing process.

The actual carpets are made with a giant welding plant where a robot welds the bars at the calculated spacings onto the carrier strips to create an accurately dimensioned reinforcement carpet. These carpets are then delivered on site and rolled out quickly and easily; two men and a crane driver can place a ton of reinforcement in 15 minutes — pretty impressive stuff! Bamtec was developed by consulting engineers Haussler, Kempten, and Nemetschek, which is not surprising when you look at the amount of Bamtec functionality built into Allplot. While it is used extensively in Germany, it has also been used on hundreds of UK projects, pioneered by Hy-Ten.

On top of typical bar reinforcement, Allplot also provides a full range of tools for Bamtec for slabs (see box out) and area and mesh reinforcement to facilitate the detailing of large areas. Here, recesses can be taken into account, and as the bars are associated with the placing polygon (or shell), any changes you make to the geometric outline of the polygon (or to the settings) are reflected in the corresponding bars.

While huge productivity gains can be made from placing standard bars, or mesh or area reinforcement, Allplot also provides a number of parametrically-defined reinforcement components, which enable standard structural concrete elements to be detailed automatically e.g. pad found-ation/columns, column/beams, stairs etc. Just as a single bar automatically locates itself within the shell, each component attempts to fit itself within the ‘formwork’ according to its pre-defined parametric properties. This has the potential to save huge amounts of time.

Naturally, as with any automatic CAD process, it’s still important to have complete control over how your reinforcement is placed and represented in the final drawings, and as a result Allplot provides you with a wide range of tools to do this. For example, you can modify shells, bar placement, bar parameters, bar marks, bar labels and hooks. Of course, whilst not a necessity by any means, your drawings can also be exported into another CAD program such as AutoCAD, to finalise your finished RC drawings, or add title blocks etc.

In conclusion

I have to say I am incredibly impressed with Allplot’s concrete detailing module. With the inherently complex nature of the discipline, working with a 3D model makes an incredible amount of sense, not only because you only need to work on one set of data to produce multiple drawings, but the system automatically creates reinforcement schedules as well. As a result any changes to the core model will automatically be updated everywhere else, which, of course, also helps reduce errors. Additionally, as with the core Architectural Allplan product, the use of the OpenGL-driven animation window makes it incredibly easy to visualise exactly where you are placing your reinforcement.

While there is an obvious advantage of using Allplot alongside the architectural module of Allplan, this is by no means a necessity. There are many Allplot users working from imported 2D or 3D models from AutoCAD or other CAD applications, or indeed starting from scratch.

As with Allplan, the Allplot interface can be a little complex and bewildering at times, but once you get used to this aspect of the program, what lies beneath is a highly sophisticated solution that has the potential to dramatically increase productivity and accuracy throughout the RC detailing process, and this in itself could be worth its weight in gold.

www.nemetschek.com

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