Reinforcement: Data versus BIM Dogma

Why do we model steel reinforcement? I think it is a classic case of ‘rendered image fixation’ where Consulting Engineers or Architects forget about the “Information” in Building Information Modelling.

I have been helping people to learn Revit for the last 8 years, and almost invariably the first thing a new user does is to forget all about the company modelling matrix, and any previous instructions about Level of Development (LOD), and try to model an item in the project that is outside the firm’s scope of works in intense geometric detail (usually with no embedded data). Reinforcement modelling seems to be part of the same problem on a bigger scale.


It is a useful exercise to refocus on the bigger picture. Concrete Reinforcement may not be everyone’s idea of an exciting topic, but it helps us understand the question of why are we doing BIM?

Building Information Modelling has multiple aims including:

  1. To assist with facilities management
  2. To assist with costing
  3. To assist with project management and phasing
  4. To assist with clash detection
  5. To produce integrated documentation

Building Information Modelling Execution Plans often specify that reinforcement needs to be modelled, but no one seems to know why. Steel fixers interpret the structural engineer’s drawings on site, and set out the reinforcement by quick and approximate measurements, checking (hopefully) as they go that they haven’t exceeded the engineers required spacing. There is no guarantee that reinforcement will end up exactly where it was modelled (unlike steel framing elements). The only exception would be welded reinforcement cages.

Modelled reinforcement won’t help with clash detection, because you can’t be 100% sure precisely where the reinforcement will sit. It won’t help with retro-fitting penetrations to slabs and walls for the same reason. Concrete X-Rays would still be required for establishing precise reinforcement locations.

Costing is probably the greatest potential use for modelled reinforcement. Quantity Surveyors (QS) can use the models to produce more accurate cost estimates. My question is, would the cost estimate be more accurate if we used the data from the model instead of just the geometry? Modelling of reinforcement is labour intensive, reinforcement laps are not often modelled correctly, and slab mesh laps are never modelled correctly, so the QS still has a bit of work to do. The spacing of beam and column ligatures and ties are never simple and usually change spacing towards the top of the column and the end of the beam.  This set out gets even more complicated in earth quake zones.

The best Building Information Modelling solution for the costing of reinforcement and facilities management is embedded data within all concrete elements. The column shown below has parameters for the vertical reinforcement, ligatures, ties, connections at the top and base, a reference to a section of the column and a reinforcement rate. Once you combine this with the volume of all similar columns within the building, which can be easily calculated using the model parameters, the QS should be able to efficiently estimate the cost of the reinforcement required.

Column Reo

These issues don’t just occur in Structural Engineering. Architects and in particular Interior designers often achieve excellent results by using embedded data over detailed geometry. Please note the examples I have given are from my own experience of reinforced concrete in Australia. The approach to concrete reinforcement, reinforcement scheduling and reinforcement detailing in the U.K and the U.S. are completely different.

I am more than happy to be proved wrong on this issue. If you work for a Quantity Surveyor or you schedule reinforcement for a living and find modelled reinforcement useful let me know.

Links for understanding LOD and facilities management

The views expressed in this blog are not necessarily those of my employer.


BIM, Structural Engineering and the Digital Divide

Any conversation with a Structural Engineer about Building Information Modelling is an odd experience.  They will either tell you it is the best thing to happen to the industry in years, or that it simply doesn’t happen and doesn’t exist. The answer is either yes or no, black or white. Comments like “we tried it once and it doesn’t work” are not uncommon.

A conversation with an architect would be somewhat different. A lot of architecture firms have a BIM statement which locks them into steady progress, they may not be setting the world alight now but they plan to be in a few years. There are many one person firms doing a great job of documenting houses using 3D models with embedded data. The point is most firms have their toe in the water to some extent. To architects the question of BIM is a graded scale. They see themselves as all involved in some form of BIM, the only difference is the extent of that commitment

This ‘yes or no’ attitude of Structural Engineers is having a polarising effect on the industry. There are a group of large and medium-sized firms who dominate the BIM niche market. They share some of the characteristics listed below


Characteristics of BIM capable Structural Engineering firms

  • A high percentage of government clients or large-scale projects
  • Transition to Revit® occurred pre-global financial crisis
  • The modelling occurs using multiple software platforms (for example Revit®, Tekla Structures and Navisworks®)  that are constantly changing
  • Highly skilled Employees
  • Low level of staff turnover
  • Often multi-disciplinary firms
  • Building modellers are engaged with architects and clients
  • Engineers and Modellers collaborate well
  • Building Modellers are perceived as adding value to projects
  • Fees and wages tend to be higher than average

The rest of the market seems to be headed in an entirely different direction.

Old drafting

Characteristics of Structural Engineering firms with no BIM capacity

  • Software tends to be several years old
  • The software that is used is not used to not used to its maximum capacity
  • Smaller commercial, residential and industrial projects
  • Higher staff turnover
  • Drafting is perceived as unskilled labour and a cost to be minimised
  • Minimal staff training
  • Lower than average fees and wages

While Building Information Modelling firms are no magical paradise, the trend is concerning. Would potential employees who had always worked outside the BIM community be able to get up to speed in less than two years? Would an engineer who had never used ETABS or Robot Analysis with Revit be able to step straight into a new project with minimal training?. The point is that the actual positions are so different, it is increasingly hard to move between the two worlds. There has been a 10 year conversation about legal issues, collaboration and level of detail, to name but a few issues, and it is difficult to enter that conversation and put those issues in context.

As the market slows down we can expect small to medium-sized consulting engineers to invest less in software, training and staff retention. Which leads to a vicious circle, the less you invest in these things, the less capable you are of landing a large project which could lead to increased profits, which could be invested in staff training and software.

Consulting engineering is a service industry. The best way to thrive long-term in such an industry is to provide the highest quality of service possible. Providing a low-cost, basic level of service may lead to short-term profits, but eventually those firms will lose out to the low-cost, basic service offered by offshore firms, who will always win any price war.

All is not lost for the ‘digital have-nots’. Firstly the current level of unemployment in the construction industry has seen many skilled engineers and modelling staff out of work. These people will eventually find employment with the digital ‘have-nots’, seeding their new ideas with their new employers. Secondly Australia must follow The United Kingdom’s and Singapore’s lead and pass Building Information Modelling legislation. Such laws (with a lengthy lead in time) would still deliver most of the pie to the BIM capable firms, but they would also deliver certainty to the industry and create a sense of urgency in the medium-sized firms that are in danger of being frozen out of a lucrative portion of the market.

The views expressed in this blog are not necessarily those of my employer.