4D BIM for Construction

Where does CPM and 2D fit in the Digital Construction Age?

Posted by Tom Dengenis on Feb 18, 2017 3:03:29 AM

Within a few years of its’ introduction, Critical Path Method (CPM)- a project modelling technique developed in the late 1950s- succeeded in making positive performance impacts in both manufacturing and the defence industries.  “The critical path method was developed at the DuPont Company in 1957 by a pair of mathematicians who were looking at ways to avoid the costs of plant shutdowns and restarts caused by inefficient scheduling. Their research showed that money could be saved by focusing efforts on performing the right tasks at the right times, rather than flooding the problem with labor to stay on schedule. This saved DuPont 25 percent on shutdowns...” (http://yourbusiness.azcentral.com/history-critical-path-method-24351.html) This created big hopes and excitement for CPM to also improve construction project delivery performance.  Construction companies began adopting CPM in the late 1950s and early 1960s. By the late 1970’s and early 1980’s, the personal computer made CPM affordable and accessible to the masses; so how has construction performance fared since  CPM became the standard for construction planning and scheduling?

For years, decades even, we have all seen the numbers and charts put up for debate showing no evidence that the original hopes and excitement of CPM is living up to its original expectations. 

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In construction, the CPM model is based on the input of individuals who use personal experience and historic project performance to inform their work.  Working from past experience and using their imagination to determine how a project will be delivered; individuals’ key in or copy/paste input into the CPM software.  To do this, people must read 2D design documents showing 1) what the project looks like first at the start (existing conditions) and 2) what the finished project will be on completion. Certainly people’s experience varies so what one person conceives as the best approach will vary from what another considers the best approach.  Because there is no way to efficiently test or analyse new or different approaches, and since construction is high cost and high risk, CPM has perpetuated decades of doing things the same way they were done in the past, with little to no innovation.    

To be clear, the construction delivery approach, the field operations plan, is created from the imagination of a person(s) who is required to envision the activities, durations, and dependencies of the specific project from seeing the existing conditions at the start and the construction design for the completed project at the end.  Once created, they can review the delivery approach with others using the Gantt chart or network diagram.

As design complexity and project constraints continue to grow, it is remarkable that the industry has  experienced only relatively modest declines in productivity.  We all value our past experience- it certainly helps to define standard means and methods and to estimate work production rates.  Standards of practice and means and methods help to conceive sequences of the imagined approach and the computer helps by rapidly processing the user’s input to run calculations and plot the tables, graphs, and charts.  But what is the impact of CPM if productivity in the industry continues to decline?  It is clear that these standard methods are not helping achieve the improvements we all desire. 

In my experience, CPM alone, following these well-worn practices, is never going to be enough to improve construction performance.  It is also clear that more experience and historic data in an ever more sophisticated CPM software system won’t enable us to meaningfully improve construction project delivery performance either.  Nevertheless, we believe it is right that CPM forms a vital part of structuring the project delivery data.  And because projects today are more likely to end in a dispute or claim rather than be completed on time or on budget, lawyers love the baseline versus actual CPM artefacts to help sort out the mess. So whatever we do as an industry we must be mindful that the CPM baseline and tracking actual performance through the schedule is not the root cause of the performance gap.  We believe CPM should remain part of the foundation for planning, scheduling and the controls systems required for managing construction operations and it will continue to be required for the foreseeable future.

If the well-worn CPM processes followed for the past 50 years alone isn’t the answer, how can we improve performance? 

Let’s step aside from the CPM focus and look at the dramatic shift happening with digital construction and modelling we label as BIM (Building- the verb meaning to build not the noun a vertical structure, Information Modelling) and VDC (Virtual Design and Construction).  To start, we should recognize that 3D design changes everything and drives complexity, and for at least 60 years all engineering lead industries have known it.  Yes, dating back to the 1950s only a few years after the digital computer was created, the auto industry invested heavily in 3D computer graphics that have led to engineering software and the amazing advancements in computing systems. 

Is BIM, 3D?

No, but it is an essential component of the digital model in that its’ objects are spatially representative of the physical aspects of the project.

Is 3D, BIM?

No, but it is an essential component of the digital model that  forms the basis of organising the information specific to the project and all of its material parts.

BIM is organised and structured by the 3D spatial model. Take the 3D model elements away and information still abounds leaving detail with no insight or visual reference.

The history of the digital computer starts with the goal of creating insight and understanding; not numbers.  In engineering design led industries, insight comes from seeing ideas using spatially oriented views for visual analysis backed by numbers, organised in charts and graphs.  Today, many construction projects utilize 3D models for the final integrated product design’s spatial coordination to avoid fabricating and installing any component in the wrong location before production operations begin.  Nowhere in the modern BIM oriented process does anyone expect software systems to use 2D drawings to identify spatial conflicts found in the project designs.

While it is not yet common to find project cost oriented models (5D), it is nonetheless a key concept in VDC and BIM that where 3D models exist, a 5D cost model can be derived by the processing power of computers.  It is reasonable to consider using the input of the 3D model to measure the designed quantities and calculate the costs of the project using a database of historic production rates; Quantity Surveyors and Cost Estimators have been doing this for decades.  Today there are 5D systems available that do precisely this. There is little disagreement that both (3D) design, its spatial coordination and (5D) cost estimating promise meaningful process improvements to create the design and to derive its anticipated costs respectively well from first using a 3D virtual model as the input.

So why is it, when it comes to 4D, the dominant industry norm for creating the project delivery approach almost universally starts with the project planner/scheduler reading 2D drawings and the keyboard input of activities, durations and dependencies to create the project schedule which is then joined up with the 3D model to visualize what was envisioned in the imagination of the project planner/scheduler?

Certainly this approach is valuable as a retrospective check that the planned approach is viable, but it certainly isn’t the most efficient method.  Everyone knows precisely how inefficient it is to start with 2D then convert it to 3D to complete the design, or start the design’s spatial coordination, or to produce the project cost calculations, but when it comes to 4D the industry is falsely led to believe that creating a schedule by reading 2D drawings and keyboarding into your legacy CPM software and then linking the CPM to the 3D model is right. For me, this simply begs a few questions:


How did that happen? And;

How can we better inform the industry so they can benefit?

The other day I was watching the new release movie (2016) Arrival (a Denis Villeneuve film staring Amy Adams, Jeremy Renner and Forest Whitaker based on the story "Story of Your Life") and one line among many in the script made me consider writing this paper.  The scene was tense, the two main character’s conversation went like this: Person 1: “Let’s say I taught them chess instead of English. Every conversation would be a game, every idea expressed through opposition. Victory... defeats. You see the problem?” Person 2 “If all I ever gave you was a hammer? Everything’s a nail.”

4D is what Synchro Software does; it is our job to teach the industry to look past the hammer where 'everything is a nail' and to look past the 4D is what you do with 3D and your CPM data after reading the 2D drawings and typing into your legacy planning and controls system like we still operate construction in the 20th century. 

4D is best when we create our construction operations directly from the 3D model - at any level of 3D model detail; it is the plan we create to deliver a project based on the conceptual level of detail we have at the start or the as-built level of detail we have at the end; and the critcal path network and 2D documents are the derivative, they are the outputs of 4D, not the inputs.  Companies using this modern digital approach experience sustainable improvement in both the project planning and controls processes and most importantly the safety and production of construction operations. 4D leads their workflow and has evolved their construction management processes into the modern digital age, it is fast, it naturally builds cooperation and because it is digital and highly interoperable, it drives efficiency improvements.  4D is our vision for the future of our industry.

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