What Does 4D BIM Mean to YOU?
Here at Trimble Buildings this week we have two teams out on the road: a large team is in Las Vegas for the World of Concrete and another team is in Orlando for the CPM for Construction Conference. In Orlando we have four different sessions on the agenda:
Wednesday, January 22nd
�9:45 – 11:00 Introduction to Trimble Schedule Planner
11:10 – 12:25 Trimble Schedule Planner Deep Dive
3:35 – 4:50 Real-World LBMS - Hospital Case Study
Thursday, January 23rd
11:10 – 12:25 Trimble Prolog for Design Change Requests
Many of our community already know that Location-Based Management System complements Critical Path Management with additional layers of logic when building out the schedule. (If you haven’t done so already, you can download a whitepaper on the subject: Comparing LBMS to CPM Construction Scheduling.) So we thought we’d pose a different question to our readers: What does 4D BIM mean to you?
We all have seen 3D BIM models in presentations. These models are perfect for visualizing how the project will look, how it fits into the current landscape, and perhaps there’s even a walk-through to show how visitors will interact and flow through the building.
But there are other uses for the geometry in the model. From the geometry and the combined experience of the Project Manager and Superintendent we can derive construction-caliber quantities; these quantities can power schedules and estimates. There is a question in the market, however, about the role of 4D BIM. Should 4D BIM represent the sequencing of the project or should it be the derivation of the schedule?
Pioneers in construction scheduling assert that 4D BIM should be both sequencing and scheduling, plus on-site production control with the Superintendent and the Subs, even going as far as invoice reconciliation with work complete on-site. These progressive GCs further assert that 4D BIM integrates quantity takeoff, location-based quantities, resources, productivity rates, and labor costs into the BIM (recall that the "I" stands for information).
Construction sequencing and planning can also produce a 4D animation. This means that elements from the model are assigned a logical construction sequence and put together in an animation which shows the Owner how the building will come together. There is a dramatic difference between a 4D animation and a 4D schedule, but many Owners are confused over this nuance.
A 4D BIM Schedule is a derivation of the 3D BIM geometry and an optimization of the resources. From the geometry, we can extract quantities and allocate these quantities to locations. Now we can apply sequencing logic, include crew sizes, productivity rates, and geography-specific pricing. By creating a schedule optimized to eliminate stops and starts and reduce project risk, we keep the project flowing smoothly.
Experts assert flowline theory offers a more competitive scheduling approach. How? Flowline offers a graphical representation of the project construction efforts. Each vertical line represents a crew; the slope of the line represents their productivity rate; the length of the line represents their unimpeded flow through locations (seen on the y-axis).
Floats and buffers play a different role in location-based management practices. Location-based schedules use quantities and productivity rates to define durations, which assume that crews can work with their optimal productivity. Location-based planning aims to achieve these optimally productive conditions by isolating the crew using buffers. In the event that something goes wrong, the buffer is absorbed before the next trade suffers.
The example above shows us that we need to rethink some of our task starting points (the red circles) and then look at our buffer decisions at the blue circles. Buffers are used to protect the continuous production of a successor task from the possible production deviations of its predecessor. When our flowline graph is free of conflicts, when the lines are continuous, and when the lines are parallel, we have an optimal schedule.
And this optimal schedule reminds us that crew location, pace (productivity), and quality all add up to an average of 10% schedule compression. How do we know this? We wrote the book on it! Location-Based Management for Construction illustrates how construction projects all over the world have benefitted from flowline theory.
Although planning is very critical to project success, controlling the project is also necessary for optimal results. To illustrate this point, recall that CPM schedules look nearly perfect up to the half-way point of the construction. And then what happens? We ask crews to increase man-power. But we all know that putting more people on the jobsite, all starting in the same locations, means nothing more than a logjam and congestion which further slows the project. In a large project, it is extremely risky to wait until the last two months to catch up.
It’s important to remember that CPM fails to change the durations of upcoming tasks based on historical performance and therefore, frequently shows an overly optimistic forecast. Location-Based Management System forecasts are based on historical performance for locations which have not yet started. Location-based management systems offer a different approach -- early warnings and early, well-measured reactions. LBMS requires a change in underlying assumptions - something real must be done to adjust manpower or productivity.
During construction, the schedule can function as an early warning system. By tracking completed locations, the total quantity of work-in-place can be easily calculated. Daily reporting of total manpower on-site makes it possible to calculate actual productivity and actual production rates. These rates can be used to forecast progress and identify problems much earlier than in CPM systems.
When the Superintendent walks the jobsite, s/he can mark the percent complete of all the tasks on the "control chart." With these charts, the on-site team can quickly adjust to real-world conditions. When crew progress fluctuates, it is very easy to see the slope of the line tilting to the left (too slow) or to the right (too fast). If the on-site team does not address this change of pace, it is very easy to track where a collision will occur. Two crews in the same location is a pile-up that can be avoided well in advance with flowline simply by adjusting the crew size and make sure that crews can work unimpeded in unique locations.
Now the onsite team has the information they need to adjust the variables to keep the project on schedule. The team has the Baseline Schedule (the plan); the Actual (from data collected in the Control Chart); and the New Forecast (the look-ahead schedule recalculated from the baseline and the actual). This constant updating alerts the team to any possible conflicts and keeps everyone focused on milestones and due dates.
There are several deliverables from the flowline schedule that GC Management Teams, Owners, and other project stakeholders can use:
>> Cost-loaded schedules
>> Manpower charts
>> Gantt charts
>> Alerts for accounting to quickly compare the Subs’
invoice amount with the percent complete onsite
>> Cash flow forecasts
>> Resource forecasts for each subcontractor for the
upcoming month
>> Percentage of production complete compared to the
plan (for the whole project and each more construction
phase)
Trimble has the software and services your team needs to get started on the path to 4D. Are you ready for true 4D BIM? Be sure to research the resources to the right to learn more. |
