Why Construction-Caliber Quantities Matter
A couple weeks ago, we published a blog article about the workflow in Vico Office going from the 3D model to the 5D estimate to the 4D schedule. It’s odd that the workflow isn’t linear, but it reflects how the estimator and scheduler interact in the real world. The estimator first defines the quantities, then s/he works with the project team to define the sequence and locations for the project. Then s/he associates the appropriate tasks to the materials creating a task list that matches the line items in the estimate. Then the scheduler can pick up the ball and apply the known productivity rates from past projects to the tasks.
We received a question from the LinkedIn Group for Building Information Management about the workflow: So that means, if one wants to create a schedule and construction simulation just to check the feasibility of the project it will not be possible until quantity takeoff is done. Is that not a limitation?
One of our scheduling experts answered the question:
As a scheduler, I find that having decent location-based quantities as input is the best starting point to create an accurate schedule and really check schedule feasibility rather than just creating a marketing schedule and rough sequencing simulation. For me it's all about driving durations with accurate quantities easily from the 3D model.
Quantities by location are the “secret sauce” for Vico. We need this granularity to better define the estimate, the schedule, and then to manage the project on-site.
If you are just looking to make a movie of how the building will be constructed, there are certainly point solutions on the market that can help you create a marketing schedule. But what are they really showing the Owner? This is part of the selling the BIM process to the Owner and generating significant “visual” value. How can we as an industry ask Owners to trust their projects to BIM if some of us are using smoke and mirrors, while others are going deep?
Pioneers in construction scheduling assert that 4D BIM should include sequencing and scheduling, plus on-site production control, with communication to both the Owner and Subs. These components should be driven by the mathematical equation: quantities divided by productivity rates = durations.
A 4D BIM Schedule is a derivation of the 3D BIM geometry and an optimization of the resources. From the geometry, we extract quantities and allocate the 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.
This video is a smart introduction to the importance of quantities by location in schedule planning…
We keep the project flowing smoothly by managing it on-site by comparing our actual progress to our schedule. And again, quantities by location play the central role. 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.
One powerful use of scheduling simulation is to identify flaws in scheduling assumptions. By quickly visualizing your schedule changes in a 4D movie, you can see where additional changes need to be made. Sometimes it's a location issues, sometimes it's a sequencing logic issue, but catching it in preconstruction is key.
At any point, in the planning and controlling process, we can produce a schedule movie which illustrates the plan. The movie can inform multiple audiences: the project team, the Owner, the subs, or even just one crew. We can even produce movies to compare two or three scenarios. The difference is this movie is an actual derivation of the quantities by location and the productivity rates. It’s a scientific rendering, not Hollywood BIM.
So when all is said and done, the quantities aren’t a limitation. In fact, they are what makes you more accurate. In the time it takes to manually link your sequence to your BIM model, you could have an optimal schedule in Vico. And because of the tight model-based integration, every time the design changes, the quantities are automatically updated. This means your schedule and estimate immediately reflect the new design. Construction-caliber quantities are key to BIM-based scheduling and estimating. Get some in Vico Office.
If you’d like to learn how an estimator gets construction-caliber quantities from Vico Office, follow along with the Vico Office Training Videos. Training Level 5 dives into model-based quantity takeoff. You can either download the complete series, or progress level-by-level on the website.