General Contractors in the US are increasingly using Vico scheduling solutions (model-based scheduling and production control) as a tool to monitor production. The implementation has typically followed the following steps:

• Analysis of a CPM schedule - and the discovery of huge inefficiencies caused by starts and stops and resource conflicts;
• Optimization of a baseline using location-based methods - continuous workflow, quantities, resources, often cash flow, as well;
• Monitoring production on site using control charts - comparisons to original baseline.

There is a big, required additional step to achieve the real benefits of location-based management.  Location-based controlling (as opposed to monitoring) needs to be implemented to maximize productivity and prevent cascading delays.  The rich information content in a location-based plan needs to be used in management decision making.

There are two types of control systems: push and pull control systems. Push control means starting work according to predetermined plan, without considering the current state of the production system.  This typically manifests as contract brokering and forcing the subcontractors to start according to their contract, or to increase their production rate just because they are delayed without considering the real value of that production rate increase.  It can be said that most construction companies today use push controlling as their control methodology.

Lean Construction is based on pull controlling.  A location-based version of pull controlling is to use the forecasts to evaluate location availability and only start new crews when production data shows that there are free locations for them.  This will increase productivity of individual operations and prevent cascading delay chains from happening (refer to my earlier post about location conflict and productivity loss and cascading delay chains). However, it requires much more data about production than available in activity-based systems.

Location-based management (and Vico scheduling software) implements pull controlling by recognizing that there are four levels of information: baseline plan, current plan, progress and forecast.

Baseline

Baseline tasks are the original strategy for building the project and form the basis of commitment between the GC and the Owner.  However, they are based on assumptions of productivity, original assumptions of means and methods, and often missing subcontractor input.  Baseline tasks can only be updated based on Owner-approved changes and delays.  Their main use from production control perspective is to establish production rate requirements and milestones for most critical tasks.  This production rate information can be used in subcontractor negotiations to ensure that selecting the cheapest subcontractor does not result in buying a process bottleneck.  Required production rate (units / week or / day) can be specified in bid documents.

All users of Vico Control start their journey by analyzing and optimizing their baseline.

Current

Current level of information is used to plan the current best understanding about how to build the project.  Current information is based on up-to-date quantities, subcontractor productivity and resource information, and results from logic workshops.  Current plans should be planned together with the team building a phase of the project (for example Foundations or Superstructure).  Current plans reflect commitments between General Contractor and subcontractors and should be updated when the basis of that commitment changes (for example, a better way to do work is found, error in quantities is discovered etc.)

The current level of information is not generally used at the moment even though it is one of the most important parts of location-based management system.  Instead, the GCs update progress information (see below) and baseline tasks.

Progress

Progress information records actual progress on site and compares it to Baseline and Current plans.  Location-based progress information includes start and finish dates of tasks and locations (or % completed in a location) and actual resources of each subcontractor.  This information is used to calculate actual production rate (units / day) and actual productivity (manhours / unit).  Progress information can be shown in Flowline figures or as a Control chart.

Although progress information is useful in explaining historical production problems, using it for control is essentially like trying to control the project by looking at rear-view mirror.  Most companies are trying to use progress information, together with baseline, to control production. This is dangerous as it typically leads to push controlling (red colors in control chart initiate action to catch up by increasing resources).

Forecast

Forecast is the most important part of Location-based management because it makes possible pull controlling and associated productivity benefits.  Forecast is calculated based on combination of progress and current plans and can be edited to enable look-ahead planning.  Tasks, resources, logic, and quantities are taken from current information (or baseline if current is not available) but productivity and production rates are taken from progress information. Critically, forecasts start where progress information ends. (see figure below)  The initial forecast shows what will happen if the production continues in the same way as previously.  Pull controlling is using the forecast information (= the situation on site) to plan control actions. Increase in resources, or suspending a task is shown by adjusting the forecast - not the original plan.  Alarms are generated if location conflicts occur.

Although forecasts can be used to successfully prevent cascading delays, there is very little evidence that this critical part of location-based of management is being implemented.

It is time to move from push controlling to pull controlling.

Figure 1: Task 1 started on time, but has had a lower production rate than planned (the dotted line has a gentler slope). If task 1 continues with the same production rate, it will cause a problem to Task 2 in location 4 (red dot, alarm).

Continue reading Part 2 of this blog: Production Control with Lean Principles.

To learn more about lean construction principles, please review the following resources:

Webinar: An Introduction to LBMS and LPS

Webinar: BIM 401 Webinar - Model-Based Scheduling

Webinar: 4D Scheduling Strategies in a Hard Bid

Webpage: Lean Construction and BIM

Webpage: Combining Location-Based Management and Last Planner 

We also offer a step-by-step guide to our 5D virtual construction workflow with video tutorials. These videos are just 2-5 minutes in length, but illustrate how to use a particular piece of functionality. You can access the video library index and view just what you need, or download the complete set of training videos. We have training videos for Estimators, Schedulers, Supers, and anyone who does CM Reporting.