3 Problems with the Production Management Systems: Understanding the problem and the context
3.3 Root causes behind the problems
3.3.3 Planning in production management
Traditionally, in construction, planning is considered to be an equivalent of creating a Gantt chart of tasks to be performed (Henrich et al., 2005). This Gantt chart on most occasions is created at the early stage of the project at the head office without consulting the project team (Ballard, 2000). At this stage of the project the reliability of information, i.e. resource availability, external conditions, client changes are not yet available and hence the reliability of the plan is quite low (Ballard, 2000). However, this master plan is taken as the base document and pushed to the site team to be followed regardless of the current situation on the ground. The other shortcoming of this plan is that it seldom shows various flows of resources such as labour, equipment, material etc., hence the site team has to decipher this detail on their own. From the discussion about current ICT systems, it is observed that not many organisations have achieved complete integration between their information systems, and this leaves the site team without the critical information regarding these resources during the execution of the project. Also, most planning methods do not include the spatial information in the plan, i.e. it does not show where the work is going be carried out and how to resources will flow during the project (i.e. smooth flow of resource between locations without interruptions). This leads to resource clashes during the execution; i.e. two work teams working within the same space, material being stacked too far from the project, not knowing where the equipment are or when they will be available. All such factors add to the inefficiencies during the execution stage. In the following
paragraphs some of the main production planning and control systems being used in construction will be discussed.
3.3.3.1 Critical Path Method (CPM)
The CPM method was developed by DuPont and Remington Rand around 1957. It was developed to mathematically calculate the sequence of activities in order to complete a project in the minimum time possible. CPM programmes show activity dependencies and duration allocated for each activity. It also allows for calculating the float of an activity, where float is the amount of time a non-‐critical activity can be delayed without affecting the overall programme. A majority of construction projects today use CPM as the main project management, planning and controlling mechanism. It is the most popular method in construction over the last five decades. The project plan is shown using Gantt charts, which are the visual representation displaying activities as horizontal bars where time is plotted on the X axis. Due to this visual representation, Gantt charts are quite easy to understand and have made the CPM method very popular amongst construction professionals. The CPM method can be seen as the direct implementation of the transformation view. It implies that by breaking the tasks into smaller chunks or by way of work breakdown structures, a project can be managed. The aspects such as flow of materials, labour, equipment or information are not taken into account (Howell & Koskela, 2000). CPM is effective in providing a big picture but if one tries to add information such as material and labour flows, it starts to get very cumbersome and difficult to manage (Peer, 1974; Birrel, 1980). Also, one further essential element that is missing from the CPM method is spatial information (i.e. smooth flow of labour and resources between locations). It is understood that construction takes place in space and time. CPM addresses the time element (although not in a complete way); the spatial element is completely missing. If one tries to add a spatial element, i.e. where a particular task will be carried out, the Gantt chart starts becoming too complicated and as a result, is seldom updated. The consequence is that without the spatial element, the programme becomes difficult to manage; as it frequently leads to resource clashes, i.e. Two labour teams working in the same place at the same time where there is not enough space,
material being stacked in the wrong place, crew sitting idle as there is no space or direction where they should work next, etc.
3.3.3.2 Line of Balance (LOB)
Line of Balance is a linear scheduling method, which shows the tasks in a project as a single line on a graph as opposed to a series of individual activities on a bar/Gantt chart. It is mostly used on projects where there are a number of repetitive activities such as a housing or a road construction project.
LOB was originally developed by the Goodyear Co. in the early 1940s and was further developed by the US Navy in the early 1950s for programming and control of both repetitive and non-‐repetitive projects. (Turban 1968; Lutz & Halpin, 1992). The LOB technique assumes that the rate of production for an activity remains uniform during the execution time. Most commonly, time is plotted on the horizontal axis where as work units are plotted on the vertical axis. The resultant chart shows sloping lines, which represent the production rate of an activity. Another characteristic of the LOB is that it represents work activities being continuously performed, even if the work is being carried out in different locations.
Recently, Seppänen (2009) has attempted to improve the location based planning tools and their processes. In the research, the author implemented the location planning methods on three case study projects and studied their performance. It was observed on the case studies that, even after project activities were subjected to cascading delays from an initial phase, the actual finish date of the project was not affected. This was due to the long end-‐buffer that was put in the schedule. Also, the author found that the problems occurring on projects could be envisaged earlier due to the location-‐based control data available.
LOB partially addresses the issue of spatial information, as there is a possibility to show the space where the task will be carried out over time on the activity line. However, there are limitations to this approach as it works well in projects where there are repetitive tasks, as LOB does not work well where the project has many unique tasks. Also, the issue of temporary structures is not addressed by the LOB method. A typical construction project during their lifetime see erection and
demolition of many temporary structures, which have to be managed during the planning and execution stage. As these are unique in nature the LOB approach does not work well in this case. The simple nature of the LOB charts also limits the amount of information that can be shown on them.
3.3.3.3 Critical Chain
Developed by Goldratt (1997), Critical Chain Project Management (CCPM) is a method of planning and managing projects that put the main emphasis on the resources required to execute project tasks. As opposed to other methods such as CPM, which advocate rigid task order and timeline based scheduling, Critical Chain requires the schedule to be flexible and tries to keep resources level throughout the project. Overall, it focuses on taking out the individual task “float” or “buffer” and allocating them to one big collective buffer. It assumes that this way the tasks are started as soon as the previous one finishes and project completes on time. The Critical Chain theory is based on the Theory of Constraints developed by Goldratt (1997) which is based on the premise that rate of goal achievement is limited by at least one constraining process. As described by Goldratt (1997) the five key steps in organisational/process improvement are:
1. Identify the constraint (the resource or policy that prevents the organization from obtaining more of the goal)
2. Decide how to exploit the constraint (make sure the constraint's time is not wasted doing things that it should not do)
3. Subordinate all other processes to above decision (align the whole system or organization to support the decision made above)
4. Elevate the constraint (if required or possible, permanently increase capacity of the constraint; "buy more")
5. If, as a result of these steps, the constraint has moved, return to Step 1. Don't let inertia become the constraint.
Koskela et al. (2010) have compared the Critical Chain Production Management to the Last Planner System™ within the context of construction management. The authors summarise that while Critical Chain endeavours to shorten the project duration with cost reductions (where other benefits are secondary), Last Planner primarily endeavours to reduce the variability in work flows, which directly leads
to increased productivity and cost reduction along with gains in safety and quality. In addition, Last Planner helps with schedule compression as it reduces variability. In criticism, Koskela et al. (2010) mention that the Critical Chain method is restricted to buffer management, as it does not try to address/reduce the cause of the buffers or variability. Hence, there is a limited scope for productivity improvement through variability reduction. In comparison, Last Planner fails to maintain an explicit link with the master plan (Junior et al., 1998), hence the current situation on site can not be readily assessed from an overall project perspective. Also in Last Planner there is no direct method of schedule compression at the master plan level.
3.3.3.4 Last Planner
The Last Planner™ system (Ballard, 2000) – as the name suggests is based on the planning and scheduling that is carried out by the people responsible for the execution of work, i.e. site manager, foreman and work crews. Traditionally, planning and production management is carried out with a top-‐down approach. Planners mostly based at the head office prepare the schedules right at the estimating stage. This is then pushed to site teams to follow during the entirety of the execution stage. Very little input window to planning is left for the site teams. As discussed, this makes the execution plans quite unreliable, as they are prepared when there is not much reliable information available.
Last Planner tries to overcome problems of traditional planning methods by introducing shorter planning cycles during the execution stage, which are prepared by the work teams and are based on work commitments on “what CAN be done” rather than “what SHOULD be done”. Here, the master schedule is taken as a guideline, and informs the work teams about major milestones and overall schedule. Based on the master schedule a look ahead plan is prepared 4-‐6 weeks in advance, which is based on the current resource situation and up-‐to-‐date forecasts. Further to this, weekly meetings are organised where all work teams take part and “pull tasks” from the look-‐ahead plan. Also, the weekly meetings are used to analyse the reasons for non-‐completion for previous week’s tasks, and a task is only selected if all the pre-‐requisites to starting that task are met. This clearly improves the reliability of the planned work and improves the efficiency of
workers. The method also builds a network of promises, as each week, all stakeholders commit to the work being planned and are then held responsible for the same. This gradually builds the trust and improves social environment (collaboration) on site as all units operate as a team.
Last Planner takes into account the flow aspects of the construction process during the execution stage. It has generally been found to improve the reliability of the projects due to the increased reliability of the plans. Here the responsibility of production control shifts from the top level to the comparatively lower ranks as the work is pulled based on all the prerequisites being met. On the other hand, commitment to the method becomes a prerequisite for all parties. As a result, last planner may not work properly in situations where it is not possible to create a network of trust. Also, in organisations where the control is mostly kept in top circles, the managers find it too difficult to allow the site team to control the production process. Again, in cultures where this is the case the system might not work in its current form (i.e. it may need adapting to suit the cultural and process issues).
Even though the Last Planner system takes into account the variability in the process, it does not go beyond the weekly planning meetings. A construction project is a dynamic environment and much could happen/change during the span of a week. Reliability can be further improved if a shorter planning cycle is introduced (Sacks et al., 2009).
3.3.3.5 Summary of planning methods
Despite its shortcomings CPM remains one of the most popular methods being taught and used in the academia and the industry. The majority of construction planning and scheduling software are also based around CPM. The linear scheduling methods help in selective projects but cannot provide an overall solution to the industry. Critical Chain is not yet followed in the mainstream construction and is undergoing further research. It has some parallels with the Last Planner System, and it can be argued that they complement each other well. The Last Planner™ system of production management and control is beginning to become popular where there is a reasonably supportive environment for its implementation. It can be concluded that there is a need for a streamlined
construction process through a systematic implementation of a production management and control system which takes into account the transformation, flow and value concepts.