Category: Insights

Activity Duration Types in Primavera P6

Activity Duration Types in Primavera P6

Posted on by Adroit

In preparing project time schedules in Oracle’s Primavera P6, project planning and scheduling professionals need to properly select duration types. Primavera P6 uses the following two formulae to determine units of work:

Resource Units = Resource Units per Time Unit * Duration

Remaining Resource Units = Resource Units per Time Unit * Remaining Duration

Based on these two formulae, the user is able to make one or two element(s) of the equation fixed, and input or change the other element(s). That way, Primavera P6 will calculate the remaining elements of the equation. To determine which element(s) of the formula to solidify, the users need to take the nature of the work or information at-hand into account and make an informed decision concerning the elements that need to be solidified. This decision then helps the user to choose among the four main types of activity duration types.

Four types of activity duration types can be defined in Primavera P6. They include 1) Fixed Duration & Units, 2) Fixed Duration & Units/Time, 3) Fixed Units, and 4) Fixed Units/Time. The following discusses each of these activity duration types in more depth:

1- Fixed Duration & Units: This types of activity duration is used in Primavera P6 when the duration and the amount of the resources are known and supposed to remain fixed in the schedule. It is recommended that project planning and scheduling professionals use this duration type for time- and budget- constrained projects prior to making schedule updates. The two possibilities include the following:

  • Option 1: Duration does not change when resources are added or removed, or if the user changes Units/Time.
  • Option 2: A change to the Duration will change the Units/Time; however, Units remains unchanged.

2- Fixed Duration & Units/Time: This type of activity duration is used in Primavera P6 when the duration and resource performance are known and are supposed to remain fixed (i.e., unchanged) in the schedule. In other words, activity durations remains unchanged in the schedule; however, the remaining units change. If an activity is supposed to be completed within a certain, fixed time frame irrespective of the number or amount of resources being assigned to the activity, this activity duration type is the right choice that needs to be used for that activity. This activity duration type is most often used if the user uses task dependent activities (not resource dependent activities). The two possibilities include the following:

  • Option 1: Duration does not change when resources are added or removed, or when Units/Time changes.
  • Option 2: A change to the Duration will change the Units; however, Units/Time remains unchanged.

The use of this activity duration type locks the duration, and the default Units/Time (productivity) values for each resource added. Nevertheless, this activity duration types allows the overall Unit cost to increase when resources are assigned to the activity. It is recommended that project planning and scheduling professionals use this duration type during the planning phase because doing so will force Primavera P6 to honor activity duration estimates and increase the work (Units) and, therefore, the budget, based on additional quantities of work performed (Units/Time).

It is important to note that this duration type disables the User Preferences, Calculations tab option Recalculate the Units, Duration, and Units/Time for existing assignments based on the activity types.

3- Fixed Units: Primavera P6 users need to use this type of activity duration if the amount of work needed to complete an activity (e.g., 8,000 bricks to be laid) is fixed. If this type of activity duration is used, decreasing units per time causes the activity duration to increase; however, if the user updates the duration or units per time, the Units remain unchanged. Increasing the resources allocated to an activity whose duration types is Fixed Unit, decreases the activity duration. It is best to use this activity duration type where the duration is “resource dependent” (and not “task dependent”). If in a project, the budget is set and it is difficult to get additional cost increases approved, the Fixed Units activity duration type is the right choice assuming the other above-mentioned requirements are also satisfied.

4- Fixed Units/Time: Primavera P6 users need to use this type of activity duration if the activity has fixed productivity output per time period (regardless of activity duration). In other words, this duration type is supposed to be used when the user would like the resource units per time to remain unchanged while the activity duration or units change. For example, if a piece of equipment requires two workers to operate, the Fixed Units/Time duration type might be the right choice. When the duration of an activity whose duration type is Fixed Units/Time increases, the amount of budgeted labor units also increases while resource Units/Time remains unchanged. This activity duration type is most often used if the user uses resource-dependent activities.

In addition, users have the choice to choose to preserve “the Units, Duration, and Units/Time for existing assignments” or recalculate “the Units, Duration, and Units/Time for existing assignments” in the User Preferences, Calculations tab of Primavera P6. This choice, as well as the choice of activity duration types, determines what element(s) remain(s) unchanged and what element(s) change(s). These scenarios are outlined in the following two tables:

The User Preferences, Calculations tab option “Preserve the Units, Duration, and Units/Time for existing assignments” is chosen when the user adds or removes multiple resource assignments on activities but would like Units, Units/Time, and Durations to remain unchanged when additional resources are assigned to an activity. When the User Preferences, Calculations tab option “Preserve the Units, Duration, and Units/Time for existing assignments” is selected, here are the various scenarios that are encountered:

The User Preferences, Calculations tab option “Recalculate the Units, Duration, and Units/Time for existing assignments” is chosen when the user adds or removes multiple resource assignments on activities and would like to determine a resource assignment’s remaining values based on the activity’s duration type. When the User Preferences, Calculations tab option “Recalculate the Units, Duration, and Units/Time for existing assignments” is selected, here are the various scenarios that are encountered:

As discussed, four types of activity duration types can be defined in Primavera P6. They include 1) Fixed Duration & Units, 2) Fixed Duration & Units/Time, 3) Fixed Units, and 4) Fixed Units/Time. It is important to pay attention to the nature of work that is being performed to select the right type of activity duration types. This article defined each of this activity duration types and explained where each option needs to be used and what the implications of using these duration types are from the scheduling perspective.

References:

Harris, Paul E (2017). Planning and Control Using Oracle Primavera P6 Versions 8 to 17 PPM Professional. Eastwood Harris Pty Ltd.

Oracle (2018). Primavera P6 Professional User Guide Version 17. Available online at: https://docs.oracle.com/cd/E80668_01/English/User_Guides/p6_pro_user/helpmain.htm?toc.htm?62789.htm

 

A critical comparison between CPM and LSM

Posted on by Adroit

In a previous article (Diagrams to illustrate repetitive construction activities), we identified the main diagrams that construction project practitioners use to illustrate repetitive construction activities. In that article, we described the two main classes of linear scheduling methods (LSM) and line of balance (LOB) techniques that are used in linear projects.

Below, we are going to provide a critical comparison between the critical path method (CPM) and linear scheduling method (LSM). As a deterministic network model, the CPM method uses duration estimate for project activities to determine the longest duration path for the project and to identify the earliest and latest dates for schedule activities based on the use of forward- and backward-pass network calculations, respectively. LSM schedules, however, use velocity diagrams representing each activity. The schedule format may provide the planned and actual production rates on a time-scaled format. The main differences between the CPM and LSM methods can be summarized as follows:

Critical Path Method (CPM)Linear Scheduling Method (LSM)
Application Although this method is typically used in non-linear projects, it can also be used in linear construction projects.It is used in linear construction projects, where the majority of the work is made up of highly repetitive activities. In these projects, a set of project activities are repeated in each location for the entire length of the work. Once a project activity is started and/or ended in one location, it is repeated in another location.
Accuracy With using forward and backward network calculations, the CPM method determines the expected project completion with accuracy. The LSM allows for accurately planning and scheduling of project activities from the perspectives of both time and location.
Uncertainty in activity durationsWith some modifications, the CPM method can change to Program Evaluation and Review Technique (PERT) which allows for randomness by introducing uncertainty to activity duration estimates (i.e., using optimistic, most likely, and pessimistic durations to calculate the expected time for schedule completion).The current forms of LSM do not allow for randomness in activity durations.
Uncertainty in activity relationships With some modifications, the CPM method can change to Graphical Evaluation and Review Technique (GERT) that allows for conditional and probabilistic treatment of logical relationships (i.e., depending on the outcome of the predecessor activities, succeeding activities may or may not be performed).The current forms of LSM do not allow for conditional and probabilistic treatment of logical relationships.
Critical pathThe CPM identifies the critical path based on forward and backward network calculations. The LSM algorithm identifies the controlling activity path (CAP) which can be considered a path with the same function as the critical path in the CPM method. The LSM also identifies location criticality.
Spatial aspectsIt might be inadequate for effective planning and scheduling of linear construction projects because it does not account for work locations or spatial aspects and does not effectively model project activities that are repetitively performed.It uses velocity diagrams representing each activity, accounts for work locations or spatial aspects, and effectively models project activities that are repetitively performed.
Readability and usefulness The CPM method becomes convoluted in complex projects because of the high number of project activities and activity dependencies. This complexity makes it difficult for practitioners to effectively use, communicate, and understand project CPM schedules in complex projects.The LSM method is easy to understand and an effective tool to communicate the project time objectives with all team members including those individuals who lack an in-depth knowledge of project planning and scheduling.
Ease of use and development Computer programs have significantly facilitated the use and development of CPM schedules; however, software programs have become complicated and require extensive training. The LSM is intuitive and can easily be produced with or without the use of computer programs. However, the limited number of computerized implementation platforms restricts the use of this method in large projects.
Ease of updating Computer programs have significantly facilitated the process of updating CPM schedules; however, updating complex CPM schedules may become challenging due to the increased number of activity, activity dependencies, activity constraints, activity calendars, and resource calendars in these schedules. Updating an LSM schedule is typically simple and intuitive.

References:

Mirhadi M. and Terouhid, A. (2018). AACE International Recommended Practice 91R-16 (RP 91R-16): Schedule Development. AACE International (The Association for the Advancement of Cost Engineering). Retrieved from https://web.aacei.org/docs/default-source/toc/toc_91r-16.pdf?sfvrsn=2

Adroit Consultants, LLC (2018). Diagrams to illustrate repetitive construction activities. Retrieved from https://www.adroitprojectconsultants.com/2018/08/06/diagrams-to-illustrate-repetitive-construction-activities/

The project scope has changed, now what?

The project scope has changed, now what?

Posted on by Adroit

Project teams need to use effective strategies to minimize changes to the project scope of work; however, change is inevitable and it arises due to a variety of reasons. Examples include the change in an owner’s needs or expectations, design errors and/or omission, differing site conditions not envisioned in the original contract price, changes to the project scope of work due to constructability issues or conflicts between systems, and modifications due to actions or inactions of third-parties. From a contractor’s perspective, the change may arise due to reasons outside the contractor’s control; therefore, it is important for contractors to know what actions they need to take if a change in the project scope of work arises.

In case of a change to the project scope of work, one of the first actions that a contractor needs to take is to provide a proper change notice to the project owner. It is important to note, however, that owners may not be the contracting party or the only contracting party that needs to be notified in case of a scope change. For example, if a scope change modifies a subcontractor’s scope of work, the subcontractor may need to notify the prime contractor first. Typically, contracts contain provisions that define the requirements for timely issuance of change notices.

Most contracts require contractors to issue proper change notices prior to proceeding with the work. They also require contractors to submit proper supporting documentation in a timely manner for reimbursement. Most contracts require that contractors provide a descriptive narrative, an adequately-detailed supplemental information to specify the changed work, and reasons for the change to ensure the changed scope of work is defined with adequate specificity and it is justified and properly documented. They also require that contractors specify the potential impacts of the change on cost, time, and productivity.

The changes to the project scope of work are categorized into the two main classes of directed and constructive changes. The differences between these two types of change are described in Table 1. The need for proper documentation of the change is more evident when a constructive change arises because, in the case of a constructive change, the owner does not specifically direct the contractor to make a change. Instead, the change arises as a result of non-owner-directed events that implicitly necessitate modifying the scope.

Table 1. The differences between directed and constructive changes

AttributeDirected ChangeConstructive Change
The role of ownersIt is issued when the owner specifically directs the contractor to make a change.This change is not a result of owner-directed changes.
Reason for changeThe change occurs because the owner’s needs or expectations have changed.The change occurs as a result of non-owner-directed events that implicitly necessitate modifying the scope.
Owners’ awareness towards the changeThe owner is fully aware of the change because the owner specifically directs the contractor to make a change.The owner does not typically have explicit acknowledgment of the change and/or need for change.
The role of contractors Contracts typically require contractors to make changes as the owner wishes.The contractor is forced to make the change and/or accept its implications.
Ease of recognizing the change It is easier to recognize. It is not easy to recognize.
Degree of complexityIt is typically not complicated because the owner specifically directs the contractor to make a change.It is typically complicated because the owner does not typically have explicit acknowledgment of the change and/or need for the change; and thus, may dispute the change.
Effect on the contractThis change may or may not affect the contract price or timeline.This change typically affects the contract price and/or timeline.
Type of effect on the contractThis change may reduce or add the contract price and/or elongate the expected project duration.This change typically increases the contract price and/or elongates the expected project duration.

Not all contracts allow for proceeding with the work prior to the signing of the change order. Also, some contracts do not contain provisions for constructive changes. Therefore, it is of utmost importance for contractors to know what the contract requirements are for documenting the change and what supporting documentation the owner expect to receive. It is recommended that contractors take the following steps if the owner has directed them to proceed with the work prior to the signing of the change order:

  1. Fully comply with the change notice requirements and give notices in a fashion promulgated by the contract
  2. After reviewing the contract documents and making sure that the scope has changed, submit a change order request, provide proper justification for the change, describe the scope of change, and provide estimates of the potential impacts of the change on time, cost and productivity.
  3. If an adequate information does not exist to prepare accurate estimates of the potential impacts of the change on time, cost and productivity, consider the need for formally reserving the rights to ensure entitlements are not unintentionally waived.
  4. If the contracting parties are not in agreement on the change or its impact, follow the steps outlined in dispute resolution procedures, and give a notice of intent (NOI) to file a claim,  if warranted.
  5. To the extent practically feasible, keep separate tracks of the costs of change using a cost coding that differs from the cost coding used for the base contract to ensure the cost impact of change can be segregated from the cost of performing the original scope of work.

Taking the aforementioned steps are important to facilitate the resolution of any modification to the project scope of work with the owner and to minimize disputes to the extent possible.

A sustainable construction practice to avoid the risk of Legionnaires’ disease

A sustainable construction practice to avoid the risk of Legionnaires’ disease

Posted on by Adroit

Facility managers and many other stakeholders are increasingly interested to find out more about effective water management strategies in buildings and facilities to prevent Legionella Infection. Legionnaires’ disease is a severe respiratory disease caused by the bacterium Legionella pneumophila. The bacteria may also cause a less serious illness that is referred to as Pontiac fever. Legionnaires’ disease is similar to other types of pneumonia, with common symptoms such as cough, fever, shortness of breath, muscle aches, and headaches, or less common symptoms such as nausea, diarrhea, and confusion. This bacteria is found in both potable and non-potable water systems (DOH, 2018a). The key question is how the risks associated with this infection can be managed.

Although the need for more effective water management strategies became more apparent in 2015 when the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) released Legionella standard, ANSI/ASHRAE 188-2015, cases of Legionella infection are still being reported. For example, in a recent case, the New York State Department of Health announced that individuals who were guests at the Watkins Glen Harbor Hotel between July 16, 2018 and August 1, 2018 or those who were in proximity to the hotel’s pool and spa may have been exposed to Legionella bacteria (DOH, 2018b).  

ANSI/ASHRAE 188-2015 is one of the main standards that define the main considerations in building water systems to manage the risks associated with Legionella infection. To implement effective water management strategies, potential risks associated with the water management systems need to be identified, assessed, and managed properly. Although risks are typically classified into positive and negative risks, this article focuses on negative risks or threats. Negative risks are any potential events or conditions that may adversely impact asset management objectives. A proper application of risk assessment techniques makes facilities less vulnerable to potential risks arisen from Legionella bacteria.  Addressing issues after the fact usually costs significantly higher compared to the amounts paid for implementing risk response strategies. Therefore, using risk management practices are important not only to protect facilities and water management systems from detrimental risks but also to ensure that facility owners, such as commercial buildings, do not incur costs due to unmanaged risks.

Risk management consists of the key processes of planning for risk management, identification, assessment, response planning (i.e., risk treatment), and risk control. To make facilities less vulnerable to potential risks arisen from Legionella bacteria, risk response strategies need to be identified for all potential risks that may arise. Risk response strategies are the actions that can be taken in case of a risk occurrence. In general, four classes of risk response strategies exist. As shown in Table 1, these classes include risk avoidance, risk transfer, risk mitigation, and risk acceptance:

Table 1. Risk-response strategies for managing negative risks

Risk response strategyDescription
AvoidEliminate the risk
TransferTransfer the risk to a third party
MitigateReduce the probability or impact of the risk
AcceptAccept the risk by taking no actions or, at most, setting aside contingency to offset the adverse effect of the risk

Risk acceptance and risk transfer are not typically among the risk response strategies that facility managers can choose to treat the risks associated with Legionnaires’ disease; otherwise, facility managers will not be able to satisfy the requirements of various standards, codes, and regulations. As such, the only two viable risk response strategies that facility managers can rely on in managing the risks associated with Legionnaires’ disease are risk mitigation and risk avoidance. To implement risk mitigation strategies, they need to reduce the probability or impact of the risk by adopting proper building water management practices. These include strategies such as keeping water at an appropriate temperature and free of impurities and verifying the effectiveness of building water management plans.

To implement risk avoidance strategies, facility managers need to eliminate the risk. Some of the building water management strategies that, to a large extent, eliminate the risk of Legionnaires’ disease, can be classified under the risk avoidance (i.e., risk elimination) category. Although these risks cannot entirely be eliminated, these strategies can play important roles in minimizing the likelihood of the risk occurrence. One of the strategies that can be classified as a risk avoidance strategy is the use of geothermal heat pumps (GHPs) in buildings. GHPs are also known as GeoExchange, earth-coupled, ground-source, or water-source heat pumps. Instead of using the outside air temperature as the exchange medium, GHPs use the constant temperature of the earth as the exchange medium. During the winter, the ground is warmer than the air above it whereas, during the summer, the ground is cooler than the air. GHPs take advantage of this characteristic of the earth by exchanging heat with the earth through a ground heat exchanger (DOE, 2018). If geothermal exchangers are incorporated during the building design process and used in place of cooling towers in buildings, they can eliminate the need for a recirculated water system that uses evaporative cooling for rejecting the heat to the air. Other benefits of GHPs include high energy efficiency, durability, and high energy efficiency (EPA, 2018). Because cooling towers, evaporative condensers, and fluid containers have been identified as one of the main sources of dispersing water-dispersed diseases such as Legionellosis disease, eliminating the need for a recirculated water system can be an effective sustainable construction strategy to avoid the risk of Legionellosis disease.

To implement effective water management strategies, potential risks associated with the water management systems need to be identified, assessed, and managed. A proper application of risk management techniques makes facilities less vulnerable to potential risks arisen from Legionella bacteria. This article identified some of the risk response strategies that can be used to ensure systems are in place to prevent and control Legionnaires’ disease. This article identified risk mitigation and risk avoidance as the two main risk response strategies for managing the risks associated with Legionella infection, and discussed the use of geothermal heat pumps (GHPs) as a way to eliminate these risks.

For more information about building water, risk assessment, and Legionella services that Adroit provides, please visit the following page or contact us:

Building Water and Legionella Services

References:

Department of Energy [DOE] (2018). Geothermal Heat Pumps. Retrieved from https://www.energy.gov/energysaver/heat-and-cool/heat-pump-systems/geothermal-heat-pumps

Department of Health [DOH] (2018a). Legionnaires’ Disease. Retrieved from https://www.cdc.gov/legionella/

Department of Health [DOH] (2018b). New York State Department of Health Warns of Potential Exposure to Legionella Bacteria in Schuyler County. Retrieved from https://www.health.ny.gov/press/releases/2018/2018-08-09_legionellosis.htm

The United States Environmental Protection Agency [EPA] (2018). Geothermal Heating and Cooling Technologies. Retrieved from https://www.epa.gov/rhc/geothermal-heating-and-cooling-technologies

Effective Water Management Strategies to Prevent Legionella Bacteria

Effective Water Management Strategies to Prevent Legionella Bacteria

Posted on by Adroit

Government agencies, water management professionals, healthcare facility managers, and many other stakeholders are increasingly interested to find out more about effective water management strategies to prevent Legionella Infection. Legionnaires’ disease is a severe respiratory disease caused by the bacterium Legionella pneumophila. This bacteria is found in both potable and non-potable water systems. The need for more effective water management strategies became more apparent in 2015 when the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) released Legionella standard, ANSI/ASHRAE 188-2015 after a consensus was reached among government agencies and industry groups concerning the general approach to preventing and controlling Legionnaires’ disease.

ANSI/ASHRAE 188-2015 identified some of the important considerations in managing water management systems to ensure proper strategies are in place to prevent and control Legionnaires’ disease. In 2015, an outbreak of Legionnaires’ disease was identified as the cause of death for 12 individuals in the South Bronx in the City of New York. This outbreak also sickened about 120 people in the same area. Several cooling towers in the affected areas tested positive for legionella. In response to this outbreak, building owners and facility managers in New York are now required to register cooling towers, evaporative condensers, and fluid containers with the Department of Buildings. After this outbreak, the Centers for Disease Control and Prevention (CDC) also reported about the increased number of Legionnaires’ disease cases and highlighted the importance of more effective building water management.  

To implement effective water management strategies, potential risks associated with the water management systems need to be identified, assessed, and managed properly. Although risks are typically classified into positive and negative risks, this article focuses on negative risks or threats. Negative risks are any potential events or conditions that may adversely impact asset management objectives. A proper application of risk assessment techniques makes facilities less vulnerable to potential risks arisen from Legionella bacteria.  Addressing issues after the fact usually costs significantly higher compared to the amounts paid for implementing risk response strategies. Therefore, using risk management practices are important not only to protect facilities and water management systems from detrimental risks but also to ensure that facility owners, such as commercial buildings and hospitals, do not incur costs due to unmanaged risks. Risk management consists of the key processes of planning for risk management, identification, assessment, response planning (i.e., risk treatment), and risk control. The following are some of the recommended practices to ensure risk management practices are properly used for water systems in buildings and facilities:

a)      Establish water management program (WMP)

Many benefits can be gained by timely establishing a water management plan (also known as water management program [WMP]) even if an audit is not forthcoming. ANSI/ASHRAE 188-2015 can be used as a guideline and a reference but other recommended practices need to be considered to determine the best strategies that can be used to protect the occupants and users of buildings and facilities against Legionnaires’ disease because cooling towers, evaporative condensers, and fluid containers have been identified as one of the main sources of dispersing water-dispersed diseases (e.g. Legionellosis).

b)     Follow your WMP and improve as needed

Property owners and facility managers protect themselves against legal and non-legal risks and expenses if they, not only prepare but also implement water management programs to demonstrate they have exercised standards of care in preventing diseases associated with water systems. Any WMP needs to be reviewed on a regular basis to identify the areas for improvements and adjust the strategies as needed.

c)       Compliance with rules and regulations

In New York, compliance with portions of ANSI/ASHRAE 188-2015 is mandatory. Other states have also started to adopt more measures in this regard to protect public safety. Therefore, it is good practice for property owners and facility managers to use proactive water management measures to ensure that their facilities meet and exceed the minimum requirements established by consensus-based standards and guidelines. Examples include ANSI/ASHRAE standard 188-2015, Legionellosis: Risk Management for Building Water Systems, and NSF Standard 453-2016.

d)      Use of proper liability insurance coverage

Another protective measure that property owners can adopt is to ensure that their liability insurance provides adequate coverage against the Legionella claims.

e)      Use internal audits for quality assurance

Quality assurance and quality control are two aspects of quality management, and both are important to ensure proper tools, techniques, and practices are used to effectively manage water systems in buildings and facilities. Quality assurance has an important role, similar to the role of the quality control; however, it may be considered a more fundamental need because it focuses on providing confidence that requirements will be satisfied. In other words, quality assurance ensures that proper water management systems, practices, and procedures are in place and followed.

To implement effective water management strategies, potential risks associated with the water management systems need to be identified, assessed, and managed. A proper application of risk management techniques makes facilities less vulnerable to potential risks arisen from Legionella bacteria. This article identified some of the recommended practices to ensure risk management practices are properly used for water systems to prevent and control Legionnaires’ disease, especially because cooling towers, evaporative condensers, and fluid containers have been identified as one of the main sources of dispersing water-dispersed diseases (e.g. Legionellosis). These practices include establishing water management program (WMP), following WMPs and improving them as needed, compliance with rules and regulations, using proper liability insurance coverage, and using internal audits for quality assurance. Using risk management practices are important not only to protect facilities and water management systems from detrimental risks but also to ensure that facility owners, such as commercial buildings and hospitals, do not incur costs due to unmanaged risks associated with Legionnaires’ disease.

For more information about building water, risk assessment, and Legionella services that Adroit provides, please check out the following page or contact us:

Building Water and Legionella Services

Diagrams to illustrate repetitive construction activities

Diagrams to illustrate repetitive construction activities

Posted on by Adroit

Dr. Maryam Mirhadi, PMP, PSP

Project planning and scheduling professional may use different project scheduling methods and techniques for different projects depending on the type, size, and nature of projects. Repetitive scheduling techniques are used is in linear construction projects. In linear construction projects, the majority of the work is made up of highly repetitive activities. In these projects, a set of project activities are repeated in each location for the entire length of the work. Once a project activity is started and/or ended in one location, it is repeated in another location. Examples of linear construction projects include pipeline projects, highway construction, highway resurfacing and maintenance, airport runway construction and resurfacing tunnels, mass transit systems, and railroads. Because of the highly repetitive nature of the work, high-rise building projects are also often identified as linear in nature.

One of the important considerations in the planning of linear construction projects is to identify a location for the working crew to move to in a manner that its work does not interfere with the work of any other construction crew. Therefore, production rates have to be coordinated to prevent a preceding process from overtaking its succeeding process(s).   

Traditional project planning and scheduling methods such as the critical path methods are typically inadequate for effective planning and scheduling of linear construction projects because these planning and scheduling methods do not account for work locations or spatial aspects and do not effectively model project activities that are repetitively performed. Due to such shortcomings, other methods such as line of balance (LOB), vertical production method (VPM), time couplings method (TCM), the repetitive project modelling (RPM), repetitive construction (REPCON), and the repetitive scheduling method (RSM) have been proposed in the literature to better satisfy the planning and scheduling needs of linear construction projects. The various repetitive scheduling techniques can be categorized into the two main classes of linear scheduling methods (LSM) and line of balance (LOB) techniques.

Line of balance techniques use three key types of charts to illustrate repetitive construction activities. These charts are objective chart, production plan, and progress chart. LOB was first used in the manufacturing industry. It starts with the end product and the ultimate output quantity and schedule in mind. This information is documented in the production plan and it is then used to establish a cumulative plan that delineates how much work ought to be delivered over time. This cumulative plan then becomes the objective chart against which the actual progress is measured using the progress chart. An example objective chart that is used in the line of balance method is shown in the figure below.

LSM schedules, however, use velocity diagrams representing each activity. The schedule format may provide the planned and actual production rates on a time-scaled format. A typical LSM diagram represents time along the X-axis (i.e., horizontal axis) and some measure of repetitive units along the Y-axis (i.e., vertical axis). This diagram also includes lines that represent all the linear activities that are involved in the completion of the repetitive units. A linear activity is a project activity that progresses along a physical path. This path is represented by the location axis in the LSM. Over the course of the project and at any point of progress along this path, the activity is completed up to that point. For instance, consider an activity that involves rough grading before finish grading in a road construction project. In this example, as the path is rough-graded, the rough-grading activity is complete up to that point of progress along the path. Once the path is rough-graded at any location, no need exists anymore to go back and rough-grade the location. Therefore, any location along the path that is behind the current work location is a work-front for succeeding activities (e.g., finish grading) to be performed. An example LSM diagram is shown in the figure below.

In a future article, further considerations in developing the linear scheduling and line of balance techniques will further be described.

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Schedule Activity Density Analysis

Schedule Activity Density Analysis

Posted on by Adroit

Dr. Maryam Mirhadi, PMP, PSP | Principal Consultant

One of the tools that can be used to assess the time-phased projected number of activities scheduled over the course of a project is the schedule activity density analysis. A schedule activity density histogram represents the cumulative number of activities that are, partly or wholly, scheduled to be performed within each time unit over the course of the project. The schedule activity density can alternatively be measured by activity-workdays scheduled per time analysis period (if activity durations are defined in days).

For instance, if a 10 and a 20 working-day activities are supposed to start and complete in a particular month, the activity-workdays for that particular month will be 30 (i.e., 10+20). If a 10 working-day activity, a 20 working-day activity, and half of an 8 working-day activity are supposed to start and complete in a particular month, the activity-workdays for that particular month will be 34 (i.e., 10+20+8/2).

As such, if a schedule activity density is high within a particular time analysis period, it can be concluded that a high number of activities are in-progress within that particular time analysis period. Therefore, it is expected that delays influence schedule activity density histograms as well because delays change the number of activities that are scheduled to be undertaken within certain time frames. Delayed work typically results in the overlapping of planned future work; therefore, delays are expected to increase the schedule’s activity density during the time frames in which planned future work will be scheduled.

Figure 1 provides an example schedule activity density histogram in which the schedule activity density is shown by the number of activity-workdays scheduled per time analysis period (i.e., monthly periods).

Figure 1. An example schedule activity density histogram

A review of Figure 1 indicates that the schedule activity density is the highest about September 2017 in which the number of activity-workdays is at the highest point whereas, in a time analysis period such as December 2017, the number of activity-workdays is at the lowest point. This indication suggests that in or about September 2017, the highest number of in-progress activities are scheduled whereas in or about December 2017, the lowest number of in-progress activities are scheduled.

Figure 2 provides an example cumulative schedule activity density histogram in which the cumulative schedule activity density is shown by calculating the cumulative number of activity-workdays scheduled per time analysis period (i.e., monthly periods).

Figure 2. An example cumulative schedule activity density histogram

Two cumulative schedule activity histograms are provided in this figure. The blue histogram represents the schedule activity density for the case where the constraint type of all project activities is set to “As Soon As Possible” whereas the red histogram illustrates the schedule activity density for the case where the constraint type of all project activities is set to “As Late As Possible”. A comparison between these two histograms indicates that the cumulative number of activity-workdays scheduled per time analysis period (i.e., monthly periods) for the late chart is always less than or equal to this cumulative number for the early chart over the course of the project because setting the constraint type of all project activities to “As Late As Possible” prevents the non-critical activities from starting on their early start date and being completed on their early finish dates. This change reduces the cumulative number of activity-workdays scheduled per time analysis period (i.e., monthly periods) for the late chart and the activity density chart shifts to the right of the X-axis suggesting that more activities are being scheduled to be performed later than their original early start and finish dates.

Delayed work typically results in the overlapping of planned future work; therefore, delays are expected to increase the schedule’s activity density during the time frames in which planned future work will be scheduled. Analyzing a schedule activity density histogram is helpful in identifying the likely causes that adversely impact project schedules. For example, delaying events that prevent a set of activities from starting or finishing on-time reduce the schedule’s activity density during the time frames in which planned work cannot be performed in a timely manner but increase the schedule’s activity density during the time frames in which planned future work is supposed to be implemented. Schedule activity density histogram provides an effective way to visualize the density of schedules and obtain a better understanding of the effect of delays on the scheduled workload. 

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Considerations in developing phasing plan in subway rehabilitation projects

Considerations in developing phasing plan in subway rehabilitation projects

Posted on by Adroit

Maryam Mirhadi, Ph.D., PMP, PSP

Subway station rehabilitation/renovation projects, also known as subway rehabilitation projects, are among the projects with special needs. These projects have special characteristics that differentiate them from other types of construction projects. The most important characteristics of subway rehabilitation projects from a project planning perspective are the need to account for the schedule of diversions, utility/infrastructure relocations, piggybacking opportunities, special permits, flagger availability, and work train availability.

Because of the special characteristics of subway rehabilitation projects, some considerations for scheduling these projects shall be applied with special attention and emphasis. The following provides key considerations for planning and scheduling of these projects. This list is not meant to be comprehensive. Instead, it identifies some of the key considerations that need to be given to the planning and scheduling of subway rehabilitation projects.

  1. Identify the activities that cannot be implemented during normal service hours (e.g., the activities that need diversion of train services). Examples include activities on the platform edge and activities on, under, or near tracks. If a project involves working on several stations on the same line, the stations that are between two immediate switches can utilize the same diversion (by piggy-backing on each other). Under these circumstances, diversion-related tasks should be scheduled properly to maximize efficiency.
    Having multiple diversions on one line and between different switches is called double-heating. If the stations are not between two immediate switches, diversions are not usually scheduled at the same time to avoid double-heating and ensure train service interruptions are minimized.
  2. Determine the preliminary number and type of the required diversions, work-trains, and other special services for the project. This determination will help the construction team consider diversions, work-trains, and other special services as project resources. This approach helps the construction team to identify the resources that are constrained. By using proper resource management strategies such as resource planning and optimization, the construction team can ensure it obtains access to these special services when the project needs these services.
  3. Review the special services identified with operations departments to ensure availability. If the requested diversions cannot be accommodated during required timeframes, the scope of work, design requirements, alternative construction methods, job phasing, or the project timeline should be reviewed and revised based on the available diversion plans. In addition to time, budget, and resource constraints, the availability of diversions is one of the major constraints that impact subway rehabilitation projects.
  4. Identify the areas and equipment that cannot concurrently be closed or taken out-of-service in each subway station to ensure of continuous and safe operation of the station. Examples include entrance stairs, platform stairs, mezzanine areas, elevators, and tracks. For instance, if two elevators in one station exist and upgrading both elevators are in the project scope of work, working on the two elevators at the same time may not be permitted.
  5. Identify hazardous materials such as lead, asbestos, and mercury. Performing abatement operations might be necessary before the commencement of work in areas in which hazard may be present. In these cases, direct communication and coordination between the client, contractor, and environmental agencies is crucial to identify the proper course of actions. In addition, removal of these materials during the construction phase may require special permits and equipment for which contractors should plan in advance.
  6. Identify the long-lead and client-furnished items. With respect to long-lead items, an opportunity may exist to fast-track some activities by creating an overlap between the design and procurement activities for the long-lead items. Moreover, early order placement for long-lead items plays an important role in making sure that long-lead items will be delivered to the project in a timely manner. In addition, the construction management needs to properly identify the client-furnished items and account for the possibility of receiving these items later than expected.
  7. Identify the activities that are supposed to be executed in areas that are not under the authority of the construction team. Examples include utility relocations or working in a public street. In addition, it should be determined if these activities require additional permits (e.g., DOT permits). The project team should be aware that these tasks have the potential to delay the project to a great extent because the project team usually has little control on expediting the permit application, inspection, or review processes.

In sum, from a project planning perspective, some of the key characteristics of subway rehabilitation projects that differentiate these projects from many other construction projects include the need to account for the schedule of diversions, utility/infrastructure relocations, piggybacking opportunities, special permits, flagger availability, and work-train availability. As such, some considerations for planning and scheduling of these projects shall be applied with special attention and emphasis. This article briefly discussed some of these requirements.

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Shortening the project longest path

Shortening the project longest path

Posted on by Adroit

The critical path represents a project’s longest continuous sequence of activities in the project schedule. This path determines the earliest time that the project can be completed. To complete a project earlier than its originally-planned completion date, the project longest path is typically shortened. Shortening a project schedule may be costly and result in unintended consequences. For example, schedule compression may cause stacking of trades and ultimately result in loss of labor and equipment productivity. Nevertheless, project teams may choose to shorten a project schedule due to a variety of reasons such as catching up to achieve the planned dates that are affected by delays or due to a need to achieve some milestone dates earlier than expected.

Due to the potential impacts of schedule compression on the project, the project teams should use proper strategies to shorten the project longest path. In accelerating project activities, priority needs to be given to the critical activities because these activities drive the expected project completion date in the schedule. If a number of options exist, priority is typically given to those critical activities whose crashing is less costly. Improper implementation of acceleration plans may result in less than expected time savings, unexpectedly high costs of crashing, quality or safety issues, and loss of labor or equipment productivity. It is important to note, however, that acceleration is not the only option for shortening the longest path.

Depending on the type of the project and its scope of work, project teams may have a number of options to compress project schedules. The following table outlines some of the example methods in each of the main phases of engineering, contracting and procurement, and implementation:

PhaseMethodMethod Description
EngineeringConstructability review and analysisThe review of designs to ensure designs can practically be implemented with cost-effective means and methods.
Incorporate modular components in designThe incorporation of modular components in design to ensure less time is needed to be spent on the jobsite to implement these components.
Reuse designs and plansThe reuse of previously-used design elements may result in saving design time and efforts.
Incorporate standard or typical components in the designThe use of standard or typical designs may help the design team save time and efforts in implementing designs.
Incorporate pre-engineered or on-the-shelf components in the designThe incorporation of pre-engineered or on-the-shelf components may reduce the need for designing new elements.
Contracting and procurementFast-trackingThe creation of an overlap between design and procurement or an overlap between procurement and implementation activities may result in time savings.
OutsourcingThe assignment of work to outside entities instead of implementing all activities in-house may help to use in-house resources in more effective ways.
Find alternative or equivalent modular products or systemsThe use of alternative or equivalent products or systems may help to save time that would have otherwise been used to fabricate or supply items.
Implementation Improve work sequenceThe improvements to the work sequence or betterment of the work schedule may help project teams identify time saving opportunities.
Shiftwork and overtimeWorking overtime or working in periods other than daytime hours may help project teams make more progress in the same or shorter amounts of time.
Expend more resources in the same or shorter time periodsThe use of higher resource usage rates and spending more resources in the same or shorter time periods may help project teams increase progress achievements.
Incentivized working schemesThe use of incentivized schemes may encourage project teams to complete activities in a shorter amount of time or work in a more effective manner.

Because of the potential impacts of schedule compression techniques on the project, the project teams should use proper strategies to shorten the project longest path. Acceleration is not the only option to shorten the longest path. If a project team is intended to shorten the project longest path, it is recommended that the team chooses the most appropriate strategies in each of the main phases of engineering, contracting and procurement, and implementation to ensure the schedule can properly be compressed using a cost-effective manner that fits the project needs.

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Strategies to Minimize the Adverse Effects of Shiftwork

Strategies to Minimize the Adverse Effects of Shiftwork

Posted on by Adroit

Dr. Maryam Mirhadi, PMP, PSP

Shiftwork is defined as working other than daytime hours. Shiftwork is the most commonly utilized alternative to overtime. Despite its potential benefits in accelerating a construction schedule, shiftwork is considered among the factors with adverse effects on labor productivity in construction.

Some of the key issues with shiftwork include its adverse effect on circadian rhythms, dilution of supervision, challenges in exchanging performance information among individuals who work in different shifts, the adverse effects of shiftwork on social interactions, and higher work setup times. A number of studies address the adverse effects of shiftwork on productivity. Some of the key studies include the Bureau of Labor Statistics, the Business Roundtable, NECA 1969 study, the Construction Industry Institute (CII), and the works of Hanna et al. (2008 and 2009). The American Association for Cost Engineering (AACE) has identified some of the recommended specialized studies that can be used to evaluate the adverse effects of shiftwork on productivity (AACE, 2004).

Despite these negative effects, construction contractors use shiftwork as a way to accelerate construction schedules. But the question is what strategies are effective in minimizing the adverse effects of shiftwork on construction work. Some of these strategies include the following:

1- Refrain from shiftwork for those who are more susceptible to health problems: Construction contractors should refrain from scheduling shiftwork for those employees who are susceptible to health problems. Workers older than 50 years or pregnant women are examples of these individuals.

2- Use rapid rotations: Instead of weekly or monthly cycles, construction contractors are encouraged to consider rapid rotations in scheduling shiftwork. The use of rapid rotations in scheduling shiftwork is recommended because rapid rotations do not significantly disrupt sleep patterns of those individuals who work on a shiftwork basis. Three examples of rapid rotation shiftwork systems are shown in the following tables (Kodak, 1986):

3- Overlap consecutive shifts in part: By providing some overlap between consecutive shifts, construction contractors can overcome the challenges in exchanging performance information among individuals who work in consecutive shifts. That way, the arriving crews become aware of what has been performed by the previous crews. To achieve this objective, construction contractors can ask the foreman of the first shift to stay one or two hours longer or the foreman of the arriving crews to arrive earlier to the extent practically needed for coordination purposes.

4- Assign independent tasks to consecutive shifts: Different shift-working teams tend to work with the same set of tools, machinery, and equipment; therefore, work setup times are typically higher when multiple teams (instead of one team) use the same set of tools, machinery, and equipment. In addition, extra time is needed in shiftwork for the process of hand-over and transition from one shift to another if the work of consecutive shift are dependent. To overcome these challenges, construction contractors can assign tasks that are totally independent from the tasks performed by the previous shift to minimize the interdependency of shifts and reduce the materials and tools that are commonly used by two consecutive shifts.

5- Properly select the work assigned to a second shift: Construction contractors should assign to shiftwork only tasks that are on the project critical path or those work elements that are justified to be accelerated. Proper selection of work assigned to a second shift also includes assigning tasks that are less demanding from the supervision or engineering support perspectives to ensure progress can be made without waiting for supervision or engineering support that may not be readily available during shiftwork periods.

6- Make proper work environment accommodations: Since shiftwork is performed in hours other than daytime hours, work environment considerations need to be identified. Examples include natural lighting vs. artificial lighting and additional demands for air conditioning. Studies have shown that safety is significantly improved by providing an adequate amount of artificial lighting. Moreover, working in places in which work environmental considerations have been taken into account help employees work in a more efficient and effective manner.

 In sum, despite the negative effects of shiftwork, construction contractors use shiftwork as a way to accelerate construction schedules. Nevertheless, construction contractors are recommended to use effective strategies to minimize the adverse effects of shiftwork on construction work. Examples of these strategies include refraining from shiftwork for those who are more susceptible to health problems, using rapid rotations, overlapping consecutive shifts in part, assigning independent tasks to consecutive shifts, properly selecting the work assigned to a second shift, and making proper work environment accommodations.

References:

AACE International (2004), Recommended Practice 25R-03 Estimating Lost Labor Productivity in Construction Claims, AACE International, Morgantown, WV. Can be retrieved from https://web.aacei.org/docs/default-source/toc/toc_25r-03.pdf?sfvrsn=4

Kodak, E. (1986). Ergonomic design for people at work. Volume, 2, 20-30.

Hanna, A. S., Chang, C. K., Sullivan, K. T., & Lackney, J. A. (2008). Impact of shift work on labor productivity for labor-intensive contractor. Journal of construction engineering and management, 134(3), 197-204. Can be retrieved from https://goo.gl/CPR9wm

Hanna, A. S., & Haddad, G. (2009). Overtime and productivity in electrical construction. In Construction Research Congress 2009: Building a Sustainable Future (pp. 171-180). Can be retrieved from https://ascelibrary.org/doi/abs/10.1061/41020(339)18

 

To learn more about the adverse effects of shiftwork on labor productivity, please read this article.

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Our posts to the Insights page share fresh insights and seasoned advice about many project and construction management topics.  To have the Insights monthly newsletter delivered automatically to your email inbox, please subscribe here.