Fragnet schedule

Definition

AACE International gives three meanings: a subnet of the project schedule that shows some work in more detail; a fragment of the network used to illustrate changes; and, in change management, "a fragment of a network schedule constructed to model the event under analysis. It should contain a network of one or more activities comprising the elements of the event and their logical relationships to the appropriate activities in the unimpacted schedule" (AACE 10S-90). On construction contracts it usually means the third: the fragnet behind a request for more time.

How a fragnet is used in a time impact analysis

A time impact analysis (TIA) is the usual way to price a change or delay in time before or while it happens. AACE's recommended practice 52R-06 describes it; in short:

1. Build the fragnet: the activities of the event (for example, wait for a redesign, then do the extra work), each with a duration and a basis for it, and links to the existing activities it follows and the ones it holds up.
2. Take a copy of the last accepted update before the event started, with no other changes.
3. Insert the fragnet, link it in, and schedule the copy.
4. Compare the completion date (and any contract milestones) with the copy before the fragnet. The difference is the impact.
5. Take off any days already granted for the same period, so no day is counted twice.

Time is granted only when the event uses up the float and pushes completion past the contract date. USACE: "No time extension will be granted unless the delay consumes all available Project Float and extends the projected finish date ('End Project' milestone) beyond the Contract Completion Date."

An example

Take the seven-activity schedule from the critical path guide: completion on day 47, critical path through site preparation, foundations, structure and finishes; utilities and paving have 28 days of float.

• Footing redesign, 8 days, linked after site preparation and before foundations. Foundations now start on day 13 instead of 5, and every activity after them moves 8 days: completion on day 55. The fragnet shows 8 days of delay on the critical path.
• Water main reroute, 10 days, linked after underground utilities and before paving. Paving now finishes on day 29 instead of 19, still well before day 47: 18 days of float are left and completion does not move. No time extension, even though the work is real; the cost of the extra work is a separate question.

What specifications require

• USACE, UFGS 01 32 01.00 10 (3.8): "Prepare a proposed fragnet for time impact analysis consisting of a sequence of new activities that are proposed to be added to the project schedule to demonstrate the influence of the delay or impact to the project's contractual dates. Clearly show how the proposed fragnet is to be tied into the project schedule including all predecessors and successors to the fragnet activities. The proposed fragnet must be approved by the Contracting Officer prior to incorporation into the project schedule." The TIA follows AACE 52R-06 and uses a copy of the last approved schedule before the delay.
• NAVFAC, UFGS 01 32 17.00 20 (1.11.1): a TIA with each cost and time proposal, with three native .xer files: the fragnet, the last accepted update as of the impact start date, and the impacted schedule with the fragnet inserted and scheduled in P6.
• Caltrans, section 8-1.02 (2022): "Submit a TIA with each request for adjustment of Contract time or whenever you or the Engineer considers that an authorized or anticipated change may impact the critical path or work progress." The impact schedule adds or deletes activities or changes durations or logic in the accepted schedule closest before the event. Caltrans does not use the word fragnet.

Sources, read 24 October 2026: UFGS 01 32 01.00 10 (August 2026); UFGS 01 32 17.00 20 (May 2025); Caltrans 8-1.02 (projects advertised from 18 April 2022).

Why reviewers reject fragnets

• The wrong base schedule: not the last accepted update before the event, or a copy with other changes in it.
• Loose ties: an open end, or a fragnet linked to activities it does not really hold up. The tie-in decides the result, so it gets the closest look.
• A constraint instead of logic: a date forced onto an activity produces the delay by itself.
• Durations with no basis: no quote, no production rate, no letter from the designer.
• Several events in one fragnet, so the effect of each cannot be told apart, or delay the contractor caused mixed with delay the owner caused.
• No effect on completion: the event used float but did not move the finish past the contract date.

Check the schedules behind a TIA

Open the base update and the impacted schedule below, one after the other, to compare their completion dates and critical paths and run the DCMA 14-point check on each: open ends, constraints and lags show up there. The files are read in your browser and never uploaded.