Time Impact Analysis Fragnet Development: A Step-by-Step Guide

The Heart of Time Impact Analysis

A fragnet — short for "fragmentary network" — is a small CPM network representing a specific delay event and its logical ties to the broader project schedule. Fragnet development is the heart of Time Impact Analysis (TIA). A well-constructed fragnet produces a defensible delay impact; a poorly constructed one produces results that will be challenged and likely rejected.

This guide walks through the fragnet development process used by professional forensic schedule analysts.

When to Build a Fragnet

Fragnets are used for specific delay events that need to be analyzed for schedule impact. Typical triggers include:

Owner-directed changes or additional scope
Design errors or omissions requiring resolution
Differing site conditions
Delayed owner responses (RFIs, submittals, inspections)
Delayed owner-furnished equipment or materials
Force majeure events (weather, pandemic, strikes)
Delayed permit approvals

Each distinct delay event should have its own fragnet. Don't combine multiple unrelated delays into a single fragnet — this muddies the analysis and creates complications in causation arguments.

Fragnet Development Process

1Identify the Delay Event: Define precisely what happened, when it happened, and how it affected the work. Gather supporting documentation — RFIs, emails, photos, daily reports, change orders. The fragnet must be grounded in factual records.

2Establish the Analysis Date: Determine the schedule status at the time the delay occurred. TIA uses the contemporaneous schedule — the most recent approved update prior to the delay event. This is your baseline for analysis.

3Identify the Impacted Activities: Determine which activities in the contemporaneous schedule are directly affected by the delay event. These may include activities that cannot proceed, activities that must be re-sequenced, or new activities added due to the delay.

4Define the Fragnet Activities: Create specific activities representing the delay impact — the delay activity itself, any new work required, and any waiting periods. Each activity should have a realistic duration based on actual conditions.

5Establish Logic Ties: Connect the fragnet to the contemporaneous schedule through appropriate predecessor and successor relationships. The ties must be logically justified and documented. Most often, the fragnet becomes a predecessor to activities that couldn't proceed until the delay was resolved.

6Insert and Recalculate: Insert the fragnet into a copy of the contemporaneous schedule and run the CPM calculation. The difference between the original completion date and the new calculated completion date represents the time impact of the delay event.

7Document Everything: Prepare a detailed TIA report including the delay description, fragnet logic diagram, before/after schedule comparison, calculated impact, and supporting documentation references.

Fragnet Construction Best Practices

Use Realistic Durations

Fragnet activity durations must reflect actual time required, not inflated estimates. Arbitrary durations will be challenged in review. Use dated records — "RFI submitted on X, response received on Y" — to establish factual durations.

Show Causation Clearly

The logic connecting the fragnet to the main schedule must show clear causation. Vague statements like "this delay affected all subsequent work" are not sufficient. Identify specific activities that couldn't proceed and explain why.

Account for Concurrent Work

If contractor-caused delays were occurring simultaneously, the fragnet must account for this. A delay that impacts a non-critical path activity may not actually delay the project if contractor issues were already driving the critical path.

Use Insertion Points Carefully

Where you insert the fragnet in the schedule matters. Insert it at the logical point where the delay event occurred in the sequence — not at the beginning or end of the activity it impacted.

Industry Standard: AACE International Recommended Practice 29R-03 "Forensic Schedule Analysis" provides detailed guidance on TIA methodology and fragnet development. This is the authoritative reference for forensic schedule analysts.

Fragnet Examples

Example 1: Delayed Design Response

Scenario: Contractor submitted RFI on March 15 for resolution of a dimension conflict. Owner responded April 20, a delay of 36 calendar days. Rebar installation couldn't proceed without the response.

Fragnet: Single activity "RFI-042 Resolution — 36 days" as a predecessor to "Rebar Installation." The fragnet shows a 36-day delay to rebar, which was on the critical path at the time. Result: 36-day impact to project completion.

Example 2: Differing Site Conditions

Scenario: Excavation revealed unexpected rock on July 8. Additional blasting and removal work required 22 days, completing August 5. Foundation concrete couldn't proceed during this period.

Fragnet: Three activities — "Notify Owner of DSC (1 day)," "DSC Investigation and Direction (8 days)," "Rock Removal (13 days)" — connected in sequence and inserted between "Excavation" and "Foundation Formwork." Total fragnet duration: 22 days.

Common Fragnet Mistakes

Missing Supporting Documentation: A fragnet without backup records will be challenged. Link every activity to specific dated records.
Assuming Critical Path Impact: Not every delay impacts the critical path. Verify that the affected activities were critical or became critical due to the delay.
Ignoring Mitigation Opportunities: If the contractor could have worked around the delay, the fragnet should reflect that — or the claim will be reduced.
Combining Multiple Events: Keep fragnets discrete. One delay event = one fragnet = one impact calculation.
Using the Wrong Baseline: Use the contemporaneous schedule, not the original baseline or the latest update. The analysis must reflect the schedule status at the time of the delay.

Final Thoughts

Fragnet development is both science and craft. The science is in the CPM calculations, which are objective. The craft is in constructing the fragnet correctly — choosing the right activities, establishing the right logic ties, and documenting causation with appropriate evidence. A defensible TIA requires mastery of both.

When in doubt, engage an experienced forensic schedule analyst. The cost of professional help is small compared to the cost of a rejected claim.

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