Analyze the Relationship Details:The table shows that Activity 3001 ("Excavation, Dam Site") and Activity 4001 ("Excavation, Spillway") have a Start-to-Start (SS) relationship with a lag of 15 days. A Start-to-Start relationship indicates that the successor activity (4001) can only start after a specified lag period once the predecessor activity (3001) begins.
Understand the Concept of Lag:In scheduling terminology, lag refers to a delay or waiting period between the start (or finish) of one activity and the start (or finish) of a dependent activity. Here, the 15-day lag means that Activity 4001 will commence 15 days after Activity 3001 has started.
Interpret the Relationship:The SS relationship combined with a lag indicates that the two activities (3001 and 4001) are not starting exactly at the same time but are still overlapping or concurrent. This concurrency happens after the lag period elapses.
Verify PSP Study Guide and Relevant Terminology:According to AACE International’s Recommended Practices and the PSP Certification Study Guide:
Start-to-Start relationships are widely used to model overlapping work in schedules where one activity can start before its predecessor is fully complete (PSP Study Guide, Chapter on Scheduling Relationships and Constraints).
Lags provide flexibility to model realistic conditions where tasks start partially overlapping or with delays (PSP Study Guide, Section 2.2.4 Relationships).
Cross-Check the Answer Options:
Option A (Correct): Matches the described logic – "These activities are concurrent with Activity 4001 starting 15 days after the start of Activity 3001."
Option B: Incorrect – Lag is applied to the successor activity, meaning 4001 cannot start earlier than 3001.
Option C: Incorrect – This relationship (SS with a lag) indicates concurrency, not series.
Option D: Incorrect – Though concurrent, the lag makes the start times offset by 15 days, so they do not start at the same time.
AACE International Recommended Practices, RP 10S-90, "Cost Engineering Terminology."
Total Cost Management Framework, Concepts of Activity Relationships and Scheduling Dependencies.
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