Original sample lesson · allow approximately 10–15 minutes
By the end of this lesson
Calculate a basic strand extension and explain why one passing reading cannot cancel the other.
A stressing operation produces two different observations: the applied force and the strand's extension. Both should be compared with their calculated values. A pressure reading is useful only through a valid jack calibration, while an elongation reading depends on the effective length, material properties and required corrections.
For a straight elastic strand, the basic relation is Δ = PL/(AE). Here P is the force increment, L is the effective length, A is strand area and E is modulus of elasticity. Keeping units consistent is part of the calculation, not a final cleanup step. Pounds, inches and pounds per square inch produce an extension in inches.
Use this original example: P = 27,000 lb, L = 1,200 in, A = 0.153 in² and E = 28,000,000 psi. The calculated extension is (27,000 × 1,200)/(0.153 × 28,000,000) = 7.56 in. This is a basic straight-strand calculation with no seating, temperature, bed-movement or friction corrections included.
Check 1: A strand is tensioned from an initial 4,000 lb to a final 30,000 lb over a 125 ft effective length. The strand area is 0.167 in² and its mill certificate gives E = 29,000,000 psi. Using Δ = PL/(AE), what basic elongation should you expect?
Real procedures may require those corrections. They must be listed and calculated separately so the final expected reading can be traced. For example, a seating movement is a physical displacement at an anchorage. It must not be hidden by changing the assumed material modulus to force agreement with a measurement.
Check 2: Your 8.05 in figure is a basic straight-strand value. The bed shortens as the group is stressed and each chuck seats. How should those two effects be handled?
If force agrees with the approved calculation but elongation does not, stop and investigate the discrepancy under the plant procedure. Confirm the measurements, length, area, modulus and corrections. For a deflected profile, friction and local force distribution also matter. The full course expands this process through worked cases and interactive questions.
Check 3: Force is within the required tolerance but elongation is not. What is the appropriate response?
Take it into your study session
Write a one-sentence explanation of the principle, then describe a situation where the wrong answer would create a problem. Revisit the questions tomorrow without looking at the explanations first.
Continue with PCI Level II
The complete course includes the full lecture library, more examples, checkpoints, quizzes and practice exams.