PE Construction common mistakes
PE Construction · Understand the traps and how to avoid them.
Determining an activity's total float by subtracting its duration from the project completion date instead of running a full forward and backward pass through the network.
Under exam time pressure, candidates shortcut float by eye, which fails as soon as an activity has more than one predecessor or successor.
What to do instead
Always compute early start/finish with a forward pass and late start/finish with a backward pass, then total float = LS - ES; do it for every activity before answering any float, delay, or crashing question.
Applying overhead and profit only to direct labor and material cost, then multiplying the marked-up unit price by quantity.
Candidates memorize a standard markup percentage without checking whether the problem or contract defines the markup base as total direct cost including subcontractor and equipment costs.
What to do instead
Write the markup base explicitly before multiplying: identify whether O&P applies to direct cost, direct plus indirect, or subcontractor cost, and follow the problem's stated basis.
Answering that a ladder or other egress is required when a trench reaches 5 ft, rather than 4 ft.
Candidates conflate the 5-ft trigger for a protective system with the 4-ft trigger for egress because both numbers appear in the same OSHA excavation standard.
What to do instead
Memorize separately: protective systems (sloping/shoring/shielding) at 5 ft depth, and ladder/ramp/other egress within 25 ft of travel at 4 ft depth; recite both thresholds before answering.
Computing lateral earth pressure below the water table using the soil's total (moist) unit weight.
The unit weight given in the problem is usually total, and candidates plug it directly into Ka times gamma times H without subtracting buoyancy.
What to do instead
Use effective unit weight (saturated minus 62.4 pcf) below the water table, add water pressure separately, and draw the pressure diagram in two layers.
Sizing a beam or checking bending stress using only the applied point or live load, omitting the member self-weight and any uniform dead load.
Self-weight is small relative to the highlighted load and easy to skip, but it changes the controlling moment.
What to do instead
Before computing reactions, list all loads including member weight and superimposed dead load, then compute the factored load combination (1.2D + 1.6L) and check the resulting moment.
Substituting watershed area in square feet into the Rational Method Q = CiA and reporting peak flow in cfs.
The formula is unit-dependent (acres, in/hr, cfs) and the problem may give area in square feet or square meters, so candidates forget the conversion.
What to do instead
Convert area to acres (divide square feet by 43,560) and confirm intensity is in in/hr before multiplying; state units at each step.
Checking a crane lift against the load chart at the required radius using only the load weight, ignoring the hook block, slings, spreader beam, and jib.
The load chart is gross capacity, and the problem typically emphasizes the weight of the pipe or module being lifted.
What to do instead
Sum all suspended weight (load, rigging, and any jib or auxiliary equipment deductions) and compare that gross weight to the chart capacity at the actual radius and boom length.
Laying out the project schedule as a list of activities in narrative order without defining predecessor and successor relationships.
Candidates treat scheduling as sequencing by the specification's table of contents, which yields a bar chart with no logic.
What to do instead
Build the network explicitly: identify each activity's predecessors and successors, then derive ES/EF/LS/LF and the critical path from the logic, not the calendar.
Using the saturated-surface-dry batch weights from a concrete mix design directly without adjusting for aggregate free moisture.
Mix designs are stated at SSD, and the aggregate moisture contents given in the problem are treated as irrelevant.
What to do instead
Adjust coarse and fine aggregate weights by (1 + free moisture) and reduce added water by the total free water, then verify the water-cement ratio.
Advising the contractor to submit a change order for a differing site condition without first checking the contract's notice and time-bar provisions.
Candidates focus on entitlement and skip the procedural condition precedent that can defeat an otherwise valid claim.
What to do instead
Read the notice clause first: identify the required written notice period (commonly 14 days) and documentation required, and state that notice must be given before entitlement is preserved.