Civil FE Exam: Common Mistakes

Always check the units given in the problem statement before starting. Write units next to every number in your calculations. Common traps include mixing kPa with psi, meters with feet, and kN with lbs. A quick unit check at the end of each problem catches most conversion errors.

Before solving, draw the full free body diagram and identify each support type. A pin support has two reaction forces (horizontal and vertical), a roller has one (perpendicular to the surface), and a fixed support has two forces plus a moment. Getting the support reactions wrong invalidates your entire solution.

Manning's equation applies to open channel flow, while the Darcy-Weisbach or Hazen-Williams equations apply to pressurized pipe flow. Read the problem carefully to determine the flow type before selecting your approach. Mixing these up gives answers that look reasonable but are completely wrong.

Always determine whether the problem requires effective stress or total stress analysis. Effective stress equals total stress minus pore water pressure. In consolidation and shear strength problems, using total stress when effective stress is needed (or vice versa) leads to incorrect answers.

LRFD and ASD use different load factors and combinations. Verify which design method the problem specifies before applying load factors. Using LRFD factors in an ASD problem (or the reverse) produces incorrect design loads that cascade through the entire calculation.