PEC EPE Civil common mistakes
PEC EPE Civil · Understand the traps and how to avoid them.
Treating the seismic base shear as a single static number and applying it uniformly over the full height, instead of distributing it in proportion to the storey weight times height (the inverted-triangular distribution).
Candidates memorize V = Cs·W from a single worked example and never internalize that the vertical distribution (Fx = V·wx·hx^k / Σwi·hi^k) is a separate, separately graded step; the k exponent changing with period is also easy to forget.
What to do instead
Before computing Fx, write down the building period, decide k (linear for short periods, parabolic for long), and tabulate storey weights, heights, wx·hx^k, and cumulative sums in a table. Check that ΣFx equals V exactly and that the roof force is the largest.
Sizing a beam or column from factored load effects without ever confirming that the section is compact or non-slender, so plastic-section assumptions are invalid.
Candidates jump straight to φMn or φPn with the plastic modulus because it is the fastest formula, and they skip the width-to-thickness classification because it feels like a preliminary detail.
What to do instead
Make a classification check a mandatory first step: compute b/t and h/tw against the compact and non-compact limits, record the class, and only then choose the resistance formula. If the section is slender, switch to elastic or effective-width methods before continuing.
Computing the tributary area for a column or footing and then applying the full unreduced live load, ignoring the live-load reduction permitted for large tributary areas and multiple storeys.
The reduction formula lives in a different code chapter from the load-takings, and candidates who learned load paths in a statics course default to 'area times pressure' without checking the live-load provisions.
What to do instead
After computing tributary area, look up the live-load reduction expression, verify the eligibility conditions (occupancy type, minimum tributary area, member type), apply the reduction factor, and state both the unreduced and reduced values so the grader can see the reasoning.
Designing a reinforced-concrete member using the strength-reduction factor for the wrong failure mode, for example using the tension-controlled φ for a section that is actually compression-controlled.
Candidates pick φ = 0.90 because it is the most familiar value and because the tension-controlled check (net tensile strain versus the limit) is an extra calculation that is easy to skip under time pressure.
What to do instead
Always compute the strain in the extreme tension steel at nominal strength, compare it to the tension-controlled and transition limits, select φ accordingly, and iterate if the section falls in the transition zone. Show the strain check explicitly in the solution.
Ignoring the difference between service and factored load combinations when checking deflection or soil bearing, and mixing the two in a single calculation.
Both checks appear in the same problem set and candidates reuse whichever load numbers they already computed, without tracking which combination produced them.
What to do instead
Label every load case at the top of the page (D, L, S, W, E) and build the required combinations explicitly. Use service combinations for deflection and bearing, factored combinations for strength, and never carry a factored number into a serviceability check.
Reporting a pipe or channel hydraulic radius using the full cross-section area and wetted perimeter, instead of the actual wetted perimeter for the flow depth.
Candidates confuse hydraulic radius with geometric radius and forget that wetted perimeter excludes the free surface; partially full pipes are especially prone to this error.
What to do instead
Sketch the flow cross-section, shade the wetted boundary only, and compute R = A/P from that sketch. For partially full circular pipes, use the central-angle formulas for area and wetted perimeter rather than interpolating from a table.
Choosing a Rational Method runoff coefficient from memory for a mixed land use without area-weighting the composite coefficient.
The coefficient table is memorized for single surface types, and candidates apply the value for the dominant surface to the whole catchment because weighting feels like an unnecessary extra step.
What to do instead
Break the catchment into subareas, assign a coefficient to each, compute the area-weighted composite C, and use that value in Q = CiA. Also verify that the time of concentration used matches the storm duration for the intensity.
Computing a horizontal curve or vertical curve using the wrong degree of curvature definition (arc versus chord) or mixing stationing with plain distances.
Both definitions appear in reference material and the difference only matters at large curvature; candidates also lose track of station arithmetic (100-ft or 1-km stations) when adding tangent lengths.
What to do instead
State which curvature definition the problem uses before computing, convert explicitly if needed, and carry all chainages in station notation with a check that the station of the curve midpoint equals the station of the point of intersection minus the external distance relationship you derived.
Treating a retaining wall or slope stability problem as a single-factor-of-safety calculation while ignoring the pore water pressure and the correct earth-pressure coefficient for the wall movement direction.
Candidates apply the active coefficient everywhere because it is the one most practiced, and they substitute total unit weight for effective unit weight below the water table.
What to do instead
Decide whether the wall can move enough to mobilize active pressure, use effective stresses and the effective friction angle below the water table, add the water pressure as a separate triangular load, and check overturning, sliding, and bearing each with its own required factor of safety.
Presenting a final numeric answer without units, sign convention, or a stated assumption for indeterminate structures, so a correct method earns no credit.
Candidates focus on getting the number and treat units and sign conventions as cosmetic, and they resolve indeterminacy by intuition rather than by stating a compatibility or stiffness assumption.
What to do instead
Adopt a fixed answer format: state assumptions, sketch the free-body diagram with a sign convention, show the compatibility or equilibrium equations, then give the result with units and direction. Reserve the last two minutes to verify units and that the answer's magnitude is physically plausible.