Iran Nezam Civil Design Exam common mistakes
Iran Nezam Civil Design Exam · Understand the traps and how to avoid them.
Treating the 2800 Standard's base shear coefficient as the final answer and skipping the distribution of lateral force over the height of the structure, then sizing members from the total base shear alone.
Candidates memorize the C = AB I / R formula from undergraduate courses and stop there, forgetting that the story shear distribution and torsional eccentricity govern member demands.
What to do instead
After computing base shear, always build the full lateral load chain: story force distribution, story shears, diaphragm forces, accidental torsion, and then member demands. Practice one complete worked example per structural system type (moment frame, braced frame, shear wall) until the sequence is automatic.
Using the simplified equivalent frame method for two-way slabs in cases where the code requires a more refined analysis, or applying direct design method outside its validity limits (fewer than three spans, unequal span ratios, live-to-dead load ratio too high).
The direct design method is the only slab method many candidates have practiced, so they force every slab problem into it rather than checking applicability conditions first.
What to do instead
Before any slab calculation, write down the three applicability checks (number of spans, span ratio, load ratio) and state explicitly which method is permitted. Drill a set of slab problems where the answer is 'direct design method not permitted' so the check becomes reflexive.
Designing steel compression members using only the gross section area and yield stress, ignoring buckling length selection and the slenderness-dependent reduction factor.
Candidates carry over the concrete habit of capacity = area times stress, and underestimate how much effective length (K-factors, unbraced length about both axes) changes the answer.
What to do instead
For every compression member, first identify the unbraced lengths about both axes and the end conditions, compute KL/r for each, take the governing one, then apply the buckling curve. Always check the slenderness limit as a separate pass/fail item.
Computing bearing capacity with the general equation but using the wrong groundwater condition, or ignoring the difference between short-term (undrained) and long-term (drained) parameters.
Candidates plug numbers into one familiar formula without deciding whether the governing case is undrained for the construction stage or drained for the service stage, and they mis-place the water table in the surcharge term.
What to do instead
For each foundation problem, explicitly state the design scenario (short-term vs long-term), the drainage condition, and the water table elevation before selecting parameters. Compute both scenarios when in doubt and design for the governing one.
Mixing service-level and factored load combinations, or applying the wrong load combination set to the wrong limit state, resulting in demands that are neither consistent nor code-compliant.
Candidates learn combinations as a list to memorize rather than as a mapping from limit state to combination set, so they grab whichever combination they recall first.
What to do instead
Build a one-page matrix: limit state (strength, serviceability, stability, seismic) versus the applicable combination set. Before computing, write the limit state at the top of the page, then select from the matrix. Do timed drills where the first scored step is choosing the correct combination.
Ignoring second-order (P-delta) effects and drift limits because the first-order analysis already produces acceptable member forces.
First-order hand analysis is what candidates are comfortable with, and stability coefficients are treated as an optional refinement rather than a required check.
What to do instead
Add a mandatory stability check to every frame problem: compute the stability coefficient or the elastic critical load ratio, compare against the code threshold, and state whether second-order analysis is required. Also check inter-story drift against the code limit as a separate line item.
Designing a concrete mix or specifying cement content by habit rather than from the exposure class, minimum cementitious content, maximum water-to-cement ratio, and required cover for the specified environmental condition.
Durability provisions are scattered across the code and are easy to skip when the candidate focuses only on strength, so the mix is proportioned for strength alone.
What to do instead
For every mix or member specification, work from the exposure class outward: exposure class, then maximum w/c, then minimum cement content, then minimum cover, then strength. Treat durability as the starting constraint and strength as the check.
Producing a construction schedule or critical path without verifying the logic links, so the calculated float and critical path are wrong even though the arithmetic looks correct.
Candidates focus on the forward and backward pass arithmetic and skip the logic review, so dangling activities, missing predecessors, or loops pass unnoticed.
What to do instead
Before any network calculation, perform a logic audit: every activity except the start has at least one predecessor, every activity except the finish has at least one successor, and there are no loops. Then compute the passes and verify that at least one path has zero total float.
Computing a closed traverse and distributing misclosure without first checking the angular misclosure against the allowable tolerance, or applying the compass rule to a survey that should be rejected.
Candidates want to finish the adjustment arithmetic and treat the tolerance check as a formality, so a blunder in the field data gets smoothed into a plausible-looking but wrong coordinate set.
What to do instead
Make the tolerance check a hard gate: compute angular misclosure, compare with the allowable based on the number of angles and instrument precision, and only then adjust. If it fails, stop and state that the survey must be repeated rather than adjusted.
Sizing sanitary and water supply pipes from a rule-of-thumb diameter instead of computing fixture units, demand flow, and then checking velocity and pressure limits along the critical path.
Plumbing design is often studied last and at low depth, so candidates substitute memorized diameters for the fixture-unit and hydraulic calculation chain.
What to do instead
Always run the full chain: fixture units, convert to probable demand, select diameter from the pipe capacity table, then check velocity and residual pressure at the most remote fixture. Practice the critical-path pressure check explicitly, since that is the step most often omitted.