Structural Engineering Flashcards

Which method is used to analyze indeterminate structures by assuming member end moments as unknowns and satisfying joint equilibrium?

Answer: Moment distribution method

The moment distribution method (Hardy Cross method) iteratively distributes unbalanced moments at joints until equilibrium is achieved at every joint.

For a rectangular reinforced concrete section under pure bending, the depth of the equivalent rectangular stress block 'a' is related to the neutral axis depth 'c' by:

Answer: a = β₁ × c

ACI 318 uses a rectangular stress block approximation where the block depth a = β₁c, with β₁ typically 0.85 for f'c ≤ 28 MPa.

In a two-hinged arch under a uniformly distributed load, the horizontal thrust H at the supports depends primarily on:

Answer: The span length, rise, and load magnitude

The horizontal thrust in a two-hinged arch is a function of the applied load, span, and rise; larger span or lower rise increases the thrust for the same load.

Which of the following best describes 'lateral-torsional buckling' in steel beams?

Answer: Out-of-plane deflection combined with twisting of the compression flange

Lateral-torsional buckling involves the beam deflecting laterally out of its original plane while simultaneously twisting, typically occurring in the compression flange region.

The modular ratio (n) in reinforced concrete design is defined as:

Answer: Ratio of modulus of elasticity of steel to that of concrete (Es/Ec)

The modular ratio n = Es/Ec allows transformed-section analysis by converting steel area into an equivalent concrete area for elastic stress calculations.

A continuous beam has more load-carrying capacity than a simply supported beam of the same span and cross-section primarily because:

Answer: Continuity redistributes moments, reducing the maximum positive moment

In continuous beams, negative moments develop at interior supports, which reduces the positive midspan moment compared to a simply supported beam, allowing smaller cross-sections or higher loads.

According to Saudi Building Code (SBC 301) seismic provisions, the seismic design category (SDC) of a structure is determined by:

Answer: The site seismic hazard level and the occupancy/risk category of the structure

The Seismic Design Category combines the spectral response accelerations (seismic hazard) with the Risk Category of the occupancy to establish design requirements.