NCARB Structural Systems 2 — Questions and Answers
Question 1: In a reinforced concrete beam, where is the primary tension steel typically located?
- At the bottom of the beam in a simply supported span (Correct answer)
- At the top of the beam throughout
- Evenly distributed across the cross-section
- In the web only
Correct answer: At the bottom of the beam in a simply supported span
In a simply supported beam, bending causes tension in the bottom fiber; steel reinforcing bars are placed there because concrete is weak in tension but strong in compression.
Question 2: What is the purpose of 'shear walls' in a building's lateral force resisting system?
- To resist lateral wind and seismic forces through in-plane shear action (Correct answer)
- To support gravity loads only
- To provide acoustic separation between spaces
- To act as fire-rated partitions only
Correct answer: To resist lateral wind and seismic forces through in-plane shear action
Shear walls resist horizontal forces by acting as vertical cantilevers, transferring lateral loads from the diaphragm down to the foundation through their in-plane stiffness.
Question 3: A post-tensioned concrete slab differs from conventionally reinforced concrete in what way?
- Steel tendons are stressed after concrete placement to place the slab in compression (Correct answer)
- The steel is placed in the top of the slab only
- No steel reinforcement is used
- The concrete is precast off-site
Correct answer: Steel tendons are stressed after concrete placement to place the slab in compression
In post-tensioning, high-strength steel tendons are stressed by jacking after the concrete cures, compressing the slab and counteracting tensile stresses from applied loads.
Question 4: What is a 'transfer beam' or 'transfer slab' in structural design?
- A heavy structural element that collects loads from columns above and redistributes them to a different column grid below (Correct answer)
- A beam at the base of a shear wall
- A foundation element spanning between piles
- A horizontal tie connecting shear walls
Correct answer: A heavy structural element that collects loads from columns above and redistributes them to a different column grid below
Transfer beams redirect column loads when the structural grid changes between floors—common in mixed-use buildings where parking columns don't align with upper floor columns.
Question 5: Which structural material has equal strength in both tension and compression?
- Steel (Correct answer)
- Concrete
- Unreinforced Masonry
- Timber
Correct answer: Steel
Steel's crystalline structure gives it roughly equal yield strength in tension and compression, making it uniquely efficient for members subject to alternating stresses like seismic loading.
Question 6: What is 'column buckling' and why is it a critical design concern?
- The sudden lateral bending failure of a slender column under compressive load before material strength is reached (Correct answer)
- Gradual compression failure of a short column
- Shear failure at the column base
- Tensile failure of the column steel
Correct answer: The sudden lateral bending failure of a slender column under compressive load before material strength is reached
Buckling is an instability failure where a slender column suddenly deflects laterally under compression, often at loads well below the material's crushing strength.
NCARB Structural Systems 2
In a reinforced concrete beam, where is the primary tension steel typically located?