Structural Engineering Exam (SE) Lateral Forces — Buildings Depth Flashcards

24 sample cards from the Lateral Forces — Buildings Depth deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What is the demand-critical weld concept in AISC 341 seismic connections?

   Demand-critical welds are those whose failure would lead to brittle, non-ductile behavior or significant strength degradation (e.g., complete-joint-penetration groove welds of beam flanges to columns). They require enhanced toughness (e.g., minimum Charpy V-notch values) and special filler metals.

2. How is the unit shear capacity of a wood structural panel shear wall determined, and what factor adjusts for unblocked panels?

   From SDPWS nominal unit shear capacity tables based on panel thickness, nail size/spacing, and framing; divided by safety/resistance factors. Unblocked diaphragms/walls use reduction factors (e.g., the $C_{ub}$ adjustment), since blocking edges increases capacity.

3. What is the aspect ratio limit for wood structural panel shear walls (SDPWS), and how is reduced capacity handled?

   Maximum height-to-width $h/b_s$ is generally $3.5{:}1$ for blocked wood structural panel shear walls (resisting seismic). For $h/b_s$ between $2{:}1$ and $3.5{:}1$, capacity is reduced by the factor $\dfrac{2b_s}{h}$.

4. For a wood shear wall, how is the chord (boundary post) tension/compression and hold-down force computed?

   By overturning: $T = C = \dfrac{V \cdot h}{b}$ (lateral shear times wall height divided by wall length), reduced by resisting dead load for the tension chord. The hold-down (tie-down) anchor must resist the net uplift $T$.

5. What deflection components make up the total deflection of a blocked wood structural panel shear wall (SDPWS 4-term equation)?

   $\delta = \dfrac{8 v h^3}{E A b} + \dfrac{v h}{1000\,G_a} + \dfrac{h}{b}\,d_a$ — bending (chord) deformation, panel shear/nail slip combined term, and hold-down/anchorage slip. ($v$=unit shear, $G_a$=apparent shear stiffness, $d_a$=anchorage slip.)

6. Define a drag strut (collector) in a light-frame building and the load it carries.

   A horizontal framing member (e.g., top plate, rim board, or added member) that collects diaphragm shear and 'drags' it into a shear wall that is shorter than the diaphragm. It carries the accumulated axial collector force = (diaphragm unit shear) × (length of diaphragm not aligned with the wall).

7. Why is continuous, spliced top-plate or a separate collector required across openings in light-frame walls?

   To maintain a continuous load path for collector/chord forces. At openings the diaphragm boundary and collector forces must be transferred around the opening; top plate splices must be designed to transmit the chord/collector axial tension and compression across the discontinuity.

8. Explain 'load path continuity' for lateral forces in a light-frame building from roof to foundation.

   Inertial forces flow: diaphragm → collectors/chords → shear walls (sheathing + nails) → wall hold-downs and sole-plate shear anchors → foundation. Every connection (blocking, straps, hold-downs, anchor bolts) must be sized so the path is unbroken from where mass originates to the ground.

9. What are the two distinct anchorage demands at the base of a light-frame shear wall?

   (1) Shear transfer—sole/sill plate anchor bolts (or shear clips) resisting the in-plane unit shear, and (2) Overturning uplift—hold-downs/tie-downs resisting the boundary tension $T = Vh/b$. These are separate connections and must both be provided.

10. In Cold-Formed Steel (CFS) lateral systems, what are the common seismic-force-resisting wall types?

    CFS shear walls sheathed with wood structural panels or steel sheet, and CFS strap-braced (X-braced) walls. AISI S400 governs their seismic design; strap-braced walls use diagonal flat straps as the tension yielding fuse.

11. For CFS strap-braced walls, what is the designated energy-dissipating (yielding) element and how are other members protected?

    The diagonal flat strap (in tension) is the yielding fuse. Chord studs, anchorage, and connections are capacity-designed for the expected yield strength of the strap, $R_y F_y A_g$, so yielding concentrates in the strap and connections remain elastic.

12. What governs the design of masonry shear walls for in-plane loading—what are the two principal limit states?

    Flexural (overturning) strength governed by axial-flexural interaction, and in-plane shear strength. The wall must have adequate flexural capacity for combined $P$ and $M$ and shear capacity $V_n$ exceeding the demand, with shear capacity-designed to exceed shear corresponding to flexural yielding in special walls.

13. Give the form of nominal masonry shear strength $V_n$ per TMS 402.

    $V_n = V_{nm} + V_{ns}$, where $V_{nm}$ is the masonry contribution (a function of $\sqrt{f'_m}$, $M/(V d_v)$, and axial load $P$) and $V_{ns} = 0.5\left(\dfrac{A_v}{s}\right)f_y d_v$ is the steel (shear reinforcement) contribution, capped by an upper limit on $V_n$.

14. What are the key prescriptive reinforcement requirements that distinguish a Special Reinforced Masonry Shear Wall (TMS 402)?

    Minimum total vertical + horizontal reinforcement ratio of $0.002$, with minimum in each direction of $0.0007$; maximum spacing of reinforcement the smaller of $\tfrac{1}{3}$ wall length, $\tfrac{1}{3}$ height, or $1.2\,\text{m}$ (48 in.); plus shear capacity design and shear-friction provisions.

15. Rank the seismic detailing/ductility hierarchy of reinforced masonry shear walls from least to most ductile.

    Ordinary plain → Detailed plain → Ordinary reinforced → Intermediate reinforced → Special reinforced masonry shear walls. Special reinforced walls have the highest $R$ and are the only masonry shear walls permitted in high SDC (D, E, F).

16. For a Special Reinforced Masonry Shear Wall, how must the design shear be related to flexural capacity (shear capacity design)?

    The wall must be designed so nominal shear strength exceeds the shear corresponding to development of $1.25$ times the nominal flexural strength (with consideration of $M/(Vd_v)$ not exceeding 1.0 for the $V_n$ calc), ensuring ductile flexural yielding precedes brittle shear failure.

17. What is out-of-plane seismic wall behavior and how is the demand characterized?

    Walls spanning vertically between diaphragms experience out-of-plane inertial forces from their own mass perpendicular to the wall plane. The wall acts as a vertical strip/beam in flexure; demand is $F_p = $ a fraction of wall weight (component force), producing bending that the wall section and reinforcement must resist.

18. How is the out-of-plane design force on a structural wall (as a component) computed per ASCE 7?

    $F_p = 0.4 S_{DS} I_e W_p$ as a minimum self-weight force (not less than $0.1 W_p$), and for wall anchorage to flexible diaphragms a larger force governs; walls are designed for out-of-plane bending under this distributed inertial load.

19. For slender masonry/concrete walls loaded out-of-plane, what second-order effect must be included, and via what method?

    The P-delta effect from axial load acting through the lateral deflection. TMS 402 and ACI use a moment-magnification or iterative deflection approach: the design moment includes $P\,\delta_u$, and service-level deflection $\delta_s$ is checked against $0.007 h$ (vertical strip / slender wall provisions).

20. Why is wall-to-diaphragm anchorage for out-of-plane forces a critical (and historically problematic) detail in concrete/masonry buildings with flexible diaphragms?

    Inadequate anchorage caused wall-diaphragm separation and collapse in past earthquakes (e.g., 1971 San Fernando, 1994 Northridge tilt-ups). The anchorage must transfer large out-of-plane inertial forces directly into the diaphragm; cross-grain bending of wood ledgers and toe-nailing are prohibited for this load.

21. What is the ASCE 7 design force for anchorage of structural (concrete/masonry) walls to supporting flexible diaphragms?

    $F_p = 0.4 S_{DS} k_a I_e W_p$, with $F_p$ not less than $0.2 k_a I_e W_p$, where $k_a = 1.0 + \dfrac{L_f}{100} \leq 2.0$ accounts for diaphragm flexibility ($L_f$ = diaphragm span in ft). Anchors must be spaced to limit wall bending between anchors.

22. What three prohibited/limited mechanisms must wall anchorage avoid in wood and steel-deck diaphragms?

    (1) Cross-grain bending or cross-grain tension in wood ledgers, (2) reliance on toe-nails or nails in withdrawal, and (3) for steel deck, using the deck alone for anchorage. Anchorage must use direct positive connections (straps, hold-downs, sub-diaphragms with continuous ties) into the diaphragm framing.

23. What is a sub-diaphragm and continuous tie system in wall anchorage design?

    A sub-diaphragm is a smaller portion of the main diaphragm with its own chords that transfers local wall anchorage forces into continuous cross-ties. Continuous cross-ties span the full diaphragm depth to carry out-of-plane wall forces across the building, providing a complete, continuous load path between parallel walls.

24. Compare the energy-dissipation mechanisms of SCBF, EBF, and BRBF braced frames.

    SCBF: brace tension yielding and inelastic compression buckling (pinched, degrading hysteresis). EBF: shear/flexural yielding of a ductile link beam (stable, braces elastic). BRBF: balanced tension and compression yielding of a buckling-restrained core (full, symmetric, stable hysteresis—highest energy dissipation per cycle).

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