Difficulty: Easy
Correct Answer: 145
Explanation:
Introduction / Context:
The slenderness ratio of lacing bars influences their ability to carry the diagonal shear and restrain the main components against buckling. Excess slenderness leads to premature local buckling and ineffective bracing.
Given Data / Assumptions:
Concept / Approach:
A well-known limit adopted in many summaries is 145 for lacing bar slenderness. This balances fabrication practicality and the need to keep lacing elements stocky enough to resist diagonal forces and secondary bending during handling and service.
Step-by-Step Solution:
Step 1: Compute effective length of the lacing bar (per connection type/pattern).Step 2: Calculate its slenderness ratio λ = l_eff / r_min.Step 3: Check λ ≤ 145. If λ exceeds 145, increase thickness/width or reduce panel length.
Verification / Alternative check:
Design question banks and handbooks consistently cite the 145 limit for lacing elements, aligning with classic steelwork practice.
Why Other Options Are Wrong:
80 and 120: Too restrictive relative to the commonly accepted limit, leading to unnecessarily heavy lacing.200 and 250: Too slender; risk instability and poor bracing action.
Common Pitfalls:
Final Answer:
145
Discussion & Comments