Fatigue life comparison — welded versus riveted steel structures In general, the ratio (fatigue life of a welded steel structure) / (fatigue life of a riveted steel structure) is:

Introduction / Context:
Fatigue performance in steel structures is governed by stress ranges and detail categories. Welded details often introduce higher stress concentrations and potential defects (undercuts, lack of fusion), which lower endurance limits compared to mechanically fastened (riveted/bolted) details.

Given Data / Assumptions:

• Comparison on similar geometry and loading, differing mainly by connection type.
• Welds considered are standard structural welds (fillet/butt) with typical workmanship quality.
• Riveted joints provide alternate load paths and lower notch severity at the net section.

Concept / Approach:
Fatigue life N typically follows S–N curves. Welded details are assigned lower detail categories (higher notch sensitivity), so for the same stress range, N_welded < N_riveted. Therefore, the ratio N_welded / N_riveted is generally < 1, unless special fatigue-rated welds or post-weld treatments are applied.

Step-by-Step Solution:
1) Identify controlling phenomenon: crack initiation and growth from stress raisers.2) Recognize welded joints have sharper notches and residual stresses.3) Conclude lower fatigue category → shorter life → ratio < 1.4) Select “smaller than 1”.

Verification / Alternative check:
Design codes assign lower allowable stress ranges for welded categories compared to comparable riveted/bolted details, confirming the trend.

Why Other Options Are Wrong:
=1 or >1 imply equal or better life for welded structures, contrary to typical S–N classifications; “> 2.1” is arbitrary and unjustified.

Common Pitfalls:
Ignoring improvement methods like peening/TIG dressing; assuming weld quality is perfect; neglecting residual stresses from welding.

Final Answer:
smaller than 1