AISC 358: Prequalified Moment Connections
Following the M6.7 Northridge Earthquake 20 years ago, an engineer performing a post-earthquake inspection of the Santa Clarita City Hall was struck in the head by a structural bolt as he removed a ceiling tile to observe the framing.
Upon scraping away fire proofing from the beam column connection above his head he found that a fracture had developed at the weld of the bottom beam flange to the column. Similar damage was observed in the Getty Museum, which was then under construction. As word of these discoveries spread, engineers began to look more carefully at steel moment frame buildings, which had initially appeared undamaged in the wake of the earthquake, and in many cases discovered similar fractures.
Modern STEEL Construction