Soft story buildings are one of the most dangerous structural conditions in seismic design, and the 1994 Northridge earthquake proved why.

In this episode, we break down the seismic irregularities that cause buildings to fail during earthquakes. You will learn the difference between a soft story and a weak story, how geometric and mass irregularities create dangerous force concentrations, and why a broken load path is the most dangerous irregularity of all.

We also cover re-entrant corners, torsional irregularity, rigid vs flexible diaphragms, and how collectors and drag struts keep the lateral load path connected.

Then we walk through the exam strategy: red flags to watch for, common fixes including moment frames, braced frames, and seismic joints, and the one principle NCARB keeps coming back to. Eliminate the irregularity entirely rather than engineering around it.

📝 Key topics covered:

Soft story buildings and the 1994 Northridge earthquake
Soft story vs weak story: bending vs breaking
Building drift and the 70% stiffness threshold
Vertical geometric irregularity and building setbacks
Mass irregularity and heavy mechanical floors
Continuous load path: roof to diaphragm to shear walls to foundation
In-plane discontinuity vs out-of-plane offset
Collectors and drag struts
Rigid vs flexible diaphragms
Re-entrant corners in L-shaped and T-shaped buildings
Torsional irregularity: center of mass vs center of rigidity
Moment frames vs braced frames
ARE exam red flags for seismic irregularities

⏱️ Chapters:

0:00) Soft Story Buildings and Northridge

(1:40) Study Notes

(3:26) Soft Story vs Weak Story

(6:36) Geometric and Mass Irregularities

(8:54) Load Path and Shear Wall Discontinuities

(13:17) Re-Entrant Corners and Torsion

(15:50) Seismic Irregularities on the ARE

(18:32) Seismic Design Key Takeaways

📖 Read the full blog post and grab free study notes: Soft Story Building: Seismic Irregularities Explained

📝 Free study notes for this episode: youngarchitect.com/seismic

🎯 ARE 101 Membership (access all courses)

🎯 ARE Boot Camp (10-week coaching program)

📚 Individual ARE Exam Courses: