Jennifer R. Bean Popehn1, Arturo E. Schultz2 and Jennifer E. Tanner3

  1. Engineer, OPUS Architects & Engineers, Minnetonka, MN 55343, USA,
  2. Professor, Dept. of Civil Engineering, Univ. of Minnesota, Minneapolis, MN 55455, USA,
  3. Prof., Dept. of Civil & Architectural Engineering, Univ. of Wyoming, Laramie, WY 82071, USA


The buckling strength and deformation capacity of an unreinforced masonry wall (URM) can be significantly affected by both initial imperfections and axial load eccentricity. To account for this decrease in strength, the 2008 TMS-402 (i.e., United States (US) masonry design provisions) Strength Design chapter includes a new provision for including second order effects through a moment magnifier. However, this method of treatment has limitations: initial imperfections are essentially not considered when the eccentricity is larger than 10% of the wall thickness. Additionally, when designing using Allowable Stress Design (ASD), the second order bending effects arising from axial load are ignored. To determine the accuracy of the ASD and SD provisions, the calculated moment magnifiers were compared to experimental data from seven slender URM wall tests conducted at the University of Minnesota. In the experimental study, three of the walls were constructed of cored clay brick, while the remaining four were fabricated using hollow concrete block. The simply-supported masonry wall tests began with a pre-selected axial load which was applied to the walls in force control using two vertical load actuators and held constant throughout the tests. After the axial load was applied to the walls, lateral load was applied with a whiffletree system operated in displacement control. The lateral displacement was increased until all lateral load capacity had diminished.

KEYWORDS: slenderness, imperfection, second order, axial load eccentricity, unreinforced masonry, buckling strength