Preliminary Assessment of the Seismic Reduction Factor (R) in Adobe Walls

Earth-based construction materials, such as adobe and rammed earth, are widely utilized, housing approximately 21–22% of the global population [1]. Countries like Peru, Morocco, India, Mexico, and Colombia have established design codes to regulate their use. However, due to their brittle nature, seismic design often relies on allowable stress methods, deviating from performance-based approaches like the Peruvian seismic-resistant design code N.T.E. E.030. Recent research advocates a performance-based design approach for adobe walls, supported by cyclic testing data. These tests reveal limited ductility and overstrength, crucial parameters for determining a seismic reduction factor (R). This factor, a function of ductility (R_u) and overstrength (R_o), can be estimated through equivalent energy-based methods and elastic demand spectra. This study analyzes existing coplanar cyclic test data on adobe walls to calculate these parameters using the elastic demand spectra method proposed by the Structural Engineers Association of California. Preliminary findings suggest a reduction factor of 1.5 may be suitable for new earth-based structures designed with a specific performance mode.