Seismic performance of innovative straw bale wall systems

  • Principal Investigator: Darcey Donovan, P.E., PAKSBAB CEO
  • Research Associates: Shannon Whitnack, Surkhab Khan, Bill Donovan
  • Sponsored By: Earthquake Engineering Research Institute, NSF-NEES Shared-Use Access through Grant CMMI-0402490

Project summary

On October 8, 2005, the northern mountainous region of Pakistan was struck by a magnitude Mw = 7.6 earthquake which killed an estimated 100,000 people, destroyed over 780,000 buildings and rendered more than 3.5 million homeless due to poor building construction.

Structurally safe building methods are largely unaffordable for the poor in developing countries such as Pakistan.

In response, Pakistan Straw Bale and Appropriate Building, or PAKSBAB, is developing simple, unique, earthquake-resistant straw bale building methods that are affordable, energy efficient, and utilize local labor and indigenous renewable materials.

The objective of this research project was to determine the capacity of clay plastered, load bearing, straw bale wall assemblies under in-plane cyclic loading, and the performance of a small full-scale straw bale house using shake table simulation.

The system was unique in that the site-fabricated bales were not as wide as those used in a typical straw bale building, and the fishing net reinforcement and gravel bag foundation were non-conventional. Designated as a shared-use project, the experimental work was conducted using the NEES facilities at the University of Nevada, Reno (NEES@UNR). EERI's Special Projects and Initiatives Committee provided a research grant from its Endowment Fund for the specimen building materials and other related expenses.

The overall research plan consists of 4 parts:

  1. Component field tests and material tests (December 2009)
  2. Wall assembly tests of varying configurations (June 2008)
  3. Bi-axial shake table tests of a 14' x 14' x 10' full-scale house (March 2009)
  4. Report of findings and seismic design and construction recommendations (January 2010)

The house construction method was a load bearing design consisting of site fabricated straw bales resting on a soil cement encased gravel bag foundation. Exterior opposing bamboo pins were used to keep the walls plumb during construction and to provide out-of-plane support. Fishing net was installed under the gravel bags, stretched up both sides of the walls and nailed to the top plates. The roof consisted of wooden I-joists insulated with light straw clay (straw tossed in a mixture of clay and water) and covered with corrugated metal roofing. Gravel bags were placed at the top of walls to simulate a light snow load. The walls were finished with clay plasters and lime wash.

The objective of the shake table tests was to assess the seismic response of a 14' x 14' x 10' full-scale house constructed with heavy detailing. The input motion was the Canoga Park Topanga Canyon record of the 1994 Northridge, California earthquake, Mw 6.7. The house was subjected to eight levels of seismic shaking, beginning at 25% of the recorded ground acceleration and increasing at 25% increments. The house survived 0.82g, twice the acceleration of the Canoga Park record. Although severely damaged, the building did not appear in danger of collapse, even at the end of the test sequence.

Advisory committee

  • Mark Aschheim, Ph.D., Santa Clara University Associate Professor of Civil Engineering
  • Ian Buckle, Ph.D., University of Nevada, Reno Professor of Civil Engineering, University of Nevada, Reno NEES Project Director
  • Craig Comartin, S.E., EERI Board of Directors and past President, Project Liaison
  • Darcey Donovan, P.E., PAKSBAB C.E.O., Principal Investigator / Committee Chair
  • Martin Hammer, Architect
  • David Mar, S.E., Tipping Mar & Associates, Principal
  • Dan Smith, Daniel Smith & Associates Architects, Principal
  • Mark Smith, G.E., S.E., Vector Engineering, Inc., Managing Director