Seismic performance factors for timber buildings with woodframe shear walls

Abstract

Seismic performance factors are an engineering tool to estimate force and displacement demands on structuresdesigned through linear methods of analysis. In Chile, the NCh433 standard provides the regulations, requirements,and factors for seismic design of several structural typologies and systems. However, when it comesto wood frame structures, previous research has found that the NCh433 provisions are highly restrictive andresult in over-conservative designs. Therefore, this paper presents an experimental and numerical investigationaimed at proposing new, less restrictive seismic performance factors for wood frame buildings. Following theFEMA P-695 guidelines and a novel ground motion set for subduction zones, this research embraced: (1) testingof several full-scale specimens, (2) developing of detailed and simplified numerical models, and (3) analyzing theseismic performance of a comprehensive set of structural archetypes. 201 buildings were analyzed and resultsshowed that changing the current NCh433 performance factors from R = 5.5 & ?max = 0.002 to R = 6.5 & ?max= 0.004 decreases the average collapse ratio of wood frame structures by 13.3% but keeps the collapse probabilitybelow 20% for all the archetypes under study. Besides, it improves the cost-effectiveness of the buildingsand enhances their competitiveness when compared to other materials, since savings of 40.4% in nailing, 15.9%in OSB panels, and 7.3% in timber studs were found for a 5-story building case study. Further analyses showedthat the buildings designed with the new factors reached the “enhanced performance objective” as defined by theASCE 41–17 standard, guaranteeing neglectable structural and non-structural damage under highly recurringseismic events. Finally, dynamic analyses revealed that the minimum base shear requirement Cmin of the NCh433standard is somewhat restrictive for soil classes A, B, and C, leading to conservative results compared to archetypeswhere the Cmin requirement did not control the structural design.