Impact of Moisture on the Cyclic Performance of a Two-Story Post-Tensioned CLT Rocking Wall with External Hysteretic Energy Dissipators


Abstract:

The development of engineered wood-based products such as Cross Laminated Timber (CLT) is creatingnew opportunities towards the development of versatile and resilient structural designs. While timber buildings have always showed great performance under seismic events, mass timber structures developed using CLT structural systems have come to fill a need for sustainable building construction, especially for mid-to-high rise structures.


Project Duration: 2017-2018

Research Team: Andre Barbosa, Arijit Sinha

Facilities: Oregon State Universty, College of Engineering, College of Forestry

  

Introduction:

CLT panels can carry loads in both directions either horizontally or vertically as free-standing components. In CLT buildings, the dissipated energy and ductility capacity of the system are provided by the connections and their detailing. Traditional CLT connection solutions (i.e. hold-downs and angle brackets) designed in Europe follow conventional prescriptive life-safety design methodologies (Cecotti et al. 2013, Pei et al. 2014). When subjected to major earthquake events, the observed modes of failure typically considered include yielding, buckling, or fracture of structural components, which results in buildings that sustain large lateral residual drifts following the extreme design event, with no possibility for people to shelter-in-place, need for post-earthquake demolition of the whole buildings, and in general nefarious economic effects.


Research details: 

Research consisted of five tasks. 

Task 1: Literature Review of CLT Hybrid Rocking Wall System Design. The most recent literature on the topic including the design of Peavy Hall and of the proposed shake-table test developed this year at UC San Diego, which also uses a hybrid rocking system, is reviewed and summarized

Task 2: Experimental Testing Prior to Moisture Exposure.

Task 3: Panel Exposure to Moisture. The CLT panel was exposed to moisture by soaking the end of the panel for 6 weeks in one to two feet of water to simulate water intrusion at the wall-to-foundation connection. The panel was periodically weighed to determine gross weight changes representative of moisture uptake/loss and then moisture meter pins were placed at strategic locations in each component to assess changes in moisture distribution over time. This approach had limitations because moisture distribution was unlikely to be even and moisture meters have limited ranges of sensitivity, so other IR methods were also tested as part of this research.

Task 4: Experimental Testing After Moisture Exposure. The work developed in Task 2 was repeated, but now for the panel after it has been exposed to moisture.

Task 5: Final Report and MS Thesis. The final report for this work will coincide with a Masters project developed by an MS student.


Results:

This project will develop new knowledge on moisture related durability that will inform engineers, architects and specifiers on the service life of the structure. The results will lead to development of engineering guidelines to improve material adoption in the mainstream construction marketplace. In addition, the work will lead to an MS thesis and a journal publication on the topic.