In-plane assessment of existing timber diaphragms in URM buildings via quasi-static and dynamic in-situ tests

From comparison between the experimental resultsand the relevant standards and guidelines on seismicassessment of existing vintage timber diaphragms,it appears that NZSEE suggests Gd values for singlestraight sheathed diaphragm that are very close tothose registered experimentally, while FEMA andASCE tend to overestimate the diaphragm stiffness.8The reason might be related to the fact that all thetests were performed in the direction orthogonalto the joists. The orthotropic behaviour of singlestraight sheathed diaphragms, in fact, is an aspectcontemplated only by NZSEE which also considersthe flooring condition. Once the plywood layer isapplied, the diaphragm response is governed bythe plywood itself (significantly stiffer than theoriginal flooring) whose behaviour is not affectedby the loading direction, due to the particular paneldisposition adopted. Consequently, the stiffness valueprovided in FEMA and ASCE is similar to that registeredexperimentally.The “re-nailing” method proved to be a validstrengthening solution. In fact, with a very lowcost-effectiveness ratio, it permitted an increasein stiffness of up to 30 %, which ensured that thetested floor section had the capacity to transfer shearloads corresponding to severe seismic events withinacceptable drift levels. An extremely stiff responsewas achieved through the instalment of a plywoodpanel overlay directly onto the existing floorboards.Such behaviour was maximised by the peculiar paneldisposition which also allowed a very fast installationprocedure.Considering the material property variability(e.g. conservation status, wood species, elementdimensions), further testing need to be performedto make the outcomes of the campaign presentedherein more representative. The test setup designedfor this experimental campaign was shown to be non-invasive, easy to install and versatile (adaptable todifferent-sized specimens). Hence, additional testingwill be performed if an opportunity presents itself.A thorough processing of the snap back tests has beenundertaken and the results will be published by theauthors in the near future.