Figure 20: Flowchart <strong>of</strong> <strong>the</strong> actions to be undertaken <strong>for</strong> <strong>the</strong> diagnosis <strong>of</strong> <strong>the</strong> building (38)These sources <strong>of</strong> in<strong>for</strong>mation will confirm (or not) <strong>the</strong> interpretative model (scenario) that hasbeen advanced. In <strong>the</strong> last case, an alternate scenario will be established and, eventually,confirmed.If <strong>the</strong> situation does not become completely clear, <strong>the</strong> best solution will be to keep <strong>the</strong>building under observation (monitoring) <strong>for</strong> a certain period <strong>of</strong> time, which will allow <strong>for</strong> <strong>the</strong>evolution <strong>of</strong> <strong>the</strong> phenomena and, subsequently, <strong>for</strong> a better understanding <strong>of</strong> what is, in fact,happening to <strong>the</strong> building.25/48
4 STRUCTURAL ASSESSMENT OF THE BUILDING4.1 IntroductionThe structural assessment <strong>of</strong> heritage buildings is <strong>the</strong> evaluation <strong>of</strong> <strong>the</strong> collected data relatedto <strong>the</strong> safety <strong>of</strong> <strong>the</strong> building, with <strong>the</strong> objective <strong>of</strong> deciding whe<strong>the</strong>r its structural safety issufficient, or not. It is an essential phase <strong>of</strong> an intervention <strong>of</strong> rehabilitation, because it iswhen it is decided if measures are necessary and to what extent.The structural assessment <strong>of</strong> <strong>the</strong> building is usually based on <strong>the</strong> modelling <strong>of</strong> its structuralbehaviour, in which, as <strong>for</strong> new buildings, through certain hypo<strong>the</strong>ses, <strong>the</strong> effects <strong>of</strong> <strong>the</strong>actions on <strong>the</strong> building are determined and combined, being <strong>the</strong> results compared with <strong>the</strong>strength <strong>of</strong> <strong>the</strong> building (or in strategic points <strong>of</strong> <strong>the</strong> building).However, due to <strong>the</strong> specifics <strong>of</strong> heritage buildings <strong>the</strong>re are substantial differences in <strong>the</strong>procedures to be used on both <strong>the</strong> structural modelling and on <strong>the</strong> safety verification, incomparison with new buildings.Concerning <strong>the</strong> modelling <strong>of</strong> <strong>the</strong> building, it is to be noted that, owing to <strong>the</strong> simplificationsthat are, in general, necessarily adopted, and to <strong>the</strong> possible lack <strong>of</strong> knowledge about <strong>the</strong>events to which <strong>the</strong> building has been subjected in <strong>the</strong> past, <strong>the</strong> results obtained are, ingeneral, less reliable than would be <strong>the</strong> case <strong>for</strong> <strong>the</strong> design <strong>of</strong> new buildings.Concerning <strong>the</strong> safety verification, specific issues also arise. In modern codes, <strong>the</strong>uncertainties, both on <strong>the</strong> side <strong>of</strong> <strong>the</strong> strength <strong>of</strong> materials and on <strong>the</strong> side <strong>of</strong> <strong>the</strong> actions, aretaken into account through <strong>the</strong> application <strong>of</strong> successive safety coefficients, which lead inpractice, to a high safety level on <strong>the</strong> buildings.This approach is, generally, well accepted by society, because <strong>the</strong> increase in safety doesnot result in a significant increase <strong>of</strong> cost. In <strong>the</strong> case <strong>of</strong> heritage buildings this approachwould be inappropriate, because it could require very intrusive and costly rehabilitationworks, which, sometimes, are not justified. Fur<strong>the</strong>rmore, as <strong>the</strong> properties <strong>of</strong> <strong>the</strong> buildingmaterials naturally decrease with time, safety levels lower than those in new buildings wouldbe acceptable <strong>for</strong> existing buildings.It is also to be noted that <strong>the</strong> safety coefficients prescribed in <strong>the</strong> design <strong>of</strong> new buildingstake into account uncertainties related to <strong>the</strong> building process, which, in <strong>the</strong> case <strong>of</strong> existingbuildings do not exist, because <strong>the</strong>ir behaviour can be observed. The possible reduction <strong>of</strong><strong>the</strong>se coefficients does not mean, necessarily, that <strong>the</strong> safety <strong>of</strong> <strong>the</strong> building is notacceptable.4.2 Safety level <strong>of</strong> <strong>the</strong> buildingIn establishing <strong>the</strong> required safety level <strong>of</strong> heritage buildings, a holistic and flexible approachshould be adopted, in a way that, to guarantee <strong>the</strong>ir safety, <strong>the</strong> streng<strong>the</strong>ning measures to becarried out will be reduced as much as possible, and <strong>the</strong> loss <strong>of</strong> <strong>the</strong> cultural value <strong>of</strong> <strong>the</strong>building will be minimized.Thus, in heritage buildings, safety levels lower than those prescribed <strong>for</strong> new buildings will beacceptable, since it will be possible to take measures in order to reduce <strong>the</strong> risk associated withdiminishing <strong>the</strong> safety level, <strong>for</strong> example, by adopting restrictions on <strong>the</strong> use <strong>of</strong> <strong>the</strong> building.26/48
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