Guide for the Structural Rehabilitation of Heritage ... - Test Input

4 STRUCTURAL ASSESSMENT OF THE BUILDING4.1 IntroductionThe structural assessment of heritage buildings is the evaluation of the collected data relatedto the safety of the building, with the objective of deciding whether its structural safety issufficient, or not. It is an essential phase of an intervention of rehabilitation, because it iswhen it is decided if measures are necessary and to what extent.The structural assessment of the building is usually based on the modelling of its structuralbehaviour, in which, as for new buildings, through certain hypotheses, the effects of theactions on the building are determined and combined, being the results compared with thestrength of the building (or in strategic points of the building).However, due to the specifics of heritage buildings there are substantial differences in theprocedures to be used on both the structural modelling and on the safety verification, incomparison with new buildings.Concerning the modelling of the building, it is to be noted that, owing to the simplificationsthat are, in general, necessarily adopted, and to the possible lack of knowledge about theevents to which the building has been subjected in the past, the results obtained are, ingeneral, less reliable than would be the case for the design of new buildings.Concerning the safety verification, specific issues also arise. In modern codes, theuncertainties, both on the side of the strength of materials and on the side of the actions, aretaken into account through the application of successive safety coefficients, which lead inpractice, to a high safety level on the buildings.This approach is, generally, well accepted by society, because the increase in safety doesnot result in a significant increase of cost. In the case of heritage buildings this approachwould be inappropriate, because it could require very intrusive and costly rehabilitationworks, which, sometimes, are not justified. Furthermore, as the properties of the buildingmaterials naturally decrease with time, safety levels lower than those in new buildings wouldbe acceptable for existing buildings.It is also to be noted that the safety coefficients prescribed in the design of new buildingstake into account uncertainties related to the building process, which, in the case of existingbuildings do not exist, because their behaviour can be observed. The possible reduction ofthese coefficients does not mean, necessarily, that the safety of the building is notacceptable.4.2 Safety level of the buildingIn establishing the required safety level of heritage buildings, a holistic and flexible approachshould be adopted, in a way that, to guarantee their safety, the strengthening measures to becarried out will be reduced as much as possible, and the loss of the cultural value of thebuilding will be minimized.Thus, in heritage buildings, safety levels lower than those prescribed for new buildings will beacceptable, since it will be possible to take measures in order to reduce the risk associated withdiminishing the safety level, for example, by adopting restrictions on the use of the building.26/48