ブックタイトル「煉瓦造建造物の保存と修復」英語版

概要

「煉瓦造建造物の保存と修復」英語版

them to be structural bodies. Therefore, they tried toconvert these masonry structures into reinforced concretestructures.What emerges as a major problem is the approach tosafety. Safety is a concept that is affected by probabilityand is determined by parameters that are definedcomplementarily. These parameters are generally necessaryfor defining the return period of fifty years. When the life ofa building is assumed to be fifty years, the strength of theconnective elements can be decided on.However, this method is targeted against earthquakes ofa scale which in the lifetime of a historic building will occuronly a few times. These historic structures have enduredmultiple earthquakes in the past because they had beenreinforced every time there was an earthquake; works ofreinforcement on these buildings have been recorded.(slide 13) This is an example of severe damage seenin a building that was reinforced by a typical methodrecommended by the Italian Building Code (Code, hereafter)enforced after the Friuli Earthquake. Although the originaltimber floor structure was replaced with a reinforcedconcrete floor structure with higher rigidity, this largedamage could not be prevented. In fact, the heavy roofstructure worked conversely to increase damage broughtabout by the earthquake. Out-of-plane failure of the wallsfalling outwards was observed.(slide 14) There is another method of reinforced injectionusing steel rods.(slide 15) Also, there is the jacketing method in whichwalls are reinforced from the outside with concrete andmortar. Although these methods have been recommendedby the Code, some have been found to be defective.Codes and Their Application for Extant Structures(slide 16) We need to change our way of thinking andthe methods to take. I’d like to explain the approach beingtaken in the present codes. First of all, to make interventionson existing structures, we need to understand their actualmechanical properties and structural behaviors. It is importantfor engineers to use personal judgments in addition tocalculations and structural models. It is required by our Codeto increase safety as much as possible when we intervene inhistoric buildings, but not necessarily up to the same levelof safety that should be demonstrated for a new structureProf. Eng. Claudio ModenaProf. Eng. Claudio ModenaCriteria of interventionSM IngegneriaCriteria of interventionSM IngegneriaThe experience of the Umbria-Marche earthquake showed the effect of stiffening the horizontaldiaphragm by substituting original wooden floors with stiff reinforced concrete floors:traditional techniques, aimed only at reducing excessive deformability of the floors, are nowproposed.Jacketing:- scarce transversal connection- scarce efficacy in the corners- oxidation problems- high stiffnessSellano, 1997Sliding of the roof floor: the masonry is notadequately strengthenedExpulsion of the facade: the tie-beam is supportedonly by the internal leaf of a multi-leafs masonry:load eccentricity and reduction of the resisting areaSellano, 1997slide 13slide 15Prof. Eng. Claudio ModenaProf. Eng. Claudio ModenaCriteria of interventionSM IngegneriaCriteria of interventionSM IngegneriaReinforced injection: - highly invasive- scarce performances- adhesion problemsMontesanto (Sellano), 1997slide 14Besides being too invasive from the point of view of the conservation of historic valuesSuch intervention proved to be inefficient from the structural point of view------------------------------Carefully considering what has be learned from the past and ongoing experiences, new conceptsand tools are entering into codes and structural design practice:? the differentiation of safety level for different classes of existing structures;? assessment of mechanical properties of structures and materials with no real statisticalevaluations (estimation based on limited data);? global and local models to be used for structural analysis;? the evaluation of safety based on pure equilibrium considerations;? the use of qualitative evaluation of structural performances (observational approach: theexisting structures as a model of itself);? formalistic safety verifications: improvement vs retrofitting;? the limitation of interventions at the minimum possible level, depending on the level ofknowledge of the structure and on the use of appropriate investigations/monitoringtechniques;? the removability of the interventions and the compatibility of traditional/modern/innovativematerials and construction techniques.slide 1650Chapter 5 Criteria and Techniques for Repairing and Strengthening Architectural Heritage: Research and Application