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

reinforcement and areas of the building to be affected wouldincrease, resulting in higher costs (economical reason).Also, in densely built groups of buildings, viewing this asone system to be affected, it would normally be difficultto apply preventive measures to the entire area and thereinforcement would only be partially effective (physicalreason). This goes the same for buildings that have becomelarger after having been repeatedly expanded. Additionally,large-scale reinforcement would have excessive impact onthe building’s significance as a cultural property (culturalproperty-related reason).There is another point which in Japan is not well madeaware of. It is that the evaluation of structural performanceafter reinforcement becomes difficult after greatly alteringthe structural characteristics of an extant building in order toconsiderably increase its seismic performance and thereforemay interrupt possibilities of controlling preventivemeasures. This is regarded to be undesirable from thestructural aspect (structural reason). As has been explainedearlier, buildings in Italy reinforced in the 1980s to meetmodern codes were damaged in recent earthquakes andthis has provided the background for present approaches inseismic protection.In Japan today, the required safety level of seismicprotection of cultural property structures open to the publicare often raised to meet that of buildings in general, and thisis the large difference from the conditions in Italy.In Italy, principles for increasing performance arefurther advanced and through monitoring of anti-seismicperformance, reinforcement is gradually increased toconfirm the effectiveness of the treatment. It is proposedfor these results to be used in deciding at each stage ofreinforcement whether additional reinforcement is necessaryand what type of reinforcement is appropriate. This way ofthinking aims at minimum reinforcement that would havethe least impact on aspects of the building as a culturalproperty and structure, while being economically viable. InJapan, although reinforcement in phases is recommendednot only for extant buildings but also for cultural propertystructures, it differs in that the entire plan for execution iscreated in the beginning.On the other hand, it appears that the treatment ofbuildings that do not reach the required seismic performancelevels continues be a very difficult problem. The requiredseismic performance differs by codes and guidelines: underthe Building Structure Code, by building use and underthe Cultural Property Guidelines, and by significance asa cultural property and building use. Property ownersare required to confirm after having had their buildingsreinforced that the treatment meets the performancedesignated for the building use. There appear to have beencases where the building use was changed to match theacquired seismic performance.3.3. Seismic AnalysisExtant buildings differ from new construction in that thereare many aspects that are unclear, making it impossible todetermine their seismic resistance or plan reinforcementmethods based only on the results of numerical analysis.Therefore, various forms of surveys including the building’shistory of alterations and construction of additions,structural analyses of the actual building through testmethods that involve very little or no destruction, or thoseemploying model specimens are indispensable for gatheringinformation.Regarding numerical analysis, it is recommended thatstudies through not only one but multiple methods be takenso that the results could be crosschecked. Also, with masonrystructures that vary greatly in material quality and degreeof deterioration, the engineer’s decision needs to be reliedon regarding how such buildings can be surveyed, howthese conditions are to be reflected on numerical analysis,as well as how the analysis results should be evaluated. Inthe Cultural Property Guidelines, as mentioned above, it isrecommended that the seismic property of masonry culturalproperty structures be evaluated not only from the results ofnumerical analysis but quantitatively and qualitatively frommultifaceted viewpoints.Concerning numerical analysis, there are the three stepsof LV1 to LV3 given in the Cultural Property Guidelines.An outline of each of the methods is as follows: LV1 is themost simple method in which seismic resistance of theentire structure is obtained from the total sum of the seismicproperty of each earthquake-resisting wall and such, fromwhich a ratio between seismic force is calculated to providethe seismic coefficient for judging seismic resistance. LV2is what is called the limit analysis method which examinesseismic performance through partial modeling of weakerareas of the building according to the typical collapsemechanism for masonry structures (figure 1). Calculation issimplified by assuming the partial model to be a rigid-bodyin which neither partial destruction nor slippage will occur,with the tensile strength at boundary surface to be zero.Seismic performance is studied by calculating the seismiccoefficient, which is the ratio of the velocity at the pointwhen the collapse mechanism will start to function and themaximum velocity of ground motion when an earthquakeoccurs. LV3 is a method for studying seismic performanceby modeling the entire building three-dimensionally throughthe finite element method and such to verify the stress38Chapter 4 Earthquake-Proofing Measures for Masonry Structures in Italy