Conservation of cultural heritage against seismic risk constitutes one of the greatest challenges of the scientific community, which is engaged in refining efficient solutions for practitioners as well as theoretical mechanical models. The response of distinctive architectural elements, like arches, domes and vaults, has attracted the interest of historical scientists, but still today comprehensive and general formulations lack a full dynamic perspective. Among architectural elements, the arch is certainly an iconography of mechanics applied to architecture. Indeed, extensive investigations are available in the literature on the response of circular arches to vertical loads, and a few full dynamic models for horizontal acceleration load can be found as well. Pointed arches, even though spread in seismic prone areas, received much less of interest. An amazing case study on which working on, consisting in a giant pointed arched system located in Afghanistan, motivated a seminal interest on the issue, toughened by the lacking literature. For these reasons, this dissertation reports on a parametric analysis of the vulnerability of pointed arches made of two circular arcs, which is the simplest thinkable pointed arch. The analysis considers variations of arch slenderness and sharpness that result from different positions of centres of circular arcs. Firstly, the arch is addressed as a rigid macro-block system, and limit analysis with the kinematic approach is exploited to determine the collapse acceleration through Non-Linear Programming optimisation. The pattern of hinges at collapse differs considerably from the one that occurs for circular arches. Moreover, the effect of arch slenderness on collapse accelerations turns out to be significantly conditioned by sharpness. Acceleration necessary to initiate motion grows with the rise, as opposed to what occurs for circular shapes. Dynamic behaviour of pointed arches for rectangular shaped and harmonic inputs are investigated as well transforming arch mechanisms into four-bar linkages. Systematic integration of the non-linear form of the distinctive ODE of the problem revealed that failure during the second half cycle of motion occurs for most of the profiles. Such a trend would have never been tackled in the framework of linearized motion, which however provides more conservative estimations. Moreover, failure during the second half cycle of motion for harmonic inputs, especially for low and medium frequencies, is found to be deeply influenced by the adopted impact model and, more importantly, by the position of hinges. A dedicated sensitivity analysis validates the procedure predicting failure of circular arches as a particular case of pointed. Considering also a micro-block approach, a wide experimental campaign addressed the equivalent static and full dynamic response of a set of 11 reduced scale model of pointed arches made of prismatic Autoclaved Aerated Concrete blocks. Global geometric characteristics of models are the same considered in the macro-block approach. Tilt tests and shake table tests uncovered the inherent sliding vulnerability of these profiles. Thus, a kinematic model capable of considering sliding, independently from the adopted friction coefficient can be represented by a two-bar model hinged at the ground and connected by a slider; outcomes tackle global sliding mechanism of thick and sharp profiles. A similar aim justified the use of the Distinct Element Method through the commercial code 3DEC. As for equivalent static tests, the range of friction coefficients necessary to initiate a hinging mechanism vary with variation in geometry of the profile, and most important, for thick and sharp profiles, the rocking mechanism can hardly be activated unless a perfect hinging interface is not assumed. Regarding dynamic tests, harmonic pulses with frequency ranging between 2Hz and 10Hz have been considered and results of analytical, numerical and experimental models have been compared. Given the stated vulnerability of pointed arches to crown sliding, the four bar linkage model will always be lacking a fundamental aspect, especially for sharp and stocky profiles subjected to high-frequency inputs. Future investigations should address vulnerability to complete time histories, and in a probabilistic framework, sliding phenomena when overloading is considered and 3D structures.

Seismic vulnerability of pointed arches under rigid body assumption. Numerical and experimental evaluations / Giulia Misseri. - (2017).

Seismic vulnerability of pointed arches under rigid body assumption. Numerical and experimental evaluations.

MISSERI, GIULIA
2017

Abstract

Conservation of cultural heritage against seismic risk constitutes one of the greatest challenges of the scientific community, which is engaged in refining efficient solutions for practitioners as well as theoretical mechanical models. The response of distinctive architectural elements, like arches, domes and vaults, has attracted the interest of historical scientists, but still today comprehensive and general formulations lack a full dynamic perspective. Among architectural elements, the arch is certainly an iconography of mechanics applied to architecture. Indeed, extensive investigations are available in the literature on the response of circular arches to vertical loads, and a few full dynamic models for horizontal acceleration load can be found as well. Pointed arches, even though spread in seismic prone areas, received much less of interest. An amazing case study on which working on, consisting in a giant pointed arched system located in Afghanistan, motivated a seminal interest on the issue, toughened by the lacking literature. For these reasons, this dissertation reports on a parametric analysis of the vulnerability of pointed arches made of two circular arcs, which is the simplest thinkable pointed arch. The analysis considers variations of arch slenderness and sharpness that result from different positions of centres of circular arcs. Firstly, the arch is addressed as a rigid macro-block system, and limit analysis with the kinematic approach is exploited to determine the collapse acceleration through Non-Linear Programming optimisation. The pattern of hinges at collapse differs considerably from the one that occurs for circular arches. Moreover, the effect of arch slenderness on collapse accelerations turns out to be significantly conditioned by sharpness. Acceleration necessary to initiate motion grows with the rise, as opposed to what occurs for circular shapes. Dynamic behaviour of pointed arches for rectangular shaped and harmonic inputs are investigated as well transforming arch mechanisms into four-bar linkages. Systematic integration of the non-linear form of the distinctive ODE of the problem revealed that failure during the second half cycle of motion occurs for most of the profiles. Such a trend would have never been tackled in the framework of linearized motion, which however provides more conservative estimations. Moreover, failure during the second half cycle of motion for harmonic inputs, especially for low and medium frequencies, is found to be deeply influenced by the adopted impact model and, more importantly, by the position of hinges. A dedicated sensitivity analysis validates the procedure predicting failure of circular arches as a particular case of pointed. Considering also a micro-block approach, a wide experimental campaign addressed the equivalent static and full dynamic response of a set of 11 reduced scale model of pointed arches made of prismatic Autoclaved Aerated Concrete blocks. Global geometric characteristics of models are the same considered in the macro-block approach. Tilt tests and shake table tests uncovered the inherent sliding vulnerability of these profiles. Thus, a kinematic model capable of considering sliding, independently from the adopted friction coefficient can be represented by a two-bar model hinged at the ground and connected by a slider; outcomes tackle global sliding mechanism of thick and sharp profiles. A similar aim justified the use of the Distinct Element Method through the commercial code 3DEC. As for equivalent static tests, the range of friction coefficients necessary to initiate a hinging mechanism vary with variation in geometry of the profile, and most important, for thick and sharp profiles, the rocking mechanism can hardly be activated unless a perfect hinging interface is not assumed. Regarding dynamic tests, harmonic pulses with frequency ranging between 2Hz and 10Hz have been considered and results of analytical, numerical and experimental models have been compared. Given the stated vulnerability of pointed arches to crown sliding, the four bar linkage model will always be lacking a fundamental aspect, especially for sharp and stocky profiles subjected to high-frequency inputs. Future investigations should address vulnerability to complete time histories, and in a probabilistic framework, sliding phenomena when overloading is considered and 3D structures.
2017
Luisa Rovero
ITALIA
Giulia Misseri
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/1079986
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