Macro-element nonlinear dynamic analysis for the assessment of the seismic vulnerability of masonry structures

Earthquakes constitutes one of the most devastating natural hazards since they lead to the collapse of buildings; and consequently, a significant number of human losses. Some typologies of buildings, namely historical and masonry constructions, are one of the most vulnerable elements at risk due to their weak performance when subjected to seismic actions. For instance, historic structures were built based on simple rules since seismic codes were not properly established at the time of their construction. On the other hand, many masonry structures, especially in developing countries, are usually constructed without taking into consideration the specifications provided by current seismic codes. These constructions are mainly characterised by a poor connection between orthogonal walls and between walls and horizontal diaphragms which lead to the occurrence of out-of-plane mechanisms. This behaviour is considered one of the most vulnerable, yet one of the most neglected failure mechanisms when assessing the seismic performance of these constructions. This thesis aims at the assessment of the out-of-plane behaviour as well as the seismic vulnerability of masonry structures with a predominant out-of-plane collapse. For this purpose, a simplified computational tool, based on a macro-element modelling approach, was extended into the dynamic field by the definition of cyclic constitutive laws and the introduction of a consistent mass matrix. This modelling approach is capable of accurately simulating the main in-plane and most importantly out-of-plane mechanisms of this type of constructions with a reduced computational burden. These features are validated by the comparison of the linear and nonlinear dynamic response of three case studies investigated by means of differential equations and sophisticated computational tools. This validation demonstrated the capability of this simplified modelling approach of accurately estimating dynamic properties and simulating the rocking motion of a rigid block and the nonlinear hysteretic behaviour of masonry structures. After validation, this modelling approach was employed for the assessment of the out-of-plane behaviour of two unreinforced masonry structures previously tested by means of shaking table tests. This investigation was carried out in the static and dynamic nonlinear fields by the application of a mass distributed lateral force and a recorded input from the experimental campaign. The unreinforced masonry structures were also investigated considering a more sophisticated numerical approach, namely Finite Element models. A comparison between these two numerical models was conducted in terms of maximum load capacity, post-elastic behaviour and hysteretic response demonstrating significant resemblance. An additional comparison was conducted taken into consideration numerical and experimental failure mechanisms. A good agreement was obtained when comparing the in-plane response of these structures. Nevertheless, the out-of-plane mechanisms were not successfully simulating evidencing the complexity of this behaviour, especially in a dynamic context. Based on these results, it was demonstrated that this simplified numerical tool can be considered as an alternative computational tool for the assessment of this type of structures since the computational burden was significantly reduced. Finally, the seismic vulnerability of one of these unreinforced masonry structures was investigated by the derivation of analytical fragility curves. For this purpose, the simplified model of such structure was subjected to a set of nonlinear dynamic analyses based on accelerogram artificially generated. In addition, three limit states, whose definition was based on an alternative procedure consisting of the application of nonlinear static analyses, were considered for the assessment of the seismic vulnerability of such structure. This was conducted concentrating the uncertainty initially on the seismic input (artificial accelerograms), and subsequently, on additional parameters such as mechanical properties, thickness of walls, and damping ratio by the definition of probabilistic models. From these assessments, it was possible to determine the probability of exceeding the three limit states due to the application of dynamic loading to masonry structures that are characterised by out-of-plane collapse mechanisms.

Name thesis:degree_name

Doctoral Thesis Civil Engineering

Grantor

Universidade do Minho

Year dc:date.issued

2018

Author dc:creator

• Espinoza, César Javier Chácara

Advisors dc:contributor.advisor

• Lourenço, Paulo B.
• Caliò, Ivo

Statement dc:rights

• openAccess

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1822/55900

OAI record oai:identifier

http://repositorium.sdum.uminho.pt/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arepositorium.uminho.pt%3A1822%2F55900