Seismic analysis of low-rise masonry structures with openings in China

Abstract

Masonry is traditionally used in the construction of low-rise buildings all over the world. Masonry construction comprises a heterogeneous material formed from a regular or irregular repetition of blocks with or without the presence of mortar between the blocks. In recent earthquakes, unreinforced masonry (URM) structures built of masonry walls containing openings such as doors and
windows have been shown to have poor seismic capacity. The poor seismic capacity of doors and windows for URM buildings can lead to significant damage or even collapse, which could threat the life of people and cause huge economic loss. Thus, it is vital to identify the structural behaviour of opening effects of URM housing and figure out solutions to reduce the seismic damage. However,
although different sizes and positions of openings are known to reduce the stiffness and strength of URM walls, the relationships between the size and position of openings and the seismic capacity of the walls are not transparent. Therefore, in this thesis, a series of numerical analyses have explored
many possible opening sizes and opening positions under simulated seismic loading (both static and dynamic). This work identifies the impact of openings on both the in-plane and out-of-plane behaviours of URM walls and a quick assessment procedure for the seismic capacity of URM structures
based on opening situations is proposed.

To investigate the impact of openings in URM walls, this thesis introduces numerical models which were built using the code “3DEC” which is based on the Discrete Element Method (DEM). The key feature of the DEM is that it allows the development of large displacements between elements with contacts being recognized automatically during the analysis. Thus, this numerical method can capture the whole degradation progress from the initial cracking of the masonry walls right through to collapse, with the bricks being modelled as rigid or deformable blocks and the mortar as Coulomb-slip joints with zero thickness. The modelling methodology and the calibration of the numerical models are
described.

For in-plane behaviour, both load-based and displacement-based quasi-static pushover analysis procedures have been studied and the results from the analyses, the crack patterns and collapse mechanisms of the masonry walls are identified and discussed, and a key output from this work is the characterization of the relationships between the sizes and positions of openings and the in-plane performance of URM walls. For out-of-plane behaviour, a series of quasi-static out-of-plane procedures under different boundary conditions and different shapes of walls have been studied. The relationships between the openings and out-of-plane performance and the crack patterns and the collapse mechanisms of masonry walls are identified and discussed.

Dynamic analyses of URM walls are also considered. Dynamic analysis (time-history analysis) is essential for URM structures because this type of analysis can replicate the real behaviour of URM buildings in earthquakes. To look at the dynamic issues associated with URM walls, six artificial earthquake input motions based on Eurocode 8 were generated and the numerical analytical procedure using 3DEC was applied, the results are compared with static analyses for both in-plane and out-of-plane behaviours.

Using the data based on the static and dynamic analyses, relationships defining capacity reduction factors for different opening sizes and positions are proposed. Finally, a quick assessment procedure for the seismic capacity of URM structures with various opening situations is suggested. To validate the assessment procedure, a real URM building in China is modelled in 3DEC and the seismic capacity is predicted according to the proposed assessment approach. The results of the predictions, proposed procedure and numerical analysis in 3DEC are compared and a possible implementation is also introduced.

Keywords: URM structures · Opening effects · Discrete element method · 3DEC · In-plane behaviour · Out-of-plane behaviour · Quick assessment procedure

Date of Award	21 Jan 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Adam J Crewe (Supervisor)