A comparison between the SLaMA method and NLFEA for 2D and 3D analyses of masonry structure

Abstract

Each year, the province of Groningen experiences many induced earthquakes due gas extraction, which has been ongoing since 1963. The earthquakes cause damage to the buildings situated in the Groningen area, and they constitute a potential danger for the safety of the residents. These buildings are typically unreinforced masonry structures which are designed without knowledge of the presence of seismic activity in this area.

It is therefore essential develop and use assessment methods that are on one end reliable and accurate, but on the other hand allow to perform a large number of assessments of the vulnerability of the buildings in a short time. In other words, the assessment of all the buildings requires a quick and reliable assessment method. Such an assessment method should offer a strong understanding of the occurring failure mechanism during an earthquake, an acceptable prediction of the ground acceleration at which the collapse of the building may occur (maximum base shear force) and the displacement capacity of unreinforced masonry (URM) building.

The NPR9998 recommends four seismic assessment approaches, which differ in complexity and assessment time needed to be performed. The most comprehensive and time-consuming assessment method is the NLTHA (nonlinear time history analysis), which includes both the dynamic and nonlinear effects. In practice, this method is used only in special cases, such as in the case of monumental buildings. A simpler approach is the NLPO (nonlinear pushover) analysis, which is static and considers the nonlinear properties of the structure. An NLPO is less time consuming than an NLTHA, even when the finite element method (FEM) is considered.

A more simplified approach is the Simple Lateral Mechanism Analysis (SLaMA). This method is a simplified mechanism-based analytical approach. If the SLaMA method predicts realistically conservative global capacities, it could serve as an effective alternative assessment method for URM buildings, and especially to the NLPO FEM analysis. This study focusses on the comparison between the SLaMA method and the NLPO FEM analysis. Therefore, this study aims to answer the following research question:

Could the SLaMA method be a realistically conservative and effective alternative to the NLPO FEM analysis in making a seismic assessment for two-storey unreinforced masonry buildings?

In conclusion, the SLaMA method could be a realistically conservative and effective alternative to the NLPO FEM analysis in predicting the maximum base shear force. The displacement capacity predicted using the SLaMA method is validated only for buildings with RC floors. This predicted SLaMA method was realistically conservative compared with the ultimate displacement achieved using the NLPO FEM analysis. The SLaMA method is overall suitable for obtaining a quick understanding of the behaviour of an URM building. However, it requires a proper evaluation of the analyses to identify properly the type and the location of the failure mechanisms. For this reason, this method could be valuable to be applied before using a more complex assessment method.