EQ-grid: A Multiaxial Seismic Retrofitting System for Masonry Buildings

During recent seismic events (2016 in central Italy, 2014 in China’s Ludian County, etc.), masonry structures have shown their vulnerability to in plane actions. A lot of retrofitting solutions are today available to increase the in-plane resistance of existing masonry walls. The seismic strengthening technique presented in this chapter is a retrofitting system for masonry buildings developed over 10 years at the Karlsruhe Institute of Technology (KIT) in Germany, Institute of Reinforced Concrete and Building Materials (Germany). It consists of a multiaxial hybrid fibre grid embedded in an inorganic natural hydraulic lime (NHL) mortar. Due to its composition, it is perfect compatible with the masonry substrate and applicable for indoor as well as outdoor applications. Moreover, it improves the local and the overall structural capacity of a masonry building with minimum mass increase. The intensive experimental campaign carried out on this strengthening system at the Karlsruhe Institute of Technology (KIT) and its results are presented and discussed in this chapter

Fragility Functions for Reinforced Concrete Structures Based on Multiscale Approach for Earthquake Damage Criteria

For seismic risk analysis, reliable predictions and estimations of earthquake damage and seismic behaviour of buildings are essential. A common method is the use of fragility curves. In this paper, fragility functions are developed based on various numerical damage criteria for five defined damage grades, from slight to destruction. The proposed new multiscale approach establishes a correlation between observed damage patterns due to foreign earthquakes and the seismic response of the building using thresholds for material-specific and global characteristics. This approach takes into account various possible damage patterns on different scales more comprehensively than the well-known approach of displacement criteria. Moreover, the approach is universal and adaptable for building classes as well as region-specific material and system characteristics. Several damage criteria with their defined limit values are assigned to the five proposed damage grades, whereby quantity and distribution of the exceeded criteria are relevant, since the first occurrence does not always lead to damage. With the new approach, damages that are not evident in the pushover curve in terms of strength degradation can be detected and taken into account for the damage thresholds. The derived displacement values associated with the damage levels are the basis for developing fragility functions. The results—damage criteria, pushover curves with damage grades, capacity curves as well as fragility functions and parameters—are presented for a four-storey reinforced concrete frame building. These results are discussed and validated with data from the literature. Comparisons to existing fragility functions in the literature show that our developed fragility functions are mostly located in the middle range, graphically as well as for the curve parameters. This specific example was chosen to present our multiscale approach, but for general building classes, numerous simulations with varying characteristics are essential and result in a higher standard deviation of the final fragility curves

Influence of vehicle traffic on modal-based bridge monitoring

In recent years, there has been a surge of interest in modal-based monitoring systems, especially for bridge structures, to detect damage at an early stage and to extend the life of existing bridges as well as to minimize maintenance costs. The modal parameters, natural frequencies and mode shapes, depend on stiffness and mass of a structure. For an economic application of a modal-based monitoring system, the estimation of the modal parameters based on the Operational Modal Analysis needs to be estimated. The Operational Modal Analysis uses the naturally existing vibration sources, such as wind and traffic, to estimate the modal parameters. A significant advantage is therefore that the bridges do not have to be closed to traffic. In this context, the modal parameters are influenced by the vehicle traffic due to the associated temporally and spatially variable mass, stiffness and damping properties of the overall system. In this paper, the influence of those operational loads and road roughness on the modal parameter estimation is numerically investigated. The vehicles are modeled as half-vehicle models. In addition, the influence of vehicle traffic is shown using in situ measurements on an existing bridge. A high sensitivity of the natural frequencies to operational loads can be shown, so that they are not reliable damage identification parameters. In contrast, the mode shapes exhibit small amplitude scatter due to the operating loads if the excitation frequency is not in the range of the natural frequency of the bridge. This is very unlikely, especially for bridges under vehicle traffic, due to the variety of vehicle designs and thus the broadband excitation