The rocking response of large flexible structures to earthquakes

The rocking response of structures subjected to strong ground motions is a problem of 'several scales'. While small structures are sensitive to acceleration pulses acting successively, large structures are more significantly affected by coherent low frequency components of ground motion. As a result, the rocking response of large structures is more stable and orderly, allowing effective isolation from the ground without imminent danger of overturning. This paper aims to characterize and predict the maximum rocking response of large and flexible structures to earthquakes using an idealized structural model. To achieve this, the maximum rocking demand caused by different earthquake records was evaluated using several ground motion intensity measures. Pulse-type records which typically have high peak ground velocity and lower frequency content caused large rocking amplitudes, whereas non-pulse type records caused random rocking motion confined to small rocking amplitudes. Coherent velocity pulses were therefore identified as the primary cause of significant rocking motion. Using a suite of pulse-type ground motions, it was observed that idealized wavelets fitted to velocity pulses can adequately describe the rocking response of large structures. Further, a parametric analysis demonstrates that pulse shape parameters affect the maximum rocking response significantly. Based on these two findings, a probabilistic analysis method is proposed for estimating the maximum rocking demand to pulse-type earthquakes. The dimensionless demand maps, produced using these methods, have predictive power in the near-field provided that pulse period and amplitude can be estimated a priori. Use of this method within a probabilistic seismic demand analysis framework is briefly discussed. © 2013 Springer Science+Business Media Dordrecht.

Assessment of the settlement vulnerability of masonry buildings

Excavation works in urban areas require a preliminary risk damage assessment. In historical cities, the prediction of building response to settlements is necessary to reduce the risk of damage of the architectural heritage. The current method used to predict the building damage due to ground deformations is the Limiting Tensile Strain Method (LTSM). In this approach the building is modelled as an elastic beam subjected to imposed Greenfield settlements and the induced tensile strains are compared with a limit value for the material. These assumptions can lead to a non realistic evaluation of the damage. In this paper, the possibility to apply a settlement risk assessment derived from the seismic vulnerability approach is considered. The parameters that influence the structural response to settlements can be defined through numerical analyses which take into account the nonlinear behaviour of masonry and the soil-structure interaction. The effects of factors like material quality, geometry of the structure, amount of openings, type of foundation or the actual state of preservation can be included in a global vulnerability index, which should indicate the building susceptibility to damage by differential settlements of a given magnitude. Vulnerability curves will represent the expected damage of each vulnerability class of building as a function of the settlement.

Coupled analysis of building damage due to tunnelling

Excavation works in urban areas require a preliminary risk damage assessment. In historical cities, the prediction of building response to settlements is necessary to reduce the risk of damage of the architectural heritage. The current method used to predict the building damage due to ground deformations is the Limiting Tensile Strain Method (LTSM). This method is based on an uncoupled soil-structure analysis, in which the building is modelled as an elastic beam subject to imposed greenfield settlements and the induced tensile strains are compared with a limit value for the material. This approach neglects many factors which play an important rule in the response of the structure to tunneling induced settlements. In this paper, the possibility to apply a settlement risk assessment derived from the seismic vulnerability approach is considered. The parameters that influence the structural response to settlements can be defined through numerical coupled analyses which take into account the nonlinear behaviour of masonry and the soil-structure interaction.

Experimental behaviour of barrel vaulted structure subjected to rocking of the abutments

In this paper, the transverse rocking mechanism of a barrel vaulted structure subjected to horizontal cyclic loads is analysed by means of experimental tests on full scale model and by means of non-linear FE analyses. The study is part of an ongoing experimental and theoretical research program, developed by the University of Brescia, concerning the seismic behaviour of ancient masonry buildings. The scope of the paper is to provide some evidence of the rocking mechanism experienced by barrel vaulted structures under horizontal loading. The understanding of the behaviour of these structural systems is necessary for their seismic vulnerability assessment, as well as for the correct design of possible strengthening techniques. A numeric FE model was validated through comparison with the experimental results and it was used to verify the efficiency of two common strengthening solutions: the technique of the overlaying reinforced concrete slab and the technique of the thin spandrel walls. Experimental and numeric results will be discussed in the paper.