Evaluation of the Seismic Response of Existing R.C. Frame Buildings with Masonry Infills

Student: Mario Galli
Supervisors: Dr Guido Magenes, Dr Stefano Pampanin

ABSTRACT

Comprehensive experimental-analytical studies on the seismic vulnerability of existing reinforced concrete frame buildings, designed for gravity-loads only as typically found in most seismic prone countries before the introduction of adequate seismic design code provisions, confirmed the inherent weaknesses of these systems, due to inadequate detailing and a general lack of capacity design principles.

Controversial effects on the global inelastic mechanism can be expected depending on the infills properties (mechanical characteristic and distribution) and the joint damage mechanism.

In this contribution, the interaction between un-reinforced masonry infills and r.c. frame systems, when appropriately considering the joint zone non-linear behavior, is investigated through pushover and non-linear time-history analyses on 2-D and 3-D multi-storey frame systems under uni-directional or bi-directional input motions.

A simplified and reliable analytical model based on a concentrated plasticity approach and validated on different experimental tests on beam-column joints and frame systems (with and without infills) is adopted and proposed for extensive studies on seismic vulnerability of existing buildings.

The presence of infills can guarantee higher stiffness and strength, reducing the inter-storey drift demand, while increasing the maximum floor accelerations. A further positive influence of the infills can be recognized in the reduction of column interstorey shear contribution as well as in the possible delay of a softstorey mechanism which might instead develop in a bare frame solution.

On the other side, the sudden reduction of storey stiffness due to the damage of the infills can lead to the formation of an unexpected soft storey mechanism, which, due to the interaction with the joint damage, can occur not necessarily at the first floor level and independently by the regular or irregular distribution of the infills along the elevation. Similarly, when investigating the response of 3-D frames under either unidirectional or bi-directional earthquake input excitation, inelastic torsion mechanisms can occur.

In conclusion, it is worth recognizing that the high dispersion of the mechanical properties of the infills can further increase the level of uncertainties in the expected performance if simplified probabilistic approach are adopted.

You may download a digital version of this MSc dissertation here.