Ilaria Senaldi

The demise of the URM building stock in Christchurch during the 2010-2011 Canterbury earthquake sequence

The progressive damage and subsequent demolition of unreinforced masonry (URM) buildings arising from the Canterbury earthquake sequence is reported. A dataset was compiled of all URM buildings located within the Christchurch CBD, including information on location, building characteristics, and damage levels after each major earthquake in this sequence. A general description of the overall damage and the hazard to both building occupants and to nearby pedestrians due to debris falling from URM buildings is presented with several case study buildings used to describe the accumulation of damage over the earthquake sequence. The benefit of seismic improvement techniques that had been installed to URM buildings is shown by the reduced damage ratios reported for increased levels of retrofit. Demolition statistics for URM buildings in the Christchurch CBD are also reported and discussed.

Shaking Table Test of a Strengthened Full-Scale Stone Masonry Building with Flexible Diaphragms

An extensive experimental campaign has been conducted at EUCENTRE to understand the dynamic behavior of historic stone masonry structures and evaluate the seismic performance of selected strengthening strategies, aimed at improving wall-to-floor connections and in-plane diaphragm stiffness. Shaking table tests were performed of full-scale two-storey buildings in undressed double-leaf stone masonry with timber floor and roof. A first prototype (Building 1), representing a vulnerable building without antiseismic detailing and devices, was tested showing a response characterized by in-plane distortion of the flexible diaphragms and local out-of-plane failure mechanisms. In Building 2 the wall-to-diaphragm connections were improved, providing only a moderate in-plane stiffening of the wooden diaphragms. When subjected to shake-table testing, the strengthened building showed a global type of structural response without the occurrence of out-of-plane mechanisms. In the present paper the strengthening interventions on Building 2 are described, and the results obtained during the dynamic tests are illustrated, focusing on the response of the structure, the evolution of damage mechanisms during the tests, in comparison to the seismic performance of the first unstrengthened reference prototype response. The improvement of the connections proved to be very effective, increasing significantly the seismic capacity of Building 2 with respect to Building 1.

The Effect of Stiffened Floor and Roof Diaphragms on the Experimental Seismic Response of a Full-Scale Unreinforced Stone Masonry Building

An extensive experimental program was carried out at EUCENTRE, within a research project on the evaluation and reduction of the seismic vulnerability of stone masonry structures. The main part of the experimental program has been devoted to the shaking table tests on three full-scale, two-story, single-room prototype buildings made of undressed double-leaf stone masonry. The first building tested was representative of existing unreinforced stone masonry structures with flexible wooden diaphragms, without any specific anti-seismic design nor detailing. In the second and third buildings, strengthening interventions were simulated on structures theoretically identical to the first one, improving wall-to-floor and wall-to-roof connections and increasing diaphragm stiffness. In particular, in the third specimen, steel and r.c. ring beams were used to improve the diaphragm connection to the walls and collaborating r.c. slab and multi-layer plywood panels were used to stiffen floor and roof diaphragms, respectively. This article describes the strengthening interventions applied to the third building prototype and presents the experimental results obtained during the shaking table tests. The results obtained permitted the calibration of a macroelement model representative of the nonlinear behavior of the structure.

Numerical Simulation of Shaking Table Tests on Full-Scale Stone Masonry Buildings

ABSTRACT Based on the outcomes of a recent experimental project addressing unreinforced stone masonry undertaken at the European Centre for Training and Research in Earthquake Engineering, the seismic response exhibited by two full-scale building prototypes during shaking table tests was simulated according to an existing equivalent frame modeling approach involving nonlinear macroelements. Given the use of different strengthening solutions, the two building specimens strongly differed in the in-plane stiffness of their timber floors and roof diaphragms. This article addresses several issues concerning numerical modeling of the seismic response of this type of masonry construction, particularly its effect upon assessing the global response of the discretization and geometry of the equivalent frame model and upon definition of model parameters based on tests of material characteristics and lateral response of structural members. Even in the case of flexible diaphragms, the results of pushover analysis of the calibrated models provided a fair approximation in terms of both envelope curve and damage pattern. The results of time history analysis accounting for cumulative damage indicate good simulation in terms of hysteretic response as well.

Damage Assessment of Unreinforced Stone Masonry Buildings After the 2010–2011 Canterbury Earthquakes

The sequence of earthquakes that has affected Christchurch and Canterbury since September 2010 has caused damage to a great number of buildings of all construction types. Following post-event damage surveys performed between April 2011 and June 2011, an inventory of the stone masonry buildings in Christchurch and surrounding areas was carried out in order to assemble a database containing the characteristic features of the building stock, as a basis for studying the vulnerability factors that might have influenced the seismic performance of the stone masonry building stock during the Canterbury earthquake sequence. The damage suffered by unreinforced stone masonry buildings is reported and different types of observed failures are described using a specific survey procedure currently in use in Italy. The observed performance of seismic retrofit interventions applied to stone masonry buildings is also described, as an understanding of the seismic response of these interventions is of fundamental importance for assessing the utility of such strengthening techniques when applied to unreinforced stone masonry structures.

Numerical Investigations on the Seismic Response of Masonry Building Aggregates

The work focuses on the analysis of the seismic response of masonry building aggregates for a better understanding of the vulnerability of single structural units and of their behaviour within the aggregates. Idealized representative models are developed based on the typical characteristics of the row conglomeration typology. The seismic response of the models is evaluated and discussed by means of nonlinear dynamic analyses.

Experimental Seismic Response of a Half-Scale Stone Masonry Building Aggregate: Effects of Retrofit Strategies

A unidirectional shaking-table test on the half-scale prototype of a natural stone masonry building aggregate was performed as part of an extensive experimental and numerical research project, investigating the seismic vulnerability of historical buildings in the city of Basel, Switzerland. The prototype structure was characterized by architectural and construction details typical of Basel’s heritage residential building stock. The specimen represented a building aggregate consisting of two adjacent structural units, poorly connected on one side as if they were built at different times. The building specimen was three-story high and was built using double-leaf random stone masonry walls with undressed blocks and river pebbles. Timber floors, simply supported by the transverse walls, constituted flexible diaphragms in their plane. The two units were covered by roofs with different truss configurations, pitches, and side-gable wall heights. Steel wall-to-diaphragm connections were pre-installed but not initially fastened to the prototype; similarly, longitudinal and transverse steel tie-rods were also pre-installed at each floor without anchor plates. Both retrofit strategies were activated after a significant damage level was reached during the dynamic tests. This paper describes the seismic behavior of the prototype, analyzing the response of the bare masonry structure at various stages of the incremental dynamic test and investigating the effects of the retrofit interventions. The analysis focuses in particular on the dynamic behavior evolution, on the hysteretic response, and on the lateral displacement demand, in relation to the damage limit states associated with the observed mechanisms.