Gabriele Guerrini

Seismic Behavior of Posttensioned Self-Centering Precast Concrete Dual-Shell Steel Columns

This paper describes an innovative bridge column technology for application in seismic regions. The proposed technology combines a precast posttensioned composite steel-concrete hollow-core column, with supplemental energy dissipation, in a way to minimize postearthquake residual lateral displacements. The column consists of two steel cylindrical shells, with high-performance concrete cast in between. Both shells act as permanent formwork; the outer shell substitutes for the longitudinal and transverse reinforcement, because it works in composite action with the concrete, whereas the inner shell removes unnecessary concrete volume from the column, prevents concrete implosion, and prevents buckling of energy dissipating dowels when embedded in the concrete. Large inelastic rotations can be accommodated at the end joints with minimal structural damage, since gaps are allowed to open at these locations and to close upon load reversal. Longitudinal posttensioned high-strength steel threaded bars, designed to respond elastically, in combination with gravity forces ensure self-centering behavior. Internal or external steel devices provide energy dissipation by axial yielding. This paper describes the main requirements for the design of these columns and also discusses the experimental findings from two quasi-static tests.

Dataset from the dynamic shake-table test of a full-scale unreinforced clay-masonry building with flexible timber diaphragms

This paper provides information related to the sensor measurements obtained from an unreinforced masonry building subjected to incremental dynamic shake-table tests at the EUCENTRE facilities in Pavia, Italy. These tests provide a unique data set that captures at full scale the in-plane and out-of-plane behavior of unreinforced masonry walls, and the influence of flexible diaphragms on the dynamic global response of a complete building. The authors made this information available to assist in the development of analytical and numerical models, necessary to estimate the dynamic response and the engineering parameters for the performance-based seismic assessment of unreinforced masonry buildings. All recorded data (acceleration and displacement time histories) and the videos of the tests can be requested online on the EUCENTRE repository at the URL www.eucentre.it/nam-project referring to EUC-BUILD-2. For further interpretation of the sensor recordings, and for a detailed discussion on the seismic performance of the building specimen, the reader is referred to the article entitled “Experimental seismic performance of a full-scale unreinforced clay-masonry building with flexible timber diaphragms” (Kallioras et al., 2018) [1].

Dynamic Shake-Table Tests on Two Full-Scale, Unreinforced Masonry Buildings Subjected to Induced Seismicity

This paper presents the results of an experimental campaign which is part of a wider research project, aimed at assessing the seismic vulnerability of buildings in the Groningen region of the Netherlands. The area, historically not prone to tectonic ground motions, has been subjected to seismic events induced by gas extraction during the last two decades. As part of this campaign, unidirectional dynamic shake-table tests were performed at the EUCENTRE laboratory on two full-scale, unreinforced masonry buildings, designed without specific seismic considerations or detailing. The first specimen simulated the end-unit of a two-story terraced house, built with unreinforced masonry cavity walls. These walls were composed of an inner load-bearing leaf, made of calcium silicate bricks supporting the floors, and an outer veneer, made of clay bricks with aesthetic and weather-protection function. The floors consisted of reinforced concrete slabs, providing rigid diaphragms; the pitched roof was made of longitudinal timber beams, supported by end gables perpendicular to the shaking direction, and wood boards. The second specimen represented a one-story detached pre-1940’s house, built with double-wythe unreinforced clay masonry walls. The structure included large openings and a re-entrant corner, causing significant horizontal irregularities; the two facades perpendicular to the shaking direction simulated two common gable geometries. The first floor was made of timber beams and planks, resulting in flexible diaphragm; the steep-pitch roof consisted of timber trusses connected by wood purlins and boards. Two similar incremental dynamic tests were performed up to the near-collapse conditions of the two buildings; the selected input ground motions represented realistic scenarios of seismic events for the examined region. This paper summarizes the main characteristics of the two specimens and the shake-table experimental results, illustrating the evolution of the damage mechanisms and the hysteretic response of the structures.

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.