Marco Preti

Infill Walls with Sliding Joints to Limit Infill-Frame Seismic Interaction: Large-Scale Experimental Test

This article presents the results of an experimental campaign on the in-plane behavior of masonry infill walls. Four tests were performed on large-scale specimens to evaluate the infill deformation capacity and damage for different drift levels. A design solution adopting horizontal sliding joints was proposed for reducing the infill-frame interaction, and its performance was compared with the configuration without joints. Both hollow-fired clay bricks and adobe were tested. The experimental tests showed the effectiveness of the sliding joints in reducing the infill wall damage and a higher performance of adobe infills with respect to hollow-fired clay specimens.

Experimental testing of engineered masonry infill walls for post-earthquake structural damage control

The paper presents the results of an experimental campaign on the behaviour of engineered masonry infill walls subjected to both in- and out-of-plane loading. The aim of the research was to develop a design approach for masonry infill walls capable of solving their vulnerability and detrimental interaction with the frame structure when exposed to seismic excitation. Tests on two large-scale specimens and sub-assemblies were performed in order to evaluate the infill deformation capacity, the damage associated with different drift levels, and the mechanical properties of the components. A design solution with sliding joints to reduce the infill-frame interaction and ensure out-of-plane stability, which was proposed in a previous study, was developed and refined with focus on construction details. The aim of sliding joints is to ensure a predetermined mechanism in the infill wall, which is governed by hierarchy of strength and is capable of ensuring ductility and energy dissipation that can be taken into account in the design practice, thanks to the predictability of the response. The two infill wall specimens, one of them including an opening, reached up to 3 % in-plane drift with very little damage and supported an out-of-plane force equivalent to a horizontal acceleration four times the acceleration of gravity. The force-displacement hysteretic curve, sliding at the joints and crack pattern show the efficiency of the construction technique, based on affordable and tradition-like construction processes and materials. The technique, presented here for hollow fired-clay masonry units, can be extended to different masonry infill typologies.

Numerical Investigation of the In-Plane Performance of Masonry-Infilled RC Frames with Sliding Subpanels

AbstractA number of construction techniques have been proposed to improve the seismic performance of infilled RC frames by increasing the strength and stiffness of the infill and/or the frame. The increase of the seismic capacity of infilled frames with these techniques can improve substantially their seismic performance as long as the demand does not exceed the capacity, but it can eventually lead to brittle failures once the capacity is exceeded. This study assesses numerically a new construction technique that introduces flexibility to the system to ensure its ductile behavior and minimal damage by splitting the infill in subportions and allowing the sliding along the horizontal joints connecting these subportions. A numerical model, validated with data from tests on the components of the proposed structural system and able to capture the interaction between them, has been developed to provide insight into the load-transfer mechanism that develops, and to optimize the proposed detailing. A parametric s...

Ductility of a Structural Wall with Spread Rebars Tested in Full Scale

The experimental work focuses on the ductility of the reinforced concrete (RC) seismic structural walls in buildings of mid-rise height. A full-scale five-story structural wall was tested to obtain results, still scarce in literature, without the influence of size effect. An unusual detailing with large diameter longitudinal rebars uniformly distributed in the wall length was adopted to prevent premature web rebar fracture and shear sliding. The plastic hinge length and deformations were evaluated in detail. The results show the high ductility of the wall that reached a total drift of 2.5%, larger than those usually required in design.

Thin-folded Shell for the Renewal of Existing Wooden Roofs

ABSTRACT In this article, a technique for the renewal of historic building wooden roofs is presented. The solution can be used for the strengthening of existing wooden roofs against excessive lateral thrusts on the peripheral wall or for the recovery of the attics, as it allows removing the existing structural elements, such as possible wooden truss-works of no artistic value. With minor adaptations, the solution can be addressed to enhance the building seismic performance. The technique is minimally impairing on existing buildings and can be applied also in new constructions. The technique is based on the construction of a thin folded shell, overlaying the existing pitches. Emphasis is given to lightweight folded shells, obtained by overlaying thin plywood panels on the existing roof rafters and planks, without modifying the overall architectural layout. The technique conceptual design is discussed and a simplified analytical method is proposed, which allows for the clarification of the role of each structural component and can be adopted for the folded shell proportioning and design. The analytical results are validated against numerical results obtained with reference to some case studies. Ultimately, emphasis is given to the detailing, whose correct execution is mandatory for the success of the proposed structural intervention.

Seismic Vulnerability for Churches in Association with Transverse Arch Rocking

The research work stems from the surveys and the analysis of the damages surveyed in several churches following the 2004 earthquake in northern Italy. Focus is paid to the rocking of the diaphragm arches, which frequently induced significant damages, such as yielding or failure of the tie rods and, in one church, the collapse of the nave vaults. The diaphragm arch-rocking collapse mechanism is studied referring to the limit analysis approach, taking into account the phenomena involved, such as the buttress action of the abutments and the confining action of the tie rods. The analytical evaluation of the collapse multiplier in the case of either over-resisting or weak ties is proposed. The analytical model is validated by comparison with the experimental behavior of an arch-to-abutment structure subjected to rocking. As an example, the analytical model is applied for the structural vulnerability assessment of two churches, which were severely damaged by the 2004 earthquake.

DISSIPATIVE ROOF DIAPHRAGM FOR THE SEISMIC RETROFIT OF LISTED MASONRY CHURCHES

ABSTRACT In the seismic retrofit of the existing masonry buildings, dissipative and deformable roof diaphragms could offer an efficient solution in cases where both the adoption of steel ties or stiff diaphragms would be ineffective. An innovative deformable, dissipative and lightweight roof diaphragm for the seismic retrofit of masonry churches is proposed. Such a diaphragm prevents the overturning of the side walls whilst allowing the onset of a controlled rocking mechanism. The specific diaphragm elasto-plastic response caps the seismic actions transferred by the roof diaphragm to the seismic resistant walls, in contrast to a rigid and a stiffened diaphragm. This effect is meant to mitigate the overload of the head walls, thus preventing their collapse or the need for their strengthening, which could require interventions invasive of the historical structure. The feasibility of the proposed retrofit strategy is assessed through the experimental characterization of a prototype diaphragm sub-assembly and non-linear dynamic analyses of the global response of two retrofitted reference buildings.

Combining seismic retrofit with energy refurbishment for the sustainable renovation of RC buildings: a proof of concept

In this paper, an integrated approach targeting sustainability, safety and resilience is envisioned for the renovation of the post-Second World War RC buildings clustered in urban outskirts. The so...

Lightweight Ribs for the Strengthening of Single Leaf Vaults Undergoing Seismic Actions

In this paper the behavior and the collapse mechanism of single leaf vaulted structures undergoing seismic loads are discussed, and an innovative technique based on the use of lightweight ribs is proposed. The efficiency of the solution is verified by means of non linear numerical analyses on a strengthened single leaf vaulted structure. The numeric model is validated through comparison with the results of experimental tests performed on lightweight ribs subjected to cyclic, unsymmetrical load conditions.

Seismic infill–frame interaction of masonry walls partitioned with horizontal sliding joints: analysis and simplified modeling

ABSTRACT This paper proposes a simplified approach to analyze the seismic performance of masonry infills with sliding joints in moment-resisting frame structures. The proposed methodology uses the equivalent strut approach, calibrated on the results of a novel analytical formulation, which considers the basic geometrical and mechanical properties of the infill. The method is validated through the comparison of the estimated infill resistance and shear demand on the column with those obtained from an extensive experimental and numerical study using refined finite element models. For the case studies considered, the simplified model offers a reliable estimate of the global and local response.