Search

The seismic resilience of structures and infrastructures is affected by damage accumulation phenomena, mainly related to the type of hysteresis. Specifically, pinching drives the cyclic response of several building materials, such as reinforced concrete and masonry. Structural systems affected by pinching phenomena are prone to exhibit a dramatic increment of their displacement response after multiple cycles (e.g. repeated earthquakes). The authors estimate a reinforced concrete pier's response using truncated incremental dynamic analysis by concatenating three earthquake scenarios. The authors adopted a Bouc–Wen class hysteresis model to simulate the reinforced concrete pier's cyclic response, matching its experimental cyclic response. The current analysis proved that ductility and resistance primarily drive the seismic response after a single earthquake. However, the performance after multiple earthquakes strongly depends on the pinching, degradation and drift accumulation, which are generally neglected in standard design practices. [ABSTRACT FROM AUTHOR]

An experimental study was performed to investigate the effect of external prestressed truss steel-bar units installed on an unreinforced masonry (URM) wall under out-of-plane loadings. The key components of this new retrofitting method are prestressed vertical and diagonal bars. The prestressed vertical bars induce a prestressing force onto the horizontal section of the URM wall and the diagonal bars resist lateral loadings. Reverse cyclic tests were conducted on a full-scale URM wall as a control specimen and URM walls retrofitted in-plane and/or out-of-plane (parallel to short intersecting walls). The test results showed that the specimen strengthened using the new technique was superior to the control specimen in terms of seismic performance, including lateral load resistance, stiffness, energy dissipation and restrained slip of the entire specimen. Two units installed on short intersecting walls exhibited the same shear strength as four units installed on the in-plane and in-plane retrofitted masonry walls. The out-of-plane masonry specimen demonstrated the best performance. It was confirmed that aligning the retrofitting method based on the loading direction was effective, despite the lower axial load level. [ABSTRACT FROM AUTHOR]

Traditional masonry buildings are highly vulnerable to earthquake loading and their dynamic response is strongly influenced by the in-plane deformability of the timber floors and the quality of the wall-to-floor connections. Understanding the behaviour of timber floors and roofs and their interaction with masonry walls is therefore fundamental for the protection of historical buildings. In a previous research project, different timber-based dry-connected strengthening solutions for timber floors were tested under in-plane loading. The experimental results showed a significant increase in shear strength and stiffness. In the current study, the discrete-element method (DEM) was used to model a simple masonry structure and evaluate the effectiveness of strengthening solutions to avoid triggering first-mode mechanisms, namely out-of-plane collapse of masonry walls. The structure was stressed by seismic ground accelerations. The unreinforced and reinforced floors were modelled with non-linear springs that reproduced their experimental hysteretic response. Parametric analyses were performed, changing the geometry of the structure and the masonry wall thickness. The comparison highlighted the effectiveness of the proposed wood-based strengthening solutions for reducing out-of-plane displacements of masonry walls, potentially matching the performance of rigid floors. [ABSTRACT FROM AUTHOR]

The effectiveness of a method to strengthen/repair unreinforced masonry (URM) by using timber-based products was investigated through experimental in situ testing. The strategy consists of timber-based panels connected to the masonry by means of screw fasteners. URM piers obtained from a century-old building were subjected to in-plane semi-cyclic quasi-static loading in as-built, repaired and retrofitted configurations. The application of the reinforcement on previously damaged piers led to a notable increase in the in-plane capacity while the initial stiffness of the repaired specimens was found to be consistent with that of the specimens tested as-built. When applied to undamaged masonry, the retrofit system allowed an in-plane force 40% higher than the capacity of the unreinforced walls, with the initial stiffness comparable with that of the repaired specimens. Both repaired and retrofitted specimens exhibited remarkable displacement capacity (drift levels > 2.0%) and energy dissipation. [ABSTRACT FROM AUTHOR]

Historic constructions are common in Europe, but natural hazards can produce significant damage. Shear reinforcement of historic walls, especially in seismic areas, is often necessary and new retrofitting methods have recently been proposed to restore or increase the lateral capacity of shear walls. In this paper the combined use of cross-laminated timber panels and steel wire ropes is proposed to reinforce rubble stone masonry walls with the aim of increasing their lateral load capacity while improving the energy performance of the building envelope. An experimental programme was carried out in the laboratory to assess the mechanical effectiveness of this retrofitting method. The results from a series of quasi-static cyclic shear tests are presented. The test programmes are described and the analysis of test results is included. The potential benefits and limitations regarding the use of the proposed combined method for reinforcing masonry structures are discussed, with an emphasis on the in-plane behaviour. [ABSTRACT FROM AUTHOR]

Historic buildings are complex structures in which all the composing elements work together. Studies of heritage structures after seismic events have shown that timber roof structures strongly influence the seismic response of masonry structures, being able to reduce or enhance the out-of-plane displacement of the structure. Starting from these observations, three different types of roof structures, from the eighteenth, nineteenth and twentieth centuries, were introduced in the finite-element simulation software SCIA Engineer. The roof structures were subsequently placed on the same eighteenth-century masonry building with a ground floor and two upper floors, respecting its geometric features. Simulations were performed considering successively rigid, hinged or sliding connections between the roof and the masonry structure. At the same time, the traditionally crafted joints of the roof structures were consecutively modelled as hinged, rigid and semi-rigid (determined using three different methods). Ultimately, the top horizontal displacement, inter-storey drift and damage level of the masonry structure were compared. The main aims of this study were to observe if roof structures have an influence on the seismic behaviour of masonry buildings and to determine if selected parameters suffer any changes depending on the roof structure type, the roof–wall connections and joints' axial stiffness. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental and numerical investigations performed on nine one-third scaled exterior beam–column joints. They were first damaged in a displacement-controlled manner with constant column axial load and reverse cyclic load at the tip of the beams. The damaged joints were then repaired with new concrete and strengthened with hybrid-fibre-reinforced polymer laminates. These had combinations of natural and glass fibre mat and chopped laminations together with eight layers of glass-fibre-reinforced polymer wrapping. The aim was to restore and enhance seismic capacity parameters such as strength, stiffness, ductility and energy dissipation. It was observed that specimens with hybrid fibre mat laminations and glass-fibre wrapping exhibited a better performance in terms of ductility, with up to 81% increase. Numerical investigations were carried out using finite-element software to validate the experimental results. It was observed that the numerical results were in good agreement. [ABSTRACT FROM AUTHOR]

The effects of masonry infill walls on the behaviour of reinforced concrete frames are often ignored in seismic engineering. A three-dimensional non-linear finite-element model is introduced in this paper to simulate in-plane and out-of-plane behaviour of masonry infilled reinforced concrete frames. It employs a surface-based cohesive contact model to capture the crack and slide failure mode of the infill wall mortar joints. Comparison with experimental data shows that the proposed numerical model provides good estimates of the strength, deformation and failure modes in both directions. Several two-way numerical tests are conducted to investigate the interaction of in-plane and out-of-plane responses. The tests include sequential out-of-plane and in-plane loading (and vice versa) as well as simultaneous application of both loadings. The results indicate that out-of-plane performance and in-plane strength are significantly decreased by the interaction of loadings in two directions. The out-of-plane loading causes the out-of-plane failure mode, which is often seen in past earthquake events, and before which the in-plane strength is not fully developed. A mathematical expression is proposed for engineering analysis. [ABSTRACT FROM AUTHOR]

The main aim of the current paper is to describe the experimental research carried out at the University of Minho, Portugal, regarding the development of an innovative reinforced brick masonry shell structural system. The concept of the system is based on the work of the engineer Eladio Dieste, and focuses on the prefabrication industry. The structural system is composed of a layer of clay bricks, reinforced concrete joints and a reinforced concrete cover layer. The constituent materials of the structural system were selected according to the necessary requirements in terms of mechanical properties and prefabrication technology. To analyse the interaction between the intervening materials, flexural, shear and biaxial tests with representative panels were carried out. To validate the developed structural system, a full scale shell was built and tested under monotonic vertical load applied at a quarter of its span. The shell performance revealed that the developed structural system is suitable for the proposed application. [ABSTRACT FROM AUTHOR]