1,721,012 research outputs found
Experimental insights into the seismic behaviour of flanged URM walls
No full textConsiderable attention has been given to understanding and modelling the seismic response of unreinforced masonry piers with rectangular cross-sections. However, the seismic performance of load-bearing masonry walls with flanges, commonly found in actual building configurations, remains less explored. This study investigates the behaviour of flanged walls through cyclic quasi-static tests on four full-scale C-shaped specimens comprising two primary seismic-resistant walls (webs) interconnected by a single flange. The construction of the specimens varied: two were built using standard solid calcium-silicate bricks with general-purpose mortar, while the other two utilised large-sized calcium-silicate blocks with tongue-and-groove interlocks and a thin layer of cement-based adhesive mortar. All specimens were subjected to cyclic horizontal loading parallel to the webs under consistent overburden load and double-fixed boundary conditions. The primary variable in testing the two walls of each type was the number of cyclic loading repetitions. This paper initially describes the key characteristics of the wall specimens, including geometry, construction details, and mechanical properties. Subsequently, it details the instrumentation plan and test protocol, and summarises the major observations from the tests, illustrating damage evolution and hysteretic force-displacement response. The results highlight the effect of the flange on initial stiffness and lateral force resistance, as well as the influence of block type and loading repetitions on failure mode, displacement capacity, and energy dissipation. Additionally, the study demonstrates the impact of floor slab uplift due to in-plane rocking of the webs on the top boundary conditions and the out-of-plane stability of the flange
Torsional shear strength of unreinforced brick masonry bed joints
No full textAn experimental programme was conducted on six different batches of unreinforced masonry (URM) considering different unit-mortar combinations to study their behaviour under torsional shear. Experiments performed included a specific characterisation test to measure the torsional shear strength of URM bed joints. Dilatancy measurements during both direct and torsional shear testing of masonry were recorded. Refined finite element modelling was then performed to evaluate whether parameters evaluated from standardised direct shear tests on masonry triplets can be used to estimate the torsional shear strength of URM bed joints. A possible mechanism by which dilatancy can increase the torsional shear resistance of bed joints without affecting the external level of applied normal force is also presented. Based on both experimental and numerical findings, a rational mechanics based formula to evaluate the torsional shear strength of URM bed joints is proposed and validated. This formula represents an improvement on currently used empirical formulation correlating the torsional shear strength of a URM bed joint to their flexural tensile strength
Shake-Table Tests on an Industrial Steel Rack Isolated with Innovative Modular Devices
No full textThis paper discusses the experimental results from dynamic shake-table tests conducted at the University of Pavia and at the EUCENTRE Foundation (Pavia, Italy) on an industrial steel rack seismically isolated with innovative devices. Despite the undeniable effectiveness of common isolators in reducing seismic demands on superstructures, their application to non-structural systems can be hindered by cost, durability, and mechanical issues. To overcome these drawbacks, an innovative isolator has been patented by Kyneprox S.r.l., based on a multiple articulated quadrilateral mechanism and named “Kinematic Steel Joint (KSJ)”. This device can be manufactured from steel sheets, possibly stainless or galvanized to mitigate corrosion issues. The KSJ imposes to the superstructure a pendulum-type motion with self-centering behavior, and its modular nature allows tailoring it to different masses. Friction within pinned joints grants some energy dissipation to the device, and replaceable fuses can be added to act as brakes before reaching the maximum displacement range. KSJ devices were installed at the base of a five-shelf, two-bay industrial steel rack, isolated in the cross-aisle direction and braced in the down-aisle one. Incremental uniaxial shake-table tests were conducted in the isolated direction under three different loading scenarios. The beneficial effects of the isolators on the dynamic response of the rack are demonstrated by the elastic response spectra of the input signal imposed to its base
Expansion of mortar joints in direct shear tests of masonry samples: implications on shear strength and experimental characterization of dilatancy
No full textThe expansion of masonry specimens during direct shear tests has been reported in several research studies. This phenomenon, known as dilatancy, is caused by the formation of cracking surfaces in mortar joints. In particular, when the cracking surface is not perfectly flat, the shear displacements tend to increase the volume of the sample. Experimental investigations focused on the characterization of this phenomenon are rather limited for masonry and the effects on shear strength have received little attention, with consequent issues for a correct interpretation of the results. The present article reports the results of an ongoing research on brick masonry aimed to characterize experimentally the dilatancy and to evaluate the role of this phenomenon in the interpretation of the direct shear test. If the expansion of the specimen is significantly restrained, the standard approaches used for the characterization of the mechanical parameters (as per EN 1052-3 and ASTM C1531) tend to overestimate the initial shear strength (fvo) and underestimate friction. Moreover, no indications are generally given to characterize dilatancy with experimental data. This aspect is particularly important for the micro-modelling of masonry because the constitutive models commonly used for mortar joints require this information. One of the objectives of the present article is to propose a simple model for a sound interpretation of the direct shear test of masonry samples taking into account the dilatancy. Several masonry samples composed of calcium silicate units and cement mortar joints have been subjected to triplet tests (EN 1052-3) and laboratory-simulated shove tests. First, a repeatable and objective methodology to measure and characterize the dilatancy is provided. Then, an extension of the standard methodology of the EN 1052-3 and ASTM C1531 that includes the contribution of this phenomenon is proposed. The novel formulation offers the possibility to characterize dilatancy with experimental data and the definition of mechanical parameters that are not biased by the presence of this phenomenon. The model presented in this article has proven to be consistent with the experimental data and it has been validated numerically in another recent research study
Design procedure for a timber-based seismic retrofit applied to masonry buildings
No full textAn innovative timber retrofit was investigated at the EUCENTRE and at the University of Pavia, Italy, as part of a comprehensive research campaign on the seismic vulnerability of existing unreinforced masonry buildings subjected to induced seismicity in The Netherlands. The retrofit system consists of timber frames, connected to the masonry piers and to the floor diaphragms, and oriented-strand board sheathing nailed to the frames and to flexible timber diaphragms. Starting from the main critical aspects observed in experimental tests, the proposed solution was conceived to enhance the in-plane and out-of-plane capacities of masonry piers, improve the overall wall-to-diaphragm connections, increase the floor diaphragm stiffness and strength, and allow possible integration with energy efficiency upgrades. This paper, the first of a series of two, focuses on the conceptual bases of the seismic retrofit system and on the analytical equations that can be used for the design of its components. Moreover, a step-by-step design procedure is presented to guide the reader through the application of these equations. A companion paper [1] will discuss the validation of the analytical formulation with the experimental data from quasi-static cyclic and dynamic shake-table tests on building components and complete specimens
A comprehensive in situ and laboratory testing programme supporting seismic risk analysis of URM buildings subjected to induced earthquakes
No full textExperimental researches on the seismic behaviour of masonry spandrels: An international perspective
No full textSeismic response of unreinforced masonry buildings is strongly influenced by in-plane behaviour and damage of spandrels. In the last decade, this issue has been one of the most investigated topics in earthquake engineering research programmes dealing with masonry structures. Several working groups in different countries have focused on numerical simulation and experimental testing of spandrels, considering their variability in terms of masonry type, presence of tensile-resistant elements such as steel ties and reinforced concrete bond beams, magnitude of gravity loads, and spandrel geometry. Some research groups have also explored the role of innovative strengthening systems aimed at increasing strength and/or deformation capacity of spandrel panels above openings. This report provides a comprehensive discussion of experimental researches carried out by four research groups in Italy, Switzerland and New Zealand. In all cases, most of experimental tests were carried out on full-scale masonry specimens, either focusing on spandrel panels or addressing the pier-spandrel interaction within in-plane laterally loaded walls. More in detail, this report is asimed at reflecting and presenting the complementary nature of recent researches on spandrels. Special emphasis is given to observed damage, force–displacement behaviour and nonlinear capacity measures of spandrels. Valuable data on energy dissipation capacity and ultimate drift of spandrel panels and perforated masonry walls are also reported and discussed. In-plane overstrength and displacement ductility capacity of masonry walls with single openings are characterised through bilinear idealisation of experimental force–displacement diagrams. All testing programmes show that the geometrical and construction features of spandrels significantly influence the in-plane seismic capacity of perforated masonry walls and their repairability after cyclic loading. The latter feature is measured through the ratio of residual drift to the maximum drift of each wall specimen. Rocking behaviour of piers notably increases demand on spandrel panels, inducing the formation of plastic hinges in reinforced concrete bond beams at spandrel-pier intersections. Finally, seismic capacity of perforated walls is also found to depend on the spandrel-pier connection, highlighting the influence of boundary conditions on nonlinear behaviour of spandrel panels. The type and amount of experimental data collected in this report can support the improvement of macro-element capacity models and building codes for seismic performance assessment of masonry buildings. Several issues require further numerical and experimental investigation and are identified in each section of the report. The extension of experimental testing to full-scale perforated masonry walls with multiple storeys and openings is one of those research needs, starting from preliminary findings on half-scale specimens presented herein
Development of a dataset on the in-plane experimental response of URM piers with bricks and blocks
No full textIn this paper, a dataset collecting the results of in-plane cyclic tests on unreinforced masonry piers, carried out within different research projects, is presented. The dataset includes brick and block walls with different materials, bed-and head-joint typologies, dimensions, boundary conditions and vertical applied loads. The development of such dataset aims at providing a tool for the improvement of the understanding and the evaluation of the main parameters that may influence and govern the lateral response of the URM piers under seismic excitation. A preliminary investigation on the in-plane lateral strength and displacement capacity, being two of the most significant parameters used in seismic analyses for the design and assessment of masonry buildings, has been proposed. The dataset, that already groups several specimens, is freely shared and might be continuously updated. This source of information of consistent and reliable test results represents a necessary step into the process of definition of shared rules within the scientific and technical community, in particular for the improvement of codified criteria, analytical and numerical models and testing procedures.Applied Mechanic
Simplified methodologies for assessing the out-of-plane two-way bending seismic response of unreinforced brick masonry walls: lessons from recent experimental studies
Full text linkThis paper describes a simplified methodology for the assessment of unreinforced masonry (URM) walls under out-of-plane two-way bending seismic action. The methodology involves a force-based check derived from the principle of virtual work. This check is proposed based on experimental observations of significant cracking resistance associated with two-way spanning URM walls, indicating methodologies considering such walls to be pre-cracked or to be non-laterally supported as overly conservative. The methodology incorporates several findings and developments from recent experimental campaigns: ranging from novel characterization tests on masonry couplets to incremental dynamic tests on full-scale buildings. Such incorporations include new formulation to calculate the torsional shear strength of a bed joint and accounting for possible changes in the boundary conditions of an OOP wall during dynamic loading. Testing standards as well as recommendations in several international guidelines for masonry structures addressing the input properties required to implement the proposed methodology are enlisted and reviewed. The methodology requires the definition of the period of vibration of the assessed URM walls, to calculate which plate theory based formulation is provided. Open research questions and potential avenues for further development of the methodology are ultimately highlighted
ISO-CLASS CURVES FOR THE ASSESSMENT OF SEISMIC/ENERGY RETROFITTING OF AN EXISTING MASONRY BUILDING THROUGH A TIMBER FRAME SYSTEM
No full textIntegrated interventions aim at improving both the seismic and the energy performance of existing buildings to optimize costs, environmental impact, and social consequences. This paper introduces the concept of iso-class curves for the selection of optimal integrated interventions, which provide the values of their economic costs and environmental impacts. The method is applied to a civil building located in Central Italy and hit by the 2016 earthquake, during which it exhibited a medium-high damage level with partial collapse. The building presents some critical aspects such as low masonry quality, in-plan irregularity, slender walls, openings close to corners, absence of structural connections and poor structural details. The seismic vulnerability and the energy performance are firstly assessed in the as-built configuration; afterwards, an innovative integrated retrofit consisting in a timber frame with OSB sheathing coupled with insulating panels is considered. The enhancement of seismic and energy performance is expressed through iso-class curves. These curves are easily readable by designers and owners to select the optimum intervention for the desired seismic or energy performance upgrade
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