1,721,241 research outputs found
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
Application of seismic design procedures on three modern URM buildings struck by the 2012 Emilia earthquakes: inconsistencies and improvement proposals in the European codes
No full textThe seismic performance of three modern unreinforced masonry buildings struck by the earthquake sequence of May 2012 in Emilia (Italy) has been investigated, to define the safety margins and possible critical issues in the seismic design according to the European seismic codes. The selected structures have been redesigned, applying linear and static nonlinear analyses, and verified against collapse according to both Eurocodes 6 and 8 and Italian Norms for Constructions. The design has provided inconsistent results, in particular with the application of Eurocodes, where none of the three buildings fulfilled the safety checks even at very low lateral action, although two of these structures did not attain any visible damage after the events of May 2012. The requirements of the Italian seismic code have provided, at least for static nonlinear analyses, results more in line with the actual seismic response of the buildings. The main issues and some proposals for the improvement of the codified procedures for seismic design of unreinforced masonry buildings are finally discussed
A comprehensive in situ and laboratory testing programme supporting seismic risk analysis of URM buildings subjected to induced earthquakes
No full text
Minimum jerk motion planning for a prosthetic finger
No full textIn this paper we propose a method, based on both physiologic and engineering considerations, for the motion planning of a prosthetic finger. In particular, we exploit a minimum jerk approach to define the trajectory in the Cartesian space. Then, cubic splines are adopted in the joint space. The redundancy problem arising from the presence of three
links is solved by assuming that there is a constant ratio between the second and the third joint motion. The value of the proportional constant is determined by minimizing the
maximum jerk in the joint space. It is found that this constant value can be suboptimally but effectively set to one for all the movements. This approach guarantees a natural movement of the finger as well as reduced vibrations in the mechanical structure and increased control performances
Local effects on RC frames induced by AAC masonry infills through FEM simulation of in-plane tests
No full textUnreinforced masonry infills are widely used in many parts of the world and it is common practice for seismic design to use simplified methods that usually do not take into account the interaction between the infill and the structure. Starting from the 1950s, many researchers have investigated the lateral response of masonry infills focusing on several different topics. The scientific interest on masonry infills is continuously raising due to the unsatisfactory seismic response of the infilled frame structures observed during post-event inspections and to the difficulty to contrive a widely scientifically and practical recognized solution. Although some modern codes consider the presence of infills with some specifications to prevent damage in the masonry panels and global and local effects on the structure, an effective evaluation of these detrimental effects has not been achieved yet. Within this paper, a FEM simulation of in-plane pseudo-static cyclic tests on a RC frame specimen infilled with unreinforced Autoclaved Aerated Concrete (AAC) masonry infill has been performed in order to study accurately the influence and the interaction of the infill with the RC structure. The experimental results performed by Calvi and Bolognini (J Earthq Eng 5:153–185, 1999), and Penna and Calvi (Campagna sperimentale su telai in c.a. con tamponamenti in Gasbeton (AAC) con diverse soluzioni di rinforzo” (in Italian), 2006) on one-bay one-storey full scale specimens are taken as reference. Non-linear static analyses using a “meso-modelling” approach have been carried out. The masonry used in the model has been calibrated according to tests of mechanical characterization and to in-plane cyclic tests on load-bearing AAC masonry conducted by Costa et al. (J Earthq Eng 15:1–31, 2011). The analyses performed have allowed to investigate the local effects on the frame and, in particular, the changes in the moment and shear demands on the RC elements due to the presence of the AAC infill in comparison with the ones in the bare structure, and to estimate the thrust and the contact length activated by the infill on the frame
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
Innovative solution for seismic-resistant masonry infills with sliding joints: in-plane experimental performance
No full textWithin the European FP7 Project “INSYSME”, a new seismic-resistant clay masonry infill system was conceived with the purpose of controlling damage in the masonry and reducing detrimental effects of the panel-frame interaction, through a combined use of sliding joints inserted in the masonry and deformable joints at the wall-frame interface. Although the idea behind the proposed solution stems from principles already implemented in the past, the originality of this work lies in the innovative development of the materials and of the construction details of the components. In order to assess the seismic performance of this new system, in-plane cyclic tests on one-storey one-bay RC frames with two different infill configurations (one solid and one with a central opening) have been performed within the framework of a wider experimental campaign and are discussed here. These in-plane test results have proved the ability of the proposed solution in limiting the level of damage along with the attainment of a wide margin towards the life safety requirements in comparison with traditional infill systems. Although design and construction optimization of the solution still needs to be further implemented, the results of the in-plane tests appear very promising about its use as an efficient seismic resistant non-structural component in RC buildings
- …
