Fatigue behaviour of composite timber-concrete beams

Refurbishment of existing buildings often claims for strengthening and stiffening of timber floors. To avoid too heavy interventions, this need is particularly relevant in seismic zones and/or for historical buildings, not only to preserve historical value, but also to contain the masses. A solution commonly adopted is to substitute the screed with a thin reinforced concrete or lightweight reinforced concrete slab duly connected to the timber beams, in such a way that a composite timber-concrete floor is obtained, granting also a sufficient rigidity in the horizontal plane. Moreover, this solution has also the advantage to improve the acoustic performance. Of course, the behavior of the composite structure depends on the rigidity of the shear connections. Since several type of shear connectors are available, the experimental assessment of its static and fatigue behavior is a prerequisite for a suitable design of the intervention. Aiming to compare their performances, an ad hoc experimental study has been carried out on three different types of shear connectors. The fatigue tests have been performed on a composite wood-concrete beam. During each test, 15000 loading-unloading cycles have been applied, recording the deformations and the relative slip. After completion of the load cycles, static load has been applied till to collapse. In the paper, the experimental tests and results are widely discussed, also in comparison with commonly used theoretical models, and relevant conclusions are draw

influence of mechanical parameters on non linear static analysis of masonry buildings a relevant case study

Abstract In seismic zones, suitable procedures to assess the seismic vulnerability of existing buildings are necessary also in view of optimal planning of interventions. Starting from the agreement between the Municipality of Florence and the Department of Civil and Industrial Engineering of the University of Pisa, a research program is ongoing, devoted to setup a simplified, fast but reliable procedure for the evaluation of seismic performance of masonry buildings. In this paper, a simplified non-linear pushover type method for the verification of unreinforced multi-story masonry buildings with both deformable and non-deformable slabs is presented, starting from some of the basic assumptions of the POR method. Various tests on the procedure show that the method is able to give results that are comparable with those obtained by the classical pushover analysis performed on equivalent frame models. The intuitiveness of the method and the low computational effort required by the new algorithm allow the evaluation of the sensitivity of non-linear static analysis regarding the definition of mechanical parameters. In particular, the relevant influence of the modulus of elasticity as well as the ultimate inter-story displacement assumed for masonry walls on the assessment of seismic performance are discussed in detail. The results are presented for a significant case study, the Primary School "G. Carducci" in Florence, a four-story masonry building, with a horseshoe layout where lateral appendixes detached from the central block

shear modulus of masonry walls a critical review

Abstract In the assessment of seismic performance of masonry buildings, the proper definition of mechanical parameters of masonry, the shear modulus in particular, is a critical issue. Moreover, considering that existing buildings are characterized by several masonry types, depending on the material as well as on the texture, mechanical parameters can vary in a very wide range, also because they depend on many other parameters and in particular on the integrity of the walls and on the stress level. Although the in situ or laboratory experimental evaluation of the G modulus has been the subject of a wide literature concerning flat jacks, diagonal and single compression and shear-compression test results, its outcomes are often contradictory. In effect, values given by different studies often differ significantly, even for the same class of masonry. Since the intrinsic scattering of the parameter is not sufficient by itself to justify the huge variability of the results, a critical discussion of the results as well as of the individual test arrangements is necessary to make the background more reliable, also in view of better addressing further studies- A huge database has been setup combining masonry test results available in the relevant scientific literature with the test results obtained in the framework of the in situ experimental campaign carried out by the authors for the assessment of seismic vulnerability of masonry school buildings in the Municipality of Florence. The analysis of the database underlines that values of the shear modulus G, which is a fundamental parameter for the definition of capacity curve for walls commonly used in non-linear static analysis, are extremely scattered. Testing methodology and arrangement are discussed and a possible procedure is proposed to arrive to sounder estimations of relevant mechanical parameter of existing building masonry

Costruzioni in zona sismica

Nel manuale sono trattati gli argomenti di base per comprendere il comportamento delle costruzioni durante un evento sismico e sono forniti gli elementi per poter affrontare la progettazione dei nuovi edifici e degli interventi di consolidamento dell'esistente. Nel capitolo che riguarda la descrizione del fenomeno sismico, si mettono in evidenza le caratteristiche che hanno maggiore influenza sul danneggiamento delle costruzioni; vi sono riportati i risultati delle più recenti ricerche italiane, che hanno dato origine alle mappe di pericolosità sismica, su cui è basata la determinazione delle azioni sismiche di progetto. I principali argomenti riguardanti la dinamica delle strutture sono richiamati sinteticamente e sono illustrate in maniera critica le attuali metodologie per la modellazione delle azioni. Con riferimento alle più diffuse tipologie costruttive, si descrive il comportamento globale delle strutture e dei singoli elementi alle sollecitazioni sismiche e, partendo da questa base, si illustrano e si giustificano i criteri di progettazione e di proporzionamento. Nel testo vi sono ampi riferimenti alle "Norme Tecniche per le Costruzioni" di cui al D.M. 14.01.2008, con l'interpretazione delle prescrizioni in esse contenute e le indicazioni utili per la comprensione e l'applicazione. Il manuale è rivolto agli allievi ingegneri civili, ingegneri edili, architetti; inoltre, poiché la recente Normativa sulle costruzioni ha introdotto concetti e metodi di progettazione innovativi, il testo può essere utile anche per i progettisti, ingegneri ed architetti, i quali necessitano e continuamente richiedono aggiornamento in materia