The anchors installed inside masonry buildings play a crucial role in guaranteeing an adequate connection between horizontal and vertical elements, especially in areas subject to strong seismic actions, where a box-like behavior must be guaranteed to redistribute the horizontal forces along all the walls, minimizing the damage caused and increasing people's safety. This type of behavior is ensured when there are effective connections between vertical walls and floors; among the possible technical solutions, the use of anchors made up of steel bars embedded in holes, pre-drilled and filled with mortar or chemical adhesives is very common. In this study, the behavior of anchors installed in line, in walls (typical solution for the connection between wall and floor), and subjected to tensile forces is analyzed. The objective of the research is to evaluate the maximum load by increasing the number of anchors. The current design guideline for masonry (EOTA - TR 054) considers, in fact, only two anchors, while in the literature results can be found for up to three anchors (NTUA-Athens) with different spacing/depth ratios. Experimental tests were therefore conducted at the laboratory of the Polytechnic University of Milan on various wall samples and with groups of up to five anchors. From experimental tests conducted on bars installed with a pitch-sinking ratio of one, different behavior emerges depending on the resistance of the base material. If the wall is weak, as the number of anchors increases, a linear increase in the maximum load is observed. In walls with stronger base material, the maximum load no longer increases linearly as the number of fixings increases. To evaluate the effect of the various parameters on the behavior of the anchor group, finite element models were created using the Midas GEN software. The models validated with the experimental tests allow to investigate the factors (imperfections) that prevent the limit load of the group of n anchors from being reached, equal to n times the load of the single anchor. Finally, the expected load was evaluated for untested configurations similar to real design cases which allow the analytical formulation to also be extended to these cases, different from the test ones. The results obtained allow us to formulate a design method for in-line anchors.
Gli ancoraggi installati all’interno degli edifici in muratura svolgono un ruolo cruciale per garantire un’adeguata connessione tra elementi orizzontali e verticali, soprattutto nelle aree soggette a forti azioni sismiche, dove si deve garantire un comportamento scatolare per redistribuire le forze orizzontali lungo tutte le pareti, minimizzando i danni provocati ed incrementando la sicurezza delle persone. Questa tipologia di comportamento è assicurata quando vi sono degli efficaci collegamenti tra pareti verticali e solai; tra le possibili soluzioni tecniche, molto comune è l’uso di ancoraggi costituiti da barre di acciaio annegate in fori, preforati e riempiti di malta o adesivi chimici. Nel presente studio si analizza il comportamento degli ancoraggi installati in linea, nelle murature (soluzione tipica per la connessione tra muro e solaio), e soggetti a forze di trazione. L’obiettivo della ricerca è quello di valutare il carico massimo incrementando il numero di ancoraggi. L’attuale linea guida di progettazione per murature (EOTA - TR 054) considera, infatti, solo due ancoraggi, mentre in letteratura si trovano risultati fino a tre ancoraggi (NTUA-Atene) con diversi rapporti di spaziatura/profondità. Si sono, pertanto, condotte delle prove sperimentali, presso il laboratorio del Politecnico di Milano, su diversi campioni di pareti e con gruppi fino a cinque ancoraggi. Dalle prove sperimentali condotte su barre installate con rapporto passo-affondamento pari a uno, emerge un comportamento differente a seconda della resistenza del materiale di base. Se la parete è debole, all’aumentare del numero di ancoraggi si osserva un aumento lineare del carico massimo. In pareti con materiale di base più resistente, il carico massimo non cresce più linearmente all’aumentare del numero dei fissaggi. Per valutare l’effetto dei vari parametri sul comportamento del gruppo di ancoraggi si sono realizzati dei modelli ad elementi finiti tramite il software di calcolo Midas GEN. I modelli validati con le prove sperimentali hanno consentito di indagare i fattori (imperfezioni) che impediscono il raggiungimento del carico limite del gruppo di n ancoraggi, pari a n volte il carico del singolo ancoraggio. Infine, è stato valutato il carico previsto per configurazioni non testate e assimilabili ai casi reali di progettazione che consentano di estendere la formulazione analitica anche a queste casistiche, differenti da quelle di prova. I risultati ottenuti consentono di formulare un metodo di progettazione per ancoraggi in linea.
Analisi del comportamento di ancoraggi in linea post-installati in murature
Maroni, Giorgia;Locatelli, Andrea
2022/2023
Abstract
The anchors installed inside masonry buildings play a crucial role in guaranteeing an adequate connection between horizontal and vertical elements, especially in areas subject to strong seismic actions, where a box-like behavior must be guaranteed to redistribute the horizontal forces along all the walls, minimizing the damage caused and increasing people's safety. This type of behavior is ensured when there are effective connections between vertical walls and floors; among the possible technical solutions, the use of anchors made up of steel bars embedded in holes, pre-drilled and filled with mortar or chemical adhesives is very common. In this study, the behavior of anchors installed in line, in walls (typical solution for the connection between wall and floor), and subjected to tensile forces is analyzed. The objective of the research is to evaluate the maximum load by increasing the number of anchors. The current design guideline for masonry (EOTA - TR 054) considers, in fact, only two anchors, while in the literature results can be found for up to three anchors (NTUA-Athens) with different spacing/depth ratios. Experimental tests were therefore conducted at the laboratory of the Polytechnic University of Milan on various wall samples and with groups of up to five anchors. From experimental tests conducted on bars installed with a pitch-sinking ratio of one, different behavior emerges depending on the resistance of the base material. If the wall is weak, as the number of anchors increases, a linear increase in the maximum load is observed. In walls with stronger base material, the maximum load no longer increases linearly as the number of fixings increases. To evaluate the effect of the various parameters on the behavior of the anchor group, finite element models were created using the Midas GEN software. The models validated with the experimental tests allow to investigate the factors (imperfections) that prevent the limit load of the group of n anchors from being reached, equal to n times the load of the single anchor. Finally, the expected load was evaluated for untested configurations similar to real design cases which allow the analytical formulation to also be extended to these cases, different from the test ones. The results obtained allow us to formulate a design method for in-line anchors.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/218296