Seismic Analysis of Masonry Infilled R.C. Frames

Experimental tests on shaking table will be carry out at LNEC in Lisbon: three scaled r.c. buildings, one with unreinforced masonry infills and two with different types of reinforcements will be tested.
The present work focus on the implementation (with the support of the software DIANA) of strut models of the structure with unreinforced masonry infills and on the results of nonlinear static (pushover) and dynamic (time-history) analysis.

Because of the regularity in plan of the building it was possible to use two planar models, one for each main direction; beam and column have been modelled with beam element, while the infills have been substituted by diagonal struts. At the beginning the analysis have been carried out on models with infills replaced by one diagonal strut (single strut model, in according with the models proposed by Fardis M.N. [1996] and by Safina S. [2002]); then has been used a more advanced model, where infills were replaced by three diagonal struts (triple strut model, in according with the model proposed by Bergami A.V. [2008]) and is so possible to take into account also the negative effects of the interaction between the panels and the frames, like brittle failure of the columns due to shear contribute that the walls pass to them.
Firstly, both of single and triple strut models, eigenvalue analysis have been realized with the purpose to value the building modal behaviour in the two main directions.
Then, static nonlinear analysis on both types of models have been carried out and some sensitive analysis have been carried out too, with the goal to calibrate some parameters of the model and to chose be best model to be used in further analysis.
Finally, dynamic behaviour of the structure has been investigate with dynamic nonlinear analysis, just on triple strut models: artificial and recorded accelerograms (unscaled and scaled) have been used for seismic input. The time-history resulting curves have been compared with the capacity curves, the maximum displacement compared with the target displacement, and the interstorey drifts have been compared too. Some sensitive analysis have been also done to check other parameters of primary importance.
The main purpose of this thesis is to create a model that could be representative of the structure that will be tested so to forecast the results of the shaking table tests; at the same time, because of that building is representative of the typical portuguese (but also italian) constructions, the model created could also be considered a suitable tool for the structural design with respect to the European Standards.
To reach this objective different types of model have been set and different types of analysis have been run to find a model that could be as reliable as possible without being too much complex: in this direction, the possibility to use two planar model because of the plan regularity of the structure is a first good step. Then it’s of main importance to check how much are the benefits of the triple strut model: namely if the shear contribution that is taken into account is determinant for a shear failure of the columns and if the global results are so different to justify the use this model.
To carry out both static and dynamic nonlinear analysis have been useful to understand some remarkable aspects and to analyze the differences: with regarding to the determination of the target displacement on the capacity curve, could be interesting compare it with maximum displacement got by time-history curve; it’s also possible to evidence divergences or convergences on results of interstorey drift calculated in the two analysis; moreover, to study the reliability of the time-history analysis, different kind of accelerograms’ set have been used: artificial, recorded unscaled, recorded scaled. Both in static and dynamic nonlinear analysis some sensitive analysis have been carried out with the aim to calibrate parameters that are no explicitly mentioned in the codes and to check the importance of other parameters that control the accuracy of the results, so to get a good compromise between models’ precision and reliability on one side, and models’ simplicity and computational time on the other side.
The last goal of this work is to verify the safety assessments required by the Eurocodes, and so understand if the use of reinforced panels, like the ones of the other two buildings to be tested, are actually essential to a good structural design of the structures.