List of publications
Publication: Combined in-plane/out-of-plane experimental behaviour of reinforced and strengthened infill masonry walls (2016)
12th Canadian Masonry Symposium
Preparation and upload by:
Filip Anic, Faculty of Civil Engineering and Architecture Osijek, Josip Juraj Strossmayer University of Osijek
Publication abstract (click to enlarge):
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This work presents experimental test results obtained on clay unit masonry infill walls for framed structures. The main aim of the tests is characterizing the out-of-plane behaviour of infill walls made with different types of masonry, under various levels of damage caused by in-plane deformation of the frame. Tests were carried out on one-bay, real scale reinforced concrete frames, by imposing
This work presents experimental test results obtained on clay unit masonry infill walls for framed structures. The main aim of the tests is characterizing the out-of-plane behaviour of infill walls made with different types of masonry, under various levels of damage caused by in-plane deformation of the frame. Tests were carried out on one-bay, real scale reinforced concrete frames, by imposing in-plane cyclic displacements at the frame top beam until reaching pre-determined drift levels. Afterwards, the infill walls were tested out-of-plane, according to a non-standard procedure, which has been already adopted in the literature.
As proven by recent earthquakes, when infill walls in reinforced concrete frames are not properly detailed and designed, they can be a cause of extensive economic losses and also a source of danger for human lives. Hence, it is necessary to reconsider the structural role of enclosures, in order to establish reliable analysis and design procedures and to update structural codes.
AIM AND SCOPE
The focus here is not on the effects of masonry enclosures on the structural system, for which already numerous studies and some code provisions exist, but on the damage to the same enclosures and on the criteria to limit it, for which a lack of knowledge is felt.
Other aims of the experimental campaign carried out are: comparing the response of plain (non-reinforced) and reinforced or strengthened types of infill wall; and evaluating the behaviour of infill walls when they fully fill the reinforced concrete frame or when they have openings (this part of the research is not described in this paper).
DESIGN AND CONSTRUCTION OF THE TEST SPECIMENS:
One of selected construction systems for infill walls, uses masonry made of clay units with vertical holes and special recesses for vertical reinforcing bars (unit dimension 195x240x300mm in height, length, thickness respectively). In these units:
(a) two webs can be removed forming an open “C” pocket that can be used to easily cast the vertical reinforcement bars
(b) Four vertical reinforcement bars (Φ=8mm) anchored both on RC base and on the upper beam, were used. The stirrups (two Φ=6mm) used for horizontal reinforcement were placed starting from second mortar bed joint every three joints. The thickness of horizontal joints is about 10mm, while the tongue and groove units allow vertical joints to be unfilled.
Experimental tests are subdivided in two steps: in-plane test and out-of-plane test. In the first phase, after loading the columns to a constant level of axial load (400 kN each) to simulate the presence of the upper floors, an in-plane cyclic horizontal displacement is imposed at the level of the top beam. The displacement history is constituted of sinusoidal cycles, of increasing amplitudes and with peaks repeated three times for each displacement amplitude, applied with a quasi-static procedure, keeping displacement ratio always lower than 0.5 mm/s. The sequence of reference drifts corresponding to the applied top displacements is: +/-0.1%; +/-0.2%; +/-0.3%; +/-0.4%; +/-0.5%; +/-0.6%; +/-0.8%; +/-1.0%; +/-1.2%; +/-1.6%; +/-2.0%; +/-2.4%; +/-3.2%; +/-3.4% (maximum jack stroke).
After carrying out the in-plane tests, horizontal displacement is brought back to zero and, with vertical columns still axially loaded, the infill wall is monotonically loaded out-of-plane. Three level of target drift were identified to stop the in-plane test and start the out-of-plane test:
1. Drift 0.5% corresponding to damage limit state for fully filled frames (according to Italian building code);
2. Drift 1.2% corresponding to a life safety limit state for the infill wall;
3. Drift of 3.4% was reached only in the case of the bare frame, to study its behaviour in the plastic phase, even though at that level of drift the bare frame did not yet reached a displacement corresponding to the ultimate limit state.
Masonry infills tested:
URM - unreinforced masonry
RM - reinfroced masonry
USM - unstrengthen masonry (both as thin and thick wall)
SM - strengthen masonry (both as thin and thick wall)
A non-standard set-up for combined tests under in-plane cyclic and out-of-plane loads was designed and used to test four types of masonry infill walls, made with different perforated clay units and different types of reinforcements or strengthening systems. The main mechanical parameters were extracted by common tests on masonry panels (such as monotonic compression and bending tests) or on constitutive materials (such as clay units, mortars and steel reinforcement). The designed test procedure could highlight the influence of in-plane damage level on the out-of-plane behaviour of the infill walls. In particular, the out-of-plane strength of thick masonry infill walls was evaluated after the application of two levels of maximum drift under in-plane cyclic tests, corresponding to two levels of damage for the infill walls.
The thick masonry systems tested (both reinforced and unreinforced) presented high of out-of-plane strength, due to the development of an arch mechanism, even for high values of attained in-plane drift. Conversely, thin masonry systems, even when strengthened, developed a bending out-of-plane failure that somehow limits the strength of the wall, with respect to the previous failure mode. The strengthening/reinforcing techniques were demonstrated to be effective in preventing out-of plane expulsion of masonry portions. The in-plane damage mechanisms were affected by the presence of strengthening or reinforcing systems and, in particular, they tended to reduce the global damage, although it was more spread over the infill walls. On the basis of the issues discussed above, it seems that limitation of in-plane drift at 0.5%, to prevent excessive damage to non-structural elements, given by the Italian building code, is adequate for the studied thick masonry systems, but it is overestimated for thin infill walls.
RECOMMENDATIONS FOR FUTURE RESEARCH
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