Modelling of spandrel elements in URM structures with RC slabs or ring beams

In many unreinforced masonry (URM) buildings reinforced concrete (RC) slabs or ring beams maintain the integrity of the building when subjected to seismic loading and redistribute forces between different URM piers. In addition, RC slabs and ring beams contribute to the global stiffness and overturning capacity of the building by acting as horizontal coupling elements between URM piers. This paper reviews current design approaches concerning the consideration of the contribution of RC slabs and ring beams to the global overturning capacity of buildings with URM piers. Numerical simulations of composite spandrels consisting of RC beam and URM spandrel are performed and the results are compared with experimental evidence from own full-scale tests on composite spandrels. Finally, different wall configurations of URM buildings with RC slabs are analysed and conclusions concerning the design and analysis of such buildings drawn.

Seismic Behaviour and Design of Mixed RC-URM Wall Structures

Alessandro Paparo

In several countries of central Europe, many modern residential buildings are braced by reinforced concrete (RC) and unreinforced masonry (URM) walls coupled with RC slabs. Such mixed constructions, in fact, behave better under seismic loading than buildings with URM walls alone. Similarly, the insertion of RC walls is a technique used to retrofit existing modern URM constructions that feature RC slabs, since both strength and displacement capacities of the repaired structure increase with respect to the un-retrofitted configuration. Although modern mixed RC-URM wall buildings are rather common, very little is known about their seismic behaviour and codes do not provide adequate design and assessment guidelines. Hence, the thesis focuses on four objectives: (1) to provide experimental data on the seismic behaviour of mixed RC-URM wall structures; (2) to formulate recommendations for setting up numerical models for structures with both RC and URM walls; (3) to develop a mechanical model that represents the interaction between RC and URM walls; (4) to propose a displacement-based seismic approach for the design of new mixed RC-URM wall structures and the retrofitting of URM wall buildings by adding RC walls or replacing URM walls with RC ones. An experimental investigation of two mixed RC-URM wall substructures leads to new findings with respect to the actual distribution of the reaction forces between RC and URM walls and gives insight into the displacement profile of mixed RC-URM wall structures. The results are used to validate two numerical strategies and recommendations for setting up models for structures with both RC and URM walls are formulated. A simple mechanical model, which takes into account the most important parameters influencing the seismic behaviour of mixed RC-URM wall structures, is proposed and validated. The model is based on the shear-flexure interaction as URM and RC walls display dominant shear and flexural deformations, respectively. In the last part of the thesis a displacement-based design approach for mixed RC-URM wall structures is developed. The design method is verified through inelastic time-history analyses (ITHA) of three-to-five-storey case study buildings. Comparison between the design values and the results from ITHA suggests that the design methodology controls the horizontal deflection of the structures, being almost linear over their height, and avoids concentrations of deformations in the bottom storey, a typical feature of URM wall structures. On the other hand, for the three-storey configurations, it was observed that the approach overestimates the maximum horizontal displacement.

EPFL2015

Experimental investigation of the cyclic behaviour of unreinforced masonry spandrels

Katrin Beyer, Alessandro Dazio

In unreinforced masonry (URM) walls the vertical piers are connected by horizontal spandrel elements. Numerical simulations have shown that spandrels influence significantly the global wall behaviour under seismic loading. Despite their importance, experimental data on the cyclic behaviour of these spandrels is very scarce. The lack of experimental data prevented in the past the validation of numerical and mechanical models regarding the cyclic behaviour of masonry spandrels. For this reason a research program was initiated in which the cyclic behaviour of masonry spandrels was investigated experimentally and numerically. Within this program different configurations of masonry spandrels were tested under quasi-static monotonic and cyclic loading. The spandrel configurations that were investigated included pure masonry spandrels and masonry spandrels which also comprise a reinforced concrete (RC) beam or slab. The latter represents spandrels in newer masonry buildings with RC slabs or RC ring beams while the former can be found in older masonry buildings. This paper presents preliminary results of the experimental program as well as some selected results of the accompanying numerical study.

2010

Experimental investigation of the effect of the longitudinal reinforcement content of ring beams on the cyclic behavior of masonry spandrels

Katrin Beyer, Alessandro Dazio

In many unreinforced masonry (URM) buildings reinforced concrete (RC) ring beams are introduced at each storey in order to maintain the integrity of the building when subjected to seismic loading. Such ring beams also contribute to the in-plane resistance of URM walls consisting of vertical piers connected by ring beams and often also by horizontal URM spandrels. The entity of the RC ring beam and the URM spandrel is in the following referred to as composite spandrel. Although numerical simulations have shown that composite spandrels have a significant influence on the seismic behavior of URM walls, their contribution has often been neglected since vital experimental evidence on the cyclic behavior of spandrel beams was lacking. The paper discusses important phenomena affecting the cyclic force-deformation behavior observed during full-scale quasi-static cyclic tests on composite spandrels. In particular the effect of the longitudinal reinforcement content of the RC ring beam on the interaction between URM spandrel and RC ring beam as well as on stiffness, strength and deformation capacity of the composite spandrel are discussed. Based on the test results first recommendations concerning the design and analysis of RC ring beams in URM structures are presented.

2011

Seismic Behaviour and Design of Mixed RC-URM Wall Structures

Alessandro Paparo

EPFL2015