Analytical models to determine in-plane damage initiation and force capacity of masonry walls with openings

Masonry panels consisting of piers and spandrels in buildings are vulnerable to in-plane actions caused by seismicity and soil subsidence. Tectonic seismicity is a safety hazard for masonry structures, whereas low-magnitude induced seismicity can be detrimental to their durability due to the accumulation of light damage. This is particularly true in the case of unreinforced masonry. Therefore, the development of models for the accurate prediction of both damage initiation and force capacity for masonry elements and structures is necessary. In this study, a method was developed based on analytical modeling for the prediction of the damage initiation mode and capacity of stand-alone masonry piers; the model was then expanded through a modular approach to masonry walls with asymmetric openings. The models account for all potential damage and failure modes for in-plane loaded walls. The stand-alone piers model is applicable to all types of masonry construction. The model for walls with openings can be applied as is to simple buildings but can also be extended to more complex structures with simple modifications. Model results were compared with numerous experimental cases and exhibited very good accuracy.Peer ReviewedPostprint (author's final draft

Experimental characterization of the axial behavior of traditional masonry wall metal tie connections in cavity walls

In recent years, the number of human-induced earthquakes in Groningen, a large gas field in the north of the Netherlands, has increased. The majority of the buildings are built by using unreinforced masonry (URM), most of which consists of cavity (i.e. two-leaf) walls, and were not designed to withstand earthquakes. Efforts to define, test and standardize the metal ties, which do play an important role, are valuable also from the wider construction industry point of view. The presented study exhibits findings on the behavior of the metal tie connections between the masonry leaves often used in Dutch construction practice, but also elsewhere around the world. An experimental campaign has been carried out at Delft University of Technology to provide a complete characterization of the axial behavior of traditional connections in cavity walls. A large number of variations was considered in this research: two embedment lengths, four pre-compression levels, two different tie geometries, and five different testing protocols, including monotonic and cyclic loading. The experimental results showed that the capacity of the connection was strongly influenced by the embedment length and the geometry of the tie, whereas the applied pre-compression and the loading rate did not have a significant influence

Numerical modelling of cavity wall metal ties

The assessment of the out-of-plane response of unreinforced masonry (URM) buildings with cavity walls has been a popular topic in regions such as Central and Northern Europe, Australia, New Zealand, China and several other countries. Cavity walls are particularly vulnerable as the out-of-plane capacity of each individual leaf is significantly smaller than the one of a solid wall. In the Netherlands, cavity walls are characterized by an inner load-bearing leaf of calcium silicate bricks, and by an outer veneer of clay bricks that has only aesthetic and insulation functions. The two leaves are typically connected by means of metallic ties. This paper utilizes the results of an experimental campaign conducted by the authors to calibrate a hysteretic model that represents the axial cyclic response of cavity wall tie connections. The proposed numerical model uses zero-length elements implemented in OpenSees with the Pinching4 constitutive model to account for the compression-tension cyclic behaviour of the ties. The numerical model is able to capture important aspects of the tie response such as the strength degradation, the unloading stiffness degradation and the pinching behaviour. The numerical modelling approach in this paper can be easily adopted by practitioner engineers who aim to model the wall ties more accurately when assessing the structures against earthquakes

Experimental results on the retrofitting of hollow brick masonry walls with reinforced high performance mortar coatings

Many masonry buildings in Europe were built after the Second World War during a booming economy when seismic risk was not properly considered and, as a consequence, seismic codes were not available yet. Several of these buildings are quite small since they are used by one or two families. Because of the huge developments in the knowledge on seismic actions, there is now a major concern for the vulnera- bility of these buildings under possible earthquakes. The present work focuses on seismic strengthening of a masonry typology widely used for social hous- ing. It is based on hollow masonry bricks with horizontal holes and poor cementitious mortar. Results of quasi-static cyclic tests carried out on full-scale unreinforced masonry walls with different geometries, representing either a shear wall or a pier-spandrel assembly, are presented. The specimens were repaired or strengthened with a thin layer of high-performance mortar reinforced with light steel-mesh. The test results show the effectiveness of the proposed technique since it provides a remarkable enhancement of both lateral strength and displacement capacity

A model for beam–column corner joints of existing RC frame subjected to cyclic loading

Beam-to-column joints are commonly considered critic regions for RC frames subjected to earthquake actions. When designed for gravity loads only, beam-to-column corner joints strongly affect the global structural behaviour of a frame, and they can be cause of its collapse, as shown by recent earthquakes in Europe. In the paper, a component-based f.e. model for external beam-to-column joints is presented to simulate the seismic behaviour of r.c. existing structures designed without any capacity design criteria (smooth bars with hooked-end anchorages and with no transverse reinforcements in the joint). The joint deformation is modelled by means of two separate contributions, the shear deformation of the panel zone, and the rotation at the interface sections between the joint and the structural members, due to the reinforcing bars' slip within the joint core. The work focuses on the evaluation of the joint strength and stiffness, and it points out the importance of modelling the bar bond slip within the panel zone to describe the actual frame response. The component-based f.e. model is validated by experimental results of tests on beam-to-column corner joints realized according to the construction practice of the 1960s-1970s in Italy, thus confirming the effectiveness of the presented model for the assessment of existing structures

A numerical model for column to foundation joint with un-bonded high strength steel bars in grouted sleeves

The present work deals with the experimental and numerical results of an innovative column to foundation connection for precast concrete elements. The joint is characterized by the use of high strength steel threaded bars in grouted sleeves to allow the bending moment to be transferred from the column to the foundation. The connecting bars are wrapped with plastic duct to allow the system to develop the lateral displacement capacity required during the seismic event. Furthermore, the un-bonded length is able to reduce the strain rate in the bar which can cause the premature fatigue failure of the steel bars. The work aims at developing a simple fem model to describe the cyclic behavior of a precast column connected to a cast in situ foundation by means the tested joint, by setting the non-linear behavior of the assembly in a non-linear spring at the base of the joint. The model accurately approximates the specimen experimental behavior

Modellazione di nodi trave-pilastro esterni di telai in cemento armato soggetti ad azioni cicliche

È ormai generalmente riconosciuto che i nodi trave-pilastro costituiscono una regione critica nelle strutture a telaio in c.a. soggette ad azioni sismiche di notevole intensità. Il comportamento del nodo influenza significativamente la risposta dell’intero sistema strutturale in termini sia di deformabilità che di resistenza, in particolare nel caso di no- di esterni di telai progettati per soli carichi gravitazionali. In questa memoria viene presentato un modello per componenti in grado di descrivere il comportamento di tale ti- pologia di nodi. Il modello permette di considerare separatamente la deformazione a taglio del nodo e le rotazioni delle sezioni di interfaccia trave-pilastro legate alla perdita di aderenza delle barre d’armatura nel nodo. Il modello proposto può costituire una semplice alternativa ai più complessi Multi Spring Models presentati in letteratura che, pur rappresentando adeguatamente il comportamento non lineare del nodo, presentano difficoltà intrinseche con- nesse alla definizione di alcuni parametri. Nella prima parte del lavoro sono presentati i metodi adottati per la stima della resistenza e della rigidezza dei nodi usati per calibrare le diverse componenti del modello. Il modello per componenti viene, infine, validato attraverso il confronto con i risultati sperimentali di una prova ciclica su un nodo esterno, presente in letteratura

A numerical model for column to foundation joint with un-bonded high strength steel bars in grouted sleeves

The present work deals with the experimental and numerical results of an innovative column to foundation connection for precast concrete elements. The joint is characterized by the use of high strength steel threaded bars in grouted sleeves to allow the bending moment to be transferred from the column to the foundation. The connecting bars are wrapped with plastic duct to allow the system to develop the lateral displacement capacity required during the seismic event. Furthermore, the un-bonded length is able to reduce the strain rate in the bar which can cause the premature fatigue failure of the steel bars. The work aims at developing a simple fem model to describe the cyclic behavior of a precast column connected to a cast in situ foundation by means the tested joint, by setting the non-linear behavior of the assembly in a non-linear spring at the base of the joint. The model accurately approximates the specimen experimental behavior