Innovative connections for steel-concrete-trussed beams: a patented solution

The most recent design strategies welcome the adoption of innovative techniques for seismic energy input mitigation, aiming to achieve high dissipation capacity, prevent the structure from collapse and ensure the serviceability of the construction. Friction damper devices have been widely adopted in framed steel structures for decades, while their introduction in different structural types is still under investigation. This paper presents the outcomes of innovative research supported by the industry and conducted on beam-to-column connections of RC structures in which the beams are Hybrid Steel-Trussed Concrete Beams (HSTCBs) and the columns are classical RC pillars. An innovative solution, recently patented, has been found for the mitigation of the effects of seismic cyclic actions on small-sized beam-column joints, typically characterised by a large amount of longitudinal reinforcement due to the small effective depth of the beam. This paper collects the main featuring steps of the innovative research, which has led to the patented solution. The calculation procedure for designing the proposed connection is shown, and the validation through 3D finite element modelling is described. For the structural analysis of the joint, several monotonic and cyclic simulations have been carried out with the scope of investigating different design moment values. The finite element results proved that the patented solution is effective in preventing beam, column and joint from damage and it is suitable for exhibiting adequate dissipative capacity ensured by a flexural behaviour dominated by wide and stable hysteresis loops

Experimental characterization of friction properties of materials for innovative beam-to-column dissipative connection for low-damage RC structures

Low-damage design of structures in seismic-prone areas is becoming an efficient strategy to obtain “earthquake-proof” buildings, i.e. buildings that, even in the case of severe seismic actions, experience a low or negligible amount of damage. Besides the safeguard of human lives, this design strategy aims also to limit the downtime of buildings, which represents a significant source of economic loss, and to ensure an immediate occupancy in the aftermath of an earthquake. In this context, focusing on momentresisting frames (MRFs), several solutions have been developed for the beam-to-column connections (BCCs) of steel and precast/prestressed concrete structures, but very few for cast-in-situ reinforced concrete (RC) structures. This paper focuses on a recently-proposed friction-based BCC for MRFs made with hybrid steel-trussed concrete beams (HSTCBs). The latter are made by a spatial lattice built using V-shaped rebars and a steel bottom plate, which eases the introduction of a friction dissipative device. HSTCBs are usually characterized by a small effective depth, which leads to a large amount of longitudinal rebars. The latter, together with a small-sized beam-column joint, make it potentially subjected to severe damage, which reduces its dissipative capacity. The shear force acting on the joint can be reduced by endowing the BCC with a friction device, with the aim of increasing the lever arm of the bending moment transferred between beam and joint, preventing the latter from damage. To evaluate the mechanical performance of the above connection, two experimental programs have been carried out at the Structures Laboratory of the University of Palermo. The first one focused on the characterization of the friction properties of two different materials (thermal sprayed aluminum and brass), by means of a linear dissipative device subjected to cyclic load. The second one tested a beam-to-column subassembly endowed with the recently-proposed connection in which the dissipative device was made with the best performing friction material tested before. The results of the cyclic tests are presented and commented, showing the promising performance of such connection in providing a low-damage behavior and a satisfactory dissipative capacity

Shear capacity in concrete beams reinforced by stirrups with two different inclinations

A model for the estimation of shear capacity in Reinforced Concrete (RC) beams with web reinforcement is provided by introducing a generalization of classical plastic Nielsen’s model, which is based on the variable-inclination stress-field approach. The proposed model is able to predict the shear capacity in RC beams reinforced by means of stirrups having two different inclinations and longitudinal web bars. A numerical comparison with the results of experimental tests and those provided by a Finite Element Model (FEM) based on the well known theory of Modified Compression Field Theory (MCFT) is carried out for validating the robustness of the proposed model. Finally, a set of parametrical analyses demonstrates the efficiency of the proposed double transverse-reinforcement system in enhancing the shear capacity of RC beam

Preliminary validation of an innovative stress sensor for the Structural Health Monitoring of masonry buildings

Structural Health Monitoring (SHM) of existing masonry constructions is a challenging topic widely studied by the scientific community. In this paper, the use of a low-cost Capacitive Stress Sensors (CSSs) is investigated as an effective tool for the detection of the compression state level in mortar joints of masonry structures. The study is conducted by means of Finite Element (FE) simulations aimed at reproducing the mechanical response of a prototype of innovative CSS, recently patented, subjected to compression forces typical of masonry buildings under serviceability conditions. The constitutive behaviour of the sensor is validated against the results of a pilot laboratory test on a mortar cylindrical specimen endowed with CSSs and LVDTs and then subjected to cyclic uniaxial compression. The FE model is built in order to simulate the capacitive sensor embedded within the mortar material; therefore, a correlation analysis is performed by comparing the numerical stress-strain output of the sensor and the experimental results. The validation procedure shows that the numerical results are in good agreement with the records obtained by the LVDTs. Moreover, the FE model is used for developing a parametric analysis aimed at highlighting the effects of mortar stiffness and strength on the efficacy of the SHM performed by the CSSs and the optimal serviceability configurations are accordingly identified

Experimental investigation on basalt grid cementitious mortar strips in tension

Fibre reinforced cementitious matrix (FRCM) composite materials are currently receiving great attention for strengthening reinforced concrete and masonry structures, especially when specific preservation criteria need to be fulfilled. FRCM composites can be a convenient alternative to fibre-reinforced polymers (FRP) for their better resistance to high temperature and compatibility with stone and masonry structures. In this work an experimental study for the tensile characterization of basalt reinforced cementitious matrix (BRCM) strips is presented. Strips with one, two or three layers of grid were tested in tension to study the effect of reinforcement ratio on the tensile stress-strain response of the composite strips. The basalt grid and matrix (cementitious mortar) were also tested in order to compare the mechanical properties of the constituent materials to the response of the composite. Strength, stiffness, failure modes and response stages of the composite strips are discussed in the paper

Experimental testing of two novel stress sensors for SHM of masonry structures

The paper presents an experimental study on the performance of two types of stress sensor for their possible use in structural health monitoring (SHM) of masonry constructions. Ceramic piezoelectric sensors and capacitive sensors were installed in mortar bed-joints of two series of masonry specimens made of calcarenite stones and clay bricks. The specimens were tested under uniaxial compression, assessing the effectiveness of the sensors in recording the stress state variation in terms of vertical stresses within different types of masonry. Experimental results show that, although both the ceramic and capacitive sensors were initially designed to be embedded in concrete elements, their application in mortar joints ensures a good agreement with records by standard measurement devices. Results also demonstrate the possibility to extend the application of these devices to existing masonry structures, where SHM becomes a challenging issu

General stress-strain model for concrete or masonry response under uniaxial cyclic compression

The paper proposes analytical forms able to represent with very good approximation the constitutive law experimentally deducible by means of uniaxial cyclic compressive tests on material having softening post-peak behaviour in compression and negligible tensile strength. The envelope, unloading and reloading curves characterizing the proposed model adequately approach structural responses corresponding to different levels of nonlinearity and ductility, requiring a not very high number of parameters to be calibrated experimentally. The reliability of the model is shown by comparing the results that it is able to provide with the ones analytically deduced from two reference models (one for concrete, another for masonry) available in the literature, and with experimental results obtained by the authors in the framework of a research in progress

Dalla Ricerca Nazionale Coordinata ASSOPREM: la duttilità delle sezioni delle travi PREM

Per supportare l'attività del Gruppo di Lavoro, nella redazione delle Istruzioni per Travi Prefabbricate Reticolari Miste, è emersa la necessità di eseguire una vasta campagna di prove sperimentali nel più breve tempo possibile. Assoprem si è fatta carico di questa esigenza finanziando un Progetto Nazionale Coordinato di Ricerca redatto dallo stesso GdL. Si tratta di un Progetto, del valore approssimativo di 100.000,00 €, che si snoda su 9 Centri di Ricerca Universitari ed 1 privato coordinati da un organismo nazionale