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The damage identification of railway bridges poses a formidable challenge given the large variability in the environmental/operational conditions that such structures are subjected to along their lifespan. Within a research project devoted to the continuous monitoring of a real in-operation bridge, the Mascarat Viaduct in Alicante (Spain), this paper investigates the potential use of strain sensors and autoregressive (AR) modelling to extract highly sensitive damage features. The viaduct, built in the beginning of the 20th century, belongs to the TRAM line 9 in the province of Alicante (Spain). The viaduct is instrumented with a dense network of strain sensors and accelerometers for monitoring the structural response under train passages. As an initial exploratory investigation, and with the aim of developing a physics-based digital twin of the viaduct, this work presents an introductory numerical assessment of the potential use of strain measurements and AR models for fast damage identification. To this aim, a finite element model (FEM) of the viaduct has been developed to simulate the dynamic response of the viaduct under moving train loads. On this basis, a two-class damage classifier (damaged or non-damaged) is developed by exploiting time series of continuously identified AR parameters. The presented results and discussion evidence the usefulness of the proposed methodology, offering an unsupervised damage detection approach with minimum computational efforts.

This work shows the preliminary results related to the evaluation of the dynamic behavior of a 5x5 m masonry cross vault after undergoing different changes in its structural behavior. It has been built using solid clay bricks and lime and sand mortar. The cross vault has been built in the laboratory specifically for carrying out these tests and evaluating its structural behavior. A device has been designed to be able to carry out a controlled settling of one of its supports without causing an instantaneous collapse of the structure. Dynamic identification using OMA was performed by installing seismic accelerometers at several selected points on the structure, using ARTEMIS software to analyze the results. The evolution of the dynamic characteristics was carried out in four different states: (i) After construction (ii) After the generation of generalized damage through the forced settlement of one of its supports. (iii) After repair using Textile Reinforced Mortars (TRM) (iv) After generating new damage by settling one of its supports in the TRM repaired structure. After the generation of the damage in the structure, important cracks are observed in various points of the structure, although no situation was reached that would foresee a possible collapse. The repair with TRM has consisted of the introduction of fiberglass mesh bands coated in lime and sand mortar. These bands have been arranged forming a cross in the upper part of the structure and in all the edge arches of the structure. In all these phases the OMA was developed under a situation of ambient vibrations, where these vibrations levels were very low due to the situation inside of a laboratory. After each of these phases, their main frequencies, their vibration modes and the structural damping factor of each of the identified modes have been obtained. It is observed how a loss of rigidity of the vault occurs after the production of damage and how it completely recovers by means of reinforcement and repair

The latest studies on failures in steel truss-type bridge found that they are highly vulnerable to damage and thus prone to potential local or total collapse. Many authors recommend monitoring the critical elements in the existing steel truss-type bridges in real time to anticipate any failures in local members. Although mechanical strain is the most frequently used variable for this purpose, this method also happens to be the most expensive monitoring strategy. This paper describes a case study of failure scenarios assessment in a steel truss-type railway bridge after extensive long-term monitoring conducted by the authors, based on measuring vertical deflections and modal frequencies. The structure has both an isostatic and a hyperstatic configuration, and was assessed by means of a combination of: (i) long-term monitoring results, and (ii) a finite element analysis to simulate several failure scenarios. A sensitivity study of the different failure scenarios has been carried out, identifying those that can be detected. The results are used to define practical recommendations for failure detection by measuring vertical deflections and modal frequencies.

Vehicular traffic represents the most influential loads on the structural integrity of railway bridges, therefore the design on dynamic criteria. This work explores the use of strain dynamic measurements to characterize the health condition of railway bridges under moving train loads. Specifically, the approach proposed in this work exploits the implementation of auto-regressive (AR) time series analysis for continuous damage detection. In this light, continuously extracted AR coefficients are used as damage-sensitive features. To automate the definition of the order of the AR model, the methodology implements a model selection approach based on the Bayesian information criterion (BIC), Akaike Information Criterion (AIC) and Mean Squared Error (MSE). In this exploratory investigation, the suitability and effectiveness of strain measurements against acceleration-based systems are appraised through a case study of a simply supported Euler-Bernoulli beam under moving loads. The moving loads problem in terms of vertical accelerations and normal strains is solved through modal decomposition in closed form. The presented numerical results and discussion evidence the effectiveness of the proposed approach, laying the basis for its implementation to real-world instrumented bridges.

A key feature that determines the seismic performance of masonry buildings is the ability of the walls to withstand in-plane cyclic loads. In this context, Textile Reinforced Mortars (TRM) have proven to be a very suitable strengthening solution, although their effectiveness after high temperature exposure is currently practically unexplored. This paper proposes an experimental campaign with full-scale brick walls and carbon fiber TRM, tested to failure under horizontal cyclic in-plane loads, after being exposed to temperatures of about 1000 °C by exposure to real fire. TRM is applied on one or both sides of the walls, and after or before exposure to fire, to simulate different scenarios that a real building could be exposed to. The results show that high temperatures can seriously compromise the integrity of the walls, while TRM can provide effective protection and prevent cracking of masonry from fire. Even after previous fire damage, the reinforcements can double the shear strength of unreinforced damaged walls, and provide high ductility and energy dissipation capacity. However, it is important to note that TRM, even undamaged, may not be able to properly retrofit a severely fire-damaged wall.

This research shows the results of an experimental campaign of masonry specimens tested until failure. The masonry is made of special voussoirs for the construction of arches and vaults. The voussoirs were made of plain concrete. The experimental campaign focused on obtaining the flexural and the compressive strength of this type of masonry specimens. Specimens were subjected to compressive loads with different eccentricities to obtain the axial load–bending moment interaction diagrams, which indicate the strength of these pieces against eccentric compression. The ultimate purpose of this research is to foresee the behavior of structural elements, such as arches and lowered vaults with a circular directrix, built using this type of voussoirs. These structural elements aim to reintroduce anti-funicular structural elements in bridges, culvert, tunnel, floor, and roof of buildings. Constructions that solve the basic needs of the population in any country. This innovative idea on a new block geometry, designed specifically for construction of arches, allows covering distances up to 6–7 m. The use of steel is not necessary; therefore, the risk of corrosion is eliminated. Finally, a study on the use of this new masonry type on the statics of arches is assessed.

This paper describes the analysis performed after the collapse of the historical EL JAUME Bell in the Cathedral of Valencia´s Micalet Bell Tower in Spain (Fig.1). When the bells were being rung during the celebration on Christmas Day 2014, a sudden collapse took place fortunately without any casualties. After several visits to the bell tower, a forensic study was carried out to determine the causes that had originated the collapse of this historical bell, which dates back to 1429. A fractographic and metallographic analysis of the steel shaft was initially carried out. This study allowed us to know the characteristics and mechanical properties. In a second phase, a fatigue damage analysis was carried out. The remaining fatigue life was estimated from the Whöler SN curves for elements subjected to rotational bending. Once this analysis was performed, it was concluded that the bell collapse was caused by fatigue damage in steel shaft, which theoretically should have been reached between 300000 and 400000 cycles. Specifically, damage propagation occurred due to an incorrect design of the steel shaft that caused a cross section with high stress concentration. Finally, the paper shows the remedial measures proposed in all the bells of the Micalet bell tower, whose steel shafts were designed under the same criteria and therefore, there was uncertainty about their remaining fatigue life.

Masonry walls exhibit low tensile strength and high material heterogeneity, which makes them especially vulnerable against accidental loadings. There are a large number of studies, both experimentally and numerically, of the masonry behaviour under accidental loadings such as earthquakes. In this regard, the most relevant research focuses on (1) evaluating the shear strength of masonry with diagonal compression tests, (2) its behavior against in-plane cyclical loadings and (3) textile reinforced mortars TRM-based reinforcement techniques. However, there are very few studies that analyse the behavior of masonry under high temperature exposure, such as those that can occur in a fire. This paper describes the preliminary results of an experimental tests in which masonry panels (reinforced with TRM and unreinforced) have been tested in diagonal compression, previously damaged by the fire exposure. For this, masonry panels were subjected to different temperature levels, up to a maximum of 600 °C using an electric oven. In general, the results show that high temperatures causes a decrease in shear strength, as well as the transverse stiffness modulus. However, the walls reinforced with TRM based on carbon fiber were the ones that presented the best performance, since their mechanical properties were reduced by a smaller percentage.

Although one of the main advantages of Textile Reinforced Mortars (TRM) is their non-combustible character, their behavior against fire or high temperatures has not been sufficiently studied at present. This work analyzes the behavior of different commercial systems containing inorganic mortars and fabric reinforcements based on glass, carbon and basalt fibers, subjected to different temperature levels. To characterize the mechanical response of the different systems, non-destructive tests have been carried out to determine the dynamic modulus of elasticity of the different materials, and subsequent destructive tests to determine their strength and stress-strain relationship. For this purpose, the TRM coupons have been subjected to uniaxial tensile tests and the deformations have been monitored using LVDT (Linear Variable Displacement Transducer) sensors and DIC (Digital Image Correlation), in order to evaluate cracking patterns and failure modes. The results show, in general terms, that the mechanical capacity of these materials is seriously compromised at temperatures in the order of 400 to 600 °C, which can easily be reached during a fire inside a building. Therefore, it can be concluded that although these systems are erroneously perceived as fire resistant in many cases, they may require additional protection depending on the specific use for which they are intended.

This study aimed to analyze the dynamic punching shear performance of slab-column joints under cyclic loads with the use of double-hooked end (5D) steel fibers. Structural systems such as slab-column joints are widely found in infrastructures. The susceptibility to collapse of such structures when submitted to seismic loads is highly dependent on the structural performance of the slab-column connections. For this reason, the punching capacity of reinforced concrete (RC) structures has been the subject of a great number of studies. Steel fibers are used to achieve a certain degree of ductility under seismic loads. In this context, 5D steel hooked fibers provide high levels of fiber anchoring, tensile strength and ductility. However, only limited research has been carried out on the performance under cyclic loads of concrete structural members containing steel fibers. This study covers this gap with experimental testing of five different full-scale subassemblies of RC slab-column joints: one without punching reinforcement, one with conventional punching reinforcement and three with 5D steel fibers. The subassemblies were tested under cyclic loading, which consisted of applying increasing lateral displacement cycles, such as in seismic situations, with a constant axial load on the column. This set of cycles was repeated for increasing axial loads on the column until failure. The results showed that 5D steel fiber subassemblies: i) had a greater capacity to dissipate energy, ii) improved punching shear strength and stiffness degradation under cyclic loads; and iii) increased cyclic loading capacity.

The behavior of masonry walls strengthened with Textile Reinforced Mortars (TRM) is a topic that has received considerable attention from researchers in recent years. However, the response of such elements after exposure to high temperature is an issue that remains to be explored extensively. This study analyzes the behavior of TRM-strengthened brick masonry panels with glass and carbon fiber meshes subjected to temperatures up to 600 °C, and subsequently tested under diagonal compression. The reinforcements were applied before or after temperature exposure, to analyze the effectiveness of damaged or undamaged TRMs, thus simulating different scenarios that might occur in a real building under a fire event. In general terms, the results showed that TRMs with carbon fibers exhibited a better response in these conditions, restoring the walls to their original capacity and providing additional ductility, whilst reinforcements with glass fibers seemed to be more affected by temperature. Finally, the experimental results are here compared to predictions from available design guides, in order to assess the accuracy that these codes would provide in these circumstances.

As structural damage or even catastrophic collapses are sometimes due to improper design, underestimated design loads or unexpectedly extreme loads, progressive collapse and structural robustness has recently received a great deal of attention, while the number of scientific papers published on the topic has grown considerably. This paper describes an analysis of the failure of a 106 m3 steel raised wine tank belonging to a local wine producer that suddenly collapsed, fortunately without personal injury, but causing significant damage to the company's facilities. The collapse generated the progressive failure of other tanks next to the first one that failed. After several visits to inspect the accident on site, a diagnosis was made to determine the causes. Possible reasons were examined by visual inspections and experimental tests on steel specimens recovered from the collapsed structures, which allowed to determine the mechanical properties and study the fracture surfaces by scanning electron microscopy and micrographs. On the other hand, the load-carrying capacities of the structure were studied by a linear-static finite-element and a nonlinear-static push-over analysis. The collapse mechanism of the system was found to be due to cyclic horizontal loads generated by a pressurized air injection system. The results allowed to conclude that this type of structure is highly vulnerable to horizontal loads and has very little capacity to activate alternative loas paths. The paper also describes a possible solution that could be used to improve the mechanical performance of this structural typology against horizontal loading, based on the lessons learned from the experience.