The Performance of Empirical Laws for Rebound Hammer Tests on Concrete Structures

The assessment of concrete compressive strength plays a key role in the analysis of the seismic vulnerability of existing buildings. However, the adoption of classical destructive tests is usually limited by their invasiveness, cost and time needed for the execution. Thus, in order to overcome these limits and allow investigations to be extended to a large number of points, the use of the rebound hammer test is investigated here with a detailed analysis of the effects on the accuracy of the strength assessment related to the choice of the conversion model relating rebound index to compressive strength. The analysis has been performed by comparing several empirical laws calibrated with data acquired in an experimental investigation of an existing concrete building. The relationships between the coefficients of the examined conversion models are then established, with the aim of reducing the unknowns in the calibration procedure. Furthermore, the influence of the coefficients of variation of concrete strength and rebound index on the results of the calibration procedure has been analyzed, thereby supporting the assessment of the accuracy of the concrete strength.This research was funded by “Studio del comportamento meccanico e del retrofitting di edifici esistenti: approcci innovativi e Life Cycle Assessment” project Politecnico di Bari FRA 2021

Grace That is Greater Than Our Sin (2): SSAA Female Voices

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FRP Confinement of Stone Samples after Real Fire Exposure

The mechanical properties of stone materials can be severely affected by exposure to high temperatures. The effect of fire on stone buildings could cause irreversible damage and make it necessary to retrofit the affected elements. Particularly, the strengthening of columns by confinement with composites has been widely improved during the last decades. Today, fiber reinforced polymer (FRP) confinement represents a very interesting alternative to traditional steel solutions. This work studied the behavior of cylindrical stone specimens subjected to real fire action and confined by means of CFRP or GFRP jackets, with the aim of assessing the effectiveness of these reinforcement systems applied to a material that has previously been seriously damaged by high temperature exposure. In general, the strengthened samples showed notable increases in strength and ductility. The response seemed to depend basically on the FRP properties and not on the degree of damage that the stone core may have suffered. Finally, the results obtained experimentally were compared with the confinement models proposed by the available design guides, in order to evaluate the accuracy that these models can offer under the different situations addressed in this research.This research was funded by the Spanish Ministry of Science, Innovation and Universities, grant number RTI2018‐101148‐B‐I00. The APC was funded by University of Alicante, grant number VIGROB 212

Experimental analysis of the loss of bond between rebars and concrete exposed to high temperatures

En el conjunto de materiales de construcción habituales en la edificación y las obras de ingeniería, el hormigón destaca entre otras razones por su excelente comportamiento frente a las altas temperaturas y la exposición al fuego. El presente estudio se centra en la adherencia residual entre el hormigón y las barras de acero corrugado soldable tras exponer probetas a altas temperaturas y enfriarlas hasta temperatura ambiente por convección natural. El estudio incluye hormigones de resistencia convencional, hormigones de alta resistencia y hormigones reforzados con fibras de polipropileno y fibras de acero. La adherencia hormigón-acero se ha medido mediante el conocido ensayo de pull-out. La campaña experimental también ha incluido la resistencia a compresión y la resistencia a tracción indirecta. Parte de las probetas se han ensayado a 28 días de edad a temperatura ambiente. A 60 días de edad se han repetido los ensayos a temperatura ambiente y se han realizado esos mismos ensayos en probetas calentadas en un horno industrial hasta tres rangos de temperatura: 450°C, 650°C y 825°C. Previo al proceso de calentamiento han sido sometidas durante 3 horas a un escalón de secado a 120°C. Mediante la metodología propuesta ha sido posible caracterizar la evolución de la pérdida de adherencia residual entre el acero y el hormigón conforme se exponen los especímenes a temperaturas más elevadas. La adición de fibras no tiene una influencia clara en la adherencia a temperatura ambiente. Sin embargo, sí se ha conseguido determinar una mejora sustancial de la adherencia residual en los hormigones, reforzados con fibras de acero sometidos a altas temperaturas.Within the context of the most usual construction materials for building and civil infrastructures, concrete stands out because of its excellent behaviour when exposed to high temperatures and fire condition. The present study focuses on the residual bond strength between concrete and steel rebars after exposure to elevated temperatures and natural cooling to room temperature. Normal strength and high strength concretes have been tested, as well as polypropylene and steel fibre reinforced concretes. The bond strength has been measured using the pull-out test. Compressive and tensile strength have also been determined. Some specimens have been tested at an age of 28 days and at room temperature. At 60 days the tests have been repeated at room temperature and after heating up to three temperature ranges: 450°C, 650°C and 825°C. Before each of the three heating phases, the specimens were pre-heated during 3 hours at 120 °C. After these experiments it has been possible to assess the loss of steel-concrete bonding for higher temperatures. The addition of fibres has no clear influence on the bonding at ambient condition. However, an improvement on the residual bonding strength has been observed for steel fibre reinforced concrete under high temperatures

Análisis por elementos finitos de losas de edificación sometidas a punzonamiento

Comunicación presentada en el VII Congreso Trienal de la Asociación Científico-Técnica del Hormigón Estructural (ACHE), A Coruña, 20-22 junio 2017.Uno de los principales problemas en las estructuras de edificación es el debido al punzonamiento en el encuentro losa-pilar. En el presente trabajo se expone un modelo numérico no lineal basado en método de los elementos finitos, y desarrollado en ABAQUS, para el análisis de la rotura por punzonamiento en losas de hormigón armado. El objeto es disponer de una herramienta de simulación que permita el estudio de forjados existentes, para la evaluación de su capacidad a punzonamiento y de un posible refuerzo. También el estudio de forjados de nueva construcción, donde se pueda optimizar la geometría y las cuantías.One of the main building structure problems is the phenomenon of punching in the slab-column connection. In this paper a nonlinear numerical model based on finite element method is exposed, and developed in ABAQUS, for the analysis of punching failure of reinforced concrete slabs. The goal is to achieve simulation tool that allows the study of existing slabs, to assess their ability to punching and a possible reinforcement. The study also concerns new constructions, where geometry and ratios can be optimized

Masonry walls strengthened with Textile Reinforced Mortars (TRM) and subjected to in-plane cyclic loads after real fire exposure

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 has been funded by the Spanish Ministry of Science, Innovation and Universities, grant number RTI2018-101148-B-I00

Textile Reinforced Mortars (TRM) tensile behavior after high temperature exposure

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.The authors would like to acknowledge Mapei Spain S.A. for the materials supplied in this work. This research has been funded by the Spanish Ministry of Science, Innovation and Universities, grant number RTI2018-101148-B-100

Shear strengthening of masonry walls with Textile Reinforced Mortars (TRM) under high temperature exposure

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.This research has been funded by the Spanish Ministry of Science, Innovation and Universities, grant number RTI2018-101148-B-100

Empleo de drones (RPAS) para la elaboración de material audiovisual docente en asignaturas de Ingeniería Civil

El presente trabajo estudia la utilización de drones telecomandados de uso comercial (RPAS) para producir material audiovisual específico de diversas asignaturas de las titulaciones de Ingeniería Civil. Se trata de un equipamiento de alta tecnología y coste relativamente asequible, en torno a 1.300 euros, para producir material audiovisual que hasta ahora únicamente podría ser obtenido empleando medios mucho más limitados (fotografías aéreas y de satélite) o mucho más costosos, tales como vuelos fotográficos específicos. De este modo, se valorará la viabilidad de introducción de una nueva herramienta tecnológica de innovación educativa hasta ahora no empleada en la elaboración de material docente, analizando sus principales ventajas y limitaciones