Study on the shear and punching-shear strength of reinforced concrete slabs subjected to point loads and in-plane tensile forces

Reinforced concrete members, especially when subjected to concentrated loads, can fail in shear. This is an undesirable and brittle failure mode preventing the structure from deforming and reaching higher load levels. It is therefore important to investigate and understand the nature of shear failures in RC beams and slabs, which are typically not provided with shear reinforcement. Despite the exhaustive research work carried out since the beginning of the XXth century, the shear behavior of reinforced concrete elements is still not fully clear. The complex kinematics and the different contribution of the widely accepted shear resisting actions, which depend, among other parameters, on the load level and the geometry of the specimens, are part of those uncertainties that have provoked the lack of consensus that currently exist around the shear problem in structural engineering. In this context, this thesis focuses on the shear behavior of reinforced concrete slabs without shear reinforcement subjected to point loads. On the one hand, part of the work carried out during this investigation deals with shear in one way slabs supported on linear supports. Thanks to the experimental work conducted in the last two decades, a significant database of test results is now available, which has allowed to develop and verify a new mechanical model to predict the shear strength of RC one-way slabs without shear reinforcement. It takes into account a significant number of variables involved in the phenomenon and is applicable to is applicable to simply supported slabs, cantilever slabs and situations with partial restraint to the rotation. The model is divided into two sub-models. One for loads applied close to supports, where the direct transmission of the load to the support plays an important role in the shear strength and a second one for loads applied away from supports where the possibility of a shear failure is assumed to coexist with the possibility of a local punching failure. On the other hand, the second part of the investigation deals with the shear behavior of reinforced concrete slabs subjected to the simultaneous action of in plane tensile stresses and out-of-plane point loads. This load case has not been exhaustively studied throughout the years, and in order to contribute to gain insight into this aspects of shear design, the mechanical model recently developed at UPC for the prediction of the punching-shear strength of two-way slabs has been extended to the case of simultaneous in-plane tensile forces. A set of experimental test for the validation of the model for the particular case of uniaxial in-plane tension is also presented. In addition to that, the particular case of one-way simply supported slabs subjected to transverse tensile stresses has also been experimentally studied. This is a seldom studied load case and the conducted set of test will help to understand the overall behavior of these elements under this particular loading condition.Los elementos de hormigón armado, especialmente cuando están sometidos a la acción de cargas puntuales, pueden alcanzar su resistencia última a esfuerzo cortante, lo cual limita su capacidad para deformarse y resistir valores de carga mayores. Este es un modo de fallo frágil y repentino, por lo que debe ser evitado. Así pues, es importante seguir investigando y comprender la naturaleza de la respuesta de vigas y losas de hormigón armado ante solicitaciones de este tipo, sobre todo cuando no están provistas de armadura de cortante. A pesar de la gran cantidad de campañas experimentales llevadas a cabo desde principios del siglo XX, el comportamiento a cortante y punzonamiento de los elementos estructurales de hormigón armado no está todavía del todo claro. La compleja cinemática y la diferente contribución de los mecanismos resistentes ampliamente aceptados, la cual depende, entre otros factores, del nivel de carga y de la geometría de los especímenes, son parte de esas incertidumbres que han provocado la falta de consenso que existe actualmente dentro del campo de la ingeniería estructural. En este contexto, esta tesis se centra en el comportamiento a cortante de losas de hormigón armado sin armadura de cortante sometidas a la acción de cargas puntuales. Por un lado, parte del trabajo realizado durante esta investigación está orientado al cortante en losas unidireccionales apoyadas sobre apoyos lineales. Gracias a todas las campañas experimentales realizadas en las últimas dos décadas, una significativa base de datos de resultados experimentales se encuentra disponible en la literatura, lo que ha permitido desarrollar y verificar un nuevo modelo mecánico para predecir la resistencia última a cortante de este tipo de elementos. Dicho modelo tiene en cuenta un número importante de variables involucradas en el fenómeno y es aplicable a losas simplemente apoyadas, en ménsula, y apoyadas en apoyos con restricción parcial al giro. El modelo se ha dividido en dos sub-modelos para facilitar su desarrollo. Uno para cargas aplicadas cerca de los apoyos, donde la transmisión directa de la carga al apoyo juega un papel importante, y un segundo para cargas aplicadas lejos de los apoyos, en donde se asume que la posibilidad del fallo por cortante coexiste con la posibilidad de un fallo local por punzonamiento. Por otro lado, la segunda parte de la investigación está focalizada en el comportamiento a cortante de losas de hormigón armado sometidas simultáneamente a la acción de cargas puntuales y tracciones en su plano. Este caso de carga no ha sido demasiado investigado a lo largo de las últimas décadas, y con la intención de contribuir a comprender esta compleja interacción, el modelo mecánico recientemente desarrollado en la UPC, para la predicción de la resistencia a punzonamiento en losas bidireccionales, ha sido extendido a este caso particular de cargas y validado con los resultados de campañas experimentales disponibles en la literatura y el conjunto de ensayos realizados como parte de esta investigación para el caso particular de tracciones unidireccionales. Adicionalmente, el efecto de las tracciones transversales en el plano en la resistencia a cortante de losas unidireccionales también ha sido estudiado experimentalmente. Esta combinación de cargas no ha sido apenas investigada y un nuevo grupo de ensayos experimentales puede contribuir a comprender el comportamiento global de este tipo de elementos ante este caso particular de carga.Postprint (published version

Strategic Thinking for Sustainability: A Review of 10 Strategies for Sustainable Mobility by Bus for Cities

The sustainable mobility of the future comes about through sustainable ways of transport, such as walking, cycling, or collective transport. This includes the bus, the underground, and trains in big cities. This article reviews bus-related policies and initiatives worldwide. It also analyses ten cities looking at medium and long-term strategies for the urban bus service. The main ideas are: the forecasts for the use of the urban bus system indicate a significant increase in demand, therefore, there is a need for expanding the offered services; efforts to change the fleets towards Compressed Natural Gas and Electric vehicles; support of technological innovation for communication and accessibility; improving commercial speed and frequencies by infrastructure improvements, operation optimisation and technology; and, the link between these strategies and the air quality of cities. The transition towards a sustainable transport will happen based on the belief that the bus service is no longer the transport of the past or the present, but of the future. Document type: Articl

Evolution towards a Sustainable Public Transport in the City of Madrid

This chapter is a vision of the path followed by EMT of Madrid, during 25 years, towards the sustainability, efficiency, and contribution to the air quality in the city, starting from a diesel fleet, until getting a fleet 100% of clean vehicles, mostly GNC, which is already a reality. It shows the evolution and the use, from the practical perspective of an operator, of all the technologies available at each moment (biodiesel, bioethanol, hydrogen, electricity, natural gas, hybridization, dualisation, start-stop, catalysis, etc.) in Madrid, in a fleet of more than 2000 buses, more than 200 lines, and more than 400 million passengers per year, which makes this case an international benchmark. In addition, EMT is currently at the end of the transition to gas vehicles (CNG) and the implementation of urban electric mobility from the double perspective of the mobile material and the associated infrastructure needed, an essential case study towards sustainable public transport

Motivaciones y obstáculos en la creación de empresas : efectos de la experiencia empresarial

El objetivo de este trabajo es analizar si existen diferencias significativas en las motivaciones y obstáculos de la creación de empresas, entre aquellos emprendedores que cuando crearon su empresa tenían experiencia empresarial previa y los que no poseían experiencia empresarial. Para ello, con información obtenida de dos encuestas a los emprendedores de la Región de Murcia, hemos procedido a caracterizar esas diferencias y a evaluar su evolución entre los años 1995 y 2001, cruzando, mediante herramientas estadísticas, las variables «motivaciones» y «obstáculos », con las variables «situación laboral previa del emprendedor», «progenitores emprendedores» y «experiencia empresarial antes de los 20 años

Diversidad sectorial en las empresas de nueva creación

Este trabajo presenta en primer lugar un análisis sobre diferentes enfoques dentro de la literatura, que a través de los factores individuales y del entorno, pretenden dar explicación a la diversidad sectorial de las empresas de nueva creación; el análisis realizado en este artículo explica esta diversidad mediante el análisis conjunto de factores individuales y del entorno, y en concreto desde: la experiencia profesional previa del emprendedor, el efecto de la dinámica empresarial de las concentraciones de empresas y la red de relaciones sociales que envuelven el proceso de creación de empresas. En este sentido, hemos comprobado desde la diversidad sectorial de las nuevas empresas industriales creadas en la Región de Murcia, que los tres factores están muy relacionados a la hora de explicar la naturaleza de las nuevas empresas; por lo que consideramos fundamental que los estudios sobre el complejo proceso de creación de empresas, se realicen desde un análisis conjunto, de forma que no se deje sin explicar la interacción que se produce entre ellos.This work first deals with the analysis of different approaches proposed in the literature that aim to explain, through individual and environmental factors, the sectorial diversity of newly created firms in a given área. This was studied at this work, by means of the joint analysis of individual and environmental factors such as: the nature of the firm where the creator has gained his professional expertise, the effect of the enterprise dynamics, and the network of social relations that was involved in the process of creation. It was found through the analysis of the sectorial diversity of industrial firms recently created in the Murcia Región, that these factors interact strongly in explaining the nature of the newly created firms. It appears therefore fundamental that the study of the complex processes that drive firm creation must be carried out through the joint analysis that includes their mutual interactions

Researching on SHRM: An analysis of the debate over the role played by human resources in firm success

Many different models have been recently proposed to explain the contribution of human resource management to organizational performance, drawing on diverse theoretical frameworks and using many different methodologies. Trying to shed light on the complex state of the art in this field of research, this paper proposes an analysis of the discipline, drawing both on a review of the literature and data obtained from an online questionnaire distributed to human resource management scholars

Energy dependency at the urban scale and its social consequences

Spatial planning & energy. Young planners workshop. Final reports - conclusion

Mechanisms Involved in Treadmill Walking Improvements in Parkinson's Disease

[Abstract] Patients with Parkinson's disease (PD) improve gait after treadmill training and while they are walking over the treadmill. However, the mechanisms of these improvements have not been addressed. We designed a treadmill simulator without a belt that could move on a walkway in a constant speed, in order to explore the mechanism underlying treadmill walking improvements in PD. All subjects were tested in three different sessions (treadmill, simulatorassisted and simulatornot assisted). In each session, subjects first walked overground and then walked using the treadmill or simulator with the hands over the handrails (simulatorassisted) or with the hands free (simulatornot assisted). Step length, cadence, double support time, swing time, support time and the coefficient of variation (CV) of step time and double support time were recorded. Over the treadmill PD patients increased their step length and reduced significantly their cadence and CV of double support time in comparison with overground walking. In the simulatorassisted condition PD patients reduced significantly the CV of double support time in comparison with overground walking. With the simulatornot assisted both groups decreased their step length and increased their cadence and CV of double support time, compared with walking overground. These findings suggest that the step length improvement observed in PD patients, walking over a treadmill, is due to the proprioceptive information generated by the belt movement, since no improvement was reported when patients using a treadmill simulator.Ministerio de Ciencia e Innovación; PSI2008-03175Xunta de Galicia; 2009/00

Three-dimensional unsteady aerodynamic analysis of a rigid-framed delta kite applied to airborne wind energy

The validity of using a low-computational-cost model for the aerodynamic characterization of Airborne Wind Energy Systems was studied by benchmarking a three-dimensional Unsteady Panel Method (UnPaM) with experimental data from a flight test campaign of a two-line Rigid-Framed Delta kite. The latter, and a subsequent analysis of the experimental data, provided the evolution of the tether tensions, the full kinematic state of the kite (aerodynamic velocity and angular velocity vectors, among others), and its aerodynamic coefficients. The history of the kinematic state was used as input for UnPaM that provided a set of theoretical aerodynamic coefficients. Disparate conclusions were found when comparing the experimental and theoretical aerodynamic coefficients. For a wide range of angles of attack and sideslip angles, the agreement in the lift and lateral force coefficients was good and moderate, respectively, considering UnPaM is a potential flow tool. As expected, UnPaM predicts a much lower drag because it ignores viscous effects. The comparison of the aerodynamic torque coefficients is more delicate due to uncertainties on the experimental data. Besides fully non-stationary simulations, the lift coefficient was also studied with UnPaM by assuming quasi-steady and steady conditions. It was found that for a typical figure-of-eight trajectory there are no significant differences between unsteady and quasi-steady approaches allowing for fast simulations.This work was carried out under the framework of the GreenKite-2 project (PID2019-110146RB-I00) funded by MCIN/AEI/10.13039/501100011033

Experimental investigation of the shear strength of one-way reinforced concrete (RC) slabs subjected to concentrated loads and in-plane transverse axial tension

This paper presents the results of an experimental campaign carried out to investigate the effects of in-plane transverse tensile forces on the shear strength of linearly supported one-way reinforced concrete (RC) slabs without shear reinforcement subjected to concentrated loads. A total of 5 half scale slabs (1650¿×¿1650¿×¿120¿mm), subjected simultaneously to different levels of in-plane tensile forces and a concentrated load were tested up to failure. The clear shear span to effective depth ratio av/d was equal to 3 in all tests, to minimize the effects of the direct transmission of the load to the closest support, the so called arching action. As observed, the shear strength barely decreases with increasing values of the tensile force applied, even for values of the external force that cracked the concrete cross-section of the slabs in the direction perpendicular to the span. These observations may indicate that the shear–flexural behavior in the spanning direction is not significantly affected by the membrane forces in the transverse direction.This work has been carried out within the framework of the research project BIA-2015-64672-C4-1-R, financed by the Ministry of Economy and Competitiveness (MINECO) of Spain, and with the invaluable help of the technicians and the director of the Laboratory of Technology of Structures and Materials of the Universitat Politècnica de Catalunya. The authors want also to thank Master students Pau Figueras and Laura Beltran who collaborated in the numerical predictions and execution of the tests, respectively.Peer ReviewedPostprint (published version