In this investigation the effect of the incorporation of additives in the mechanical properties of LLDPE films, made to be used as greenhouse covers, was analyzed. All films were fabricated by the method of extrusion blow. Two types of formulations are raised in order to determine the influence of the concentration of one additive and identify the existence of some synergy by combining active ingredients in the formulations. Modulus of elasticity, yield stress and tear resistance of the films were evaluated. The results indicate that variation in the concentration of an additive in the mixture does not generate significant changes in the physical-mechanical properties of the films. However, the incorporation of the UV light absorber and Smartlight photoselector in formulations favors their mechanical properties. Compared with the reference film, an increase higher than 200% in modulus of elasticity and yield stress of the films was determined.

Actualmente la modelación estructural se centra en el análisis de estructuras convencionales como pórticos y armaduras. A pesar de la existencia de métodos para el análisis de estructuras más complejas, hay una tendencia a modelar los mismos tipos de estructuras. El método de los elementos finitos y su implementación por medio de aplicaciones computacionales, permite modelar todo tipo de estructura, hasta aquellas en las que aun no se tienen claros los diferentes comportamientos que se generan frente a diferentes tipos de solicitaciones; algunas de estas estructuras son las ménsulas, las zapatas sobre pilotes, los cascarones y las conexiones de concreto. Los programas especializados en la modelación por medio del método de los elementos finitos, interpretan el comportamiento de las estructuras de una forma gráfica, en donde se pueden discutir las diferentes zonas críticas y proporcionar resultados más aproximados debido al buen manejo de fronteras. Este método se basa en la conversión de las ecuaciones de equilibrio a sistemas lineales o no lineales para llegar a la solución de un análisis tanto estático como dinámico. A partir de la utilización de un programa especializado, en este caso Ansys Civilfem, se reconoce que el método de los elementos finitos proporciona la mayor aproximación del comportamiento de una estructura bajo condiciones reales, facilitando la búsqueda de las falencias y también de las formas y diseños óptimos con los cuales se puede mejorar su desempeño.

The strut-and-tie method (S-T) is a practical tool for the seismic design of reinforced concrete elements. Experimental and analytical research with low-rise concrete walls was carried out for assessing the S-T method proposed by the current ACI-318 building code. Four specimens designed to fail during shear and shaking table tests were included in the experimental programme. The variables studied consisted of the type of concrete (normal and cellular weight), the amount of steel web (0.125% and 0.25%) and the type of web reinforcement against shear (corrugated bars and welded wire mesh). Wall properties were typical of low-rise housing in Mexico. When the calculated shear strength was compared with the measured one it was found that the S-T method proposed by the ACI-318 building code suitably estimated the shear capacity of the models being studied. However, the walls shear failure mode, loading rate, the number of cycles and the cumulative energy dissipated would noticeably affect the degradation in strength of low-rise, reinforced concrete walls.