Poly(vinylidene fluoride/trifluoroethylene) copolymers of different molar ratios in the range between 60:40 and 80:20 have been studied by thermally stimulated processes, namely thermally stimulated depolarization current, thermally stimulated current and differential scanning calorimetry, and by dielectric constant measurements. The results obtained show unequivocally that a ferroelectric-to-ferroelectric phase transition exists for 70:30 and 75:25 copolymers, in addition to the well-known ferroelectric-to-paraelectric transition, which has already been observed in all copolymers.

This paper aims to analyze the thermal behavior and residual mechanical properties of concrete hollow-blocks structural masonry and its component materials in fire situation using experimental investigation. Compression tests were carried out on blocks, prisms and small walls at room temperature and after being exposed for 70 minutes to the ISO 834 Standard Fire. The test at high temperatures was run using a furnace powered by natural gas and instrumented with thermocouples to measure temperatures in the specimens. The influence of the initial concrete strength on masonry behavior was evaluated considering the use of blocks with different strengths at room temperature. In addition, exposure to fire was also investigated considering masonry elements with no coverings and submitted to two different fire exposure conditions: one or both sides. The results indicate a substantial loss in the masonry load capacity at high temperatures, especially in cases of fire exposure on both sides, where the residual compressive strength resulted, on average, between 20% and 27% for the blocks and approximately 14% for prisms and small walls. Its performance with fire heating up on only one face is much higher, with an average residual masonry strength equal to 46% compared to its strength at room temperature. The obtained results are also useful for evaluating masonry regarding the integrity and thermal insulation criteria, the latter achieved with little over 60 minutes of testing.

The bare steel structural members have a low fire resistance. However, in steel and concrete composite members, the concrete encasement, besides the contribution to the stiffness of the whole system, reduces the amount of heat that reaches the steel profile, increasing the its fire resistance. The aim of this paper is to conduct a numerical study on the behavior of steel and steel and concrete composite columns in fire, in order to compare their performance based on the variation of parameters such as the stiffness of the surrounding structure, geometric imperfection and load ratio. It has been found that, in general, the intensity of the geometric imperfection and stiffness of the surrounding structure does not affect the fire resistance of steel and composite columns. However, the stiffness of the surrounding structure raised the maximum value of the restraining forces generate throughout the heating. Regarding the load ratio, when increased, the fire resistance and critical temperature decreased.

No abstract

The authors have developed a model for explaining the thermally stimulated depolarization current obtained for a ferroelectric 60:40 mol.% VDF/TrFe (vinylidene fluoride-trifluoroethylene) copolymer, combining a slow process with a fast one. Initially the polarization decays slowly due to either the thermal depolarization of dipolar units originating in the beta -phase crystallites or the variation of the pyroelectric current. Subsequently the decay is accelerated and eventually brought to an end by the ferroelectric to paraelectric transition. Results of the measurements could be fitted by a theoretical curve.

Using recycled aggregates in the production of concrete has been a viable alternative for sustainable development. Notwithstanding advanced information on this material at room temperature, its behavior when exposed to fire is still incipient. Thus, based on experimental analyses, the objective of this article is to evaluate the behavior of concrete produced with recycled aggregates for thermal insulation of steel elements, as well as to verify the physical and mechanical properties of these mixtures. For this purpose, eight prototypes, one made of steel and the others coated with different types of concrete, conventional and with recycled aggregates, were inserted in a horizontal oven and heated for 2 h. Based on experimental tests, numerical models were proposed and tested using the ABAQUS computational code, with consistent results when coherent thermal properties were adopted. The experimental results show that recycled aggregate concrete (RAC) has great thermal insulation potential and sustainable benefits, considering that the steel elements coated with this type of material, with the exception of those that underwent spalling, presented temperatures close to or below compared with concrete with natural aggregates. In this regard, it is observed that the thermal conductivity of RACs was inferior to conventional concrete, indicating that this material is a promising strategy for thermal insulation of steel structures.

No abstract

No abstract