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In this paper, a nonlinear three-dimensional finite element (FE) model was developed and validated to study the effect of seismic damage location on the response of concrete filled tube (CFT) columns at fire after earthquakes. Three analyses were conducted consecutively in the modelling, namely, cyclic, thermal and structural. Results of the cyclic loading analysis comprising residual deformations were applied as the Initial condition to the thermal-stress model, replicating the seismic performance of column.
Following, a nonlinear sequentially coupled-thermal stress Analysis was carried out to investigate the fire response of CFT columns after the seismic event. Three damage scenarios were contemplated, considering any possible potential damages that could be generated by the earthquake loading on CFT columns. The accuracy of the proposed FE model was examined by comparing the numerical results with that of available tests on fire and cyclic loading. By means of the validated model, the performance of damaged CFT columns was then investigated under fire after earthquakes. The level of damage was assumed as a high damage level, presuming that the column reached 50% of ist lateral resistance while still maintaining its overall stability after the earthquake. The results were presented broadly, including the axial deformation history as well as the fire resistance time for CFT columns. To have a comprehensive insight on the influence of damage location in columns, the fire response of damaged specimens was compared with that of an intact one.
The EQUFIRE project aims to study the post-earthquake fire Performance of steel frame structures and is part of the Transnational Access activities of the SERA project (www.sera-eu.org) at the ELSA Reaction Wall of the European Commission - Joint Research Centre. As it has happened in many historical occasions, after an earthquake, earthquakeinduced rupture of gas piping, failure of electrical systems, etc. may trigger fire. The structural fire performance can deteriorate because the fire acts on a previously damaged structure. In addition, the earthquake may have damaged fire protection elements and the fire can spread more rapidly if compartmentation walls have failed. This is particularly relevant for steel structures as the high thermal conductivity of elements with small thickness entails quick temperature rise with consequent fast loss of strength and stiffness.
EQUFIRE studied a four-storey three-bay steel frame with concentric bracings in the central bay. The structure was designed for reference peak ground acceleration equal to 0.186g, soil type B and type 1 elastic response spectrum according to Eurocode 8. Tests were performed at the ELSA Reaction Wall and at the furnace of the Federal Institute for Materials Research and Testing (BAM).
The experimental activities at the ELSA Reaction Wall comprise pseudo-dynamic tests on a full-scale specimen of the first storey of the building, while the upper three storeys are numerically simulated. The aim is to study the response of the structure and fire protection elements, including their interaction, under the design earthquake and for different configurations: bare frame without fire protection, specimen with three fire protection solutions (conventional and seismic-resistant boards, and vermiculite sprayed coating) applied on the bracing and one column, and with conventional and seismic-resistant fire barrier walls built in the two external bays of the specimen. The testing programme at BAM included fire tests of five columns (two specimens without fire protection elements and three specimens with the types of fire protection mentioned above). Before the fire test, each column was subjected to a horizontal and vertical displacement history resulting from the seismic action. During the fire tests, the effect of the surrounding structure was simulated by limiting the axial thermal expansion.
The experimental results will serve to study the response of structural and non-structural components to fire following earthquake scenarios, with a view to improving existing design guidelines and future standards.
High-throughput fire tests and weathering-induced degradation behaviour of intumescent coatings
(2018)
In this work, the weathering-induced degradation of intumescent coatings was investigated by a systematic and comprehensive approach. A mechanism is revealed that is proposed to be responsible for the loss of function of intumescent coatings induced by weathering.
First, the thermal decomposition of artificially weathered intumescent coatings was examined. To get a better understanding of the weathering and ageing phenomena, the degradation behaviour of the single ingredients during the weathering process was investigated, as well as their chemical and physical interactions. For the systematic approach, the materials that are essential for intumescence (ammonium polyphosphate, pentaerythritol, titanium dioxide, melamine and the binder) are treated with moisture, elevated temperature and UV radiation.
Thermogravimetry (TG) and IR spectroscopy were used to compare the initial samples with their different grades of weathering. We demonstrate that ammonium polyphosphate, melamine and the binder are mainly responsible for the ageing process. Further, it was demonstrated that TG and IR spectroscopy are suitable measuring methods to detect the effects of weathering on intumescent coatings.
Finally, a small-scale fire test procedure is introduced. Based on the reduction of the sample size, up to 50 samples can be tested in a single fire test. The results of this fire test have the same quality as the results from standard intermediate fire tests corresponding to DIN 4102-8.