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- Constitutive equation (3)
- Fire (3)
- Creep (2)
- Acoustic emission (1)
- Carbon fibre reinforced plastics CFRP (1)
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Organisationseinheit der BAM
Most of the previous studies on reinforced concrete columns with elastically restrained thermal elongation were carried out on square, rectangular or ‘+’-shaped cross sections. The fire resistance of these columns is probably more compromised than in circular columns due to the phenomenon of concrete detachment in the corners of the cross-section. In order to examine the influence of several parameters on the behaviour in fire of circular reinforced concrete columns with restrained thermal elongation, several fire resistance tests were carried out. The parameters tested were load, restraint level, slenderness of the column and the longitudinal reinforcement ratio. In the fire resistance tests the specimens were exposed to the ISO 834 Standard fire curve and the critical time and temperature and failure modes were determined. The test results mainly indicated that the spalling phenomenon may also occur in circular columns and so reducing its fire resistance. The restrained level might not so much relevant concerning the fire resistance of circular reinforced concrete columns.
The phenomenon of creep of structural steel in fire engineering is gaining more and more interest. Due to shortcomings of the EC3 constitutive model and other approaches based on classical creep theory an alternative approach mainly based on the ideas of Krempl is proposed. Due to this so-called operator approach the material as well as the constitutive model is looked upon as an operator. The application of this view serves as a guide through the analysis of the relationship between experimental facts and constitutive theory especially in the context of transient creep.
Intermediate-scale testing is indispensable when investigating the fire resistance under simultaneous compressive load of components made of glass- and carbon-fibre-reinforced composites (GFRP and CFRP). BAM is successfully operating an intermediate-scale test stand, developed for a specimen size of 500 mm x 500 mm (1000 mm). The fire resistance in terms of fire stability of CFRP and GFRP sandwiches are investigated, e.g. at 20 % of their compressive failure load at room temperature. Times to failure increase by up to a factor of 4 due to intumescent coatings. For GFRP sandwiches, different core structures with and without additional flame retardants show an astonishing impact on time to failure. CFRP shell structures are investigated on the intermediate scale with and without stringer reinforcements, resulting in completely different mechanical failure behaviour in the ultimate load test as opposed to the fire resistance test. The stringers become the only load-carrying part, while the shell acts as a protective layer. Thus the design exploiting this self-protection potential, i.e. the residue of the front skin protecting the load-bearing structure, is highlighted as a most promising route to enhance the fire resistance of lightweight materials.
Experimental and numerical study of high performance concrete columns subjected to fire loading
(2009)
Although identified on the basis of so-called instationaiy creep-tests the constifrvtive model of Eurocode 3 (EN 1993-1-2, 2010) - hereinafter refened to as EC3 - represents a non-linear rateindependent relationship between stress and meclianical strain. I.e. the experimentally observed phenomenou of creep at constant stress but linear time varying temperature is described only through the temperature dependence of the material parameters characterizing the EC3 constitutive model. As a consequence some important phenomena cannot properly be described: E.g. creep or relaxation at constant temperature, creep or relaxation at non-monotonic temperature rates or sensitivity of the instationary creep process on the temperatme rate.
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.
Originally introduced in the field of earthquake engineering hybrid testing, i.e. the simultaneous combined application of numerical simulation techniques and execution of experiments, is nowadays used in different areas of experimental analysis. The focus of this paper is on the presentation of the so-called substructuring method as a hybrid method in fire engineering. Motivation are EU standards for fire resistance tests of columns or beams. According to these codes building elements are considered as stand-alone elements whereas in real fires each building element interacts with its adjacent elements. Therefore, to conduct a fire test in a more realistic fashion, the concept of hybrid substructuring as a special experimental technique has been adopted to fire engineering. Due to this concept the entire building, which is exposed to a real fire, is decomposed into two parts. One part is represented by the building element under test in a special furnace, whereas the remaining building environment is simulated by a model, based on the equations of thermomechanics. The paper addresses the historical development of the substructuring method in fire engineering supplemented by presentation of the results of realized fire resistance tests in substructuring mode on different types of specimens.
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.
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.