JMF01: Modelling of Flexible End Plate Connections in Fire Using Cohesive Elements

JMF01: Modelling of Flexible End Plate Connections in Fire using Cohesive Elements By Ying Hu, Ian Burgess, Buick Davison Comments: This paper will repot a series of high-temperature experimental tests at the University of Sheffield focusing on the issues of tying resistance and tying ductility when simple steel connections are exposed to a fire. Numerical calibration work will be carried out. The results will be useful for many if us trying to gain knowledge in connection behaviour in fire.

The fire behaviour of steel joints remains always a sensitive topic for global stability of steel buildings. To provide a good modeling in this field is also very important for better prediction of the global behaviour of steel structures. In particular, the fact that the actual paper gives a modeling validated by fire tests will be much more convincing than a simple finite element modeling. Compares analysis with testing. Uses analyses to investigate extension of testing to cover wider range of parameters. Important topic in practice. The effect of fire on steel connections is a subject of research in several projects. The chosen combination of fire testing and expansion of the results through fem seems ok. However the fem should go further than where testing can go: provide evidence on actual failure limits and realistic collapse of structures and also on recommendations to optimise connections. JMF02: Prediction of intumescent coating performance under cone calorimeter - A mathematical approach for performance based design under different fire conditions By J F Yuan, Y C Wang, The University of Manchester, UK Comments: A method is established to predict intumescent coating behaviour under different fire conditions by modelling chemical reactions existing within the coating system under external heat. The investigation will focus on how to extract key parameters of the model for general applications from a limited number of experimental tests, and how to make use of the model in different applications. Authors are expected to present new data from the experiment and new applications based on the test results. Material testing together with reaction modelling to predict fire performance. No direct structural content. Understanding the performance of fire protection materials under different heating conditions is a critical research need. The authors have used cone-calorimeter tests, but they provide very little information on how these tests help in modelling the chemical reactions and the overall performance. The abstract is very general and does not provide any specifics regarding the work. intumescents are widely used, but their potential is still much larger; this approach gains insight in the actual behaviour and paves the way for further application. Currently intumescent materials are fully optimised for standard fire exposure. To obtain a better behaviour in real fires (i.e. a safer building), knowledge on intumescent behaviour under different heating regimes is valuable. 03 Fire Induced Thermal and Structural Response of the World Trade Center Towers. Prasad, Hamins, McAllister and Gross

Criteria 1: The approach that the authors have taken in analysing the reponse of the WTC towers structure to a complex CFD calculate heat input is indeed novel. It is however at the same time very simplistic and is really a “fall-back” solution when ones structural models fail to work because of the complexity of the fire and the nonlinearities of the structural response. It completely ignores the load redistribution that takes place when structural members lose stiffness. I would like the authors to consider how they could improve their method by including some way or redistributing loads away from weakening members.

Criteria 2: There is a great deal of interest in NIST’s work on understanding the WTC failures and this paper should certainly present original information for some people (however I am not sure it this will be very different from what is in the reports already). In my opinion this paper merits a presentation in the main international structures in fire conference just because of the subject it addresses. This paper present again calculation work done on the WTC fire. They propose a “new” way of calculation the time dependent demand-to-capacity ratio for axial forces. This new method seems to be quicker than FEM Calculation but it’s not really clear what will be proposed in this paper. The basic analysis procedure presented in this paper has been largely presented during previous SIF workshop and other conferences so no new interesting information from this paper. In addition, the coupling procedure used in this study seems to be only applicable for structures inside the fire compartment. In this case, the benefit that engineer can draw from it is very limited. Simplified computer model for use in sensitivity analyses. Uses WTC as case study for demand-to-capacity ratio analyses as done in earthquake engineering studies. 04 EFFECTS OF SPALLING ON THE FIRE RESISTANCE OF REINFORCED CONCRETE SLABS

This paper deals with the effects of spalling in a parametric way. A shortcoming is that the spalling levels will be assumed rather than predicted. The indicated outcomes of the case study make sense, and could be anticipated without a parametric study. The question to answer is how realistic the assumed spalling levels are, and how the influence of spalling on the temperature distribution is modelled. The effect of spalling on fire resistance of concrete slabs is investigated experimentally. This paper could potentially have a large effect on fire induced response of structures. The abstract is very well written and the subject matter is consistent with the goals of the conference. 05 Analytical web post buckling model for steel and composite cellular beams under fire conditions. Vassart, Bouchaïr, Muzeau and Nadjai

Criteria 1: There has been considerable work on cellular beams in the recent years and its not clear from the abstract if this is work adds considerably more value to what already in the public-domain

Criteria 2: The authors intend to present a new model which they claim improves upon those given in codes (which codes? is not specified). If this is indeed the case they may have something original to offer. Comments: The paper is expected to address the requirements for intumescent protection of beams with web openings. The investigation is largely based on numerical analysis with some experiments done on beam at ambient and elevated temperature. New results from the investigation will constitute to progress in our discipline. the research is a logical next step in further development of applicable design rules; the paper should indicate that the work provides insight in the influence of certain parameters, otherwise the simplified model has less relevance This paper addresses one of the main mechanisms which cause failure of composite cellular beams. It should be both interesting and timely (although somewhat behind the times in referring to the “20% Rule” which was abandoned a few years ago). It combines furnace testing, numerical modeling using FE software and the practical outcome of an adaptation to an established design procedure. The subject is rightly referred to as controversial, and the paper should make a worthwhile contribution to an area which is of growing commercial importance. 06 Innovative application of advanced structural fire analysis. Jowsey, Lim, Heise and Lane

Criteria 1:This paper promises a case study the fire engineered design of a tall building with a geometrically complex plan. Three separate floor plates have been analysed for severe fire attack. Its not clear how the response is different from more regular geometry models that have been analysed by many others before and how this work adds to that knowledge.

Criteria 2: The authors claim to have carried out some novel investigation on the diagrid structure of the building subjected to combined effect of wind and fire. Multi-hazards are certainly and interesting area for SiF (if not they should be!). It is unclear if this analysis is part of the single floor fire analysis or something separate. Perhaps the authors can bring out the coherence of this work in the full paper. This paper presents a really good case study of a very ambitious structure. The FEM model used seems to be very advanced. But even if this case study will show really advanced calculation procedure, the possibility for anyone else to benefit from this calculation procedure is small. The advantage of using detailed sub-models for verifying larger model output in terms of localized buckling is not really something new. It is not clear where the innovation lies in applying ABAQUS to modelling the shown structure. Nevertheless, the paper could have some (non-archival) value towards highlighting current practice and issues faced in modelling the structural fire response of iconic structures. The paper has an element of “we can do it”, but it is still useful to have the perspective of engineering practice. 07 The calculation of a beam submitted to a traveling localized fire is not really something new. A lot of European R&D projects were leaded on this subject in the scope of Fire in Car Park. Nevertheless, the followed approach looking simultaneously the heating and the cooling phase seems to be interesting. JMF07: Fundamentals of structural behaviour during a horizontally travelling fire By: Adam Ervine, Charlotte Roben, Martin Gillie Comments: This paper examines the fundamental mechanics of beams subject to horizontally travelling fires. The investigation is expected to yield interesting results showing that assuming a uniform fire may not necessarily lead to a conservative analysis. If the paper is focused on structural behaviour during a horizontally travelling fire, it would be more realistic to do it with real restraining effect but not fully restraining effect which is much more severe than reality. Moreover, it is not clear about the length of the beam to be used in such study. Nevertheless, it is a very interesting to provide such type of information to all fire engineers. Analytical study only. More detailed than related work done elsewhere. Material outlined would need more than one paper. 08 The abstract does not emphasise the new findings and novelty of this work. It seems that the main outcome relates to the influence of board separation, and the good comparison against tests that are not described. It is an interesting area, but the quality of the work is not evident from the abstract. Compares testing with simplified computer model based on heat transfer equations. This appears to be reporting on a computational model which performs thermal analysis of a timber floor, a fairly simple assembly in structural terms, and then uses the degradation of material properties caused to calculate the reduced strength and deflection of the assembly. Deformation of gypsum board is included, but the way this is modelled is not stated. The abstract is unspecific about whether any account is taken of pyrolysis of timber, but the implication is that this is not considered. 09 Fire after earthquake. Pintea, Zaharia and Dubina

Criteria 1: There are not many papers in this important area, so this paper fills an important gap. I am concerned that the authors are too concerned about what the code says about various things and perhaps not focused enough on the details of mechanics and structural behaviour. Such as how do they plan to include the damage due to the earthquake in their models? How will the fire affect the damaged material and structural members? I would like the authors to address issues such as these in the full paper.

Criteria 2: If the authors change the tone of the paper in a more scientific direction (away from codes!) then this could be a very useful, valuable and original contribution. It is really questionable how to combine the effect of earthquake and fire. It seems that the paper propose only different fire scenarios to take account of the effect of earthquake. But other questions remain fully unsolved, such as the effect of earthquake on structural stiffness and resistance. In addition, what type of structure is investigated in this paper? Computer simulation. Not clear how the earthquake and fire simulations will be coupled. Not clear how any particular level of earthquake damage will be arrived at. 10 Computational Modelling of Concrete Exposed to Fire: The Effects of Coupled Hygro-Thermal-Mechanical Behaviour on the Development of Spalling in Concrete Structures

Interesting work on a timely problem. While it is not clear whether the proposed approach has already been developed and provides good predictions of concrete spalling, the presentation of this work would be of significant value Concrete material modeling at high temperature, including the effect of spalling is an important research need. It would be useful if the authors could also develop simple models that capture the important physics based on these very detailed / complex models. Integrated modelling of hygral/thermal/mechanical behaviour is not unique so the paper should make proper reference to ongoing work elsewhere in the world. However if in this case the mechanical part of the model has reached more than a “damage model” level, this is something that has not been done before and which is very relevant for a proper prediction of spalling of concrete. 12 3-D versus 2-D modeling of high-rise steel framed building under fire This paper presents an academic case study of a multi storey building structure. The innovation in the scope of this paper will not be huge, the paper will highlight the advantages and inconvenient of using 2D or 3D models that is something already pointed out. But the scientific approach seems to be good. In case of pure steel frames, it can be expected that the 2-D frame modeling gives close results to 3-D modeling. However, it is much less clear whether the slab is taken into account or not in the modeling in this investigation. In general, it is also very logic to get quite different results between 3-D and 2-D modeling of a steel beam if the lateral effects is taken into account. It is not clear whether this abstract refers to composite or non-composite construction – although since the contribution of slabs is referred to in the context of filler beams I assume it is the former. In either case this ground has been well covered before, and I doubt that the full paper will contain any radical revelations in the SiF context. I think it is rather misleading to frame the discussion in terms of the responses of individual elements when it is now well established that 3-D interactions, including the influence of differential thermal expansions, diaphragm action and restraint conditions, are key factors in the behaviour of framed structures in fire. 13 Behavior of steel building structures under realistic fire loading. Varma, Agarwal, Hong and Prasad.

Criteria 1: Many analyses of this type have been done and its not clear what value will the authors add to the knowledge that already exists on the analysis of whole frames and load redistributions so obtained. The also mention the analysis to be using the arc length approach (Riks in ABAQUS) in their analyses. In the opinion of this reviewer this approach is not available for thermo-mechanical analyses. Perhaps the authors can check if they are really using this or the program over-rides the option.

Criteria 2: The authors seem to have run a number of cases of corner, full floor and propagating fires, which may produce new insights in behaviour if the authors are careful and meticulous in interpreting and presenting their results. This has the potential to produce original information of interest to SiF. This paper presents a case study made on a multi-storey building in Chicago. The followed approach will highlight the global redistribution in case of local failure in order to ensure the Robustness of the structure and simple design guidelines based on the overall structural behaviour will be summarized. The followed approach seems to be really interesting. Comments: This paper will present the development and verification of simple numerical models that can be used to predict the fundamental and the overall behavior of structural components (columns, beams, and floor systems) under realistic fire loading conditions (including the cooling phases) and various loading and boundary conditions. Based on the abstract, the models seem to be very comprehensive and were verified using results from standard and non-standard (characteristic) fire tests. The authors are reminded that significant progress has been made in three-dimensional frame analysis including the effect of fire. Therefore, the authors should be able to produce new results of significant important and to discuss how the use of advanced modeling can contribute to the progress in structural fire engineering. On the face of it this abstract describes work on a numerical global modelling approach for structural behaviour in fire which seems very similar to those which have been in existence in other parts of the world for some years now. I do not doubt that the work is sound, that it may contain some novel aspects, or that the validations will make a contribution to the worldwide pool of knowledge on structural modelling in fire. However it is a redevelopment rather than a radical departure from what exists. 14 Tensile membrane action on composite slab panels in fire - simple Vs. advanced models It is not the first time that the membrane effect will be highlighted using FEM and simplified models. But here, this comparison is made using a parametrical study and could highlight some interesting conclusions. The only weak point in this abstract is the absence of integrity criteria of the concrete slab. It is the basic principle that the simple calculation method shall be conservative than advanced calculation method. It is true that FEM model will predict higher fire resistance of composite floor but several questions remain to be solved, such as the cracking of concrete and the possible modification of loading condition if the deflection of the floor becomes too important. It seems that the consideration of only the aspect related to loadbearing capacity is not fully relevant for a good fire safety engineering. Comparison of two analytical method – simplified and advanced. No comparison with tests. Similar comparisons have probably been carried out before. JMF15: A very simple method for assessing tall building safety in major fires By Asif S. Usmani Comments: This is an interesting paper that will point to the direction of how tall buildings can be assessed for the risk of collapse under multiple floor fire using simplified method. Such method is of great practical value as it may not always require rigorous, labour intensive and time consuming finite element or other analyses. 15 This paper is really interesting because it highlight the effect of the slab behaviour on the column in multi-storey fire. This effect could only be quantified using FEM model and here, the author will present a simplified approach. The progressive collapse of high rise buildings is a very important feature to be considered in their fire design. If it is possible to have an efficient simple design tools to deal with the robustness of such type of buildings in case of consequent fires, it will be very useful for fire safety engineering. Therefore, the method presented in this paper could be discussed for further improvement. the authors have a promising model, ready for designers and easy to comprehend for authorities for complex situations; the approach is as how it should be: use of advanced models to generate simplified rules to be used in every day consultancy and design. The paper should clearly demonstrate that the “very simple model” gives a good prediction compared to full scale fires (tests) and advanced models. JMF16 ANALYSIS OF THE FIRE PERFORMANCE OF R.C. FRAMES The authors have performed an interesting study on RC 2D frames using the FIRES-RC2 numerical code. I do not see how the methodology is significantly different from earlier approaches. I also do not see evidence of a new physical behavior that has been discovered in this paper. I have given this paper an average grade for these reasons. the paper is addressing a well known problem, studied by many authors and the abstract should make more clear what new results can really be expected, and what this will bring the concrete industry This abstract describes a project in which the structural performance in fire of simple RC members, as determined by simplified code-of-practice procedures, is compared with their performance as part of 2-D continuous frames of 2 bays x 2 or 3 storeys. It is observed that such members have very different internal forces, including inversion of bending curvatures. None of this is surprising, and such analyses have been done for some time, although mainly in the context of steel/composite frames. Unfortunately the restraint to beams provided by columns, which is represented in such studies, tends to be only one of a number of mechanisms at work when a structural frame is subjected to fire attack and to high deformations, and it may be misleading to concentrate on the beams as if their load-carrying function remains the same as at ambient temperature. Although fire analysis of RC buildings is less developed than that of composite buildings, the interest has to be on their resistance as 3D frames including slabs rather than as 2D skeletal frames. 17 This paper will present a simple case study of a multi-storey building. It’s not the first time that such approach and methodology is followed to asses the fire behaviour of a building. JMF17: The practical application of structural fire engineering on a retail development in the UK Comments: This is one of the very few papers describes the practical application of structural fire engineering methods on real project in U.K. Finite element software will be used to analyse the behaviour of multi-storey building under various design fire scenarios in order to optimise the amount of applied passive fire protection to the structure. This paper will compare the results obtain from simpler model considering individual bays only and therefore do not consider the effects of the surrounding structure. The membrane effect with steel and concrete floor is proved by different fire tests to be extremely efficient in case of fire. The application of this concept should be promoted as wide as possible for steel buildings. Therefore, it is very important to show the real application cases of such concept in order to convince all fire engineers. This paper does not report a new physical behavior that would be useful for the SiF community nor does it provide a new method for analysis and design. It reports on application of structural engineering on a retail development. There are very few details in the abstract and it was difficult for me to figure out, what exactly was accomplished. 18 Radiative heat transfer for structural members exposed to fire. Wang and Tan

Criteria 1: The abstract presents a review of what is inadequate in the current ways of dealing with radiative heat transfer from a fire to the structure and suggests a new method for improving this.

Criteria 2: I am not confident in judging the merit or originality of the suggested improvement, however it appears a worthwhile paper from the general point of view of estimating accurate radiation heat transfer. This paper deals purely with heat transfer (ie. no structural response). The work appears to be technically challenging, but it is not clear whether the proposed approach has been validated against experiments. This paper aims to predict the radiative heat transfer from a fire to a structural member. The approach is similar to many other tools that have been developed in the past. I have given this paper a low grade since determination of the thermal environment created in the fire compartment, is not within the scope of SiF’08 which focuses on structural behavior. the abstract highlights a rather less relevant subject; the accuracy of temperature assesment for unprotected steel is sufficiently studied. 19 Analytial temperature formulations for 2d- and 3d- structural components in standard fire. Wang and Tan

Criteria 1: It is very difficult to know what new knowledge this paper brings to the field. As the authors mention, there are analytical solutions available for 1D heat conduction and also many empirical solutions. The added value may come from the way 1-D solutions are extrapolated to obtain 2D and 3D fields.

Criteria 2: The examples chosen are relative simple geometric shapes (plate, cylinder etc). I assume that these area also homogenous/isotropic bodies and have none of the complexity of say concrete or intumescent coated steel. I would recommend that authors provide some context to how this helps advance the knowledge (as it exists) and practice of structures in fire. This paper deals only with the thermal response; similar to the first paper it does not consider the structural response. I would rate slightly higher than the previous paper, since it deals with simplified analytical formulations that could have practical application, and importantly because there is an element of verification again more detailed numerical modelling. This paper develops an analytical model for predicting the thermal response of structural components under fire loading. I have given this paper a low grade since it does not fit within the scope of the SiF’08 conference. This is because determination of the thermal environment created in the fire compartment (focus of the current paper) is outside the scope of SiF’08. 20 The impact of various material models on structural fire behavior prediction

Very interesting paper which sheds light on the significance of different material models on the structural response under elevated temperature. In particular, the situations under which the transient concrete strain becomes important are highlighted. It is well know that different materials models for steel and concrete can have a large effect on structural performance. This paper quantifies these effects by evaluating various material models in a numerical model. It would be more useful, if the research could identify which material property should be measured accurately to predict the structural behaviour accurately. This abstract introduces a paper which will discuss the effects of different material models, for steel but more significantly for concrete, on the predictions of structural behaviour in fire given by numerical modeling software. This is becoming an important issue as performance-based design for fire resistance is increasingly based on 3-D modeling of large subframes. Particularly for concrete a range of constitutive models of the material behaviour exist. It is easy to assume that these are simply different expressions representing essentially the same observed behaviour, but in fact the choice of material model (particularly that for concrete transient strain) can lead to dramatically different predictions. This paper will be of interest to researchers who wish to model the structural behaviour of steel, composite and RC buildings in fire. JMF21: Mechanical characterization of fibre reinforced polymers for numerical fire endurance modelling By: E. U. Chowdhury, R. Eedson, L. A. Bisby, M. F. Green, N. Bénichou, and V.K.R. Kodur Comments: This paper presents an experimental investigation to characterize the mechanical properties of some currently available FRPs under various loading and thermal regimes ranging from ambient temperature to 600ºC. Only the experimental procedure and results of the initial mechanical testing will be presented. The authors are urged to discuss application of the test results and how they can be used for numerical modeling of FRP strengthened members so that progress can be made in the design of FRB members against fire attack. Experimental investigation to characterise temperature dependent material properties. No structural content. FRP application is steadily increasing. The insight in fire behaviour is still rather poor and can often be a limitation to the application of FRP. The abstract promises very interesting new test results, useful for model development and calibration. The work to be reported concerns experimental quantification of the mechanical stress-strain behaviour of fibre-reinforced polymers at constant elevated temperatures. From the abstract it seems as if the testing programme has not yet started, but I guess this is the authors’ risk if it is the case. No mention is made of strain-rate or the material’s sensitivity to this parameter, which I think might cause some variation of properties. This is clearly original work which is intended to lead to workable characterization of these increasingly important materials for performance- based modeling. 22 Effect of Fire Scenario and Restraint Conditions on the Behavior of RC Beams. Dwaikat and Kodur

Criteria 1: This sounds like an excellent and novel paper both from a modeling and experimental point of view and should produce considerable new knowledge and understanding on the behaviour of concrete beams in fire under realistic fire and boundary restraint conditions

Criteria 2: Should produce lots of useful and original results of use to SiF members. An interesting paper which proposes a numerical model for the response of RC beams under fire including spalling effects. Importantly, this work appears to be validated against experimental results. This paper will report on the results of a programme of numerical modeling of RC beams in fire conditions, with the results being compared to a series of tests performed by the authors using beams subjected to standard and parametric fire temperature curves. Different conditions of axial and rotational restraint are also applied. The modeling uses an interesting hydrothermal model to predict spalling, but structurally is fairly conventional. The comparisons with testing are of interest, because RC has received much less attention experimentally than steel/composite, and it will be interesting simply to understand the extent to which it is possible to tie down the characteristics of concrete so that numerical modeling is worthwhile. I am personally slightly sceptical about the practical usefulness of either testing or modelling of beams under artificially imposed restraint conditions, but as an exercise in understanding principles and in correlation with modelling this is very useful.