Parametric study of the load-bearing mechanisms in RC beam-grids to resist progressive collapse

Recently, several structural failures demonstrated the disastrous consequences of progressive collapse and raised the awareness of the engineering community. However the low probability of progressive collapse makes it uneconomical to design every building against progressive collapse using conventional design methods. Furthermore in most cases the initiating events of progressive collapses are unknown during the design. As such, consideration of secondary load-carrying mechanisms can be an effective alternative. These mechanisms include compressive arch action (CAA) and tensile catenary action (TCA) in reinforced concrete (RC) beams. Several researchers have investigated the effects of CAA and TCA experimentally and numerically in individual RC beams. However to date limited studies have been carried out to study these mechanisms in RC beam-grids. Hence in this contribution a validated numerical model is developed to study and quantify the individual contributions and development of the different mechanisms in RC beam-grids. Parametric studies are performed in relation to the influence of the aspect ratio of the grid, reinforcement ratio and ultimate reinforcement strain

Application of a multi-level probabilistic framework for the risk-based robustness assessment of a RC frame structure

Despite the increased interest and research about structural robustness, one has to notice that no practical framework is available yet to quantify and assess the robustness of structures which takes into account both local structural behavior of the elements under large deformations and the uncertainties of the acting loads and materials. In this contribution advanced calculation methods and risk-based quantification approaches for robustness are combined by a multi-level calculation scheme which is applied for two alternative designs. The developed approach is able to quantify the reliability and structural robustness of planar reinforced concrete frames in an objective way while using a conditional risk-based robustness index and taking into account the developed membrane action. Additionally the assessment and influence of the direct and indirect costs on risk-based robustness quantification are studied

Parametric study and reliability-based evaluation of alternate load path design in reinforced concrete slabs

In normal design situations, RC slabs are in general designed using small deformation theories while taking into account linear elastic behaviour. However as indicated by previous large structural failures the importance of considering the behaviour of RC slabs at large deformations is as important. Based on multiple experimental studies it is clear that RC slabs can develop alternate load paths and consequently generate a significant strength reserve by membrane action once large deformations occur due to the removal of a load-bearing element. This strength reserve is of major importance as this could result in an important increase of the structural robustness for RC buildings. In this contribution a parametric study with a numerical model is performed to investigate the design possibilities on membrane action in RC slabs. Next the reliability of the developed membrane action and alternate load path is calculated for a reference case which is subjected to the removal of a central support considering the static and pseudo-static behaviour

Tests on the application of high stength self-compacting fibre reinforced concrete in foundation elements

Traditionally industrial foundation elements are manufactured using reinforced concrete. For these elements a lot of reinforcement is necessary as these foundation elements are usually loaded by the combination of large shear forces and bending moments. Moreover, splitting and spalling reinforcement is crucial to transfer the internal stresses as very large concentrated loads are present. Due to the combination of the different reinforcement requirements the production process of these foundation elements is complex and requires a lot of time and labor. Simplification of the production process for foundation works will result in a more effective execution and de-risking of the construction schedule. Therefore, the idea was born to use self-compacting high performance fibre reinforced concrete (SCHPFRC) reinforced with traditional steel only for bending. The steel fibres will take over the functions of all other types of traditional reinforcement, i.e. shear reinforcement, transverse reinforcement, skin reinforcement, minimum reinforcement and additional reinforcement required to control crack widths. To test the capabilities and the behavior under large concentrated loads of this SCHPFRC, two extensive test series are performed at the Magnel laboratory for Concrete Research at Ghent University. The first test series consisted of the development of a mix design for the SCHSFRC, 12 CMOD tests on SCHPFRC prisms, 6 full scale loading tests on SCHPFRC beams subjected to a concentrated load to test the shear resistance and 6 full scale loading tests on SCHPFRC slabs. In the second test series additional tests are performed to confirm the findings from the first test series, to investigate the influence of the steel fibers on the anchorage length of the steel rebars and to investigate the punching resistance and the three-dimensional load-transfer of the foundation elements in more detail. Based on the outcome of the experiments the applicability of SCHPFRC is evaluated and practical design guidelines are derived

Structural reliability calculations considering concrete tensile membrane action using the probability density evolution method

Based on experimental research on a real-scale one-way reinforced concrete slab with two spans for which the internal support was removed, a numerical model in ABAQUS was developed and validated. The model is subsequently used to investigate the uncertainty of the load bearing capacity of the damaged slab considering four key random variables. Further, the probability density evolution method (PDEM) is applied for the reliability assessment. Although PDEM has in general been applied to solve dynamic reliability problems, in this contribution this method was adapted and applied to a static problem. The PDF of the load bearing capacity is calculated considering the ultimate load bearing capacity of the slab in its damaged state, i.e. the load corresponding with the rupture of the reinforcement bars at the inner support due to the developed tensile membrane action (TMA). Taking into account the obtained PDF for the capacity of the damaged system, the reliability index of the damaged slab is assessed

Reliability-Based design for robustness : evaluation of progressive collapse in concrete structures taking into account membrane action

Constructieve veiligheid en robuustheid zijn twee bijzondere aandachtspunten geworden bij het ontwerp van bouwkundige constructies. De significante gevolgen gerelateerd aan enkele catastrofale instortingen in de voorbije decennia, hebben het belang van deze aspecten dan ook in de schijnwerpers geplaatst. Bovendien kan de huidige tendens tot verregaande optimalisatie van het constructief ontwerp en de trend om het bouwproces te versnellen resulteren in een robuustheidsreductie. Om de huidige ontwerprichtlijnen kritisch te analyseren worden numerieke modellen ontwikkeld waarmee ook de ontwikkeling van alternatieve draagwegen in gewapendbetonconstructies wordt onderzocht. Aan de hand van parameterstudies wordt aangetoond dat de huidige ontwerpregels voor robuustheid niet altijd bepalend zijn voor het ontwerp en voor sommige gevallen als inadequaat kunnen worden beschouwd. Om het stochastische karakter van materiaaleigenschappen in rekening te brengen en de constructieve veiligheid van gewapendbetonelementen te evalueren worden de ontwikkelde numerieke modellen gecombineerd met de zogenaamde ‘Latin hypercube’ simulatietechniek. Verder wordt een rekenprocedure ontwikkeld om de constructieve veiligheid en robuustheid te begroten van een gewapendbetonsysteem. Hierbij worden membraanwerking en structurele interacties binnen het systeem efficiënt in rekening gebracht door het systeem op te delen en verschillende structurele idealisatie toe te passen. Tenslotte worden er praktische aanbevelingen opgesteld om het ontwerp voor robuustheid te verbeteren

Assessment of current design guidelines for vertical ties in relation to progressive collapse of RC structures

Despite the recent amount of theoretical and technological developments, structural robustness is still an issue of controversy being underlined by several structural failures in the past. Current design codes point out different strategies, among which strategies to limit damages due to the collapse of a load-bearing member by applying prescriptive design and detailing mies. For example for consequence class 2 structures EN1991-1-7 defines a risk class CC2b for which also vertical ties are required. Flowever, the background of the design values of vertical ties in current codes is not clear and their adequacy should be validated. Moreover effects such as membrane action and Vierendeel action are important to consider when assessing structural robustness and are difficult to incorporate when applying only traditional design methodologies. To this extent a set of numerical simulations have been executed in this contribution in order to verify the Progressive collapse behaviour of RC frames including the response of the vertical ties in the columns

A multilevel calculation scheme for risk-based robustness quantification of reinforced concrete frames

Structural robustness has become an important research topic in the engineering community since several large failures in the past decades led to the public awareness and indicated the importance to consider structural robustness during the structural design. So far most research has been focusing on structural measures to improve structural robustness and on theoretical methods to quantify structural robustness. However with respect to the analysis of concrete frames, there are only a limited number of examples which try to quantify the achieved robustness level for the available structural measures, such as the development of alternate load paths by membrane action. In this paper both advanced calculation methods and quantification approaches for robustness are combined by a computational efficient calculation scheme which considers different levels of structural idealisation. The developed approach is able to quantify the reliability and structural robustness of planar reinforced concrete frames in an objective way while using a conditional risk-based robustness index and taking into account the developed membrane action. As an illustration the developed calculation scheme is applied and discussed for two alternative designs of a regular office building. The results show the importance of the uncertainty on membrane action effects on the structure in case of an unforeseeable event leading to a notional column removal

Reliability-based resistance of RC element subjected to membrane action and their sensitivity to uncertainties

Reinforced concrete structures are often subjected to corrosion, inducing a decreasing reliability over time. This corrosion often exhibits spatial variation, which can be modelled by random fields. To improve the accuracy of the estimated reliability, measurements can be performed. In this work, focus will be on static strain data. Taking into account these measurements leads to updated distributions of the corrosion parameters and an updated reliability. However, modelling errors will arise due to an inadequate choice of the spatial correlation model. These are present since the perfect model is not known. By assuming an inaccurate correlation model, a bias on the distribution of the reliability index might arise. In this work, the influence of this modelling error is investigated by assuming a different correlation model in the calibration of the model and the generation of the data. Different correlation models are considered and the most robust spatial correlation model is searched for. This problem is considered first for a simply supported beam subjected to corrosion, with the aim of identifying the most robust model. Next, it is investigated whether this model also performs well for a bridge structure

Quantitative evaluation of eurocode provisions with respect to structural robustness on the basis of numerical analysis of RC beams including membrane action

Following multiple large structural failures most Western countries developed some regulations and structural guidelines to decrease the risk of progressive collapse and increase the structural robustness. For instance in Eurocode EN 1991-1-7 (2006) some prescriptive tie forces are recommended for framed structures to increase the structural integrity. However, although this is not specifically mentioned in the codes, it is of crucial importance that the structural members are able to develop considerable plastic rotations and displacements in order to fully activate these tie elements. Hence in this paper a more detailed numerical analysis is performed to assess the effectiveness of these ties and their contribution to the structural robustness in case of a RC frame taking into account the nonlinear compressive and tensile membrane action. To evaluate the effectiveness of the ties the robustness of the system is quantified in an objective way using probabilistic numerical analyses and structural reliability calculations