Ana Blanco

Application of constitutive models in European codes to RC-FRC

Abstract The recent publication of codes for the design of FRC is a major step towards extending the use of the material. An in depth analysis indicates several differences between the constitutive models proposed in the existing codes. In this study, these models are compared and a numerical simulation is performed to evaluate their differences in terms of the structural behavior predicted and measured in an experimental program of RC–FRC elements. The predictions provided by the models fit satisfactorily the experimental results for elements with steel fibers and with plastic fibers.

New analytical model to generalize the barcelona test using axial displacement

The Barcelona Test has proved to be very suitable for the systematic control of the tensile properties of Fibre Reinforced Concrete (FRC). Nevertheless, the need to measure the total circumferential opening displacement (TCOD) of the specimen entails the use of an expensive circumferential extensometer. In order to simplify the test, studies from the literature propose the use of the axial displacement of the press (δ) instead of the TCOD, obtaining empirical equations to correlate the energy estimated with both measurements. However, these equations are only valid for δ ranging from 1 to 4 mm and were adjusted based on the test results of just a few types of FRC. The verification of this formulation for other types of FRC shows an average error of 51.1%, thus limiting the simplification proposed for the test. In this paper, a new analytical model to convert the δ into the TCOD is developed and validated for a wide range of FRC. Besides being applicable to the whole range of δ, the new model provides a clear physical understanding of the main mechanism observed during the test and shows an average error of only 6.7%, making it possible to simplify the Barcelona test.

Structural Diagnosis of a Concrete Dam with Cracking and High Nonrecoverable Displacements

AbstractExpansions in concrete dams may be caused by chemical or physical sources; however, in certain occasions the evidences observed in the dam may not be attributed to a single cause. Mequinenza is an example of a concrete dam affected by expansions and high nonrecoverable displacements that cannot be explained by the most frequent pathologies. This paper presents new hypotheses that could justify such behavior by assuming the superposition of a global phenomenon of water induced expansion in concrete in the entire dam and a localized effect consisting in the opening of cracks in the construction joints located in one of the blocks. This is validated by conducting numerical analyses through 2D finite element models that consider the nonlinear behavior of the construction joints and use zero-thickness interface elements to simulate the potential cracking planes in the dam. The results confirmed the diagnosis proposed and the capability of the model to reproduce the behavior of the dam, revealing the si...

Performance-Based Procedure for the Definition of Controlled Low-Strength Mixtures

Controlled low-strength material (CLSM) is a self-consolidating cementitious material used as backfill in narrow trenches. The high content of aggregates and water in CLSM leads to a special behavior that is closer to soil than concrete. Consequently, mixture proportioning methodologies for conventional concrete do not apply to CLSM. The objective of this paper is to propose a new methodology to achieve the optimal composition that fulfills the flowability and compressive strength requirements of the material. Instead of computing the aggregate or the cement separately, all solid particles in the mixture are considered concurrently to estimate the water content in terms of water-to-solid ratio (W/S). In this way, the compressive strength can be modified without compromising the desired flowability. An example application is presented and an experimental program is conducted to validate this philosophy. The results confirm that the methodology proposed provides compositions that satisfy the main requirements of CLSM, thus representing a contribution to the use of more economical and adequate materials.

Flexural Post-cracking Creep Behaviour of Macro-synthetic and Steel Fiber Reinforced Concrete

In this paper the post-cracking creep behaviour of FRC beams under flexural load is evaluated in order to determine whether under certain loading conditions plastic fibres may be safely used in the long-term without compromising the serviceability requirements. For that, an experimental program was conducted that involved the testing of 30 beams with dimensions of 150 × 150 × 600 mm reinforced either with plastic or steel fibres. The creep test setup consisted in a four-point bending test in previously cracked beams up to crack widths of 0.25, 1.50 and 2.50 mm. The sustained load ranged between 50 and 60 % of the cracking load and was applied by means of a lever system. The sustained load was controlled throughout the test with a load cell. The tests were performed under two different environmental conditions during 6 months. Despite the large deformations exhibited by plastic fibres under sustained load over time, their use as reinforcement should not be discarded as long as the effects of creep are considered in the design.

Self-compacting concrete in the Temple of Sagrada Familia

The Temple of Sagrada Familia presents singularities in terms of both the original design by architect Antoni Gaudi and the duration of the construction, which started more than 120 years ago. In fact, its design was conceived before the development of reinforced concrete. Therefore, the construction materials and processes have evolved to adapt new technologies without compromising the vision of Gaudi. This willingness to maintain the original designs has obliged the technicians to resolve details that were not defined in the project, including the issue of how to cast elements at great heights and with a high amount of reinforcement. In this context, the possibility of using self-compacting concrete (SCC) emerged. This paper describes the different experiences in the Temple of Sagrada Familia with SCC, from requirements that led to using this material to the design of the mixes and the casting of the elements in situ.

Creep Behaviour of Cracked High Performance Fibre Reinforced Concrete Beams Under Flexural Load

The investigation on flexural creep of high performance fibre reinforced concrete (HPFRC) is still scarce. Even though the presence of fibres in concrete helps to control the deformations, these may increase under the effect of a sustained load. To analyse the effect of creep in pre-cracked HPFRC elements, twelve beams reinforced with either glass or steel fibres with dimensions 40 × 80 × 1200 mm were tested under a three-point configuration. For that, a new type of frame was designed and constructed to test the HPFRC beams under flexural load in a climate-controlled room with constant temperature and relative humidity. The loading mechanism was based on a lever system, applying sustained load ranging between 25 and 50 % of the load at which the first crack appeared. The deflection at the mid-span was registered by means of LVDT transducers. Additionally, the influence of the curing procedure (with or without aluminium tape wrap) was assessed. In general, glass fibre reinforced beams presented higher deflections than steel fibres, even though at low load levels the type of fibre did not have significant influence on the deformation.

Size effect on post-cracking strength of high performance fibre-reinforced concrete

The size effect is a well-known phenomenon in the design of reinforced concrete structures. Although it has been studied extensively for conventional concrete with or without traditional reinforcement, its influence on the post-cracking behaviour of fibre-reinforced composites is scarcely reported in literature. This is particularly true in the case of high performance fibre-reinforced concrete (HPFRC), which allows the design of very thin elements and whose behaviour may be highly influenced by their size. The aim of this research was to evaluate the influence of the size of HPFRC beams on the mechanical performance at a cross-sectional level. An experimental program involving three-point bending tests of HPFRC on beams of dimensions 40 × 40 × 160, 100 × 100 × 400 and 150 × 150 × 600 mm was conducted. Three steel fibre contents were investigated: 90, 140 and 190 kg/m3. These bending tests were also simulated via a sectional analysis model, taking as a reference the constitutive law described in the fib Model Code for Concrete Structures 2010. The results suggest that the values of stress in the constitutive model should depend upon the cross-sectional size of the beam. This is reflected when adjusting the parameters of the MC2010 to fit the experimental values, resulting in a coefficient of determination above 0.88 when comparing the ratio between these two parameters and the size of the cross section.