Albert de la Fuente

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.

Multicriteria decision-making method for sustainable site location of post-disaster temporary housing in urban areas

AbstractMany people lose their homes around the world every year because of natural disasters, such as earthquakes, tsunamis, and hurricanes. In the aftermath of a natural disaster, the displaced people (DP) have to move to temporary housing (TH) and do not have the ability to choose the settlement dimensions, distributions, neighborhood, or other characteristics of their TH. Additionally, post-disaster settlement construction causes neighborhood changes, environmental degradation, and large-scale public expenditures. This paper presents a new model to support decision makers in choosing site locations for TH. The model is capable of determining the optimal site location based on the integration of economic, social, and environmental aspects into the whole life cycle of these houses. The integrated value model for sustainable assessment (MIVES), a multicriteria decision making (MCDM) model, is used to assess the sustainability of the aforementioned aspects, and MIVES includes the value function concept, w...

Multi-criteria decision-making model for assessing the sustainability index of wind-turbine support systems: application to a new precast concrete alternative

AbstractA multi-criteria decision-making system based on the MIVES method is presented as a model for assessing the global sustainability index scores of existing wind-turbine support systems. This model is specifically designed to discriminate between tower systems in order to minimize the subjectivity of the decision and, thus, facilitate the task of deciding which system is best for a given set of boundary conditions (e.g., height, turbine power, soil conditions) and economic, social and environmental requirements. The model’s versatility is proven by assessing the sustainability index of an innovative new precast concrete tower alternative also described in this paper. As a result of this analysis, some points of improvement in the new system have been detected.

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.

Barcelona Test as an Alternative Method to Control and Design Fiber-Reinforced Concrete Pipes

The use of fibers as primary reinforcement for concrete pipes (CPs) is known by both industrial and scientific researchers as an attractive alternative to steel. However, the use of fibers in CPs has not yet been well established in this industry because of, among other reasons, the lack of systematic quality control of fiber-reinforced concrete pipes (FRCPs). Therefore, an experimental program involving the production and testing of 600 mm (23.6 in.) internal-diameter FRCPs was performed using low contents of steel (10 and 20 kg/m3 [0.62 and 1.25 lb/ft3]) and polypropylene (2.3 and 4.6 kg/m3 [0.14 and 0.29 lb/ft3]) fibers. These FRCPs were expected to be viable alternatives to those unreinforced and steel bar-reinforced concrete pipes corresponding to low- to moderate-strength classes. A numerical simulation of the tests using the constitutive equation derived from the Barcelona test was carried out, aimed at confirming that both can be an innovative combination to deal with both the characterization of the FRC tensile behavior and the direct design of these pipes. In this regard, those pipes containing 20 kg/m3 (1.25 lb/ft3)of steel fibers reached the C60 strength class in the TEBT (equivalent to ASTM C76 Class I). Consequently, the steel bars could be completely replaced by fibers. This fact led to an effective reduction of 20% of steel as well as to the elimination of those operations related to the reinforcement preparation. Simultaneously, these FRCPs represent a challenge at a numerical level because the model could be insensitive to this low amount of fibers. The comparisons between the experimental and numerical results have confirmed the suitability of both the model and the constitutive equation to simulate the pipe response when subjected to the TEBT.

Complementary use of inductive test and bending test for the characterization of SFRC

Many researches have been conducted in past decades for promoting the application of steel fibre reinforced concrete (SFRC), either conventional or self-compacting. However, the differences of post-crack behaviour and the properties of these two types of concrete remains unclear. The objective of this paper is to analyse such differences in terms of flexural behaviour, fibre orientation and contribution as well as the fibre content. For that, an extensive experimental campaign was carried out. In total 3 mixes of self-compacting and 3 mixes with traditional concrete were produced with the nominal fibre contents of 30kg/m3, 45kg/m3 and 60kg/m3. In each series, specimens were produces and characterized by three point bending test (code EN 14651) and inductive test. The results illustrate how fibre orientation and distribution justify the differences in the mechanical behaviour of the materials and the scatter of the bending test results.

Suitability of Different Decision-Making Methods Applied for Analysing Sustainable Post-disaster Temporary Housing

Increasing population of urban areas by 2050, especially in areas highly prone to natural hazards, could potentially threaten vulnerable cities in the face of future disaster events. Alternative temporary housing (TH) needs to be assessed as an important element of local resiliency. In this regard, there are some interrelated factors that can have antithetical impacts on the different cases of TH. Thus, proper decision-making models can be highly useful to deal with this complex multifaceted process. These models should be flexible and adaptable to existing local and boundary conditions since a TH strategy could lead to different satisfactions and perceptions. This chapter aims to present a multi-criteria decision-making (MCDM) method for choosing the most sustainable temporary housing alternative. To this end, general requirements of the decision-making process for dealing with temporary housing selection are specified and organized based on the assessed cases. Finally, all possible decision-making methods are assessed to determine the most suitable one based on correspondence between the methods and the requirements. As a result, this study concludes that a robust MCDM method should incorporate concept method to objectively measure the satisfaction degree of every stakeholder involved. In this sense, the Integrated Value Model for Sustainable Assessment (MIVES) is a suitable method for assessing the sustainability of temporary housing since this includes the value function method (based on the utility theory).

Partial Safety Factor for the Residual Flexural Strength of FRC Precast Concrete Segments

The use of fibre reinforced concrete (FRC) to produce segmental linings of TBM-constructed tunnels is an increasing tendency. So far, more than 50 tunnels have been constructed with this structural material, in some of these even using solely fibres as reinforcement. Moreover, several design guidelines (e.g., fib Model Code 2010) already include the FRC as structural material. There also exist specific guidelines for the design of FRC precast segment linings (e.g., ITAtech Report/7-15 and ACI 544.7R-16). These guidelines deal with the design of FRC considering the traditional limit state safety format. Therefore, partial safety factors for both the loads (γ L ) and material strengths (γ M ) must be considered. In particular, the magnitude of γ M considered for compressive and tensile FRC strengths are assumed to be the same. Nonetheless, this assumption can be unrealistic, particularly in terms of flexural residual strength (f R ) since this property present higher scatter than the compressive strength (f c ). This is particularly true for elements with a reduced cracking surface (e.g., beams) due to the higher impact that uncertainties like fibre orientation and distribution have on the variability of f R . Therefore, this assumption can lead to lower reliability indexes (β) than those established for traditional reinforced concrete structures. However, this variability tends to decrease with the increase of the width of the cracked sections (e.g., slabs). The results of a structural reliability analysis carried out to calibrate partial safety factors for f R is presented. Full-scale bending tests on precast segments with different dimensions, amounts and type of fibers were considered. This partial safety factors could be used in the design of future precast FRC tunnel linings.

Lateral Stability of Prestressed Precast Concrete Girders During Lifting: Study Case

Improvements in concrete technology, reinforcing systems and manufacturing processes enable the use of increasingly long reinforced precast concrete girders, contributing to the competitiveness of girders in concrete in comparison with other alternatives. The weight of the girders should be limited however, in order to achieve an optimum between span length and lifting and transportations costs. The current tendency in design is to minimize the width of the flanges, thus the girder becoming more flexible laterally and more prone to suffer instability phenomena during transient loading situations. An increasing number of accidents and damages associated with this instability problem are reported in the technical literature (e.g., Hurff 2010; Rose 2013). The main objective of this study is to describe a real case of lateral instability of a long prestressed concrete bridge girder during lifting as well asto perform a parametric study to understand the limits of the problem observed. Special attention is paid to the evaluation of the provisions gathered in the Model Code 2010 (MC - 2010) regarding the lateral stability, since these might not be sufficient to cover limit cases.