Influence of the type of fiber on the structural response and design of FRC slabs

Most codes for the design of fiber reinforced concrete (FRC) structures are based on the experience achieved throughout the years with steel fibers. Recent codes include the possibility of applying the same considerations for FRC structures with plastic fiber. However, the consequences of assuming identical design considerations regardless of the type of fiber is scarcely known in terms of the structural behavior of full-scale elements. The main goal of this paper is to assess the influence of the type of fiber on the performance of full-scale concrete slabs, emphasizing on the consequences of using a common design approach. For that, a comparative experimental study was conducted in order to expose differences regarding the crack pattern and load-deflection behavior. Then, finite element simulations were performed using the constitutive equations from the Model Code 2010. The results indicate distinct levels of overestimation of the structural behavior measured experimentally, confirming that specific design considerations are required depending on the type of fiber used. Based on the findings, correction factors are proposed for the design of FRC slabs with each fiber.Peer ReviewedPostprint (author's final draft

Reinforced concrete slab elements under bending and twisting moments

Abstract unavailable please refer to PD

The effects of protected beams and their connections on the fire resistance of composite buildings

According to full-scale fire tests, it is noticed that tensile membrane action within the concrete floor slabs plays an important role in affecting the fire resistance of composite buildings. It is well known that the development of tensile membrane actions relies on the vertical support along the edges of the slab panel. However, there is at present a lack of research into the influence of vertical supports on the tensile membrane actions of the floor slabs. In this paper, the performances of a generic three dimensional 45m x 45m composite floor subjected to ISO834 Fire and Natural Fire are investigated. Different vertical support conditions and three steel meshes are applied in order to assess the impact of vertical supports on tensile membrane action of floor slabs. Unlike other existing large scale modelling which assumes the connections behave as pinned or rigid for simplicity, two robust 2-node connection element models developed by the authors are used to model the behaviour of end-plate and partial end-plate connections of composite structures under fire conditions. The impact of connections on the 3D behaviour of composite floor is taken into consideration. The load-transfer mechanisms of composite floor when connections fail due to axial tension, vertical shear and bending are investigated. Based on the results obtained, some design recommendations are proposed to enhance the fire resistance of composite buildings

Pressure-impulse diagram method:a fundamental review

Accidental and deliberate explosions stemming from catastrophic events in the petroleum industry, incidents during complex manufacturing processes, mishandling or failure of domestic gas appliances or installations, terrorist attacks and military engagements, are becoming increasingly relevant in structural design. Pressure‐impulse (P‐I) diagrams are widely used for the preliminarily assessment and design of structures subjected to such extreme loading conditions. A typical P‐I diagram provides information concerning the level of damage sustained by a specific structural member when subjected to a blast load. This paper presents a state‐of‐the‐art review describing the development of the P‐I diagram method over the last 70 years, the main assumptions upon which its development is based and the framework through which such the method is applied in practice. The structural analysis methods used for the derivation of P‐I curves are discussed and the existing approaches are categorised according to algorithms used. A review of the P‐I curve formulae proposed to date is performed, where the formulae are classified according to the formulation methods

Experimental and Theoretical Investigation of the Crack Behavior of RC-slabs Subjected to Biaxial Bending

This thesis presented a comprehensive study on the influence of transverse reinforcement on the cracking patterns of RC slabs, including both slab-strips under uniaxial bending and also slabs subjected to biaxial bending

Image post-processing method for quantification of cracking in RC precast beams under bending

Image processing methods are increasingly used in civil engineering, especially in the maintenance of concrete structures. Current digital cameras and post-processing methods allow verifying qualitatively the state of conservation of wide areas of concrete in dams and bridges. When dealing with building refurbishments and rehabilitation, it is important to verify that existing structural elements fit the requirements of the standards; in the case of structures formed by traditional RC joists, cracking of the bottom-face provides information about the serviceability of these elements. This research proposed and put in practice through experimental tests an image post-processing method for quantification of cracking (five specimens were used and calibrated). Based on a sequence of shots and through a complex step-by-step post-processing, cracks were identified and measured to calibrate this method for real purposes. The method quantifies the crack opening width and spacing by analyzing the bottom-face of the joists through the shots. Measured values of crack spacing are very similar to those predicted by the standards, while the values of crack opening width differ more from theoretical ones due to the scattering of results. However, the proposed method has been proved as suitable and useful for fast inspections of RC elements under bending. © 2018 by the authors.Peer ReviewedPostprint (published version

The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams

This is the accepted version of the following article: [Cladera, A., Marí, A., Bairán, J. M., Ribas, C., Oller, E. and Duarte, N. (2016), The compression chord capacity model for the shear design and assessment of reinforced and prestressed concrete beams. Structural Concrete, 17: 1017–1032. doi:10.1002/suco.201500214], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/suco.201500214/fullA simplified mechanical model is presented for the shear strength prediction of reinforced and prestressed concrete members with and without transverse reinforcement, with I, T or rectangular cross-section. The model, derived with further simplifications from a previous one developed by the authors, incorporates the contributions of the concrete compression chord, the cracked web, the dowel action and the shear reinforcement in a compact formulation. The mechanical character of the model provides valuable information about the physics of the problem and incorporates the most relevant parameters governing the shear strength of structural concrete members. The predictions of the model fit very well the experimental results collected in the ACI-DAfStb databases of shear tests on slender reinforced and prestressed concrete beams with and without stirrups. Due to this fact and the simplicity of the derived equations it may become a very useful tool for structural design and assessment in engineering practice.Peer ReviewedPostprint (author's final draft

Design of RC thin surface structures

Technical report 04-DEC/E-0

Membrane action in simply supported slabs

Abstract unavailable please refer to PD

Evaluation of the influence of post-cracking response of steel fibre reinforced concrete (SFRC) on load carrying capacity of SFRC panels

To develop a reliable methodology for the design of steel fibre reinforced concrete (SFRC) slabs, an extensive experimental program was carried out with SFRC square panels simply supported in their contour. By adopting a moment-rotation approach, a numerical model was developed capable of taking into account the constitutive laws of the SFRC for the prediction of the force-deflection response of variety of panel tests recommended in the international standards. The predictive performance of the model was assessed by considering results available in the bibliography and those obtained on the experimental program. The proposed model was utilized in a parametric study to assess the influence of toughness classes of SFRC on the behaviour at serviceability limit conditions, on the load carrying capacity, and on the deformational response of SFRC round panels.This work is supported by the FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project SlabSys-HFRC-PTDC/ECM/120394/2010. The first author acknowledges the FCT PhD Grant SFRH/BD/71934/2010. The authors would like to acknowledge the materials supplied by Maccaferri (fibres), SECIL (cement), SIKA and BASF (superplasticizers), OmyaComital (limestone filler), and Pegop (Fly ash). Special thanks for CiviTest Company that developed the SFRCs and executed the specimens of the experimental program.Fundação para a Ciência e a Tecnologia (FCT