Analytical modeling of reinforced concrete columns subjected to bidirectional shear

Under general seismic loading, reinforced concrete columns may be subjected to lateral loads in more than one direction. Available experimental data on columns subjected to bidirectional forces indicate that higher levels of damage and a higher loss of ductility and strength have been observed compared to similar tests under unidirectional shear forces. In this study, an experimental program was conducted in which six lightly reinforced concrete columns were subjected to unidirectional and bidirectional cyclic shear forces. This observation was used to identify the mechanisms and parameters governing the behavior of columns subjected to cyclic bidirectional lateral loads. Hence, a new conceptual model was developed to obtain the capacity of member. The shear forces were analyzed and an analytical formulation was derived to account for the effects in the concrete stress-strain relationship, the moment-curvature diagram and the plastic hinge length. These equations were used along with a structural model with concentrated plastic hinges to obtain the capacity curve of the column. The results of the formulations developed were verified using the results of the experiments performed on columns subjected to unidirectional and bidirectional cyclic lateral forces.Peer ReviewedPostprint (author's final draft

3D FEM model development from 3D optical measurement technique applied to corroded steel bars

Understanding the mechanical effects of the corrosion pits on the steel surface requires an accurate definition of their geometry and distribution along the rebar. 3D optical measurement technique is used to obtain the outer geometry of artificially corroded bars tested under cyclic or monotonic loads. 3D FEM model development from the 3D scanning results were carried out in order to investigate the failure process and local effects on the pits, which are responsible of the variation of the mechanical properties in corroded steel reinforcement. In addition, a validation of a simplified model, which allows the mechanical steel properties determination given an estimated corrosion level, is presented. 3D models were convenient to observe and measure the local effects on the pits.Peer ReviewedPostprint (author's final draft

Influence of time-dependent restrained strains in the shear response of RC frames

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0875-8Time-dependent strains, when restrained, can lead to important tensile forces and damage, affecting, among other aspects, the shear response and ultimate load carrying capacity of shear-critical RC frames. This paper presents a detailed study of this problematic by means of an extension of a shear-sensitive fibre beam model to time dependent behaviour of concrete. The model is firstly validated with experimental tests on diagonally pre-cracked beams under sustained loads. From these analyses, the contributions of shear distortions and bending curvatures to the total long-term deflection of the beams are discerned. Afterwards, the model is applied to study the influence of restraining strains due to long-term creep and shrinkage in the service and ultimate shear response of frames. In contrast with flexural resistant mechanisms, delayed strains may influence the latter shear resistance of integral structures by reducing the concrete contribution to shear resistance and leading to a sooner activation of the transversal reinforcement. These aspects can be relevant in assessing existing structures and this model, due to its relative simplicity, can be advantageous for practical applications.Peer ReviewedPostprint (author's final draft

Contribution of externally bonded FRP shear reinforcement to the shear strength of RC beams

An experimental program of T-beams strengthened in shear by CFRP sheets has been developed with two longitudinal reinforcement ratios and different externally bonded CFRP shear strengthening amounts in a discontinuous or continuous U-shaped configuration with and without mechanical anchorages. The effectiveness of the external reinforcement without anchorages was low regardless the CFRP reinforcement ratio. There is an evidence of the interaction of the different shear strength components, concrete Vc, transverse steel Vs, CFRP sheets Vf that have been obtained from the registered data of the instrumentation. This interaction might explain that the ultimate shear force of some CFRP-strengthened beams was lower than the one of the control beam. There is a significant difference between the sum of the Vc, Vs, and Vf components and the total shear force. This difference is assumed to be carried out by the flange (including its internal transverse reinforcement), which represents a significant percentage of the total shear strength (with a mean value of 38%). Finally, the contribution of the CFRP has been obtained by different existing guidelines and has been compared to the experimental values.Peer ReviewedPostprint (author's final draft

Quality control test for SFRC to be used in precast segments

Current methods to measure tensile strength and toughness in Steel Fiber Reinforced Concrete (SFRC) show a considerable scatter. That scatter makes difficult the quality control, in particular when such properties are taken into account in the evaluation of overall strength of the precast tunnel lining segments, as in the case of the Line 9 of the subway in Barcelona. In order to improve the material assessment procedure, the Double Punch Test (DPT) has been recovered for the quality control of the tension behavior of SFRC. Results of an initial feasibility research are presented, showing a significant reduction of the scatter in the values of the tension strength and in the toughness. Other advantages shown by this test are: (1) the reduced size 150x150 mm of the cylindrical specimens, compared with those used in beam test, and (2) the use of a conventional compression press controlled by displacement.Peer Reviewe

Refuerzo de estructuras de hormigón armado con laminados de fibra de carbono (CFRP)

El uso de los materiales compuestos en el campo del refuerzo estructural ha experimentado un notable crecimiento en los últimos años gracias a sus elevadas relaciones resistencia/peso y rigidez/peso, que permiten reducir costes de mano de obra respecto al empleo de otros materiales más convencionales. Los polímeros reforzados con fibras (FRP) se pueden aplicar como refuerzo de estructuras de hormigón armado o pretensado a flexión, cortante o confinamiento. Independientemente del tipo de refuerzo, uno de los principales inconvenientes o condicionantes en el dimensionamiento es el fallo por el desprendimiento prematuro del refuerzo, antes de alcanzar la resistencia última del mismo, por la concentración de tensiones en la interfase entre el laminado y el soporte

Structural effects of steel reinforcement corrosion on statically indeterminate reinforced concrete members

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0836-2Steel corrosion in reinforced concrete structures produces loss of reinforcement area and damage in the surrounding concrete. As a consequence, increases in deflections, crack widths and stresses may take place, as well as a reduction of the bearing capacity, which depends on the structural scheme and redundancy. In this paper an experimental study of twelve statically indeterminate beams subjected to different levels of forced reinforcement corrosion is presented. Different sustained loads were applied during the corrosion phase to assess their influence on the effects of corrosion. An important increase in deflections was registered in all corroded beams, especially in those subject to higher load levels. It was also found that the rate of corrosion was affected by the load level. Internal forces redistributions due to induced damage were measured. Finally, the experimental results were compared with those predicted by a non-linear time-dependent segmental analysis model developed by the authors, obtaining in general good agreement.Peer ReviewedPostprint (author's final draft

Damage investigation of a tunnel subjected to an unplanned surface load through non-linear analysis

First published by the International Association for Bridge and Structural Engineering (IABSE), Zurich, Switzerland, www.iabse.org; in Structural Engineering International 2017, Vol.27, issue 3, pg. 422-428.A description of the deformations and damage that occurred in a segmental tunnel lining as a consequence of an unplanned surface load is presented, as well as the numerical analyses performed for its safety assessment. The tunnel in study is located in soft soil conditions and presents a low overburden. Few months after tunnel drilling, a new bridge was constructed at surface level, placing an access embankment over the tunnel path. Monitoring points were installed along the affected section which recorded the deformation of the tunnel caused by the embankment weight. More worryingly, despite no additional loads were introduced, the deformation of the lining continued increasing significantly along the next months, indicating the existence of soil consolidation phenomena. As a consequence, structural cracks emerged along the affected section. Non-linear finite element models that realistically simulate the behaviour of the non-linear segment joints and the concrete cracking were used to characterize the actual response and strength of the lining. The results showed that most significant damages should occur at the non-visible extrados side, and characterized how they evolve along the soil consolidation process. Finally, the adopted tunnel strengthening procedure is described.Peer ReviewedPostprint (author's final draft

Analysis of FRP shear strengthening solutions for reinforced concrete beams considering debonding failure

In this paper, a fiber beam model previously developed by the authors for the nonlinear analysis of strengthened elements, including the effects of shear, is used to predict the response of reinforced concrete (RC) beams strengthened in shear with fiber reinforced polymers (FRP) sheets. In the previous version of the model, debonding failure of FRP was not included; hence, its application was limited to the simulation of wrapped configurations. The model is now extended to account for debonding failure in order to allow for its application to beams strengthened with U-shaped and side-bonded configurations. Existing experimental tests on RC beams strengthened in shear by FRP sheets in both wrapped and U-shaped configurations were numerically simulated. The model reproduces, with reasonable accuracy, the experimental failure loads, the load-deflection behavior, and the strains in FRP and stirrups with increasing load. The advantages of this proposal are related with the simplicity and straightforwardness of the beam models to be applied in practical engineering problems.Peer ReviewedPostprint (author's final draft

Evaluación de la eficiencia de soluciones de refuerzo en estructuras de hormigón mediante análisis no lineal evolutivo

When designing a structural strengthening solution, the influence of the previous state of the structure on the capacity of the strengthened structure must be evaluated. In addition, strengthening interventions may involve operations such as partial unloading of the structure, placement and removal of temporary shores, application of loads or pre-deformations, restoring of damaged reinforcement or spalled con-crete or constraining of lateral strains. Therefore, changes in the cross-section geometry and reinforcement, longitudinal scheme, support conditions, loads and state of stresses and strains, may take place. Furthermore, occurrence of phenomena producing a premature failure or a change in the failure mode, should be avoided. In order to account for such a large variety of causes and phenomena affecting the structural response, a nonlinear and time-dependent analysis model of 3D reinforced and prestressed concrete frames, capable of capturing different failure modes and taking into account the structural history, is described. The model has been verified with tests on strengthened structures available in the literature and has been applied to an actually remodeled structure, comparing the advantages and disadvantages of two different strengthening proposals, showing its capabilities to assess the efficiency of structural strengthening systems.This paper is dedicated to the memory of an extraordinary engineer and human being, Luis Ortega Basagoiti, who was an example and reference for structural engineers and researchers along his professional career. The works described in this paper have been developed in the framework of the following research projects funded by the Spanish Science and Technology Ministries and by the European Funds for Regional Development, ADRESS (BIA2009-11764), REHABCAR (IPT-370000-2010-029), HORVITAL (BIA2015-64672-C4-1-R) and STRADURAVIUS (RTI2018-097314-B-C21).Peer ReviewedPostprint (published version