Carlos Zanuy

Sectional Analysis of Concrete Structures under Fatigue Loading

Fatigue is a continuous and progressive microcracking mechanism leading to increasing permanent strains and decreasing stiffness in concrete. This paper proposes a time-dependent (i.e, cycle-dependent) model for concrete that accounts for the changes of the mechanical properties during the fatigue life. The proposed method can be useful in estimating the fatigue-carrying capacity of existing structures that will be subjected to higher loads in the future. The model is implemented into a sectional algorithm to reproduce the evolution of the stress-strain state of reinforced concrete members. Redistribution capacity is found to be the main governing factor of the final failure mode. A comparison of theoretical results with existing experimental data of reinforced concrete beams indicates that the model is accurate in the prediction of strain evolution, fatigue life and the mode of fatigue failure.

Evaluation of Fatigue Bond Strength of Anchorage Zones with a Mechanical Model

AbstractThe paper describes a numerical model to analyze the fatigue behavior of RC anchorage zones. The model takes into account the cycle-dependent bond-slip behavior at the steel-concrete interface and is able to reproduce the experimental increase of the relative slip developed with number of load cycles, as well as the process of redistribution of stresses that takes place over the anchorage length as a result of fatigue damage. The results compare satisfactorily with existing experimental results. The model has been used to derive S-N curves to provide the fatigue strength of anchorage zones under different confinement conditions and various values of the anchorage length-to-diameter ratio and the steel diameter. The results indicate that the confinement degree plays a significant role in the fatigue bond strength: no fatigue problems are found for the well-confined concrete condition, but significantly short fatigue strength is obtained under the moderately confined and unconfined concrete conditions.

Utilization of the Capacity for Energy Absorption of Concrete Structures under Impact

Concrete structures subjected to impact have shown a higher sensitivity to develop a brittle shear failure than under quasi-static loading. The differences between the dynamic and static behavior are due to the strain-rate dependence of material properties and the presence of inertial forces. Both effects should be accounted for when performing analyses of structures under impact. In the present paper, a simplified three-degree-of-freedom model is used to understand the improved impact response of reinforced concrete when steel fibers are added to the concrete matrix. The analysis shows that the higher capacity for energy absorption of fiber-reinforced concrete (FRC) may avoid local shear failure when the FRC is able to develop strain hardening prior to the peak strength. Various analyses are presented in order to understand the influence of different types and contents of fibers.

Impact Performance of Low-Fiber Content HPFRCC: From Material to Structural Behavior

It has been typically observed that concrete structures have a brittle failure mode by shear or punching under high-loading rates. The small capacity for energy absorption of plain concrete is responsible of such brittle failure development upon diagonal crack formation. High-performance fiber-reinforced cement composites (HPFRCCs) have superior performance than plain concrete in tension, not only by the higher tensile strength but especially regarding the energy absorption capacity associated to multiple cracking and crack-bridging ability. In order to understand the possible benefits of using HPFRCC under impact loading in structural applications, research must be done at both material and structural level. The present contribution deals with an experimental study on HPFRCC specimens subjected to impact. Reference quasi-static tests have been also carried out. The HPFRCC mix was reinforced with 1.6% volumetric amount of short straight high-strength steel fibers. The study at material level has focused on prismatic specimens subjected to pure bending, which allows to analyze the flexural strength and specific energy absorption capacity. Structural tests have consisted of beams reinforced with conventional longitudinal steel bars without stirrups, thereby assigning the resistance of the webs against shear to the contribution of the fibers. The results are presented in comparison with companion specimens of conventional plain concrete, which has allowed showing the higher strength, ductility and energy absorption capacity achieved with the utilization of the properties of the HPFRCC under both quasi-static and impact loading conditions.

Fatigue Behavior of Reinforced Concrete Haunched Beams without Stirrups

In this paper, results of fatigue tests on reinforced concrete haunched beams without stirrups are presented for the first time. Two types of failure modes have been obtained, either due to fatigue of the reinforcement or due to shear fatigue. In addition, progressive increase of deflections with load cycles was measured. An analysis of tests is carried out in terms of the consequences of fatigue loading on ultimate strength and serviceability of reinforced concrete. Regarding fatigue strength, the limitations of existing models are shown and discussed. Regarding serviceability, it is shown that deflections are even higher than those theoretically obtained by the fully cracked member. This is due to development of shear deformations, cyclic creep, and negative tension stiffening during unloading stages.

Discussion of "Experimental Study on the Performance of Approach Slabs under Deteriorating Soil Washout Conditions"

Carlos Zanuy and Luis Albajar Assistant Professor, Dept. of Continuum Mechanics and Structures, Escuela Tecnica Superior de Ingenieros de Caminos, Canales y Puertos, Univ. Politecnica de Madrid, Calle del Profesor Aranguren S/N, 28040 Madrid, Spain (corresponding author). E-mail: czs@caminos.upm.es Associate Professor, Dept. of Continuum Mechanics and Structures, Escuela Tecnica Superior de Ingenieros de Caminos, Canales y Puertos, Univ. Politecnica de Madrid, Calle del Profesor Aranguren S/N, 28040 Madrid, Spain.

Fatigue Sensibility of R/C Secondary Elements of Bridges

The influence of fatigue may be an important but not usually contemplated aspect on the behavior of some components of concrete structures. Here a study on the bridge approach slabs is presented. It is shown how the cyclic load causes a progressive deterioration of the compression zone of concrete and its contribution in the tensile chord between cracks. The increase of deflections and crack widths along the fatigue life is observed experimentally, under maximum and minimum loads. The growth of the remnant values of these variables evidences the important irreversibility of the fatigue degradation.