Damage tolerance of cold drawn ferritic-austenitic stainless steels wires for prestressed concrete

Damage tolerance of high strength cold-drawn ferritic–austenitic stainless steel wires is assessed by means of tensile fracture tests of cracked wires. The fatigue crack is transversally propagated from the wire surface. The damage tolerance curve of the wires results from the empirical failure load when given as a function of crack depth. As a consequence of cold drawing, the wire microstructure is orientated along its longitudinal axis and anisotropic fracture behaviour is found at macrostructural level at the tensile failure of the cracked specimens. An in situ optical technique known as video image correlation VIC-2D is used to get an insight into this failure mechanism by tensile testing transversally fatigue cracked plane specimens extracted from the cold-drawn wires. Finally, the experimentally obtained damage tolerance curve of the cold-drawn ferritic–austenitic stainless steel wires is compared with that of an elementary plastic collapse model and existing data of two types of high strength eutectoid steel currently used as prestressing steel for concrete.

Modelling of corrosion-induced cover cracking in reinforced concrete by an embedded cohesive crack finite element

Corrosion of a reinforcement bar leads to expansive pressure on the surrounding concrete that provokes internal cracking and, eventually, spalling and delamination. Here, an embedded cohesive crack 2D finite element is applied for simulating the cracking process. In addition, four simplified analytical models are introduced for comparative purposes. Under some assumptions about rust properties, corrosion rate, and particularly, the accommodation of oxide products within the open cracks generated in the process, the proposed FE model is able to estimate time to surface cracking quite accurately. Moreover, emerging cracking patterns are in reasonably good agreement with expectations. As a practical case, a prototype application of the model to an actual bridge deck is reported.

Effect of adhesive thickness and concrete strength on FRP-Concrete Bonds

The use of fiber-reinforced polymer (FRP) composites for strengthening, repairing, or rehabilitating concrete structures has become more and more popular in the last 10 years. Irrespective of the type of strengthening used, design is conditioned, among others, by concrete-composite bond failure, normally attributed to stress at the interface between these two materials. Single shear, double shear, and notched beam tests are the bond tests most commonly used by the scientific community to estimate bond strength, effective length, and the bond stress-slip relationship. The present paper discusses the effect of concrete strength and adhesive thickness on the results of beam tests, which reproduce debonding conditions around bending cracks much more accurately. The bond stress-slip relationship was analyzed in a cross section near the inner edge, where stress was observed to concentrate. The ultimate load and the bond stress-slip relationship were visibly affected by concrete strength. Adhesive thickness, in turn, was found to have no significant impact on low-strength concrete but a somewhat greater effect on higher strength materials.

Failure mechanism of reinforced concrete structural walls with and without confinement

This paper presents the results of cyclic loading tests on two large-scale reinforced concrete structural walls that were conducted at Purdue University. One of the walls had confinement reinforcement meeting ACI-318-11 requirements while the other wall did not have any confinement reinforcement. The walls were tested as part of a larger study aimed at indentifying parameters affecting failure modes observed to limit the drift capacity of structural walls in Chile during the Maule Earthquake of 2010. These failure modes include out-of-plane buckling (of the wall rather tan individual reinforcing bars), compression failure, and bond failure. This paper discusses the effects of confinement on failure mode. Distributions of unit strain and curvature obtained with a dense array of non-contact coordinate-tracking targets are also presented.

A shake table test of typical mediterranean reinforced concrete structures

This research investigates the ultimate earthquake resistance of typical RC moment resisting frames designed accordingly to current standards, in terms of ultimate energy absorption/dissipation capacity. Shake table test of a 2/5 scale model, under several intensities of ground motion, are carried out. The loading effect of the earthquake is expressed as the total energy that the quake inputs to the structure, and the seismic resistance is interpreted as the amount of energy that the structure dissipates in terms of cumulative inelastic strain energy.

An analytical model for simulating the bond of prestressed concrete during the prestressed force release

A bond analytical model is proposed in this paper. The model is capable of reproducing the bond stress developed between the steel and concrete, in precast prestressed elements, during the entire process of prestressing force release. The bond stress developed in the transmission zone, where the bond stress is not constant, is also obtained. The steel and concrete stresses as well as the slip between both materials can be also estimated by means of the relation established in the model between these parameters and the bond stress. The model is validated with the results of a series of tests, considering different steel indentation depths and concrete covers and it is extended to evaluate the transmission length. This has been checked by comparing the transmission length predicted by the model and one measured experimentally in two series of tests.

Specific skills assessment learned by students of building engineering and technical architecture in topics relating to durability and control of concrete structures

In many university courses such as Building Engineering or Technical Architectural, the high density of the contents included in the curriculum, make the student, after graduation, unable to develop the skills already acquired and evaluated in the disciplines of the first courses. From the Group of Educational Innovation at the Polytechnic University of Madrid (UPM) "Teaching of Structural Concrete" (GIEHE) we have conducted a study in which are valued specific skills acquired by students after the first courses of career. We have worked with students from UPM fourth-year career and with Technical Architecture students who have completed their studies and also have completed the Adaptation Course of Technical Architecture to the Building Engineer. The work is part of the Educational Innovation Project funded by the UPM "Integration of training and assessment of generic and specific skills in structural concrete" We have evaluated specific skills learned in the areas of durability and control of structural concrete structures. The results show that overall, students are not able to fully develop the skills already acquired earlier, even being these essential to their professional development. Possibly, the large amount of content taught in these degrees together with a teaching and assessment of "flat profile", ie, which are presented and evaluated with the same intensity as the fundamental and the accessory, are causes enough to cause these results.

Concrete Swelling in a Double Curvature Dam

Se describe el problema del hinchamiento del hormigón en las presas de doble curvatura. Several chemical reactions are able to produce swelling of concrete for decades after its initial curing, a problem that affects a considerable number of concrete dams around the world. The object of the work reported is to simulate the underlying mechanisms with sufficient accuracy to reproduce the past history and to predict the future evolution reliably. Having studied the available formulations, that considered to be more promising was adopted and introduced via user routines in a commercial finite element code. It is a non isotropic swelling model,compatible with the cracking and other non-linearities displayed by the concrete. The paper concentrates on the work conducted for a double-curvature arch dam. The model parameters were determined on the basis of some parts of the dam’s monitored histories, reliability was then verified using other parts and, finally, predictions were made about the future evolution of the dam and its safety margin.

Critical comparative evaluation of design methodologies for the ultimate limit state of fatigue in concrete structures

La aparición de la fatiga ha sido ampliamente investigada en el acero y en otros materiales metálicos, sin embargo no se conoce en tanta profundidad en el hormigón estructural. Esto crea falta de uniformidad y enfoque en el proceso de verificación de estructuras de hormigón para el estado límite último de la fatiga. A medida que se llevan a cabo más investigaciones, la información sobre los parámetros que afectan a la fatiga en el hormigón comienzan a ser difundidos e incluso los que les afectan de forma indirecta. Esto conlleva a que se estén incorporando en las guías de diseño de todo el mundo, a pesar de que la comprobación del estado límite último no se trata por igual entre los distintos órganos de diseño. Este trabajo presentará un conocimiento básico del fenómeno de la fatiga, qué lo causa y qué condiciones de carga o propiedades materiales amplían o reducen la probabilidad de fallo por fatiga. Cuatro distintos códigos de diseño serán expuestos y su proceso de verificación ha sido examinado, comparados y valorados cualitativa y cuantitativamente. Una torre eólica, como ejemplo, fue analizada usando los procedimientos de verificación como se indica en sus respectivos códigos de referencia. The occurrence of fatigue has been extensively researched in steel and other metallic materials it is however, not as broadly understood in concrete. This produces a lack of uniformity in the approach and process in the verification of concrete structures for the ultimate limit state of fatigue. As more research is conducted and more information is known about the parameters which cause, propagate, and indirectly affect fatigue in concrete, they are incorporated in design guides around the world. Nevertheless, this ultimate limit state verification is not addressed equally by various design governing bodies. This report presents a baseline understanding of what the phenomenon of fatigue is, what causes it, and what loading or material conditions amplify or reduce the likelihood of fatigue failure. Four different design codes are exposed and their verification process has been examined, compared and evaluated both qualitatively and quantitatively. Using a wind turbine tower structure as case study, this report presents calculated results following the verification processes as instructed in the respective reference codes.

Design equations for reinforced concrete members strengthened in shear with external FRP reinforcement formulated in an evolutionary multi-objective framework

Methods for predicting the shear capacity of FRP shear strengthened RC beams assume the traditional approach of superimposing the contribution of the FRP reinforcing to the contributions from the reinforcing steel and the concrete. These methods become the basis for most guides for the design of externally bonded FRP systems for strengthening concrete structures. The variations among them come from the way they account for the effect of basic shear design parameters on shear capacity. This paper presents a simple method for defining improved equations to calculate the shear capacity of reinforced concrete beams externally shear strengthened with FRP. For the first time, the equations are obtained in a multiobjective optimization framework solved by using genetic algorithms, resulting from considering simultaneously the experimental results of beams with and without FRP external reinforcement. The performance of the new proposed equations is compared to the predictions with some of the current shear design guidelines for strengthening concrete structures using FRPs. The proposed procedure is also reformulated as a constrained optimization problem to provide more conservative shear predictions.

An analytical model for simulating the bond of prestressed concrete during the prestressed force release

A bond analytical model is proposed in this paper. The model is capable of reproducing the bond stress developed between the steel and concrete, in precast prestressed elements, during the entire process of prestressing force release. The bond stress developed in the transmission zone, where the bond stress is not constant, is also obtained. The steel and concrete stresses as well as the slip between both materials can be also estimated by means of the relation established in the model between these parameters and the bond stress. The model is validated with the results of a series of tests, considering different steel indentation depths and concrete covers and it is extended to evaluate the transmission length. This has been checked by comparing the transmission length predicted by the model and one measured experimentally in two series of tests.

Concrete Meccanos: Precast Constructions after the Second World War in the Netherlands

Estudio de soluciones prefabricadas de hormigón no estandarizadas en los Países Bajos tras la Segunda Guerra Mundial.

Modelling of chloride penetration into non-saturated concrete: Case study application for real marine off shore structures

The aim of this paper is to explain the chloride concentration profiles obtained experimentally from control samples of an offshore platform after 25 years of service life. The platform is located 12 km off the coast of the Brazilian province Rio Grande do Norte, in the north-east of Brazil. The samples were extracted at different orientations and heights above mean sea level. A simple model based on Fick’s second law is considered and compared with a finite element model which takes into account transport of chloride ions by diffusion and convection. Results show that convective flows significantly affect the studied chloride penetrations. The convection velocity is obtained by fitting the finite element solution to the experimental data and seems to be directly proportional to the height above mean sea level and also seems to depend on the orientation of the face of the platform. This work shows that considering solely diffusion as transport mechanism does not allow a good prediction of the chloride profiles. Accounting for capillary suction due to moisture gradients permits a better interpretation of the material’s behaviour.

Analysis of punching of a reinforced concrete slab within IRIS_2012

As part of the IRIS_2012 international benchmark, simulations were conducted to analyse impacts on reinforced concrete slabs by both rigid and deformable missiles. The analytical results were compared with physical tests conducted by the Technical Research Center VTT of Finland. In the impact discussed here, a rigid missile perforates the concrete slab. The missile is a thick steel tube filled with concrete with a total mass of 47.4 kg and strikes the target at 136 m/s. The target is a 250 mm thick, reinforced concrete slab that spans 2 m by 2 m and is held in a rigid supporting frame. Characterisation tests were provided for calibration of the parameters of the concrete models selected by the participants. Having reproduced those tests, the authors developed models for the slab and the missile. A damaged plasticity model was used for the concrete and the rebars were explicitly represented. The results obtained were very satisfactory in respect of the damage patterns caused in the concrete and the reinforcement; also, the calculated and measured values of the energy spent by the missile in perforating the slab differed by only 4%.

Concrete constitutive model, calibration and applications

A methodology has been developed for characterising the mechanical behaviour of concrete, based on the damaged plasticity model, enriched with a user subroutine (V)USDFLD in order to capture better the ductility of the material under moderate confining pressures. The model has been applied in the context of the international benchmark IRIS_2012, organised by the OECD/NEA/CSNI Nuclear Energy Agency, dealing with impacts of rigid and deformable missiles against reinforced concrete targets. A slightly modified version of the concrete damaged plasticity model was used to represent the concrete. The simulation results matched very well the observations made during the actual tests. Particularly successful predictions involved the energy spent by the rigid missile in perforating the target, the crushed length of the deformable missile, the crushed and cracked areas of the concrete target, and the values of the strains recorded at a number of locations in the concrete slab.