276 research outputs found
Micromechanical modeling of tension stiffening in FRP-strengthened concrete elements
This article presents a micromodeling computational framework for simulating the tensile response and tension-stiffening behavior of fiber reinforced polymerâstrengthened reinforced concrete elements. The total response of strengthened elements is computed based on the local stress transfer mechanisms at the crack plane including concrete bridging stress, reinforcing bars stress, FRP stress, and the bond stresses at the bars-to-concrete and fiber reinforced polymer-to-concrete interfaces. The developed model provides the possibility of calculating the average response of fiber reinforced polymer, reinforcing bars, and concrete as well as the crack spacing and crack widths. The model, after validation with experimental results, is used for a systematic parameter study and development of micromechanics-based relations for calculating the crack spacing, fiber reinforced polymer critical ratio, debonding strength, and effective bond length. Constitutive models are also proposed for concrete tension stiffening and average response of steel reinforcing bars in fiber reinforced polymerâstrengthened members as the main inputs of smeared crack modeling approaches
Assessing the efficiency of CFRP discrete confinement systems for concrete cylinders
Concrete columns requiring strengthening intervention always contain a certain percentage of steel
hoops. Applying strips of wet lay-up carbon fiber reinforced polymer (CFRP) sheets in-between the existent
steel hoops might, therefore, be an appropriate confinement technique with both technical and economic
advantages, when full wrapping of a concrete column is taken as a basis of comparison. To assess the
effectiveness of this discrete confinement strategy, circular cross section concrete elements confined by distinct
arrangements of strips of CFRP sheet are submitted to a direct compression load up to the failure point. The
influence of the width of the strip, distance between strips, number of CFRP layers per strip, CFRP stiffness and
concrete strength class on the increase of the load carrying capacity and ductility of concrete columns, is
evaluated.
An analytical model is developed to predict the compressive stress-strain relationship of concrete columns
confined by discrete and continuous CFRP arrangements. The main results of the experimental program are
presented and analyzed and used to assess the model performance
Modelling the influence of age of steel fibre reinforced self-compacting concrete on its compressive behaviour
Steel fibre reinforced self-compacting
concrete (SFRSCC) can combine the benefits of
self-consolidating concrete technology with those
derived from adding steel fibres to quasi-brittle
cement based materials. In a recent applied research
project joining pre-casting industry, private and
public research institutions, a method was developed
to design cost-competitive SFRSCC of rheological
and mechanical properties required for the prefabrication
of SFRSCC facžade panels. To assure safe
demoulding process of the panels, the influence of the
concrete age on the compression behaviour of the
SFRSCC should be known. For this purpose, series of
tests with specimens of 12 h to 28 days were tested in
order to analyze the age influence on the compressive
strength, strain at peak stress, Youngâs modulus, and
compressive volumetric fracture energy. The experimental
program was divided in two groups of test
series, one with SFRSCC of a volumetric fibre
percentage of 0.38% and the other with 0.57%. To
apply the obtained data in the design and numerical
analysis framework, the influence of the age on
these SFRSCC properties was modelled. This work
describes the carried out experimental program, presents and analyzes the obtained results, and
provides the derived analytical expressions
Deflection control for reinforced recycled aggregate concrete beams: Experimental database and extension of the fib Model Code 2010 model
Recycled aggregate concrete (RAC) has emerged as a viable solution for
solving some of the environmental problems of concrete production.
However, design guidelines for deflection control of reinforced RAC
members have not yet been proposed. This study presents a
comprehensive analysis of the applicability of the fib Model Code 2010
(MC2010) deflection control model to reinforced RAC beams. Three
databases of long-term studies on natural aggregate concrete (NAC) and
RAC beams were compiled and meta-analyses of deflection predictions
by MC2010 were performed. First, the MC2010 deflection control model
was tested against a large database of long-term tests on NAC beams.
Second, a database of RAC and companion NAC beams was compiled
and initial and long-term deflections were calculated using the MC2010
model. It was shown that deflections of RAC beams are significantly
underestimated relative to NAC beams. Previously proposed
modifications for MC2010 equations for shrinkage strain and creep
coefficient were used, and new modifications for the modulus of elasticity
and empirical coefficient ÎČ were proposed. The improved MC2010
deflection control model on RAC beams was shown to have equal
performance to that on companion NAC beams. The proposals presented
in this paper can help engineers to more reliably perform deflection
control of reinforced RAC members.This is the peer-reviewed version of the article:
N. ToĆĄiÄ, S. MarinkoviÄ, and J. de Brito, âDeflection control for reinforced recycled aggregate concrete beams: Experimental database and extension of the fib Model Code 2010 modelâ, Structural Concrete, vol. 20, no. 6, pp. 2015â2029, 2019 [https://doi.org/10.1002/suco.201900035
Analytical model for residual bond strength of corroded reinforcement in concrete structures
Bond strength deterioration in corrosion-damaged reinforced concrete structures significantly affects serviceability and load-carrying capacity in their remaining service life. This paper presents a new analytical model for predicting the cracking development in the surrounding concrete and the residual bond strength of rebar in concrete structures due to reinforcement corrosion. The proposed analytical method adopts the thick-walled cylinder model for the cover concrete and considers the realistic properties of the corrosion-induced cracked concrete such as anisotropic behavior, residual tensile strength, and reduced tensile stiffness. As corrosion progresses, three phases for bond strength evolution associated with concrete cracking development are defined and the corresponding corrosion levels in each phase are determined. By using the constructed new governing equation, the crack width growth in the concrete cover and the radial bursting pressure at the bond interface are evaluated. The ultimate bond strength is then estimated from the contributions of adhesion, confinement, and corrosion pressure as a function of corrosion level. Finally, the effectiveness of the proposed analytical model is demonstrated by comparing the predicted results with experimental data available, and the results show that the proposed model is useful for predicting the bond strength evolution of the corroded rebar in concrete structures
Numerical modelling of composite floor slabs subject to large defections
This paper is concernedwith the ultimate behaviour of composite floor slabs. Steel/concrete composite structures are increasingly common in the UK and worldwide, particularly for multi-storey construction. The popularity of this construction formis mainly due to the excellent efficiency offered in terms of structural behaviour, construction time and material usage all of which are particularly attractive given the ever-increasing demands for improved sustainability in construction. In this context, the engineering research community has focused considerable effort in recent years towards understanding the response of composite structures during extreme events, such as fires. In particular, the contribution made by the floor slab system is of crucial importance as its ability to undergo secondary load-carrying mechanisms (e.g. membrane action) once conventional strength limits have been reached may prevent overall collapse of the structure. Researchers have focused on developing the fundamental understanding of the complex behaviour of floor slabs and also improving themethods of analysis. Building on thiswork, the current paper describes the development and validation of a finite element model which can simulate the response of floor slab systems until failure, both at ambient and elevated temperature. The model can represent the complexities of the behaviour including the temperature-dependent material and geometric nonlinearities. It is first developed at ambient temperature and validated using a series of experiments on isolated slab elements. The most salient parameters are identified and studied. Thereafter, the model is extended to include the effects of elevated temperature so it can be employed to investigate the behaviour under these conditions. Comparisons with current design procedures are assessed and discussed
Modeling for assessment of long-term behavior of prestressed concrete box-girder bridges
Large-span prestressed concrete (PC) box-girder bridges suffer excessive vertical deflections and cracking. Recent serviceability failures in China show that the current Chinese standard modeling approach fails to accurately predict long-term deformations of large box-girder bridges. This hinders the efforts of inspectors to conduct satisfactory structural assessments and make decisions on potential repair and strengthening. This study presents a model-updating approach that aims to assess the models used in the current Chinese standard and improve the accuracy of numerical modeling of the long-term behavior of box-girder bridges, calibrated against data obtained from a bridge in service. A three-dimensional finite-element model representing the long-term behavior of box-girder sections is initially established. Parametric studies are then conducted to determine the relevant influencing parameters and to quantify the relationships between those and the behavior of box-girder bridges. Genetic algorithm optimization, based on the response-surface method (RSM), is used to determine realistic creep and shrinkage levels and prestress losses. The modeling results correspond well with the measured historic deflections and the observed cracks. This approach can lead to more accurate bridge assessments, which result in safer strengthening and more economic maintenance plans
CFRP flexural and shear strengthening technique for RC beams : experimental and numerical research
Near surface mounted (NSM) technique has proved to be a very effective
technique for the flexural strengthening of RC beams. Due to the relatively small
thickness of the concrete cover that several beams present, cutting the bottom arm of
steel stirrups for the installation of NSM laminates might be a possible strategy, whose
implications on the beamâs load carrying capacity need to be assessed. When steel
stirrups are cut, however, the shear resistance can be a concern. This also happens
when a strengthening intervention is carried out to increase the flexural resistance of a
beam, since in certain cases it is also necessary to increase the shear resistance in order
to avoid the occurrence of brittle shear failure. The present work assesses the
effectiveness of a technique that aims to increase both the flexural and shear resistance
of RC beams that have the bottom arm of the steel stirrups cut for the application of
NSM laminates. This assessment is performed by experimental and numerical
research. The main results of the experimental program are presented and analyzed,
and the innovative aspects of a constitutive model implemented in a computer program
are described, being their virtues and deficiencies discussed.The study reported in this paper forms a part of the research program "CUTINEMO - Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures" supported by FCT, PTDC/ECM/73099/2006. The authors wish to acknowledge the support also provided by the S&P, Casais and Artecanter Companies. The second Author acknowledges the grant under the aforementioned research project. The third author acknowledges the financial support of FCT, PhD Grant number SFRH/BD/23326/2005
Reliability analysis of moment redistribution in reinforced concrete beams
Design codes allow a limited amount of moment redistribution in continuous reinforced concrete beams and often make use of lower bound values in the procedure for estimating the moment redistribution factors. Here, based on the concept of demand and capacity rotation, and by means of Monte Carlo simulation, a probabilistic model is derived for the evaluation of moment redistribution factors. Results show that in all considered cases, the evaluated mean and nominal values of moment redistribution factor are greater than the values provided by the ACI code. On the other hand, the 5th percentile value of moment redistribution factor could be lower than those specified by the code. Although the reduction of strength limit state reliability index attributable to uncertainty in moment redistribution factors is not large, it is comparable to the reduction in reliability index resulting from increasing the ratio of live to dead load
- âŠ