CEB-FIP MC90 Research Articles

Numerical Analysis of Deep Tunnels in Viscoplastic Rock Mass Considering the Creep and Shrinkage of the Concrete Lining

This paper aims to show, through numerical parameter analysis on a finite-element method with axisymmetry hypothesis, the long-term effect involving the creep and shrinkage of the concrete lining in deep tunnel problems. The excavation process is simulated by the deactivation and activation method. A viscoplastic constitutive model for the rock mass and an elastic and viscoelastic constitutive model for the lining are used in the software ansys. Perzyna’s viscoplastic constitutive model with an associated flow rule with von Mises yield surface is considered. The viscoelastic model is implemented in ansys using the customization feature. The shrinkage is given by the CEB-FIP MC90 formulation and the creep part is modeled through a Generalized Kelvin chain, according to the solidification theory of Bažant and Prasannan, whose parameters are adjusted with the creep function of the CEB-FIP MC90. Compared with an elastic lining, the viscoelastic line showed a difference (in average terms), in the equilibrium convergence at the end of tunnel construction between 6% and 37%. This value increases to 8% and 72% in the long-term convergence.

Customization of a software of finite elements to analysis of concrete structures: long-term effects

Abstract Concrete is a material that presents time-delayed effects associated with creep and shrinkage phenomena. The numerical modeling of the creep is not trivial because it depends on the age of the concrete at the time of loading, which makes necessary to store the history of loads to apply the principle of superposition. However, a problem formulated in finite elements has many points of integration, making this storage impossible. The Theory of Solidification, together with incremental algorithm developed by Bazant e Prasannan ([1], [2]), solves this problem. Therefore, this paper presents the adaptation of this algorithm to a finite element commercial software (ANSYS) considering the creep, according to the CEB-FIP Model Code 1990 [3]. The results demonstrate that the deformations provided by this adaptation are in accordance with the analytical solution given by the CEB-FIP MC90, including cases where the loads are applied at different ages of the concrete.

Creep behavior of precast segmental box girder bridge

The concrete creep effect is more obvious when the box girder is assembled by segment. It is necessary to consider the influence of the loading value of the section at different time and the different age of concrete at different stages. In this paper, ACI209R-92, CEB-FIP MC90 and B3 and other concrete creep models are compared. The results show that the B3 model has many factors to consider and the calculation accuracy is high. Secondly, this paper discusses the influence of the segmental construction technology on the creep calculation, and puts forward the characteristics of the stress analysis of the segmental box girder. Finally, on the basis of the B3 model of concrete creep, the Midas software is used to establish the calculation model of segmental box girder, and the internal force and deformation of the box girder are calculated. The results show that the internal force and deformation of the box girder is too large due to the poor integrity of the segmental assembling process, which will seriously affect the normal service performance.

Failure Mode Prediction for One-Way Reinforced Concrete Flat Slabs with Rectangular Columns

Flat slabs are reinforced concrete plates directly supported on columns, without intermediary beams. This structural system has been sufficiently used in the last decade, mainly for successful reach large spans and allowing "layouts" flexible. On the other hand, these slabs can be characterized as two-ways or one-ways, depending on the loading conditions, it is still stand out that NBR 6118 does not distinguish the types of flat slabs and make no reference to how much the punching resistance in the case of the one-ways flat slabs and it is known that normally these flat slabs presents low failure loads compared to the two-ways one. In this work presents a proposal, completely detailed in Damasceno’s master thesis (2007), for forecast the failure mode of one-way flat slabs with rectangular columns and without shear reinforcement, based on the prescriptions of CEB-FIP MC90 and on the Yield Line Theory. Equations that describe the behavior of the slabs in the limit between punching shear and flexure failures, considering the material’s properties, dimensions of the flat slab and the column’s cross sections, rate of flexure reinforcement in two directions, etc. are presented, parameters that influence on the slabs’ behavior. The estimates had been satisfactory and able to forecast one-way flat slabs’ failure modes.

A Comparative Study of the Shear Strength Prediction for Reinforced Concrete Beams without Shear Reinforcement

This paper focuses on the assessment of the shear strength prediction established in the brazilian concrete code, NBR6118/2007[1], for reinforced concrete beams without web reinforcement. The values obtained by using the brazilian code equation are compared with a significant number of available experimental data and with those predicted by the expressions of other national and international codes, such as CEB-FIP MC90[2] and ACI-318/11[3]. The brazilian concrete code regarding shear capacity of reinforced concrete elements are explicitly assumed to be valid only for concrete strengths up to 50 MPa. It is shown that the code equation may be unconservative in a large number of cases. This discrepancy increases with increasing concrete strength, decreasing longitudinal reinforcement ratio and increasing beam depth.

Evolutionary multivariate adaptive regression splines for estimating shear strength in reinforced-concrete deep beams

This study proposes a novel artificial intelligence (AI) model to estimate the shear strength of reinforced-concrete (RC) deep beams. The proposed evolutionary multivariate adaptive regression splines (EMARS) model is a hybrid of multivariate adaptive regression splines (MARS) and artificial bee colony (ABC). In EMARS, MARS addresses learning and curve fitting and ABC implements optimization to determine the optimal parameter settings with minimal estimation errors. The proposed model was constructed using 106 experimental datasets from the literature. EMARS performance was compared with three other data-mining techniques, including back-propagation neural network (BPNN), radial basis function neural network (RBFNN), and support vector machine (SVM). EMARS estimation accuracy was benchmarked against four prevalent mathematical methods, including ACI-318 (2011), CSA, CEB-FIP MC90, and Tang’s Method. Benchmark results identified EMARS as the best model and, thus, an efficient alternative approach to estimating RC deep beam shear strength.

Experimental Study on Creep Behavior of Prestressed Concrete Beams with Pretensioned Bent-Up Tendons for 600 Days

The prestressed concrete beam with pretensioned bent-up tendons combines many advantages of the straight-line pretensioned prestressed beams and the curvilinear posttensioned beams. To improve its application in bridges, long-term deformation should be exactly predicted and controlled. Three prestressed concrete beams with pretensioned bent-up tendons XPB1,XPB2, XPB3 were fabricated, and XPB1 and XPB3 were put in standard curing room, but XPB2 were put in outdoor environment. All the experimental beams were simple supported under long-term loads. Their deformation such as creep strain and long-term deflection in mid-span section were observed about 600 days. By analyzing the influence factor and time-history law of creep coefficient and long-term coefficient, creep coefficient equation of the test beams was fitted and compared with the code model such as ACI209R-92, CEB-FIP MC90 and 86 model proposed by China Academy of Building Research, and the ±10% margin error of this model was pointed out. All these results may offer the initial value of long-term deformation of the prestressed concrete beams with pretensioned bent-up tendons.

Mechanical properties of prestressed self-consolidating concrete

Since the mix design of self-consolidating concrete (SCC) differs from that of conventional concrete, mechanical properties of SCC may differ from those of vibrated concrete. An experimental program was performed to evaluate mechanical properties of SCC used for precast, prestressed applications. Sixteen SCC mixtures with a fixed slump flow of 680 ± 20 mm were prepared with different mixture parameters, including binder content and binder type, w/cm, dosage of viscosity-modifying admixture, and sand-to-total aggregate volume ratio. Two high-performance concrete mixtures that represent typically concrete used for precast, prestressed applications were investigated for the control mixtures. They were proportioned with 0.34 and 0.38 w/cm and had slump values of 150 mm. Mechanical properties of SCC were compared to code provisions to estimate compressive strength, elastic modulus, and flexural strength. The modified ACI 209-90 and CEB-FIP MC90 codes are found to provide good estimate for compressive strength prediction. The AASHTO 2007 model can provide good prediction of the elastic modulus and flexural strength of SCC.

Tempiamųjų GelžBetoninių Elementų Diskrečiųjų Plyšių Modelio Analizė

Adequate modelling of reinforced concrete (RC) cracking, particularly post-cracking behaviour (tension stiffening), as one of the major sources of nonlinearity, is the most important and difficult task for deformation analysis. Deformationbehaviour of the cracked RC members is a complex process, including a wide range of effects such as differentstrength and deformation properties of steel and concrete, concrete cracking, tension-softening and tension-stiffening,bond slip between reinforcement and concrete etc. Even under low load, behaviour can be non-linear, which presents a challenge for calculating the deformations of RC members.When stress in concrete first reaches tensile strength at the weakest section,cracking occurs. After the formation of the first primary crack up to the final one, concrete contribution steadily decreases. At the final cracking point, the stable crack pattern has been reached. Increase in load will result in a further decrease of concrete contribution due to bond-slip causing cover-controlled cracks to develop between the primary cracks and a gradual breaking down of the bond. This process can be imagined as the formation of internal secondary cracks along the deformed bar due to bond stress transfer to sound concrete in between primary cracks. Total stresses in the cracked tensile reinforcement consisted of genuine stresses corresponding to the average strain of steel and additional stresses due to tension-stiffening. The internal forces that represent the latter stresses are called the residual and can be used for assessing the average bond behavior of RC members. This paper investigates tension-stiffening effect in RC members. The discrete cracking model of RC member is described in the paper. The discussed approach is based on bond-slip relationship that models the bond-action between concrete and reinforcement. This approach is realistically capable of modelling cracking and determining crack widths and deformations. However, the accuracy of calculation results depends on the assumed bond stress-slip relationship. A number of recent investigations aimed at developing and modifying such models were performed intending that discrete cracking modelling technique could become a powerful tool for the analysis of reinforced concrete members. The present study is dedicated to deformation analysis of reinforced members that are subjected to pure tension and is based on the results of the experimental program reported in literature. The average deformations of such members were calculated applying the discrete cracking method using different bond stress-slip relationships and compared with test results reported in literature. It was concluded that relationship recommended by CEB-FIP MC90 was unacceptable for the analysis performed.

The creep feature analysis of the high performance concrete

In order to seek the creep change rules of used concrete with two different mix proportions, the test is carried out in the situation which is similar to that of the creation of concrete C60, and the creep test on the concrete of two different mix proportions is done under standard lab. Based on creep test of the high performance concrete, the creep degree and the creep coefficient are obtained. By comparing with the wide-adopted models of ACI209 (1997) and CEB-FIP MC90, it is found that the test result is good at its regularity and the research results offer reference to the calculating analysis of the on-the-spot experimental data.