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 polymer–strengthened 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 polymer–strengthened members as the main inputs of smeared crack modeling approaches

Prediction of the shear strength of reinforced masonry walls using a large experimental database and artificial neural networks

This paper analyses the accuracy of a selection of expressions currently available to estimate the in-plane shear strength of reinforced masonry (RM) walls, including those presented in some international masonry codes. For this purpose, predictions of such expressions are compared with a set of xperimental results reported in the literature. The experimental database includes specimens built with ceramic bricks and concrete blocks tested in partially and fully grouted conditions, which typically present a shear failure mode. Based on the experimental data collected and using artificial neural networks (ANN), this paper presents alternative expressions to the different existing methods to predict the in-plane shear strength of RM walls. The wall aspect ratio, the axial pre-compression level on the wall, the compressive strength of masonry, as well as the amount and spacing of vertical and horizontal reinforcement throughout the wall are taken into consideration as the input parameters for the proposed expressions. The results obtained show that ANN-based proposals give good predictions and in general fit the experimental results better than other calculation methods.This work was supported by the Fondo Nacional de Ciencia y Tecnologia de Chile, (Fondecyt de Iniciacion) [grant number 11121161].Aguilar, V.; Sandoval, C.; Adam Martínez, JM.; Garzón-Roca, J.; Valdebenito, G. (2016). Prediction of the shear strength of reinforced masonry walls using a large experimental database and artificial neural networks. Structure and Infrastructure Engineering. 12(12):1661-1674. https://doi.org/10.1080/15732479.2016.1157824S16611674121

Procedures for vibration serviceability assessment of high-frequency floors

Manufacturing plants that produce micro-electronic components, and facilities for extremeprecision experimental measurements have strict vertical vibration serviceability requirements due to sub-micron feature size or optical/target dimensions. Failure to meet these criteria may result in extremely costly loss of production or failure of experiments. For such facilities floors are massive but stiff, generally have first mode natural frequencies above 10Hz and are typically classed as ‘high frequency floors’. The process of design to limit in-service vibrations to within specific or generic vibration criteria is termed ‘vibration control’. Several guidance documents for vibration control of high frequency floors have been published, for different applications. These design guides typically propose simplifications of complex floor systems and use of empirical predictive design formulae. A recently published guide uses a more rigorous approach based on first-principle modal analysis and modeling footfalls as effective impulses, but there remain unresolved issues about its application, and this paper addresses these in order to develop an improved methodology. First, the significant but conventionally discounted contribution of resonance well above the conventionally accepted boundary between low and high frequency floors is examined. The level of necessary modeling detail is then considered along with the effect of accounting for adjacent bays in simulation of a regular multi-bay floors. Finally, while it is assumed that contributions of higher modes to impulsive response decrease so that a cut-off frequency can be prescribed, simulations demonstrate that with both effective impulse and real footfall forces, there is not necessarily asymptotic response with rising floor mode frequency. The conclusion is that there are no shortcuts to predicting response of high frequency floors to footfall excitation. Simulations must consider resonant response due to high order harmonics, provide adequate detail in finite element models and adopt a cutoff frequency that depends more on usage than on features of the floor or of the walking