Nino Spinella

Nonlinear Analysis of Beams Reinforced in Shear with Stirrups and Steel Fibers

The modified compression field theory (MCFT) and the disturbed stress field model (DSFM) are often used to predict the nonlinear behavior of reinforced concrete structures. This study presents several extensions of the MCFT and DSFM to the case of high-strength steel fiber-reinforced concrete beams subjected to transverse loads. Experimental four-point bending tests were conducted on 12 concrete beams with a different percentage of fibers and/or stirrups. To validate the updates introduced in the analytical models, numerical analysis was performed using nonlinear finite element software. Modeling of the post-peak softening branch of the tensile and compressive constitutive curves of fibrous concrete was included in the MCFT-based analytic procedures to capture the structural behavior of the specimens. The numerical results indicate that the model is effective in predicting the structural response of both members reinforced with steel fibers only and beams with stirrups and steel fibers as transverse reinforcement. The experimental and numerical results highlighted the capacity of steel fibers to partially substitute the stirrups as shear reinforcement in beams. Coupled transverse reinforcement, provided by both stirrups and steel fibers, can optimize cost and structural performance considerations.

Simple Plastic Model for Shear Critical SFRC Beams

A simple physical model, for prediction of ultimate shear strength of steel fiber-reinforced concrete (SFRC) beams is developed on the basis of a plastic approach originally proposed for reinforced concrete beams without stirrups. It is founded on the hypothesis that cracks can be transformed into yield lines, and thus is know as crack sliding model (CSM). First, the CSM is improved to take into account the shear strength increase for deep beams, due to the arch effect. Then, the effectiveness factors for fibrous concrete under biaxial stresses are evaluated, taking into account the postcracking tensile strength of SFRC and its ability to control slippage along shear cracks. With the aim of providing a handy and fast tool for design of SFRC beams without stirrups, a simplified design model is also derived. Finally, the proposed models are validated by the results of a large set of experimental tests taken from literature.

Stress-Strain Law for Confined Concrete with Hardening or Softening Behavior

This paper provides a new general stress-strain law for concrete confined by steel, fiber reinforced polymer (FRP), or fiber reinforced cementitious matrix (FRCM), obtained by a suitable modification of the well-known Sargin’s curve for steel confined concrete. The proposed law is able to reproduce stress-strain curve of any shape, having both hardening or softening behavior, by using a single closed-form simple algebraic expression with constant coefficients. The coefficients are defined on the basis of the stress and the tangent modulus of the confined concrete in three characteristic points of the curve, thus being related to physical meaningful parameters. It will be shown that if the values of the parameters of the law are deduced from experimental tests, the model is able to accurately reproduce the experimental curve. If they are evaluated on the basis of an analysis-oriented model, the proposed model provides a handy equivalent design model.

Shear strength degradation due to flexural ductility demand in circular RC columns

An analytical model was developed to estimate the shear-strength degradation and the residual capacity of circular reinforced concrete (RC) columns subjected to seismic action. The proposed model is an upgrade of a previously proposed model for axial force

Experimental Tests and FEM Model for SFRC Beams under Flexural and Shear Loads

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Increasing the Capacity of Existing Bridges by Using Unbonded Prestressing Technology: A Case Study

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Stress Field Model for Strengthening of Shear-Flexure Critical RC Beams

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