Theodoros C. Rousakis

Concrete confined by FRP material: a plasticity approach

Carbon fiber-reinforced polymer (FRP) material has proved to be more efficient than other composites when applied to concrete columns as an external reinforcement. Because of its enhanced durability characteristics compared to glass or aramid, and its relatively high E-modulus, carbon FRP shows a higher confining performance. The behavior of 22 cylindrical 200×320 mm specimens (height to diameter ratio 1.6) that are externally wrapped by carbon FRP sheets in low volumetric ratios (0.23–0.7%) is presented. The specimens are subjected to axial monotonic load until failure occurs. Carbon FRP confinement, even in low volumetric ratios, seems to considerably increase the strength and especially the ductility of concrete. A constitutive model based on plasticity theory is applied. The model proposed and applied to steel-confined concrete in this paper is modified and calibrated so as to incorporate the dilation characteristics of the FRP-confined concrete. The model provides the stress–strain curves of axially loaded circular columns that are confined by FRP reinforcement. It can be used in FRP tube-encased concrete as well as in FRP sheet-wrapped concrete. Satisfactory correlation of experimental and analytical results is observed.

Design-Oriented Strength Model for FRP-Confined Concrete Members

AbstractThis study concerns assessing 20 existing models for predicting the compressive strength of concrete uniformly confined externally with composite materials. An extended database of 471 experiments on cylindrical concrete columns is utilized for the comparisons. The research classifies the experimental data in three distinguished subcategories according to the information available for the mechanical properties of the FRPs to investigate their effect on the divergences of the models. Apart from the use of the tensile strength obtained from coupon tests, the use of properties from the manufacturer data on FRP fibers can lead to minimum error of predicted strength of concrete externally wrapped or encased in FRP tubes. The study results in the proposal of an upgraded empirical model that indirectly encompasses the unique deformational characteristics of different Young’s moduli of FRP sheets and tubes. The model utilizes the strong linear dependence of the product of the varying effective strain at f...

Hybrid Confinement of Concrete by Fiber-Reinforced Polymer Sheets and Fiber Ropes under Cyclic Axial Compressive Loading

AbstractThis study looks into the mechanical behavior of concrete lightly confined by fiber-reinforced polymer (FRP) sheets made with glass fibers and by polypropylene fiber ropes (PPFRs). PPFRs have ultrahigh deformation at failure. The hybrid confining technique suggests applying the fiber rope on already cured FRP jackets as external unbonded reinforcement. No impregnation or gluing resins are necessary for the fiber rope (FR) application. The technique uses mechanical anchorage for the ends of the FR. Sixteen confined standard concrete cylinders, in two series and with different concrete qualities, were tested under repeated axial compression cycles of increasing displacement. They included confinement of one layer of glass FRP and FR confinement in different volumetric ratios. The investigation also compares columns confined only by glass fiber–reinforced polymer (GFRP) jackets or only by PPFR wrapping. The elaboration evaluates the axial stress versus axial and lateral strain behavior of the columns...

Axially Loaded Reinforced Concrete Columns with a Square Section Partially Confined by Light GFRP Straps

The study presents the experimental behavior of reinforced concrete columns strengthened externally by transverse glass fiber-reinforced polymer (GFRP) sheets. The columns had a square section and very low concrete strength. The internal steel reinforcement comprised sparse stirrups and longitudinal bars with two different qualities, S220 or B500C. The specimens were lightly confined by full wraps or partial GFRP straps. The straps were placed in between the existing steel stirrups. Three different widths of GFRP straps were examined. A series of plain concrete columns with identical GFRP strengthening was designed in order to assess the partial wrapping effects and compare them with reinforced concrete columns. The columns were subjected to axial compressive monotonic load up to failure. The achieved strength and ductility levels of the strengthened columns suggest that partial wrapping can efficiently upgrade the mechanical behavior of columns with a square section. Fully or partially GFRP wrapped columns with S220 slender bars require relatively higher GFRP strengthening than their counterparts with B500C columns to achieve similar ultimate strains.

CONCRETE CYLINDERS CONFINED BY CFRP SHEETS SUBJECTED TO CYCLIC AXIAL COMPRESSIVE LOAD

T. ROUSAKIS , C. S. YOU , L. DE LORENZIS , V. TAMUŽS , R. TEPFERS 5 1 Dept. of Civil Eng., Democritus University of Thrace, Xanthi, Greece 2 Dept. of Mechanical Eng., Pohang Univ. of Sci. and Tech., Pohang, South Korea 3 Dept. of Innovation Eng., University of Lecce, I-73100 Lecce, Italy 4 Institute of Polymer Mechanics, Univ. of Latvia, Aizkraukles 23, Riga, Latvia 5 Dept. of Building Materials, Chalmers University of Tech., Goteborg, Sweden

EXPERIMENTAL AND NUMERICAL RESPONSE OF CFRP-STRENGTHENED CONCRETE BEAMS WITH LOW OR MEDIUM STEEL CORROSION

The present study deals with the validation of a numerical model that can approximate the flexural behavior of corroded reinforced concrete beams patch repaired and strengthened with carbon fiber reinforced polymer (CFRP). Six reinforced concrete beams were corroded under an accelerated corrosion technique to low and medium corrosion levels respectively. Two beams were used as control, while the remaining four were patch repaired and strengthened with externally bonded reinforcement (EBR) and near surface mounted reinforcement (NSM) with equivalent axial rigidity. After repairing the concrete substrate and subsequent bonding of the CFRP reinforcement, the beams were tested to failure under fourpoint loading. The developed 3D finite element models take into account the different mechanical properties and detailing of corroded bars and of the mortar patch as well as of the existing concrete – mortar patch interface and of the NSM or EBR FRP – mortar patch interface. The FE analyses may reproduce the observed modes of failure including crushing of the concrete after steel yielding and debonding of CFRP. The analytical load-deflection curves compare well with the experimental flexural behavior of the corroded RC beams patch repaired and strengthened with EBR and NSM CFRP laminates. 343 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 343-352