Hugo C. Biscaia

In-Plane Displacement and Strain Image Analysis

Measurements in civil engineering load tests usually require considerable time and complex procedures. Therefore, measurements are usually constrained by the number of sensors resulting in a restricted monitored area. Image processing analysis is an alternative way that enables the measurement of the complete area of interest with a simple and effective setup. In this article photo sequences taken during load displacement tests were captured by a digital camera and processed with image correlation algorithms. Three different image processing algorithms were used with real images taken from tests using specimens of PVC and Plexiglas. The data obtained from the image processing algorithms were also compared with the data from physical sensors. A complete displacement and strain map were obtained. Results show that the accuracy of the measurements obtained by photogrammetry is equivalent to that from the physical sensors but with much less equipment and fewer setup requirements.

Composites and FRP-Strengthened Beams Subjected to Dry/Wet and Salt Fog Cycles

AbstractCarbon (CFRP) and glass (GFRP) fiber-reinforced composites of epoxy matrix are considered in the study, with greater emphasis on GFRP. Accelerated conditioning was imposed in the form of salt fog cycles, hygrothermal cycles (tap water), and tidal-like cycles (aqueous solution of NaCl, 50  g/L), both on laminate composites and on beams externally reinforced with fiber-reinforced polymers (FRP) on their soffit. Freeze/thaw cycles were also applied to the study of degradation of the laminates. Mechanical tests showed degradation due to damage to the matrices, fiber-matrix linkage or bond between FRP and concrete. Several advanced techniques were used to interpret the results and enable better understanding of the phenomenological data. Changes on the glass transition temperature (Tg) of the epoxy matrix are reported as possible indicators of decrease of the tensile strength of the GFRP composite. Attention is given to the evolution of the relative values of the tensile strength of concrete and adhesi...

Influence of Temperature Cycles on Bond between Glass Fiber-Reinforced Polymer and Concrete

Reinforced concrete (RC) beams externally strengthened with glass fiber-reinforced polymer (GFRP) strips bonded to the soffit may see their load-carrying capacity reduced due to environmental conditions-especially due to the deterioration of bond between the adhesively bonded laminates and concrete, causing premature failure. More research has been published on the detachment of the laminate progressing from the anchorage zone than on failure induced by the formation of flexural or shear-flexural cracks in the midspan followed by fiber-reinforced polymer (FRP) separation and failure designated as intermediate crack (IC) debonding. An experimental program to study degradation of the GFRP laminate beam specimens after accelerated temperature cycles, namely: 1) freezing-and-thawing type; and 2) cycles of the same amplitude (40°C [104°F]) and an upper limit approximately 70% of the glass vitreous transition temperature of the resin, Tg, is described. Effects on the bond stress and ultimate capacity are reported. Substantial differences between shear and bending-induced failure and a decrease of bond stresses and engagement of the laminates on the structural response are analyzed.

Mechanical response of anchored FRP bonded joints: A nonlinear analytical approach

ABSTRACT This article presents a nonlinear analytical solution for the prediction of the full-range debonding response of mechanically anchored, fiber-reinforced polymer (FRP) composites from the substrate. The nonlinear analytical approach predicts, for any monotonic loading history or bonded length, the relative displacements (or slips) between materials, the strains in the FRP composite, the bond stresses within the interface, and the stresses developed in the substrate. The load-slip responses of FRP-to-substrate interfaces with short and long bonded lengths are motives of analysis and discussion. The solutions obtained from the proposed approach are also compared with other experimental results found in the literature.

Influence of External Compressive Stresses on the Performance of GFRP-to-Concrete Interfaces Subjected to Aggressive Environments: An Experimental Analysis

AbstractDespite the fact that fiber reinforced polymer (FRP) composites are a reliable structural material with reasonable durability performance, the environment to which the strengthened structure is exposed can make the strengthening system vulnerable. In this study, the effectiveness of externally bonded reinforcement (EBR) systems when external compressive stresses are applied to glass fiber reinforced polymers (GFRP)-to-concrete interfaces in several aggressive environments is analyzed. The compressive stress imposed on the GFRP-to-concrete interface intends to simulate, for instance, the effect produced by a mechanical anchorage system applied to the EBR system. The design and the region to set those mechanical anchorage systems are not yet well understood and are mostly applied without really knowing how they will behave. This work shows an exhaustive experimental program based on several double shear tests subjected to salt fog cycles, dry/wet cycles and two distinct temperature cycles: from −10°...

Old Suspended Timber Floors Flexurally-Strengthened with Different Structural Materials

The design of timber beams has strict limits when it comes to the Serviceability Limit States (SLS) either in short-term or in long-term deflections. In order to face this aspect efficiently, the increase of the cross section of the beams might be considered as a solution. However, the prohibitive increase of the costs associated to this solution or the change of the initial architecture design of the building, opens the opportunity to find new and more efficient solutions. In that way, the use of additional reinforcements to the timber beams may be seen as a promising solution because either new or old structures would keep always their original aesthetical aspect with no significant self-weight increase and improving their behaviour to short and long-term actions. Therefore, the current study is dedicated to the analysis of composite timber beams where Fiber Reinforcement Polymers (FRP), steel or stainless steel are used to improve the stiffness, strength and deflection behaviour of old suspended timber floors. An experimental program was conducted where old suspended timber floors reinforced with CFRP strips were subjected to 4-point bending tests. A simplify nonlinear numerical model was developed to simulate the bending behaviour of the specimens and several other cases with other reinforcement configurations and different structural materials were assumed. The numerical analysis herein presented also takes into account both Ultimate and Serviceability Limit States of the reinforced specimens.

Cyclic Loading Behaviour of Double Strap Bonded Joints with CFRP and Aluminium

The adhesively bonded joints behaviour under cyclic loading is not yet well understood due to its inherent complexity. Numerical approaches appear, therefore, as the easiest way to simulate such mechanical behaviour. In this work, double strap bonded joints with Carbon Fibres Reinforced Polymers (CFRP) and aluminium are numerically simulated and subjected to a cyclic loading history. In the numerical simulation, the Distinct Element Method (DEM) is used and it is assumed cohesive bi-linear bond-slip models with local damage of the interface. The evaluation of the bonded joints under cyclic loading is made by comparing the results with those simulated with a monotonic loading.

A Simple Analytical Approach for Creep Analysis of EB-FRP Systems

Based on a few experimental results available in the literature, this work presents a simple analytical approach that allows the study of the long-term behaviour of CFRP-to-concrete interfaces under an initial sustaining load. Only the elastic regime is studied, which means that the interfacial maximum bond stress and maximum slip are never exceeded. Therefore, the maximum initial load to be sustained by the joints is limited by its corresponding elastic value. The analytical results provided by the proposed model are compared with some experimental results found in the literature. The results showed strain redistribution throughout the bonded length over the time.

Durability of GFRP Strengthening under Environmental Degradation

Degradation of properties of (i) laminated plates of polymeric matrix and (ii) RC members with GFRP as their outer reinforcement, due to artificially accelerated aging, is described and interpreted. The effects of environmental exposure on bond between GFRP strips and concrete are examined, namely the ensuing decrease of the structural strength of the beams. Cycles of environmental aggression are shown to reduce the tensile strength of GFRP flat coupons testing, but to have relatively scarce consequences on the overall capacity of confined concrete columns. The comparison of different aging processes shows, e.g., that salt fog cycles reduced the compressive strength of the columns, and that a further reduction resulted from immersion in salt water. RC beam specimens with external tensile reinforcement of GFRP were subjected to bending along stages of artificial aging to study the effects of the latter on bond. Failure took place, most often, by rupture of concrete at a short depth from the interface with the GFRP reinforcement. Preliminary computational modeling is described that utilizes experimental data generated in the study.