The paper presents experimental and numerical investigations on the behaviour of rubberized concrete short columns confined with aramid fibre reinforced polymer (AFRP) subjected to compression. Additionally, the possibilities to substitute fine aggregate with crumb rubber granules, obtained from discarded worn tires, in structural concrete is also assessed. Because replacing traditional concrete aggregates by rubber particles leads to a significant loss in compressive strength, the authors highlight the use of AFRP confinement to partially or fully restore the compressive strength by applying a number of 1, 2, and 3 layers. Analytical models available for confined regular concrete are used to predict the peak stresses and the corresponding peak strains. Some analytical models give accurate results in terms of peak stress while others better approximate the ultimate strain. The full stress-strain curve of rubberized concrete and the experimentally obtained values for the material properties of AFRP are used as input data for the numerical modelling. A good agreement is found between the results obtained for the peak stress and corresponding axial strain from both the numerical simulations and the experimental investigations.

The investigation of the interlaminar damage evolution on multi-layered composites as well as the numerical modelling techniques available for the simulation of the interface delamination are still a current concern. The complexity of modelling the mechanical behaviour and fracture modes of composite laminates is increased because of the anisotropic behaviour of the material, the fibre arrangement or other important parameters, such as stacking sequence, fibre orientation angle and the configuration of the composite laminates. Different failure modes may occur on multi-layered composites, which can lead to significant stiffness and strength reduction or to the complete loss of the load carrying capacity. The interlaminar stresses are the main factors responsible for the initiation and growth of the interlaminar failures such as delamination. They may occur as a result of manufacturing defects, low-velocity impacts or as an effect of the presence of the free edges. The delamination onset can lead to serious problems such as the premature buckling of the laminates, moisture infiltration, and stiffness degradation or even to progressive delamination growth and the separation of the layers of the composite laminates. The paper presents the numerical modelling of a multi-layered composite subjected to the tensile opening fracture mode as well as the investigation of the delamination growth. The purpose of the analysis is to study the delamination evolution on a symmetric composite laminate, starting from a preexisting initial crack, at the interface between the adjacent layers from the middle plane. The numerical modelling approach for the simulation of the delamination evolution is conducted based on the Cohesive Zone Method. The results are presented in terms of the total displacement jump and equivalent stress distributions on the layers of the composite laminates.

A growing interest is nowadays directed towards the numerical modelling and monitoring of the interlaminar damage evolution of composite laminates, but also to the numerical mathematical models and techniques for simulation of the interface delamination. Modelling and investigation of the mechanical behaviour and fracture modes of the multi-layered composites is a complex issue, since other important parameters, such as fibre orientation angles, stacking sequences and configuration of the composite laminates are added to the anisotropic character of the composite materials. Different failure modes may occur on multi-layered composites, while the delamination type fracture may lead to a considerable decrease of the load carrying capacity of the composite structures. Interlaminar stresses, which occur in composite laminates as an effect of the presence of the free edges, have a major influence on the delamination onset and the delamination growth. The paper summarizes the numerical methods and the approaches considered in the simulation of the delamination growth of composite laminates. The obtained results are figured in terms of the opening displacement at the interface crack tip and stress distributions on the plies of the multi-layered composites.

The results of a complex research and development program relating to the use of fiber reinforced polymeric composite strengthening solutions carried out at the Faculty of Civil Engineering and Building Services Iasi, are presented in this paper. The program has included the conceiving of the structural rehabilitation systems, the detailing and experimental testing of some solutions applied to reinforced concrete beams, slabs and columns (with circular and square cross-section). An efficient use of the component materials to improve the structural performance of the studied reinforced concrete element has been the main target of the research program. The main benefits resulted from the research program refer to the increase of the load capacities, the improvement of the structural response of all strengthened elements and a better control of the failure modes.

The high complexity of the load transfer mechanism at the steel column base connection yields for special care in both analysis/ design as well as in the actual errection stage of frame steel structures. Describing the real behaviour of the joint represents a key aspect in the overall structural analysis. The fully rigid or fully pinned assumptions on the column base joint behaviour have already been surpassed by more complex approaches in the analysis. As the dissipative capacity assessement is still under debate among specialists, the paper aims at delivering additional data to the problem. Laboratory tests, backed-up by numerical modeling investigations were performed on two natural scale steel columns base connection configurations under cyclic lateral loading conditions. Results of in terms of load - displacement and moment - rotation diagrams are hereinafter advanced for further studies purposes.

The interface behaviour of fibre reinforced polymer carbon plates bonded to concrete represents a key issue in the efficiency of the strengthening solutions based on externally bonded composite plates. An extensive research program was developed at the Faculty of Civil Engineering and Building Services from Iasi, to study the interfacial behaviour between carbon fibre reinforced polymeric composite (CFRP) plates and concrete. The study includes nine strengthened concrete elements which were tested under double shear pull testing set up. On the basis of the performed tests the recorded failure mode was the same for all tested specimens namely the interfacial failure. It essentially occurs in concrete close to the FRP plate-concrete interface. The recorded data have been used to plot the load-slip curves and strains distributions along the composite bonded plates. Together, they served later on to calibrate the finite element method (FEM) based modelling accompanying the laboratory tests.

The paper presents the results of a study including experimental tests and numerical modelling performed to investigate the influence of the edge distance and of the tightening torque on the behaviour of steel bolted lap joints of composite plates made of glass fibre reinforced polyesters (GFRP) manufactured by pultrusion. The experimental program analysis and testing of eighty samples corresponding to four assembly configurations with a variable number of bolts, with different marginal distances and two steps of tightening torques. Numerical models based on finite elements using ANSYS software package were designed for each assembly configuration tested experimentally, and the obtained results on bearing capacities for the studied joints have been compared.

The paper presents the capabilities of LUSAS software in predicting the structural behavior of FRP confined square columns by the use of the nonlinear concrete Drucker-Prager material model. The numerical modeling study was intended to accompany laboratory tests in describing the structural behavior of the analyzed structural elements. Results obtained on 1000mm high, 200mmx200mm cross-sectioned, ordinarily reinforced concrete (RC) square columns, in unconfined (UC) and confined (CC) configurations are discussed. Concrete was modeled with 8 nodded, HX8 type 3D solid elements while for internal steel reinforcements 2 nodded BRS3 bar elements were used. For the CFRP confined column, the external membrane was modeled with 4 nodded QTS4 type 2D thick shell finite elements (FE). Appropriate nonlinear material laws were used for steel and concrete, with modeling parameters calibrated based on the experimental results. The results show that LUSAS software can successfully be used for predicting the structural behavior of natural scale RC square cross-sectioned columns confined with external carbon fiber reinforced polymer (CFRP) membranes. Specific characteristics, such as the active area, stress concentrations, stress-strain relationships are satisfactorily highlighted. Key-Words: FRP confinement; square RC columns; Drucker-Prager; FE modeling

The Composite in Construction Research Group (CCRG) developed within the Faculty of Civil Engineering and Building Services Iasi, Romania has a good expertise in implementing Fiber Reinforced Polymer (FRP) composites based solutions for strengthening structures made of traditional materials such as reinforced concrete, masonry, timber and, more recently, steel. In an extended research program, the effects of external carbon FRP wrapping of non-circular reinforced concrete (RC) columns loaded in axial/ eccentrical compression have been studied. Results obtained on square, RC, externally CFRP wrapped columns loaded in eccentrical compression are presented and commented. Experimental laboratory works are backed-up by a numerical Finite Element Method (FEM) based modeling. Although the FRP confined columns have an improved overall structural response, the effectiveness is diminished due to the load eccentricity. Key-Words: FRP confinement; square RC columns; Eccentric loading, FEM Modeling

The flexural behavior of hybrid systems made of wood and carbon fibre reinforced polymer (CFRP) composite strips subjected to bending is analysed in this paper. The analysis is completed with an optimization study, based on the percentage of CFRP reinforcement and the strength classes of wood, relating to the hybrid beams. The results obtained from the analytical study are compared to those determined from numerical modelling, revealing the efficiency of the discussed reinforcing solutions based on CFRP strips. Finally, the authors highlight the importance of using these hybrid systems to achieve lightweight structures with convenient properties that meet the design requirements imposed by using large spans and resisting additional loads.

Construction has always been considered a major producer of serious environmental problems due to large consumption of resources in terms of materials and energy accompanied by environmental pollution; therefore, the projects aiming to reduce these damaging effects are more than welcome. The objective of sustainable development is difficult to be performed by civil and structural engineers at a global scale. However, some solutions and systems for load bearing and cladding elements that make the buildings or other types of civil engineering applications may contribute, at least partially, to attaining some goals of sustainability. Fiber reinforced polymeric (FRP) composite structures and hybrid systems may become sustainable when they utilise minimum material resources, increase the life span of buildings, have a very low environmental impact and ensure the high quality of civil infrastructures. The main objectives of the paper are related to the use of FRP composites in new construction components as well as rehabilitation of deteriorated civil engineering structures aiming to achieve sustainable solutions in civil and structural engineering. Starting from the concept of FRP composites and hybrid systems the authors describe a number of research and development projects carried out by the Composite in Construction Research Group (CCRG) at the Faculty of Civil Engineering, “Gheorghe Asachi” Technical University of Iasi. After a critical evaluation of FRP composite materials applied in construction, the authors describe and analyse their results which addressed a long term program including: all composite structures, multilayered sandwich construction, concrete elements reinforced with FRP composite bars, and modern solutions for structural rehabilitation of load carrying elements made of traditional building materials aiming to improve the building components performance.

Summary An international Round Robin Testing (RRT) programme on FRP reinforcement was conducted within the framework of the Marie Curie Research Training Network, ENCORE, and with the support of Task Group 9.3 of the International Federation for Structural Concrete (fib). Eleven laboratories and six manufacturers and suppliers participated in this exercise. As part of this exte nsive experimental endeavour, one or more of the following tests were performed by the partic ipating laboratories: 1) tensile tests on FRP bars and strips; 2) tensile tests on FRP lamina tes; 3) double bond shear tests on FRP laminates (Externally Bonded Reinforcement, EBR) and FRP bars/strip (Near Surface Mounted reinforcement, NSM). This paper will discusses the results of the RRT initiative, among which the experimental results of bond tests on concrete specimens strengthened with EBR and NSM FRP.

Structural rehabilitation of concrete columns using confining with composite membranes has become a largely accepted technique. An extensive experimental program has been carried-out at the Faculty of Civil Engineering and Building Services, lasi, aiming to evaluate the efficiency of the confining effect on concrete columns using fiber reinforced polymer (FRP) composite membranes. The results have established the effectiveness of wrapping solution, based on glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites, in increasing both strength and ductility. A predictive equation has been proposed by the authors, based on experimental results, in good agreement with existing models.

The large variety of modern composite materials and products existing nowadays in the construction market provides multiple and convenient possibilities to use them in both structural and nonstructural industrial construction elements. The main advantages of modern composite materials such as: corrosion resistance, high strength and modulus values compared to their density, acceptable deformability, tailored design and excellent formability enable the fabrication of new elements and the structural rehabilitation of the existing parts made of traditional materials. The high potential of the applicability of polymeric composites in new industrial construction correlated with fabrication procedures as well as the use of composites in modern strengthening solutions are presented in the paper.

Masonry as a structural material has high compressive strength and versatility, in achieving different structural and architectural shapes with attractive features. Masonry walls, arches and vaults are frequently used as components of the monumental buildings, many of them belonging to the historical heritage. Since the tensile strength of masonry is very low, under certain loading conditions in particular concentrated and nonsymmetrical forces, the masonry elements are vulnerable to cracking and to various failure mechanisms. Previous theoretical and experimental studies carried out by our research team have proven that the use of textile composite materials has a favourable influence upon the structural response and the load bearing capacity of the construction elements. The results of an experimental study on the structural behaviour and failure mechanisms of unstrengthened and strengthened masonry curved elements are presented in this paper. The experimental results describe the mechanical behaviour of masonry arches and vaults under typical loadings for monumental buildings. The strengthening schemes of the walls and curved elements have been designed and applied on the members utilizing textile composite membranes sometimes connected through textile composite strips. The overall behaviour and the failure mechanisms have been certainly improved in all cases, especially in masonry arch and vault type elements.

Recent advances in fiber reinforced polymer (FRP) composite technologies have resulted in alternative reinforcing materials that can be used efficiently as supplemental, externally bonded reinforcement, also contributing to the development of performant hybrid structures. However, the application of these hybrid solutions is associated with considerable difficulties due to the bond behaviour between FRP composites and traditional building materials. In bonded application, the interfacial behaviour and strength between the FRP materials and the substrate plays a major role in the structural behaviour and capacity of the hybrid system. An extensive experimental program has been initiated at the Faculty of Civil Engineering, the Technical University of Iasi, Romania to study the interfacial behaviour between carbon fiber reinforced polymer (CFRP) composite sheets and concrete as a preliminary required step to develop hybrid structures made of polymeric composites and traditional building materials. The experimental results obtained during the carried out tests provide an adequate characterization of the interfacial region regarding the force-slip behaviour, ultimate shear strength of the interface and the types of failure. It has been proven that the association of CFRP sheets and concrete is possible and a good bonding behaviour could be achieved.

Glass fibre reinforced polymer (GFRP) composites are currently being used as reinforcing bars in concrete and hybrid structures. An appropriate characterization of GFRP bars for concrete reinforcement is required by the structural designers prior to their use in structural applications. An extensive experimental program has been carried-out and the test results obtained from tensile tests on samples made of glass fibres and vinyl ester resins are presented and analysed in the paper. The experimental tests have been accompanied by a numerical modelling performed to characterize the stress field in the bar ends and along the test portion of the specimens. Three sets of 10 bars with diameters 8, 12 and 16 mm have been tested in tension, determining the ultimate tensile strength, the elastic longitudinal modulus and the ultimate tensile strain. The experimental results are in line with similar work carried out by other research teams. It has been found out that the experimental procedure and the accompanying numerical modelling provide an adequate characterization of the GFRP bars giving the main properties needed for design.

Mechanical joining techniques are used in construction industry all over the world on a daily basis. A further method of joining has proven to be highly successful – adhesive bonding. Known for thousands of years, adhesive bonding has become as important as other joining techniques as a result of the pace of developments in recent years. In many areas, this bonding technology has become a key technology. Virtually, all solid materials can be connected with one another using adhesives. Although bonding fibre reinforced polymeric composites to the concrete substrate is a relatively simple technique, the proper installation of the fibre reinforced polymeric composites is essential to ensure the adequate performance of the hybrid system. Since the installation procedures differ from one system to another, appropriate specifications will be clearly presented. The paper will include requirements to provide a quality joint assembly, meaning the special pre-treatments of the concrete surface. The material to be bonded is cleaned and prepared so that adhesives can adhere better to them.

Ageing construction infrastructure made of traditional materials is facing nowadays the challenge of upgrading. Quicker procedures are urgently needed and one of them is based on the use of fiber reinforced polymer (FRP) composite strengthening techniques. The paper presents the main strengthening techniques of structural members using FRP composite systems, studied and tested by the Composite in Construction Research Group (CCRG), from the Faculty of Civil Engineering lasi, These new solutions represent modern approaches based on recent advances in composite materials and strengthening technologies. Plate bonding to increase the bending capacity, shear strengthening using textile composite membranes, confining of circular and square columns with composite wrapping are among the most efficient strengthening methods utilized in civil engineering structures. The paper also describes some results on the FRP strengthening systems applied on masonry arches and timber elements.

Fibre reinforced composite materials are becoming more frequently used in civil engineering structures. One of the most practical applications of these new materials concerns the strengthening of reinforced concrete columns by means of confinement with fibre composite sheets. In the literature, various theoretical models have been proposed to describe the behaviour of confined concrete columns. The principal advantages of this technique are the high strength-to-weight ratio, good fatigue properties, non-corroding characteristics of the fibre reinforced polymers (FRP), and the facility of its application. The maximum efficiency of confining systems using FRP materials is reached in case of columns with circular cross-section and is explained by the fact that the entire section of the column is involved into the confinement effect. Rectangular confining reinforcement is less efficient as the confinement action is mostly located at the corners This paper reveals the most utilized techniques of performing composite confining systems for reinforced concrete columns, with their advantages and also disadvantages.