Ourania Tsioulou

Monolithic coefficient values for design when seismically strengthening RC columns with jackets

Monolithic coefficients correlate the behavior of strengthened reinforced concrete columns to that of respective monolithic columns and can be used to estimate strengthened column response. Finite element analyses are performed with different values of normalized axial load, jacket thickness, and jacket concrete strength. Four- and three-sided jackets are examined. Monolithic coefficients for strength, stiffness, and displacement at yield and failure are obtained by comparing results of strengthened and monolithic specimens. Calculated values are compared to existing code values and useful conclusions and practical guidance concerning the effect of the examined parameters on monolithic coefficient values are presented.

Biaxial stress due to shrinkage in concrete jackets of strengthened columns

The effect of restrained concrete shrinkage on the strength of concrete used to strengthen existing structures is investigated in this study. A series of compressive tests are performed on square prism concrete specimens where steel plates are placed in order to restrain free shrinkage. Results indicate that there is a significant reduction of concrete strength (20 to 30%) due to a biaxial stress state induced by the restrained concrete shrinkage. The experimental results are used to validate a numerical procedure proposed to simulate concrete shrinkage. A numerical investigation is then conducted on models that represent the concrete of a reinforced concrete jacket applied to an original column for strengthening purposes where the degree of restraint is different to that of the examined square prism specimens. It was found that that there is a further reduction of concrete strength (30 to 40%).

Effect of connection procedures on the behaviour of RC columns strengthened with RC layers and jackets

This study examines the behaviour of reinforced concrete (RC) columns strengthened with either a RC jacket or an additional RC layer. The main object of this work was to evaluate the behaviour of the strengthened specimens for different connection procedures used to bond the old and new concrete. For the column strengthened with a concrete jacket, the effect of the roughness of the interface on the behaviour of the strengthened specimen was examined. For the column strengthened using an additional RC layer, the presence of shear connectors between the old and new reinforcement was also examined to provide adequate connection between the two concrete members. The strength degradation of the interface because of the cyclic loading was taken into account. Using the results of the analyses, monolithic coefficients (these are special coefficients that correlate the behaviour of the strengthened specimens to the respective monolithic) were calculated for the different connection procedures examined.

Experimental Investigation on Thermal Conductivity and Mechanical Properties of a Novel Aerogel Concrete

Concrete is one of the most commonly used construction material worldwide (Kosmatka et al. 2008) with relatively low cost and good durability. Concrete has high compressive strength, high fire resistance, and also it is easy to be cast in any desire shape. On the other hand, the main drawbacks of concrete are related to its low tensile strength, high carbon dioxide emissions as a result of the use of Portland cement, and high thermal conductivity properties.

Numerical Investigation of Strengthened Unreinforced Masonry (URM) Structures with Ultra High Performance Fibre Reinforced (UHPFRC) Layers

A novel strengthening technique has been examined in this study using additional Ultra High Performance Fibre Reinforcement Concrete (UHPFRC) for the improvement of the structural performance of existing masonry structures. UHPFRC is a material with enhanced cementitious matrix and high percentage of steel fibres which is characterised by considerably improved compressive strength, tensile strength, and ductility.

Shrinkage Effect on Beams Strengthened with Additional Concrete Layers

A common technique used to increase the flexural capacity of reinforced concrete beams is theaddition of concrete layers in the compressive or in the tensile side. Until now, there are limitedstudies for the effect of the concrete shrinkage on the performance of the strengthened beams. Inmost of the published studies, concrete shrinkage is ignored and perfect connection is assumedbetween the old and the new concrete which is not conservative. In this study full scale beamsstrengthened with additional concrete layers in the tensile side have been investigated. The resultsof an experimental investigation together with numerical and analytical results are presented. Thecrucial effect of the concrete shrinkage on the slip of the interface is highlighted and the interactionbetween the slip induced by concrete shrinkage and the slip due to bending loading is presented.

RESTRAINED CONCRETE SHRINKAGE IN CASE OF STRENGTHENED BRIDGE PIERS BY CONCRETE JACKETING

Reinforced concrete (RC) jacketing of weak bridge pier columns is an effective ret- rofitting technique, particularly in seismic regions . The effect of restrained concrete shrink- age on the strength of concrete jackets is investigated in this study. A series of compressive tests are performed on square prism concrete specimens where steel plates are placed to rep- resent the restrained shrinkage effect on the concrete of the jacket. Then, a numerical proce- dure to simulate the concrete shrinkage effect using the finite element method is proposed and results are justified and validated using the experimental data. The results indicate that re- strained concrete shrinkage considerably reduces the stiffness and the maximum load of the strengthened elements.

Analytical prediction for the capacity of old-new concrete interfaces

The ANSYS computer program has been used to examine the behaviour of the interface between old and new concrete in a column strengthened by the addition of a concrete jacket. The friction, the cohesion and the thickness of the jacket are the three parameters that have been examined. Friction and cohesion are considered as the parameters that influence the strength at the interface. The maximum shear strength at the interface is given by the equation T lim = μP+c, where: μ is the frictional coefficient, P is the contact normal pressure and c is the contact cohesion. Initially, a smooth contact, where the friction and the cohesion are very small, has been examined. Then a rough contact surface was used. Finally, a column that has been strengthened with thicker concrete jacket has been investigated. After all of the above have been examined and with an adequate knowledge of the influence of the three parameters on the strength of the old-new concrete interface, an estimation of the appropriate attachment condition at the interface has been made in order to make the composite element behave as if it were monolithic. To achieve this, suitable coefficients of friction and cohesion have been determined.