This research project will investigate the behaviour of reinforced concrete walls with openings and the possibility of strengthening them using fibre reinforced composites that use cement based matrices.
In recent years there has been a continuously increasing interest in reshaping the interior spaces in existing buildings by connecting adjacent rooms and creating openings in structural walls. Large openings in reinforced concrete structural walls reduce the load bearing capacity and decreases the stiffness. This generates the need for strengthening of such elements weakened by openings.
The goal is to develop a design method for strengthening systems that use carbon fibres embedded in a cement based matrix for reinforced concrete walls with openings
In order for any strengthening system to be successfully applied a comprehensive design method is needed. The design guide based on large scale test and numerical analysis will be the result of this project.
Fig.1 - Strengthening system schematic
The aim of this work is to develop a methodology for repair/strengthening/upgrading wall with opening using fiber reinforced cement based systems.
The first objective of the project is to aggregate the latest advances in FRP materials and to investigate the potential for developing new strengthening applications for FRCM systems. The second objective is to understand the behavior of reinforced concrete walls with openings and of the strengthened ones based on laboratory tests and numerical analysis. The 3rd formulate design model that will address strengthening of walls using these systems with consideration to the influence of the size and positioning of openings.
How can we strengthen reinforced concrete walls weakened by openings using carbon fiber reinforced cement composites? Can we obtain the full capacity the same capacity for a damaged wall? How efficient is this strengthening method compared to other traditional or modern methods?
In order to answer these questions it is necessary to understand the behavior of such elements subjected to a specific type of loading, in this case gravitational forces.
A series of test will be carried on reinforced concrete walls, a solid wall with no opening, a wall with a small opening, and one with a large opening, a schematic is represented in Fig.2. The purpose of these tests is to determine the ultimate load bearing capacity of each wall, the failure mode and the distribution of cracks in the element. Understanding their behavior is necessary in order to be able to design an efficient strengthening system.
Prior to testing FEM analysis have been carried out. The analysis has been done with the software Atena. The calculated load bearing capacity of the walls is presented in Table 1.
Fig.2 - Experimental specimens
Table 1 - Load bearing capacity according to FEM
Fig.3 - FEM results: a) deformed shape of 3D model, b) distribution of cracks, c) concrete strain distribution, d) strain in reinforcement
Linear displacement sensors will be used to measure the deformations of the tested specimens. Strain in reinforcement will be monitored with strain gages installed on the reinforcing mesh in the element construction phase. Strain in concrete will be measured using strain gages installed on the compressed side of the element. A digital image correlation system will be used to monitor strain in concrete on the tension side of the specimen and also to measure field displacements of the monitored area.
The strengthening system will then be applied walls casted at the same time with the reference ones. The testing will undergo a similar procedure and instrumentation. Result will then be compared in terms of ultimate force, stiffness, displacements and strains. This way the efficiency of the strengthening system can be evaluated.
Data recorded using 3D image correlation system during the testing of the three specimens has been analyzed in order to better understand the behavior of two way action walls.
A state of the art report regarding fiber reinforced cementitious composites has been done in order to gain important knowledge needed for choosing an appropriate system for strengthening the specimens.
In November the early stage researcher has started a 3 month secondment at University of Padova. The purpose of this secondment is to gain further knowledge into the use of FRCM for strengthening RC elements. And to assist experimental tests carried out on reinforced concrete beams with DIC measurements.
The ESR completed a 3 month Secondment in the partner University of Padova. The porpoise was to study the behaviour of FRCM composites. During the secondment an experimental campaign on the bond behaviour FRCM – concrete joints has been carried out. Experimental test on RC beams have been postponed and instead DIC measurements were carried out on the lap-shear tests. In total 36 specimens have been fabricated and tested. Currently test results are being analysed and both ESRs are collaborating on publishing the results.
the endure meetings and teaching during the FRP Course 2016 at University of Ghent in Belgium provided the ESR with experience complementary to research. Networking within the international environment of experienced researchers helped the ESR contributed to a better understanding of the FRP strengthening subject.
Preparations for strengthening and testing five reinforced concrete wall specimens are on the way. Two commercially available strengthening systems have been chosen based on the literature study and practical experience obtained during the ESRs secondment.
Detailed finite FEM simulations have been done in order to estimate the load increase compared to the unstrengthened specimen.