Energy dissipation and equivalent damping of RC columns subjected to biaxial bending: an investigation based in experimental results

The cyclic behaviour of reinforced concrete columns have been object of many experimental studies in the recent past years. However, the experimental studies on the biaxial response of RC columns are still limited. In this paper are presented the main results of an experimental study of 24 full-scale rectangular building columns tested for different loading paths under uniaxial and biaxial conditions. The experimental results are presented and discussed in terms of global behaviour, particularly focusing on the stiffness and strength degradation due to the increasing cyclic demand, and energy dissipation evolution. The equivalent viscous damping was estimated based on the experimental results of the RC columns tested under biaxial loading and empirical expressions are proposed

Simplified model for the non-linear behaviour representation of reinforced concrete columns under biaxial bending

In the present paper a simplified model is proposed for the force-deformation behaviour of reinforced concrete members under biaxial loading combined with axial force. The starting point for the model development was an existing fixed-length plastic hinge element model that accounts for the non-linear hysteretic behaviour at the element end-sections, characterized by trilinear moment-curvature laws. To take into account the section biaxial behaviour, the existing model was adopted for both orthogonal lateral directions and an interaction function was introduced to couple the hysteretic response of both directions. To calibrate the interaction function it were used numerical results, obtained from fibre models, and experimental results. For the parameters identification, non-linear optimization approaches were adopted, namely: the gradient based methods followed by the genetic, evolutionary and nature-inspired algorithms. Finally, the simplified non-linear model proposed is validated through the analytical simulation of biaxial test results carried out in full-scale reinforced concrete columns

Out-of-plane in situ cyclic testing of unreinforced stone masonry walls with distributed loads

The present paper reports an in situ experimental test campaign carried out on existing buildings, in order to investigate the seismic behaviour of traditional masonry walls subject to out-of-plane loads. For the testing proposes, an experimental test setup based on a selfequilibrated scheme was developed and optimized to be applied in situ in two specimens on original and strengthened conditions. The obtained results are presented and carefully discussed namely from the reinforcement solutions’ efficiency point-of-view, as well as compared to previous experimental data obtained for the same type of masonry walls. Additionally, a simplified linearized displacement-based procedure was adapted in order to characterize the nonlinear force-displacement relationship for unreinforced traditional masonry walls and to analytically predict the experimental test results. The confrontation between the experimental and the analytical results are presented and discussed

Behaviour of reinforced concrete column under biaxial cyclic loading: state of the art

The cyclic behaviour of reinforced concrete columns has been object of many experimental studies in the last years, mostly focused on the unidirectional loading of columns under constant axial load conditions. In this research work, the existing test on reinforced concrete (RC) columns under biaxial load has been reviewed, underlying their main findings. In general, the experimental results show that the RC columns' response is highly dependent on the loading pattern, and the biaxial loading induces a decrease in the maximum strength and anticipates each damage state. Thus, in columns where demands are expected with large moments in both directions, specific detailing should be provided in their critical regions in order to improve the columns' performance and avoid premature failure

Comparison of different modelling strategies for the representation of non linear response of RC columns subjected to biaxial loading

Aiming at studying the performance of different non-linear modelling strategies for RC columns subjected to axial load and cyclic biaxial horizontal loading, several analyses were developed using the computer code SeismoStruct. This study comprised the simulation of 24 cantilever RC columns quasi-statically tested under constant axial force and cyclic uniaxial and biaxial displacements imposed with different loading paths. The results show that all adopted modelling strategies (distributed-inelasticity and lumped-plasticity) lead to similar accuracy in terms of restoring shear-force evolution. Generically, they were found suitable for accurately predicting the cyclic response of RC columns, with standard material parameters, although the models may not succeed in representing the strength degradation for cyclic loading

Evaluation of damage in reinforced concrete columns under biaxial loading

The present study is focused on the analysis of damage evolution observed in an experimental campaign on 24 RC columns tested under uniaxial and biaxial loading. The observed damage evolution and damage states are compared for uniaxial and biaxial loading conditions. The test results show that for biaxial loading conditions each damage limit state occurs for lower drift demands when compared with the corresponding test for uniaxial demand (a reduction of 50–75% was found). The deformation demand associated with each damage state is compared with performance objectives proposed in international guidelines. Finally, and based on the philosophy of the Park & Ang uniaxial damage index, two new expressions are proposed for the evaluation of damage in RC elements under biaxial loading. These expressions are calibrated against the experimental results obtained with the tests on columns based on a scoring process to choose the best DI estimator

Experimental study on the biaxial bending cyclic behaviour of RC columns

The available experimental studies on the inelastic 3D response of axially loaded members under biaxial bending moment loading histories are limited. Possibly, this is partially due to the uncertainty of combining bending moment’s histories in the two orthogonal directions that adds considerable complication to the problem. Three types of cantilever reinforced concrete columns with constant axial load were subjected to cyclic uniaxial and biaxial tests. It was intended to gain enhanced knowledge concerning the behaviour or RC columns that allows for the calibration of simplified non-linear models. The experimental campaign is described, test results are presented and discussed comparing the uniaxial and the biaxial tests and the effect of the different biaxial load paths in the columns behaviour

Seismic behaviour and strengthening of existing reinforced concrete structures

The seismic vulnerability associated to existing reinforced concrete buildings, constructed until the late 1970’s, in urban areas of many European countries with moderate to high seismic hazard, is of extreme importance. In that period, reinforced concrete buildings were designed and constructed without considering adequately earthquake provisions, constituting therefore a significant source of risk for our cities. Recent major earthquakes around the world have evidenced that this type of existing buildings lacking appropriate seismic resisting characteristics are very vulnerable. The present paper focus in four important subjects regarding the seismic behaviour of reinforced concrete buildings, first the importance of the experimental studies on full-scale buildings in particular with two full-scale four-storey reinforced concrete frames tested, in these tests two problems were under study the presence on infill masonry panels in the structure and the use of smooth reinforcement bars, that induces a sudden loss of concrete-steel bond is one of the sources of brittle failure in RC elements. For the presence infill masonry panels it’s presented a simplified macro-model that is able of represents the global behaviour of infill masonry panels and its interaction with RC elements and its application to a case study. Regarding the study of RC buildings smooth reinforcement bars it’s presented the experimental campaign ongoing and the first results and conclusions. Another identified problem in the seismic behaviour of RC buildings is the behaviour of axially loaded reinforced concrete members under biaxial bending moment. It’s presented the actual lack of experimental studies and the nonexistence of simplified models able to represent these effects and the experimental study of RC columns under uniaxial and biaxial bending

Comparative analysis of RC irregular buildings designed according to different seismic design codes

The present paper presents a comparison of the seismic provisions of the three seismic design codes, namely the Philippine code (National Structural Code of the Philippines or NSCP2010), the European code (Eurocode 8 or EC8), and American code (2009 International Building Code or 2009 IBC), to the most common ordinary residential building of standard occupancy. Two regular and irregular reinforced concrete (RC) frames were analysed and compared for four storey and eight storey buildings. The response spectrum function of NSCP 2010 was considered for the horizontal load action with different load combinations. Response spectrum analysis was performed using SAP2000 software package. Five representative columns for each RC frames were analyzed and based from the results of column axial load - bending moment interaction diagrams, EC8 was found to be conservative as compared to NSCP 2010 and 2009 IBC. The conclusion is that for the design and analysis of ordinary RC residential building with certain irregularity, EC8 provisions were considered to be safer

Cyclic behaviour analysis of RC elements with plain reinforcing bars

The seismic performance of RC elements with plain reinforcing bars is particularly sensitive to the bond-slip mechanism. In this paper are described the cyclic tests performed on a two-spans beam with plain reinforcing bars and two beam-column joints with the same geometry and reinforcement detailing, one with plain reinforcing bars and the other with deformed bars. The main experimental results are presented and the comparison between the global behaviour of the two joints is established. A numerical model of the beam was developed within the OpenSees platform and calibrated with the experimental results. Particular attention was given to the bond-slip mechanism. Additional numerical analyses were developed without considering bond-slip. The comparison between the main numerical and experimental results shows the great importance of considering the bond-slip mechanism in the numerical models in order to have a precise simulation of the cyclic response of RC elements with plain reinforcing bars