Gravity load effects on the behaviour of reinforced concrete beam critical zones subjected to cyclic loads,
Gião, Rita, Lúcio Valter, and Chastre Carlos
, Engineering Structures, 2019/02/15/, Volume 181, p.503-518, (2019)
AbstractThe aim of the present study was to proceed to a numerical analysis of the gravity load effects on the behaviour of reinforced concrete beam critical zones when subjected to cyclic loads. A parametric study to assess the influence of different levels of gravity load on RC beam critical zones subjected to cyclic loading was carried out. For this purpose, assuming the level of gravity load as a variable parameter, a nonlinear numerical model of a beam-column connection, previously calibrated with experimental data, was used. In order to evaluate the gravity load effects in the global response, a numerical study of a RC frame system is also presented. The numerical results are analysed in terms of global hysteretic response, accumulated energy dissipation and equivalent viscous damping ratio. In this numerical study, it was observed that the hysteretic response depends on the load path. In the presence of higher gravity load levels, the structure hysteretic behaviour exhibits higher damage levels, associated to a failure mechanism corresponding to the formation of four span plastic hinges. Thus, the proper test procedure should involve the imposition of a reverse cyclic displacement history starting each cycle from the gravity load effects.
New Methodology For Reinforced Concrete Beam-Column Cyclic Test,
Gião, Rita, Lúcio Valter, Chastre Carlos, and Proença Jorge
, International FIB Conference "Concrete - 21st Century Superhero, London, (2009)
AbstractThe aim of the present communication is to present an analysis of the gravity load influence on the hysteretic behaviour of a beam-column connection. For this purpose, in the experimental campaign a new procedure for RC cyclic tests is presented in order to reproduce closer demands on the beam critical zone than the traditional procedures. The Experimental campaign included cyclic tests of the specimens according with the ECCS recommendation and an innovate procedure. The test results are presented, compared and analysed. A numerical simulation of the tests is presented where the model for the hysteretic response of the beam was calibrated with the experimental results. Finally, the behaviour of a portal frame system under cyclic displacements up to a drift of 3.5% was analysed, assuming that the non-linearity is concentrated on the plastic hinges, considering different levels of gravity load. Thus it is intended to assess the influence of the gravity load on the behaviour of a structure subjected to cyclic loads.
Assessment of the influence of gravity load in RC beams’ critical zones subjected to cyclic loading,
Gião, Rita, Lúcio Valter, and Chastre Carlos
, Proceedings of the fib Symposium 2019: Concrete - Innovations in Materials, Design and Structures, May, 27-29, 2019, Kraków, Poland, p.497-504, (2019)
AbstractThe aim of the present paper is to evaluate the gravity loads effect in the behaviour of reinforced concrete beams critical zones subjected to cyclic loads. A numerical study to assess the influence of gravity load on RC beam critical zones subjected to cyclic loading is presented, assuming the level of gravity load as a variable parameter. For this purpose, the non-linear model was previously validated with an experimental campaign carried out on RC beam connection subject to cyclic loading with and without gravity loads. The consideration of the gravity load effects led to an accumulation of negative (hogging) deformation and the formation of an unidirectional plastic hinge. In order to validate this behaviour in an overall structural response, a non-linear numerical analysis of a RC frame system under cyclic loads, subject to different levels of gravity load, is also presented. The numerical results are analysed in terms of global hysterical response, accumulated energy dissipation and equivalent viscous damping ratio. In this numerical study was observed that the hysteretic response depends on the load path. In the presence of higher gravity loads levels, the structure hysteretic behaviour exhibits higher damage levels and the failure mechanism is prone to the formation of four plastic hinges. This phenomenon is analysed and discuss in the present paper. © Federation Internationale du Beton (fib) - International Federation for Structural Concrete, 2019.
Assessing the behaviour of RC beams subject to significant gravity loads under cyclic loads,
Gião, Rita, Lúcio Válter, and Chastre Carlos
, Engineering Structures, 2//, Volume 59, Number 2, p.512-521, (2014)
AbstractGravity loads can affect a reinforced concrete structure’s response to seismic actions, however, traditional procedures for testing the beam behaviour do not take this effect into consideration. An experimental campaign was carried out in order to assess the influence of the gravity load on RC beam connection to the column subjected to cyclic loading. The experiments included the imposition of a conventional quasi-static test protocol based on the imposition of a reverse cyclic displacement history and of an alternative cyclic test procedure starting from the gravity load effects. The test results are presented, compared and analysed in this paper. The imposition of a cyclic test procedure that included the gravity loads effects on the RC beam ends reproduces the demands on the beams’ critical zones more realistically than the traditional procedure. The consideration of the vertical load effects in the test procedure led to an accumulation of negative (hogging) deformation. This phenomenon is sustained with the behaviour of a portal frame system under cyclic loads subject to a significant level of the vertical load, leading to the formation of unidirectional plastic hinges. In addition, the hysteretic behaviour of the RC beam ends tested was simulated numerically using the nonlinear structural analysis software – OpenSees. The beam–column model simulates the global element behaviour very well, as there is a reasonable approximation to the hysteretic loops obtained experimentally.
UFRG – Unidirectional fibre reinforced grout as strengthening material for reinforced concrete structures,
Gião, R., Lúcio V., Chastre C., and Bras A.
, BEFIB2012 – Fibre reinforced concrete, Guimarães, (2012)
AbstractThe present study is part of an extensive research project, where the main objective is to evaluate a strengthening solution for reinforced concrete structures using a small thickness jacketing in the compression side of the RC element with unidirectional fiber reinforced grout - UFRG.
For this purpose a high performance cementitious grout reinforced with continuous and unidirectional non woven fibermat has been developed. It was expected that the use of these type of fibers allowed an optimization of its percentage and orientation. It was expected that the use of these type of fibers allowed an optimization of its percentage and orientation. Besides, for continuous fibers (with an aspect ratio, defined as the length-to-diameter ratio, l/d=∞), the composite should attain higher tensile strength since the fiber embedment length is enough to prevent fiber pullout.
The experimental campaign included a set of preliminary tests that allowed the design of the fiber reinforced grout, sustained with rheological parameters [7] and mechanical characterization tests of the materials.
Finally, an experimental campaign was carried out in order to proceed to the mechanical characterization of the unidirectional fiber reinforced grout. Compressive tests were conducted in small thickness tubular specimens that enable the determination of the compressive strength and the static modulus of elasticity of the material. The tensile strength of the material was obtained using splitting tests of cubic specimens (according the standard DIN 1048-5). The experimental results are presented and analyzed.
Characterisation of unidirectional fibre reinforced grout as a strengthening material for RC structures,
Gião, Rita, Lúcio Valter, and Chastre Carlos
, Construction and Building Materials, Volume 137, p.272-287, (2017)
AbstractThe main goal of the present research work is to characterise a unidirectional fibre reinforced grout (UFRG), developed as an alternative material to strengthen RC structures using small thickness jacketing. A high performance cementitious grout reinforced with continuous and unidirectional non-woven steel fibre mat has been developed for this purpose. It was expected that the optimization of the percentage and alignment of the steel fibres would yield a more efficient fibre grout. In fact, the composite should attain higher tensile strength with continuous fibres since the fibre embedment length is enough to prevent fibre pull-out. An experimental programme was carried out to characterise the UFRG’s mechanical properties. Compressive tests were conducted on small thickness tubular specimens to enable the determination of the compressive strength and the static modulus of elasticity. The tensile strength was obtained from splitting tests performed on cubic specimens (DIN 1048-5). Semi-empirical equations, based on the experimental results, are proposed to estimate UFRG’s modulus of elasticity, compressive strength and tensile strength. Two strengthening solutions for RC structures using small thickness CFRP jacketing are presented.