Assessing influence of active and passive confinement on flexural behaviour of CFST beams

U radu se analizira utjecaj aktivnog i pasivnog ovijanja na ponašanje pri savijanju betonom ispunjenih čeličnih cijevi. Dvanaest ovijenih uzoraka podvrgnuto je ispitivanju čvrstoće na savijanje u tri točke. Osnovni varijabilni parametri bili su: odnos promjera i debljine cijevi (20, 30 i 60), tlačna čvrstoća betonske jezgre (15 MPa i 45 MPa) i vrsta ovijanja (aktivno ili pasivno). Ispitana je savojna čvrstoća, apsorpcija energije, fleksibilnost i način popuštanja ovijenih uzoraka, isto kao i način pucanja betonske jezgre u točki sloma. Rezultati pokazuju da aktivno ovijanje dovodi do manje duktilnosti uzoraka koji se odlikuju većom čvrstoćom betonske jezgre.The aim of this study is to investigate the effect of active and passive confinement on the flexural behaviour of concrete-filled steel tubes. Three-point flexural test is carried out on twelve confined specimens. The main variable parameters are: tube diameter to thickness ratio (20, 30, and 60), compressive strength of concrete core (15 MPa and 45 MPa), and type of confinement (active or passive). The flexural capacity, energy absorption, flexibility and failure mode of confined specimens, as well as the cracking pattern of concrete core at failure point, are evaluated in this study. The results show that active confinement leads to lower ductile behaviour in specimens with higher strength of concrete core

Three-Dimensional Finite Element Analysis of Compressive Behavior of Circular Steel Tube-Confined Concrete Stub Columns by New Confinement Relationships

Abstract This paper presents a nonlinear analysis of axially loaded steel tube-confined concrete (STCC) stub columns with new confinement relationships. For this aim, a 3-D finite element model of STCC columns using ABAQUS program is developed and validated against the experimental data. Proper material constitutive models are proposed and the confinement parameters of confined concrete are determined by matching the numerical results via trial and error. The parameters considered for quantitative verification of the FE model include five different factors indicating the behavior of STCC columns: compressive strength corresponding to steel yielding point, initial peak strength and ultimate strength as well as longitudinal to circumferential stress ratio of steel tube at steel yielding point and initial peak point. For the qualitative verification, the axial and lateral stress-strain relationships of STCC columns are taken into account. The comparison results indicate that the model can accurately predict the compressive behavior of STCC stub columns. Finally, a parametric study is also performed to evaluate the effect of tube diameter-to-wall thickness ratio (D/t), concrete compressive strength (fc ) and steel yield strength (fy ) on the compressive behavior of STCC columns. According to the results of the parametric study, the interface shear stress and lateral confining pressure are not affected by fc while significantly increase with decreasing D/t

Experimental study and calculation of confinement relationships for prestressed steel tube-confined compressed concrete stub columns

The current paper aims to present the results of an experimental investigation into the compressive strength of pre-stressed steel tube-confined compressed concrete (PSTC) stub columns. Here, to prestress the confined concrete, an innovative technique is utilized, in which the fresh concrete is subjected to compression while the steel tube is simultaneously preten-sioned laterally by applying external pressure to the fresh concrete. A total of 135 confined specimens were tested under axial compressive loading to determine the confinement strength of the specimens. Moreover, new confinement relationships for the load-carrying capacity of the PSTC columns were proposed in terms of the prestressing ratio ( r P ), reference concrete strength ( c f), and tube outer diameter to wall thickness ratio ( / Dt ). Finally, a parametric study was conducted to evaluate the effect that the parameters r P, c f , and / Dt have on the compressive strength of the prestressed confined concrete. The results indi-cate that the confined concrete prestressed by the present technique demonstrates significantly enhanced load-carrying capacity; however, increasing the prestressing level slightly affects it

A comparative study of mechanical properties and life cycle assessment of high-strength concrete containing silica fume and nanosilica as a partial cement replacement

peer reviewe