Cyclic Performance of Beam-Column Joints with Extended Column Fixed at Base: Part I - Experimental Investigation

http://www.icevirtuallibrary.com/content/journals “Permission is granted by ICE Publishing to print one copy for personal use. Any other use of these PDF files is subject to reprint fees.”The seismic performance of a non-seismically detailed reinforced concrete (RC) beam–column joint with column pinned and fixed at the base is experimentally investigated in this paper. Six half-scale RC beam–column specimens were tested to study the effect of inflection point on the cyclic behaviour of beam–column sub-assemblages. The specimens were separated into two groups. The shape of specimens in the first group was cruciform; the size of the column in those specimens was varied while the size of beam was kept nearly constant. The dimensions and reinforcing detail of specimens in the second group were identical to those in the first one except that the column was extended to the footing and fixed at the base. The main variable in this study was the relative stiffness between beam and column, which affects the position of the inflection point. The test results demonstrated a significant effect of inflection point position on the load capacity, joint shear stress and failure mode

Cyclic Performance of Beam-Column Joints with Extended Column Fixed at Base: Part I - Experimental Investigation

http://www.icevirtuallibrary.com/content/journals “Permission is granted by ICE Publishing to print one copy for personal use. Any other use of these PDF files is subject to reprint fees.”The seismic performance of a non-seismically detailed reinforced concrete (RC) beam–column joint with column pinned and fixed at the base is experimentally investigated in this paper. Six half-scale RC beam–column specimens were tested to study the effect of inflection point on the cyclic behaviour of beam–column sub-assemblages. The specimens were separated into two groups. The shape of specimens in the first group was cruciform; the size of the column in those specimens was varied while the size of beam was kept nearly constant. The dimensions and reinforcing detail of specimens in the second group were identical to those in the first one except that the column was extended to the footing and fixed at the base. The main variable in this study was the relative stiffness between beam and column, which affects the position of the inflection point. The test results demonstrated a significant effect of inflection point position on the load capacity, joint shear stress and failure mode

Behavior and failure mode of reinforced concrete members damaged by pre-cracking

The effect of pre-cracking on the behavior and failure mode of reinforced concrete beams damaged by pre-cracking is experimentally studied in this paper. The control beam was designed to fail in ductile flexural yielding under four-point bending and in brittle shear under three-point bending. The effect of precracking is studied under both four-point bending and three point bending. In the former, pre-cracks are inclined with respect to the beam axis and the shear span is short, hence the external load is resisted by diagonal compression strut. In the latter, pre-cracks are orthogonal to the beam axis and the shear span is moderately long, hence the external force is transferred through concrete tensile strength, i.e., shear in moderately slender beam. The tests under these two load conditions therefore cover the effect of pre-cracking on concrete under compression and tension where the mode of load resistance is different. It is shown that when the shear span is short, pre-crack reduces the shear crushing capacity due to the reduction in effective contact area and compressive strength deterioration due to micro-fracturing damages. The presence of precracks can change the failure mode from ductile flexure to brittle shear. On the other hand, when the shear span is longer, pre-crack elevates the shear capacity through crack arrest mechanism. In both cases, the precracking is demonstrated to be structurally significant and should be properly taken into account when analyzing existing members

Behavior and failure mode of reinforced concrete members damaged by pre-cracking

The effect of pre-cracking on the behavior and failure mode of reinforced concrete beams damaged by pre-cracking is experimentally studied in this paper. The control beam was designed to fail in ductile flexural yielding under four-point bending and in brittle shear under three-point bending. The effect of precracking is studied under both four-point bending and three point bending. In the former, pre-cracks are inclined with respect to the beam axis and the shear span is short, hence the external load is resisted by diagonal compression strut. In the latter, pre-cracks are orthogonal to the beam axis and the shear span is moderately long, hence the external force is transferred through concrete tensile strength, i.e., shear in moderately slender beam. The tests under these two load conditions therefore cover the effect of pre-cracking on concrete under compression and tension where the mode of load resistance is different. It is shown that when the shear span is short, pre-crack reduces the shear crushing capacity due to the reduction in effective contact area and compressive strength deterioration due to micro-fracturing damages. The presence of precracks can change the failure mode from ductile flexure to brittle shear. On the other hand, when the shear span is longer, pre-crack elevates the shear capacity through crack arrest mechanism. In both cases, the precracking is demonstrated to be structurally significant and should be properly taken into account when analyzing existing members

Cyclic behavior of non-seismically designed interior reinforced concrete beam-column connections

This paper presents a test of non-seismically detailed reinforced concrete beam-column connections under reversedcyclic load. The tested specimens represented those of the actual mid-rise reinforced concrete frame buildings, designedaccording to the non-seismic provisions of the ACI building code. The evaluation of 10 existing reinforced concrete frameswas conducted to identify key structural and geometrical indices. It was found that there existed correlation VS structuraland geometrical characteristics and the column tributary area. Hence, the column tributary area was chosen as a parameterfor classifying the specimens. The test results showed that specimens representing small and medium column tributary areafailed by brittle joint shear, while specimen representing large column tributary area failed by ductile flexure, even thoughno ductile seismic details were provided

Shear Strengthening of RC Deep Beams with Sprayed Fiber-reinforced Polymer Composites (SFRP): Part 2 Finite Element Analysis

AbstractThis paper presents the finite element analysis conducted on SFRP strengthened reinforced concrete (RC) deep beams. The analysis variables included SFRP material (glass and carbon), SFRP thickness (3 mm and 5 mm), SFRP configuration and strength of concrete. The externally applied SFRP technique is significantly effective to enhance the ultimate load carrying capacity of RC deep beams. In the finite element analysis, realistic material constitutive laws were utilized which were capable of accounting for the non-linear behavior of materials. The finite element analysis was performed using computer software WCOMD. In the analysis, two dimensional eight-node reinforced concrete planar elements for concrete and planar elements with elastic-brittle behavior for SFRP were used to simulate the physical models. The concept of smeared cracking in concrete and steel was adopted over the element. The calculated finite element results are found to be in good agreement with the experimental results and to capture the structural response of both un-strengthened and SFRP strengthened RC deep beams. A comparison between the finite element results and experimental data proved the validity of the finite element models. Further, the finite element models were utilized to investigate the behavior of RC deep beams strengthened with different directions of SFRP Strips (vertical and horizontal). The vertical SFRP strips are found to be more effective than horizontal ones

Finite element analysis of FRP-strengthened RC beams

This paper presents a non-linear finite element analysis of reinforced concrete beam strengthened with externally bonded FRP plates. The finite element modeling of FRP-strengthened beams is demonstrated. Concrete and reinforcing bars are modeled together as 8-node isoparametric 2D RC element. The FRP plate is modeled as 8-node isoparametric 2D elastic element. The glue is modeled as perfect compatibility by directly connecting the nodes of FRP with those of concrete since there is no failure at the glue layer. The key to the analysis is the correct material models of concrete, steel and FRP. Cracks and steel bars are modeled as smeared over the entire element. Stress-strain properties of cracked concrete consist of tensile stress model normal to crack, compressive stress model parallel to crack and shear stress model tangential to crack. Stressstrain property of reinforcement is assumed to be elastic-hardening to account for the bond between concrete and steel bars. FRP is modeled as elastic-brittle material. From the analysis, it is found that FEM can predict the load-displacement relation, ultimate load and failure mode of the beam correctly. It can also capture the cracking process for both shear-flexural peeling and end peeling modes similar to the experiment

NONLINEAR FINITE ELEMENT ANALYSIS OF NONSEISMICALLY DETAILED INTERIOR RC BEAM-COLUMN CONNECTION UNDER REVERSED CYCLIC LOAD

This paper presents a nonlinear finite element analysis of non-seismically detailed RC beam column connections under reversed cyclic load. The test of half-scale nonductile reinforced concrete beam-column joints was conducted. The tested specimens represented those of the actual mid-rise reinforced concrete frame buildings designed according to the non-seismic provisions of the ACI building code.  The test results show that specimens representing small and medium column tributary area failed in brittle joint shear while specimen representing large column tributary area failed by ductile flexure though no ductile reinforcement details were provided. The nonlinear finite element analysis was applied to simulate the behavior of the specimens. The finite element analysis employs the smeared crack approach for modeling beam, column and joint, and employs the discrete crack approach for modeling the interface between beam and joint face. The nonlinear constitutive models of reinforced concrete elements consist of coupled tension-compression model to model normal force orthogonal and parallel to the crack and shear transfer model to capture the shear sliding mechanism. The FEM shows good comparison with test results in terms of load-displacement relations, hysteretic loops, cracking process and the failure mode of the tested specimens. The finite element analysis clarifies that the joint shear failure was caused by the collapse of principal diagonal concrete strut