Failure Analysis of Steel Fiber-Reinforced Concrete T-Beams without Shear Stirrups

The shear failure of a reinforced concrete member is a sudden diagonal tension failure; flexible failure is gradual, associated with significant cracks, and leads to extensive sagging. Therefore, reinforced shear rebars are commonly used to ensure that flexible failure occurs before shear failure under extreme conditions. Extensive efforts are underway to replace conventional shear reinforcements with steel fibers. Here, a nonlinear analysis of a steel fiber-reinforced concrete T-beam was performed in order to estimate the maximum shear capacity with the aid of experimental test data. A continuum-damaged plasticity model and modified compression field theory were used for nonlinear analysis. Three 360 × 360-mm web elements were selected between the shear span; changes in the principal axis caused by crack development and propagation were traced. Changes in the crack angle according to the average strain of the bottom longitudinal reinforcement and the vertical strain of the web element were also determined. For verification, a strut-tie model was used to predict shear capacity. The experimental results and the finite element analyses were in good agreement.

Shear strength evaluation of reinforced recycled aggregate concrete beams

A theoretical study is conducted to investigate the shear behaviour of recycled aggregate concrete (RAC) beams with and without shear reinforcements along with the performance evaluation various Code based/other existing equations in predicting shear strength. In addition, three artificial neural network (ANN) models for shear strength prediction of RAC beams with and without shear reinforcements are developed and their performance validated by using 108 beams from available research studies. Most of the Codes and existing methods underestimate the shear capacity of RAC beams with/without shear reinforcement. However, over estimation of shear strength by Codes/existing methods for about 10% RAC beams needs to be addressed when using such Codes/existing methods for shear strength prediction. All three ANN models are found to predict shear strength of RAC beams. Developed ANN models are able to simulate the effect of shear reinforcement on the shear strength of RAC beams.

Shear strength evaluation of reinforced recycled aggregate concrete beams

A theoretical study is conducted to investigate the shear behaviour of recycled aggregate concrete (RAC) beams with and without shear reinforcements along with the performance evaluation various Code based/other existing equations in predicting shear strength. In addition, three artificial neural network (ANN) models for shear strength prediction of RAC beams with and without shear reinforcements are developed and their performance validated by using 108 beams from available research studies. Most of the Codes and existing methods underestimate the shear capacity of RAC beams with/without shear reinforcement. However, over estimation of shear strength by Codes/existing methods for about 10% RAC beams needs to be addressed when using such Codes/existing methods for shear strength prediction. All three ANN models are found to predict shear strength of RAC beams. Developed ANN models are able to simulate the effect of shear reinforcement on the shear strength of RAC beams.

Numerical Analysis of Corrosion Reinforcements in Fibrous Concrete Beams

This paper offers a finite element method (FEM) to simulate the behavior of steel fiber reinforced concrete (SFRC) beams with corrosion of the longitudinal reinforcement using the ABAQUS package. This work was undertaken with the concrete damaged plasticity model (CDP). The expansion of corrosion product was utilized to represent the steel-concrete boundary to study the behavior of SFRC beams. Three beams with three volume fractions of steel fiber (0.8 %, 1.2 %, and 1.8 %) and three reinforced concrete (RC) beams with and without stirrups were created and tested under four-point loading to assess the shear capacity of beams. Corrosion of rebars at one of the RC beams that does not contain shear reinforcements will be studied. The crack patterns and load deflections of these beams were compared with experimental results found by the authors. The conclusions of this analysis will be valuable in considering the structural behavior of SFRC structures with uniform steel bar corrosion using FEM. Analytical results showed that the suggested model is qualified in better simulation and in accuracy of numerical and experimental results. The differences between analytical and experimental results were less than 8 % for load carrying capacity and 14 % for deflection; these differences are also satisfactory within the limits of the engineering conclusion.

Evaluation of Design Provisions for Horizontal Shear Strength in Composite Precast Concrete Beams with Different Interface Conditions

In a precast concrete (PC) composite beam, the horizontal interface between the PC beam and the cast-in-place (CIP) slab is located either on the compression side or on the tensile side of the cross-section. If the CIP slab is on the compression side, it becomes C-type interface, and if it is on the tensile side, it becomes T-type interface. Tensile cracks in the CIP slab may cause the horizontal shear strength of composite beams to decrease because of the reduced anchorage performance of shear reinforcements as well as the sliding on the interface. Such a tendency can be found from previous test results of specimens having T-type interface. In this study, the results of the push-off test and the beam flexure test were collected and analyzed to evaluate effects on the horizontal shear strength depending on the interface conditions, such as the interface location, surface roughness, concrete compressive strength, and clamping stress by shear connectors. The horizontal shear strength equations of ACI, PCI, AASHTO LRFD, and MC 2010 were evaluated with a database composed of 84 push-off tests and 95 beam tests from previous studies. According to the evaluation, evaluation results show that the design codes predict the horizontal shear strength conservatively for conditions other than the interface location. The horizontal shear strength deviated largely depending on the interface locations. The design codes conservatively estimate the horizontal shear strength for C-type interface, but the horizontal shear strength of T-type interface is overestimated. Based on current studies, it is recommended to use a friction coefficient of 0.7 as MC 2010 when calculating the horizontal shear strength of a composite beam with roughened T-type interface.

Combined Effect of Low and High Rate of Corrugated Steel Fiber and Stirrups on Mechanical Performance of SFSCC Beams

In order to improve the fragile nature of concrete, and its low tensile strength, and with a view to giving it the desired properties, which serve to build more durable structures at less cost, the association of a self-consolidating concrete with fiber, is considered a wise combination. However, given the limited amount of research on the response of SFSCC structures, designers and engineers do not use this material with confidence. In the present work, an experimental companion was conducted, in the interest of examining, the combined effect of fibers and stirrups include low and high rate of steel fiber, on the behavior of SFSCC beams. This choice allowed working on economically viable SFSCC. Beams were made also with ordinary concrete and others with self-consolidating. Thirty-six beams were of identical cross-section 10x20cm and length of 120cm; carried out with or without longitudinal and transverse reinforcement. Before proceeding with the main part of the research program, the concrete mixtures were characterized first in the fresh state by the following tests: Slump Flow, Time Flow T500; J-Ring, L-Box, V-Funnel and Sieve stability, and then in the hardened state: compressive and tensile strengths. In the light of the results obtained, it was found that adding steel fibers to fresh self-consolidating concrete decreased its workability and fluidity, but improved its hardening properties. Subsequently, the addition of the steel fibers increased the flexural capacity of the beams significantly, and improved their ductility. Also, an addition of the steel fibers in an adequate percentage, in this case at 0.9%, made it possible to replace the shear reinforcements, and can lead to changing the mode of failure from a collapse by brittle shear, to a mechanism of ruin in ductile bending.

Optimization of a flat slab with different type of punching reinforcement

Several types of punching shear reinforcements are available for increase of the maximum resistance against punching shear failure of flat slabs. Conventional punching shear reinforcement in form of stirrups or double headed studs are in use for decades. They are well known due to their simplicity and good performance. A new type of punching reinforcement has been developed for the case, where the flat slab exposed to extreme load and resistance of conventional type of punching shear reinforcement is not sufficient. Another designs point out that new construction system can reduce the amount of CO2. This paper presents some results of parametric study focused on design of the flat slab using different types of punching shear reinforcement and considering the concrete consumption.