IIT-H to host CARRS 2020

Indian Institute of Technology-Hyderabad (IIT-H) will host an International Conference on Assessment, Rehabilitation and Retrofitting of Structures (CARRS) 2020 from December 14 to 16, 202

IIT Hyderabad to host conference on retrofitting of structures

Indian Institute of Technology-Hyderabad (IIT-H) will host an International Conference on Assessment, Rehabilitation and Retrofitting of Structures (CARRS) 2020 from December 14 to 16, 202

Nonlinear Finite-Element Analysis of RC Bridge Columns under Torsion with and without Axial Compression

Finite-element (FE) modeling of RC structures under combined loading has received considerable attention in recent years. However, the combination of torsion and axial compression has been rarely studied in spite of its frequent occurrence in bridge columns under earthquake loading. This paper aims at creating a nonlinear FE model to predict the behavior of RC bridge columns under combined torsion and axial compression. A number of circular and square columns were analyzed. The developed FE model was calibrated on local and global behavior through comparison with test data. The overall torque-twist behavior of the members was captured well by the developed FE models. The predicted values of strain in the longitudinal and transverse reinforcement matched closely with the experimental results. An increase in transverse steel ratio was found to increase the torsional capacity and limit the damage of columns under torsion. It was further observed that at a low level of axial compression, the torsional capacity of columns is enhanced. In addition, the FE analysis showed a good agreement on the identification of the damage mechanism and the progression of failure. The shape of the cross section is found to play a major role in the distribution of torsional damage in the columns. Square columns exhibited a more localized damage due to presence of warping, whereas circular columns exhibited damage distributed along their length. (C) 2015 American Society of Civil Engineers

Experimental and numerical studies on flexural behaviour of lightweight and sustainable precast fibre reinforced hollow core slabs

This study reports experimental and numerical studies on the flexural behaviour of sustainable fibre reinforced lightweight hollow core slabs (FR-LWHCS). An innovative and sustainable LWHCS is proposed for structural applications using a lightweight concrete mix of 1800 kg/m3 density, previously developed by authors. Full-scale precast LWHCS specimens are cast and tested under flexure using a four-point loading configuration. A high shear span to depth (a/d) ratio of 10 is chosen to have flexure dominant behavior. FR-LWHCS is made using sintered fly ash aggregate (SFA) as coarse aggregate and monofilament macro synthetic fibres of different volumetric fibre dosages (0.4 % and 0.6 %). A small dosage of micro synthetic fibres of 0.02 % by volume is also added to arrest shrinkage cracks. Two control slabs, one constructed with lightweight concrete and the other with conventional normal density concrete, are tested. The digital image correlation (DIC) technique is used to track the cracks and failure modes. A 3D finite element analysis is performed to supplement the test results. Test results show that FR-LWHCS satisfies all the structural requirements, leading to economy and sustainability. FR-LWHCS with 0.6 % fibre dosage performed better than hollow core slabs made of normal density concrete. Though the addition of fibres did not considerably increase peak load, a minimum dosage of fibre addition is warranted in LWHCS to improve the serviceability performance. Fibre addition significantly improved the strain energy absorption

Experimental and numerical study on behaviour of fibre reinforced lightweight hollow core slabs under different flexure to shear ratios

The current work explores the behaviour of fibre-reinforced lightweight hollow core slabs (FR-LWHCS) intending to develop sustainable construction solutions. The FR-LWHCS investigated in this work contains sintered fly ash aggregate (SFA) as coarse aggregate. Due to the use of SFA, the behaviour of LWHCS is expected to be different from the hollow core slabs (HCS) constructed using normal density concrete. FR-LWHCS are tested at different shear span to depth (a/d) ratios of 3.5, 7 and 10 to understand the shear and flexure behaviour. Twelve full-scale hollow core slab (HCS) specimens of 3400 mm length, 600 mm width, and 150 mm thickness are tested. FR-LWHCS consists of monofilament macro synthetic fibre dosages of 0.4 %, and 0.6 %, along with fibrillated micro fibre of 0.02 % dosage. The digital image correlation (DIC) technique is adopted to understand the strain profile on the HCS at different levels of loading. The numerical analysis is performed using a commercially available finite element software and is corroborated with experimental findings and parametric studies have been performed. Both LWHCS and normal HCS specimens failed in shear, flexural-shear and flexure modes at a/d ratios of 3.5, 7 and 10, respectively. The addition of fibres increased the peak load by 65 % compared to control LWHCS specimens tested at an a/d ratio of 3.5. The use of fibres increased strain energy absorption and changed the failure to less brittle mode at all a/d ratios. The fibre reinforced specimens have nearly 3.5 times, 2.5 times and 1.3 times the strain energy absorption of the control LWHCS when tested at a/d ratio 3.5, 7 and 10 respectively

A Study on Residual Compression Behavior of Structural Fiber Reinforced Concrete Exposed to Moderate Temperature Using Digital Image Correlation

Fire ranks high among the potential risks faced by most buildings and structures. A full understanding of temperature effects on fiber reinforced concrete is still lacking. This investigation focuses on the study of the residual compressive strength, stress strain behavior and surface cracking of structural polypropylene fiber-reinforced concrete subjected to temperatures up to 300 A degrees C. A total of 48 cubes was cast with different fiber dosages and tested under compression after exposing to different temperatures. Concrete cubes with varying macro (structural) fiber dosages were exposed to different temperatures and tested to observe the stress-strain behavior. Digital image correlation, an advanced non-contacting method was used for measuring the strain. Trends in the relative residual strengths with respect to different fiber dosages indicate an improvement up to 15 % in the ultimate compressive strengths at all exposure temperatures. The stress-strain curves show an improvement in post peak behavior with increasing fiber dosage at all exposure temperatures considered in this study

Optimization Based Improved Softened Membrane Model for Rectangular Reinforced Concrete Members under Combined Shear and Torsion

Reinforced concrete (RC) elements are often subjected to combined actions including torsion under seismic events. Understanding the behavior of RC members under combined actions including torsion is essential for safe design. Behavioral predictions of RC columns under combined loading can be improved by including the bi-directional stress effects. The objective of this work is to propose improved combined actions softened membrane model (CA-SMM) for predicting the behavior of RC elements under combined torsion (T) and shear loading (V). In this approach, the rectangular cross-section is modeled as an assembly of four cracked shear panels. The applied external loads are distributed among these four shear panels. This assumption helps in reducing the complex stress state from combined loading to four different simple stress states on these panels. Additional equilibrium and compatibility conditions are imposed, and the system of non-linear equations are solved by using an optimization technique called gradient descent method. The developed improved model (CA-SMM) is validated with the experimental data available in the literature. After that, an interaction between the shear and torsion is developed to understand the behavior under various combinations of torsion and shear. A parametric study is carried out for understanding the effect of various sectional parameters such as longitudinal reinforcement ratio, transverse reinforcement ratio, and concrete strength. The predictions of the improved model had a close correlation with the test results

Behavior of Hybrid NSM Reinforced and Externally Confined Reinforced Concrete Columns under Eccentric Compression –Experimental and Numerical Studies

The effectiveness of hybrid combination of ne ar surface mounted (NSM) and externally confined (EC) FRP strengthenin g on the performance of RC column elements under uniaxial eccentric compression is investigated. In total, ten short RC column elements were cast. Carbon FRP is used for strengthening due to its inherent stiffness and strength properties on par with other FRP materials. The columns were strengthened using NSM CFRP laminates, EC using CFRP fabrics and their hybrid combi nations. A non-linear finite element model is developed using ABAQUS and the numerical model is calibrated using the experimental results to improve the accuracy of the predict ions. Experimental results revealed that hybrid strengthening of RC columns was able to show a better performance in terms of stiffness, strength, ultimate displacement ductility when compared to other FRP strengthening techniques. The numerical predictions obtained were able to better capture the initial stiffness, peak load and post-peak behavior. Thus, the proposed hybrid strengthening technique for RC columns possess the capability of restoring the loss in stiffness, strength and ductility due to additional bending moment induced by the eccentric compression loading

Numerical and Analytical modelling of reinforced concrete circular columns subjected to torsion

This paper compares the efficiency of tension stiffened softened truss model (TS-STM) and a nonlinear finite element (FE) model to predict the behaviour of reinforced concrete (RC) circular columns under torsional loading. Predictions of the models are calibrated with test data on two circular columns taken from literature. Overall torque – twist behaviour and average strain in the transverse reinforcements were parameters for comparison. It is observed that both the models predicted the overall torsional behaviour of the test specimens reasonably well. However, the peak twist and post peak behaviour were better captured by the TS-STM. Average strain in transverse reinforcements predicted by the TS-STM was also closer to the measured values compared to the FE predictions. On the whole, it can be concluded that, TS-STM performs better than nonlinear FE model in capturing the overall response of circular RC columns subjected to torsional loading