Journal Oct 2020

In-situ π-anchor for fiber-reinforced polymer U-wraps used for strengthening shear deficient reinforced concrete beams A. Ghani Razaqpur, Clinton D’Souza

An in-situ carbon fiber-reinforced polymer (CFRP) π-anchor is developed for CFRP U-wraps used to strengthen reinforced concrete beams in shear. Fourteen beams were tested, and a segment of some beams was diagonally pre-cracked at 30 or 45° inclination. The cracked segment was not provided with internal stirrups but strengthened by surface bonded CFRP full wraps or U-wraps. The U-wraps fitted with the new anchor fully restored the beam strength. In a beam with a 30° diagonal crack, the U-wraps with the π-anchor increased the beam strength 74% more than the strength of the companion beam with twice the U-wrap but without anchor.

Flexural strengthening of an existing multi-storey structure using high tensile GFRP composite reinforcement by near-surface mounted (NSM) technique R. N. Krishna

Strengthening of structures considerably prolongs the functional service life by restoring strength of damaged structures. While there are several methods of strengthening, a new method of concrete reinforcement using near surface mounted (NSM) technique is gaining considerable attention worldwide. In the absence of Indian Standard (IS) code and relatively scant data on this method, an empirical approach was successfully adopted for structural strengthening. This paper describes a novel approach to flexural strengthening of an existing multi-storey reinforced concrete (RC) beam using NSM technique. Alkali-resistant high-tensile glass fiber-reinforced plastic (GFRP) bars were used with a proprietary structural adhesive. Although the research on NSM technique is still in its infancy, existing data promises a wide scope of application possibilities for this technique in repair and rehabilitation of structures.

Seismic resistant behavior of exterior beam-column joint with fiber hybridization R. Siva Chidambaram, Pankaj Agarwal

The combined diagonal compression and tension allows the formation of cracks in the beam column joint region. The poor tensile property of concrete allows the formation of early cracks which significantly affects the bonding between the longitudinal reinforcement and allows reinforcement slippage. This research article presents an experimental study conducted to investigate the effectiveness of fiber hybridization in physical properties of concrete and cementitious composites and its effectiveness in joint shear resistance. Cylindrical specimens and prism specimens were used and tested under uni-axial compression and bending to examine the physical properties of different matrix. Steel fibers in different forms and polypropylene fibers were employed in fiber reinforced concrete (FRC) and fiber reinforced cementitious composites (FRCC) with and without hybridization in different fiber volume. The mix proportions of FRC and FRCC are distinct and have no relation with each matrix. The composites have been used in the exterior beam column joints without critical confinement in the joint hinge region to examine its resilience against reverse cyclic loading. The comparative cyclic performance of FRC and FRCC has been studied using the hysteresis curve, stiffness behavior, energy dissipation and damage tolerance. It is understood that the FRC and FRCC exhibits better lateral resistance and energy dissipation compared to the FRC specimens.

Resilient sacrificial protection system for concrete slab under blast loading M. D. Goel, N. S. Choudhary, Sandeep Panchal

Resilient structures with the use of advanced engineered materials are the need of near future particularly under extreme loadings such as the loading resulting from an explosion. It necessitates the investigation of different materials and their combinations to arrive at technically and economically viable solutions. In this study, a sacrificial system comprised of hollow metal tubes to protect a concrete slab subjected to blast loading is analyzed with 3-D non-linear finite element (FE) software ABAQUS/Explicit®. Square concrete slabs with four different thicknesses (ts) are modeled. Mild steel hollow tubes of different diameters as per Indian Standard: 1161 (1998) along with steel sheet are used to protect these slabs under blast loading. Simplified concrete damage plasticity (SCDP) material model is used to define the material behavior of the concrete slabs. ConWep Program developed by the U.S. Army is used for applying blast loading to the concrete slab. Performance analysis of the tubes with different outer diameter (Do) and varying lengths (L) is carried out with a constant scaled distance (Z) of 0.425 m/kg1/3. It is observed that thin section and lower diameter tubes perform better than the thick section and higher diameter tubes in the considered sacrificial system. Furthermore, tensile damage on lower surface of concrete slab is drastically reduced after using sacrificial system. Additionally, based on this study, it is observed that the impingement of steel sheet with concrete slab only occurs in the tubes with lesser lengths and lower outer diameter.

Numerical analysis of reinforced ECC portal frames Preethy Mary Arulanandam, S. B. Singh, Madappa V. R. Sivasubramanian

The present research study is based on numerical modeling for predicting the response of steel-reinforced engineered cementitious composite (ECC) portal frames under monotonic loading through finite element (FE) analysis on ABAQUS platform. For this purpose, a total of six portal frames chosen from the literature are modeled and analyzed. Among these six frames, two are fully made of concrete, two are fully made of ECC and remaining two are partially made of ECC and concrete following two reinforcement patterns prescribed in Indian Standard: 13920 (1993) and IS: 456 (2000). The results are obtained in terms of load-deflection response and the load-strain response at strategic locations, and damage patterns. Further, the load-deflection response and damage patterns of the frames from the FE analysis are compared with the experimental results available in the literature. It is observed that the results from the present numerical study show close agreement with the experimental results, which confirms the robustness of the modeling procedure employed.

Development of hierarchically engineered cementitious composites through nano-/micro-scale investigations for disaster resilient concrete structures S. Sindu, Saptarshi Sasmal

To significantly reduce the requirement of special detailing which leads to extremely complicated and uneconomical design solutions for disaster resilient concrete structures, advanced fiber-reinforced cementitious composites/concrete are used in the critical regions. Besides the attempts of using single or multiple (type) fiber-reinforced cement system, efficient composite can be developed by tailoring the material at different length scales owing to the unique multi-scale microstructure. In this study, a new class of hierarchically engineered cementitious composite with high ductility, strain capacity, and energy dissipation capacity, is developed through elaborate investigations starting from molecular scale and appropriately tailoring the material at different length scales (bottom-up approach).

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