Strengthening of Axially Loaded Circular Concrete Columns using Stainless Steel Wire Mesh (SSWM)

Abstract

Buildings, which are not adequately designed and detailed as per relevant standards, are highly vulnerable to earthquake ground motions. Such buildings need to be strengthened to enhance their seismic capacity. The load bearing columns are the most important structural elements of a concrete structure. The failure of columns under gravity loads or seismic loads results in catastrophic failure of the structures. Therefore it is necessary to strengthen the columns to take up designed loads in case of structural degradation or to take up additional loads due to change in use or change seismic requirements. The strengthening of existing columns using steel and concrete jacketing has been used since long for retrofitting of columns. Fiber Reinforced Polymer (FRP) wrapping has emerged as a new method for strengthening of columns. Common types of wrapping materials used are carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), and aramid fiber reinforced polymer (AFRP). Steel fiber reinforced polymer (SFRP) composite materials have been recently introduced as an alternative to GFRP and CFRP composite materials. In this research Stainless Steel Wire Mesh (SSWM) as an alternative material for strengthening of structural elements has been explored. Review of latest research work on use of carbon fiber, glass fiber, aramid fiber and steel fiber reinforced polymer composites for strengthening of columns for axial load has been carried out. Stainless steel wire mesh made up of weaving very thin stainless steel wires (thickness 0.27 mm) available in local market is explored as a material for strengthening of concrete elements. Therefore application of SSWM is explored in present study as a substitute for CFRP, GFRP, AFRP and SFRP. SSWM has sufficient tensile strength, ductility, high bond strength with concrete, corrosion resistance, fire resistance and is an economical alternative of present FRP materials. An experimental investigation is carried out in present research work for evaluation of axial strength of M15, M20, and M25 grade plain cement concrete (PCC) circular columns strengthened with locally available stainless steel wire mesh (SSWM). Column specimens of 200 mm diameter with various heights 400 mm, 800 mm and 1200 mm are used in the study. Specimens are strengthened with one and two wraps of SSWM applied using Sikadur 30LP epoxy. The performances of strengthened specimens under axial load in terms of load- displacement behaviour, ultimate load are compared with control specimens without strengthening. Ultimate tensile strength of SSWM and bond strength of SSWM with concrete are studied to check the feasibility of SSWM for strengthening. From study of 54 columns specimens, it is found that axial compressive strength is increased in range of 15% to 61% and 39% to 86% when columns are strengthened with one and two wraps of SSWM respectively. Numerical investigation using Finite Element Analysis (FEA) is carried out using ABAQUS software. Nonlinear material properties for concrete and SSWM are considered. SSWM properties found experimentally are used for modelling and nonlinear FE analysis of SSWM strengthened columns. Concrete is modelled with 4-node linear tetrahedron element and SSWM is modelled as 4-node doubly curved thin or thick shell, reduced integration, hourglass control, finite membrane strains. Perfect bond is considered between concrete and SSWM element and two different wraps of SSWM element. In most of the cases results of numerical simulation closely matches with experimental investigation. Analytical studies have been made to find the axial load capacity of columns wrapped with SSWM using ACI 440.2R 2008 and CNR-DT 200/2004 guidelines. The comparison of the results has been made for increase in axial load carrying capacity of columns with increase in number of wraps, grade of concrete and different height of columns from experimental investigation, numerical simulation and available design guidelines. It is observed that experimental results closely match with results from CNR DT 200/2004 design guidelines. Based on present study, it is concluded that SSWM can be used for strengthening of circular concrete columns of low to medium strength. In the existing RCC buildings, the columns having reduced load bearing capacity due to reinforcement corrosion and concrete spalling can be strengthened with SSWM wraps without increasing the size of the columns. The SSWM used in experimental investigation is locally available material having inherent ductility, good bond with concrete surface, resistance to corrosion, lightweight in comparison to steel plates. SSWM is much cost effective alternative of CFRP, GFRP materials. Guidelines for design and installation of SSWM are given.