Papers by Keyword: Strengthening

Abstract: This article aims to verify the possibility of strengthening existing flat slabs against punching by concrete overlay and the effectiveness of this type of strengthening. The method of strengthening by concrete overlay was verified on a theoretical level using the currently valid Eurocode 2 and other standards. A non-linear analytical model was developed in Atena 3D software, and the results of this model were compared with previous results from calculations according to the valid standards. The article also contains previous research results of Hugo Fernandes, who dealt with a similar type of strengthening method and this research was also based on experimental study. An important aspect is the detailing of the interface between the two concrete layers namely the roughening the existing surface or the use of studs, which ensure a minimum longitudinal displacement of the two layers. Two non-linear model approaches were presented. The results based on nonlinear analysis show that when using a simple model of two macroelements and defining the parameters of one interface, the punching shear resistance is higher than the actual resistance, in this case by of about 13% on the dangerous side.

Abstract: UHPC (ultra-high performance concrete) is an excellent material applicable also for strengthening of existing structures. Recently published papers were focused mainly on the behaviour of strengthened slabs subjected to bending, in this paper, experiments on punching and on strengthening of columns are mentioned. Strengthening of bridge decks requires a special composition of UHPC with high fibre contents and with the ability of casting in the slope. The appropriate mix for UHPC was developed within the research project. The experience gained from the extensive experimental program resulted in development of rules for strengthening of existing structures using UHPC, which follow the European codes and Czech recommendations for design of structures made of UHPC.

Abstract: This study is aimed at strengthening the working surfaces of the jewelry tool - scraper. This tool is used for fine cutting work. The object of research is a method of additional thermofrictional hardening of samples of jewelry tool - scrapers made of carbon steel tool grade U8A. In the course of work the complex of metallographic, mechanical and analytical researches of samples in an initial condition after hardening and low-temperature release which includes is carried out which includes:1) preparation of samples in the form of plates and their preliminary heat treatment;2) surface thermofrictional strengthening (STS);3) conducting metallographic analysis of samples; measuring the microhardness and depth of the layer with a changed cross-sectional structure of the samples after STS;4) analysis of the influence of STS on changes in the structure and properties of steel on the basis of the obtained results, as well as identification of the degree of its strengthening and the role of deformation.The methodology of experimental researches is presented. Photographs of samples and some equipment at different stages of the study are given. Data on the distribution of microhardness, photographs of microstructures in cross section of samples after additional strengthening are presented. The efficiency of strengthening of samples after use of additional processing is shown.

Abstract: This study investigated numerically the effect of small and large rectangular web openings in unstrengthened and strengthened steel I-beams and columns. With the use of a numerical model, 25 simply supported steel I-beams were subjected to a four-point bending test. In addition, 25 steel I-columns were tested numerically under axial compressive load. All steel I-beams and columns were compared with solid reference specimens without web openings (control specimen), where all specimens have the same 400 mm depth and 177 mm width steel section dimensions. Twelve of the 25 steel I-beams and columns with openings were strengthened with steel plates, and all had different web openings that were symmetrically located near the support areas. The performance of all steel I-beams and columns was compared before and after a strengthening procedure. The selected opening depths ranged from 40 to 280 mm. Aspect ratios of opening length to opening depth of 1.0, 2.0, and 3.0 were chosen. ABAQUS software was used to perform numerical analysis on I-sections (beams and columns) that were either unstrengthened or strengthened. All specimens were analyzed in terms of their load-displacement characteristics and failure modes. Finite element analysis showed that those beams and columns with small web openings have a slight decrease in strength and stiffness, which is considered to be within acceptable limits unlike solid steel beams and columns (control specimen). I-section beams and columns that have been strengthened have significant effects on increasing the load-displacement characteristics.

Abstract: Old and seismically prone buildings are in need of strengthening in order to comply with the latest building codes and to prolong their service life. For over two decades fiber-reinforced polymers (FRP) have been successfully used for this purpose. However, the poor performance in high temperatures of organic matrices has led researchers to investigate the use of inorganic matrices. Consequently, textile-reinforced mortars (TRM) have been opted for strengthening, since they incorporate textiles impregnated in inorganic cementitious matrices. Lately, in order to promote sustainability and lower the high carbon emissions of cement, alkali-activated mortars, also called geopolymers, have been investigated as an alternative. Their high performance and fireproof properties have made them excellent candidates as matrices in advanced composites for strengthening. This study aims to provide an overview of research in the field of advanced composites with alkali-activated matrices used for strengthening of concrete members. Systems implementing either fiber sheets or meshes have been used so far to strengthen reinforced concrete members, indicating promising results of the new advanced composite.

Abstract: Fiber Reinforced Cementitious Matrix (FRCM) composite materials represent one of the most interesting retrofitting methods for improving the out-of-plane flexural capacity of masonry walls. Despite their use is becoming more and more widespread, the actual knowledge about the out-of-plane behavior of FRCM-strengthened masonry panels needs further improvements, analyzing in particular the effectiveness of the reinforcement under cyclic loads. In this framework, an innovative experimental set-up, capable of applying a vertical axial load and cyclic out-of-plane horizontal forces on full-scale masonry panels, was used for testing walls retrofitted with glass, aramid-glass, basalt and steel fabrics. The presented experimental study is focused on the analysis of the effectiveness of the different FRCM systems, analyzing in detail failure modes, maximum capacity and the potential performance degradation of the strengthened panels under cyclic actions, providing also a useful comparison with the corresponding monotonic results.

Abstract: Masonry made with soft clay brick is commonly used in gravity load bearing of construction in India. The masonry piers and walls typically fail by vertical splitting. The purpose of this study is to improve the strength of masonry columns under compression using wrapping for additional confinement. The compressive load carrying performance and capacity of masonry columns wrapped with fiber reinforced composites in organic and inorganic matrixes are compared. For the purpose of overall improvements in cost and durability, glass and basalt fiber reinforcement is used. 30-40% improvement in the compressive performance of masonry prisms was achieved for both Organic and Inorganic matrixes. However, the specimens with inorganic matrixes were found to exhibit higher ductility compared to organic matrixes. Glass fibers were found to be more effective in wrapping masonry specimens compared to Basalt fiber specimens owing to its higher fiber count per unit length. Analytical models for predicting the compressive capacity of masonry columns with wrapping are verified against the experimental results.

Abstract: A large experimental study was conducted at IIT Patna, India to evaluate the effectiveness of different types of cementitious matrix grids (CMGs) in improving the flexural performance of unreinforced masonry specimens. Four types of masonry wallettes: brick-lime mortar, brick-cement mortar, brick-mud mortar and autoclaved aerated concrete (AAC) block masonry were prepared in the laboratory. In this study, eleven different CMG comprising of glass fabric and steel wire meshes embedded in the five different grades of cementitious matrix were used to strengthen the masonry assemblages. The aim of this study is to understand the role of various parameters such as tensile strength of CMG, compressive strength of masonry and cementitious matrix in influencing the efficiency of the strengthening scheme. In total 130 specimens with failure plane-parallel and perpendicular to the bed joint were prepared and tested under quasi-static displacement control loading. Considering the ease of installation, the fabric was directly placed on the masonry wallette using mechanical anchors and then covered with a thick layer of cementitious matrix.Test results highlights that all strengthening schemes are effective and can significantly enhance the flexural moment capacity in the range of 2.5 - 63.0 times the flexural moment of the respective control specimens. These strengthening schemes effectively mitigate the brittle behaviour of masonry wallettes and improved the deformation capacity by 1.2 - 18.1 times when compared to the respective control specimens. The study also illustrated that the strength of cementitious matrix can play an important role in contributing to the strength and deformability of the masonry specimens strengthened with CMG. For low strength cementitious matrix, debonding failure was commonly observed, whereas, for high strength cementitious matrix, the failure/rupture of reinforcement was noticed. In addition, the shear failure of masonry or debonding failure of reinforcing mesh was observed for specimens in which CMG had higher percentage of reinforcement.

Abstract: The present study investigates the use of Flax Textile-Reinforced Mortars (FTRM) as a strengthening and seismic retrofitting solution for unreinforced masonry. The FTRM system comprised flax textiles embedded in lime-based mortar and was externally bonded to the surface of four medium-scale masonry walls on both sides, in strengthening configurations including one and two FTRM layers. One bare wall and one wall strengthened only with lime-based mortar were additionally examined as reference samples. All specimens were tested in in-plane shear under quasi-static cyclic loading conditions, while axial load equal to 10% of the masonry compressive strength was constantly applied throughout the test. The effectiveness of the developed FTRM system is assessed in terms of strength, deformability, energy dissipation and failure modes. The obtained results highlight the promising potential of this system as an in-plane strengthening solution for masonry, with FTRM-retrofitted specimens able to promote strain redistribution and ensure the structural integrity. Two-layer configurations were evidenced to sustain up to 118% higher load capacity, improved ductility, and provided significant energy dissipation capacity.

Abstract: The restoration, the protection, or the creation of earthen buildings require improving the mechanical strength of the material. The first way to do that is to use inorganic additives, but these additives change the structural properties of earth and have a high carbon footprint. In contrast, the other way to consolidate is the use of organic additives such as vegetal derivatives that rearrange the minerals in the earth, with the lowest carbon footprint as they are from waste management. After preliminary tests with ten different organic additives from traditional recipes, we found that wheat starch improves the earth strength up to 50 %. In this study, we related the mechanical strengthening to the physicochemical interactions between clays and starch. We focus on three clays that represent the three main groups of clays: kaolinite, illite and montmorillonite. For this study, we mainly focused on compressive test and rheological tests. We showed that the improvement of the mechanical strength with starch is depending on clay nature and their chemistry. Then, we can recommend formulations based on the earth nature for new sustainable buildings. Furthermore, we can understand why it was an interesting way to use starch as a strengthening agent in traditional recipes and how it could be used to repair and protect buildings made of earthen material.