Use of steel fiber reinforced mortar for seismic strengthening Tug ˘çe Sevil a , Mehmet Baran b , Turhan Bilir c, * , Erdem Canbay a a Department of Civil Engineering, Structural Mechanics Laboratory, Middle East Technical University, Cankaya, Ankara 06531, Turkey b Department of Civil Engineering, Kirikkale University, Yahsihan, Kirikkale 71450, Turkey c Department of Civil Engineering, Eskisehir Osmangazi University, Bati Meselik, Eskisehir 26480, Turkey article info Article history: Received 1 April 2010 Received in revised form 23 June 2010 Accepted 29 June 2010 Available online 22 July 2010 Keywords: Steel fiber reinforced mortar Hollow brick infill wall Reinforced concrete Strengthening abstract The objective of this research was to develop an economical, structurally effective, and practically appli- cable steel fiber reinforced mortar (SFRM) which could be applied onto the hollow brick infills of a rein- forced concrete (RC) structure. Masonry walls were almost converted into strong and rigid infills with the application of SFRM. Two different mix proportions were produced with the composition of Portland cement, fine aggregate, water, and plasticizer or bonding agent as the chemical admixture. Tests were carried out to determine the optimum steel fiber content (1%, 2%, or 4% by volume) and to clarify the use of plasticizer or bonding agent in the mortar in the context of sticking ability, flexural, compressive, and adhesion strengths. As a result, mortar with plasticizer and 2% steel fiber (by volume) came out to be the optimum mortar mixture as strengthening material. The performance of RC frame strengthened with SFRM containing plasticizer and 2% steel fiber by volume was compared to those of the hollow brick infilled RC frame without strengthened mortar and the hollow brick infilled RC frame with reference mor- tar. It was observed that the specimen strengthened with the optimum mortar mix satisfied the target objectives of this study. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction In many countries, considerable number of existing building stock waits seismic vulnerability assessment followed by seismic retrofitting since they are seismically deficient and endanger pub- lic safety in a possible future earthquake. Among the available strengthening techniques, adding new cast-in-place RC infill walls to RC framed buildings was found to be the most appropriate and reliable method of system improvement in the studies conducted by Ersoy and Uzsoy [1], Altin et al. [2], Miller and Reaveley [3], Gregorian and Gregorian [4], Turk [5], Canbay et al. [6] and Sonuvar et al. [7]. Addition of cast-in-place RC infills increases both the strength and stiffness of the structure considerably. However, the workmanship in this technique is difficult and time-consuming. In addition, it necessitates evacuation of the building since large amounts of construction materials are transported into the build- ing. Recently, researchers all around the world have focused on developing economical, effective, and practical strengthening tech- niques. Among several studies on occupant friendly strengthening techniques, use of diagonal carbon fiber reinforced polymer (CFRP) sheets, precast concrete (PC) panels, and wire mesh reinforced shotcrete can be listed. Application of mortar onto the non-struc- tural masonry walls comes out to be a convenient strengthening technique, since it is cheap to produce, easy to apply, and structur- ally effective in use. Brittleness and low tensile strength are major drawbacks of concrete. The product obtained by randomly adding a small quan- tity of short fibers into a cementitious matrix is known as fiber reinforced composite (FRC) and improve many of its properties, such as compressive, split tensile, flexural, shear, impact, fatigue and abrasion strength, deformation capacity, load bearing capacity after cracking, and toughness properties [8–18]. The degree of improvement depends upon many factors such as size, type, aspect ratio, and volume fraction of fibers [19]. In the studies conducted by Bentur [20,21], crack propagation that occur due to internal stress in concrete were prevented by the use of steel fibers in conventional concrete. This was attributed to stress transfer capability of fibers. This behavior of fibers domi- nates the use of steel fiber reinforced concrete (SFRC) compared to the plain concrete. Many researches have been conducted to study different char- acteristics of SFRC. In a study conducted by Shah and Rangan [22], it was observed that the post-cracking resistance of the mate- rial was considerably influenced by the length, orientation, and stiffness of the fibers used. Batson et al. [23] conducted an experi- mental study in which conventional RC beams were tested in flex- ure where the shear stirrups were replaced by fibrous concrete containing steel fibers of various shapes, sizes, and volume frac- tions. According to Tran et al. [24], the use of overlay materials 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.06.096 * Corresponding author. Tel.: +90 222 239 37 50x3226. E-mail address: tbilir@ogu.edu.tr (T. Bilir). Construction and Building Materials 25 (2011) 892–899 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat