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    Behavior and strength of hidden Rc beams embedded in slabs
    (ELSEVIER, 2020) Ozbek, Eray; Aykac, Bengi; Bocek, Meryem; Yilmaz, Mahmut Cem; Mohammed, A. B. Khadeeja; Er, Sule Bakirci; Aykac, Sabahattin
    Reinforced concrete (RC) beams protrude from the ceiling, unless there is an infill wall beneath. Sometimes the construction of these beams is avoided due to aesthetic concerns, and instead a reinforcement arrangement with an equivalent bending moment capacity in the slab is made; this is named as a hidden beam. However, since such a design based only on strength can change the behavior to a great extent, the drawbacks of hidden beams were experimentally investigated. A total of fourteen half-scale specimens, including conventional T-beams and slabs with identical flexural capacities (hidden beams), were tested to failure under four-point loading. Reinforcement ratio and slab thickness were adopted as test parameters. The results indicated that hidden beams were able to achieve reference strengths after excessive (up to eight times larger) deformations, or they occasionally could never achieve these capacities. Experimental data were also compared with analytical deflection approaches.
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    Behavior of Postfabricated RC Beams under Monotonic Transverse Loading
    (Asce-Amer Soc Civil Engineers, 2019) Aykac, Sabahattin; Jamal, Rohullah; Ozbek, Eray; Kalkan, Ilker; Aykac, Bengi
    Postfabricated beams, that is, newly constructed beams in an existing structural system, provide an effective remedial solution to the serviceability and strength problems in an existing floor system and the discontinuities and irregularities in the seismic-force-resisting system of a structure, mostly caused by design and construction errors or intended omissions of certain members. The purpose of this study is to develop new techniques for postfabrication of these beams and connecting the postfabricated beams to the existing columns and slab. In this respect, an experimental study was planned and a total of 16half-scale specimens, including 3 monolithic (slab, columns, and beams cast monolithically) specimens and 13 specimens with postfabricated beams, were tested under monotonic vertical loads. The longitudinal reinforcement ratio of the postfabricated beam and the connection techniques of the postfabricated beam to the surrounding columns and slab constituted the test parameters. The tests indicated that the specimens with postfabricated beams were able to reach the strength and behavior of the monolithic specimens.
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    Behaviour of brick infill walls strengthened with expanded steel plates
    (Springer, 2016) Cumhur, Alper; Altundal, Adil; Kalkan, Ilker; Aykac, Sabahattin
    The present study was dedicated to investigate an effective, economical and convenient method for strengthening brick infill walls, i.e. the use of externally-bonded expanded steel plates. A total of 30 plastered wall assemblies were tested under monotonic diagonal loading to investigate the contribution of these plates to the load capacities, ductilities and rigidities of brick walls. The plate thickness, bolt spacing and location of the plates in the wall were the parameters of the test program. The experiments indicated that application of the plates on the outermost fine plaster layer significantly improves the diagonal load-deflection behaviour of infill walls and reducing the bolt spacing provides the strengthened walls with higher load capacity values. An analytical expression was developed for estimating the diagonal load capacities of plated brick walls. The analytical load estimates were found to be in close agreement with the experimental values.
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    Behaviour Of Reinforced Concrete Weak Column-Beam Connections
    (Gazi Univ, Fac Engineering Architecture, 2014) Bakirci Er, Sule; Aykac, Sabahattin; Can, Husnu
    In this study the behavior of RC weak column-beam connections which have no joint stirrups and lack of column stirrups, are investigated experimentally under earthquake loads. Edge beam to column joints were tested under reversed cyclic loads. It is the prestudy of which has seven joint strengthening techniques. 1/2 scaled one reference and seven weak joint specimens with no stirrups were prepared and tested. The building defects in real structure exactly tried to create when producing the weak specimens. These building defects include lacking stirrups in joint region, low compressive strength of concrete and in progress of time pouring out of concrete cover. The weak specimens' behaviors compared with the reference specimen and load-deflection graphics taken. The main parameters are constant axial load and the distance of lacking stirrups at the joint region. As a result of the experimental study in reference specimen achieved to carrying capacity from the beam. Damages in joints are dangerous. In all weak specimens reached to carrying capacity from the joint before the beam. In some weak specimens columns' shear damages and joints' hard damages together determined the carrying capacity.
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    Discussion on "Seismic capacity of masonry infilled RC frame strengthening with expanded metal ferrocement" by A. Leeanansaksiri, P. Panyakapo, A. Ruangrassamee [Eng. Struct. 159 (2018) 110-127]
    (Elsevier Sci Ltd, 2018) Aykac, Sabahattin; Ozbek, Eray; Kalkan, Ilker; Aykac, Bengi
    A discussion on the paper by Leeanansaksiri et al. (2018) is presented. In the paper, strengthening of the masonry infill walls using ferrocement reinforced with standard expanded steel plates (EMS) was investigated experimentally. A bare frame without infill wall, a frame with a plain (unstrengthened) infill wall and a frame with a strengthened infill wall were tested under reversed cyclic lateral loading. The type of EMS to be used for strengthening was decided based on compressive strength tests on plain (unstrengthened) and strengthened masonry prisms and monotonic diagonal loading tests on wall panels. The results of the prism and panel tests were also used to determine the parameters of the analytical hysteric models, which closely estimated the experimental results of the frame tests. While the paper reached important conclusions related to the proposed strengthening technique, the authors of this discussion felt obliged to present their significant findings on the issues, raised in the paper for further research to increase the efficiency of the proposed technique. Furthermore, this discussion summarizes the findings of the authors on the strategies to investigate the efficiency of an infill wall strengthening technique.
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    Flexural Behavior and Strength of Reinforced Concrete Beams with Multiple Transverse Openings
    (Amer Concrete Inst, 2014) Aykac, Bengi; Aykac, Sabahattin; Kalkan, Ilker; Dundar, Berk; Can, Husnu
    Reported are the results of experiments on 10 rectangular reinforced concrete (RC) beams with and without multiple web openings. The effects of opening geometry, the-use of longitudinal stirrups in the posts between the openings, the use of diagonal reinforcement around openings, and the longitudinal reinforcement ratio on the flexural behavior of RC beams with openings were investigated. The stirrups in the posts were shown to have a significant contribution to the ductility of an RC beam with openings if no diagonal reinforcement is used. For the same reinforcement details, RC beams with circular openings were found to have higher load capacities and ductilities than beams with rectangular openings. The experiments indicated that the posts between the openings need to be prevented from undergoing shear failure to avoid Vierendeel truss action and allow a beam to develop its ductility and bending capacity.
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    Flexural behavior of RC beams with regular square or circular web openings
    (Elsevier Sci Ltd, 2013) Aykac, Bengi; Kalkan, Ilker; Aykac, Sabahattin; Egriboz, Yusuf Emre
    This paper presents a study aimed at investigating the influence of multiple web openings along the length of an RC beam on its flexural behavior. A total of nine rectangular beams were tested. Diagonal reinforcement around openings effectively prevented premature failure of some specimens due to Vierendeel action, the expected failure mode according to bending moment-axial force interaction diagrams. Longitudinal rebars and full-depth stirrups adjacent to openings and short stirrups in the chords prevented beam-type and frame-type shear failures. The length of the plastic failure mechanism increased in the presence of multiple openings compared to beams with a single opening. (C) 2013 Elsevier Ltd. All rights reserved.
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    Flexural strengthening and repair of RC slabs by adding a new RC layer
    (Ernst & Sohn, 2016) Aykac, Sabahattin; Kalkan, Ilker; Tankut, Tugrul
    The present paper summarizes the findings of an experimental programme to investigate a strengthening/repair technique through the introduction of a new RC layer to an existing slab. Six RC slabs, composed of twelve cantilever and six interior spans, were tested under monotonic transverse loading. The behaviour of statically determinate cantilever spans and indeterminate interior spans was examined by comparing the test results of these specimens to the results of reference slabs, in which the existing and additional layers were cast monolithically. The influences of recovering the permanent slab deformation before repair and the spacing of the shear connectors between the existing and additional layers were investigated. The tests indicated that recovering the permanent deformations of a slab before repair substantially reduces its rigidity while having little influence on the ultimate load. Furthermore, debonding of the reinforcement was observed to considerably decrease the load capacities and rigidities of the slabs.
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    Lateral stability of reinforced-concrete beams with initial imperfections
    (Ice Publishing, 2016) Kalkan, Ilker; Bocek, Meryem; Aykac, Sabahattin
    The paper presents the results of an analytical study aimed at investigating the lateral stability of reinforced-concrete (RC) beams with initial geometric imperfections. Based on the experimental results in the literature, a general buckling moment expression was developed, linking the limit moment of a RC beam with an initial sweep and twist to the critical moment of its geometrically perfect configuration. This expression takes into account the initial geometric and material non-linearities of the beams, the elastic-inelastic material properties of concrete and steel, the cracking of concrete due to restrained shrinkage and in-plane flexure, and the contribution of longitudinal reinforcement to stability. The formula was applied to three standard types of Aashto I-girders to determine the critical unbraced length of each type. Finally, an analytical equation was developed for estimating the lateral deflections of RC beams with initial geometric imperfections. The limit moment and lateral deflection equations were shown to provide close and conservative estimates for RC beams.
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    New Experimental Setup for Seismic Testing of Exterior RC Beam-Column Joints
    (Amer Soc Testing Materials, 2015) Aykac, Sabahattin; Kalkan, Ilker
    Exterior beam-column joints are commonly tested to investigate the influence of different strengthening and repair techniques on the seismic performances of RC structures. All of the internal forces developing at the ends of the beams and columns need to be applied to the test specimens and these forces need to be proportioned similar to the proportions of the forces in a structure to simulate the conditions of an actual structure during an earthquake. This paper presents a new experimental setup developed to realistically represent the seismic response and behavior of an exterior RC beam-column joint under earthquake excitations. This setup offers a quite economical alternative to the available loading and testing assemblies, made up of several costly loading devices and support fixtures to approximate the conditions of a joint in an earthquake. The present setup was established by using widely-available and inexpensive components to make seismic testing of joints more feasible considering the financial and space limitations of the researchers, particularly in developing countries. The setup also takes into account the influence of the presence of the slab and transverse beams framing into the planar beam-column connection. Three-dimensional exterior RC beam-column connections were successfully tested using this setup.
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    Strengthening and Repair of Reinforced Concrete Beams Using External Steel Plates
    (Asce-Amer Soc Civil Engineers, 2013) Aykac, Sabahattin; Kalkan, Ilker; Aykac, Bengi; Karahan, Servet; Kayar, Sinan
    The study presents the results of an experimental program aimed at investigating the flexural behavior of externally plated RC beams. A total of 13 full-scale rectangular RC beams were tested. The effects on the behavior of the plate thickness, the anchorage of the plate to the beam through anchor bolts or side plates (collars), and the use of perforated plates instead of solid ones were investigated. The experiments indicated that the beam ductility increases as the plate thickness decreases, and the anchorage of the plate to the beam through bolts or collars proves to be an efficient method for preventing the premature plate peeling failure and achieving sufficient ductility in beams strengthened with thick solid plates. Anchor bolts had adverse effects on the ductilities of the beams with thin plates, and the use of perforated steel plates was found to be an efficient method for increasing the ductility of a strengthened beam. The beams repaired with perforated plates anchored to the beam with collars had load-carrying capacities close to those of the undamaged beams. (C) 2013 American Society of Civil Engineers.
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    Strengthening of hollow brick infill walls with perforated steel plates
    (Techno-Press, 2014) Aykac, Sabahattin; Kalkan, Ilker; Seydanlioglu, Mahmut
    The infill walls, whose contribution to the earthquake resistance of a structure is generally ignored due to their limited lateral rigidities, constitute a part of the lateral load bearing system of an RC frame structure. A common method for improving the earthquake behavior of RC frame structures is increasing the contribution of the infill walls to the overall lateral rigidity by strengthening them through different techniques. The present study investigates the influence of externally bonded perforated steel plates on the load capacities, rigidities, and ductilities of hollow brick infill walls. For this purpose, a reference (unstrengthened) and twelve strengthened specimens were subjected to monotonic diagonal compression. The experiments indicated that the spacing of the bolts, connecting the plates to the wall, have a more profound effect on the behavior of a brick wall compared to the thickness of the strengthening plates. Furthermore, an increase in the plate thickness was shown to result in a considerable improvement in the behavior of the wall only if the plates are connected to the wall with closely-spaced bolts. This strengthening technique was found to increase the energy absorption capacities of the walls between 4 and 14 times the capacity of the reference wall. The strengthened walls reached ultimate loads 30-160% greater than the reference wall and all strengthened walls remained intact till the end of the test.
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    Strengthening Of Plastered Hollow Brick Infill Walls Using Strip Concrete/Reinforced Concrete Panels
    (Gazi Univ, Fac Engineering Architecture, 2014) Baran, Mehmet; Aktas, Merve; Aykac, Sabahattin
    In Turkey, majority of the building stock is known to be inadequate against earthquake and is required to be strengthened. Cast-in-place reinforced concrete (RC) infill walls, connected to the frame systems by use of epoxy glued anchorages, improve the behavior of the building significantly. However, requirements of this technique such as evacuation of the building and converts it to a construction area for a long time have directed the researchers developing occupant friendly, economic and structurally effective strengthening techniques. The principle of the technique presented in this paper is based on bonding strip concrete panels on some of the plastered hollow brick infill walls available in the building such that they will behave as RC infill walls. For this purpose, seven plastered hollow brick infill wall specimens with a scale of 1/2 were tested under reversed cyclic lateral loading. Six wall specimens were strengthened with strip concrete/reinforced concrete (RC) panels. Test results showed that application of concrete panels increased lateral strength of the test specimens and improved their behavior.
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    Strengthening of RC T-beams with perforated steel plates
    (Ice Publishing, 2013) Aykac, Sabahattin; Kalkan, Ilker; Aykac, Bengi; Ozbek, Eray
    The study investigates the flexural behaviour and ductilities of reinforced concrete (RC) T-beams strengthened with perforated steel plates. A total of eight full-scale RC T-beams were tested. Three strengthened beams and a reference unplated beam were reinforced with closely spaced stirrups, while the remaining plated beams and reference beam did not have adequate amounts of shear reinforcement (shear deficient). Shear strengthening with post-tensioned anchors was found to shift the failure mode of a shear-deficient beam from shear to flexure. The post-tensioning forces in the anchors were established to be kept at an optimum level to provide adequate shear strength to the beam and to prevent overstraining of the soffit plate between the shear anchor locations. The perforations increased the ductilities, energy absorption capacities and permanent deformations of the specimens. The use of compression plate in addition to the tension (soffit) plate greatly contributed to the ductilities of specimens with adequate and inadequate shear strength.
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    Strengthening of reinforced concrete beams with epoxy-bonded perforated steel plates
    (Techno-Press, 2012) Aykac, Sabahattin; Kalkan, Ilker; Uysal, Ali
    Although being one of the most popular strengthening techniques in reinforced concrete beams, the use of steel plates bonded to the soffit raises problems of ductility. This study aims at investigating the influence of the use of perforated steel plates instead of solid steel plates on the ductility of reinforced concrete beams. A total of nine reinforced concrete beams were tested. In addition to an unplated beam, eight beams with perforated steel plates of two different thicknesses (3 mm and 6 mm) were subjected to monotonic loading. Effect of bonding the plates to the beams with anchor bolts and with additional side plates bonded to the sides of the beam with and without anchors is also investigated. The use of bolts in addition to epoxy was found to greatly contribute to the ductility and energy absorption capacity of the beams, particularly in specimens with thick plates (6 mm) and the use side plates in addition to the bottom plate was found to be ineffective in increasing the ductility of a concrete beam unless the side plates are attached to the beam with anchors bolts. The thickness of the plate was found to have little effect on the bending rigidity of the beam.