Challenge Journal of Structural Mechanics
Osman Fatih BAYRAK (M. Sc.)
Seda YEDEK (M. Sc.)
M. Musab ERDEM (PhD.)
Prof. Dr. Murat BIKCE
January 23, 2018
Infill walls consisting of materials such as bricks, briquettes and autoclaved aerated concrete (AAC) are not only preferred in reinforced concrete (RC) buildings but also in steel frame structures. It is a well-known fact that infill walls limit the displace-ment of frames under horizontal load. However, they may also bring about certain problems due to being placed randomly in horizontal and vertical directions for some architectural reasons. Moreover, cracks in steel-wall joints are observed in steel frame structures in which ductile behaving steel and brittle behaving infill walls are used together. In this study, the effect of infill walls on steel frames has been investigated. In the steel frame structure chosen for the study, four different situations consisting of different combinations of infill walls have been modeled by using ETABS Software. Later, the static repulsion anal-yses have been performed for all the models and their results have been compared. As a result of the analyses done by using the equivalent compression bar model, it has been found out that infill walls limit the displacement of steel frames and increase the performance of a structure. However, it has been also determined that in the steel frame structure in which the infill walls have been asymmetrically placed vertically and horizontally, infill walls may lead to irregularities such as soft stories and tor-sion. As a result, it is possible to observe cracks in the joints of infill walls and steel, the deformation properties of which differ, unless necessary precautions are taken.
Investigating the Effect of Infill Walls on Steel Frame Structures (Read More)
The columns and beams of the steel frame that has been examined are made of an IPE300 steel profile. Hollow frame has been defined as Type 1. Type 2-4, which have been examined to understand asymmetrical effect of infill walls horizontally and vertically.
consisting of infilled steel frames, provides more rigidity and increases strength when compared to the frames without infill walls. Figure 6c shows Type 3, in which the basement floor is without infill walls because of various reasons such as commercial purposes and architectural decisions, the floor without infill walls behaves like a soft story under the earthquake force, and the infill wall upstairs moves as a whole. Torsion has been observed in the frame of Type 4 in which infill walls are formed asymmetrically.
While the plastic hinges have spread properly in two stories in Type 1, the plastic hinges have formed in the basement floor without walls in Type 3 which is under the effect of soft story. Since there are not many plastic hing-es, Type 2 is stable; however, in Type 4, in the areas where there are no walls, plastic hinges have increased and thereby a failure mechanism has been observed.
Frames with infill walls provide support to the rigidity and strength of a structure under earthquake load. Although this is considered positive by engineers, it is mostly disregarded as an extra safety reserve for a structure. However, infill walls might also lead to some irregularities in the structure, since placing infill walls asymmetrically in vertical and horizontal directions causes certain changes in the rigidity and strength of the structure That's why, in the draft of 2016 Turkish Earthquake Code, using flexible joint connection between these two elements is stated as an option in order to minimize the effect of infill walls compromising of brittle material on frames. In this study, to investigate the effect of infill walls on steel frame structures, four different cases have been deter-mined and their repulsion analyses have been performed. As a result of the analyses, it has been determined that infill walls increase strength and limit displacements. Yet, it has also been seen that placing infill walls asymmetrically in vertical and horizontal directions may lead to some irregularities such as soft story and torsion. Steel frames that are structurally more ductile than infill walls cause deformations under horizontal load, whereas infill walls limit this situ-ation. However, when infill walls and steel materials which have different deformation properties come together, cracks might occur in joint points unless necessary precautions are taken.