Mustafa Comert

Evaluation of FRP Confinement Models for Substandard Rectangular RC Columns Based on Full-Scale Reversed Cyclic Lateral Loading Tests in Strong and Weak Directions

Although many theoretical and experimental studies are available on external confinement of columns using fiber-reinforced polymer (FRP) jackets, as well as numerous models proposed for the axial stress-axial strain relation of concrete confined with FRP jackets, they have not been validated with a sufficient amount and variety of experimental data obtained through full-scale tests of reinforced concrete (RC) columns with different geometrical and mechanical characteristics. Particularly, no systematical experimental data have been presented on full-scale rectangular substandard RC columns subjected to reversed cyclic lateral loads along either their strong or weak axes. In this study, firstly, test results of five full-scale rectangular substandard RC columns with a cross-sectional aspect ratio of two (300 mm × 600 mm) are briefly summarized. The columns were tested under constant axial load and reversed cyclic lateral loads along their strong or weak axes before and after retrofitting with external FRP jackets. In the second stage, inelastic lateral force-displacement relationships of the columns are obtained analytically, making use of the plastic hinge assumption and different FRP confinement models available in the literature. Finally, the analytical findings are compared with the test results for both strong and weak directions of the columns. Comparisons showed that use of different models for the stress-strain relationship of FRP-confined concrete can yield significantly non-conservative or too conservative retrofit designs, particularly in terms of deformation capacity.

Performance Based Rapid Seismic Assessment Method (PERA) for Reinforced Concrete Frame Buildings

Recent destructive earthquakes have shown that many existing buildings, particularly in developing countries, are not safe against seismic actions. Since code-based seismic safety evaluation methods generally require detailed and complex structural analysis, the necessity for simplified, yet sufficiently accurate evaluation methods emerges for reducing cost and duration of assessment procedures. In this study, a performance based rapid seismic safety assessment method (PERA) is proposed for reinforced concrete buildings. The overall structural performance is determined based on the demand/capacity ratios of individual columns, as well as their failure modes (brittle/ductile), confinement characteristics, and levels of axial and shear stresses. The lateral drift of the critical story, calculated through a simplified approach, is also taken into account during determination of the global structural performance. The predictions of this method are compared with the results of conventional detailed seismic safety assessment analyses carried out for 672 different cases representing typical reinforced concrete frame buildings in Turkey. Good agreement is obtained between the predictions of the proposed algorithm and code-based structural performance assessment procedures. Finally, predictions of the proposed approach are compared with actual damages observed in 21 existing buildings in Turkey after destructive earthquakes that have occurred during the last two decades. These comparisons also point to an acceptable level of accuracy and sufficient conservatism for the methodology proposed.

Explosion Performance of a Ball Powder Production Facility

A ball powder production facility recently experienced two subsequent explosions which occurred due to the detonation of 2,800 kg and 17,000 kg ball powder components in the mixer building and the temporary storage building, respectively. Consequently, three persons were killed; and these two structures were damaged heavily. In this study, the outline of the mixer building is explained as well as the details of explosion and the behavior of the structural system of the mixer building against explosion. The observed damage mechanism of the mixer building is explained through a nonlinear dynamic blast load analysis as well as the evaluation of the original design, in situ material characteristics, and construction details. Furthermore, the potential reasons of the second explosion in the temporary storage building and the effects of this explosion are discussed considering the separation and public route distances given in related standards.

Code Based Performance Prediction for a Full-Scale FRP Retrofitted Building Test

Lack of adequate ductility in substandard reinforced concrete buildings is a major reason for significant amount of life and economic losses experienced during major earthquakes. Laboratory tests realized at member level (i.e. column and beam tests) show that external wrapping of potential plastic hinging regions of columns with Fiber Reinforced Polymer (FRP) sheets, can significantly enhance the ductility capacity. Thus, major seismic retrofitting documents available worldwide interpret this retrofit approach as a viable alternative and lay the rules for retrofit design with these materials. In this study, a very recent experimental activity that included the full-scale testing of a substandard building retrofitted with the above mentioned approach is briefly presented. Then, the performance prediction of the Turkish Seismic Design Code (2007) for this building is evaluated. Finally, a revision is proposed for the FRP effective rupture strain value defined by this code.

Seismic Performance of a Full-Scale FRP Retrofitted Sub-standard RC Building

External jacketing of columns with Fiber Reinforced Polymers (FRPs) is a promising retrofitting technique for improving seismic performance of sub-standard reinforced concrete (RC) buildings. The enhancement in deformation capacity and shear strength of jacketed members helps to prevent the brittle collapse mechanism of buildings with inadequate ductility. This paper provides an overview on the retrofitting of columns with FRP jacketing for particularly ductility enhancement and gives a brief summary of seismic strengthening recommendations of various design documents. In addition, a recent full-scale test conducted simultaneously on an as-built and a FRP retrofitted building, which are identical with design geometry, material quality and seismic deficiencies, is briefly presented and the performance of the retrofitting technique is evaluated. Finally, analytical behavior obtained through nonlinear static analyses executed using FRP-confined concrete models recommended in different technical documents are reviewed in comparison with the experimental behavior.

Evaluation of diaphragm conditions in AAC floor structures with RC beams

Diaphragm action in floor structures is an important aspect that affects both local behaviors of individual members and consequently, the global response of a structure. The diaphragm action of a built structure, therefore needs to be compatible with the assumed diaphragm condition in the design phase to prevent unpredicted overloading of load bearing members in a seismic action. Autoclaved aerated concrete (AAC) is a cost-effective, lightweight and energy efficient material, and its usage as a construction material has rapidly increased in recent decades. However, there is a limited experience regarding the in-plane behavior of the floor structures made of AAC panels in terms of diaphragm action. In this paper, the in-plane response of AAC floors is experimentally investigated and the floor performance of a typical building is analytically investigated according to ASCE 7-16 (ASCE/SEI in Minimum design loads for buildings and other structures, The American Society of Civil Engineers, Reston, 2016). Full-scale experiments carried out through loading AAC floors in lateral directions to the panels, either parallel or perpendicular, provided important information about the damage progress and overall performance of such floors. A number of finite element modeling techniques that are generally used for modeling of AAC floors were examined and then validated through comparisons with test results. Finally, the diaphragm condition of a three-story building made of AAC walls and floor panels was assessed. The results indicated that the AAC floors in the examined building can be idealized as rigid diaphragms according to ASCE 7-16.

Seismic Performance of Full-Scale FRP Retrofitted Substandard RC Columns Loaded in the Weak Direction

FRP confinement of sub-standard columns with low quality concrete, light transverse reinforcement and improper reinforcement detailing is widely accepted as an efficient retrofitting strategy. This paper introduces an improved method using carbon fiber reinforced polymers (CFRP) and external steel ties for seismic retrofitting of full-scale rectangular reinforced concrete columns loaded in their weak directions. Three cantilever columns with a cross-sectional aspect ratio of two (600 mm x 300 mm) are tested under constant axial load and reversed cyclic lateral loads. The columns are representative of existing substandard members with characteristics such as low concrete quality, low transverse reinforcement ratio, plain bars and high axial load level. The test results indicate that columns retrofitted with FRP jacketing and external steel ties significantly benefit from the applied retrofit scheme particularly in terms of ductility and energy dissipation. Additionally, the experimental results are compared with the performance predictions of seismic assessment and design documents.