15 research outputs found
Study on transferred impulse and response of steel plate walls under various impulsive loading considering mesh size effects
Get PDFThe behavior of steel plate walls (SPWs) under various impulsive loadings and the effects of different mesh sizes are investigated in this paper. With the aim of accurately inspecting SPWs, a series of analyses with 250 models with different plate geometric assumptions and different blast impulsive loadings are performed to study the SPWs’ out-of-plane behavior. The mild steel material specifications are adopted for SPWs with different thickness and stiffener arrangement and ABAQUS software is utilized for the Finite Element analysis. Results of transferred impulse, maximum displacement and Von Mises stress of SPWs show that SPWs with thickness of 5 mm are the best choice against various impulsive loadings in comparison with SPWs with thickness of 20 mm. In fact, the SPWs having the thickness of 5 mm show better performance as a result of more energy dissipation against various impulsive loadings. Finally, the Von Mises stress contours investigated for some models show 28% more stress in P5 SPW than that in P20 SPW. Also, it can be concluded that various sizes of mesh have no remarkable effect on unstiffened SPW while effect of different mesh sizes is more significant with increasing the number of stiffeners
Experimental study on damage detection of RC bridge piers under ambient vibration
Get PDFThis paper presents an experimental method for damage detection of bridge piers as the basic and strategic elements in such engineering structures. Definition of percentage and location of damage are considered as initial data to solve damage detection problems. Nowadays, regarding the development of inverse methods for damage detection such as definition of objective functions and optimization approaches, the present experimental study can be utilized as initial stage of such methods. In this study, three 1/3 scaled test specimens of RC bridge piers are casted. Spacing of transverse reinforcements is considered as the main variable parameter for test specimens. The constant vertical loads and low vibrations as cyclic loads are applied to the specimens and the results including the hysteresis behavior of specimens and the backbone curves are investigated. The damage percentage per first four steps is also extracted to utilize the results using Banon-Veneziano method. Also increase in lateral displacement during first steps initiated micro cracks propagated along nearly one tenth of the piers length (0.1L) above the foundation. The cracks were propagated after an increase in displacement from fourth step and were separately observed. Finally, the ultimate failures were observed along nearly one fifth of the piers length (0.2L). Finally, the results revealed that the proposed method is an appropriate method to determine the severity of damage and its location as the primary information in reverse-optimization methods
Experimental study on damage detection of RC bridge piers under ambient vibration
Get PDFThis paper presents an experimental method for damage detection of bridge piers as the basic and strategic elements in such engineering structures. Definition of percentage and location of damage are considered as initial data to solve damage detection problems. Nowadays, regarding the development of inverse methods for damage detection such as definition of objective functions and optimization approaches, the present experimental study can be utilized as initial stage of such methods. In this study, three 1/3 scaled test specimens of RC bridge piers are casted. Spacing of transverse reinforcements is considered as the main variable parameter for test specimens. The constant vertical loads and low vibrations as cyclic loads are applied to the specimens and the results including the hysteresis behavior of specimens and the backbone curves are investigated. The damage percentage per first four steps is also extracted to utilize the results using Banon-Veneziano method. Also increase in lateral displacement during first steps initiated micro cracks propagated along nearly one tenth of the piers length (0.1L) above the foundation. The cracks were propagated after an increase in displacement from fourth step and were separately observed. Finally, the ultimate failures were observed along nearly one fifth of the piers length (0.2L). Finally, the results revealed that the proposed method is an appropriate method to determine the severity of damage and its location as the primary information in reverse-optimization methods
APPLICATION OF TADAS DAMPERS TO IMPROVE THE BEHAVIOR OF STRUCTURES WITH RC SHEAR WALLS
No full textThe use of concrete shear walls in lateral resistance systems comes with certain disadvantages. Low ductility against lateral loadings due to their high stiffness and low vibration period of these systems can be mentioned as their drawbacks. Inadequate attention to shear capacity of the connecting region of roof and shear wall is also worth noting. These problems can increase the
vulnerability of the structure when subjected to lateral loads. Previous studies have demonstrated the benefits of providing energy dissipation devices to improve structure behavior. Metallic dampers, such as Added Damping and Stiffness (ADAS) and Triangular Added Damping and Stiffness (TADAS), are among the simplest energy dissipating devices that are being used in design of the
new generation of earthquake-resistant structures. Application of such devices in the lateral resistance system of a structure imposes a reduced maximum on internal forces. In this article, a more practical arrangement of yielding metal dampers has been proposed to reduce the base shear of the structure and improve its response and, as a result, diminish the seismic damages caused by earthquakes. The proposed arrangement is designed in a way that can allow the largest displacements and cause the highest energy dissipation.To demonstrate, a numerical example of optimal damper designs with different excitation inputs was presented. Ground acceleration records of the Imperial Valley, Kobe, Loma Prieta, and Northridge earthquakes were used as the disturbing ground motion in a series of numerical simulations of a multi-story steel building. The numerical simulations were carried out using Sap2000 program and the nonlinear dynamic behaviors of the different systems were compared to those of the conventional reinforced concrete shear wall equipped structure. Results indicated that the TADAS devices exhibited excellent energy dissipation and ductility leading to a massive increase in period of the first mode of vibration accompanied with up to 40 percent decline in peak values of base shear and absolute accelerations of the stories
Numerical Study of Progressive Collapse in Intermediate Moment Resisting Reinforced Concrete Frame Due to Column Removal
No full textProgressive collapse is a chain reaction of failures propagating throughout a portion of the structure disproportionate to the original local failure occurring when a sudden loss of a critical load‐bearing element initiates a structural element failure, eventually resulting in partial or full collapse of the structure. Both General Services Administration (GSA) and United States Department of Defense (DoD) guidelines incorporate a threat-independent approach to progressive collapse analysis. Therefore, there is an international trend for updating structural design requirements to explicitly design structures to resist progressive collapse. This paper presents simple analytical approach for evaluating progressive collapse potential of typical concrete buildings, comparing four methods for progressive collapse analysis by studying 5 and 10-story intermediate moment-resistant reinforced concrete frame buildings, employing increasingly more complex analytical procedures: linear-elastic static, nonlinear static, linear-elastic dynamic, and nonlinear dynamic methodologies. Each procedure is thoroughly investigated and its common shortcomings are identified. The evaluation uses current GSA progressive collapse guidelines and can be used in routine design by practicing engineers. These analyses for three column-removal conditions are performed to evaluate the behavior of RC buildings under progressive collapse. Based on obtained findings, dynamic analysis procedures -easy to perform for progressive collapse determination- yielded more accurate results
Modeling impact damper in building frames using GAP element
No full textMain effective factor in impact dampers to control vibration is to create disruption in structural oscillation amplitude using small forces induced by auxiliary masses to reduce strong vibrations. So far, modeling of the impact damper has been conducted solely through MATLAB software. Naturally, the functional aspects of this software are limited in research and development aspects compared to the common programs such as SAP2000 and ETABS. In this paper, a Single Degree of Freedom System, SDOF, is first modeled under harmonic loading with maximum amplitude of 0.4g in SAP2000 program. Then, the results are compared with numerical model. In this way, the proposed model is validated and the SDOF system equipped with an impact damper is investigated under the Kobe and Northridge earthquake records using SAP2000 model. Based on obtained results, the system equipped with an impact damper under the Kobe and Northridge earthquakes for structures considered in this study would have better seismic performance in which maximum displacements are reduced 6% and 33% respectively. Finally, impact dampers are modeled in a 4-story building structure with concentric bracing leading to 12% reduction in story drifts
Improving Emergency Training for Earthquakes through Immersive Virtual Environments and Anxiety Tests: A Case Study
No full textBecause of the occurrence of severe and large magnitude earthquakes each year, earthquake-prone countries suffer considerable financial damages and loss of life. Teaching essential safety measures will lead to a generation that can perform basic procedures during an earthquake, which is an essential and effective solution in preventing the loss of life in this natural disaster. In recent years, Virtual Reality (VR) technology has been a tool used to educate people on safety matters. This paper evaluates the effect of education and premonition on the incorrect decision-making of residents under the stressful conditions of an earthquake. For this purpose, a virtual model has been designed and modeled based on a proposed classroom in a school in the city of Tehran to simulate a virtual learning experience. In contrast, the classroom represents a realistic method of learning. Accordingly, each educational scenario, presented in reality and the virtual model, respectively, was conducted on a statistical sample of 20 students within the range of 20 to 25 years of age. Among the mentioned sample, the first group of 10 students was taught safety measures in a physical classroom. The second group of 10 students participated in a virtual classroom. Evaluation tests on safety measures against earthquakes were distributed after two weeks. Two self-reporting tests of Depression, Anxiety, Stress Scale (DASS) and Beck Anxiety Inventory (BAI) tests were assigned to the second group to evaluate the effect of foresight under two different scenarios. The results indicate that teaching through VR technology yields a higher performance level than the in-person education approach. Additionally, the ability to detect earthquakes ahead is an influential factor in controlling anxiety and determining the right decisions should the event occur
Experimental investigation of utilizing TLD with baffles in a scaled down 5-story benchmark building
No full textA tuned liquid damper (TLD) is a special type of auxiliary damping device, which relies on the sloshing of a liquid (water) in a container to counteract the forces acting on the structure. Damping in the TLD is introduced as a result of liquid sloshing and wave breaking. A conventional TLD is generally tuned to the main frequency of the building and is less efficient in other frequencies. Because of this limitation, the TLD is usually used to control the structural response of structures, which could be simulated as a SDOF structure, and mostly due to wind forces. In this paper a new kind of tuned liquid damper with some installed rotatable baffles is studied experimentally. The main idea behind installing such baffles is to compensate the effects of probable mistuning of the TLD and also it is an effort toward making the TLD more controllable, i.e. a semi-active damper. Response of a five story benchmark building was utilized to investigate the contributions of these baffles on efficiency of tuned liquid damper under dynamic and earthquake excitations. By observing the performance of TLD with baffles, the study investigates the influence of a number of parameters, include the following: baffles angles, frequency ratio, mass ratio and especially the effects of probable mistuning with changing the depth of water and orientation of baffles. The damping ratios of the building for a range of baffles angles were evaluated using logarithmic decrement technique. The results that are obtained in this paper show that the displacement and acceleration responses of the structure under the free vibration test utilizing the baffles reduced up to 2.5% and 3.9%, respectively, when compared with the case where no baffles are employed. Also the dynamic magnification factor under harmonic excitation reduced up to 2.7% proportional to baffles angles. Damping of the structure equipped with this type of TLD increased in a range of 3.93-6.38% when compared to the case of using no damper. The displacement and acceleration responses of the building under scaled down earthquakes also decreased up to 24.07% and 27.24%, respectively, with some of the best control results occurring before full closure of baffles. © 2011 Elsevier Ltd
Improving Emergency Training for Earthquakes through Immersive Virtual Environments and Anxiety Tests: A Case Study
No full textBecause of the occurrence of severe and large magnitude earthquakes each year, earthquake-prone countries suffer considerable financial damages and loss of life. Teaching essential safety measures will lead to a generation that can perform basic procedures during an earthquake, which is an essential and effective solution in preventing the loss of life in this natural disaster. In recent years, Virtual Reality (VR) technology has been a tool used to educate people on safety matters. This paper evaluates the effect of education and premonition on the incorrect decision-making of residents under the stressful conditions of an earthquake. For this purpose, a virtual model has been designed and modeled based on a proposed classroom in a school in the city of Tehran to simulate a virtual learning experience. In contrast, the classroom represents a realistic method of learning. Accordingly, each educational scenario, presented in reality and the virtual model, respectively, was conducted on a statistical sample of 20 students within the range of 20 to 25 years of age. Among the mentioned sample, the first group of 10 students was taught safety measures in a physical classroom. The second group of 10 students participated in a virtual classroom. Evaluation tests on safety measures against earthquakes were distributed after two weeks. Two self-reporting tests of Depression, Anxiety, Stress Scale (DASS) and Beck Anxiety Inventory (BAI) tests were assigned to the second group to evaluate the effect of foresight under two different scenarios. The results indicate that teaching through VR technology yields a higher performance level than the in-person education approach. Additionally, the ability to detect earthquakes ahead is an influential factor in controlling anxiety and determining the right decisions should the event occur
