Evaluation of Seismic Behavior and Select Optimal Situation of Cylindrical Frictional Dampers in Steel Structures

In this investigation, seismic response of steel structures utilizing Cylindrical Frictional Dampers (CFD) is studied. CFD is an innovative frictional damper which comprises two principal elements, the shaft and the hollow cylinder. These two elements are assembled such that one is shrink-fitted inside the other. If the damper’s axial force overcomes the static friction load, the shaft inside the cylinder will move and results in considerable mechanical energy absorption. To assess the efficacy of CFD 6 story steel frame are constructed and analyzed. Nonlinear time history analyses are applied to the frames and clear distinction has been drawn between the frames comprising CFD and the counterparts without CFD to emphasize the effectiveness of CFD in altering seismic responses. The results show that CFD extremely improves the seismic response of the structure. Considering that we can install this damper in various situations to absorb energy, the behavior of this damper is evaluated in these situations. Response of structure (such as displacement, base shear, etc) represents the best and most effective position and optimal situation of the damper which is in diagonal brace

A System Identification-Based Damage-Detection Method for Gravity Dams

Dams are essential infrastructures as they provide a range of economic, environmental, and social benefits to the local populations. Damage in the body of these structures may lead to an irreparable disaster. This paper presents a cost-effective vibration-based framework to identify the dynamic properties and damage of the dams. To this end, four commonly occurred damage scenarios, including (1) damage in the neck of the dam, (2) damage in the toe of the structure, (3) simultaneous damage in the neck and the toe of the dam, and (4) damage in the lifting joints of the dam, are considered. The proposed method is based on processing the acceleration response of a gravity dam under ambient excitations. First, the random decrement technique (RDT) is applied to determine the free-vibration of the structure using the structural response. Then, a combined method based on Hilbert–Huang Transform (HHT) and Wavelet Transform (WT) is presented to obtain the dynamic properties of the structure. Next, the cubic-spline technique is used to make the mode shapes differentiable. Finally, Continuous Wavelet Transform (CWT) is applied to the residual values of mode shape curvatures between intact and damaged structures to estimate the damage location. In order to evaluate the efficiency of the proposed method in field condition, 10% noise is added to the structural response. Results show promising accuracy in estimating the location of damage even when the structure is subjected to simultaneous damage in different locations

Free and Forced Vibration Analysis of an Infilled Steel Frame: Experimental, Numerical, and Analytical Methods

Structural frames with masonry infill panels make up a significant portion of the buildings constructed in earthquake-prone areas prior to the developing of the seismic design standards. In this paper, the effects of masonry panels on the vibration response of an infilled steel-frame building are investigated. Various ambient and steady state forced vibration tests are carried out to realize the dynamic characteristics of the system. 3D finite element models of the building with and without infill panels are provided based on marcomodeling theorem. A set of analytical approximate formulas are also derived to estimate the vibrational period. The natural frequencies of the building are computed using numerical, analytical, and experimental methods. The results show that neglecting the effect of infill panels leads to considerable error. Moreover, it is shown that there is good agreement among the results obtained by the three methods considering the effect of infill panels

Exploring the Effect of Near-Field Ground Motions on the Fragility Curves of Multi-Span Simply Supported Concrete Girder Bridges

Investigating the impact of near-field ground motions on the fragility curves of multi-span simply supported concrete girder bridges is the main goal of this paper. Fragility curves are valuable tools for evaluating seismic risks and vulnerabilities of bridges. Numerous studies have investigated the impact of ground motions on the fragility curves of bridges. Ground motions are commonly categorized into two sets, based on the distance of the recorded station from the seismic source: far-field and near-field. Studies examining the influence of near-field records on bridge fragility curves vary depending on the specific bridge type and type of fragility curve being analyzed. Due to the widespread use of multi-span simply supported concrete girder bridges in the Central and Southeastern United States, this study makes use of this bridge type. This research investigates the component fragility curves for column curvatures, bearing deformations, and abutment displacements by employing 3-D analytical models and conducting nonlinear time history analysis. These curves illustrate the impact of near-field ground motions on different components. The component fragility curves for two sets of records, 91 near-field ground motions and 78 far-field ground motions, were obtained and compared. These findings demonstrate that near-field ground motions have a greater damaging effect on columns and abutments than far-field earthquakes. When it comes to bearing deformations, the far-field earthquake impact is more severe at lower intensities, whereas the impact of the near-field ground motion is stronger at higher intensities

Nonlinear Seismic Performance Evaluation of Flexural Slotted Connection Using Endurance Time Method

The equivalent statistical methods, spectral analysis, and time history analysis are usually offered in the steel structure design regulations. Among these methods, the third one is more accurate; however, it requires more time to align the accelerometers due to a large number of analyses. In the endurance time (ET) method, incremental acceleration functions gradually and uniformly increases over time while their linear and nonlinear response spectra are proportional to the mean of the real seismic spectrum. These functions are used as input functions to analyze the nonlinear time history of structures, and the performance of structures is evaluated based on the maximum length of time they can meet specified performance goals. A three-story steel bending frame with (slotted web) SW and (web unslotted flange) WUF connection is examined through the performance time method in performance-based design. This article aimed at evaluating the seismic performance of these connections in the bending frame through endurance time analysis to predict the structural response in the probabilistic evaluation of the seismic performance of the structures. It is found that the endurance time analysis is justified with the seismic performance of the connections with low computational cost and proper accuracy. The results of comparing both SW and WUF connections indicated that the SW connection prevents the connection welding area from being failed due to transferring the plastic joint into the beam and in an area away from the column face and causes less damage compared to the WUF connection

Explosive Performance Assessment of Buried Steel Pipeline

It is so important to consider the passive defense problem in any places there have been attacks by varies kinds of military threats and terrorists. It is certain that social security is related to overcoming on these perils and protection from country. Vital facilities are one of examples that should be protected. Vital facilities include roads, bridges, transmission lines, and telecom and media network. With attention to the intense dependent to export and transmit of oil and gas and with consideration of this point that many places are full of gas and oil resource, the protection of these lines is very important. In recent years, occurrence of varies kinds of terrorist accidents in relation to important structures in all the world causes that the explosion loads have special attention. Explosion can generate much damage with vibration in vast soil media. Thus, it is important to predict the dynamic impact load and its treatment response. With attention to regardable development of numerical methods in recent decades, it is possible to investigate the explosion effects on surface and underground structures. In this research, the newest applied method modeling of the explosion phenomenon has been investigated and comprehensive information has been earned. In this investigation, problem of explosion wave’s propagation effects on buried pipes simulated by ABAQUS/CAE 6.10-1 was studied based on the finite element method. Surface explosion effects on gas buried pipe lines and their dynamic response have been investigated depending on properties and their characteristics. The variation of buried pipe depth effects and variation effects in soil properties around pipe in different cases has been considered, and the results are here. The results showed that in buried pipes under surface explosions, displacements, major stresses, and strains decrease in clay, dense, and loose sands with increase of buried depth. These results obtain that because of increase of closuring of pipes in soil when internal friction angle increases for a kind of soil, the stress on pipe rim will decrease also. It was also observed that the pipe performance in clay and loose sands is better than that in compacted sand, respectively