Performance Assessment of Steel Moment Connections Retrofitted with Various Reduced Section Patterns

It is of high importance in seismic retrofitting of lateral load-bearing systems to increase the connections performance. The crucial point in the steel frame retrofitting process is to create plastic hinges in these types of frames. The formation of plastic hinges in beams and near columns generates large strains on column flanges as well as welding metal and heated surroundings, which can lead to brittle failure. The connection should be designed in such a way as to allow plastic hinge formation at certain points of the beam. One such method suggested for retrofit connections is to reduce the beam section locally away from the connection zone. There are various patterns available to locally reduce the beam section, such as circular, elliptical, and symmetric/asymmetric. In recent years, different proposals have been presented to design these connections which vary from older instructions. For this study, radiused cuts in the flange and slotted holes in the web of connection beams were selected for retrofitting analysis. Cyclic behavior, energy damping levels, and ductility of these connections were studied and compared before and after the retrofit by using nonlinear dynamic analysis. The results showed that the symmetrical circular hole pattern in the beam flanges demonstrated reliable performance

Performance Assessment of Steel Moment Connections Retrofitted with Various Reduced Section Patterns

It is of high importance in seismic retrofitting of lateral load-bearing systems to increase the connections performance. The crucial point in the steel frame retrofitting process is to create plastic hinges in these types of frames. The formation of plastic hinges in beams and near columns generates large strains on column flanges as well as welding metal and heated surroundings, which can lead to brittle failure. The connection should be designed in such a way as to allow plastic hinge formation at certain points of the beam. One such method suggested for retrofit connections is to reduce the beam section locally away from the connection zone. There are various patterns available to locally reduce the beam section, such as circular, elliptical, and symmetric/asymmetric. In recent years, different proposals have been presented to design these connections which vary from older instructions. For this study, radiused cuts in the flange and slotted holes in the web of connection beams were selected for retrofitting analysis. Cyclic behavior, energy damping levels, and ductility of these connections were studied and compared before and after the retrofit by using nonlinear dynamic analysis. The results showed that the symmetrical circular hole pattern in the beam flanges demonstrated reliable performance

Statistical prediction of probable seismic hazard zonation of Iran using self-organized artificial intelligence model

The Iranian plateau has been known as one of the most seismically active regions of the world, and it frequently suffers destructive and catastrophic earthquakes that cause heavy loss of human life and widespread damage. Earthquakes are regularly felt on all sides of the region. Prediction of the occurrence location of the future earthquakes along with determining the probability percentage can be very useful in decreasing the seismic risks. Determining predicted locations causes increasing attention to design, seismic rehabilitation and evaluating the reliability of the present structures in these locations. No exact method has been approved for predicting future earthquake parameters yet. In recent years, more attention is paid to the earthquake magnitude prediction, but no study has been done in the field of probable earthquake occurrence hazard zonation. In this study, locations of future earthquakes in Iran were predicted by self-organized artificial neural networks (ANN). Then probable seismic risk zoning map was drawn by the statistical analyses, and the results indicated that the maps can properly predict future seismic events

Experimental and numerical investigations of a new hysteretic damper for seismic resilient steel moment connections

In this study, a novel hysteretic damper is proposed for beam-column steel connections to dissipate seismic energy. The proposed system is classified as a low-damage device and the energy dissipation in the connection is provided through the bending deformations in hourglass shape steel pins inside the hysteretic damper. At the first stage, full-scale experimental prototypes have been fabricated and tested in the dynamic testing laboratory. In the next stage, micro- and macro-modelings of the proposed device calibrated through the experimental testing have been investigated using ABAQUS and OpenSees platforms, respectively. Both experimental and finite element simulations indicated that the proposed damper has a high capacity of energy dissipation without a significant decline in the resistance through loading cycles. Applying this damper to the connection helps all structural members including beams and columns to maintain in the elastic region, and will improve the ductility and seismic resilience of the whole building structure. The proposed damper has the easiness of fabrication, installation, and replacement

Estimation of vibration frequency of structural floors using combined artificial intelligence and finite element simulation

Floor vibration due to human activities (walking, running, etc.) and operating machines generally makes inconveniences for residents. The natural vibration frequency of beams is determined as the main source and also the controlling parameter of such the phenomenon. Many studies have been conducted on determining the natural frequency of beams in recent years; however, the proposed formulations in many of them are not very practical for vibration control of tall building floors. In this paper, the finite element method (FEM), nonlinear (NL) dynamic analyses, and artificial intelligence (AI) techniques were adopted to constitute the simple frequency equations of the fixed ends and cantilever steel beams for controlling the floor vibration. The input data required for training the AI-based model are simulated in a NL FE platform considering various cases of the steel moment connections. The analysis outcome of several hundred beams with different properties indicated that the calculated vibration frequency values of the fixed ends and cantilever beams were respectively 2.07 and 0.33 times larger than the frequency value of the simply supported beams with similar conditions. To this, the implemented soft computing technique was determined as an effective approach to improve the computational efficiency of the NL-FE simulations

Seismic Behavior of Earth Dams with Different Reservoir Water Levels Under Near-Field and Far-Field Earthquakes

The height of reservoir water is one of the important factors affecting the seismic behaviour of earth dams. A large number of earth dams have been constructed in different countries that are sometimes located in a high-risk geographical zone. The studies on the seismic behaviour of earth dams have been conducted for several decades. However, this study, considering the importance of the subject, it investigates the seismic behaviour of Sumbar rock-fill embankment dam under near- and far-field earthquakes with variation in the water level behind the dam. The ratio of water height of the dam to dam height is considered as an important indicator to investigate the seismic performance of these structures. The analyses were performed using the ABAQUS finite element platform, under 7 near-field and 7 far-field earthquake records. In this research, the changes in dam stresses, displacements, and failure of the dam have been discussed. The results indicated that the effect of near-field earthquakes on the seismic behaviour of earth dams is more significant than far-field earthquakes

Effect of foundation flexibility on the seismic performance of a high-rise structure under far-field and near-field earthquakes

In this study, the seismic performance of a 20-storey steel structure with a mat foundation located on layered soil is investigated under an array of strong ground excitations, which includes 6 far-fault and 6 near-fault earthquakes. Eight different modes for soil layering have been considered in the numerical simulation. FLAC 2D nonlinear platform has been used to model the near-realistic behavior. To this end, hundred lines of codes and subroutines have been developed in this platform to perform the analysis. The results of the analyzes include the absolute displacement of the floors, the ratio of the relative displacement of the floors, the shear force, the axial force, and the bending moment of the columns. It was concluded that for a 20-story structure on a mat foundation under both far-field and near-field earthquakes, the most reliable type of soil is the dense sandy soil and the most critical case is the soft clay soil. It was also observed that the near-field strong ground motions have imposed more critical structural responses compared to far-field records

Seismic Performance and Global Ductility of RC Frames Rehabilitated with Retrofitted Joints by CFRP Laminates

This paper presents a new FRP retrofitting scheme to strengthen local beam-column joints in reinforced concrete (RC) frames. The new retrofitting scheme was proposed following a preliminary study of four different existing retrofitting schemes. A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure. Local confinement effects due to varying retrofitting schemes in the joints were simulated in the frame model. The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames. The results demonstrated that the new proposed retrofitting scheme was robust and promising, and finite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints

Development of probabilistic seismic hazard microzonation maps at the surface level for central-east Iran (Kerman region), using a hybrid site condition model

This study presents the spatial distribution of a grid-based probabilistic seismic hazard model at the surface level for the Kerman region in central-east Iran, using a hybrid site condition model. The hazard model has provided the variation of the peak ground acceleration (PGA), and 5% damped spectral accelerations (SA) at the fundamental periods of 0.2 and 1.0 seconds (s) on 0.05° grids. The study has used a seismotectonic dataset including ∼400 linear seismic sources to characterize the seismic source models. In order to capture the uncertainties of the seismic hazard sources, the model used a logic tree approach, including eight ground motion prediction equations (GMPEs), three characteristic source models, two different declustering methods, three choices for earthquake recurrence parameters, and three alternatives for the maximum credible earthquake. Besides, various GMPEs have been evaluated against local datasets. For this, a series of GMPEs developed based on local, regional, and global data have been selected to find their compatibility with the studied area through statistical analyses, so-called likelihood (LH), and log-likelihood (LLH) tests. Generally, the results display that a wide range of seismic hazards can be expected in the region. For instance, the horizontal PGA with a 10% probability of exceedance in 50 years, ranges between ∼(0.1–0.5)g in the north-eastern and south-western parts of the region, respectively. Moreover, the results indicate that the ad-hoc 1.5 factor to scale a 475-year return period (RP) spectrum for making the ground shaking similar to a 2475-year RP not only is unrealistic, but also creates substantially an underestimated ground shaking; thus, it seems too crude for the seismic design purposes. We have also developed some relationships, dependent on site conditions, for describing general relations between the obtained results in the return periods of 475- and 2475-years for PGA, SA (0.2s), and SA (1.0s). The computed hazard spectra have also been compared to the minimum acceptable level of seismic hazard in the region, according to the latest version of the Iranian national seismic hazard map. In addition, in order to make the results more transparent to the scientific and engineering community, the range of uncertainty contributed to the hazard modeling has also been explored in terms of a relative uncertainty metric. In total, the outcome of this study can make transparency into the picture of the seismic hazard level in central-east Iran and shed insight into possible developing plans

A reappraisal of active faults in central-east Iran (Kerman province)

Fault lineaments are the main input data in earthquake engineering and seismology studies. This study presents a digitally-based active fault map of the Kerman region in central-east Iran which experienced several devastating earthquakes on poorly exposed and/or not identified active faults. Using Landsat 8 data, we have carried out the image-based procedures of fault mapping, which include applying the contrast stretching technique, the principal component analysis, the color composite technique, the spectral rationing, and creating the false-color composite images. Besides, we have cross-checked the resulting map with the geological maps provided by the Geological Survey of Iran to decrease the associated uncertainties. The resulting map includes 123 fault segments, still, a part of which has been expressed in the previously compiled active-fault maps of Iran. Indeed, the new one is mapping the poorly exposed active faults, so-called secondary faults, which are able to produce strong events. These faults are primarily associated with poorly defined areas that accommodate low levels of seismicity; however, sporadic strong events are likely to occur. It has also been investigated that these kinds of faults are seismogenic and are able to produce destructive events. In total, the outcome of this study can also be jointed with seismic studies for investigating parts of the earthquake activity in central-east Iran, in particular for the fault-based approaches in impending earthquake-resistant buildings