Journal of Seismology and Earthquake Engineering
Volume:22 Issue: 3, Summer 2020

An effective Earthquake Early Warning System (EEWS) has to provide accurate estimates of the location and magnitude of an earthquake that has the potential to cause destructive ground motions. All this must happen within a few seconds after the first P-wave is detected by recording stations and before the arrival of strong S and surface waves. The largest earthquake (Mw 7.3) of the past century in the Zagros region (Iran) occurred on November 12, 2017 and was felt in several neighbouring countries; nevertheless, no EEWS was operating in the region. In this short article, an evolutionary real-time location estimation method (but retrospectively examined in the current study) based on the combination of the Voronoi diagram and Kalkan [1-3] algorithms has been used to simulate the potential of an EEWS to estimate the Sarpol-e Zahab earthquake's hypocentre. The employed algorithms use information on the successive triggering of stations by the P wave, from the first station (for which the estimate has low accuracy) up to a maximum of three stations (for which the estimate has acceptable accuracy). The depth of the earthquake is then determined using the arrival time of the S wave. The estimated hypocentre is in good agreement with offline reports by BHRC [4]. Moreover, an EEWS would ensure a meaningful warning time. As the main finding of the present study, for many locations and major cities, a time alert of more than 20 s for strong shaking (macroseismic intensity VI or above) locations and many tens of seconds for weaker shaking are estimated. Therefore, the establishment of an EEWS should be encouraged to improve the resilience of this region of high seismic hazard.

Optimization of sustainable seismic design (SSD) of building structures has been one of the most challenging and ongoing research subjects in the earthquake and structural engineering worldwide during the past ten years. The purpose of the current research article is to supplement recently developed concepts of sustainable seismic design of building structures through the limitation of damage, repairability, purpose-specific detailing, form optimization, material, and construction optimization, and development of practical technologies to achieve cost-efficient construction and post-earthquake realignment and repairs (PERR). Earthquake resisting moment frames of minimum-weight have been introduced as essential parts of SSD. Global stiffness reduction (GSR) and restoring force adjustment (RFA) concepts have been introduced to facilitate post-earthquake realignment and repairs. The rocking core-moment frame (RCMF) is the key part of the archetype in combination with other structural systems. SSD is a concept that requires a thorough appreciation of the mechanics of structural optimization, sequential failures, recentering, and earthquake-induced P-delta and residual effects. Article results show utilizing the proposed archetype can provide sustainability as well as weight and construction optimization. The archetype components are one of the conventional structural systems with no significant change in the construction procedure. Several cases have been discussed in detail to illustrate the applications of the proposed concepts.

The accuracy of local contractors in constructing Low-rise RC structures located in small towns is subjected to substantial fluctuations that increase the vulnerability of these structures, especially when sequential excitations are under consideration. Four major construction deficiencies are identified in this study by an initial field survey and are then considered in numerical modeling of a 3-story RC moment frame. The median collapse capacity (MCC) of Low-rise RC moment frames under sequential excitations is evaluated in presence of construction faults identified in a field study. Various mainshock levels represented by their maximum inter-story drifts are then imposed on the as-designed and the deficient structures. Following each mainshock, the median collapse capacities (MCCs) of the structures under the aftershock are computed using the IDA method. Investigating the obtained MCCs showed that unintended increase of the beams’ width can help in reducing structure’s vulnerability against sequential excitations. Despite this, the comparison of the residual drifts imposed by the mainshocks showed the decreased ductility caused by this construction deficiency. Ranking the MCC reductions caused by the other deficient models, the highest vulnerabilities were posed by the models that caused larger column plasticities at the collapse state and prevented effective yielding of the beams.

Progressive collapse is defined as the expansion of local failure which damages the entire structure or a big part of it. The failure created is very widespread compared with the initial event. The effect of debris, which is normally produced during a progressive collapse, has not been studied yet sufficiently. Despite, it is very important in the progressive collapse, based on experimental accidents. In this paper, the response of a building structure is investigated to consider the influence of separation of debris from one story and falling on the bottom floor. Nonlinear dynamic analyses have been performed on a four-story, four-span steel frame. A sensitivity analysis on the debris amount and its detachment time is carried out by OpenSEES. The obtained results indicate that the greater amount of debris leads to more intensive progressive collapse. In the case of detachment time, the most damaging effect occurs if debris is separated at the same moment when the top point of the removed column experiences its most vertical displacement. Debris amplifies the maximum and residual displacement of the top point of the deleted column up to 3.65 and 4 times, respectively. This shows that debris has a considerable effect and cannot be ignored in progressive collapse analyses.

In this study, a displacement monitoring technique using an economy camera based on the vision-based method is proposed and developed. The structural displacement can be extracted by utilizing an ordinary shiny device that is attached to one of the elements of the structure and monitoring its motion by an economy video camera. In the proposed vision-based methodology, shiny targets such as LED targets are used to obtain more high-quality images with higher contrast that lead to getting better displacement recording from the captured video. First, a LED centroid recognition and scaling method are described to obtain the time history of structural movements due to the ambient vibration. Next, the natural frequencies of the structure can be determined by utilizing different classical system identification methods in the frequency domain and time domain, like the Peak Picking method and the SSI method. Finally, as a case study, the proposed methodology used for the Tabiat bridge in Tehran, which is a three-dimensional steel truss bridge for pedestrians over a heavy traffic highway, the results are compared with those obtained from the high-accurate and expensive wireless seismic sensors. The results show that although the vision-based proposed technique is a fast and low-cost method, it can investigate the dynamic characteristics of the structure with reasonable precision.

Highway bridges are amongst the most expensive, most widely used, and most vital infrastructures subject to the earthquake hazard. Seismic demand for bridges can be reduced by adding isolation systems. Lead-Rubber Bearing (LRB) isolators are widely used isolating devices whose optimal utilization studied in this article by using the Genetic Algorithm (GA). In this research, the analysis and design of deck-isolated bridges using Lead Rubber Bearings (LRBs) is carried out in accordance with the construction site, AASHTO criteria, and procedural rules for seismic bridge design. The LRB properties, along with the piers dimension selected as optimization variables. These variables’ values applied in objective function using AASHTO design equations as constraints. Various pier heights and LRB placement scenarios regarded for assessing the sensitivity of optimum results. According to the results of the investigation, the research subject was repeated for not using LRB isolators in the side spans. Finally, a comparison of all the results showed that the larger LRB demands increased the effectiveness of LRBs in absorbing input vibrations and mitigating the bridge’s seismic demand by about 20 to 50 percent. Also, it showed that it is more economical to exclude LRBs from abutment supports and limit their usage to the inner supports of the deck.