Severe Earthquake Shaking Research Articles

SEISMIC ANALYSIS OF MULTISTORIED OPEN GROUND STORY BUILDING WITH DIAGONAL STRUT AND SHEAR WALLS

The Open Ground Story (OGS) building is a functional need of all urban areas so cannot be eliminated. According to studies from previous earthquakes, when there is severe earthquake shaking, Reinforced Concrete (RC) frame buildings with open ground levels function badly. In this work, four models of G+14 RC frame buildings with and without a shear wall, coupled sheal wall, and diagonal strut were modeled and analyzed using ETABS-2018 software's static and dynamic response spectrum method. Model 1 open ground story RC building without strut and the shear wall was compared to the other three models that included a shear wall, coupled shear wall, and diagonal strut. As a result of the findings, it has been determined that shear wall, coupled shear wall, and diagonal strut not only increased the stiffness but also reduced displacement. A model with a combination of shear wall and coupled shear wall showed a minimum base shear and overturning moment than all other models.

Study of a Flat Slab Building with a Shear Wall at Periphery and X-Bracing

Abstract: Flat slab construction practice faces great risk during severe earthquake shaking. In the study two different types of flat slab buildings are taken into account; flat slab with shear wall at X-Bracing and flat slab with at periphery. This lateral force resisting mechanism strengthens structural stiffness of these flat slab structures. It is observed that the lateral force resisting capacity of flat slab structure increases significantly with the use of shear wall.

Static Test and Seismic Dynamic Response of an Innovative 3D Seismic Isolation System

Seismic isolation is an efficient strategy to protect structures from the effects of moderate to severe earthquake shaking. Conventional isolation devices can reduce the structural response in horizontal directions only; however, three-dimensional (3D) ground motions have been observed in earthquake records. In this paper, an innovative 3D seismic isolator is proposed. A new kind of asymmetric oblique hysteretic model is illustrated, and a quasistatic compression test of a model device using three lead rubber bearings (LRBs) is conducted. The test results and theoretical model results match well. A significant asymmetric property is observed in the hysteretic curves. The proposed hysteretic model can efficiently simulate the vertical mechanical behavior of a 3D seismic isolation system. The effects of different parameters are highlighted based on the theoretical mechanical model. The inclination angle, friction coefficient, and second shape factor of the inclined LRBs strongly influence the vertical behavior of the proposed device. A dynamic response analysis of the substructure of a nuclear power plant (NPP) is conducted. The hysteretic curves have the shape of an asymmetric quadrangle; this shape is similar to that observed in the test results. The vertical acceleration response of the vertical isolation structure is reduced by 33% compared with that of a fixed-base structure and reduced by 58% compared with that of a horizontal isolation structure. The proposed 3D isolator can sufficiently isolate the seismic input.

Experimental and Numerical Investigation of Strongback Braced Frame System to Mitigate Weak Story Behavior

AbstractMultistory steel braced frames tend to concentrate damage in a few weak stories in response to severe earthquake shaking. This paper presents the numerical and experimental results for a st...

Stiffness-based approach for Belleville springs use in friction sliding structural connections

Sliding hinge joints (SHJs) used in beam-to-column connections of moment frames have a moment-rotational behaviour that depends on asymmetric friction connection (AFC) sliding behaviour. The AFC is also applied to column base connections and friction sliding braces. In the AFC, the slotted sliding plate is clamped between one ideally fixed surface and one partially floating surface. In current practice, the AFC bolts are fully tensioned at installation (i.e. yielded) to provide the clamping force. The AFC bolts are subjected to moment, shear, and axial force (MVP) interaction during joint sliding that is expected to occur only in severe earthquake shaking. The AFC bolt tension as well as SHJ elastic strength are reduced after a few sliding cycles. In this paper, the reasons for the AFC bolt tension loss are discussed, and solutions to prevent this bolt tension loss, including the optimum use of Belleville springs (BeSs) and installing the bolts within the elastic range, are proposed. This paper analytically shows that these solutions can generate significantly improved retention of AFC bolt tension, improved AFC sliding behaviour, higher displacement capacity to accommodate prying effects, and better AFC self-centering characteristics. Examples of AFC bolt installation within elastic range and tension loss with and without BeSs are provided. Similar models are developed for symmetric friction connections (SFCs) and compares differences in behaviour.

Seismic isolation of buildings for power stations considering soil-structure interaction effects

Nowadays, the power industry in Mexico is building encapsulated power stations, because they are a more efficient, safer and cheaper technology for power transformation, and they also require of smaller spaces. Encapsulated power stations have been already built in cities of Mexico where the seismic risk and hazard is negligible. Given all the advantages described above, Comisión Federal de Electricidad (CFE), the Mexican power company, is studying the possibility to build this type of station in the Valley of Mexico, where the earthquake risk and hazard are high. Encapsulated power stations are composed of a series of high diameter pressured steel pipes that contain a toxic gas as an insulation media for the electric cables that host inside. Therefore, it is required that for severe earthquake shaking, encapsulated power stations remain fully operational and that there will be no risk of a gas leaks, particularly in the soft soil sites of the Valley of Mexico. The use of base isolation in soft soils such as those found in the lakebed region of Mexico City is atypical and must be seriously evaluated. In soft soils, there is a higher risk of dynamic instability of base isolated structures for severe earthquake shaking due to the likeliness of resonant response with the ground, global rocking effects or sudden differential settlements of the ground. Research studies devoted to assess the feasibility of employing pendular isolation systems for the benchmark architectural model of SF6 power stations for six soft soil sites in the Valley of Mexico are summarized in this paper. Soil-structure interaction (SSI) effects have been included. The results of the study allowed concluding that pendular isolation systems can be used for an effective seismic isolation of SF6 power stations in relatively soft soils.

Proposed design models for the asymmetric friction connection

SummaryThe Asymmetric Friction Connection (AFC) remains elastic during moderate earthquake shaking but slides and dissipates energy through friction during severe earthquake shaking. The sliding friction forces developed are dependent on the clamping force in the connection which is provided by fully tensioned bolts which pass through slotted holes. During sliding these bolts are subject to moment and shear as well as axial force. Moment–shear–axial force interaction reduces the clamping axial force on the sliding interfaces thereby reducing the sliding shear resistance (Vss). Two methods to evaluate the moment–shear–axial force interaction have been proposed so that the sliding shear strength can be quantified, but as yet, these methods are not robust. This paper describes the results of 60 tests undertaken to improve the two methods, namely the moment–shear–axial force bolt model and the effective coefficient of friction method, for AFCs with high hardness steel shims. The bolts were M16 to M30 bolts and cleat thicknesses ranged from 12 mm to 25 mm. It is shown that either method may be used in design as the results obtained are similar. Copyright © 2014 John Wiley & Sons, Ltd.

SEISMIC ISOLATION OF NUCLEAR POWER PLANTS

Seismic isolation is a viable strategy for protecting safety-related nuclear structures from the effects of moderate to severe earthquake shaking. Although seismic isolation has been deployed in nuclear structures in France and South Africa, it has not seen widespread use because of limited new build nuclear construction in the past 30 years and a lack of guidelines, codes and standards for the analysis, design and construction of isolation systems specific to nuclear structures. The funding by the United States Nuclear Regulatory Commission of a research project to the Lawrence Berkeley National Laboratory and MCEER/University at Buffalo facilitated the writing of a soon-to-be-published NUREG on seismic isolation. Funding of MCEER by the National Science Foundation led to research products that provide the technical basis for a new section in ASCE Standard 4 on the seismic isolation of safety-related nuclear facilities. The performance expectations identified in the NUREG and ASCE 4 for seismic isolation systems, and superstructures and substructures are described in the paper. Robust numerical models capable of capturing isolator behaviors under extreme loadings, which have been verified and validated following ASME protocols, and implemented in the open source code OpenSees, are introduced.

Cyclic Behavior of Asphalt Concrete Used as Impervious Core in Embankment Dams

Asphalt concrete is used as a water barrier (interior core or upstream facing) in embankment dams. This paper investigates the behavior of hydraulic asphalt specimens subjected to cyclic loading in a triaxial cell. The specimens were tested at various sustained static stress states and temperatures and at maximum cyclic shear stress levels corresponding to severe earthquake shaking of the dam. The cyclic modulus versus mean sustained static stress showed an approximately linear relationship in a logarithmic diagram, and an empirical expression was developed to determine the cyclic modulus. At a mean sustained stress of 1.0 MPa, the cyclic modulus at 20°C was about 900 MPa; at 9°C, it was 1900 MPa and at 3.5°C, about 2500 MPa. The damping ratio was found to be between 0.07–0.30, depending on stress state and temperature level. The number of load cycles (up to 6000) had no significant effect on the magnitude of cyclic strain, and the cyclic loading was documented to have little effect on the postcyclic monotonic stress-strain-strength behavior and permeability (watertightness) of the asphalt concrete.

Effects of Ground Motion Parameters and Cyclic Degradation Behavior on Collapse Response of Steel Moment-Resisting Frames

This paper examines the collapse response of Japanese low- and medium-rise steel moment-resisting frames, which may suffer stiffness degradation and strength deterioration after column buckling in severe earthquake shaking. The ground motions used were artificial accelerograms with an identical Fourier amplitude spectrum. The maximum scale for artificial accelerograms not to collapse the systems and the corresponding energy-based velocities were investigated. This study has confirmed that far-field ground motions induced smaller plastic deformations when compared to near-field ground motions, thereby allowing the systems to absorb more energy before collapse. The results from comparing the scale indicated that in moderate degradation the maximum intensities for far-field ground motions not to collapse the systems were larger than those for near-field ground motions. This trend increased with intensive degradation but reversed with slight degradation. Moderate degradation was selected to further validate the real records and damping effects. This study has provided an insight into the collapse response with respect to the type of earthquake wave and to the extent of structural degradation.

Earthquake Performance of Porcelain Transformer Bushings

The earthquake performance of 196-kV, 230-kV, and 550-kV porcelain transformer bushings was studied by earthquake-simulator experimentation and analysis. The fundamental frequencies of the 196-kV, 230-kV, and 550-kV bushings were identified to be approximately 15 Hz, 18 Hz, and 8 Hz, respectively, using resonance-search testing on the simulator. The corresponding damping ratios were between 2 and 4 percent of critical. The 196-kV and 230-kV bushings survived severe earthquake shaking and were qualified to the High Level per the IEEE 693-1997 standard. The discrepancy between excellent behavior in the laboratory and poor behavior in the field of these types of bushings calls into question the procedures used for qualification of substation equipment. The 550-kV bushing survived shaking at the moderate performance level with limited damage and minor oil leakage. Current procedures for fragility testing of transformer bushings were evaluated and found to be neither appropriate nor conservative.

Rubber bearings in base-isolated structures

The paper discusses the use of rubber bearings in base isolated structures. In Japan alone there are likely to be 100 base-isolated buildings completed by the end of 1994 all of which will be on rubber bearings [Ref 1.2]. A distinction is drawn between the use of rubber bearings in bridges where they are subject to both the fatigue of traffic loading and diurnal temperature movements throughout their life, and their use in buildings where the loading is comparatively static until severe earthquake shaking occurs, which at a particular location is not likely to occur more than about once a century. Vertical load capacity and characteristics of vertical deflection in relation to rubber layer thickness and instability are discussed. Shear stiffness and deflection characteristics are outlined together with methods used for providing damping, including damping in lead-rubber bearings. The design of the high-stability aseismic bearing for loads of 1 tonne upwards is discussed in relation to its stability characteristics. It is suggested that tensile forces should be permitted in the short-term loading induced by earthquakes and this is confirmed by current Japanese practice in using fully bonded bearings. The development of self-damping rubber bearings is discussed.

Seismic Testing of Eccentrically Braced Dual Steel Systems

Two six-story eccentrically braced dual steel systems (EBDSs) were tested as part of the U.S.-Japan Cooperative Earthquake Research Program. The first, a full-scale structure ( prototype) was pseudo-dynamically tested in the Large Size Structures Laboratory of the Building Research Institute in Tsukuba, Japan. The second, a similitude scaled replica of the first, was tested on the earthquake simulator at the University of California at Berkeley. The prototype was designed for the minimum earthquake forces specified by the 1981 Japanese Aseismic Code and satisfied the current earthquake-resistant design regulations in the U.S.A. (1985 UBC, 1984 ATC 3-06 and 1986 SEAOC). The performance of the EBDS (both prototype and model) was outstanding in terms of its elastic strength and stiffnesses during minor earthquake shaking and its ability to absorb and dissipate energy, without strength and stiffness degradation, during severe earthquake shaking. Substantial overstrengths of both EBDSs with respect to their nominal yielding strengths were observed during severe earthquake shaking. However, the response modification factors currently adopted by the ATC and SEAOC significantly overestimated the experimental values in both instances.

Seismic Safety Analysis of Lower Crystal Springs Dam: A Case History

The reservoir impounded by Lower Crystal Springs Dam lies in the rift valley of the San Andreas fault zone, some 20 mi (32 km) south of San Francisco. The curved, concrete gravity dam was built in 1890 and survived the great earthquake of 1906 (estimated M = 8.3) (Richter, 1977) even though it stands very close to the eastern margin of the fault zone. The stability of the dam is now crucial to the protection of large downstream populations that have grown up since the dam was built, and a seismic safety evaluation was conducted during 1976 and 1977. Field investigations provided geologic data regarding the width of the fault zone in the reservoir area, located the 1906 line of ground rupture, explored the foundation bedrock at the dam site, and evaluated the potential for faulting beneath the dam. Hazards to the dam from anticipated movement on the San Andreas fault were also evaluated. Design earthquakes were applied to a finite element model of the dam and its foundation to permit analysis of the structure9s dynamic response to severe earthquake shaking. It was concluded that the dam would be able to withstand an earthquake of 8.5 magnitude, and that the physical properties of the foundation rock—an apparently hard but microscopically brecciated sandstone—contribute significantly to the satisfactory response of the dam.

Liquefaction of soils induced by earthquakes

abstract The conditions under which liquefaction effects are known to have occurred are reviewed and their generic cause is discussed. Special attention is given to the delay with which liquefaction effects appear on surface deposits originally stable. It is suggested that little damage to structures on poor soil can occur as the direct result of severe earthquake shaking and that damage observed is almost entirely due to foundation failures, ground settlements and tilting. Field evidence suggests that earthquakes are incapable of densifying originally loose deposits to a stable mass, and that such deposits neither experience nor transmit severe shaking.