Papers by Keyword: Seismic Response

Abstract: In the seismic design of flexible cantilever walls retaining cohesive backfill soil, the common practice is to neglect the cohesion effect. Dynamic lateral earth pressure is typically evaluated based on approaches primarily intended for cohesionless soils or through analytical pseudo-static methods. Nevertheless, both experimental and theoretical evidence has demonstrated significant effects due to soil cohesion that are not accounted for by these methods. This study involved finite element modeling (FE) of a flexible cantilever wall with a height of 5.4m, supporting homogeneous cohesive backfill under initial static and seismic loadings. The calculated active earth thrust was then compared with values obtained experimentally and through conventional analytical methods. The obtained results indicate that the presence of soil cohesion significantly reduces seismic demands on flexible cantilever retaining walls, resulting in a substantial reduction of seismic active earth pressures and total seismic thrust by up to 50% and 52%, respectively. It enhances also the overall stability of the system by shifting the point of application of seismic thrust toward the base of the wall, thereby increasing the safety margin. In addition, it significantly decreases the wall displacement at the stem top, with reductions of up to 104% compared with the case involving cohesionless backfill. It was observed that the conventional methods recommended by some seismic regulations largely underestimate seismic active pressure.

Abstract: Liquid storage tanks are among vital structures widely used in various fields. Estimating the sloshing wave height in storage tanks during seismic events is very important to avoid seismic damage. Despite its importance, only a few studies have addressed the sloshing wave height in storage tanks considering the soil-structure and fluid-structure coupling effects. This paper used finite element numerical simulation method to study the seismic response of rectangular concrete liquid storage tanks. Three aspect ratios, three liquid heights, nine earthquake records with different frequency content, and three different topography conditions were considered. The obtained results indicated that the liquid storage tank models involved in this study were more sensitive to high-frequency earthquake events, and the step-like irregular topography could amplify the sloshing wave height of the storage tanks. Besides, Eurocode 8 underestimated the peak sloshing wave height of the storage tanks when subjected to earthquakes with high-frequency content.

Abstract: Recent earthquakes have dramatically shown the seismic vulnerability of existing masonry structures and highlighted the urgent need of developing suitable strengthening solutions. In order to gain an improved understanding of the seismic response of masonry constructions and of the most appropriate technologies for their retrofitting, a shake table test was performed on a full-scale U-shaped tuff masonry structure, provided with an asymmetric plan with openings and with an inclined roof. The specimen was tested unreinforced and then repaired and retrofitted with composite reinforced mortar (CRM), comprised of a glass fibre reinforced polymer mesh applied with a lime mortar. Natural accelerograms were applied with increasing scale factor to collapse. Results provided information on the dynamic behaviour of masonry structures strengthened with CRM and on the enhancement of seismic performance provided by the retrofitting work.

Abstract: When analyzing the seismic response of a very long elevated structure such as a Shinkansen viaduct, it is common practice to analyze a cutout of the structure under consideration and treat its both ends as free boundaries. This is attributable to the assumption that seismic response analysis assuming free boundary conditions is more conservative than one assuming non-free boundary conditions. In this study, after finding out that response to harmonic ground motion can be greater than under free-boundary conditions if outward energy dissipation occurs from the analysis domain, a series of numerical experiments was performed to determine whether such phenomena occur in seismic response. Then, after confirming that the frequency components of ground motion that satisfy the wave propagation condition greatly affect seismic response, the study showed that the area of the wave propagation condition region of the Fourier spectrum can be used as an indicator by which to judge the likelihood of occurrence of such phenomena.

Abstract: Current seismic design practice assumes the base of the building to be fixed and does not consider the flexibility of foundation and soil. This assumption is realistic only when the structure is founded on solid rock or when the relative stiffness of the foundation soil compared to the superstructure is high. Whereas, in reality due to natural ability of soil to deform, supporting soil medium modifies the response of the structure during earthquake to some extent. In this work the effect of soil structure interaction on seismic response of building resting on different types of foundation was studied. Present work aims to study the effect of soil structure interaction on seismic response of building resting on fixed base, pile foundation, raft foundation and combined pile-raft foundation. G+9 RCC building is analyzed for earthquake loads considered in zone III by response spectrum method and storey displacement and base shear force of building by considering and without considering SSI effect is found out by using MIDAS GEN software.

Abstract: The seismic performance of an existing 8-storey EBF with shear-critical links located in Victoria, BC, is assessed. The frame is designed according to 1995 NBCC and the CSA S16-94 steel design standard. Seismic assessment is first performed in accordance with recommendations of the User’s Guide to NBCC 2015 using equivalent static force procedure, response spectrum analysis and linear time history analysis. A Tier 3 systematic evaluation according to ASCE 41-13 is then carried out using a linear static and dynamic procedure. Even though the original frame design was based on capacity design principles, both procedure revealed an inadequate strength of the frame members and the need for strengthening. Although the ASCE 41 procedure resulted in a less severe assessment, failures were predicted for most of the columns and for some outer beams. Considering bending as deformation-controlled action alleviated outer beam response.

Abstract: The use of BRBs into a typical European building with braced structure, whereby all the beam-to-column connections are perfectly pinned, may be low effective. In fact, these structures are low-redundant and prone to develop soft story collapse mechanisms. The concentration of drift demand in few stories precludes the full exploitation of the deformation capacity of all the BRBs inserted into the frame, and it partially reduces the benefit they can provide. A more effective structural system may be obtained by coupling frames with BRBs with frames with semi-rigid connections. This paper proposes a design procedure for this dual system and presents the calibration of the behavior factor. To this end, a set of frames is designed considering several values of behavior factor and the response of the obtained frames is determined by nonlinear dynamic analysis. Hence, the behavior factor that allows the frames to meet the performance objective requirement of EuroCode 8 is determined.

Abstract: Structural vulnerability of buildings to damage needs to be identified during the time of earthquake for reliable seismic design. Conventional linear elastic design methods cease to predict seismic damages in buildings. Pushover analysis is a popular displacement-based nonlinear structural analysis procedure employed to predict the seismic behaviour of structures. Generally, buildings are designed based on the assumption that they are fixed at their base, without considering the foundation as well as soil. But in reality, when a structure is subjected to an earthquake excitation, it interacts with the soil, influencing the structural response. In this study, a multi-bay building with different heights are modelled and analysed, duly considering Soil-Structure Interaction (SSI). The study can form foundation for rigorous performance-based seismic design procedure, considering the effect of soil beneath the structure.

Abstract: This paper addresses the usage of new construction materials made of natural fibre reinforced polymer and concrete composite for future earthquake-resistant structures. The structure considered is a simple circular bridge pier. To evaluate the seismic performance of the structure shake table experiments were performed. To reveal the consequence of the magnitude of the ground excitation for the structure the effect of a gradual increase of the peak ground displacement is investigated. The results show that although external damage to the structure cannot be observed the bond between polymer and concrete is a significant factor that determines the performance of the structure.

Abstract: A 1/25 scale-down specimen was constructed of a reinforced concrete reactor building used in the nuclear power plant. The non-demoulding technology and self-consolidating concrete were used to cast the specimen with a length of 2.9 m, width of 2.9 m, height of 2.9 m and weight of 28 tons. The entirety struc-ture was composed of a primary containment (thickness of 10 cm), a secondary containment (thickness of 7.5 cm) and three floors (thickness of 30 and 15 cm). Shaking table tests were conducted on it in the National Center for Research on Earthquake Engineering. Testing results indicated that the scale-down specimen kept the structural integrity under a 0.6 g specific seismic wave hit. In addition, the ETABS model accurately represented the dynamic characteristics of the scale-down specimen by numerical method obtained the conservative results.