Seismic Base Research Articles

Dynamic reliability-based assessment for the seismic performance of semi-actively base-isolated buildings with hydraulic dampers

Seismic base isolation faces the challenge of the large displacement demands for the isolators in case of long-period ground motions. Semi-active control has the potential to mitigate the risk against such extreme scenarios and therefore increase the seismic reliability of base-isolated structures. However, the superstructural nonlinearity and the time delay in the control system are always neglected in related studies. Such a knowledge gap may overestimate the benefit of semi-active control in enhancing the seismic reliability of base-isolated buildings. This study explores the seismic reliability of semi-actively base-isolated buildings with realistic considerations of the superstructural nonlinearity and the time delay in a practical hydraulic control system in a fully probabilistic framework. It features the use of the probability density evolution method (PDEM) and the development of a MATLAB-OpenSees interaction technique. The reliability of the semi-actively isolated structure and its passive counterpart are compared, highlighting the effects of nonlinearity and time delay. The results show the superstructural nonlinearity and the inevitable time delay in a practical hydraulic control system may significantly degrade the control performance of semi-actively base-isolated buildings, potentially leading to higher failure probabilities than passive buildings.

Simplified design approach of a negative stiffness-based seismic base absorber via multi-objective optimization

In the field of seismic base absorption, the KDamper constitutes an innovative and effective vibration absorber, characterized by the incorporation of a negative stiffness element. Recent developments have introduced variants like the Extended KDamper (EKD) and the Seismic Base Absorber (SBA), elevating the performance and reliability of the original concept. However, the optimization of these devices relied exclusively on the application of the single-objective Harmony Search optimization algorithm. In this study, the EKD is optimized using the non-dominated sorting genetic algorithm type II (NSGA-II), which incorporates the crowding distance operator (CDO). The purpose of this multi-objective optimization is to explore the EKD’s full potential in simultaneously reducing the induced base displacements and superstructure’s dynamic responses. To simplify the design process and reduce computational complexity, a simplified design approach is introduced. According to this approach, the EKD device is integrated in the base of a single-degree-of-freedom (SDOF) system with a variable natural period, ranging from 0.1 s to 2.0 s (SDOF-EKD system), representing multi-story buildings that range from 1 to 20 stories. In addition, a scaling method is employed, using the SDOF-EKD optimization results to guide the design of EKD for multi-story buildings (MDOF-EKD systems), constituting an indirect optimization of these systems. A comparison is conducted between the generated Pareto fronts as emerged from the simplified design approach and those obtained by optimizing the EKD directly installed in the base of multi-story buildings. Furthermore, a numerical case study is performed in a 3-story benchmark building and the proposed optimized vibration control system is compared in terms of superstructure’s dynamic responses and base displacements with a conventional and a highly damped base isolated building of similar characteristics.

Development of a Matrix for Seismic Isolators Using Recycled Rubber from Vehicle Tires.

Over recent decades, numerous strong earthquakes have caused widespread devastation, including citywide destruction, significant loss of life, and severe structural damage. Seismic base isolation is a well-established method for mitigating earthquake-induced risks in buildings; however, its high cost often limits its implementation in developing countries. Simultaneously, the global rise in vehicle numbers has led to the accumulation of discarded tires, intensifying environmental challenges. In response to these issues, this study investigates the development of a seismic isolator matrix using recycled rubber from vehicle tires, proposed as a sustainable and cost-effective alternative. Ten recycled rubber matrices were experimentally evaluated for their physical and mechanical properties. The matrix with optimal granulometry and binder content, demonstrating superior performance, was identified. This optimized matrix underwent further validation through compression and cyclic shear tests on reduced-scale prototypes of fiber-reinforced isolators, which included five prototype designs, two of which featured flexible reinforcement. The best-performing prototype comprised a recycled rubber matrix with 15% binder and glass fiber, exhibiting vertical stiffness and damping characteristics superior to those of natural rubber. Specifically, this prototype achieved a damping ratio of up to 22%, surpassing the 10% minimum required for seismic isolation, along with a vertical stiffness of 45 kN/mm, critical for withstanding the vertical loads transferred by buildings. These findings suggest that the recycled tire rubber matrix, when combined with glass fiber, is a viable material for the production of seismic isolators. This combination utilizes discarded materials, contributing to environmental sustainability.

Experimental Study on Seismic Performance Evaluation of a Multi-Story Steel Building Model with Rolling-Type Seismic Base Isolation

Critical structures such as hospitals, high-precision manufacturing facilities, telecommunications centers, and fire stations, especially, need to maintain their functionality even during severe earthquakes. In this sense, seismic isolation technology serves as a vital design method for preserving their functionality. Seismic isolators, also known as earthquake isolation systems, are used to reduce the effects of earthquakes on buildings by isolating them from the ground they are located on. By ensuring that less acceleration and force demand is transmitted to the superstructure, both the building and the equipment and the devices in the building are prevented from being damaged by earthquakes. This experimental study aims to conduct vibration tests on a small-scale multi-story steel-building model equipped with a specially designed rolling-type seismic base isolation system. The relationship between the test model and the prototype was achieved by frequency simulation. The tests will be performed on a shake table under six different earthquake accelerations to examine the model’s dynamic behavior. The primary goal is to evaluate the isolation performance of the rolling-type seismic base isolator under seismic loads, with a focus on recording the vibrations at the top of the test building. It has been observed that the isolator placed at the base of the building significantly reduced the peak acceleration and displacement values of the floor motion. Under the most severe earthquake record applied to the shake table, the acceleration at the top of the building with the isolator was found to be reduced by approximately 50%, compared to the non-isolated case.

Evaluasi Desain Struktur Gedung Pondok Pesantren At-Tibyan Deli Serdang

The structural design of this three-story Islamic boarding school building, the results obtained after analysis include; risk category II so that the earthquake priority factor is 1. The soil site class is soft soil. In the structural system, it is designed using a special moment resisting frame system (SRPMK). The seismic design category obtained is category D. Seismic inspection starting from checking irregularities, diaphragm design, checking the number of structural vibration variations, determining the fundamental period of the structure, seismic response coefficient values, seismic base shear, checking the deviation between floors is carried out based on SNI 1726-2019. for column elements, beams and also plates in existing conditions after analysis have met the requirements based on SNI 2847-2019. The conclusion in this final project research is based on the results of the analysis that the design of the Attybian Islamic boarding school building still meets the requirements based on SNI 1726-2019 concerning procedures for earthquake resistance planning for buildings and non-buildings and also for beam, column and plate elements have met the requirements based on SNI 2847-2019 concerning reinforced concrete structures. However, for the beam elements for the reinforcement requirements, it is still too wasteful so that in this analysis, the amount of reinforcement is reduced because in the planning principle it must be safe and economical.

Seismic Isolators Layout Optimization Using Genetic Algorithm Within the Pymoo Framework

In most previous studies, seismic base isolation system optimization has mainly focused on determining isolation layer parameters. However, the subsequent steps of isolator device selection and positioning can significantly impact overall system performance. To address these shortcomings, we propose an alternative optimization approach demonstrated through two models: regular and irregular 8-storey reinforced concrete structures. This approach utilizes the Pymoo framework and commercially available isolators to find optimal isolator layout configurations in two steps. First, using the equivalent lateral force (ELF) procedure, an initial population of seismic isolators meeting shear strain, base shear coefficient, and buckling requirements was randomly selected from suppliers' elastomeric bearing catalogs. Second, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was used to improve the seismic response of the models under the fast nonlinear analysis (FNA) method by minimizing peak roof acceleration, inter-story drift ratio, displacement of the isolated base layer, as well as maximizing the fundamental period. The results underscore the effectiveness of this approach in improving seismic response. Compared to fixed-base structures, the optimal solutions achieved more than double the fundamental period, reduced peak roof acceleration by over 70%, and diminished base shear force by approximately 50%. This methodology can serve as a reference for future research across various structure types, including hybrid isolation systems and steel structures. Doi: 10.28991/CEJ-2024-010-08-07 Full Text: PDF

Architectural Design of New Buildings with Seismic Base Isolation and Energy Damping Systems

Architectural Design of New Buildings with Seismic Base Isolation and Energy Damping Systems

Seismic design optimization of space steel frame buildings equipped with triple friction pendulum base isolators

To increase the seismic resilience of structures, it is necessary to utilize seismic isolation to increase structural periods and reduce story drifts. When seismic isolation is implemented, structures are capable of deforming by remaining within safe limits. Thus, more seismically resilient designs are achieved compared to conventional fixed-based structures since lighter structural design weights are attained. The principal aim of this study is to achieve the comparative design optimization of space steel frame buildings equipped with seismic base isolation and to examine the effect of seismic base isolation on optimum structural design weight by comparing the same structures with conventional rigid-based ones. For seismic base isolation, triple friction pendulums are implemented into steel frame buildings. For this aim, four different space steel frame buildings with 4-, 6-, 8-, and 10-story are treated as design examples. A novel design optimization algorithm is encoded, which includes nature-inspired metaheuristic artificial bee colony, crow search, and Archimedes optimization algorithms to achieve design optimizations of triple friction pendulums equipped with seismic-isolated space steel frame buildings. The practice code provisions of load and resistance factor design specification for structural steel buildings have been applied to control the structural design constraints of inter-story drift, top-story drift, strength, displacement, and connections geometry of beams and columns. Eventually, it has been remarked that seismic base isolation significantly reduces the structural optimal design weight of space steel frame buildings.

Earthquake Resisting Building by using Base Isolation

Abstract: Natural disasters have been always been a part of human life since the beginning of time, causing destruction to our lives and properties. Earthquake plays a major role in wreaking this havoc upon us. Various challenges have occurred to withstand structures on earth due to sudden moment of ground it also results in collapse of structure, due to inappropriate design consideration of structure without any seismic resistance. Various techniques to make the building earthquake resistant as well as various shapes and materials are being considered to achieve required strength to resist seismic forces. Various techniques like shear walls, bearings and base isolation are used to withstand the structure against seismic forces. In this project we have used base isolation technique, it is also known as seismic base isolation or base isolation system is a prominent technique to protect the structure against earthquake.

Experimental Study on the Cyclic Performance of Novel Seismic Base Isolators Made by Scrap Tire Rubber Pads

Experimental Study on the Cyclic Performance of Novel Seismic Base Isolators Made by Scrap Tire Rubber Pads

Effect of Bearing Friction on Seismic Performance of Bridges with Massive Piers Isolated by Friction Pendulum Bearings

Although seismic isolation is a well-accepted design strategy for bridges to provide structural earthquake resistance, for bridges with massive piers, it may unexpectedly pose an abnormal influence on the seismic response of bridges due to the effect of substructure mass. This study investigates the effects of bearing friction and pier mass on the seismic performance of bridges isolated by friction pendulum bearings (FPBs). Nonlinear time history analysis is conducted to demonstrate the variation of the bridge peak responses with different bearing frictional coefficients and pier mass. The inherent influential mechanism of the frictional coefficient of FPBs is also discussed in the current study. The results of the analysis show that for FPB-isolated bridges with massive piers, the peak base shear forces of piers first decrease and then increase with the increase of the bearing frictional coefficient. Such a phenomenon may be attributed to the fact that the inertia force of the massive piers will be altered by the variation of bearing friction. The outcome of this study provides a useful reference for practical engineering that the seismic base force of massive bridge piers calculated under a specified bearing frictional coefficient may be smaller than the actual response and cause reduced safety to bridges.

Seismic Isolation Effects on Elevated and Ground-Supported Flexible Concrete Cylindrical Tanks Under Bi-Directional Excitation Using an Advanced Mechanical Model

In this paper, the effectiveness of seismic isolation using lead rubber bearings (LRBs) and friction pendulum systems (FPSs) for slender and broad, grounded and elevated tanks (two seat locations of isolation systems in elevated tanks) is investigated under bi-directional excitation of up to 10 records of earthquakes. An analytical mechanical model for a flexible, concrete cylindrical tank, taking into consideration the effect of wall mass and sloshing, is used. The assumptions underlying the mechanical model are basic equations of the motion according to the theory of fluid dynamics. So, the assumptions are more realistic and the results therefore are more accurate than the previous models. The results show that by selecting the best mechanical properties of base isolation systems, reductions of seismic base shear in the grounded broad tanks are around 35% and 30% and for the grounded slender tanks are around 55% and 58% in the x- and y-directions, respectively. Maximum total hydrodynamic pressure is reduced considerably by about 40% on average in all grounded and elevated models. As a result of isolation, elevated tanks are concluded to be better candidates in terms of more effective application of seismic isolation.

Weak axis low-damage performance of seismic resilient rocking steel column base with friction connection

Rocking column bases with friction connections are a critical technology employed in the low-damage design of steel structures. In this study, cyclic loading tests were conducted along the weak axis of the column, incorporating INITIAL, AFTERSHOCK, and REPAIR cases, with a maximum drift ratio of 3%. In the AFTERSHOCK case, both the sliding and maximum moments at the column base exhibited a significant decrease of 67% and 16%, respectively. To address the decrease in sliding strength attributed to the loss of bolt tension, Belleville Springs (BeSs) were employed, and the bolts were maintained within the elastic range. The results demonstrate that the hysteretic curves of the column base almost perfectly align in all three cases, revealing a strength loss of less than 2% and a significant enhancement in seismic resilience. This low-damage column base proves well-suited for deployment in regions with high seismic risk, especially for buildings subjected to continuous seismic excitation. A finite element analysis (FEA) model was developed to quantitatively evaluate the damage, sliding, bolt tension loss, and energy dissipation performance of the column base. Finally, a simplified flag-shaped analytical model was proposed to guide the design of such low-damage column bases, providing a basis for their integration into overall structural analyses.

Seismic Performance of Infilled Reinforced Concrete Frame with Crumb Rubber Mortar Wall Panel

In this paper, the seismic performance of reinforced concrete (RC) frames with crumb rubber mortar wall panels is reported. The tests of the crumb rubber mortar were conducted to obtain model parameters for equivalent diagonal compression struts. With a higher percentage of sand replacement by crumb rubber, the unit weight, the compressive strength, the tensile strength, and the modulus of elasticity of the crumb rubber cement mortar are decreased. Nonlinear pushover analysis of a simple frame shows that the RC frame with a wall panel with less crumb rubber demonstrates lower lateral deformation ability. The failure modes are affected by the amount of crumb rubber and are dependent on the modeling choice of the equivalent compression strut as the wall panel representative. Finally, the seismic performance of the RC building was studied by the equivalent static approach to explore the influence of the crumb rubber mortar wall panels on internal forces and deformations of the frame. With a higher percentage of crumb rubber, the weight of the infill wall panels and the overall weight of the building are reduced, which meets lower seismic base shear demand. This benefit is, however, traded off with higher lateral deformation and also higher inter-story drift of the studied building frames. Doi: 10.28991/CEJ-2024-010-02-09 Full Text: PDF

The Role of a Simple Inerter in Seismic Base Isolation

The present study investigates the role of a simple inerter in supplemental devices for possible implementation in the mature seismic base isolation technique. Firstly, the response of the base-isolated structure with an optimally tuned mass damper inerter (TMDI) is investigated to see the tuning effects. The time required to tune the TMDI was found to be significantly longer than the duration of a strong-motion earthquake. There was still a reduction in the response of the isolated structure, which is primarily due to the added damping and stiffness (ADAS) of TMDI and not because of the tuning effects. Hence, it is proposed that the corresponding ADAS of the TMDI be directly added to the isolation device. Secondly, the response of the base-isolated structures to the fluid inerter damper (FID) is studied. It was observed that the inerter of the FID does not influence the displacement variance of an isolated structure under broadband earthquake excitation. It implies that the response of the isolated structure to FID is primarily controlled by its counterpart fluid damper (FD). The performance of optimal TMDI, ADAS, FID, and FD to mitigate the seismic response of the flexible multi-story base-isolated structure under real earthquake excitations is also investigated. In terms of suppressing the displacement and acceleration responses of the isolated structure, it has been found that TMDI and ADAS perform similarly. Comparing the response of the isolated structure with FID and FD demonstrated that the inerter in the FID has detrimental effects on the isolated structures, in which the top floor’s acceleration and base shear are substantially increased.

The Behaviour of Building Frames on Raft Foundation using Dynamic Analysis

When designing building frames for seismic reasons, the effect of soil flexibility is typically disregarded, and the design is executed using the outcomes of dynamic analysis with a fixed base condition. Because the overall lateral stiffness of the structure decreases as a result of soil flexibility, the lateral natural period lengthens. The building frames situated on the Raft foundation may experience a significant change in seismic response due to this extension of the lateral natural period (T). Therefore, it is imperative to consider the soil's flexibility, also known as soil structure interaction, when doing analysis on the foundation's supporting layer.
 This paper examines how asymmetric building frames with raft footings behave dynamically when subjected to seismic forces that involve soil-structure interaction. The analysis is performed with SAP 2000*V21 FEM software. The structure is idealized as a three-dimensional space frame, with slabs modeled as a thin shell with four noded plate elements and six degrees of freedom at each node, and beams and columns modeled as two noded line elements. The soil is represented as equivalent springs with one (Winkler) and six (Modified Winkler) degrees of freedom; the stiffness of these springs varies depending on the type of soil and is determined by its dynamic shear modulus and poissons ratio. The Modified Winkler and Winkler raft foundations are modeled as thin shells with four noded plate elements, each with six degrees of freedom, and are criticized so that the element aspect ratios are equal to one.
 
 To assess the impact of soil structure interaction on building frames, the response is compared for a range of building frames with and without consideration of soil flexibility in terms of fundamental Natural Period, Seismic Base Shear, and Max. Lateral Displacement. The parametric study for Zone V takes into account the influence of various parameters, including the number of bays, stories, span lengths, and soil types (i.e., soft, medium, and stiff).
 
 It is discovered that the fundamental lateral natural period and seismic base shear of the system are significantly altered by the influence of soil flexibility on building frames. As soil stiffness decreases, the lateral natural period and seismic base shear increase as a result of soil flexibility. Additionally, it has been noted that as the number of bays increases, so do the building's base shear and lateral period. As the number of bays and stories increases, so does the maximum lateral displacement. 

Validation of numerical results of complex seismic analysis through simple analytics

The paper analyzes the application of the numerical findings of the program, which is becoming increasingly difficult for civil and structural design. Since, as in many other countries, the verification of design using a software model is now required by current Italian codes as well. Given this, the structural engineer must provide a technical report using a licensed software tool, attached to other project documents to get the Seismic Authorization at the local Civil Engineering Department offices. Following a brief explanation of structural analysis methodologies, this study presents a criterion for assessing the applicability of numerical findings obtained using any structural software. Three case studies of this criterion are shown to demonstrate how to check them using simple manual calculations: (i) the normal stress in RC columns subjected to gravity loads; (ii) the periods of vibration, participating masses, and seismic base shear derived from dynamic modal analysis; and (iii) the main parameters characterizing the pushover curves of existing buildings. Finally, this work underlines the significance of confirming the application of numerical results obtained by software in civil and structural design. The offered criteria and scenarios exhibit realistic techniques to ensure accuracy and reliability in structural performance assessment, according to the structural requirements imposed by current codes in Italy and similar countries.

Prediction of Damping Capacity Demand in Seismic Base Isolators via Machine Learning

Prediction of Damping Capacity Demand in Seismic Base Isolators via Machine Learning

Comparative Study Dynamics Analysis of a Multi-story Building with and without a Floating Column

Parking spaces, lobby areas, terrace gardens, and other amenities are highly sought-after in densely populated urban regions. Although floating columns can be useful and an achievable choice, it is important to research their structural performance and cost-effectiveness in the event of substantial ground motion imposed on by an earthquake. A building’s overall dimensions, geometry, and shape all impact how it acts and acts when subjected to seismic loads. For this reason, it is necessary to assess how well floating column buildings perform in seismically vulnerable places in comparison to conventional buildings. In this work, the performance of structures with floating columns for seismic loading is observed using dynamic analytic techniques in accordance with IS 1893 (2005). This study analyses both the floating columns and the conventional building without floating columns. When compared to a regular building, the research reveals that the floating column buildings exhibit a very quick increase in base shear and story displacement. The horizontal displacements experienced by floating column buildings are proportionally larger due to an increase in the fundamental time period. If the lateral displacement exceeds the codespecified maximum limit, damage to structural and non-structural parts may result. Because of the discontinuity in the load distribution path, seismic base shear and overturning moment are also increasing in the case of buildings with floating columns. Additionally, while asymmetrically introducing floating columns, torsional irregularity has been produced but the modal mass participation ratio has decreased. While it is true that the use of floating columns in high-rise structures allows for continuous open floor plans, they are also dangerous and susceptible in seismically active locations

The Thermal Structure of Central Te Riu a Māui/Zealandia Continent as Determined From the Depth to Base of Magnetic Sources

AbstractTo investigate the thermal structure of central Te Riu a Māui/Zealandia continent we estimate the depth to base of magnetic sources (DBMS), using an updated compilation of magnetic data. We calculate thousands of power spectral density estimates and solve an analytic solution for the fractal distribution of magnetization using a Bayesian method constrained by a sediment thickness model. Our DBMS results are broadly similar to a global model yet show complex relationships with independent models of crust and elastic thicknesses, and depth to base of seismicity (D90). Across central Zealandia, DBMS occurs above, coincident with, and below the Moho reflecting that factors additional to temperature influence DBMS. Away from subduction zones crustal thickness likely modulates DBMS while plate margins show varying influence dependent on margin characteristics. In the Taupō Volcanic Zone we interpret DBMS to reflect Curie point temperature at an average depth of 9–11 km. Error analysis shows that the choice of prior influences the posterior standard deviation and can result in counter intuitive error versus DBMS relationships. We use the DBMS as a basal temperature isotherm in heat flow models to compare with heat flow derived from borehole temperature measurements. Using the standard Curie point temperature of 580°C we find that DBMS derived heat flow models over estimate heat flow in areas underlain by plutonic rocks. We propose this reflects a higher titanomagnetite content in these rocks, although detailed studies of the magnetic mineralogy of Zealandia's plutonic rocks are required.