Fixed-base Model Research Articles

Seismic analysis of a soil-liquid tank system using the two-step method

Seismic analysis of soil-structure interaction (SSI) is a challenge due to the non-linearities of soil-foundation interaction (SFI). The reliability of the design and the analysis results will suffer if SSI is ignored. In this paper, a two-step method based on the superposition theorem is used to perform a seismic analysis of a soil-foundation-tank-liquid system (soil-liquid tank system). The SFI analysis was conducted in the first step using the CyclicTP program's finite-element method. Meanwhile, the liquid tank system was analyzed in the second step using the lumped-parameter method. Numerical simulations conducted in homogeneous strata of sand soil demonstrated that the responses of the liquid tank were 24–70% higher than the results of the fixed-base model. Compared to the sway-rocking model, these responses did not differ by 20%. This study also investigated cohesive soils of homogeneous clays and multiple strata. The paper recommends that future research investigate the experimentation, the geometric nonlinearity of the soil-foundation system, and the stress-strain analysis of the tank wall

Effects of dynamic load application, irregular wave conditions, and base flexibility on the structural response of a vertical pile platform

The dynamic structural response of a vertical pile port platform under the action of irregular wave loads considering soil-structure interaction is studied. Deck displacement and bending moment on the piles were evaluated for a set of structural, hydraulic, and geotechnical parameters. Static structural analyses with the maximum base shear produced by wave loads and dynamic time-history analyses are performed to study the effects of dynamic amplification on the structural response of the platform. Two types of waves are analyzed, regular and irregular, to analyze the amplification effects due to the superposition of a wave train of different periods in the case of irregular waves. Cases with fixed base support and non-linear spring-modeled soil are considered to evaluate the effect of considering a flexible base for the platform. Eight structures composed of a different number of piles and with different heights were analyzed. Six wave conditions with different characteristics are used, varying the wave period and mean water height. Two sandy and two clayey soil profiles are considered with different densities and consistency. The results show that resonance effects associated with dynamic loading and small-period wave superposition in cases of irregular waves significantly affect the response. Furthermore, considering a flexible base tends to decrease the response for short wave periods, concluding that, in most cases, for wave periods close to 5 s, considering a fixed base model overestimates the response.

Experimental investigation of sliding-based isolation system with re-centering functions for seismic protection of masonry structures

A sliding-based isolation system is an efficient strategy to enhance the seismic performance of low-rise brick masonry buildings, a common type of construction across the globe. The previously developed isolation systems lack a proper re-centering mechanism. Therefore, in this study, a low-cost isolation system, termed reinforced cut wall (RCW) with an appropriate re-centering mechanism, is designed and tested experimentally using a shake table, which hasn’t been tested previously. Two unconfined reduced scale (1:3) brick masonry buildings were subjected to frequency-based seismic excitation, and the model's corresponding acceleration and displacement response were captured. Compared to the fixed base model, considerable reductions were observed in the acceleration and displacement response in the case of the isolated model. Similarly, the inter-story drift and floor relative displacement response was also reduced in the isolated model. Furthermore, the rebars used for the re-centering mechanism remained within the linear viscoelastic range. Based on the experimental validation, the proposed low-cost RCW isolator was found to be an efficient isolation strategy for low-rise masonry buildings in high seismic regions.

Seismic pounding of adjacent buildings considering torsional effects

This study aims to evaluate pounding effects in fixed-base models by considering torsional irregularity. For this purpose, 8 different adjacent building combinations were created by using 3-dimensional 5- and 9-story building models. In adjacent building models, the most critical situation was determined by evaluating the gap distance, different sequences of the same building models and regular or irregular plan view and if the structures are irregular, their eccentricity cases relative to each other. Nonlinear behavior of structural elements was taken into account for examine the change in the seismic behavior of structural elements due to pounding and torsion effects. The nonlinear time history analysis of the adjacent models was performed for 11 pairs of spectrum compatible ground motion recordings in the SAP2000 program. The results of 176 different analyzes show that the displacement demand, interstory drift ratio, damage ratio and torsional irregularity coefficient values tend to increase in general with the combined effects of pounding and torsion. The absolute maximum and most critical values of the relevant parameters were calculated in irregular structures with pounding where the eccentricity of buildings is in the same direction and same side. In addition, the large standard deviation of the result values according to the ground motion records indicates that care should be taken in choosing the number of ground motion records.

Site Specific Non-Linear Ground Response Analysis and Soil Structure Interaction Study of Newly Constructed Dharahara Tower

This study investigates the seismic performance of the recently reconstructed Dharahara tower, a historically significant monument in Nepal that has experienced damage in past earthquakes and was completely destroyed in the recent Gorkha earthquake. Ground Response Analysis (GRA) and Soil-Structure Interaction (SSI) investigations are conducted to assess its structural behavior. GRA includes free field and structure-influenced analyses, with subsequent comparative assessment. Additionally, 3D non-linear finite element analysis is employed to derive equivalent spring constants representing soil and foundation characteristics, which are incorporated into the SSI analysis. These computed spring constants are used to model support conditions, allowing for an evaluation of the super-structural response. The study also employs non-linear dynamic analysis to compare structural responses between fix-based and spring-based models. The results indicate that the presence of the structure significantly influences surface wave motion amplification in GRA, resulting in peak ground accelerations (PGAs) that exhibit de-amplification in the free field and amplification in the presence of the structure. Furthermore, the introduction of an equivalent spring system in the soil-structure model changes the system's vibration period and damping characteristics, leading to enhanced dynamic response compared to the fixed-base model.

Seismic performance investigation of building structures equipped with MTMDs considering soil-structure interaction

The traditional tuned mass damper (TMD) design criterion is obtained with the fixed base model, which is suitable for the case without significant soil-structure interaction (SSI) effects. However, when the SSI effects are notable, the TMD designed based on the fixed base model will degrade its performance and even magnify the seismic response of the main structure. Since accurately evaluating the effects of SSI on the natural frequencies of the main structure is difficult due to soil nonlinearity, single tuned mass dampers (STMDs) may easily undergo tuning failure due to frequency-limited control bandwidths. Applying multiple tuned mass dampers (MTMDs) to attenuate the vibration of the main structure may be a promising solution. In this paper, the seismic performance of a 10-story steel structure equipped with MTMDs considering SSI is investigated. A three-dimensional refined finite element model is first built. Then, a comprehensive analysis is presented by considering the different MTMDs design parameters and earthquakes. The research results show that when the SSI effect is significant, the MTMDs in reducing the seismic response of the structure have better effectiveness than the STMDs. With other MTMDs design parameters determined, the MTMDs performance is strengthened by increasing the mass ratio and the number of TMDs. The central frequency ratio is taken as the optimum frequency ratio. The bandwidth is limited to the region formed by 0.9–1.1 times the TMD optimal design frequency. The performance of the MTMDs is less influenced by the different TMD installation positions. Moreover, the MTMDs still have good robustness when considering the SSI effect.

Seismic control of T-shape in plan steel high-rise buildings with SSI effect using tuned mass dampers

A steel high-rise building (HRB) with plan irregularity is a major challenge in engineering design, especially under seismic loads. Soil–structure interaction (SSI) is one of the most important factors in designing steel high-rise structures. Herein, a T-shape in plan steel HRB subjected to four different earthquakes will mitigate the vibration and control the displacements and base straining actions resulting from earthquakes by using tuned mass dampers (TMDs) systems, and the most controlling arrangement of TMDs, in the fixed base HRB model and in the SSI HRB model, will be examined. Three-dimensional models of the steel high-rise building (HRB) with a T-shape in the plan subjected to four different earthquakes fixed or with the SSI effect were analyzed to investigate the seismic mitigation effect of six different plan arrangements of TMDs applied on the top plan of the fixed HRB model, while for the SSI HRB model, these TMDs distributions were applied on the top plan and additionally on two intermediate plans along the HRB height. The TMDs for the T-shape in plan steel HRB are more effective in the SSI model than in the fixed base model. In the SSI effect model, the distributions of the TMDs not only on the top plan of the model but also through the model (on two additional plan levels along the height) further reduced the HRB seismic response and this three-level TMDs distribution was required for the plan arrangement of 2 or 4 TMDs.

Effects of constitutive soil models on the seismic response of an offshore jacket platform in clay by considering pile-soil-structure interaction

Offshore jacket platforms are widely used for wind energy generation and gas and oil field development. The South Pars gas field, located in the Persian Gulf, stands as one of the largest gas fields in the world. This gas field is situated in a seismically active region predominantly characterized by clay soil. Considering the significant impact of clay soil on the seismic response of offshore structures and their vulnerability to damage, it is essential to conduct comprehensive studies on the seismic behavior of offshore structures in this particular area while considering the nonlinear behavior of soil and pile-soil-structure interaction (PSSI). However, due to the laboratory limitations, it is difficult to experimentally investigate the seismic behavior of these structures on a real scale by considering the actual soil environment. This paper aims to adopt a nonlinear kinematic hardening model for clay in Abaqus software and calibrate this model parameters for the South Pars gas field region to carefully investigate the effects of nonlinear behavior of soil and PSSI on the seismic response of an offshore jacket platform. In addition, the perfectly elasto-plastic Mohr-Coulomb model is employed as a simple and common constitutive soil model to compare the results. To achieve the study goals, firstly, the numerical modeling techniques are validated. Subsequently, the main parameters of the nonlinear kinematic hardening model are calibrated for the South Pars gas field region, which has not been done for this region in previous works. Detailed numerical models, including the fixed-base model and the pile-soil-structure (PSS) model, are then developed and analyzed using different selected ground motion records. The results indicate that considering the effect of PSSI has a significant effect on the seismic responses of the structure. Moreover, PSSI effect has a great dependence on the constitutive soil model. The results of this study are expected to provide useful insights into the seismic design of offshore structures in similar geological conditions.

Seismic Performance of RC Moment Frame Buildings Considering SSI Effects: A Case Study of the New Venezuelan Seismic Code

The Soil–Structure Interaction (SSI) effect has been widely evidenced during several earthquakes around the world. In the Venezuelan context, the seismic event in Caracas in 1967 showed the significant consequences of designing buildings without considering the SSI effect. Nevertheless, limited research on the seismic performance of concrete moment frames (commonly used as structural systems in office and residential buildings in Venezuela and Latin America) considering the SSI effects has been developed, although there have been continuous updates to the Venezuelan Seismic Code. In this research, the influence of the SSI on the seismic performance of RC moment frame buildings designed according to the New Venezuelan Seismic Code was studied. An extensive numerical study of 3D buildings using concrete moment frames supported by mat foundations on sandy and clayey soils was performed. The response spectrum method, non-linear static analysis, and non-linear dynamic analysis were used to assess the seismic response of the archetypes studied. The results show that SSI effects can have a significant impact on the seismic response of RC moment frame buildings, increasing the interstory drift ratio and decreasing the shear forces. As is shown in fragility curves, the probability of collapse increases for cases with flexible bases in comparison to the cases of models with fixed bases. Additionally, in the 24-story archetype, the fixed-base model reached a maximum probability of collapse. Finally, a new proposal for the reduction of the strength-reduction factor (R) must be incorporated into the Venezuelan Seismic Code to improve the safety of the structures. Limitations in the use of RC moment frames must be incorporated for high-rise buildings since, as the present work demonstrates, for high-period structures, the normative provisions are not reached.

Nonlinear time-domain soil-structure interaction analysis of a mid-rise building benchmarked against earthquake recordings: A case study of the BRI's annex building

Performing soil-structure interaction (SSI) analysis under strong shaking scenarios using the direct method is becoming more prevalent in engineering practice. However, given the pronounced nonlinearity in soil, structure, and foundation response, the robustness of current methodologies is open to question, and benchmarking these methodologies against instrumented case histories is needed to identify the strengths and weaknesses in the approach. In this study, a three-dimensional (3D) Nonlinear (NL) Soil-Structure Interaction (SSI) analysis methodology in the time-domain code LS-DYNA is benchmarked against the actual recordings for a mid-rise building. The well-instrumented Building Research Institute (BRI) Annex Building (ANX) in Tsukuba City northeast of Tokyo, Japan, which features an adjacent free-field geotechnical downhole array, is used for this case study. A Finite Element (FE) three-dimensional 3D SSI model of the site, including the BRI ANX building, that considers both material and geometric nonlinearities is first developed. Two events are applied to the model: the 2011 Tohoku-Oki earthquake main shock (Mw9.1), referred to as the Great East Japan Earthquake (GEJE), and the 2002 Southern Ibaraki Prefecture earthquake (Mw4.9), selected from the BRI strong motion network due to the relatively wide amplitudes recorded at the site. The former event induced maximum shear strains in the soil of 1.6%, while the latter event induced maximum shear strains of 0.08%. For both horizontal and vertical components of shakings, the predicted response of the structure and adjacent free-field downhole array are compared with the corresponding recordings. The results show that the structural response is significantly affected by the accuracy of the predicted free-field ground surface response, especially at the structural fundamental period as opposed to the site period. In addition, results indicate that the fixed-base and flexible-base structural models’ responses are substantially different, mainly attributed to the SSI effects that cannot be captured in the fixed-base model. Finally, a comprehensive discussion on the minimum amount of data required to adequately capture nonlinear structural response using the proposed SSI methodology is provided in this case study.

Simple Soil Effect Analysis in a Base and Mid-Story Isolated 15 Story Building

In this study the effect of soil-structure interaction on seismic performance is investigated considering a 15 story building incorporating base and mid-story seismic isolation. The cases that are taken into account are; fixed base model, base isolated model and base and mid-story isolated model. All three models are analyzed by excluding and including soil-structure interaction. Three different earthquakes are used for the time-history analysis. It is concluded that the seismic performance is enhanced by the implementation of base and mid-story isolation to the structure. In addition, it is observed that soil-structure interaction had a small effect on seismic performance of the structure depending on the base soil type.

Seismic response analysis of high-rise frame-core tube building on fluid-saturated soil considering soil-pile-structure interaction

This paper proposed a three-dimensional (3D) refined finite element method (FEM) to determine seismic responses of the high-rise buildings resting on fluid-saturated soil considering the soil-pile-structure interaction (SPSI) and the dynamic characteristics of two-phase media, using a user-defined element with ABAQUS. The theory and method to develop the FEM were introduced in detail, including the user-defined element, material constitutive models, boundary conditions, earthquake input methods, specific implementation procedures, and verifications. Then, the FEM was adopted to investigate the seismic responses of a 51-story high-rise building with a frame-core tube system subjected to six earthquake records. Discussions were conducted on the acceleration, displacements, inter-story drifts, story shear force, and damage behavior to interpret the seismic characteristics of the superstructure. A fixed-base model was also considered to reveal the SPSI effect under the same conditions. The results demonstrate that the SPSI lightens acceleration and total story shear force but amplifies displacements, inter-story drifts, and column shear force. Without regard to the SPSI, no apparent change appears for the damage of floor plates, whereas the core tube suffers more severe damage than under the SPSI conditions. For high-rise buildings, the SPSI does not always provide conservative seismic performance evaluations. It is of fundamental importance to include the SPSI effect during the performance-based seismic design of high-rise buildings for comprehensive understanding. The proposed FEM can also be access to seismic SSI analysis for other types of structures in the saturated field.

Revised Fixed-base Model for Estimation of Adult Mortality in Developing Countries

This paper presents a revised Fixed-base model (RFBM) for the estimation of adult mortality in developing countries. The RFBM also derives estimates of adult mortality from the age distributions of two censuses by 5-year age-groups. Unlike the original version, RFBM does not depend on person – years lived between exact ages 0 and 5 years ( 5L0 ) and the mid-point population of those aged 0 – 4 years ( 5N0 ) . Both 5L0 and 5N0 are known to be affected by under-reporting in most developing countries. The estimates of the RFBM appear to have improved and compare favourably with estimates from other methods. We recommend the use of the model, especially when there is insufficient data for direct estimation of adult mortality in developing countries, among others.

A comparative study to determine seismic response of the box culvert wing wall under influence of soil-structure interaction considering different ground motions

The present study deals with evaluation of the effects of different ground motions, backfill-structure interaction (BSI) and soil-structure interaction (SSI) on dynamic response of a box culvert wing wall. In obtaining numerical results, five different earthquake records with different frequency contents, five different backfill types and four different subsoil types are taken into account. Firstly, a finite element model (FEM) and three analytical models are proposed for analysis of the wing wall-backfill system under fixed-base case, and these fixed-base models are compared with each other through both modal analysis and displacement time-history analysis under the assumption of linear-elasticity. After validating the ability of the FEM approach, by extending the fixed-base FEM to take account of elastoplastic behavior of soil and SSI, a three dimensional (3-D) model has been described, and 3-D nonlinear analyses have been carried out in time domain. The numerical results show that the seismic response of the wing walls are affected remarkably by the SSI, BSI and frequency content of the earthquake.

Effect of SSI and Fixed-base Concept on the Dynamic Responses of Masonry Bridge Structures, Dalal Bridge as a Case Study

Historical masonry structures are very important as they carry cultural heritage, so it is important to protect these structures from natural disasters such as earthquakes and transferred to the next generations. It is known that masonry structures are weak against earthquakes, therefore, a suitable analysis method for assessment and retrofitting purposes is a must. Generally, the fixed-base concept is used for analysis and design purposes, however, in reality, the structures are not fixed-base but they are resting on soils. The aim of this study is to make a comparison study between dynamic responses of fixed-base and soil-structure interaction (SSI) models for bridge masonry structures, the historical Dalal bridge was selected as the case study. First, the bridge was modeled as a fixed base model, and then three different soil profiles (hard, medium and soft soils) were added to the underneath of the structure. The numerical models were analyzed under Elcentro earthquake record. Results indicating a good agreement between the fixed base and the case of hard soil base. However, considerable differences were observed for medium and soft soil profiles.

Effects of Plan Irregularities of Multi-Storeyed Structure Resting on Sloping Terrain with Soil Structure Interaction

Abstract: Structures resting on sloping ground are highly vulnerable to earthquakes due to irregularities in plan and elevation. Structures are often analysed under earthquake loadings, without considering the effect of soil–structure interaction (SSI).In the present study the irregular G+4 storey structure has resting on sloping terrain. The influence of the soil structure interaction in the dynamic behaviour of the structure is reflected in an increase in the vibration period as well as increase in the system damping in comparison with the fixed-base model, which does not consider the supporting soil. 4 types of sloping angles are considered in the present study. The considered structure have been modelled and analysed in ETAB2016 software. The considered building has been subjected to earthquake forces. Non linear time history method is considered to perform on structures models. Performing soil structure interaction for all three types of soil Hard, Medium and Soft by applying point spring at the footing. The design and analysis of structure is carried out in ETABS2016 and calculation of spring constants are carried out manually with standard data of it. Keywords: Multi storied RC structures, Plan irregularities, Sloping Terrain, Soil Structure Interaction(SSI), Non linear Time History Method(NLTHM)

Seismic behavior of mid-rise reinforced concrete adjacent buildings considering soil-structure interaction

This study aims to investigate the effects of structure-soil-structure interaction (SSSI), soil-structure interaction (SSI) and fixed-base (FB) assumptions on seismic behavior in mid-rise reinforced concrete (RC) buildings located on soft soil. Three–dimensional (3D) high ductility RC frames 5-, 8-, 10-, 13-, and 15-storey buildings are modeled as a fully nonlinear frame element. Five different structural cases were created: SSSI models with and without pounding, FB models with and without pounding, and SSI models. In the scope of this study, direct finite element modeling of 3D inelastic soil volume was considered. A detailed investigation has been carried out considering 65 different model combinations to reflect SSSI, SSI and FB modelling approaches. As a result, total of 1365 analyses using 21 different ground motion records, the lateral displacement demands and displacement profiles of the buildings were examined and presented. It is found that the seismic behavior of adjacent buildings located on soft soils is different from the fixed-base assumption. The buildings should not be evaluated alone, as neighboring buildings on soft soils affect each other. Neighboring building and soil effects should be considered for buildings up to 8-storey even no collision occurs. For buildings with higher than 8-storey, it may be reasonable to consider SSI only with neglecting neighboring building effects if there is no collision. If the seismic gap distance between adjacent buildings is insufficient and seismic pounding potential exists, neighboring building effects with soil-structure interaction should be taken into account independent from building height.

Numerical Study of the Soil-Structure Interaction Considering the Dynamic Response of the Soil

Abstract This paper presents the process of modeling a structure using the finite element method. There are two approaches through which the seismic behavior of structures can be modeled. Generally, the analysis of seismic behavior assumes the structures have a fixed base. The second method to model and analyze the seismic behavior of structures involves considering the soil-structure interaction by modeling the soil underneath the building. This paper also presents a comparison of the results of two finite element simulations, one of them considering the structure has a fixed base and the other having a flexible base. The results have shown that the fixed base model leads to higher frequencies and uneven distribution of stresses compared with the results of the flexible base model.

RC Medium-Rise Building Damage Sensitivity with SSI Effect.

Global vibration-based methods in the field of structural health monitoring are intended to capture structural stiffness changes of buildings or other civil engineering structures. Natural frequencies of buildings or bridges are commonly used parameters to monitor these stiffness changes. Therefore, it is essential to clarify the limit at which this method is no longer sensitive enough to be useful for structural health monitoring purposes. This paper numerically investigates the effect of structural damage and soil–structure interaction on cellular-type reinforced concrete buildings’ natural frequencies. These buildings are a common housing stock of Eastern Europe but are rarely investigated in this context. Comparisons with a reinforced concrete frame and infill structure building are made. Finite element models representing three structural system types of nine-story reinforced concrete buildings were used for the numerical simulations. Furthermore, a five-story finite element model was used for a damage sensitivity comparison. It is established that, for cellular-type structure buildings to detect damage comparable to that investigated in the paper, structural health (fixed base model frequency) should be monitored directly. Then, a statistical significance level for frequency changes of no more than 0.1% should be adopted. Conversely, the rocking frequency is a very sensitive parameter to monitor building base condition changes. These changes are often a cause of the cracking of building elements.

Model updating of a masonry tower based on operational modal analysis: The role of soil-structure interaction

Vibration-based finite element model (FEM) updating of cultural heritage assets is gaining so much attraction these days since destructive tests are usually not allowed to be performed. In this study, a framework for developing three-dimensional (3D) FEMs is proposed using 3D laser scanners and applied on Slottsfjell tower, a stone masonry tower in Tønsberg, Norway. Operational modal analysis (OMA) was done based on the ambient vibration testing (AVT) data to define the frequency values and corresponding mode shapes of the tower. Mechanical properties of the tønsbergite stone were utilized to derive the base values of the material properties of the homogenized masonry for performing sensitivity analysis and FEM updating. To investigate the effect of the soil-structure interaction (SSI) on the FEM updating results, three FEMs are developed. The fixed-base model is the FEM without considering the SSI effects, and two other FEMs are developed using the substructure and direct methods for simulating the SSI effects. Sensitivity analysis was performed to investigate the effective parameters on the dynamic characteristics of the models. FEM updating was conducted on the three FEMs, and results are compared to each other to show the role of the SSI on the FEM updating results. The resonance effect can cause damages to buildings located even in low seismicity zones. For this aim, the risk of resonance effect has been evaluated for the tower. Finally, linear dynamic analysis was performed on the three calibrated models, and the results were compared to each other.