Effect Of Soil Flexibility Research Articles

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. 

Effects of shear wave velocity and soil structure interaction on the structural pounding during earthquakes

It has been found that in the event of a strong earthquake, and due to insufficient distance between two adjacent structures, the lateral movement at the top of structures may cause collisions between them. This phenomenon, commonly known as seismic collision, can generate impact forces that were not considered during the initial design of the structure. These forces can cause significant structural damage or lead to complete collapse of the structure. The main purpose of this paper is to study the coupled effects of soil flexibility and impact between adjacent buildings undergoing seismic excitation. To capture the impact forces between the structures during the collision, a modified linear viscoelastic model was used effectively. Particular attention has been paid to studying the effects of shear wave velocity, first on the soil structure interaction and then on the collision response of adjacent structures. Three configurations of adjacent structures were analyzed: light-light, light-heavy, and heavy-heavy structures. The results obtained through this analysis showed that the dynamic response and the impact force of the structures depend essentially on the interaction between the structure, the foundation, and the soil.

On the influence of soil flexibility in structural topology optimization

AbstractThis paper investigates for the first time the effect of soil flexibility in structural topology optimization. The case of a structure resting on an underlying soil is explored. The response of the soil is modeled using the Indirect Boundary Element Method (IBEM). The structure is modeled using Finite Element Method (FEM) and the soil domain is coupled by imposing continuity and equilibrium conditions at the soil‐structure interface. Original soil stress influence functions are derived to model voids in the soil. The optimization is carried out by using the Topology Optimization of Binary Structures (TOBS), a recently developed method that employs sequential integer linear programming and the branch‐and‐cut algorithm. Structural compliance minimization subject to a volume constraint is solved. Selected optimization problems are solved for various soil‐to‐structure flexibility ratios. Results show that the soil flexibility may have a significant impact in both the optimized topology and in the achievable compliance of the structure. Results considering voids on the soil, which increases the soil flexibility, affected the final topology of the structures as well as the optimized values.

Seismic Fragility of Aging Elevated Water Tank with Smooth Bars Considering Soil Structure Interaction

The functionality of elevated water tanks is pivotal to assure after an earthquake as water supply is expected to be uninterrupted. Although elevated water tanks with deformed bars are widely studied, limited works exist for water tanks with smooth bars, although such tanks comprise a considerable fraction, even in the high seismic regions. To quantify the seismic vulnerability of aging elevated water tanks with smooth bars, we created analytical fragility functions for full, half, and empty reservoir conditions, considering fluid–structure and soil–structure interactions. The sum of findings reflects that soil flexibility and the amount of water present in the tank have a significant effect on overall seismic fragility, especially at higher damage states. The tanks are found to be most vulnerable when they are fully filled with water. The effect of soil flexibility is more pronounced at higher damage states. The difference between the fragility of flexible base and fixed base structures is found to increase with increasing ground motion intensity and it is the highest for the empty tank condition.

Effect of Soil Flexibility on Building Frame Analysis and Practice in Bangladesh

Effect of Soil Flexibility on Building Frame Analysis and Practice in Bangladesh

Effect of Soil Flexibility on Seismic Fragility of Code-Designed Reinforced Concrete Framed Buildings

The seismic response of structures is very complex owing to the behaviour of soils during an earthquake. Traditional seismic designs rely on the assumption that the base of the foundation is fixed. However, the foundation tends to displace owing to the flexible nature of the soil. Indian seismic code and other codes though incorporate the effect of soil-structure-interaction (SSI), but in a very broad sense, and thus are inadequate. This study aims to understand the seismic performance of reinforced concrete (RC) framed buildings designed according to the Indian code, considering soil flexibility. The seismic vulnerability of buildings is investigated through pushover and fragility analysis. Six RC framed buildings with different heights, encompassing low-, mid- and high-rise buildings, covering a wide range of lateral periods (short-, medium- and long-periods), are considered. These buildings are considered to be resting on raft foundations. The soil flexibility for four types of soft clay soil is computed based on shear velocity, shear modulus and density. A variational study for a range of soft soils in combination with short-, medium- and long-period structures is carried out. Fragility curves and damage probability matrices are developed using push over analysis incorporating SSI. The overall conclusions from the fragility curves are that the soil flexibility may significantly increase the seismic vulnerability of low-rise RC framed buildings, and the performance of high-rise buildings may be improved by taking this into consideration.

Vibration Reduction of Eccentric Steel 3D Framed Building Considering Soil Flexibility

Seismic demand can be reduced by modifying the structural response of the system. Viscous dampers are an effective passive control device for reducing vibrations in building structures. The present study investigates the performance of linear viscous dampers in vibration control of multi-storey building structures under seismic excitation considering the effect of soil flexibility. Six-storey steel 3D framed buildings with three different building plans, namely symmetric, T and L shapes, are modeled using SAP 2000. Soil type I (hard) and type II (medium) are considered as per IS 1893:2002 to incorporate the effect of soil flexibility by using springs at supports for medium type soil and fixed supports for hard soil. The spring constants are obtained from Gazetas’ equations. To measure the control performance, inter-storey drift and maximum top displacement are considered as objective functions. Linear time history simulation is performed using white noise (ensuring wider frequency content) to quantify the objective functions. After performing the analysis and comparing with the uncontrolled case for both hard and medium soil, it is observed that maximum reduction in inter-storey drift and average top displacement can be obtained. Eccentric plans have larger uncontrolled values than the symmetric plans, thus additional design criteria to be followed when opting for eccentric plans. The study reveals that application of supplemental viscous dampers results in greater control of vibrations in such plans. Vibration control of viscous damper is comparatively better in hard soil than in medium type soil.

Residual displacement estimation of simple structures considering soil structure interaction

As the residual displacement and/or drift demands are commonly used for seismic assessment of buildings, the estimation of these values play a very critical role through earthquake design philosophy. The residual displacement estimation of fixed base structures has been the topic of numerous researches up to now, but the effect of soil flexibility is almost always omitted. In this study, residual displacement demands are investigated for SDOF systems with period range of 0.1-3.0 s for nearfield and far-field ground motions for both fixed and interacting cases. The elastoplastic model is used to represent nondegrading structures. Based on time history analyses, a new simple yet effective equation is proposed for residual displacement demand of any system whether fixed base or interacting as a function of structural period, lateral strength ratio and spectral displacement.

Effect of soil condition on seismic response of isolated base buildings

In the present paper, nonlinear time history and response spectrum analyses were carried out using Etabs-2015 software to study the influence of soil condition beneath the isolated base. The effects of soil flexibility are considered in the current study to examine the differences in spectral acceleration, base shear, story displacements, story drifts and story shear obtained following the seismic provisions of Indian standard code. Various soils are systematically compared and discussed for a seismic performance of multistory buildings. Parametric analysis of the buildings fitted with isolation devices is carried out to choose the appropriate type of soil. The study shows that the value of base shear increases with an increase of soil flexibility and superstructure stiffness. It also observed that the spectral acceleration (SA) and spectral displacement (SD) are higher in soft soil condition, which gives us evidence that the response spectral of a structure is associated with soil condition. The paper concluded that the hard soil and medium soil are suitable for base isolation building. In addition, analysis and design considerations for base isolated and conventional structures are suggested to enable the designer to get a better understanding at the preliminary design stage.

Performance-based assessment of response reduction factor of RC-elevated water tank considering soil flexibility: a case study

The seismic design codes/standards of most countries include the nonlinear response of a structure implicitly through a response reduction/modification factor (R). It is the factor by which the actual base shear should be reduced to find the design base shear during design basic earthquake considering nonlinear behavior and deformation limits of structures. In the present study, attempts are made to determine the ‘R’ factors of four existing RC staging elevated water tanks, which are designed as per draft Indian standards for seismic design of liquid and RC designs and having a ductile detailing considering the effects of soil flexibility. The elevated RC water tanks are analyzed using displacement controlled non-linear static pushover analysis to evaluate the base shear capacity and ductility of tank considering soil flexibility. The ‘R’ factor is obtained for four realistic designs of elevated RC water tanks having different capacities at two performance levels. The evaluated values of ‘R’ factor are compared with the values suggested in the design code. The results of the study show that the flexibility of supporting soil has considerable effect on response reduction factor, period and overall performance of water tank, indicating that idealization of fixity at base may be seriously mistaken for soft soils. All the studied water tanks were designed with higher safety margin than that of specified in Indian Standards.

Incorporation of Dynamic SSI Effects in the Design Response Spectra

Many studies in the past on dynamic soil–structure interactions have revealed the detrimental and advantageous effects of soil flexibility. Based on such studies, the design response spectra of international seismic codes are being improved worldwide. The improvements required for the short period range of the design response spectra in the Indian seismic code (IS 1893:2002) are presented in this paper. As the recent code revisions has not incorporated the short period amplifications, proposals given in this paper are equally applicable for the latest code also (IS 1893:2016). Analyses of single degree of freedom systems are performed to predict the required improvements. The proposed modifications to the constant acceleration portion of the spectra are evaluated with respect to the current design spectra in Eurocode 8.

Investigation of Shear Wave Velocity by Using Multi-Channel Analysis of Surface Wave Method for Microzonation Map Development and Its Application to Industrial Frame Structures

The present study focuses on determining soil dynamic property, specifically the shear wave velocity at the top 30 m, to establish seismic microzonation maps and to evaluate the effect of soil flexibility on the frame structures of industrial building design in terms of drift. The model of industrial building steel frame was built on the basis of a 3D model using the SAP2000 software. The applications of spring stiffness for rigid footing spring constraints include average shear wave velocity to define the shallow foundation of the structure. The flexible- and fixed-base models were developed to evaluate the structural performance.

Seismic Response of Steel Braced Building Frame Considering Soil Structure Interaction (SSI): An Experimental Study

Conventional fixed-base analysis ignoring the effect of soil-flexibility may result in unsafe design. Therefore, to evaluate the realistic behavior of structure the soil structure interaction (SSI) effect shall be incorporated in the analysis. In seismic analysis, provision of bracing system is one of the important option for the structure to have sufficient strength with adequate stiffness to resist lateral forces. The different configuration of these bracing systems alters the response of buildings, and therefore, it is important to evaluate the most effective bracing systems in view point of stability against SSI effect. In present study, three RC building frames, G+3, G+5 and G+7 and their respective scaled down steel model with two types of steel bracing system incorporating the effect of soil flexibility is considered for experimental and analytical study. The analytical study is carried out using Elastic continuum approach and the experimental study is carried out using Shake Table. The influence of SSI on various seismic parameters is presented. The study reveals that, steel bracing system is beneficial to control SSI effect and it is observed that V bracing is more effective, in resisting seismic load considering SSI.

A Case Study: Effect of Soil-Flexibility on the Seismic Response of Reinforced Concrete Intermediate-Rise Regular Buildings in Halabja City

A Case Study: Effect of Soil-Flexibility on the Seismic Response of Reinforced Concrete Intermediate-Rise Regular Buildings in Halabja City

Performance Assessment of RC Framed Buildings with Shear Wall Due to Effect of Soil Flexibility

Performance Assessment of RC Framed Buildings with Shear Wall Due to Effect of Soil Flexibility

SEISMIC RESPONSE OF COMPOSITE BUILDING FRAME WITH ALTERNATE BRACING SYSTEM CONSIDERING SOIL STRUCTURE INTERACTION (SSI)

Conventional fixed-base analysis ignoring the effect of soil-flexibility carried out for the seismic design of buildings may result in unsafe design. Therefore, the effect of SSI is an important issue from the viewpoint of design considerations. Thus to evaluate the realistic behavior of structure the soil structure interaction (SSI) effect shall be incorporated in the analysis. In seismic analysis provision of bracing system is one of the important option for the structure to have sufficient strength with adequate stiffness to resist lateral forces. The different configuration of these bracing systems alters the response of buildings, and therefore, it is important to evaluate the most effective type and location of the bracing systems in view point of stability against SSI effect. In present study, two RC building frames, G+10 and G+15 with six different combinations of steel bracing system at alternate locations incorporating the effect of soil flexibility is considered in order to investigate the effectiveness of bracing system to control SSI. The seismic analysis is carried out using equivalent static method as per IS 1893-2002 The study is carried out using Elastic continuum approach(ECM) The influence of SSI on various seismic parameters and the flexural parameters are presented. The changes in all these parameters due to provision of steel bracing system are studied in order to evaluate its effectiveness in controlling the SSI effect. The study reveals that, steel bracing system plays important role to control SSI effect and it is observed that diagonal bracing placed at mid periphery are more effective, in resisting seismic load considering SSI.

Seismic behavior of RC framed shear wall buildings as per IS 1893 and IBC provisions

Usually the analyses of structures are carried out by assuming the base of structures to be fixed. However, the soil beneath foundation alters the earthquake loading and varies the response of structure. Hence, it is not realistic to analyze structures by considering it to be fixed. The importance of soil-structure interaction was realized from the past failures of massive structures by neglecting the effect of soil in seismic analysis. The analysis of massive structures requires soil flexibility to be considered to avoid failure and ensure safety. Present study, considers the seismic behavior of multi-storey reinforced concrete narrow and wide buildings of various heights with and without shear wall supported on raft foundation incorporating the effect of soil flexibility. Analysis of the three dimensional models of six different shear wall positions founded on four different soils has been carried out using finite element software LS DYNA. The study investigates the differences in spectral acceleration coefficient (Sa/g), base shear and storey shear obtained following the seismic provisions of Indian standard code IS: 1893 (2002) (IS) and International building code IBC: 2012 (IBC). The base shear values obtained as per IBC provisions are higher than IS values.

Evaluation of soil flexibility of the reclaimed area in Penang using the non-destructive method

Rapid development in urban area needs solutions to address scarcity of land for the development and infrastructure. Land reclamation has played an important role in the process of urban development in Malaysia especially in Penang area. However, the land reclamation usually comes along with challenges such as instability of the reclaimed platform and soil liquefaction. Furthermore, the assumption of fixed-base structure in the current building design practice is realistic only when the structure is founded on soil class B (rock). The main objective of this study was to investigate the soil classification and liquefaction potential of the reclaimed land and to study the effect of soil flexibility on low- and medium-rise structure in terms of structure drift. In this study, two areas in Penang have been used as a case study, namely Seri Tanjung Pinang (STP) and Bandar Sri Pinang (BSP). The multichannel analysis of surface wave (MASW) method was implemented to investigate the soil classification and the soil liquefaction for the two case study areas. In addition, the pushover analysis was performed in order to study the effect of soil flexibility on low- and medium-rise structures in terms of drift. Based on the shear wave velocity (Vs30) from MASW, the STP and BSP can be categorized as soil class D (stiff soil) and E (soft soil), respectively. Results also showed that the STP area has no threat to the liquefaction potential compared with BSP area. In terms of drift, it is clearly shown that the difference of flexible-base structures at STP and BSP is 6 and 19 %, respectively, and are larger than fixed-base structure.

Soil–Structure Interaction Effect on Seismic Force Evaluation of RC Framed Buildings with Various Shapes of Shear Wall: As Per IS 1893 and IBC

Behaviour of a structure is altered by the interaction amid the structure, foundation and the soil medium below the foundation. This mutual dependent behaviour of structure and soil is called as soil–structure interaction (SSI). Hence, it is not realistic to analyse a structure as per conventional structural design practice which considers the base to be fixed. Comparative study on seismic provisions of Indian seismic code, IS 1893:2002 (IS) and International building code IBC:2006 (IBC) is carried out in present study to look into the effect of soil flexibility on variation in natural period, spectral acceleration coefficient, base shear and storey shear. Multi-storey reinforced concrete framed buildings of varying height with various shapes of shear walls over raft foundation were considered. Analysis of 3D SSI models with three different shear wall shapes founded on four different soil types which are classified based on shear wave velocity has been carried out using finite element software LS DYNA. Study shows the significant effects of SSI in altering the seismic response of structure. It also shows that the base shear obtained as per IBC are higher than the IS values and the corrugated shape of shear wall experience the lowest base shear compared to cylindrical and rectangular shape shear walls for buildings with aspect ratio below 3.

Dynamic soil-structure interaction studies on 275m tall industrial chimney with openings

In this paper, a three dimensional soil-structure interaction (SSI) is numerically simulated using finite element method in order to analyse the foundation moments in annular raft of tall slender chimney structures incorporating the effect of openings in the structure and the effect of soil flexibility, when the structure-soil system is subjected to El Centro (1940) ground motion in time domain. The transient dynamic analysis is carried out using LS-DYNA software. The linear ground response analysis program ProShake has been adopted for obtaining the ground level excitation for different soil conditions, given the rock level excitation. The radial and tangential bending moments of annular raft foundation obtained from this SSI analysis have been compared with those obtained from conventional method according to the Indian standard code of practice, IS 11089:1984. It is observed that tangential and radial moments increase with the increase in flexibility of soil. The analysis results show that the natural frequency of chimney decreases with increase in supporting soil flexibility. Structural responses increase when the openings in the structure are also considered. The purpose of this paper is to propose the need for an accurate evaluation of the soilstructure interaction forces which govern the structural response.