Sharif Digital Repository

Observed performance of nonstructural components and building contents during recent earthquakes demonstrated their significance to control economic seismic losses and downtime. Since a large portion of nonstructural equipments installed in buildings are acceleration sensitive devices, reasonable estimation of the acceleration they undergo during an earthquake has an important role in rational design of secondary systems and subsequently in reducing the earthquake damages. Although a comprehensive amount of research studies have been conducted to date to approximate the floor acceleration demands of a multistory building subjected to the earthquake ground motion, in most work, the soil... 

This existing research has been conducted to reach quick evaluation instructions to pipe earthquake damages in the piping systems inside the industrial complexes. In the old complexes of such kinds there are cases where field inspections and quality evaluations are urgently required subject to peculiar conditions affecting each piping system inside the units and in certain cases subject to lack of access to the as built-drawings. However, so far any definite instruction hasn’t been available for a quick evaluation of likely damages in piping system: all because of various pipe types, complexity of pipes geometry, different temperatures and pressures in different sections. In this research... 

Earthquakes are one of the greatest natural hazards. Hazard mitigation requires studies in many areas including geotechnical aspects of earthquake engineering. Characteristics of seismic waves change significantly as they pass through soft soil layers near the earth's surface. This phenomenon, commonly known as site effects or site response, is a major factor influencing the extent of damage on structures. Processing of seismic data recorded during earthquakes is one of the most reliable methods to study site effects. The ground motions generated during earthquakes are nonstationary with respect to both amplitude and frequency. The state-of-the-art time-frequency distributions when applied... 

Controlling damage level of structures for an earthquake with certain intensity is the main purpose in seismic performance based design. This is done by estimating and confining the structure displacements and related global and local response parameters. Even though nonlinear time history analysis method is the most exact method for predicting seismic behavior of structures, but its application is limited because of being complex. Nonlinear static analysis procedure (Pushover analysis) which is based on analyzing the structure subjected to the incremental lateral load is an alternative method that has been recommended by recent structural codes. In order to consider the soil-structure... 

Non rigidity of the soil beneath the structure, alters elastic and inelastic response of it. This effect is caused by the soil-structure interaction. The effect of soil-structure interaction is studied in two parts, Kinematic interaction and inertial interaction. Among these, kinematic interaction effects are often assumed to be negligible so that even in existing regulations it has been ignored. While the kinematic part of soil-structure interaction effect could produce a rocking input motion that might be important. In recent years, according to expanding usage of performance based design philosophy, researches on inelastic behavior of the soil-structure systems has been done which is... 

Soil-Structure Interaction (SSI) has been widely studied theoretically and experimentally due to its importance effects on the responses of structures. In experimental studies, acceleration responses recorded during previous earthquakes are generally used in order to investigate the contribution of underlying soil to the response of soil-structure systems. Since acceleration responses are affected by higher modes of vibration, studying the effect of SSI on dynamic characteristics of higher modes are of great importance in these studies. However recent theoretical studies indicate that the influence of SSI on the higher vibrational modes is very much dependent on the behavioral model (bending... 

The effect of soil structure interaction, on displacement modification factor in constant reduction factors (CR) is evaluated, studied for SDOF structures placed on flexible base modeled by 3DOF system as the base foundation (a sway, a rocking and an internal degree of freedom to see the frequency dependency of dynamic stiffness of soil). 60 records of FEMA-440 for 3 types of soils (B, C and D) are analyzed for 28 different soil-structure conditions, 6 different level of reduction factors, and varied secondary hardening for 2 different hysteresis behavior to see the effect of stiffness hardening. Results are plotted in spectrums to see the role of Tn.
Final results show that effect of... 

Soil-structure interaction has significant effect on dynamic behavior of the super structure. This effect is usually investigated in two separate parts, i.e., the Kinematic Interaction effect and the Inertial Interaction effect. The first modifies the input ground motion to the foundation as a result of difference in soil and foundation stiffness. The later, i.e., the II effect, introduces the effect of soil flexibility and radiation of waves into the supporting medium on the response of the structure. These effects are usually considered by introducing a replacement oscillator with modified natural period and damping ratio subjected... 

The concept of equivalent linearization in which the actual nonlinear system is substituted by an equivalent linear single-degree-of-freedom (SDOF) system is extended to soil-structure systems with elastic and inelastic behaviors. Equivalent linearization is one of the approximate methods widely used to estimate the response of nonlinear structures in seismic performance based design procedures as a basis of Capacity Spectrum method. Period and damping of equivalent linear model should be evaluated in a way to predict the maximum inelastic displacement demand of the structure with sufficient accuracy. In recent years, comprehensive statistical studies have been performed to improve the... 

In order to simplify the dynamic analysis of soil-structure systems, the structural element of the foundation is usually assumed to be rigid. While the rigid foundation assumption is acceptable for block-type machine foundations, it may influence the dynamic response of other structures such as structures with a central rigid core. Previous research has shown that the flexibility of the foundation structural elements affect dynamic stiffness of underlying soil so it can change the structural response. The aim of this thesis is to study the influence of foundation flexibility on the global response of soil-structure systems including structures with a rigid core. Since the response of the... 

Base flexibility of structures, cause changes in seismic input motions to the structure, and hence, result in variations in structural seismic responses. This phenomenon is commonly referred to as soil-structure interaction (SSI). The effect of base flexibility on seismic responses is usually investigated from two main aspects: 1) Kinematic interaction (KI) , 2) Inertial Interaction (II). KI effects are induced, first, because of the stiffness contrast between the foundation and the flexible base, and second, because of phase difference of the receiving waves in the contact boundary between the foundation and the flexible base. These effects may results in variations in frequency content of... 

It is several decades that the effect of soil-structure interaction (SSI) has been known to engineers. Many methods have been developed to estimate this effect, but modal analysis of soil-structure systems is one of the most popular techniques due to its simplicity and better insight. Due to this reasons, modal analysis found its place in codes and provisions such as NEHRP. Presence of soil beneath the structure not only would alter the natural periods and damping ratio of structure but also would impose some new vibration modes to the system due to soil’s degrees of freedom. Consequently, response of structure is a combination of the effects of all these modes. But, in practice,... 

Usually the structures are designed based on the fixed-base assumption; however this assumption is not always correct and the bed flexibility should be considered. This effect which is called soil-structure interaction, change the response of structure on both elastic and inelastic behavior. In the regulations for the design of structures on flexible base, generallysoil-structure system is replaced with an equivalent fixed base structure; in the way that the design force of soil-structure system with reasonable accuracy can be estimated by equivalent fixed-base structure. In some regulations, dynamic characteristics of equivalent structure have been determined on elastic state and the... 

Dynamic characteristics of structures—viz., natural frequencies, damping ratios, and mode shapes—are central to earthquake resistant design (model validation) and health monitoring. For civil structures like buildings and bridges, these characteristics can be highly influenced by surrounding soil in addition to the super-structure’s properties and cannot be correctly estimated using numerical modeling. For example, soil’s flexibility decreases the natural frequencies of the system; and in most cases, soil provides additional damping due to material hysteresis and radiation. On account of this fact, system identification techniques must be applied to extract such information from field data,... 

In conventional method of modeling and design of structures it is assumed that structures are fixedly supported, however, this assumption is generally far from reality; because, not only the majority of buildings’ bases are not stiff enough to suppose them rigid, but also if their foundations are shallow there exist no piles underneath them, they may separate from their bases – the event which is called foundation uplift. Although according to past studies permission of foundation uplift as well as incorporation of base flexibility may markedly affect any structure’s dynamic response, is spite of about half a century which has elapsed since the beginning of these studies, it seems that still... 

In the last few decades Seismic Regulations attitude’s has been undergone significant changes from various aspects. One of these aspects is entering new topics based on the latest scientific achievements. Soil-Structure Interaction terms was from such issues which had found their ways into Seismic codes as an optional effective factor. In recent years, Based on this new attitude and Scientific achievements, Soil-Structure Interaction terms entrance into Iranian seismic code (2800 Standard), is also has been studied. Naturally, applying these criteria will impact on the design and performance of structures, because of reducing effect of soil structure interaction on decreasing base shear... 

Usually the structures are designed based on the fixed-base assumption; however thisassumption is not always correct and the bed flexibility should be considered. This effectwhich is called soil-structure interaction, change the response of structure on both elasticand inelastic behavior. In the regulations for the design of structures on flexible base,generally soil-structure system is replaced with an equivalent fixed base structure; in theway that the design force of soil-structure system with reasonable accuracy can beestimated by equivalent fixed-base structure. In some regulations, dynamic characteristicsof equivalent structure have been determined on elastic state and the results have... 

Since the early 1980s, it is well-known that the dynamic properties of structures are effected by flexibility of the underlying soil due to Soil-Structure Interaction (SSI). As a result, the soil-structure systems usually has a longer natural period and higher damping ratio that structure would have in the fixed-base state. The importance of SSI effect as well as the complexity of the phenomenon have made it the subject of several researches for the last four decades. It also has found its way into some seismic codes and provisions as simplified guidelines.In the present paper, a simplified 3DOF model is suggested as the soil-structure system by replacing the structure by a SDOF model using... 

Regarding to the value and the modeling, damping has remarkable effect on the response of the systems. More over the structural damping the soil damping also exist in the soil-structure systems. Damping resources in soil include material damping and radiation damping. The high amount of radiation damping in some cases have been led to paying less attention to material damping in some studeis. Although in many cases this is not true and in systems with little radiation damping the material damping could be really important. Generally the role of soil damping depends on the properties of the structure. On the other hand in structures with multi-degree of freedom, soil existence affects the... 

It is well-known that the behavior of soil-structure systems can be well described using a limited number of non-dimensional parameters. This is the outcome of researches based on the premise that the foundation is bonded to the ground. Here, it is shown the concept can be extended to systems with foundation uplift. A set of non-dimensional parameters are introduced which controls the main features of uplifting systems. The super-structure is modeled as an equivalent single-degree of freedom system with elastic behavior mounted on a rigid foundation resting on distributed tensionless Winkler springs and dampers. The effect of foundation uplift on response of soil-structure systems are...