Sharif Digital Repository

The effect of inertial forces on the Structural Dynamics (SD) behaviour of Elastic Flapping Wings (EFWs) is investigated. In this regard, an analytical modal-based SD solution of EFW undergoing a prescribed rigid body motion is initially derived. The formulated initial-value problem is solved analytically to study the EFW structural responses, and sensitivity with respect to EFWs' key parameters. As a case study, a rectangular wing undergoing a prescribed sinusoidal motion is simulated. The analytical solution is derived for the first time and helps towards a conceptual understanding of the overall EFW's SD behaviour and its analysis required in their designs. Specifically, the EFW transient... 

The Endurance Time (ET) method is a time-history based dynamic pushover procedure for seismic analysis and design of structures. In this procedure, structures are subjected to a specially designed intensifying accelerogram and their Endurance Time is measured based on the time interval during which they can resist the imposed dynamic actions. In this paper, application of the ET method in linear seismic analysis of structures has been investigated. The procedure for generating code compliant uniformly intensifying ET accelerograms has been explained. A set of three such accelerograms have been applied to various moment and braced steel frames and the results of analysis are compared to... 

Prefabricated funicular shells were constructed using a stretched membrane as a mould. Forty-five shells with various rises and different types of reinforcement were loaded to failure and their behaviour in the elastic and non-linear range was investigated. The experimental values of membrane and bending stresses in the elastic range along diagonal sections of funicular shells subjected to uniform loading were calculated and compared with the results of numerical analysis. The results are generally found to be in close agreement with theory. Experimental values of vertical deflections along the longitudinal and transverse sections of the shells also compare favourably with the theory. The... 

In the Endurance Time (ET) method, structures are subjected to a calibrated intensifying accelerogram and their performance is assessed based on their response at various equivalent intensity levels. Application of the ET method in performance-based design of structures has been studied by introducing a continuous performance target curve, which expresses the limit of the proper seismic performance of a structure along various times of the ET accelerogram. The correlation between time in the ET method and the return period for different structural periods is investigated. The procedure is based on the coincidence of response spectra obtained from the ET accelerogram at different times and... 

A new method, based on the concepts of matrix analysis as well as the learning capabilities of neural networks, for the analysis of nonlinear trusses under dynamic loading is presented. The method can be applied to static trusses too. While there have been attempts in the past to use neural networks to identify and model different structures based on data measured on structural response directly, the main feature and advantage of this new method is in its capability to model a nonlinear truss by assembling the data collected on the response of its members. The basics of the method are: (1) for each truss member, a neural network is trained to learn and simulate its loadresponse behavior, (2)... 

Localization and quantification of structural damage and estimating the failure probability are key outputs in the reliability assessment of structures. In this study, an Artificial Neural Network (ANN) is used to reduce the computational effort required for reliability analysis and damage detection. Toward this end, one demonstrative structure is modeled and then several damage scenarios are defined. These scenarios are considered as training data sets for establishing an ANN model. In this regard, the relationship between structural response (input) and structural stiffness (output) is established using ANN models. The established ANN is more economical and achieves reasonable accuracy in... 

In this investigation, seismic behavior and design coefficients of the ribbed bracing system (RBS) are evaluated by considering various archetypes that reflect configuration variability. RBS is a lateral bracing system with a unique mechanics that prevents buckling-induced damage by allowing free deformation of brace under compression. After successful experimental validation and numerical evaluation of RBS specimens in previous studies, FEMA P695 methodology is adopted in this study to subject 48 archetype structures to incremental dynamic analysis (IDA) procedure. Evaluation of the probabilistic collapse capacity of the archetypes against the code requirements reveals that RBS system can... 

This paper presents the probabilistic generation of collapse fragility curves for evaluating the performance of 3D, reinforced concrete (RC) moment-resisting building models, considering soil-structure interaction (SSI) by concentration on seismic uncertainties. It considers collapse as the loss of lateral load-resisting capacity of the building structures due to severe ground shaking and consequent large interstory drifts intensified by P-Δ effects as well as the strength and stiffness deterioration of their lateral load carrying systems. The estimation of the collapse performance of structures requires the relation between the intensity measure (IM) and the probability of collapse... 

Various durations of Endurance Time Acceleration Functions (ETAFs) associated with different seismic hazard levels are presented to enable Endurance Time (ET) method for use in probabilistic seismic demand assessment studies. Various Intensity Measures (IMs) were, first, considered for establishing multiple "IM-duration" relationships. A set of 30 RC moment resisting frames were, then, subjected to IDA analysis using 44 ground motion records and the median IM values corresponding to different structural response levels were extracted. These values were compared with the ET-derived IMs by computing the errors corresponding to various demand levels and summating these errors over a complete... 

The endurance time (ET) method is a dynamic analysis in which structures are subjected to intensifying excitations, also known as ET excitation functions (ETEF). The ET method is a tool for structural response prediction. The main advantage of the ET method over conventional approaches is its much lower demand for computational efforts. The concept of acceleration spectra is used in generating existing ETEFs. It is expected that ETEF acceleration spectra increase consistently with time and remain proportional to a target spectrum. Nonlinear unconstrained optimization is commonly used to generate ETEFs. Generating new ETEFs is a complicated time-consuming mathematical problem. If the target... 

The effect of soil conditions on strength reduction factors (SRFs) is investigated. Both site effect and soil-structure interaction (SSI) effect are considered in the study with special emphasis on the latter effect. The structure is modeled as an elasto-plastic single degree of freedom (SDOF) system, whereas the underlying soil is considered as a homogeneous half-space. The half-space is also replaced by a simplified 3DOF system, based on the concept of Cone Models. The whole 4DOF model is then analyzed under a total of 54 strong motions recorded on different soil types. A parametric study is done for a wide range of non-dimensional parameters, which completely define the problem. It is... 

Application of the base-isolation systems, as a means to limit the seismic-induced response of structures, has attracted the attention of many engineers and researchers. Due to their importance, the Uniform Building Code (UBC) has incorporated a special section for the seismic analysis and design of base-isolated structures since its 1991 edition. The present work investigates the vertical distribution of the lateral seismic force for base-isolated structures provided by the 1997 edition of UBC (UBC97). Different 6 and 8-story, 3-D base-isolated structural models with LRB isolators are considered, having a variety of effective periods and effective damping ratios. The UBC97 analysis... 

A new method for seismic analysis of containers in three-dimensional space is introduced in which the effects of both impulsive and convective components and their corresponding damping are accounted for in time domain. A case study is performed to investigate the behaviour of a concrete rectangular container under the effects of horizontal and vertical ground motions using the scaled earthquake components of the 1940 El-Centro earthquake record. Two-dimensional behaviour of the tank is assumed. The results of the study are compared with those obtained using the current practice and those determined from finite element (FE) analysis based on a lumped mass model. The results of the FE... 

The present study aims to reliably quantify the seismic response parameters of steel diagrid structural systems. To this end, in addition to the conventional Static Pushover Analysis (SPA), Dynamic Pushover Analysis (DPA) based on Incremental Dynamic Analysis (IDA) technique was taken into account. FEMA P-695 recommends a methodology for establishing Seismic Performance Factors (SPFs). The objective of the present study was to propose a simpler framework for estimating and validating SPFs while applying the concepts of FEMA P-695 guideline. The results showed that the R factors obtained through SPA procedure for steel diagrid systems were conservative and the IDAbased probabilistic method... 

Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic... 

Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic... 

Recently, various approaches have been introduced to estimate the response of offshore structures in different sea states by stepwisely intensifying records. In this article, a more practical approach entitled Modified Endurance Wave Analysis (MEWA) considering the random and probabilistic nature of wave loading and utilizing optimal time duration is introduced. Generation procedure of this approach is described based on two practical wave theories: random and constrained new-wave. In addition, assessment of a simplified model representing a typical fixed offshore platform under extreme wave conditions in the Persian Gulf is performed making use of MEWA. A comparative analysis has been also... 

Dynamic characteristics of structures - viz. natural frequencies, damping ratios, and mode shapes - are central to earthquake-resistant design. These values identified from field measurements are useful for model validation and health-monitoring. Most system identification methods require input excitations motions to be measured and the structural response; however, the true input motions are seldom recordable. For example, when soil-structure interaction effects are non-negligible, neither the free-field motions nor the recorded responses of the foundations may be assumed as 'input'. Even in the absence of soil-structure interaction, in many instances, the foundation responses are not... 

An effective procedure to incorporate kinematic interaction (KI) aspects in seismic analysis of soil-structures systems was presented. In this regard, first, the effect of KI on the structural response was investigated with special focus on the role of rocking component of foundation input motion (FIM). This was performed parametrically for a wide range of selected nondimensional parameters, which well define the introduced simplified soil-structure model. It was observed that ignoring the effect of rocking input motion may introduce errors, which can be on the unsafe side especially for slender structures with large embedment ratios. On the other hand, it was known that introducing the... 

Damage assessment of concrete arch dams is carried out through nonlinear Incremental Dynamic Analysis (IDA) of a typical arch dam. In this study the Morrow Point arch dam is subjected to a set of 12 three-component earthquakes each scaled to 12 increasing intensity levels. The dam-foundation interaction effects have been investigated by varying foundation's modulus of elasticity to be equal and half of dam concrete's modulus of elasticity. Damage propagation through the dam body is investigated and various IDA curves are created. The performance and various limit-states of the dam structure are examined based on the obtained results. Simple damage indices are proposed through comparison of...