Sharif Digital Repository

The use of braced frames has become more popular in seismic design of buildings because of the simplicity in design and construction. The first event that occurs in the earthquake for a concentrically brace frame (CBF), is the buckling of the strut. The inelastic behavior of CBF systems is dominated by brace buckling, yielding and the post buckling behavior. The Inelastic performance of the brace is nonsymmetrical, because of the difference in the tensile and compressive strength of the brace and the deterioration in the resistance after buckling. so we have too complexity in modeling the inelastic performance of brace members. Also the subject of the near fault ground motion and design of... 

Iran plateau is situated over the Alpide-Himalaya earthquake belt. Tectonic studies indicate that this plateau has a very high density of active and recent faults; as a result, Iran is at risk of damaging earthquakes. Experience of past severe earthquakes shows previous designed structures do not have enough strength instead of real earthquake forces, therefore vulnerability study of existing structures and give a technical and economical retrofitting plan of them is required. Conventional methods of seismic rehabilitation for example using concrete shear walls or steel braces are not suitable for some buildings. Nowadays, passive control systems have been successfully used for reducing the... 

Structures face various loadings and confront different circumstances as they are built and used. This situation causes the aging structures to deteriorate, which would lead to a decrease in reliability and safety. In the recent decades, the need for systems to assure the integrity of structures in terms of their age, usage and level of safety when experiencing infrequent and extreme forces such as earthquakes, tornados, hurricanes, large waves has deeply been recognized. These systems are often referred to as structural health monitoring (SHM) in the literature. The main objective of such system is to increase reliable operating lifetime. In the case of offshore structures, utilizing... 

A structural system will normally fail as a result of a chain of failures of different components. In this thesis, fatigue reliability of fixed offshore platforms is investigated through analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, each failure scenario is divided into a finite number of sub-scenarios. To do this, all combinations of time sequences are generated for a given sequence of failures, using a specially developed program.
In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. Knowing that there are a large number of... 

This thesis encompasses a number of issues in earthquake engineering which may appear quite diverse in nature. Several methodological aspects of both conventional and novel approaches to probabilistic seismic hazard assessment are discussed here along with subjects more strictly pertinent to structural and geotechnical engineering. This work, however, has a unique, ultimate goal: to provide procedures for an effective and practical probabilistic estimation of structural demand of offshore platforms due to seismic ground shaking. In modern multi-level design and rehabilitation procedures, structural performance is in fact quantified by deformation demand levels exceeded with a specified... 

Assessment of existing jacket type offshore platform against environmental wave loading hazard is the central component of this work. Two general approaches exist in this context, deterministic and probabilistic assessment. In this study, a new probabilistic method (reliability analysis) to assess offshore structures under environmental loading (extreme wave) is introduced. Before describing this approach, several necessary elements such as collapse analysis, sampling methods and wave hazard analysis should be investigated. First of all, deterministic assessment of SPD2 platform located in Persian Gulf, which is the case study considered in this dissertation, is conducted utilizing... 

One of the most important elements of performance-based seismic engineering elements is precision in determination of seismic displacement demand evaluation. Although seismic demands which are estimated by utilizing non-linear dynamic analysis are most effective, but with regards to inherent complexities of these methods and demands for time-consuming calculations , non-¬linear static methods seems to be an appropriate representative and is recently considered by engineers. In countries with oil resources including Iran, offshore jacket platforms are among outstanding structures being considered. Inasmuch as high design and execution expenses of these structures and also important role of... 

In this thesis, a novel probabilistic framework named Probabilistic Spectral Fatigue Analysis (PSFA) will be introduced for the purpose of assessing the performance of jacket offshore platforms under high-cyclic short-waves fatigue degradation. This method can take into account the uncertainties in three main elements consisting of material properties, sea state parameters and collapse capacity of structure. The main advantage of PSFA approach is the ability to recognize the fatigue failure scenarios and specifies the limit state function of critical members as a super-branch or sub-branch of those scenarios. Therefore, a new and accurate method is proposed for combination of scenarios’... 

Ground motions in close proximity to the causative fault of an earthquake can be significantly affected by the propagation of rupture. In particular, when the rupture and slip direction relative to a site coincide and a significant portion of the fault ruptures towards the site, the ground motion can exhibit the effects of Forward-Directivity (FD). Pulse-like near-fault ground motions resulting from directivity effects are a special class of ground motions that are challenging to characterize for seismic performance assessment. These motions contain a pulse in the velocity time history of the motion, often occurring in the direction perpendicular to the fault rupture at locations near the... 

One of the most common failure modes of structures in earthquakes is soft story failure which causes by discontinuity of lateral force resisting elements like braces. so the ground floor acts as a soft floor. In this case columns are imposed to large deformation and plastic hinges are formed at top and bottom of the columns. This case is named as story mechanism (severe drift of the story). In most of this case building collapsed or going to collapse. To resolve this problem, different solutions are presented. One of the strategies under section (2-10) 2800 code is increase of designed load in columns of the soft floor. This measure cause to Significant increases in the sections of the... 

In order to improve the performance of structures against earthquake loads, engineers believe that both minimizing the rigidity and maximizing the ductility; can lead to minimization of the energy input of the structure. However, the minimized energy shall be depreciated as much as possible in different stories so that the damage to the main and Irreplaceable structural members remains as low as possible.
Steel with high strength and ductility is relatively an ideal material for this purpose; however, the ductility level of this material is much higher than that is normally in use. In order to have a better utilization of the steel ductility, RBS (Ribbed Bracing System) was invented in... 

Since oil is the essential foundation of Irans economy and our country has access to deep water, the extraction of oil from the deep water is essential to our country. So far, due to the possibility of oil exploration in the shallow water of the Persian Gulf, need to invest in deepwater oil industry has not been one of the priorities. However, it seems that in the near future we will need to invest in deepwater. Among subsea structures which we need to use to extract the oil in deepwater, we can mention wellhead manifolds that are used to expand the oil field, optimisation of pipeline length, gathering and distribution of production and injection of water or gas into the wells. In some cases... 

Employing dampers to control wave-induced and seismic vibrations of offshore jacket platforms is an attractive method in order to mitigate fatigue and seismic damage. However, adjustable parameters of a damper are designed by considering only one type of environmental loads; either normal-condition load or extreme-condition load. So, it is important to investigate effectiveness of damping system, for both of two main categories of environmental loads. Also it is ideal for the system to have an acceptable performance in both normal and extreme conditions. The idea investigated in the current study is to use a friction damper device (FDD) and a tuned mass damper (TMD) simultaneously in... 

Offshore platforms are of the economic life lines of oil rich countries. These infrastructures are located at severe environmental conditions, their construction and installation involves expense and these justify utilization of these structures with novel auxiliary vibration control device. Two passive vibration control systems have been evaluated in this study aiming to fatigue damage mitigation in offshore steel jacket platforms. Performances of tuned mass damper and friction damper to suppression of wave induced vibrations in fixed offshore platforms have been investigated in this study. Due to the random nature of ocean waves, a fully stochastic analysis method has been used to evaluate... 

High construction and installation costs of offshore platforms, and also harsh environments in which they operate, make health monitoring of these structures more important. Conventional methods to solve the health monitoring problem are deterministic, whereas much uncertainties are imposed to the problem. In most methods of health monitoring methods we try to identify natural frequencies and mode shapes of structures by using its dynamic response. This set of data is then compared to results of modal analysis performed on a finite element model of structure in order to detect any possible damage. In deterministic methods each response of structure is pertained to one damage state, in a... 

Offshore platforms are the most important and enormous wealth of each country that these structures are in situation thatthelikelihoodof damageinhigh. With considering this pointthatplatformsaresubjected to oscillatinglateralloads, so the occurrenceand growth offatigue crack sinthe misvery common. These cracks are always seen in jacket connections, cause these connections are bearing large forces and have massive welding and the presence ofresidualstresses. The fatigue crack caused negligible change in stiffness of connections and in consequence insignificant change in stiffness of structure; So for this reason, they are difficult to detect in global methods. Fiber optic sensors and... 

Assessment of existing jacket type offshore platforms in Persian Gulf for life extension is of great importance in the field of offshore platforms in recent years. The main question to answer is whether an existing platform is safe enough to be used beyond the design life. Evaluation of existing jacket type offshore platforms under extreme environmental (wave) loading in Persian Gulf is a part of this major assessment. Two general approaches exist in this context, deterministic and probabilistic assessment. In this thesis, a new probabilistic method (reliability analysis) to assess offshore structures under environmental loading (extreme wave) is introduced. This method is a... 

Jacket type offshore platforms are classified as expensive and also strategic structures, and the cost of their maintanace is considerable. Therefore, any inspection and retrofit plans for life extension of the existing structures is economically and logically preferable rather than making decision for design and construction of new structures. The first stage of assessment plan is monitoring the performance of structure during critical loadings for which the structure is designed. One of the critical loads that should be considered in assessment of jacket structures is seismic loading. Due to dynamic nature of the applied loads in seismic assessment of jacket structures the accuracy of... 

In this thesis several methodological aspects of both conventional and novel approaches to probabilistic seismic hazard assessment are discussed here along with subjects more strictly pertinent to structural and geotechnical engineering. This work, however, has a unique, ultimate goal: to provide procedures for an effective and practical probabilistic estimation of structural demand of offshore platforms due to seismic ground shaking.In modern multi-level design and rehabilitation procedures, structural performance is in fact quantified by deformation demand levels exceeded with a specified annual frequency of structural life. We refer to this as Probabilistic Seismic Demand Analysis (PSDA).... 

Assessment of existing jacket-type offshore platforms in Persian Gulf for life extension or operative conditions is a major concern for oil offshore companies in recent years. Significant damage to offshore platforms as well as their contents will induce significant losses such as financial losses, fatalities and casualties. On the other hand, extreme waves or earthquakes are low-probability, large-consequence and large-uncertainty hazards that can affect these critical facilities; therefore, the assessment of existing offshore platforms subjected to each of these sources can be successfully carried out by a probabilistic approach. In this dissertation, a unique probabilistic...