نشریه مهندسی سازه و ساخت
پیاپی 1 (زمستان 1393)

Public private partnership has been used extensively in both developing and developed countries in delivering various types of projects, ranging from transportation projects, health care facility and power plants. The high speed rail projects which implemented by public private partnership in recent years has faced with difficulties. This paper aims to develop an identification and assessment method for critical risks of public private partnershiphigh speed rail project in Iran. In this research at first, risks of public private partnershiphigh speed rail projects are identified by integration of extensive literature review and Public private partnership high speed rail project experience in Iran and other countries. In the next step, the identified risks are assessed by questionnaire survey and multivariate statistical analysis. Analytical investigations show that the number of critical risks in high speed rail projects and their mean importance is higher than that of general public private partnership projects. In this study in addition of confirming pre identified risk groups consisting political and financial groups, two major groups of initialisation and contractual risks specific to high speed rail projects are identified and two groups specific to developing countries named circumstances and private risks are proposed. Because of insufficient studies and lack of experience in developing countries about transportation mega projects via Public private partnership this study can be a helpful reference for public private partnership implementation of high speed rail mega projects in developing countries.

Due to earthquake science advances, the prediction of probable earthquake intensity in different regions is approximately possible. But it is not possible to predict the time of earthquake occurrence, so there should be considered some other measures to have the lowest losses during this natural event. This research aims to predict the losses and damages caused by the earthquake and to utilize statistics and population structure using SELENA software. HAZARD US method is used in this study. In this method, the response curve achieved based on soil type and IBC-2006 standard and damping effect of structures listed on the FEMA 440 approach is applied. The results show that because of old structures and population density, the fabric of the old city including regions 1 to 4 and 10 to 12are more vulnerable.

Having very simplicity, nonlinear static procedures (NSPs) are the most popular tools for estimation of structural capacity. These approaches construct a graphic display of the overall structural response via a pushover curve. The overall response of the system provides a direct simulation of the building as single degree of freedom (SDOF) system that simplifies the design and evaluation of the structure. In this research, the first step in any nonlinear static analysis or in other words perform a pushover analysis has been studied. Applied lateral load to the structural model not only affects the overall responses of the structure through structural capacity curve, but also directly affects the local responses of the structure. In order to evaluate these lateral loads, steel buckling restrained braced frame structures are examined by advanced modal pushovers. Next, the results of these pushover analyses will be compared with nonlinear time history analysis as the most accurate method. Finally, the most efficient method in this particular structure is introduced. The analysis conducted in these structures shows that the lateral load pattern based on story shears offers a good prediction of the maximum response of the concentrically buckling restrained braced frame buildings.

Usually structures are designed under codes based on the assumption that the soil stiffness is infinite, so the foundation rests firmly on the soil. In many cases, the overturning moment due to the lateral forces may exceed the resisting moment due to the gravity forces. Thus, this may cause a foundation uplift because in reality the soil stiffness is not infinite and the structure stands up under gravity forces. The phenomenon of foundation uplifting and its impact on the soil are known as the rocking motion.This study investigates the influence of the rocking motion and interaction by the yielding base plates on the nonlinear behavior of steel structures under dynamic analysis. More specifically, Three- five and seven -storied structuresare designed with ordinary ductility, then the structuresare analyzed in rigid and deformable base plate cases with using the ABAQUS software.The results show that the rocking motion and Interaction decrease the response of buildings such as the base shear, the axial force of columns and the strain energy but also increase the natural period.

Common attenuation equations are developed by seismic records which belong to earthquakes that have happened so far. Although there are many recorded data during last 50 years, it is not possible to consider all possible wave propagation paths, site types and fault rupture mechanisms inclassical attenuation relations. This fact becomes more serious in near field cases and a common shortcoming in most attenuation equations is their low accuracyin estimation of near field parameters.Many important cities of the world such as Tehran are located nearby some active faults. For example, the North Tehran Fault is such a closeseismic source to Tehran Metropolitanarea andcould be considered asa near field source. Therefore, it is necessary to evaluate near field effects in most of hazard analyses, risk management programs, structural designs, etc.In past, it was routine to use attenuation equations in hazard analyses. In this project for avoiding from insufficient performance of attenuation equations in near field, proposed simulation datum byZafarani, et al., (2012), were used directly in the hazard analysis without converting them into attenuation equations.Besides, time dependent hazard analysis (Non-PoissonianModel) was used to taking into account the probable seismic activity of the North Tehran Fault.

In risk allocation process, it is not correct to pass the whole responsibility of some risks to the contractor. The reason is that some defensive strategies such as lowering the work quality and lodging claim and litigation may be implemented by the contractor that may increase the project cost and duration. It is therefore necessary to share the responsibility of these risks between contracting partiesandin the other words to perform the risk allocation process quantitatively. In the negotiation process performing to determine the percentage of risk allocated to each of the contracting parties, there exists a willing to cooperate and reach an agreement in spite of the existed conflicts in the revenues of these parties. In this research, the game theory that is the study of mathematical models of conflict and cooperation between intelligent rational decision-makers is used for quantitative risk allocation. The proposed model presents a powerful tool that satisfies desirable criteria such as efficiency and fairness and the equitable percentage of risk allocation is determined. To evaluate the capabilities and performance of the proposed model, it is implemented in sample project and the risk allocation percentage between the client and contractor is determined for one of the identified risks.