پژوهشنامه زلزله شناسی و مهندسی زلزله
سال شانزدهم شماره 1 (پیاپی 59، بهار 1392)

There are many parameters that influence the dynamic response of structures in contact with fluid medium. One of these parameters is the direct effect of reservoir، especially for high structures during severe earthquakes، so there are an extensive amount of publications about the analysis of fluid-structure interaction systems in different engineering branches. In this research، studies in the field of civil engineering with an emphasis on dams will be considered. The different methods of analysis of the fluid-structure interaction problems are reviewed and then some case studies for structures such as retaining walls، concrete، CFR and embankment dams، are discussed. Due to the development of numerical methods in recent years، the studies done using such methods are considered with more emphasis. However، analytical methods such as Westergard and Chopra cases are presented and discussed in this paper. Studies in the field of concrete dams are presented in two divisions as modeling approaches and boundary condition effects. Then the studies about the seismic interaction of reservoir-CFR dams are presented in the related section. Also analysis of seismic coupled reservoir-structure systems for a concrete dam and a CFR dam، which have been conducted by the authors with ADINA software، are presented and compared with the results of the previous studies. This comparison shows the accuracy of the results of ADINA software in the field of dynamic coupling of water-structure systems for concrete and CFR dams. Finally، the previous studies for the dynamic interaction of embankment dam-reservoir system are presented and the related results are discussed. It is concluded from reviewing the previous study that the amount of hydrodynamic force in the fluid domain is a function of the frequency content of incident seismic wave and the ratio of the natural frequency of dam to reservoir one. Therefore، there is not a certain height restriction for unconsidering the effect of interaction of reservoir-dam. Also، if the frequency content of energy of seismic wave is less than the natural frequency of reservoir، the effect of considering the coupled water-structure system would be less. Consequently، the final results of such system would be less affected by the reservoir. As another result، if the ratio of the natural frequency of reservoir to dam is almost «2»، the interaction of reservoir-structure has no considerable effect on the final seismic response of coupled system. In the special case of CFR and embankment dams، there are fewer researches in comparison with concrete dams. The main reason can be related to the low slope of upstream face of the dam which reduces the hydrodynamic force of the reservoir. But there are not sufficient available researches that improve the accuracy of such arguments in many different conditions of incident wave (magnitude of PGA، the frequency content of seismic wave، spatial ground motion condition)، and variation of some parameters such as per- meability coefficient of shell materials، height of dam، and slope of upstream face. Therefore، it seems that in the future، more studies should be done in the field of embankment dam-reservoir coupled system.

Infills are normally used in buildings for architectural purposes. It has been shown that they have considerable influences on stiffness and strengths of the structures. However، their effects are just considered as 20% reduction in the building natural period of vibration and other global and local structural effects are normally ignored in analysis and design phases. Experience of previous earthquake shows that infills have significant influences specially on connections of the surrounding frames. Some failure modes of connection on during previous earthquakes are shown in this paper. Harmful influences of infills on connections are investigated in this paper، specially for simple connections with seat angles as well as for saddle connections. Simple connec-tions having flexible seat angle is very common in steel structures. In this kind of connections، the beam is placed on an angle which transfers the shear of the beam to the column. Another angle is applied on top of the beam as well to prepare lateral support for compression flange of the beam. This angle is normally designed only for 10% of the shear force that applies on the bottom angle or even not designed. Behavior of simple connections، with seat angles، in bays having infill walls shows that the infill reaction force practically applied to the connection، is greater than the assumed one of the designing phase. The local force of the infill to the frame may cause large and residual displacement or even failure in the connection weldings. In this regard، saddle connections، in which the beam is connected to the column by two angles at the top and the bottom، is similar to seat angle connections and may be affected by infill panels. Furthermore، the saddle connections may have a considerable twisting moment as well. In this paper، the influence of infill walls on the loads of such connections are investigated and some suggestions are proposed for their safety in earthquakes. The obtained results and formulas of this paper can be applied for designing of new buildings with simple or other types of connections، and seismic rehabilitation of existing buildings for considering infill panel effects. In this regard، some formulas of the literature for estimating the applied load of the infill to the frame are discussed. Then an example is solved to show inadequacy of connections، which are designed based on the codes، in which influences of infills are ignored. Subsequently، a formula is presented to estimate the applied loads on the connections.

Given the incidents occurred around the world، it has been identified that due to the different characteristics of blast loads، the behavior of structures under these loads are not the same as the other loads. Because of the strategic privileged position of most cities of Iran and rich natural resources، external threats are exposed. Hence، structural engineers need to understand the risks and how to deal with such terrorist attacks and suicide bombings. Building structures should also be designed for such dangers. In many earthquakes and blasts، most of the deaths have occurred due to collapsing of buildings than due to any direct effect of the earthquakes or blasts. Therefore، it is of primary importance to ensure that buildings will not collapse which requires a considerable enhancement in the ductility of the building. The behavior of structures against impulsive loads is affected by structural charac-teristics that are also important for seismic resistance. Deformability، strength، stiffness، and stability of the structural framing system and elements and resistance to progressive collapse are factors that play important roles on the stability of buildings under both blast and seismic loads. The significance of these structural parameters on blast resistance of reinforced concrete buildings should be assessed through structural analysis. Due to the special position of reinforced concrete in the construction industry، widespread use of moment resisting frame systems in building structures and vulnerability of this type of building systems against blast loads، the objective of this study is to evaluate the exact response of a seismic rehabilitated nine-story reinforced concrete building to the impact load. Assuming the structure is located in an area with high seismicity، first، the building is rehabilitated under the seismic forces، then، the rehabilitated building is subjected to the blast load. Two strengthening scheme، including strengthening of reinforced concrete frames and strengthening with adding shear walls are proposed. Each strengthening plan is then analyzed for its response to the blast loading. The blast and progressive collapse analyses demonstrate that the strengthening plan of moment resisting frame would significantly reduce the amount of blast-induced damage and subsequent progressive collapse، compared with the response of the original building. The results also show that the strengthening plan with shear walls is effective but compared with the strengthening of moment resisting frame is less effective in reducing blast and progressive collapse damage. It can be seen that strengthening of perimeter elements enhanced the performance of the building subjected to blast loading.

Due to both topography and economical conditions، the construction of skewed bridges is being more popular all around the world and thereby their design become of paramount importance among structural engineers. The most vulnerable bridge type in a transportation network is skew bridge. Because of its geometry، the response of the skew bridge during earthquake is more severe than for a straight bridge with identical mass and dimensions. The skew bridges have coupled response in global co-ordinate system and the seismic response increases with the increase in skew angle. Skewed bridges are often encountered in highway design when the geometry cannot accommodate straight bridges. These bridges are found to be quite susceptible to severe damage during past earthquakes. When the skew angle gets large it can significantly alter the response of the bridge. Investigative reports on the 1989 Loma Prieta and 1994 Northridge earthquakes in California indicated significant damage experienced by skewed highway bridges. In both earthquakes، less than five percent of the bridges exposed to ground shaking were damaged. Specifically، the damage sustained by the Pico-Lyons Bridge near Newhall، California، was noted to have been triggered by the skewed geometry of the bridge. The study showed that cases in which the angle of skew is approximately 40°، the percentage increase in stress due to the skewness effect at the end girders can be as high as 50–60%. Although the static and dynamic behavior of skew bridges has been investigated by various researchers، some phenomena are yet to be defined. This study focuses on evaluating the seismic behavior of typical single-span skewed concrete precast girder bridges by taking into account the variation of deck geometrical characteristic including length، width and the bridge skew angle. The main objective is to investigate unseating of the bridges subjected to seven sets of ground motions. The three-dimensional nonlinear finite element models of bridges using the CSI’s most renowned software، i. e. SAP2000 were developed and nonlinear time-history analyses were performed. The results indicate that by increasing the skew angle the unseating occurs due to combination of displacements in longitudinal and transverse directions، whereas for non-skewed bridges or the bridges with a small skew angle، the deck doesn’t experience significant rotation or permanent transverse displacement and only longitudinal displacement causes the deck to become unseated. It was found that for 60-degree skew bridges despite the fact that the bridges experience less longitudinal and transverse displacements، the superstructure undergoes significant rotations about the vertical axis and is permanently displaced laterally from the original location. Thus، by increasing skew angle the higher magnitude of deck rotation causes the deck to become unseated rather than the displacements and the deck rotation built up during the initial peak cycles of shaking of all input ground motions.

In this research، for the purpose of nonlinear analyzing of RC columns and investigating the bar’s buckling، separate degrees of freedom are used for the reinforcing bars and concrete to allow for the difference in displacement between the reinforcing bars and the surrounding concrete. The capacity of the reinforced concrete (RC) sections was formed based on the interaction between reinforcing bars and the surrounding concrete. Contact between concrete and the longitudinal bars is provided by a bond force around the bars. A computer program is created in MATLAB software. For modeling a column element، a length segment of an RC element is considered as the combination of a length segment of a 2-node concrete element and a number of steel bar elements. Contact between concrete and the longitudinal bars is provided by a bond force around the bars. The buckling effect is considered in the numerical modeling of the bars. Buckling of longitudinal reinforcement has more important role in the behavior of RC members by increasing the stirrup spacing. The weak form of displacement based finite element formulation is determined and the ability and reliability of the numerical method has been assessed through the verification of numerical and experimental results. The buckling effect of longitudinal bars on the nonlinear pushover and cyclic behavior of the RC columns is investigated. Also، in the presence of buckling effect، a comparison is carried out between numerical capacity calculated from analysis and ultimate capacity calculated from ACI criteria. Several numerical analyses were carried out and the capacity of the stocky columns is investigated. The results show، that in pure axial compressive force condition، the numerical capacity with buckling is only about 4% lower than that obtained without buckling. Based on ACI criteria، the nominal capacity (calculated capacity without strength reduction factor φ) is conservative and less than numerical capacity. The ultimate capacity of the section (calculated capacity after applying reduction factor φ)، which represents the ultimate design capacity، is more conservative. In pure bending condition، the numerical capacity with buckling is only about 2% lower than that obtained without buckling. Based on ACI criteria، the ultimate capacity is conservative and less than numerical capacity. In the presence of axial force with eccentricity، the numerical capacity with buckling is about 10% lower than that obtained without buckling. Based on ACI criteria، the ultimate capacity is conservative and ensures less than numerical capacity. The results show that، bar''s buckling has considerable effect on the capacity. But، the fact that the beneficial effect of stirrups confinement on the concrete compressive strength is neglected in the ACI criteria for capacity estimation، and also the use of the reduction factor φ، does not make any modification necessary for considering buckling effect on the ultimate capacity of RC section calculated by ACI criteria، since the results are conservative anyway. However، buckling of reinforcing bars has considerable effect on the ductility and strength reduction rate in the post-yielding state. This effect will be more by increasing the bar’s percentage of the RC sections.

The purpose of this paper is to identify the strengths and special needs of women in the natural disasters (with especial emphasis on earthquakes) and applying the feasibility of these in a future possible earthquake in the Islamic Republic of Iran. The present study is based on literature review and brainstorming meetings with women who have suffered the Bam earthquake on December 23، 2003 in Bam and others who have been affected in different ways. The above constituted the main source of information for this research. In this regard، four meetings with number of active women within of the NGO organization (Charity organization of Ban followers)، advisor to Bam governor in women’s affair and members of Red Crescent of Islamic Republic of Iran have been organized. In each session 10 to 15 women participated and four principles of brainstorming meetings were emphasized by team leaders: thought should be focused on quantity contents، with no criticism of each other، accepting unusual ideas and improving new ideas in each session. Immediate needs of women after Bam earthquake were listed in each session and، and methods of providing the needs by disaster management authorities were discussed، and finally recommendations were presented. After the Bam earthquake، many items and primary needs of affected people have been distributed by volunteers or rescuers without considering their needs. In this study، in order to understand women''s needs after an earthquake; women''s empowerment; women clothing; health; pregnancy and lactation; cosmetic needs; mental and psychological effects of earthquakes on women، security during temporary sheltering and the way women can cooperate after a disaster event have been discussed.