جستجوی مقالات مرتبط با کلیدواژه « RC MOMENT FRAME » در نشریات گروه « عمران »

In procedure for analysis, design and optimization of reinforced concrete buildings, for most or maybe all regular buildings, different parts of the procedure for different parts of the building, including main structure and its foundation, are usually carried out independently. This means that these structures are mainly analyzed and designed by supposing a fixed-base, and then, forces at the foot of columns are obtained and used to analyze and design the foundation. Thereby, no attention is paid to the effects of foundation settlements on the distribution of forces in structural elements. Interaction between the structure, the foundation and its subsoil (flexible-base), changes the actual behavior of the structure compared to the method in which the structure is investigated alone (fixed-base). In this paper, various RC buildings, including low-, mid- and high-rise types, with foundations and soil under their foundations in three different layers, with a depth of each layer equal to ten meters, are modeled using SAP2000. Also, all the frames are optimized using Artificial-Bee-Colony algorithm in MATLAB, subject to stress and drift constraints. The results show that, since in a structure with optimal design the values of stress in elements and drift of stories are usually very close to the maximum allowable limits, hence, a slight increase in structural response, induced by soil-structure interaction effects, may lead to the violation of optimal design constraints. Therefore, taking not into account such effects in design optimization of structure, may lead to not only a non-optimal but also an infeasible design.

In this paper, the seismic response of base-isolated and fixed-base concrete structures with soil-structure-interaction effect was investigated. The structures with 4, 8, and 12 stories with lead rubber bearing isolators on three types of soils including soft, medium, and firm soils as well as on rigid foundation modeled using OpenSees software v 2.5.0. The ACI 318-02 code was used to design of RC intermediate moment frames. The incremental dynamic analysis was performed to determine the structural response under six near field and six far-field earthquakes recorded with the same seismic parameters but with different stations. The inter-story drift ratio and failure probability for each level of damage (slight, moderate, extensive and complete) were calculated and the fragility curves for maximum inter-story drift in different levels of PGA were drawn. The results indicated that considering the soil-structure-interaction decreased the structural damage on both isolated and fixed base structures. Softening the soil under isolated structures resulted in increasing the median fragility acceleration in each level of damage. Furthermore, considering the soil-structure-interaction effect in the low-rise to medium-rise structures (4 and 8 story buildings) has a more significant effect on median fragility accelerations than high-rise buildings. While, the effect of the base shear on the 12-story frame was more considerable.

Progressive collapse can be caused by the failure and instability of a small part of the structure that gradually develops as a chain function and eventually leads to collapse of an important part of the structure. Progressive collapse may happen due to explosion, fire, earthquake, vehicle collision and errors in design and construction of building with any system type. Reinforced concrete (RC) load bearing wall system is one of the appropriate structural systems for average height buildings that Based on the number of walls in plan and reduction in lateral force contribution, this system in addition to its strength against earthquake, according to volume of construction materials is economic. It can be constructed with high speed, accuracy and quality. In this thesis, the effect of progressive collapse on RC load bearing wall system has been studied and its performance is compared to RC moment frame. For this purpose three-dimensional models of 10-story structures with the same plan in both systems, have been selected. The effects of geometric and material nonlinearity are considered and cross sections are modeled by fiber elements. To ensure the accuracy of modeling by fiber section method, the analysis results are validated by an experimental model of RC load bearing wall. .

Natural hazards and human activities bring about overall or local ground subsidence. Predicting the effects of large differential settlement on response of structural frames, especially in congested urban areas, is a main issue in design process as inadvertence can lead to irrecoverable human and financial losses. In order to better understand the consequences of the subsidence phenomenon on the superstructure, a three dimensional reinforced concrete (RC) moment frame designed according to the current Iranian codes of practice is analyzed due to six separate nonlinear analysis cases considering three locations for the increasing differential settlements (under corner, exterior, and interior columns) as well as two support conditions (fixed and flexible); Various results including change in pattern of bridging beam bending moments, axial force redistribution in columns, and also maximum tolerable elastic and inelastic settlements are evaluated. Based on the findings of the numerical models, although cases with the settlement imposed under an interior column have the least vertical downward displacement at formation of first plastic hinge in a beam compared to corresponding cases, the highest capacity to bear differential settlement occurs due to one of the cases of a corner column location. Moreover, formation of plastic hinges and redistribution of axial forces in first-story columns are highly affected by the modeled support conditions.

Sequential quakes as shock-aftershocks result in nonlinear response of buildings and in many cases lead to severe destruction such as accumulative structural damages in compare to single shock quakes. In current study, the shock-aftershock sequence effect on the nonlinear seismic performance of reinforced concrete (RC) moment frames is studied in detail. In this way, nonlinear numerical method is selected as the study approach and preliminary models are calibrated based on existing shake-table experiments. In advance, four-story and eight-story frames are modeled using flexibility-based finite element code and are subjected to quake sequences. Three types of seismic sequences are assumed for study: (1) single shock quakes; (2) similar shock-aftershock quakes; (3) dissimilar far field-near fault shock-aftershock quakes. Discussions are based on the maximum and residual inter-story drift ratios. Results reveal that the residual drifts are increased in seismic sequences. In addition, four-story frames experience higher maximum drift ratio than the eight-story frames during the aftershocks. The increase of residual drift ratio in more apparent for four-story frames than eight-story frames in the case of dissimilar seismic sequences. For all the assumed cases, top stories experience the highest values of maximum and residual drift ratios which show the sensitivity of top stories to the seismic sequence. Thus, the collapse probability of top stories is high during shock-aftershock sequences and needs to be considered in further seismic design.