نشریه آنالیز سازه - زلزله
سال چهاردهم شماره 3 (پاییز 1396)

In this study to determine the reduce beam section effect, on intermediate moment frame system behavior and its results, are discussed. For this purpose, non-linear static analysis is used. Generally, two types of structures have been selected in this study, the first 5, 10 and 15-story moment frame and the second with a cross section reduction in beam structures. Since this research has been done using software OpenSEES also to modeling reduce beam section, we used Krawinkler-Ibarra rotational spring model with concentrate plasticity on beams. After verification of RBS for a cantilever beam, this model has been extended to multi degree of freedom buildings. Finally different models have been subjected to incremental dynamic analysis and the results of analyzing the flexural structures of the frame and RBS structures have been used to calculate and extract the fracture curves of the structures and compare them. With respect to the fracture curve graphs of intermediate structures, the probability of colliding the IMF model with the RBS is higher.

The present paper investigates the buckling behaviour of single layer geodesic and reticulated dome form of space structures. For this purpose, three aims have been pursued. Initially, the results of linear and non-linear buckling analysis have been compared by finite element method. Correctness of the utilized finite element method has been checked by results of previous articles, then with description of slenderness factor of dome as geometrical parameter of dome, by investigating the results of non-linear buckling analysis that resulted for domes with different slenderness factors, the rage that general buckling, dimple buckling and member buckling can occur have been determined. The ultimate aim is earning relations for estimating critical buckling load of single layer geodesic and reticulated dome form of space structures. By using these relations, buckling loads of domes could be estimated accurately without any need to time-consuming non-linear analysis and complicated mathematical calculations. In order to achieve to these three goals, the geometrical modelling of structures has been performed by programming at MatLab and coordinates of dome's joints have been determined.

Infill walls are one of the most important elements in the buildings that should be considered in design and construction stages. In architectural design masonry infills are used to separating spaces and areas, but these elements are effective in seismic behavior because of stiffness and strength of masonry infills adjacent to the structural frames. The interaction of masonry infill with concrete frame create short column. Shear failure is a critical kind of concrete column failure that occurs in short columns during earthquake because of low ductility and brittle behavior of these types of columns. It is important to investigate the behavior of short columns. In this paper interaction of masonry infill with concrete frame with 1 bay and 1 story is surveyed. SAP2000 and OpenSees are used for analysis and comparison. The results show that shear reinforcement of concrete columns in ordinary design is not sufficient so plastic hinges form and shear failure happen and increasing in the stiffness and strength of frame because of infill wall should be considered during both the design and construction stages.

Foam concrete is new cover for several usages in building industry that is very useful because of its unique specification. The high value of strength to weight ratio, low Thermal conductivity Coefficient and the high Heat insulation and soundproof ability is the most advantage of this type concrete. In this investigation we use Polypropylene fibers, Synthetic fibers, rice husk ash and nano silica to improve the foam concrete abilities. The fibers are used as additive and rice husk ash & nano silica are replaced as cement. The compressive strength test, tensile strength test and lentgh change test are performed on all foam concretes. Maximum compressive strength belongs to designs containing 1% synthetic fibers and 1% nano-silica. Finally, it was determined that rice paddy ash in 5% replacement has a 9% increase in compressive strength of 28 days and a 17% increase in tensile strength of 28 days. Compressive strength is not affected by Polypropylene fibers in 0.1% and 0.2%, and in 0.3%, compressive strength decreases. Adding 1% of synthetic fiber to concrete foam has 17% growth in compressive strength and 75% growth in tensile strength. Adding 1% nano-silica to foam concrete has a 20% growth in compressive strength and 38% growth in tensile strength. Nanosilica and rice husk ash decreased by 21% and 9% decrease in concrete shrinkage due to decreased absorption of foam concrete. Polypropylene and synthetic fibers cause 6 to 15% reduction in the contraction due to concrete drying.

Structural analysis is very complicated in terms of actual behavior of its connections, and for this reason, by employing the concept of the beam line, certain stiffness is attributed to each connection and thus the connections are categorized. In this research, a semi-rigid connection with stiffener plates is considered in the connection between a beam web and a column. For this purpose, 64 analytical models are utilized, in which the features of stiffener plates, such as height, width, and thickness are changed. There are four variable modes for height, four variable modes for widths, and four variable modes for thickness, making a total of 64 different models. The connections were modeled under a nonlinear static analysis and then the momentum-rotation diagrams were plotted for each mode. So that, the behavior of the semi-rigid connection and the impact of the connecting plates on its performance was investigated. Finally, by comparing the results, a relationship was provided for estimating the rigidity percentage of a semi-rigid connection

In this paper, the redundancy factor at buildings with nonparallel systems irregularity has been investigated. For this purpose, four concrete moment resisting frames with different heights and spans designed in ETABS software. Because of irregularity of the studied buildings in plan, the story which resist more than 35% of the base shear in the direction of interest should be found. Then, loss of moment resistance at the beam-to-column connections at both ends of a single beam should be tested. The obtained results show that the story strength reduced less than 33% and the resulting system have not an extreme torsional irregularity. So, the redundancy factor at studied buildings is equal one.

The main role of connections, the transfer of forces between structural members and maintaining the integrity of the structure under the influence of load loads. Many structural failures are not simply due to defects in the design and analysis of structural members, but rather due to the non-respect of the behavior and design of joints. Even when member structures of the structure are accurately known, there is no complete understanding of the behavior of the joints. For this reason, in this research, a K-shaped connection under the uniform load loading model was modeled by Abacus software and validated by the results of previous research. Then, 8 numerical analytical models with different variables including steel yielding stress, compressive strength of concrete, angle of the steel tube and the presence of a stud have been developed to predict different characteristics of the responses. Their overall results indicated that the use of flint glass in the main pipe, which was filled with concrete, increased the stress intensity of the steel materials and the compressive strength of the filler concrete. An increase of 25% and 50% of the subsidence stresses of the secondary steel pipes increased the final bond strength by 22.9% and 74.6%, respectively, and the strength of the aggregate increased by 24.9% and 52.1%, respectively. The reduction of the angles between the sub-tubes and the main pipe in the K-shaped steel pipe connection showed that by decreasing the angle between the sub-tubes and the main pipe, the final quantity and initial hardness decrease, but the structural ductility increases. In general, it can be concluded that increasing the subsidence tension of the sub-tubes has the greatest effect on improving the behavior of the K-shaped joint, which, in addition to increasing the final load and the formability, also increased the initial hardness of the load-displacement curve. In contrast to the increase in the tensile strength of the main steel pipe, the final load and bond strength were reduced due to the simultaneous loading of the sub-channels and only increased the initial hardness to some extent.