نشریه سازه و فولاد
سال شانزدهم شماره 33 (پاییز 1400)

The purpose of this study is to investigate and improve the performance of energy absorption and dissipation system in the steel moment frames with short span lengths and deep beams. One of the challenges for designing a steel moment frame system is the existence of some code limitations such as minimum span length and beam depth that designers are required to follow in order to form the plastic hinges at both beam ends. By weakening a part of the beam in its middle, the mechanism of energy dissipation is changed from bending to shear, and this defect is practically eliminated. One of the studies on weakening the middle of the beams is to make circular holes in the beam web. By changing the shape of holes from circular to elliptic and changing the arrangement of the elliptic holes and the angles of the elliptical axes relative to each other and by maintaining constant the hole area reduced from the beam web, according to the models built in Abaqus software and comparing the response of different hole arrangements with circular ones, more ductility has been reported. Thus, in the models in which a combination of vertical and horizontal elliptical holes is used, more energy dissipation has been observed compared to other elliptical cases and 16% more energy dissipation has been calculated compared to the circular case.

Damage to structures is inevitable. Besides, the accumulation and spread of local damage can be a source of global damage; hence, the significance and necessity of monitoring the health of the structure. Wavelet analysis of structural responses is a method of damage detection with optimal performance in the time-frequency domain, which yields more information from the analyzed response of the structure in both time and frequency domains. As beams and columns are among the most fundamental structural elements and, expectably, the last elements to be damaged, it bears greater importance to identify damage in them than in other structural elements. This paper draws on modal analysis data of steel beams modeled in Abacus and a proposal of the wavelet analytical method to track different positions of damage along the beam, where the damages are defined as a decrease in the elastic modal. A decreasing shift in frequency values occurred in all modes due to damage. To detect the damage, the mode shape signal was defined as the damage mode shape and the differentiation between the healthy and the damage mode shapes as the wavelet transform input signal. The output signals from the wavelet analysis of the input signal indicated maximum and minimum relative fluctuations in different situations of damage so that the centers of damage were identified with zero error. The results also revealed that with increasing the severity of the damage, only the irregularity of the wavelet coefficients of that damage position increases.

Due to the increase in construction costs of new structures, it is expected that attempts to develop new techniques to accelerate the ‎return of earthquake-damaged structures to service. One of the methods that can be used is re-‎aligning the structure. In this research, ‎three models of steel moment frame structures with different numbers of stories, were analyzed by nonlinear ‎dynamic analyses with the help of Abaqus software. The studied models have ‎been subjected to several different records.‎ Each record is applied to each model under three separate ‎fashions. In the first case, only one earthquake record is applied to the model alone. In the second ‎case, IDA analysis is performed, and the structure is subjected to successive earthquakes from ‎low to high intensity. In the third case, the ‎analyzes are similar to the second case under seismic sequences, with the difference that after ‎applying each earthquake intensity and before applying the next intensity, the residual ‎displacements of each floor were made zero, which is an example of aligning the structure. ‎It was concluded that in most cases, the second series of ‎analyzes, have the ‎maximum drift and residual drift ratios.

The use of corrugated-web has been considered due to the increase in off-plane stiffness and its buckling strength in the design and construction of deep beams. In this study, the performance of a moment resistant connections with reduced beam section (RBS) beam and trapezoidal corrugated web were investigated under cyclic loading. The variable parameters in the constructed models are defined as the corrugated web angle and the RBS parameters. Two specimens were made with corrugated sheet angle of 45 and 30 degrees. Also, in another sample, the RBS characteristics of the beam wing were changed in accordance with the design criteria. The AISC cycle loading protocol was used for testing and a maximum of 40 cycles were loaded until connection failure. The results show the stability of the specimens and their acceptability according to the regulations and no instability was observed in the hysteresis curves up to the point of failure of connections. According to the results of the experiments, by reducing the corrugated web angle, the bending capacity of the connection is reduced by about 10% and the amount of energy absorption is reduced by about 27%. Based on the observations as well as the recorded deformations, in all three specimens the panel zone showed linear behavior.

The need for more high-rise buildings that have complex reactions to earthquakes makes controlling soil-structure interactions particularly important. Also, the architectural and aerodynamic requirements of high-rise buildings that lead to post-deposition necessitate further studies is inevitable on the effects of post-depositional and soil-structure interactions. In this study, a three-dimensional, 25 floors reinforced concrete frame with a particular moment frame structural system along the x,y line in a very dangerous area (a =0.3g) with two models with the height of floors (3.2-4.2) has regular (1-12) and with post-depositional (13-25) floors on the soil (I, II, and III) is assumed without soil-structure interaction. The purpose of the present study was to determine the maximum horizontal lateral displacement (absolute, drift) floors, base shear and invert anchor frames. To model the sub-foundation soil from Themickwolf's cone model, determination of coefficient of dynamic stiffness of spring and damping coefficient using discrete model based cone model in half homogeneous space for the analysis of soil-structure interaction from the subsurface method. For seismic load analysis, the nonlinear time history dynamic analysis method by direct integration method under seven accelerometers was used and geometric modelling was performed on all sap2000-v18 software. The result shows that with change in soil type (II to I, III to I, and III to II) without and with soil-structure interaction, the trend of the maximum lateral displacement (absolute, drift) in two model (1 and 2) of storeys (1-25) along (x, y) increasing, maximum percent increase in lateral displacement (absolute-drift) from the floors (13-25) to the floors (1-12) respectively, lateral displacement (decrease-increase) and soil (II to I) without and with soil-structure interaction from the floors (1–25) due to stay periodic the soil (I, II) does not change. Also, the maximum base shear is reduced of model 2 to 1 the soils (i, ii, iii) without and with interaction along (x, y), and the maximum overturn anchor is increased.

In this research, a review was conducted on the characteristics of strong ground motions in near-fault zones, as well as the analysis of its effects on seismic behavior of mid-rise structures with two types of earthquake resistant skeletons. The studied structural models are mid-rise 10 story buildings with bundled tube frame and 3d moment frame. Also, the analytical capability of the modal pushover analysis (MPA) method has been studied on the estimation of structural response parameters. The maximum inter-story drift, axial force, roof maximum displacement of the studied structures was determined by conducting nonlinear dynamic time history (NTH) analyses and MPA method under the effects of an ensemble of lateral loads. An analytical comparison was accomplished among the obtained results.