Fundamental period of vibration is one of the most critical parameters to evaluate in the seismic design of new buildings, considering its role in the seismic forces estimation. The challenge of this ...research is to define a new approach for predicting the fundamental period of vibration for reinforced concrete buildings, designed according to the new generation seismic codes. The proposed formulations in this paper represent useful tools in the pre-design phase and they are based on some global parameters including mass and stiffness properties. To this scope, a set of 40 new buildings have been collected and modelled, considering bare and infilled frame configurations. Through regression analysis procedures two new formulations have been firstly proposed, compared with other existing formulations and finally validated through some case studies proposed in the recent scientific literature. The results show a good agreement with some of the existing formulations and a nearly perfect prediction of the fundamental period of vibration for the selected case study buildings.
Full text
Available for:
BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
•Conservative antisymmetric constant force oscillators are considered.•Two approaches are developed for obtaining their motion in terms of Jacobi elliptic functions.•First approach starts from the ...period of vibrations.•Second approach starts from the expression for the acceleration.•Both computational approaches give original and new results for this kind of oscillators.
This study presents how the motion, velocity and acceleration of conservative antisymmetric constant force oscillators can be expressed in terms of Jacobi elliptic functions. Two approaches have been developed. In the first approach, one starts from the known period of vibrations and the solution for motion expressed in terms of Jacobi elliptic functions. The second approach is also shown, starting from the expression for the acceleration in terms of the Jacobi elliptic functions, and then deriving the expression for the velocity and motion. As far as the author is aware, both computational approaches give original and new results for this kind of oscillators.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Pushover analysis has been recommended as a reliable tool to estimate the seismic capacity of the structures. Vertical irregular structures are highly vulnerable during earthquakes due to stiffness ...irregularity in their elevations. Hence, seismic capacities of these types of structures need to be re-estimated during structural design stage. So, in this paper, an attempt has been made to assess the actual seismic performance of buildings with two common types of vertical irregularities such as; soft story and setback in comparison with regular (reference) building. These types of vertical irregularities are studied in individual cases, combined in one story, and combined in two different stories of the building models, while most previous studies satisfy with individual type of vertical irregularity case in the studied model. In addition, combined vertical irregularity generates extra weak points, which alter the seismic capacities, failure mode mechanism, and performance point location. Three-dimensional numerical models are created to find out significant response demand such as; the variation in periods of vibration, lateral displacement, inter-story drift, pushover curve, and plastic hinges formation. The results showed that vertical irregular buildings are subjected to early damages and have less seismic capacity than regular one. The fundamental time period becomes misleading term in seismic force calculation for vertical geometric irregular buildings and needs to be re-considered. In addition, extra lateral displacement and inter-story drift are passively generated in the vertical irregular buildings due to sudden change in stiffness. Significant negative variation in the pushover curves, ductility ratios, and plastic hinges’ formation is observed when combinations of pre-mentioned vertical irregularity cases occur. Buildings with open soft ground story with asymmetric setback should have additional precautions from international codes during structural design stage according to their irregularity ratio. Therefore, response modification/reduction factor (
R
) may be scaled-down to adapt these negative variation in seismic capacities.
The determination of fundamental period of vibration for structures is essential to earthquake design. The current codes provide empirical formulas to estimate the approximated fundamental period and ...these formulas are dependent on building material, height of structure or number of stories. Such a formulation is excessively conservative and unable to account for other parameters such as: length to width ratios, vertical element size and floors area. This study investigated the fundamental periods of mid-rise reinforced concrete moment resisting frames. A total of 13 moment resisting frames were analyzed by ETABS 15.2.2, for gross and cracked eigenvalue analysis and Extreme Loading for Structures Software® or ELS, for non-linear dynamic analysis. The estimated periods of vibration were compared with empirical equations, including current code equations. As expected, the results show that building periods estimated based on simple equations provided by earthquake design codes in Europe (EC8) and America (UBC97 and ASCE 7-10) are significantly smaller than the periods computed using nonlinear dynamic analysis. Based on the results obtained from the analyzed models, equations for calculating period of vibration are proposed. These proposed equations will allow design engineers to quickly and accurately estimate the fundamental period of moment resisting frames with taking different length to width ratios, vertical element size, floors area and building height into account. The interaction between reduction factor and the reduced period of vibration is studied, and it is found that values of maximum period of vibration can be used as an alternative method to calculate the inelastic base shear value without taking reduction factors in consideration.
Stairs play an important role as an escape way and are considered a source of safety in the building during an earthquake. Neglecting the stairs in the 3D analysis model is the main cause of the ...stairs' failure during the earthquake. Although the previous researchers had focused on the behavior of stairs when changing single variables such as height, location, and layout under seismic loads, no detailed investigation that gathers these variables together was considered. This research studies the effects of changing the number of storeys for a building subjected to an earthquake when considering and neglecting stairs in the 3D analysis with and without shear walls. The effect of the volume and location of the shear wall has been considered through conducting computational analysis using ETABS software to help the structural engineer choose the proper system of stairs and shear walls. Neglecting the staircase in the 3D analysis affects the structure's performance, which leads to ignoring many stresses transferred to the stairs, causing several damages to the stairs during an earthquake. For the existing building without a shear wall, considering the staircases in the analysis improves the performance of the structure under seismic loads. Doi: 10.28991/CEJ-SP2021-07-08 Full Text: PDF
The paper aims to investigate the accuracies of idealization methods of the well-known shear-building models. Five idealization methods are adopted to idealize the structural story capacity curve ...within the range from zero to the deformation corresponding to the peak shear point. After the peak shear point, a skew branch followed by a constant branch are used to approximate the capacity curve. The five idealization methods are verified by using four reinforcement concrete (RC) frames with 3, 8, 12, and 18 stories. Results reveal that all the five idealization methods may cause remarkable errors in prediction of the period, displacements and accelerations of the actual buildings. The errors of the structural period by the five idealization methods are almost above 10–40%. The errors of the structural displacements and accelerations by the five idealization methods are almost above 30–90%. For all the five idealization methods, the prediction accuracy on displacement and acceleration will be dramatically increased if the comparison is only focused on the maximum value within all story rather than the maximum values of each story. The initial stiffness method provides the best predictions on periods of the actual buildings. The farthest point method provides better prediction than the other four idealization methods.
Braced frames are frequently used as lateral load resisting systems in steel buildings due to their cost-effectiveness and efficiency in resisting earthquake loads. Evaluating the seismic loads on ...those buildings requires estimating the fundamental period of vibration of the buildings at first. Most design codes use empirical formulas that depend only on the height of the buildings without considering the effect of bracing configurations or building irregularities. This paper aims to develop new equations to estimate the fundamental period of vibration of irregular steel buildings occupied with different bracing systems. For this purpose, 176 prototype buildings with different bracing configurations and irregularities have been selected and modeled using ETABS finite element program. Three types of irregularity have been considered: vertical, horizontal, and combined irregularity. Then, the fundamental periods of vibration have been estimated through analysis and optimal building design using nonlinear regression analysis. According to the findings, the configuration of the bracing system and the building irregularity influence the fundamental period of vibration of buildings of the same height, where vertical and combined irregularities decrease the period values by about 20% for CBFs. This indicates the importance of incorporating new equations in calculating the fundamental period of these types of steel structures.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
PDF
