Fundamental Period Of Building Research Articles

Effects of Interior Partition Walls on Natural Period of High Rise Buildings

In regions of low to moderate seismicity, serviceability limits states such as inter-story drift under wind load govern the design of the lateral load resisting structural systems of high rise buildings. The key objective in this regard is to provide adequate lateral stiffness to control lateral deflections and inter-story drifts. Current design practice assumes that the structural system alone provides lateral resistance against wind, the dominant load considered for countries like Australia. The contribution of nonstructural components (NSCs) such as interior partition walls on lateral stiffness is generally disregarded in the analysis of the buildings, even though it is commonly acknowledged that the NSCs play a significant role on the lateral stiffness of buildings. This technical note presents the results of a parametric study on the effects of NSCs, in particular, the effects of masonry interior partition walls on the fundamental period of buildings. The parameters considered in this study include: the number and length of walls, their material properties, the number of parallel moment resisting frames and the height of buildings. The results of this study indicate that interior walls can have significant effects on the lateral stiffness of buildings.

Period Formula for Reinforced Concrete Buildings with Infill Walls

The calculation of fundamental time period of vibration is a crucial step in seismic design and analysis of the structures to assess global response of the structure. Different international code proposed empirical expressions considering only height for bare frame structures and height and width of the buildings with infill to estimate the fundamental time period. This paper summaries the effect of the following parameters of building height, bay width, number of bays, cracked or un-cracked section of the structural member and support condition at the base on the fundamental time period of reinforced concrete bare frame and buildings with infill. Modal analysis of 360 building models with selected parameters is investigated in this study. A new equation, which is a function of the selected parameters (building height, bay width, number of bays, type of support condition, cracked or un-cracked sections and type of frame chosen for analysis) is also proposed using multiple linear regression analysis for predicting the fundamental period of buildings. The proposed simple model, including the building height, bay width, number of bays, type of support condition, cracked or un-cracked sections and type of frame chosen for analysis, showed better estimate in predicting the fundamental period of buildings compared to the code equations.

Influence of soil–structure interaction (structure-to-soil relative stiffness and mass ratio) on the fundamental period of buildings: experimental observation and analytical verification

In order to investigate the influence of soil–structure interaction (SSI) on the dynamic characteristics of buildings, a series of free-vibration experiments were performed on a 1/4-scale steel-frame structure. The structural fixed-base fundamental period was for the first time determined by experiments as to avoid evaluation errors in the conventional SSI analyses, and its numerical counterpart obtained by using SAP2000® was also given for comparison. A total of 34 scenarios, which varied with regard to overall stiffness and mass of the structure, were examined in the experiments and the numerical simulations. In each experimental scenario, the fundamental period of the structure was determined under fixed-base and flexible-base conditions. A newly proposed method by Luco using Dunkerley’s formula to evaluate the lower bounds for structural natural frequencies considering SSI was validated by both experimental and numerical results. This method was found to exhibit excellent accuracy in predicting the fundamental period of the structure with SSI. This experimentally verified formula, having a broader application potential than the Jennings and Bielak and Veletsos and Meek expressions, could apply to a variety of researching areas in earthquake engineering and would be a useful reference for future seismic code revisions in assessing the basic period of the structure with SSI.

Prediction of inelastic response periods of buildings based on intensity measures and analytical model parameters

This paper investigates the elongation of the fundamental period of reinforced concrete buildings that occurs during earthquake loading and its correlation with various intensity measures and engineering demand parameters. For this purpose, five buildings designed according to modern seismic codes are studied through equivalent single degree of freedom nonlinear systems with hysteretic laws that represent various levels of stiffness degradation, strength deterioration and pinching. By means of an extensive parametric analysis using a large set of earthquake ground motions and a rigorous validation procedure, the period elongation is quantitatively assessed as a function of building configuration and design (structural system and ductility class), ground motion characteristics (peak ground acceleration, spectral acceleration, frequency content) and demand parameters (displacement ductility). The results indicate that structures, designed according to modern seismic codes, are expected to exhibit low-to-moderate period elongation even for twice the intensity of the design earthquake. Given that the fundamental period of buildings is a key parameter in most seismic code procedures for ground motion selection, design and assessment, the implications of the predicted period lengthening are also discussed. The results are of interest to designers and analysts, as well as code-development committees.

Determination of Time Period of Vibration Effect on Seismic Performance of Building

Most seismic codes specify empirical formulas to obtain the fundamental period of buildings. The equations specified in present IS codes, are according to the available data on the time period of buildings measured from their recorded accelerograms. Shear-wall dominant reinforced concrete buildings, constructed, using codes specification are commonly built in different countries, facing a substantial seismic risk, in spite of their high resistance against ground motions. Current seismic code provisions including the Uniform Building Code (International Conference of Building Officials, Whittier, CA, 1997) and the Indian Seismic Code (Criteria for earthquake resistant design of buildings, fifth revision, 2002) are considered to evaluate the effect of time period on seismic behavior of building.In this study, time period obtained by code formulas are compared with those obtained by modal analysis in SAP2000. Also the top story displacement (as an adequate parameter of determination the seismic performance of building) correspond to the values of mentioned time period are estimated using uniform building code and software respectively. It is observed that current empirical equation for calculating the time period of RCC buildings is rather inaccurate. Also it is shown that the time period has very effective influence on seismic performance of building.

Influence of the soil–structure interaction on the fundamental period of buildings

AbstractThis paper includes an investigation of the influence of the soil–structure interaction (SSI) on the fundamental period of buildings. The behaviour of both the soil and the structure is assumed to be elastic. The soil‐foundation system is modelled using translational and rotational discrete springs. Analysis is first conducted for one‐storey buildings. It shows that the influence of the SSI on the fundamental frequency of building depends on the soil–structure relative rigidity Kss. Analysis is then extended for multi‐storey buildings. It allows the generalization of the soil–structure relative rigidity Ks to such complex structures. Charts are proposed for taking into account the influence of the SSI in the calculation of the fundamental frequency of a wide range of buildings. Copyright © 2007 John Wiley & Sons, Ltd.

Neural Networks and Principal Component Analysis for Identification of Building Natural Periods

This paper deals with an application of neural networks for computation of fundamental natural periods of buildings with load-bearing walls. The analysis is based on long-term tests performed on actual structures. The identification problem is formulated as the relation between structural and soil basement parameters, and the fundamental period of building. The principal component analysis for compression of input data is also used. Backpropagation neural networks are applied in the analysis. Results of neural network identification of natural periods are compared with data from experiments. The application of the proposed neural networks enables us to identify the natural periods of the buildings with quite satisfactory accuracy for engineering practice. The compression of the input data to principal components by principal component analysis makes it possible to design much smaller neural networks than those without data compression with no greater increase of the neural approximation errors. It appears that this technique would also be very useful in damage detection and health monitoring of structures.

Une relation simplifiée pour le calcul de la période fondamentale de certains types de bâtiments irréguliers

ABSTRACT Building codes, as Algerian code RPA 99, don't allow the use of the equivalent static load method to design buildings presenting a setback in plan and elevation when submitted to seismic loads. One of the reasons is that this method is based on the fundamental period that is calculated using simplified expressions valid only for regular buildings. The objective of this study is to present a dynamic model for estimate the fundamental period of buildings with one level in elevation presenting a setback. The model is based on a two degrees of freedom system accounting for the upper and the lower part of structure. A simple relation to calculate the fundamental period of such buildings is proposed. This relation can be introduced to different design codes.

Period Formulas for Concrete Shear Wall Buildings

Most seismic codes specify empirical formulas to estimate the fundamental vibration period of buildings. Evaluated first in this paper are the formulas specified in present U.S. codes using the available data on the fundamental period of buildings “measured” from their motions recorded during eight California earthquakes, starting with the 1971 San Fernando earthquake and ending with the 1994 Northridge earthquake. It is shown that current code formulas for estimating the fundamental period of concrete shear wall buildings are grossly inadequate. Subsequently, an improved formula is developed by calibrating a theoretical formula, derived using Dunkerley's method, against the measured period data through regression analysis. Also recommended is a factor to limit the period calculated by a “rational” analysis, such as Rayleigh's method.

Period Formulas for Moment-Resisting Frame Buildings

Most seismic codes specify empirical formulas to estimate the fundamental vibration period of buildings. Evaluated first in this paper are the formulas specified in present U.S. codes using the available data on the fundamental period of buildings “measured” from their motions recorded during eight California earthquakes, starting with the 1971 San Fernando earthquake and ending with the 1994 Northridge earthquake. It is shown that, although the code formulas provide periods that are generally shorter than measured periods, these formulas can be improved to provide better correlation with the measured data. Subsequently, improved formulas for estimating the fundamental periods of reinforced concrete (R/C) and steel moment-resisting frame buildings are developed by regression analysis of the measured period data. Also recommended are factors to limit the period calculated by a rational analysis, such as Rayleigh’s method.