Assessment of Design Recommendations for Torsionally Unbalanced Multistory Buildings

2003 ◽  
Vol 19 (1) ◽  
pp. 47-66 ◽  
Author(s):  
Jaime De-la-Colina
Keyword(s):  
Amplification Factor ◽  
Building Design ◽  
Lateral Force ◽  
Reduction Factor ◽  
Earthquake Ground Motion ◽  
Structural Systems ◽  
Design Recommendations ◽  
Multistory Buildings ◽  
Accidental Eccentricity ◽  
Factor Α

Multistory models are studied to assess design recommendations for torsionally unbalanced multistory buildings. Structural systems are assumed as shear beams with nonlinear lateral-resisting elements oriented along two orthogonal directions and subjected to a bidirectional earthquake ground motion. Five-story rigid-diaphragm models with mass or stiffness eccentricity are considered in the study. Accidental eccentricity is not included in the modeling and, therefore, its related recommendations are not assessed. Design recommendations studied here are based on the simple static procedure and include two values and an expression for the amplification factor α to compute story eccentricities, three values of the torsion-shear reduction factor δ, an additional lateral force Ft to be applied at the building top level, and a minimal story eccentricity for the building. Design recommendations to control ductility demands of torsionally unbalanced multistory buildings are given.

Probabilistic Study on Accidental Torsion of Low-Rise Buildings

2004 ◽  
Vol 20 (1) ◽  
pp. 25-41 ◽  
Author(s):  
Jaime De-la-Colina ◽  
Cristina Almeida
Keyword(s):  
Ground Motions ◽  
Center Of Mass ◽  
Random Variable ◽  
Lateral Force ◽  
Reduction Factor ◽  
Ductility Demand ◽  
Accidental Eccentricity ◽  
Force Reduction Factor ◽  
Probabilistic Study ◽  
Force Reduction

A probabilistic study on accidental torsion is presented. Multistory shear systems, representative of low-rise buildings and subjected to bidirectional earthquake ground motions are considered. Ductility demands of lateral resisting elements (LREs) due to uncertainties on (1) center-of-mass locations, (2) LRE stiffness, and (3) LRE yield forces were studied. Building code recommendations on accidental torsion as well as the effects of both eccentricity and lateral-force reduction factor are assessed. Results indicate that considering one random variable in the accidental torsion problem can lead to larger ductility-demand probabilities of exceedance than using two or more variables. Individual effects of each one of the variables considered are not superimposed when all variables take place at the same time. For systems designed for torsion, ductility demands of LREs decreases for increasing eccentricities. Increments of yield forces and decrements of probabilities of exceedance due to the use of increasing values of factor β associated with the accidental eccentricity are presented.

Ductility Reduction Factors for Steel Buildings Modeled as 2D and 3D Structures

2014 ◽  
Vol 595 ◽  
pp. 166-172
Author(s):  
Alfredo Reyes-Salazar ◽  
Eden Bojorquez ◽  
Achintya Haldar ◽  
Arturo Lopez-Barraza ◽  
J. Luz Rivera-Salas
Keyword(s):  
Lateral Force ◽  
Reduction Factor ◽  
Steel Buildings ◽  
Structural Representation ◽  
Global Response ◽  
A Value ◽  
Mdof Systems ◽  
Moment Resisting ◽  
2D And 3D ◽  
Reduction Factors

The global ductility parameter (μG), commonly used to represent the capacity of a structure to dissipate energy, and the associated ductility reduction factor (Rμ), are estimated for steel buildings with perimeter moment resisting frames (PMRF), which are modeled as 2D and 3D complex MDOF systems. Results indicate that the μG value of 4, commonly assumed for moment resisting steel frames, cannot be justified. A value of 3 is more reasonable. The values of μG and Rμ may be quite different for 2D and 3D structural representations or for local and global response parameters, showing the limitation of the commonly used Equivalent Lateral Force Procedure (ELFP). Thus, the ductility and ductility reduction factors obtained from simplified structural representation must be taken with caution.

Influence of P – Delta effects on seismic design

1981 ◽  
Vol 8 (1) ◽  
pp. 31-43 ◽  
Author(s):  
C. James Montgomery
Keyword(s):  
Ground Motion ◽  
Seismic Design ◽  
Time History ◽  
Building Design ◽  
Earthquake Ground Motion ◽  
Stability Factor ◽  
The Stability

The influence of P – Delta effects on the response of buildings subjected to earthquake ground motion is illustrated using time – history studies. It is shown that the influence of P – Delta effects is of great importance for buildings responding in a highly inelastic manner. However, for buildings responding in an elastic or slightly inelastic manner, the influence of P – Delta effects is relatively small. The stability factor approach for estimating the influence of P – Delta effects is reviewed. It appears that this approach gives reasonable results only for systems responding in an elastic or slightly inelastic manner. The strength and drift characteristics of buildings are briefly described. The results presented suggest that the response of certain types of well-designed buildings will not be significantly influenced by P – Delta effects. Finally, recommendations are made for assessing the significance of P – Delta effects for a given building design.

scholarly journals Effect of Building Configuration on Overstrength Factor and Ductility Factor

2021 ◽  
Author(s):  
Sagun Kandel ◽  
Rajan Suwal
Keyword(s):  
Residential Buildings ◽  
Pushover Analysis ◽  
Large Earthquake ◽  
Lateral Force ◽  
Reduction Factor ◽  
Base Shear ◽  
Response Reduction Factor ◽  
Overstrength Factor ◽  
Ductility Factor ◽  
High Level

It is important for the structure to be economical and still have a high level of life safety. The lateral force sustained by the structures during a large earthquake would be several times larger than the lateral force for which the structures are designed. This is opposite to the fact that design loads such as gravity in codes are usually higher than the actual anticipated load. It is based on the probability that the occurrence of large earthquakes is quite rare and the capacity of the structure to absorb energy. The co-factors of response reduction factor which is the overstrength factor and ductility factor reduce the design horizontal base shear coefficient. A total of 36 low-rise residential buildings having different storey, bay and bay lengths are selected and analysed in this paper. NBC 105: 2020 is selected for the seismic design of RC buildings while provision provided in FEMA 356:2000 is used to carry out non-linear pushover analysis. The results indicated that between the different structures, the value of overstrength factor and ductility factor has a high deviation.

scholarly journals Variation Evaluation of Path Characteristic and Site Amplification Factor of Earthquake Ground Motion at Four Sites in Central Japan

2021 ◽  
Vol 11 (5) ◽  
pp. 7658-7664
Author(s):  
T. Nagao
Keyword(s):  
Ground Motion ◽  
Amplification Factor ◽  
Hazard Analysis ◽  
Strong Motion ◽  
Site Amplification ◽  
Earthquake Ground Motion ◽  
Constraint Condition ◽  
Central Japan ◽  
Source Characteristic ◽  
Site Amplification Factor

The considered parameters in seismic design vary, with the Earthquake Ground Motion (EGM) having the largest variation. Since source characteristic, path characteristic, and Site Amplification Factor (SAF) influence the EGM, it is crucial to appropriately consider their variations. Source characteristic variations are mainly considered in a seismic hazard analysis, which is commonly used to evaluate variations in EGM. However, it is also important to evaluate variations in path characteristic and SAF with only a few studies having individually and quantitatively examined the variations of these two characteristics. In this study, based on strong-motion observation records obtained from four sites in central Japan, the three characteristics were extracted from seismograms using the concept of spectral inversion. After removing the source characteristic, the path characteristic and SAF were separated, and the variations in these two characteristics were quantified. To separate and obtain each characteristic from the observed record, one constraint condition must be imposed, whereas the variations in the constraint condition must be ignored. In that case, the variations in the constraint condition are included in the variations of the separated characteristics. In this study, this problem was solved by evaluating the variation in the constraint condition, which is the SAF at a hard rock site, by the use of the vertical array observation record at the site.

TORSION EFFECTS IN BUILDING SEISMIC PERFORMANCE

2020 ◽  
Vol 7 (2) ◽  
Author(s):  
Marija Demsic ◽  
Mario Uros ◽  
Marta Savor Novak ◽  
Josip Atalic
Keyword(s):  
Seismic Performance ◽  
Parametric Analysis ◽  
Dynamic Effect ◽  
Building Design ◽  
Major Influence ◽  
Seismic Action ◽  
Accidental Eccentricity ◽  
Torsion Moment ◽  
Seismic Forces ◽  
Mathematica Software

The paper considers torsion effects that occur during the building response to seismic action. Computation and parametric analysis are conducted for various values of building eccentricity induced by mass and stiffness variation. Such a model accounts for the actual dynamic effect of accidental eccentricity, usually considered in building design by quasi-static value of the torsion moment. Two types of models are employed to explore dynamic parameters of the building. The models are formed using Wolfram Mathematica software in which the mass and stiffness properties are parametrically related to the basic dynamic characteristics of the building. The commercial software package CSI ETABS ver.17 is used for validation of the model. Seismic performance of the building is evaluated, and the results of the parametric analysis are presented using the shear forces and torsion moment. The analysis showed that the nature of eccentricity has a major influence on distribution of seismic forces due to the torsion.

Period-dependent seismic force reduction factors for short-period structures

1991 ◽  
Vol 18 (4) ◽  
pp. 568-574 ◽  
Author(s):  
W. K. Tso ◽  
N. Naumoski
Keyword(s):  
Reduction Factor ◽  
Structural Systems ◽  
High Ductility ◽  
Base Shear ◽  
Ductility Demand ◽  
Seismic Design Code ◽  
Short Period ◽  
Seismic Force ◽  
Force Reduction ◽  
Reduction Factors

The seismic force reduction factors proposed in the seismic provisions of the National Building Code of Canada 1990 (NBCC 1990) are examined using ground motion records from two recent Canadian earthquakes. The displacement ductility demands are analyzed for structural systems with different ductility capacity. It is found that the NBCC 1990 force reduction factors, which are period independent, lead to a very high ductility demand for short-period structural systems. To avoid this, two types of period-dependent force reduction factors for short-period structures are investigated. The results show that the linearly varying period-dependent reduction factor represents a viable means to resolve the high ductility problems associated with short-period structural systems. Key words: earthquake, seismic, design, code, response, spectra, ductility, reduction factor, base shear.

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