Seismic Design Aspects of Vertically Irregular Reinforced Concrete Buildings

2003 ◽  
Vol 19 (3) ◽  
pp. 455-477 ◽  
Author(s):  
Satrajit Das ◽  
James M. Nau
Keyword(s):  
Seismic Design ◽  
Lateral Force ◽  
Masonry Infills ◽  
Irregular Structures ◽  
Dynamic Analyses ◽  
Moment Resisting ◽  
Linear And Nonlinear ◽  
Definition Of ◽  
Design Earthquake ◽  
Nonlinear Dynamic Analyses

Seismic building codes such as the Uniform Building Code (UBC) do not allow the equivalent lateral force (ELF) procedure to be used for structures with vertical irregularities. The purpose of this study is to investigate the definition of irregular structures for different vertical irregularities: stiffness, strength, mass, and that due to the presence of nonstructural masonry infills. An ensemble of 78 buildings with various interstory stiffness, strength, and mass ratios is considered for a detailed parametric study. The lateral force-resisting systems (LFRS) considered are special moment-resisting frames (SMRF). These LFRS are designed based on the forces obtained from the ELF procedure. The results from linear and nonlinear dynamic analyses of these engineered buildings exhibit that most structures considered in this study performed well when subjected to the design earthquake. Hence, the restrictions on the applicability of the equivalent lateral force procedure are unnecessarily conservative for certain types of vertical irregularities considered.

A Seismic Design Lateral Force Distribution Based on Inelastic State of Structures

2007 ◽  
Vol 23 (3) ◽  
pp. 547-569 ◽  
Author(s):  
Shih-Ho Chao ◽  
Subhash C. Goel ◽  
Soon-Sik Lee
Keyword(s):  
Seismic Design ◽  
Lateral Force ◽  
Elastic Response ◽  
Force Distribution ◽  
Relative Distribution ◽  
Inelastic Behavior ◽  
Seismic Demands ◽  
Framed Structures ◽  
Dynamic Analyses ◽  
Nonlinear Dynamic Analyses

It is well recognized that structures designed by current codes undergo large inelastic deformations during major earthquakes. However, lateral force distributions given in the seismic design codes are typically based on results of elastic-response studies. In this paper, lateral force distributions used in the current seismic codes are reviewed and the results obtained from nonlinear dynamic analyses of a number of example structures are presented and discussed. It is concluded that code lateral force distributions do not represent the maximum force distributions that may be induced during nonlinear response, which may lead to inaccurate predictions of deformation and force demands, causing structures to behave in a rather unpredictable and undesirable manner. A new lateral force distribution based on study of inelastic behavior is developed by using relative distribution of maximum story shears of the example structures subjected to a wide variety of earthquake ground motions. The results show that the suggested lateral force distribution, especially for the types of framed structures investigated in this study, is more rational and gives a much better prediction of inelastic seismic demands at global as well as at element levels.

An evaluation ofP-Δ amplification factors in multistorey steel moment resisting frames

1999 ◽  
Vol 26 (5) ◽  
pp. 535-548 ◽  
Author(s):  
R Tremblay ◽  
B Côté ◽  
P Léger
Keyword(s):  
Amplification Factor ◽  
Ground Motions ◽  
Beam Model ◽  
Steel Moment Resisting Frames ◽  
Moment Resisting Frame ◽  
Dynamic Analyses ◽  
Moment Resisting ◽  
Shear Beam ◽  
Nonlinear Dynamic Analyses ◽  
Shear Beam Model

Three different amplification factors that have been proposed to account for P-Δ effects in the seismic design of multistorey building structures are described and compared. Nonlinear dynamic analyses of a typical 20-storey steel moment resisting frame are carried out under earthquake ground motions typical of eastern and western Canada to evaluate the gravity load effects and to assess the effectiveness of each type of amplification factor in accounting for these effects. All three approaches maintain the ductility demand within the level computed without P-Δ effects, but lateral deformations are generally larger than those obtained neglecting the gravity loads. Nonlinear dynamic analyses are also performed on a shear-beam (stick) model of the same building to examine the possibility of using such simple models for studying the dynamic stability of buildings subjected to ground motions. The shear-beam model does not predict adequately the seismic behaviour of steel moment resisting frames for which P-Δ effects are significant.Key words: ductility, earthquake, ground motion, lateral deformation, moment resisting frame, P-Δ effects, push-over analysis, seismic, shear-beam model, stability coefficient, amplification factor.

scholarly journals Review of the Soft First Story Irregularity Condition of Buildings for Seismic Design

2010 ◽  
Vol 4 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Arturo Tena-Colunga
Keyword(s):  
Seismic Design ◽  
Nonlinear Dynamic ◽  
Substantial Reduction ◽  
Shear Stiffness ◽  
Building Codes ◽  
Lateral Shear ◽  
Dynamic Analyses ◽  
Nonlinear Dynamic Analyses

The present study evaluates how the soft first story irregularity condition should be defined: (a) as a significant reduction of the lateral shear stiffness of all resisting frames within a given story, as established in the seismic provisions of Mexican building codes or, (b) as a substantial reduction of the lateral shear stiffness of one or more resisting frames within a given story, as proposed by the author. Both definitions are evaluated through nonlinear dynamic analyses of buildings systems with a suspected soft first story condition in order to discern which option is closer to define the soft fist story condition.

scholarly journals Considerations for a "design" earthquake

1972 ◽  
Vol 5 (2) ◽  
pp. 47-50
Author(s):  
G. L. Evans
Keyword(s):  
Soil Properties ◽  
Seismic Design ◽  
Soil Mass ◽  
Soil Dynamics ◽  
Simplifying Assumptions ◽  
Acceleration Method ◽  
Risk Magnitude ◽  
Definition Of ◽  
Design Earthquake ◽  
Relative Factors

Any structure is only as good as its foundation material. Under earthquake the properties of foundation materials can change drastically. Recent advances in soil dynamics indicate that the simplifying assumptions on which our seismic building code is based, are not adequate to cater for the variations in foundation conditions. The code provides
clear definition of seismic design forces, in terms of acceleration and period, but ignores any possible effects of displacement, velocity or wavelength. Currently available methods of design and analysis can provide for calculation of ground period, displacements, velocities, accelerations and stress values at any point in a soil mass. Although not perhaps suitable
for detailed code recommendations these methods can be used by designers where needed and the code could contain simplified but conservative data on the use of such methods, The design forces to be imposed on a structure and variations of these are defined exactly in the code, but these are not matched by the definition of base motions, which are influenced by magnitude of the earthquake, distance and soil properties. It should be possible to provide for a "design earthquake" which takes into account, type of structure, nature of
 risk, magnitude of earthquake, distance from active seismic areas and soil properties. Even relative factors, initially based on overseas research, relating these things would provide a more rational basis for seismic effects on structures than the simplified structure mass acceleration method used at present.

Effects of Masonry Infills on Seismic Response of Steel Structures

2013 ◽  
Vol 274 ◽  
pp. 112-116
Author(s):  
Marco Valente
Keyword(s):  
Steel Structure ◽  
Steel Structures ◽  
Load Resistance ◽  
Earthquake Intensity ◽  
Masonry Infills ◽  
Frame Building ◽  
Dynamic Analyses ◽  
Story Drift ◽  
Design Earthquake ◽  
Sudden Decrease

The effects of masonry infills on the seismic performance of a multi-story steel frame building were investigated through nonlinear static and dynamic analyses. Three variants of masonry infills, aimed at simulating weak, intermediate and strong infill panels, and the presence of masonry openings were considered in the numerical analyses. Strong masonry infills significantly contributed to the lateral stiffness and load resistance of the steel structure, but a sudden decrease of strength was observed after the failure of infills. This phenomenon was less evident in presence of openings. The results of the nonlinear dynamic analyses confirmed the satisfactory performance of masonry infilled steel structures under the design earthquake intensity. The presence and the mechanical properties of the infills affected the distribution of damage throughout the structure. The maximum inter-story drift occurred at the third level for the bare structure, whereas in the structures infilled by strong masonry panels the maximum inter-story drift was registered at the first level.

Robustness Based Structural Design: An Integrated Approach for Multi-Hazard Risk Mitigation

2011 ◽  
Vol 82 ◽  
pp. 770-777
Author(s):  
Dan Dubina ◽  
Florea Dinu
Keyword(s):  
Seismic Design ◽  
Structural Design ◽  
Risk Mitigation ◽  
Integrated Approach ◽  
Building Structures ◽  
Frame Buildings ◽  
Dynamic Analyses ◽  
Nonlinear Dynamic Analyses ◽  
Story Building ◽  
Multistory Frame

Multi-story building structures can suffer local damage or even structural collapse in case of extreme natural or man-made hazards. While all buildings are at a certain risk, some attributes can reduce the risk by reducing the vulnerability. One such attribute is the use of structural systems which can ensure that, in case of abnormal loads or failure of some elements, the collapse is prevented and the risk to occupants is reduced. Mitigation of some specific hazard can also help to reduce the risk, eg. protective barriers against impact or stand-off distance against direct effects of blast. Past experience has shown that structures that are designed according to seismic design philosophy can survive to a multiplicity of hazards. The objective of the paper is the adaptation of seismic design methodology to robust design demands of multistory frame buildings prone to multi-hazard scenarios. The hazard is modeled by removal of critical members. Nonlinear dynamic analyses are carried out in order to evaluate their robustness.

Seismic Responses From Linear and Nonlinear Dynamic Analyis of RC Shear Walls

2018 ◽  
Author(s):  
Do Yeon Kim
Keyword(s):  
Numerical Model ◽  
Dynamic Analysis ◽  
Nonlinear Dynamic ◽  
Damping Ratio ◽  
Shear Walls ◽  
Seismic Responses ◽  
Rc Structures ◽  
Dynamic Analyses ◽  
Linear And Nonlinear ◽  
Nonlinear Dynamic Analyses

Seismic responses from linear and nonlinear dynamic analyses of reinforced concrete (RC) shear walls are compared to see how the damping ratio and cracking behavior affect the dynamic response of the RC structures used in the nuclear power plant. The nonlinear dynamic analyses are conducted based on the numerical model which is developed to simulate the nonlinear hysteretic behavior of RC structures subjected to in-plane shear. Through comparison of the obtained numerical results with experimental data such as load-displacement relationships and response time-histories, the developed numerical model is validated. The acceleration response spectra from the nonlinear dynamic analysis results of selected RC shear wall and those from linear dynamic analysis with combinations of the damping ratio and concrete stiffness considerations according to the level of earthquake loads and the resultant stresses are addressed.

scholarly journals Assessment of Seismic Vulnerability of Steel and RC Moment Buildings Using HAZUS and Statistical Methodologies

2017 ◽  
Vol 2017 ◽  
pp. 1-16 ◽  
Author(s):  
Iman Mansouri ◽  
Jong Wan Hu ◽  
Kazem Shakeri ◽  
Shahrokh Shahbazi ◽  
Bahareh Nouri
Keyword(s):  
Seismic Vulnerability ◽  
Fragility Curves ◽  
Limit State ◽  
Moment Frames ◽  
Limit States ◽  
Rc Frames ◽  
Dynamic Analyses ◽  
Damage States ◽  
Definition Of ◽  
Nonlinear Dynamic Analyses

Designer engineers have always the serious challenge regarding the choice of the kind of structures to use in the areas with significant seismic activities. Development of fragility curve provides an opportunity for designers to select a structure that will have the least fragility. This paper presents an investigation into the seismic vulnerability of both steel and reinforced concrete (RC) moment frames using fragility curves obtained by HAZUS and statistical methodologies. Fragility curves are employed for several probability parameters. Fragility curves are used to assess several probability parameters. Furthermore, it examines whether the probability of the exceedence of the damage limit state is reduced as expected. Nonlinear dynamic analyses of five-, eight-, and twelve-story frames are carried out using Perform 3D. The definition of damage states is based on the descriptions provided by HAZUS, which gives the limit states and the associated interstory drift limits for structures. The fragility curves show that the HAZUS procedure reduces probability of damage, and this reduction is higher for RC frames. Generally, the RC frames have higher fragility compared to steel frames.

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