Seismic Design Of Building Structures Research Articles

Nonstructure–structure interaction with respect to mass ratio: Numerical analysis and free vibration tests

The dynamic interactions between nonstructural components (NCs) and the main building structure cannot be neglected because the dynamic properties of the main structure are modified, particularly for heavy NCs. The mass ratio (MR) is a parameter that incorporates the nonstructure–structure interaction (NSI) between the NCs and main structure. In this study, to investigate the seismic interaction in terms of the MR, a four-story steel moment frame was constructed and free vibration tests were carried out. The equivalent mass of the NCs was connected to various floor levels, neglecting their stiffness and damping. The vibration mode and period of the steel frame were obtained numerically. At MR = 25 %, the period generally increased with increasing MR. The modal contribution factors in terms of the roof displacement and base shear were analyzed. The findings show that it would be safe to consider the 1st mode only when using the roof displacement, whereas more modes should be considered when the base shear is used. The experimental damping ratios correlated with the magnitude of the MR without a representative trend. The damping ratio generally increases with an increase in the number of floors hosting additional masses. The experimental period increased almost linearly with the MR irrespective of the number of floor-hosting masses. An equivalent single-degree-of-freedom model is developed to predict the frame period. The predicted periods generally matched the experimental results. The normalized height of the equivalent model and period ratio vary with the MR and are correlated with the number of floors hosting the mass. The results of this study will be beneficial for the seismic design of building structures with heavy NCs.

Analysis of the seismic effects of the local slope site of Longtoushan market town in Ludian Ms6.5 earthquake

In the Ludian Ms6.5 earthquake (Yunnan, China), Longtoushan market town and its vicinity showed significant differences in earthquake damage. To explain this phenomenon, this paper discusses the local engineering geological conditions, local topographic effects, and seismic response of the soil layer in Longtoushan market town. The results show that complex topography and varied engineering geological conditions will lead to significant differences in ground motion, and then lead to significant differences in building earthquake damage. Slope topography has an obvious influence on ground motion. From the foot of the slope to the top of the slope, the degree of influence gradually increases, and the influence in different directions is different, as shown: the closer to the top of the slope, the more significant the difference. This indicates that the serious damage to buildings built on the slope is caused by the amplification effect of local terrain and the differential effect of ground motion. Although the site belongs to Class II site, the near-surface geotechnical properties and their combination characteristics, the physical state and thickness of the overlying soil layer, the variation characteristics of shear wave velocity, the non-linear dynamic characteristics of the soil, and other factors play a decisive role in the amplification degree of ground motion. The significant difference in ground motion on the surface of the slope site leads to a significant difference in seismic damage to buildings on the site. The covering soil layer has a significant effect on the acceleration response spectrum. The conclusions obtained in this paper can provide a scientific basis for the site selection of engineering construction and seismic design of building structures.

A MEMS Electrochemical Angular Accelerometer Leveraging Silicon-Based Three-Electrode Structure.

This paper developed an electrochemical angular micro-accelerometer using a silicon-based three-electrode structure as a sensitive unit. Angular acceleration was translated to ion changes around sensitive microelectrodes, and the adoption of the silicon-based three-electrode structure increased the electrode area and the sensitivity of the device. Finite element simulation was conducted for geometry optimization where the anode length, the orifice diameter, and the orifice spacing of the sensitive unit were determined as 200 μm, 80 μm, and 500 μm, respectively. Microfabrication was conducted to manufacture the silicon-based three-electrode structure, which then was assembled to form the electrochemical angular micro-accelerometer, leveraging mechanical compression. Device characterization was conducted, where the sensitivity, bandwidth, and noise level were quantified as 290.193 V/(rad/s2) at 1 Hz, 0.01–2 Hz, and 1.78 × 10−8 (rad/s2)/Hz1/2 at 1 Hz, respectively. Due to the inclusion of the silicon-based three-electrode structure, compared with previously reported electrochemical angular accelerometers, the angular accelerometer developed in this article was featured with a higher sensitivity and a lower self-noise level. Therefore, it could be used for the measurement of low-frequency seismic rotation signals and played a role in the seismic design of building structures.

A Damage‐Controlled Behavior Factor (EC8) for Seismic Design of Steel Irregular Space MRFs

AbstractA main aspect to consider in seismic design of building structures according to EC8 is the selection of the behavior factor, q, which is directly related to the energy dissipation capacity of the structure. The prescribed values of q (1) are referred only to one limit state; (2) depend on the structural system and on the ductility class; (3) are constant; and (4) are not directly related to structural and non‐structural demands. Based on the literature, the inelastic seismic response of irregular building structures cannot be always estimated with safety by utilizing the methods of current seismic design codes. In this work, a preliminary performance‐based seismic design method which incorporates deformation‐controlled q factors, to better control the structural and non‐structural damage, is developed for space steel moment resisting frames irregular in plan view and in elevation within the framework of hybrid force/displacement (HFD) seismic design method. A large seismic response databank is generated on the basis of 88 space irregular MRFs, subjected to 42 pairs of ordinary ground motions, to develop the necessary empirical equations employed by the HFD. A realistic design example serves to demonstrate the advantages of the proposed method over the seismic design procedure of EC8.

Improved damping reduction factor models for different response spectra

The rationality and reliability of the damping reduction factor are of great significance to the seismic design of building structures. However, the values of damping reduction factor predicted by the existing models have great dispersions, which are mainly related to the regression model and the considered influencing factors. Based on the linear time history analysis of a single-degree-of-freedom system under 4716 ground motions, the influence degrees of the damping ratio, the natural vibration period, the ratio between the ground predominant period and the natural vibration period, the earthquake magnitude, the rupture distance, the site type (the average shear wave velocity in the top 30 m of soil), the significant duration, and the peak ground velocity to acceleration ratio (PGV/PGA) on the damping reduction factor are evaluated by the Spearman rank correlation coefficient. After that, improved damping reduction factor models are respectively proposed for different response spectra, in which only the damping ratio and the natural vibration period are considered as variables. Through the comparison with the existing damping reduction factor models and the robustness test under different natural ground motions, the improved damping reduction factor models are proved to have a reasonable expression form and strong robustness, which can accurately predict the damping reduction factors for different response spectra.

Development of risk-targeted seismic hazard maps for the Iranian plateau

This study aims to provide the risk-targeted seismic design maps and corresponding adjusting coefficients for different intensity measures on the Iranian plateau, using the iterative risk integral approach. The main purpose of this study is to provide the risk-targeted hazard maps with a uniform level of risk based on an acceptable collapse probability and risk threshold. The investigation applies the most recent and notable seismic hazard model for the studied region, namely the Earthquake Hazard Model of the Middle East (EMME). Having done the preprocessing procedures for characterizing the possible bias in the input data, hazard curves on 0.1° grids were extracted from the median values of the logic tree of the EMME model. Utilizing the deliberately rational values of the required parameters by the risk-targeting approach, i.e. 2% exceedance probability in 50 years as the 10% quantile of the fragility function, leads to reach some multiple uniform seismic risk maps with 1% probability of collapse in 50 years for each intensity measure. The imaginable inconsistency of the maps with historical data (as a picture of reality) has also been assessed in terms of underestimations or overestimations, using a two-sided statistical test at a 95% confidence level. The outcome of this study can be incorporated in the next revision of the national seismic code for a more reliable and robust seismic design of building structures.

Special Issue on Advanced Methods for Seismic Performance Evaluation of Building Structures

When an earthquake occurs, it causes great damage to a large area. Although seismic engineering continues to develop, it is reported that recently occurred earthquakes inflicted major damage to various structures and loss of human lives. Such earthquake damage occurs in high seismic regions as well as low to moderate seismic regions. This special issue contains topics on newly developed technologies and methods for seismic performance evaluation and seismic design of building structures.

Probabilistic Approach to Account for Soil-Structure Interaction in Seismic Design of Building Structures

AbstractThis paper proposes a novel probabilistic approach to account for soil-structure interaction (SSI) in the seismic design of building structures. In this approach, an SSI response modificati...

Analysis of the Application Example of the Assembled Over-limit and High-rise Seismic Design

The paper focuses on the analysis and research of the high-rise seismic design of prefabricated over-limits, and analyzes and explores the specific cases, systematically analyzes the design method of the entire prefabricated structure, especially important for the seismic design of building structures. It lays a good guarantee for ensuring the overall safety and stability of the prefabricated building structure.

Evaluation of natural periods and modal damping ratios for seismic design of building structures

A comprehensive technique for identification of modal properties (i.e. natural periods and equivalent modal damping ratios) of building structures is presented. The proposed identification technique employs a combination of multiple system identification methods; it utilizes the benefits and suppresses the shortcomings of each method to provide a succinct set of modal properties for building structures. Using the proposed modal identification technique, modal properties of 80 buildings with a total of 896 distinct seismic event and building direction records were identified. Simplified and practical equations for modal quantities along with the variation of such parameters for different structural system types, building height, and amplitude of excitation are studied and presented. A critical assessment of other similar studies and results are presented.

A universal approach for evaluating earthquake safety level based on societal fatality risk

Residual risk exists in our buildings even if they were designed in conformance with modern codes of practice. Various approaches have been implemented or proposed in the last decade for setting risk-based performance requirements for seismic design of building structures. However, there is insufficient consideration about the aggregated risk for society, which could be significant especially for a densely populated metropolitan city. This paper introduces a rational and universal approach for evaluating the adequacy of structural safety requirements by comparing societal risk functions based on probabilistic loss assessment with a proposed regulatory requirement that aims to limit the mortality rate to “as low as reasonably practicable (ALARP)”. The proposed approach is then applied to Melbourne, Australia, in a case study, which shows that the earthquake fatality risk for the society appears to be unacceptable. The outcome can be used for justification of a seismic retrofitting policy or a required change of the design code level. The proposed scheme is also applicable to other natural hazards and for safety engineering applications generally.

A “direct five-step procedure” for the preliminary seismic design of buildings with added viscous dampers

In the present work a direct procedure for the preliminary seismic design of building structures with added dampers is described which represents the simplification of the so-called “five-step procedure” originally developed in 2010 by some of the authors. The procedure is applicable to yielding frame structures with a generic along-the-height distribution of inter-storey viscous dampers. It is aimed at guiding the structural engineer through the sizing of both viscous dampers and structural elements making use of an equivalent static analysis approach. First, the peak structural response under earthquake excitation is reduced by imposing an overall reduction factor accounting for both the ductility demand and the viscous damping provided by the added dampers. Second, linear damping coefficients are calculated in order to reduce the structural response according to the selected target damping ratio. Then, analytical formulas allow the estimation of peak velocities and forces in the dissipative devices, and an energy criterion is used to identify the non-linear mechanical characteristics of the actual manufactured viscous dampers. Finally, the internal actions in the structural elements are estimated through the envelope of two equivalent static analyses (ESA). At this initial stage of the research, the procedure appears suitable for the preliminary design phase, while correction factors for the higher modes contributions need to be applied to improve its accuracy, especially for high-rise buildings. A numerical verification of the final behaviour of the system by means of non-linear time-history analyses is recommended. An applicative example is finally developed to highlight the soundness of the procedure.

Seismic performance of L-shaped multi-storey buildings with moment-resisting frames

Recent earthquakes have demonstrated that buildings with irregular configuration are more vulnerable to earthquake damage. Moreover, the configuration irregularities introduce major challenges in the seismic design of building structures. One such form of irregularity is the presence of re-entrant corners and torsional irregularity that causes stress concentration due to sudden changes in stiffness and torsion amplification in buildings. Constructive research into re-entrant corner and torsion-irregular buildings is therefore needed to evaluate the seismic response demands for reducing the potential damage. The aim of the study reported in this paper is to grasp the seismic performance of L-shaped irregular buildings with moment-resisting frames through an evaluation of the irregularity effects on measured seismic response demands. The results for inter-storey drift, storey shear force, overturning moment, torsion–moment responses at the base and along the building height, top-floor displacement and torsional irregularity coefficient prove that buildings with irregularity are more vulnerable than those with a regular configuration resulting from stress concentration and coupled lateral–torsional behaviour.

Seismic behavior of steel coupling beam with different buckling constraint materials

With constrained plates on both sides of steel coupling beam web, the continuous strengthening can be achieved in steel coupling beam subject to cyclic shear loading with web shear yielding failure. Compared to traditional steel coupling beam which sets stiffeners on the web, the local buckling of the new type of steel coupling beam with shear yielding will not occur, before the steel web reaches its ultimate shear strain, resulting in excellent energy dissipation capacity. Eight quasi-static tests on buckling constraint steel coupling beams with shear yielding had been carried out to study the impact of various constraint manners on seismic behavior of this type of steel coupling beam. Tests results showed that all the test specimens realized shear yielding and strengthening of bearing capacity, and major failure mode included weld joint fracture between flange and endplate and failure of constrained plate. Average over strength factor of the test specimens was 1.38, above 1.1, the minimum requirement of Code for Seismic Design of Building Structures. Among them, the over strength factor of test specimens which used 50mm-thick reinforced concrete constrained plates and 25mm-thick wooden constrained plates exceeded 1.5. Test specimens with different constraint methods showed similar yield shear strain. While test specimens without constrained plates showed the minimum ultimate shear strain, test specimens with 25mm-thick wooden constrained plates showed the maximum, approaching the ultimate shear strain of the web’s steel in material property test.

A direct design procedure for frame structures with added viscous dampers for the mitigation of earthquake-induced vibrations

A direct procedure for the seismic design of building structures with added viscous dampers is described in this paper. The procedure is applicable to regular multi-storey frame structures which are characterized by a period of vibration lower than 1.5 s. It aims at providing practical tools for the direct identification of the mechanical characteristics of the manufactured viscous dampers as well as for the structural design of the frame members’ so that a target level of performance is achieved. The design philosophy is to limit the structural damages under severe earthquakes. First, a target damping reduction factor is selected to achieve the desired reduction in the peak structural response. The linear damping coefficients of the equivalent linear viscous dampers are calculated taking advantage of modal damping ratios properties of classically damped systems. Then, simple analytical formulas for the estimation of peak inter-storey velocities are used, together with an energy criterion to identify the non-linear mechanical characteristics of the manufactured viscous dampers. Finally, the internal actions in the structural elements are estimated through the envelope of two equivalent static analyses (ESA), namely: ESA1 in which the naked structure is subjected to a first set of equivalent lateral forces, and ESA2 in which the structure, with rigid diagonal braces substituting the added viscous dampers, is subjected to a second set of equivalent lateral forces. At this preliminary stage of the research, the procedure is targeted for the preliminary design phase, since correction factors to improve the accuracy in the estimation of the peak inter-storey velocities needs to be calibrate. Therefore, for final design, non-linear dynamic analyses are recommended.

IRREGULARITY EFFECTS ON THE SEISMIC PERFORMANCE OF L-SHAPED MULTI-STORY BUILDINGS

Past and recent earthquakes events demonstrate that buildings with configuration irregularity are more vulnerable to earthquake damages. So it's essential to investigate the seismic response of these structures in active seismic zones to reduce the potential seismic damages. The configuration irregularities introduce major challenges in the seismic design of building structures. One such form of irregularity is the presence of re-entrant corners that causes stress concentration due to sudden changes in stiffness and torsion amplification in the buildings; hence causes early collapse. This, the conventional design codes have not recommendations for proper evaluation of these buildings yet. Thus, a constructive research into re-entrant corner irregularity problems is essentially needed greater than ever. The objective of this study is to grasp the seismic behavior of the buildings with irregular plan of L-shape floor plan through the evaluation of the configuration irregularity of re-entrant corners effects on measured seismic response demands. The measured responses include inter-story drift; story shear force; overturning moment; torsion moment at the base and along the building height; top floor displacement; and torsional Irregularity Ratio. Three dimensional finite element model of nine stories moment resisting frame buildings as reference model is developed; six L-shaped models are formulated with gradual reduction in the plan of the reference model. The models are analyzed with ETABS using Equivalent Static Load (ESL) and Response Spectrum (RS) Methods. The results prove that buildings with severe irregularity are more vulnerable than those with regular configuration resulting from torsion behavior, and the additional shear force produced in the perpendicular direction to the earthquake input. Also, in the codal empirical equation for the calculation of fundamental period of vibration could not grasp significant higher vibration modes such as torsional vibration of irregular buildings that could significantly affect seismic demands.

Erratum to: Crescent shaped braces for the seismic design of building structures

Erratum to: Crescent shaped braces for the seismic design of building structures

Seismic Response of a Four-Story Miniature Building with Replaceable Plastic Hinges

To emphasize on linear and nonlinear seismic behavior of building systems in education, a four-story miniature moment-resisting frame steel building was designed, built, and tested in a shaking table at the Structures Laboratory of the Department of Civil Engineering at the University of Canterbury, New Zealand. A prominent feature of the building is the incorporation of elements designed to form plastic hinges that can be easily replaced after a test with minimum effort and at a very low cost. This model is mainly aimed at education in undergraduate and graduate structural dynamics/earthquake engineering courses and it has also been used to support research. This article describes in detail the main features of the building, its design, and discusses the response of the building to two input ground motions. Because the use of pushover analyses is becoming an industry standard, the some relevant results will be compared with those predicted by such kind of analyses. This article is written in very simple terms and is aimed at the undergraduate and graduate student, at educators in structural design and at structural engineers involved in seismic design of building structures. This article covers many aspects that are seldom highlighted in building behavior to earthquake excitation and that are not always covered in design codes or guidelines.

Crescent shaped braces for the seismic design of building structures

This paper introduces a special lateral-resisting element, herein referred to as Crescent Shaped Brace (CSB). CSBs are characterised by a geometrical configuration which is “ad hoc” defined in order to provide the structure with prescribed multiple seismic performances, within the performance based seismic design framework. In detail, the present work gives analytical, numerical and limited experimental results in order to provide a comprehensive understanding of the mechanical behaviour of these devices, with special attention devoted to the seismic design purposes.

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

A composite shear wall concept based on concrete filled steel tube (CFST) columns and steel plate (SP) deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements: CFST columns; SP deep beams; and reinforced concrete (RC) strips. The RC strips are intended to allow the core structural elements — the CFST columns and SP deep beams — to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.