SEISMIC DEMAND OF BUCKLING-RESTRAINED BRACES INSTALLED IN STEEL ARCH BRIDGES UNDER REPEATED EARTHQUAKES

A steel arch bridge originally designed against moderate earthquakes is retrofitted by installation of buckling-restrained braces (BRBs) to sustain severe earthquakes. Two retrofitting methods are considered to obtain good seismic performance of this arch bridge. The original model and retrofitted models subjected to the major earthquakes are investigated by dynamic analyses using 12 patterns of severe (level 2) earthquakes as input ground motions. It is found that the retrofitted models using BRBs can greatly improve seismic performance (displacement, section force, strain, reaction force, etc.) of the steel arch bridge. In addition, to investigate the influence of repeated earthquakes on the seismic responses of the main structure and the demands of BRBs, 12 patterns of earthquake ground motions are repeated by three times. Based on the analytical results, the seismic demands of BRBs against repeated earthquakes are obtained, and the required capacity of BRBs is recommended using a safety factor concluded by comparing the demands under the earthquake applied one and three times. Finally, the influence of the different yield stress on the demand of BRBs is examined by changing the steel grade of BRBs.

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A Seismic Effective Method for Double-Layer Reticulated Shell Using Buckling-Restrained Braces

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.163-167.2852 ◽

2010 ◽

Vol 163-167 ◽

pp. 2852-2856

Author(s):

Chang Wu ◽

Xiu Li Wang

Keyword(s):

Double Layer ◽

Seismic Performance ◽

Linear Time ◽

Ground Motions ◽

Equations Of Motion ◽

Time History ◽

Original Structure ◽

Loading Test ◽

Strong Earthquakes ◽

Buckling Restrained Braces

In this study a kind of buckling-restrained braces (BRBs) as energy dissipation dampers is attempted for seismic performance of large span double-layer reticulated shell and the effectiveness of BRBs to protect structures against strong earthquakes is numerically studied. The hysteretic curve of such members is obtained through the simulation of the cyclic-loading test, and the equations of motion of the system under earthquake excitations are established. BRBs are then placed at certain locations on the example reticulated shell to replace some normal members, and the damping effect of the two installation schemes of BRBs is investigated by non-linear time-history analyses under various ground motions representing major earthquake events. Compared with the seismic behavior of the original structure without BRBs, satisfactory seismic performance is seen in the upgraded models, which clarifies the BRBs can reduce the vibration response of spatial reticulated structure effectively and the new system has wide space to develop double layer reticulated shell.

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Comparative Study of the Inelastic Seismic Demand of Eastern and Western Canadian Sites

Earthquake Spectra ◽

10.1193/1.1586178 ◽

2001 ◽

Vol 17 (2) ◽

pp. 333-358 ◽

Cited By ~ 33

Author(s):

Robert Tremblay ◽

Gail M. Atkinson

Keyword(s):

Current Practice ◽

Ground Motions ◽

Seismic Demand ◽

Uniform Hazard Spectra ◽

Damage Potential ◽

Single Degree Of Freedom ◽

Dynamic Analyses ◽

Damage Law ◽

Nonlinear Dynamic Analyses ◽

R Factors

The damage potential of earthquake ground motions compatible with site-specific 2% in 50 year uniform hazard spectra is compared at two North American sites in areas of moderate seismic hazard: Montreal, in the east, and Vancouver, along the west coast. For Vancouver, crustal, subcrustal and Cascadia subduction ground motion earthquake ensembles are considered. Nonlinear dynamic analyses of bi-linear single-degree-of-freedom oscillators exhibiting various ductility levels and damage laws were performed to determine R factors required to prevent structural collapse for each site and each system. Then, inelastic response parameters were computed for the general design case, wherein a prescribed R factor is used for a given system irrespective of tectonic region or structural period. The results show that the R factors vary with the ductility level, the damage law, the structural period, and the tectonic region. Neglecting the latter two dependencies in design, as is current practice, may lead to significant discrepancies in the level of protection achieved for different structures in different regions.

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DEVELOPMENT OF AN IMPROVED INTENSITY MEASURE IN ORDER TO REDUCE THE VARIABILITY IN SEISMIC DEMANDS UNDER NEAR-FAULT GROUND MOTIONS

Journal of Earthquake and Tsunami ◽

10.1142/s1793431112500121 ◽

2012 ◽

Vol 06 (02) ◽

pp. 1250012 ◽

Cited By ~ 5

Author(s):

A. YAHYAABADI ◽

M. TEHRANIZADEH

Keyword(s):

Seismic Performance ◽

Ground Motions ◽

Intensity Measure ◽

Seismic Performance Assessment ◽

Seismic Demands ◽

Demand Prediction ◽

Near Fault ◽

Long Period ◽

Short Period ◽

Pseudo Spectral

Intensity measure (IM) which describes the strength of an earthquake record plays an important role in the seismic performance assessment of structures. An improved IM that can reduce the variability in seismic demands helps reducing the number of records necessary to predict the seismic performance with sufficient accuracy. In this study, an improved RMS-based IM is developed based on the results obtained from incremental dynamic analyses of short-to relatively long-period frames under an ensemble of near-fault pulse-like earthquake records. It is observed that the root-mean-square value of pseudo spectral accelerations, (Sa) rms , is generally superior to that of spectral velocities, (Sv) rms , in seismic demand prediction under near-fault records. To compute (Sa) rms as IM, two appropriate period ranges are suggested for short- and moderated-to relatively long-period frames, respectively. Comparing the efficiency of (Sa) rms with several advanced IMs shows that (Sa) rms is more efficient in predicting the inelastic response and collapse capacity of short-period frames. It is also found that intensity measure (Sa) rms is sufficient with respect to the magnitude and source-to-site distance for all frames of various heights under near-fault ground motions.

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Seismic Performance Evaluation of a Multi-Span Existing Masonry Arch Bridge

The Open Civil Engineering Journal ◽

10.2174/1874149501711011191 ◽

2017 ◽

Vol 11 (1) ◽

pp. 1191-1207 ◽

Cited By ~ 15

Author(s):

Michele D’Amato ◽

Michelangelo Laterza ◽

Vito Michele Casamassima

Keyword(s):

Seismic Performance ◽

Second World War ◽

World War ◽

Masonry Arch ◽

Arch Bridge ◽

Seismic Performance Evaluation ◽

Strategic Role ◽

Arch Bridges ◽

Second World ◽

Masonry Arch Bridge

Introduction: Existing old masonry arch bridges represent an architectural and cultural heritage of inestimable value because most of them were built in the last century and are still in service. They represent a very important part of roads and railways networks, having also an important strategic role. They are actually serving roads characterized by transit loads definitively heavier and more frequent than the ones of the past. Moreover, very often maintenance absence and material worn away, increased by the way by the environmental conditions, accelerate more and more the elements deterioration with a consequent loss of integrity and reduction of their carrying capacity. Methods: In this paper the seismic assessment of an old multi span masonry arch bridge still in service is evaluated. The bridge, located in Southern Italy, was built before the Second World War and crosses the “Cavone” River, from which it takes the name. Results and Conclusion: A series of numerical analyses are performed in order to evaluate its seismic performance and the model sensitivity with respect to the assumed masonry mechanical properties.

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Design Seismic Demands from Seismic Response Analyses: A Probability-Based Approach

Earthquake Spectra ◽

10.1193/1.3533035 ◽

2011 ◽

Vol 27 (1) ◽

pp. 213-224 ◽

Cited By ~ 19

Author(s):

Brendon A. Bradley

Keyword(s):

Seismic Response ◽

Ground Motions ◽

Design Guidelines ◽

Rational Approach ◽

Seismic Demand ◽

Seismic Demands ◽

Sample Mean ◽

Routine Design ◽

Earthquake Resistant Design ◽

The Mean

Earthquake-resistant design guidelines commonly prescribe that when conducting seismic response analyses: (i) a minimum of three ground motions can be used; (ii) if less than seven ground motions are considered, the maximum of the responses should be used in design; and (iii) if seven or more ground motions are considered the average of the responses should be used in design. Such guidelines attempt to predict the mean seismic response from a limited number of analyses, but are based on judgment without a sound, yet pragmatic, theoretical basis. This paper presents a rational approach for determining design seismic demands based on the results of seismic response analyses. The proposed method uses the 84th percentile of the distribution of the sample mean seismic demand as the design seismic demand. This approach takes into account: (i) the number of ground motions considered; (ii) how the ground motions are selected and scaled; and (iii) the differing variability in estimating different types of seismic response parameters. A simple analytic function gives a ratio which, when multiplied by the mean response obtained from the seismic response analyses, gives the value to be used in design, thus making the proposed approach suitable for routine design implementation.

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Seismic Performance Spectra

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.163-167.443 ◽

2010 ◽

Vol 163-167 ◽

pp. 443-453

Author(s):

Wen Feng Liu ◽

Xing Pan Fu

Keyword(s):

Seismic Performance ◽

Seismic Design ◽

Response Spectra ◽

Seismic Demand ◽

Three Dimension ◽

Seismic Demands ◽

Performance Objective ◽

Objective Performance ◽

Performance Based Seismic Design ◽

Ground Motion Records

The seismic performance spectrum is a new kind of the response spectra which is formed according to the designated performance objectives. The performance objectives are changed according to the performance objective level and period of structure, and are different in the acceleration sensitive, velocity sensitive and displacement sensitive range in the seismic performance spectrum. The seismic performance spectrum formulas are derived, which demonstrate the mathematic relationship between the seismic demands of the different performance objective levels and the period of structure. The fitted formulas of the seismic performance spectra for seismic design are obtained due to statistical result of 1085 ground motion records. The new seismic performance spectra are shown in visual three-dimension figures which can represent the seismic demand, performance objective and period of structure in this paper. The philosophy of the seismic performance spectrum is analyzed which reveals the rules for estimating seismic demand of structure at the different performance objective levels. So the multi-objective performance-based seismic design is also proposed using the seismic performance spectrum.

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Effectiveness of earthquake selection and scaling method in New Zealand

Bulletin of the New Zealand Society for Earthquake Engineering ◽

10.5459/bnzsee.40.3.160-171 ◽

2007 ◽

Vol 40 (3) ◽

pp. 160-171 ◽

Cited By ~ 6

Author(s):

Rajesh P. Dhakal ◽

Sandip Singh ◽

John B. Mander

Keyword(s):

New Zealand ◽

Ground Motion ◽

Ground Motions ◽

Time History ◽

Seismic Demand ◽

Scaling Method ◽

Ground Acceleration ◽

Seismic Demands ◽

Least Squares Fit ◽

Ground Motion Records

In New Zealand, time history analysis is either the required or preferred method of assessing seismic demands for torsionally sensitive and other important structures, but the criteria adopted for the selection of ground motion records and their scaling to generate the seismic demand remains a contentious and debatable issue. In this paper, the scaling method based on the least squares fit of response spectra between 0.4-1.3 times the structure’s first mode period as stipulated in the New Zealand Standard for Structural Design Actions: Earthquake Actions (NZS1170.5) [1] is compared with the scaling methods in which ground motion records are scaled to match the peak ground acceleration (PGA) and spectral acceleration response at the natural period of the structure corresponding to the first mode with 5% of critical damping; i.e. Sa(T1, 5%). Incremental dynamic analysis (IDA) is used to measure the record-to-record randomness of structural response, which is also a measure of the efficiency of the intensity measure (IM) used. Comparison of the dispersions of IDA curves with the three different IMs; namely PGA, Sa(T1, 5%) and NZS1170.5 based IM, shows that the NZS1170.5 scaling method is the most effective for a large suite of ground motions. Nevertheless, the use of only three randomly chosen ground motions as presently permitted by NZS1170.5 is found to give significantly low confidence in the predicted seismic demand. It is thus demonstrated that more records should be used to provide a robust estimate of likely seismic demands.

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