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A methodology for assessing the seismic capacity of existing frames in terms of energy is proposed. It estimates the global amount of input energy—in form of a factor AEIU—and hysteretic energy that the overall structure can dissipate until collapse under earthquake-type loadings. The method requires static pushover analyses to determine the ductility factor and energy shape of an equivalent single-degree-of-freedom system for the first—two or more—modes. The procedure accounts for the relation between the frequency content of the earthquake expected at the site and the dynamic properties of the existing structure. It can be useful for evaluating the possible deficit on energy dissipation capacity of existing structures, and for designing seismic retrofit solutions. Finally, the methodology is applied to reinforced concrete frames with wide beam-column connections representative of existing post-1970 buildings located in the earthquake-prone southern part of Spain. 相似文献
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A. Benavent-Climent F. López-Almansa D.A. Bravo-González 《Soil Dynamics and Earthquake Engineering》2010
Energy input spectra applicable to the seismic design of structures in moderate-to-high seismicity regions are proposed. Such design inputs are derived from the bilinear envelope of individual spectra obtained for 144 ground motions recorded in Colombia. In the short period region the spectra account for the increase of input energy, due to plastification of the structure, through a new formula derived from extensive nonlinear analyses. The proposed energy input design spectra are compared with the provisions of the Colombian seismic code, and with those proposed for Japan, Spain, Iran and Greece. It is found that the proposed spectra are more demanding than the current Colombian seismic code, and that they agree with those developed recently for six cities in Greece, yet applying a different approach. An empirical equation for estimating the portion of the total seismic input energy that contributes to structural damage is also developed. 相似文献
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A seismic index method for vulnerability assessment of existing frames: application to RC structures with wide beams in spain 总被引：1，自引：1，他引：0
A. Benavent-Climent 《Bulletin of Earthquake Engineering》2011,9(2):491-517
A method for assessing the vulnerability of existing frames in terms of an energy-based seismic index is proposed. The ground
motion is characterized by the so-called Seismic Hazard Energy Factor AE
I
, and the susceptibility of the frame to damage is a function of two counterpart energy factors, AE
IS
and AE
IU
. AE
IS
represents the level of the “maximum earthquake” that the frame can sustain within the elastic range. AE
IU
characterizes the level of the “ultimate earthquake” associated with the collapse of the structure. The procedure takes into
account the relation between the dynamic properties of the existing frame and the spectral shape of the ground motion expected
at the site. The seismic index used by the method has a transparent and direct physical meaning; thus, it is useful not only
for screening existing buildings but also to design a seismic retrofit solution, if needed. The method is applied to reinforced
concrete frames with wide beam-column connections built in the southern part of Spain during the 1970’s, 1980’s and 1990’s. 相似文献
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This paper proposes a method for the seismic retrofitting of existing frames by adding hysteretic energy dissipating devices (EDDs). The procedure is based on the energy balance of the structure, and it is used to determine the lateral strength, the lateral stiffness and the energy dissipation capacity of the EDDs needed in each story to achieve prescribed target performance levels for a given earthquake hazard. The performance levels are governed by the maximum lateral displacement. The earthquake hazard is characterized in terms of input energy and several seismological parameters, and further takes into account the proximity of the earthquake to the source. The proposed method deals with the effect of the EDDs explicitly in terms of hysteretic energy, bypassing equivalent viscous damping approximations, and directly quantifies the cumulative damage induced in the EDDs. The validity of the method is assessed numerically through nonlinear dynamic response analyses with near-fault and far-field ground motions, as well as experimentally through dynamic shaking table tests. 相似文献
6.
The seismic performance of two RC interior wide beam-column connections representative of existing frames designed and detailed
according to past construction practices in the moderate-seismicity Mediterranean area was investigated experimentally. The
specimens were subjected to axial loads, moderate levels of gravity loading and cyclic displacements up to failure. The specimens
exhibited a “strong column-weak beam” type of flexural yielding mechanism. The wide beams did not reach the expected capacities
corresponding to the formation of a full-width plastic hinge. The wide-beam longitudinal bars exhibited significant slippage,
and the transverse beams underwent severe torsion cracking and even failure; this caused severe pinching in the load versus
displacement hysteretic loops and exacerbated the intrinsic flexibility of this type of connection. The average drift ratios
at first yielding of the wide beam longitudinal reinforcement and at failure were 2.7 and 4.5%, respectively. The displacement
ductility ratio was about 2.8. The ultimate energy dissipation capacity of each specimen—obtained by dividing the total plastic
strain energy by the product of the yield load and yield displacement—was approximately 9, which is about one fourth of the
value recommended for providing adequate seismic performance. Finally, a simple approach is suggested for prediction of the
bending capacity of existing connections. 相似文献
7.
The bidirectional response of a portion of a reinforced concrete (RC) waffle-flat plate (WFP) structure subjected to far-field ground motions is studied through shake table tests. The test specimen is a scaled portion of a prototype structure designed under current building codes and located in a region of moderate seismicity of the Mediterranean area. The specimen was subjected to a sequence of tests of increasing acceleration amplitude that respectively represented very frequent, frequent, design, and very rare earthquakes at the site. The test structure performed well (basically in the elastic domain) under very frequent and frequent earthquakes, approached the boundary between the performance levels of life safety and near collapse under the design earthquake, and collapsed under the very rare earthquake. Damage concentrated at column bases and at the transverse beams of the exterior plate-to-column connection. Columns dissipated about 10% of the total energy that contributes to damage, and the rest was dissipated by the exterior plate-column connection. The total energy input on the structure until collapse under the bidirectional seismic action was very close to the value obtained in previous studies on a similar specimen tested under unidirectional ground motions. The capacity curve estimated from the experimental base shear vs top displacement relationship suggests it is best to use a behavior factor of at most q = 2 when designing WFP structures with the reduced-spectrum force-based approach. 相似文献
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F. López-Almansa A. U. Yazgan A. Benavent-Climent 《Bulletin of Earthquake Engineering》2013,11(4):885-912
This work proposes design energy spectra in terms of an equivalent velocity, intended for regions with design peak acceleration 0.3 g or higher. These spectra were derived through linear and nonlinear dynamic analyses on a number of selected Turkish strong ground motion records. In the long and mid period ranges the analyses are linear, given the relative insensitivity of the spectra to structural parameters other than the fundamental period; conversely, in the short period range, the spectra are more sensitive to the structural parameters and, hence, nonlinear analyses are required. The selected records are classified in eight groups with respect to soil type (stiff or soft soil), the severity of the earthquake in terms of surface magnitude $M _\mathrm{s} (M_\mathrm{s} \le $ 5.5 and $M _\mathrm{s} >$ 5.5) and the relevance of the near-source effects (impulsive or vibratory). For each of these groups, median and characteristic spectra are proposed; such levels would respectively correspond to 50 and 95 % percentiles. These spectra have an initial linear growing branch in the short period range, a horizontal branch in the mid period range and a descending branch in the long period range. Empirical criteria for estimating the hysteretic energy from the input energy are suggested. The proposed design spectra are compared with those obtained from other studies. 相似文献
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It is not common to purposely subject the web of wide‐flange or I‐sections to out‐of‐plane bending. However, yielding the web under this loading condition can be a stable source of energy dissipation as the transition at the corner from the web to the flanges is smooth and weld‐free; this prevents stress concentrations causing premature failure and eliminates uncertainties and imperfections associated with welding. Further, short segments of wide‐flange or I‐sections constitute a simple and inexpensive energy dissipating device as minimum manufacturing is required and leftovers not useful for other structural purposes can be re‐utilized. This paper proposes a new type of seismic damper in the form of braces based on yielding the web of short length segments of wide‐flange or I‐shaped steel sections under out‐of‐plane bending. The hysteretic behavior and ultimate energy dissipation capacity is investigated via component tests under cyclic loads. The experimental results indicate that the damping device has stable restoring force characteristics and a high energy dissipation capacity. Based on these results, a simple hysteretic model for predicting the load–displacement curve of the seismic damper is proposed, along with a procedure for predicting its ultimate energy dissipation capacity and anticipating its failure under arbitrarily applied cyclic loads. The procedure considers the influence of the loading path on the ultimate energy dissipation capacity. Finally, shaking table tests on half‐scale structures are conducted to further verify the feasibility and effectiveness of the new damper, and to assess the accuracy of the hysteretic model and the procedure for predicting its failure. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
Ariel Catalán Amadeo Benavent-Climent Xavier Cahís 《Soil Dynamics and Earthquake Engineering》2010,30(1-2):40-49
The behaviour of a building during an earthquake depends on many factors including the characteristics of the ground motion, the configuration and dynamic characteristics of the structure, the hysteretic behaviour of the structural components, the building's non-structural parts, and the local soil behaviour. When conducting seismic assessment studies, controlling the first factor involves selecting and scaling appropriate earthquake records. It is a common practice to scale the records to fit a target acceleration response Sa determined from a pre-determined spectrum or attenuation law. In doing so, two key-problems must be faced: (i) the value adopted for the “effective” period T1,which lengthens as the structure enters the non-linear range, and (ii) the reliability of the reference value adopted for Sa(T1). In this work, the influence of selecting appropriate values for these two parameters—T1 and Sa(T1)—on the response of the building is investigated from the study of two structures, of 4 and 8 stories. The study does not focus on evaluating a particular seismic code; rather, it uses a European attenuation model as the target spectrum. Non-linear dynamic response analyses are carried out to investigate the Collapse Prevention State of these structures subjected to records representative of a Performance-based Earthquake Engineering level characterized by 2% exceedence in 50 years with 2475 years of return time. The records are selected from a database of European earthquakes, and the failure of the structures is evaluated by statistical means. From the results of the analyses, it is proposed that in seismic assessment studies the reference period for scaling should be 1.1 times the fundamental period of the structure, and at least 30 records should be used to guarantee reliable results. 相似文献