Damage potential of Loma Prieta ground motions

1991 ◽  
Vol 81 (5) ◽  
pp. 2048-2069 ◽  
Author(s):  
Helmut Krawinkler ◽  
Aladdin Nassar ◽  
Mohsen Rahnama
Keyword(s):  
Ground Motions ◽  
Soft Soil ◽  
Structural Performance ◽  
Damage Potential ◽  
Seismic Demands ◽  
Single Degree Of Freedom ◽  
Loma Prieta Earthquake ◽  
Single Degree ◽  
Loma Prieta ◽  
Attenuation Characteristics

Abstract This article focuses on an engineering evaluation of the ground motions recorded during the Loma Prieta earthquake. Regression analysis is employed to evaluate the attenuation characteristics of the elastic and inelastic strength demands imposed by rock and alluvium ground motions on bilinear single degree of freedom (SDOF) systems. Several records are used to illustrate the large seismic demands generated by soft soil ground motions. Strength capacities of modern code-designed structures are compared to the strength demands in order to assess the damage potential of the Loma Prieta ground motions. The Cypress structure is used as an example to illustrate the application of simple demand / capacity concepts for an evaluation of structural performance.

On the characteristics of local geology and their influence on ground motions generated by the Loma Prieta earthquake in the San Francisco Bay region, California

1992 ◽  
Vol 82 (2) ◽  
pp. 603-641 ◽  
Author(s):  
Roger D. Borcherdt ◽  
Gary Glassmoyer
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
San Francisco Bay ◽  
Ground Motions ◽  
Loma Prieta Earthquake ◽  
Franciscan Complex ◽  
Horizontal Acceleration ◽  
Geological Conditions ◽  
Peak Horizontal Acceleration ◽  
Loma Prieta

Abstract Strong ground motions recorded at 34 sites in the San Francisco Bay region from the Loma Prieta earthquake show marked variations in characteristics dependent on crustal structure and local geological conditions. Peak horizontal acceleration and velocity inferred for sites underlain by “rock” generally occur on the transverse component of motion. They are consistently greater with lower attenuation rates than the corresponding mean value predicted by empirical curves based on previous strong-motion data. Theoretical amplitude distributions and synthetic seismograms calculated for 10-layer models suggest that “bedrock” motions were elevated due in part to the wide-angle reflection of S energy from the base of a relatively thin (25 km) continental crust in the region. Characteristics of geologic and geotechnical units as currently mapped for the San Francisco Bay region show that average ratios of peak horizontal acceleration, velocity and displacement increase with decreasing mean shear-wave velocity. Ratios of peak acceleration for sites on “soil” (alluvium, fill/Bay mud) are statistically larger than those for sites on “hard rock” (sandstone, shale, Franciscan Complex). Spectral ratios establish the existence of predominant site periods with peak amplifications near 15 for potentially damaging levels of ground motion at some sites underlain by alluvium and fill/bay mud. Average spectral amplifications inferred for vertical and the mean horizontal motion are, respectively, (1,1) for sites on the Franciscan Complex (KJf), (1.4, 1.5) for sites on Mesozoic and Tertiary rocks (TMzs), (2.1, 2.0) for sites on the Santa Clara Formation (QTs), (2.3, 2.9) for sites on alluvium (Qal), and (2.1, 4.0) for sites on fill/Bay mud (Qaf/Qhbm). These mean values are not statistically different at the 5% significance level from those inferred from previous low-strain data. Analyses suggest that soil amplification and reflected crustal shear energy were major contributors to levels of ground motion sufficient to cause damage to vulnerable structures at distances near 100 km in the cities of San Francisco and Oakland.

Inelastic Response of a Spectrum-Compatible Artificial Accelerogram

1989 ◽  
Vol 5 (3) ◽  
pp. 477-493 ◽  
Author(s):  
Michael E. Barenberg
Keyword(s):  
Response Spectrum ◽  
Ground Motions ◽  
Normalization Procedure ◽  
Target Response ◽  
Single Degree Of Freedom ◽  
Inelastic Response ◽  
Strong Ground Motions ◽  
Single Degree ◽  
Initial Frequency ◽  
Strong Ground

The validity of evaluating the inelastic response of a structure subjected to an artificial accelerogram in lieu of a suite of eight recorded ground motions is determined by analyzing the inelastic response of single-degree-of-freedom oscillators over a range of frequencies from 1.0 to 10.0 Hz. A normalization procedure to minimize the dispersion in the ductility response of the oscillators subjected to the recorded ground motions is investigated. The artificial accelerogram is derived by superimposing closely spaced sine waves in order to match a target response spectrum. The results show that the artificial accelerogram is expected to produce the same amount of damage as the average of the recorded strong ground motions for structures with an initial frequency of less than 5.0 Hz and close to the average for the entire suite of ground motions for structures with frequencies greater then 5.0 Hz.

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

2001 ◽  
Vol 17 (2) ◽  
pp. 333-358 ◽  
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.

Impact of Near-Fault Ground Motions on the Efficiency of Viscous-Damping Systems

2016 ◽  
Author(s):  
Yin-Nan Huang ◽  
Chia-Ren Liu
Keyword(s):  
Energy Dissipation ◽  
Ground Motions ◽  
Viscous Damping ◽  
Major Focus ◽  
Seismic Demands ◽  
Single Degree ◽  
Near Fault ◽  
Long Period ◽  
The Impact ◽  
Damping Systems

Energy dissipation systems can effectively reduce the seismic demands of structures and protect them from damage. However, the effectiveness of the systems is not entirely independent from the dynamic characteristics of ground motions and may be challenged by long-period velocity pulses in near-fault ground motions. The major focus of this study is to clarify the impact of the characteristics of near-fault ground motions on the effectiveness of energy dissipation systems, particularly, structures equipped with viscous dampers. A series of response-history analyses are conducted using single degree-of-systems (SDOF) with periods varying between 0.2 and 5 seconds and damping ratios between 5% and 50% and subjected to fault-normal components of 91 sets of near-fault ground motions identified in a literature prepared by Prof. Jack Baker in 2007. The effectiveness of damping in reducing seismic demands of SDOF systems subjected to near-fault motions are discussed and a model are proposed to describe their relationship.

scholarly journals Rupture model of the 1989 Loma Prieta earthquake from the inversion of strong-motion and broadband teleseismic data

1991 ◽  
Vol 81 (5) ◽  
pp. 1540-1572 ◽  
Author(s):  
David J. Wald ◽  
Donald V. Helmberger ◽  
Thomas H. Heaton
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Strong Motion ◽  
High Gain ◽  
Temporal And Spatial Distribution ◽  
Origin Time ◽  
Loma Prieta Earthquake ◽  
Motion Data ◽  
Teleseismic Data ◽  
Loma Prieta

Abstract We have used 24 broadband teleseismic and 48 components of local strong-motion velocity records of the 1989 Loma Prieta earthquake in a formal inversion to determine the temporal and spatial distribution of slip. Separate inversions of the teleseismic data (periods of 3 to 30 sec) or strong-motion data (periods of 1 to 5 sec) result in similar models. The data require bilateral rupture with relatively little slip in the region directly updip from the hypocenter. Slip is concentrated in two patches: one centered 6 km northwest of the hypocenter at a depth of 12 km and with a maximum slip of 350 cm, and the other centered about 5 km southeast of the hypocenter at a depth of 16 km and with a maximum slip of 460 cm. The bilateral nature of the rupture results in large amplitude ground motions at sites located along the fault strike, both to the northwest and the southeast. However, the northwestern patch has a larger moment and overall stress drop and is, consequently, the source of the largest ground motion velocities, consistent with the observed recordings. This bilateral rupture also produces relatively modest ground motion amplitudes directly updip from the hypocenter, which is in agreement with the velocity ground motions observed at Corralitos. There is clear evidence of a foreshock (magnitude between 3.5 and 5.0) or a slow rupture nucleation about 2 sec before the main part of the rupture; the origin time implied by strong-motion trigger times is systematically 2 sec later than the time predicted from the high-gain regional network data. The seismic moment obtained from either of the separate data sets or both sets combined is about 3.0 × 1026 dyne-cm and the potency is 0.95 km3.

Damage to buildings due to the 1989 Loma Prieta earthquake — a Canadian code perspective

1990 ◽  
Vol 17 (5) ◽  
pp. 813-834 ◽  
Author(s):  
Denis Mitchell ◽  
René Tinawi ◽  
Richard G. Redwood
Keyword(s):  
Seismic Design ◽  
Soft Soil ◽  
Steel Structures ◽  
Building Structures ◽  
Limit States ◽  
Loma Prieta Earthquake ◽  
Loma Prieta ◽  
October 17 ◽  
Design Earthquake ◽  
Observed Damage

Damage to building structures during the October 17, 1989, Loma Prieta earthquake prompted site visits by the authors. This paper presents examples of damage to buildings constructed with reinforced concrete, steel, masonry, and timber. The observed damage is used to illustrate some of the seismic design clauses in the 1990 National Building Code of Canada, the 1984 Canadian Standards Association (CSA) Standard for the Design of Concrete Structures for Buildings, and the 1989 CSA Standard for the Limit States Design of Steel Structures. The important roles played by the presence of soft soil, poor structural layouts, inadequate detailing, the lack of reinforcement in masonry, as well as inadequate connections to foundations are highlighted. Examples of the performance of upgraded structures are also given, and the concern over the presence of existing hazardous buildings in significant seismic zones in Canada is emphasized. Key words: seismic design, earthquake, Loma Prieta, structures, codes, concrete, steel, masonry, timber, upgrading.

Estimation of Hysteretic Energy of MDOF Structures Based on Equivalent SDOF Systems

2007 ◽  
Vol 340-341 ◽  
pp. 435-440
Author(s):  
Hong Nan Li ◽  
Feng Wang ◽  
Zhao Hui Lu
Keyword(s):  
Ground Motions ◽  
Estimation Method ◽  
Degree Of Freedom ◽  
Energy Relation ◽  
Energy Estimation ◽  
Single Degree Of Freedom ◽  
Hysteretic Energy ◽  
Single Degree ◽  
Energy Demands ◽  
The Relationship

It is important for obtaining the relationship between seismic energies of single degree-of-freedom (SDOF) systems and multiple degree-of-freedom (MDOF) structures in engineering. In this paper, the formula of hysteretic energy between the MDOF structures and equivalent SDOF systems is developed. Here is also presented the procedure for estimating hysteretic energy of MDOF structures subjected to severe ground motions employing the energy relation equation based on equivalent SDOF systems. Eight examples for two regular and six irregular MDOF structures show that the procedure to obtain the hysteretic energy demands of MDOF structures may be used as a simple and effective energy estimation method.

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