Earthquake Spectra

The displacement coefficient method proposed in FEMA 440 was evaluated using response statistics from a comprehensive set of nonlinear simulations of multi degree of freedom systems under both far-fault and near-fault ground motions. The study finds that it is practically difficult to achieve high relative strength factors (R values equal to or greater than 6.0) for very stiff systems thereby dictating the need to define R-dependent demand coefficients. The approximate expressions proposed in FEMA 440 for the C₂ coefficient is shown to underestimate the displacement demand of stiffness-degrading short period systems. Additional nonlinear simulations were performed to investigate the combined effect of strength degradation and P-Delta effects on the displacement demands of MDOF systems. A new expression for the modification factor that reflect combined P-Delta and degrading effects for the estimation of displacement demands is proposed.

In contrast to building structural components, very little is known about the dynamic behavior of nonstructural components and systems (NCSs) within buildings. These systems come in such a variety of types that it can be overwhelming from an analysis perspective. Furthermore, an overarching issue is the limited test data available for characterizing their dynamic behavior. In this paper, an interior monitoring system is presented and used to monitor the response of a variety of NCSs within a full-scale building subjected to forced-vibration loading. The remotely operated monitoring system consists of an integrated array of off-the-shelf components, including; analog and digital (camera) sensors, acquisition PCs, and GPS synchronization equipment. Within the test building, the NCSs monitored include: (1) bench and shelf furnishing systems, (2) furnishing mounted equipment, and (3) piping systems. Results from the building vibration tests indicate that the interior furnishing systems considered here are very stiff with first mode frequencies in the range of 7–11 Hz and damping ratios between 4%–13%. Motion amplification at the top of the furnishing systems ranged between 1.5 and 4 times the floor level motion. These measurements highlight the importance of considering the transmissibility characteristics of building furnishings when estimating building NCS dynamic response.

This paper discusses the effects of using different input-motion-boundary-conditions on the sensitivity of numerical simulations results to errors in material properties of a specimen tested on a shaking table. In the flexible-actuator-prescribed-force-boundary-condition, input is specified by a force across an actuator element that connects the shaking table to a reaction mass. In the prescribed-displacement-boundary-condition, the measured shaking table motion in the experiment is prescribed in the simulation. The flexible-actuator-prescribed-force approach yielded smaller, almost constant sensitivity of simulation results to input properties. The prescribed-displacement approach yielded larger and more variable sensitivities. The sensitivity of results depends on the how the boundary conditions are handled has further implications: the assessment of a comparison between a simulation and an experimental result should be performed with due consideration to the effect of the boundary conditions on the comparison, and numerically determined sensitivities may not be physically meaningful if the boundary condition is not accurately modeled.

The safety of building structures and contents, as well as the comfort of occupants, under such strong forces as earthquakes and typhoons remain major engineering concerns. In order to improve our understanding of building structural responses, records of a structural array in the 30-story PS Building in Taipei from the M7.6 Chi-Chi earthquake and Typhoon Aere are analyzed. In addition, wind data measured at the Taipei Meteorological Station are also used. First, the field measurement data clearly demonstrate that serviceability of the PS Building met the criteria for occupant comfort during Typhoon Aere. Secondly, several structural vibration parameters of this highrise building, including the transfer functions, natural frequencies, damping ratios and mode shapes, excited by the Chi-Chi earthquake, Typhoon Aere, and ambient vibrations are also determined and compared. The results show the frequency of the first mode for the longitudinal components is approximately 8.6% lower for the earthquake than the ambient vibrations. The transverse mode frequencies behave similarly. In contrast, frequency changes from the typhoon to ambient vibrations are in the third decimal (1.3% and 0.9% lower in the longitudinal and transverse directions, respectively), indicating little nonlinearity. The damping ratios of the PS Building apparently increase with vibration amplitudes. Finally, results of a spectral ratio analysis of the Chi-Chi earthquake data do not indicate significant SSI effects in the longitudinal and transverse directions.

The M_w6.4 Achaia–Elia (Greece) earthquake on 8 June 2008 was a right-lateral strike-slip event on a nearly vertical faul. Moment tensor solutions coupled with geologic structure and aftershock distributions suggest a fault strike of approximately 210° on a previously unmapped fault. Rupture appears to have been concentrated over a 10–25 km depth range and did not break the surface. The northern rupture limit appears to correspond to a NW-striking normal fault near the Kato Achaia coastline. The mainshock was recorded by 27 accelerometers at distances from the surface projection of the fault ranging from approximately 15 to 350 km. The data demonstrate faster distance attenuation than predicted by contemporary Greek ground motion prediction equations (GMPEs). On the other hand, an NGA GMPE generally captures the distance attenuation but shows underprediction bias at short and long periods. Despite the presence of a range of site conditions at recording stations in the city of Patras, we find no obvious effect of sediment depth on response spectra. We show the possible presence of rupture directivity at the north end of this bilateral rupture, but no apparent effect at the southern end. We described several relatively well-documented incidents of nonground failure and ground failure associated with liquefaction/lateral spreading and landslides.

Recent earthquakes in Pakistan demonstrated that the region is highly seismic. Masonry buildings constructed with stones, concrete blocks, and fired-clay bricks and concrete buildings were damaged during the 8 October 2005 Kashmir earthquake. This paper presents the seismic behavior of reinforced concrete and masonry buildings in northern part of the North-West Frontier Province (NWFP) and Kashmir during the earthquake. Most of the buildings were observed to be nonengineered or semi-engineered. The paper presents an overview of the 1937 Quetta building code and the 1986 and 2007 building codes of Pakistan. Lessons learned during the earthquake are also presented.

A study for the Multidisciplinary Center for Earthquake Engineering Research (MCEER) provides fragility functions for 52 varieties of mechanical, electrical, and plumbing (MEP) equipment commonly found in commercial and industrial buildings. For the majority of equipment categories, the MCEER study provides multiple fragility functions, reflecting important effects of bracing, anchorage, interaction, etc. The fragility functions express the probability that the component would be rendered inoperative as a function of floor acceleration. That work did not include the evidence underlying the fragility functions. As part of the ATC-58 effort to bring second-generation performance-based earthquake engineering to professional practice, we have compiled the original MCEER specimen-level performance data into a publicly accessible database and validate many of the original fragility functions. In some cases, new fragility functions derived by ATC-58 methods show somewhat closer agreement with the raw data. Average-condition fragility functions are developed here; we will address in subsequent work the effect of potentially important—arguably crucial—performance-modifying factors such as poor anchorage and interaction.

The seismic response of the twelfth-century Byzantine church of Panhagia Krina in Chios, Greece, is investigated in this paper. The numerical model implements all the details of the geometry of the structure and is validated by comparison of the dynamic characteristics with ambient vibration measurements. Time-history elastic analyses are performed for selective seismic motions, chosen to comply with the expected ground motion in the area. The results show that the linear elastic approach can predict the existing damage quite accurately and explain the collapses that occurred during the 1881 earthquake. The effectiveness of several interventions is also examined; in some cases, cracks were introduced in the model to overcome the limitations of the elastic analysis. The proposed interventions enhance the structure but they cannot eliminate the possibility of severe damage or even local collapses during future seismic events. This is because there are inherent problems in the structure, e.g., the large size of the dome of the main church compared with the overall size of the structure and the structurally weak system of support of this dome.

The M_w 8.4 23 June 2001 Southern Peru earthquake generated intense ground motions in a large region encompassing southern Peru and northern Chile. The earthquake was recorded by seven strong motion stations with peak ground accelerations ranging from 0.04 g to 0.34 g for site-to-fault distances ranging from about 70 km to 220 km. At this time, there are no other strong motion records for an earthquake of this magnitude. Hence, the strong motion data set from this earthquake is unique and of particular interest to engineers dealing with seismic design in subduction regions. This paper presents an engineering analysis of the strong motion records. Shear-wave velocity profiles were measured using Spectral Analysis of Surface Waves methods at four stations. Measured shear-wave velocities are high, indicating that all sites classify as stiff soil sites (Site C) according to the International Building Code classification scheme. The strong motion set is characterized by strong high frequency content at large distances from the fault. Site response contributed at least in part to the observed high frequency content in the ground motions. In general, current attenuation relationships for spectral acceleration underpredicted the observed ground motions.

Using ground motion residuals of four NGA models, directivity effect and the dependence of directivity on various seismological and geometrical parameters were studied and correction terms for the four models were obtained. Directivity was clearly seen in the ground motion residuals of most earthquakes in the NGA database. Specifically, this phenomenon was found to be significant for large earthquakes, but it was not consistently observed for small events. It was seen to strongly depend on period of ground motion and on source distance, having its largest values in the very near-source region and for long periods. This study further demonstrated that the intensity of directivity depends on the geometry of the fault, orientation of fault surface with respect to the site, and the location of hypocenter. Applying the correction terms to the NGA models resulted in considerable reductions in the uncertainty term sigma, especially at long periods and at short distances.

Two one-third-scale three-story models of special inverted-V-braced frames with zipper struts were tested under quasistatic cyclic loads. Zipper frames utilize a vertical element at the intersection of chevron braces and floor beams to distribute the unbalanced vertical forces due to brace buckling. Two ground motions representative of a far-field (Chile 1985) and a near-field earthquake (Kobe 1995) were selected for the tests. Two tests with two different amplitudes of the 1985 Chile earthquake were conducted on one frame; three tests with three different amplitudes of the 1995 Kobe record on the other. For each specimen, a pre-experiment numerical model was used to generate the three floor displacement histories that were applied to the test frame. Comparison of the results for the hysteretic behavior of the braces, zipper struts, and overall frame validated the partial-height zipper mechanism envisioned in proportioning the specimens. The frames showed good dissipating-energy capacity and large deformation ductilities without significant strength losses. Moreover, they remained stable even after fracture of some braces occurred and showed significant residual strength.

The Next Generation Attenuation (NGA) relationships were developed using a large database of strong motion recordings of shallow crustal earthquakes. The functional form of the relationships provides an opportunity to assess and update if necessary the site class coefficients provided in the NEHRP Provisions and ASCE-7. Site amplification factors estimated using the Boore and Atkinson, Campbell and Bozorgnia, and Chiou and Youngs NGA relationships are computed and averaged for a combination of magnitude, distance, faulting type and period and for NEHRP/ASCE-7 Site Classes B, C, D and E and boundaries A/B, B/C, C/D and D/E. The average NGA site amplification factors show a clear dependency on period for V_S30 smaller than 270 m/s and are substantially greater than the current NEHRP site class coefficients in some cases. The use of the NEHRP/ASCE-7 site class coefficients and spectral demands for the reference site condition computed using the NGA relationships may produce erroneous results. A family of site class coefficients is proposed to address these issues in a format suitable for inclusion in the NEHRP Provisions and ASCE-7.