The seismic design of most civil structures is usually accomplished using the response spectrum approach or simplified equivalent lateral force methods. However, some special tasks require the use of dynamic time history analyses. In the nuclear industry, for example, dynamic analyses are required in the design verification and seismic assessment of critical buildings and in the development of floor response spectra and free-field ground response spectra. The input motion for these analyses requires acceleration time series whose response spectrum matches a target design spectrum. This article revises the continuous wavelet transform (CWT) approach to generate spectrum-compatible records from the modification of acceleration time histories recorded in actual seismic events. The computational efficiency of the algorithm is increased greatly by performing the wavelet decomposition and details reconstruction via fast convolution using fast Fourier transforms. The new algorithm is evaluated using a typical design spectrum from the nuclear industry and different seed records.

The feasibility of using output-only model-free wavelet-based techniques for damage detection in reinforced concrete structures subjected to seismic loads is explored through the analysis of the results of a full scale shake table test of a reinforced concrete bridge column recently performed at the NEES Large High Performance Outdoor Shake Table. The evaluated approaches are based solely in the analysis of the acceleration time histories recorded in the structure. The viability of using numerical models to validate this type of damage detection methodologies is also evaluated. Wavelet analyses were capable of identifying the rebar fracture episodes and partially identified the frequency shifts in the structure as the inelastic demand increased. It was also found that, depending on the methodology employed, the use of numerical models to validate damage detection techniques can oversimplify the actual problem and/or induce spurious irregularities.

This article presents an evaluation of the capabilities of wavelet-based methodologies for damage identification in civil structures. Two different approaches were evaluated: (1) analysis of the structure frequencies evolution by means of the continuous wavelet transform and (2) analysis of the singularities generated in the high frequency response of the structure through the detail functions obtained via fast wavelet transform. The methodologies were evaluated using experimental and numerical simulated data. It was found that the selection of appropriate wavelet parameters is critical for a successful analysis of the signal. Wavelet parameters should be selected based on the expected frequency content of the signal and desired time and frequency resolutions. Identifications of frequency shifts via ridge extraction of the wavelet map were successful in most of the experimental and numerical scenarios investigated. Moreover, the frequency shift can be inferred most of the time but the exact time at which it occurs is not evident. However, this information can be retrieved from the spike location from the Fast Wavelet Transform analysis. Therefore, it is recommended to perform both type of analysis and look at the results together.

This article investigates the level of influence that strong motion duration may have on the inelastic demand of reinforced concrete structures. Sets of short-duration spectrally equivalent records are generated using as target the response spectrum of an actual long-duration record. The sets of short-duration records are applied to carefully calibrated numerical models of the structures along with the target long-duration records. The input motions are applied in an incremental dynamic analysis fashion, so that the duration effect at different levels of inelastic demand can be investigated. It was found that long-duration records tend to impose larger inelastic demands. However, such influence is difficult to quantify, as it was found to depend on the dynamic properties of the structure, the strength, and stiffness degrading characteristics, the approach used to generate the numerical model and the seismic scenario (target spectrum). While for some scenarios, the dominance of the long record was evident; in other scenarios, the set of short records clearly imposed larger demands than the long record. The detrimental effect of large strong motion durations was mainly observed in relatively rigid structures and poorly detailed flexible structures. The modeling approach was found to play an important role in the perceived effect of duration, with the lumped plasticity multilinear hysteretic models suggesting that the demands from the long records can be up to twice the inferred from distributed plasticity fiber models.