F. López-Almansa

Numerical efficiency assessment of energy dissipators for seismic protection of buildings

SUMMARY This paper presents a two-dimensional numerical study on the nonlinear seismic response of buildings equipped with two types of energy dissipators: Constant Friction Slip Braces (CFSB) and Adding Damping and Sti⁄ness (ADAS). Three types of reinforced concrete buildings with 3, 7 and 15 storeys, representatives of the short-medium- and long-period ranges, are considered. Dissipators are placed in steel diagonal braces in all the floors. The sliding threshold (or yielding) forces for each mechanism are selected using two di⁄erent criteria: (i) they are taken as 50, 75 and 100 per cent of those generated by the equivalent static lateral forces recommended by the UBC-91 for a ductile moment resisting frame and (ii) they are constant in the whole building (this constant value is chosen equal to the maximum forces obtained with the previous criterion). The input consists of ten recorded earthquakes (normalized with respect to their Housner intensity) corresponding to medium and sti⁄ local soil conditions. Average values on the ten registers are given for the maximum horizontal displacement, the base shear, the energy dissipated and the interstorey drift. The possibility of failure in some devices has been numerically simulated to assess the robustness of the system. The obtained results show that both devices are useful to reduce the response compared to the bare frame and that CFSB is more eƒcient than ADAS; for 7and 15-storey frames the lateral displacement with CFSB is even smaller than the one for the braced frame (rigid connections instead of dissipators). The conclusions are expected to provide simple design guidelines. ( 1998 John Wiley & Sons, Ltd.

Optimal sensor location in active control of flexible structures

This paper presents a new algorithm for the optimal distribution of concentrated sensors to measure displacements or strains in flexible structures; this procedure is applicable in quasistatic shape control (e.g., parabolic mirrors). The proposed approach is based on the analysis of the properties of a linear matrix equation describing the modal strain decomposition, where observable as well as interfering modes are taken into account

Optimal Location of Piezoelectric Actuators

A new model of flexible plate (equipped with piezoelectric wafers) applicable for design and simulation of active control process is demonstrated. In particular, a concept of continuously distributed’active distortions’ describing interactions between piezoelectric wafers and the structure itself allows us to formulate properly the problem of optimal distribution for these control devices. The standard way to describe the interaction between piezoelectric devices and the controlled structure by means of concentrated forces applicable at the edge of actuator is not suitable to discuss the optimal location problem. Restricting control action to a chosen set of independently modificable eigenmodes of vibration and applying the criterion of maximization of available substitutive control action the discrete optimization problem can be finally formulated. A numerical procedure for solving this problem and corresponding testing example is presented.

Numerical study on the relevance of columns hidden failure modes in the seismic capacity of non-ductile RC Frames

ABSTRACT In simplified seismic structural analyses, not all the deterioration modes are adequately considered. This work discusses the relation among the hidden failure modes of columns of non-ductile reinforced concrete building frames and their global collapse mechanism. With this aim, a numerically efficient model is developed and implemented in OpenSEES. Two benchmark problems are analyzed with this model: the well-known Van Nuys Hotel and a prototype building designed for gravity loads only; in this last case, the results are compared with experiments on a one-third scale model. The obtained results confirm that simplified models grossly overestimate the building capacity.

Generating damping modification factors after artificial inputs in scenarios of local records scarcity

The damping modification factors are utilized to alter the design spectral ordinates for constructions whose damping differs significantly from 5%, this being the level that is routinely considered by most codes. Such factors are habitually evaluated after suites of historical inputs representing the local seismicity. However, such records may not be readily available, due either to moderate seismicity or to limited seismological network; in such cases, representative artificial accelerograms might be used instead. This paper proposes a methodology for establishing damping modification factors after artificial inputs generated to match the 5% design spectra; this approach can be used for countries, regions or cities. The proposed methodology is based on performing dynamic analyses on underdamped and overdamped SDOF linear systems by using the aforementioned selected accelerograms. Although previous studies have highlighted the differences among factors generated after natural and artificial inputs, it has been observed that such discrepancies are mainly due to the longest significant (Trifunac) duration of the artificial accelerograms. Therefore, the artificial inputs are generated as their duration fits those of the available local strong motion records. An application to Colombia is presented; the results are compared with those for some available Colombian records. The sensitivity of the calculated factors to the soil type, period and seismic zone is investigated; matching expressions are provided. Such expressions are compared with the prescriptions of major design codes and with other studies. The suitability of the proposed formulation is further verified in an example on an isolated hospital building.