Gustavo Ayala

SEISMIC FRAGILITY OF LRC FRAMES WITH AND WITHOUT MASONRY INFILL WALLS

This paper summarises the first phase of the fragility analyses of generic (representative) buildings in the area of Memphis, Tennessee, USA. The study was conducted at Cornell University as a part of the project Loss Assessment of Memphis Buildings (LAMB) for the National Center for Earthquake Engineering Research (NCEER). In this study, the fragility analyses focus on low-rise Lightly Reinforced Concrete (LRC) frame buildings with and without infill walls. The obtained fragility curves are compared with those of ATC-13 for different facility classes. Based on the obtained fragility curves, it is concluded that adding masonry infill walls to low-rise LRC frame buildings significantly reduces the likelihood of seismic damage.

RESPONSE OF INFILLED FRAMES USING PSEUDO-DYNAMIC EXPERIMENTATION

SUMMARY An accurate and practical testing technique to study seismic performance of multi-storey infilled frames is formulated. This technique is based on the pseudo-dynamic method which can provide an acceptable approximation of the dynamic performance of structures under the influence of earthquake excitation. The pseudo-dynamic experimental technique is outlined and applied for testing a two-bay, two-storey gravity load designed steel frame infilled with unreinforced concrete block masonry walls. From the discussion of the results, the dynamic performance of the tested structure is assessed. ( 1998 John Wiley & Sons, Ltd. Pseudo-dynamic experimentation is a testing procedure in which the dynamic response of the structure is calculated and the obtained displacements are statically applied to the structure in an on-line procedure. This technique is essentially identical to traditional time domain analysis but rather than idealizing the non-linear sti⁄ness characteristics of the structure, the static restoring forces are directly measured from the specimen as the experiment proceeds. Computation of displacements is based on numerical integration of the governing second-order di⁄erential equations of motion of a system with assumed mass and damping properties and with a forcing function corresponding to a selected dynamic loading. During the test, actual displacements and restoring forces are measured using equipment normally used for static experiments. These measured quantitites are utilized in subsequent calculations. In this way, both dynamic e⁄ects and progressive damage of the specimen are included in the imposed displacements, and the procedure allows for an in-depth monitoring of the performance of the structure for the entire duration of realistic earthquake excitation. Infilled frames have been investigated experimentally by many researchers, most often with monotonic (see e.g. Reference 1) or quasi-static cyclic loading (see e.g. Reference 2), and in a few cases with actual dynamic

Modal Irregularity in Continuous Reinforced Concrete Bridges. Detection, Effect on the Simplified Seismic Performance Evaluation and Ways of Solution

This chapter presents the preliminary results of an ongoing investigation on the modal irregularity in structures, particularly in reinforced concrete viaduct-like bridges, and the effect of this structural/demand characteristic on the seismic performance evaluation of such structures using simplified methods of analysis. The main objective of this chapter is to understand modal structural irregularity and its effects on the performance results obtained from approximate elastic analysis procedures prescribed by most codes or simplified nonlinear analysis methods using modal spectral analyses. It is shown that modal irregularity may be present in bridges with relatively close modes, and it may also occur when, in the inelastic range, the instantaneous modes of the bridge change their composition and that this irregularity may lead to erroneous results, particularly when a modal combination rule is involved. To overcome this problem, a new analysis method for the seismic performance evaluation of bridges exhibiting modal irregularity is presented. This method has as origin a simplified seismic evaluation method based on the performance of a reference single degree of freedom system derived from the capacity curve of the bridge, calculated using evolutive modal spectral analyses with their corresponding dissipated hysteretic energy correction. To show the application of this method, the seismic performance of two bridges, one considered regular and the other with evident modal irregularity, subjected to an earthquake record of two different intensities, one that keeps them within the elastic range of behaviour and the other that takes them into the inelastic range. Finally, the validity of this approximation is shown by comparing the “exact” seismic performance of the bridges, obtained by nonlinear step-by-step analysis, with the corresponding performances obtained using the simplified method. To show the validity of the procedure proposed for the construction of the capacity curve of a bridge, a comparison of results obtained from conventional force pushover analysis, evolutive modal spectral analysis with a correction for hysteretic energy dissipation and the incremental dynamic analysis; using as reference the last one and stressing the potential and limitations of the second.