Earthquake Spectra

The investigation described in this paper looked at both laminated elastomeric bearings and lead-rubber bearings in order to obtain a better understanding of the real bearing behavior under the combined action of shear and axial loads when used in a seismic-isolation system. In particular, the investigation focused on the distributions of vertical pressure on the bearing faces and the degree of lift-off of the edges of the bearings as the shearing displacement and the angle of rotation increased.

The investigation described in this paper looked at both laminated elastomeric bearings and lead-rubber bearings in order to obtain a better understanding of the real bearing behavior under the combined action of rotation and axial loads when used in a seismic-isolation system. In particular, the investigation focused on the distributions of vertical pressure on the bearing faces and the degree of lift-off of the edges of the bearings as the angle of rotation increased.

A nonlinear model and an analytical procedure for calculating the cyclic response of nonductile reinforced concrete columns are presented. The main characteristics of the model include the ability to represent flexure or shear failure under monotonically increasing or reversed cyclic loading. Stiffness degradation with cyclic loading can also be represented. The model was implemented in a multipurpose analysis program and was used to calculate the response of selected columns representative of older construction. A comparison of the calculated response with experimental results shows that the strength, failure mode and general characteristics of the measured cyclic response can be well represented by the model.

Spectral ratios obtained for lakebed sites with respect to the average Fourier spectra of the Southwest hill-zone sites in the Mexico City Valley are presented. The amount and quality of data used allowed us to measure relevant amplification characteristics. For all earthquakes, the ratios are relatively constant regardless the magnitude, epicentral distance and azimuth of subduction and normal faulting earthquakes. With data recorded at Station Central de Abastos, it is shown that these ratios are a much better approach than horizontal to vertical ratios, which yield only a rough estimation of site amplification. Also for Central de Abastos, where little nonlinear behavior has been observed, an empirical approximation is used to account for these effects. We also built maps of equal amplification that exhibit those zones that have experienced damage during earthquakes and those at the highest risk. The ratios presented here are useful and reliable to accurately predict the amplification of motion.

In studies of damage to classes of property in earthquakes, the damage ratio for a class as a whole, denoted D¯ _r , can differ appreciably from the mean damage ratio D _rm of properties in the class. Two factors that influence the propensity of D¯ _r and D _rm to differ are the skewness of the distribution of property values and any systematic relation that may exist between property value and damage ratio. The existence of such relations is demonstrated using data from two major New Zealand earthquakes, at Napier (M _w 7.8, 1931) and Edgecumbe (M _w 6.5, 1987). A common trend is that the probability of a property being damaged increases with increasing value. The damage ratio may tend to increase or decrease with property value, depending on the type of property. The observed relations can be partially explained on physical grounds, and have implications for earthquake resistant design and earthquake insurance.

Incorporated at various levels of a structural frame, ADAS devices may be used to improve the response of the structure during earthquakes. A design method of a passive control system for multistory structures using optimal Adding Damping And Stiffness (ADAS) dampers is presented. Optimal Control Theory (OCT) is commonly used to obtain the levels of viscous damping at each story. The optimization leads to different levels of damping at each story. Therefore, a solution with viscous dampers is inconvenient and can be expensive. The proposed method enables the use of relatively less expensive optimal ADAS devices dissipating energy which is equivalent to that of viscous dampers. The method is examined in a numerical analysis of a seven-story shear framed structure. Significant improvement was obtained in the behavior of the ADAS damped structure compared to the uncontrolled one.

The Uniform Building Code (UBC) is perhaps one of the most advanced seismic codes worldwide. The 1997 version of the Uniform Building Code (UBC-97) has important modifications with respect to previous versions, among other changes, the introduction of structural overstrength, redundancy and reliability factors for the design of structural elements. In addition, the UBC-97 code revises seismic zoning for areas outside the United States under Division III, Section 1653. In fact, practically the entire world is zoned by the UBC-97 under this section, and many practicing engineers worldwide may feel confident to use the UBC code for the design of civil structures in countries other than the United States, particularly because it is written in this section that “Note: This division has been revised in its entirety”. This paper discusses whether or not Section 1653 of the UBC-97 code has any justification for Mexico, by comparing the UBC design criteria with the criteria established by ruling Mexican codes. According to Mexican authorities, only the referenced Mexican building codes should be used for the design of civil structures in Mexico, so the UBC-97 cannot be used for the seismic design of civil structures in Mexico legally.

Current design procedures for steel special moment frames (SMF) promote panel zone yielding. Reliance on this yielding is likely to result in poor frame performance in spite of the fact that it has been demonstrated that panel zones can yield. Eight previously tested subassemblies are analyzed for compliance with current code design procedures. The observed behavior of these subassemblies is discussed and contrasted to behavior objectives of steel SMF's. Revised design procedures are proposed.