The use of concentrically braced steel frames to satisfy lateral force requirements is a common design practice in regions of strong seismicity. They provide a very efficient means of fulfilling the dual objectives of earthquake resistant design, that is, damage control and collapse prevention. While tensile yielding and inelastic buckling of bracing elements provide the basic energy absorbing mechanism, there are inherent problems with member behavior under multiple cycles of inelastic deformations. Inelastic energy dissapation, however, may also be provided by friction resistance in slotted bolted connections, thus eliminating the need for inelastic member buckling. Limited laboratory tests indicate that this concept may be a viable alternative for use as a lateral force resisting system for both new construction and the seismic upgrading of existing structures.
A simple Markov distribution relates the probability of occurrence of five discrete damage states for a specific building type in an earthquake. Within the model the damage distribution depends on parameters that represent the building's structural system, the matching of the site and building periods, and the site materials, and the site's acceleration. The constants in the model were determined using a maximum likelihood formulation and damage observations for a series of California and Chinese earthquakes. Model predictions of damage distributions agree well with reserved damage data not used in determining the constants. A maximum likelihood method allows determination of ground motion, attenuation, and/or earthquake moment magnitude from observations of damage for different types of structures located at diverse sites. A simple relationship exists for average damage estimate that closely matches historical observations.
SummaryThe Thiel–Zsutty (TZ) model predicts mean and the probability distribution function for earthquake damageability of building as a function of peak ground acceleration. ATC‐13‐1 provides an alternate damageability model based on modified Mercalli intensity characterization of ground motion and a beta distribution function for selected building types. This paper provides a reconciliation of the TZ and Applied Technology Council (ATC) methods. It is shown that the beta distribution can provide a continuous representation of the step‐wise TZ Markov distribution function. When the TZ model uses a compression factor for the standard deviation to represent the degree of uncertainty in the parameters, then the TZ results are found to be consistent with the ATC‐13‐1 distribution function for a specific compression factor of 0.40. This paper provides a new, simply applicable method to determine the damage distribution function for a given site, building type, and site conditions; using a beta distribution and allowing inclusion of the degree of confidence the assessor has in the determination of the parameters. New equations are provided to estimate the mean, standard deviation, and upper confidence limit of the damage ratio.
How long can a seismically deficient building be used until the seismic risk becomes too high to be acceptable? A model interim use plan is developed with requirements to abandon the building if retrofit is not completed in the use period. Acceptable seismic performance is keyed to American Society of Civil Engineers (ASCE) 41 levels.The acceptable occupancy or use period is limited to that which results in the same probability of performance as stated for an ASCE 7-16-compliant building, except that the total risk in the use period is due to all possible earthquakes impacting the site, not just the maximum considered earthquake. The Thiel-Zsutty damage model is used to determine the probabilities for assigned threshold ranges where unacceptable performance can occur. Other response prediction models can be used if they provide an annual probability of a given performance level exceedance. Example applications are given for both marginally and highly deficient buildings located at 17 national sites in high and moderate seismic hazard regions and include ASCE 7 Risk Class I-IV buildings. This approach may be applied to any risk decision-making issue for which there is an annual probability of damage exceedance.
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