CE227_HMK4_06 - University of California at Berkeley Civil...

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University of California at Berkeley Civil and Environmental Engineering Instructor: Stephen A. Mahin Spring Semester 2006 CEE 227 -- Earthquake Resistant Design In Problems 9 and 10, we developed a set of linear elastic response spectrum for use in design. One was based on an earthquake with a 50% probability of exceedence in 50 years and the other corresponded to an earthquake a much smaller probability (i.e., 2% in 50 years.). The first of these spectra will be used subsequently in our building design considering a requirement to maintain serviceability following a frequent earthquake (continued occupancy), and the latter spectrum is intended to evaluate the collapse prevention limit state. However, the second response spectrum must be interpreted, since the structure will not be expected to remain elastic under such a rare event. Note howevere, that the structure must eventually satisfy some requirements associated with both spectra. We will not see how higher modes affect nonlinear response until later in the course, but as we saw in earlier assignments, this structure responds primarily in its first mode. For the moment and, for this structure especially, it will suffice to consider only the first mode. It is also worth noting in passing that the structure’s dynamic characteristics being used here are still trial values based on member sizes resulting from the 1994 UBC design, and will thus change when we revise the design of the structure to reflect the new design spectra and criteria we are using. Thus, the overall design process is iterative and, consequently, a high degree of accuracy is not yet required. Nonetheless, these old values provide a good starting point to assess the feasibility of our structure, and to conduct preliminary proportioning. In practice, the whole process will be repeated with new modal values (periods and mode shapes based on new member sizes) and revised masses until we converge upon an acceptable design satisfying all of our performance criteria. Problem 11 - Estimation of Inelastic Design Forces/Displacements
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CE227_HMK4_06 - University of California at Berkeley Civil...

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