Adjusting for Changes in Mass and Stiffness

Structural design of tall buildings is driven by forces of nature, including wind and earthquakes. As buildings get taller, wind-induced dynamic response dictates the design of the lateral system to meet both serviceability and survivability limit states. Structural engineers rely upon wind tunnel consultants to determine equivalent static loads (ESL) and top floor accelerations (TFA). This becomes increasingly important for tall and slender towers where across-wind effects dominate. …

This article summarizes the author’s experience in developing a structural model to analyze and design a structure for the Victor Valley (California) Wastewater Reclamation Authority that is approximately 50 feet wide by 300 feet long. Because the structure has significant horizontal and vertical irregularities, and is in a high seismic area of southern California, design codes specified three methods of analysis: (A) Modal Response Spectrum Analysis (MRSA) for structures with horizontal irregularities; (B) Tank Hydrodynamics for water basins; and (C) Equivalent Lateral Force (ELF) for regular structures. …

We had an Earthquake in Virginia – Now what?

The need to address regional aspects of the Eastern United States (EUS) in model building codes became even more evident with the 2011 Mineral, Virginia earthquake, the most felt event in modern US history, considering the extraordinarily large felt geographic area combined with a high population density. This article presents some facts of the 2011 earthquake that, when coupled with evidence from analytical studies and better understanding of the local geology and tectonic setting, highlight key seismic design issues that are not addressed sufficiently in present codes. …