![]() Quote: Repair work paused on S.F.'s Millennium Tower due to continued sinking Heavier materials are inherently better at sound reduction, but they are no good if they resonate at a frequency that occurs commonly in the building. It's a tricky science because one material that blocks one set/range of frequencies might not block another. determining if any materials resonate at a common frequency, then dampening or de-coupling that material designing acoustical treatments to block those common frequencies measuring to determine the most common frequencies and their respective amplitudes (sound intensity) Sound reduction engineering comes down to the following: ![]() It comes down to whether the developer or tenant(s) is willing to pay for these treatments. With that said, there are acoustical treatments that can be added to reduce sound afterwards. Though reinforced concrete floors aren't that thick themselves (4-6 inches, typical), they are still somewhat thicker than slab on deck (2.5+ inch top cover). Slab on metal deck is pretty thin.I've heard that makes it far less effective for limiting sound transmission. Therefore, it's best to have a naturally fireproof structural material that does not require periodic maintenance, and reinforced concrete fits the bill (that is, as long as there are no water problems that may damage the reinforcement over time). ![]() But in residential buildings, condo owners would likely balk at regular intrusions into their space. That may be feasible in office buildings, where tenant turnover and facility renovations are fairly regular. Steel fireproofing is fairly flimsy and weak, and often needs to be inspected and re-applied as-needed. Steel is not fireproof (as we all have been aware for almost 20 years), and needs to be fireproofed. Therefore, reinforced concrete structures are better for residential needs.įinally, fireproofing. Residential buildings have fewer MEP needs, so they have no need for a cavernous empty space above drop ceilings. Commercial offices need substantial MEP services (HVAC, electrical wiring, data lines, fire sprinklers, etc.), and the space above the drop ceilings can be used to hide these mechanical elements. The next reason (based on my hypothesis) is MEP services. Therefore, reinforced concrete structures can achieve a higher "nominal" ceiling height while minimizing actual floor-to-floor height. Whereas, for reinforced concrete buildings, the underslab joists are much thinner and built monolithically with the floor above using a single pour of concrete. For aesthetic purposes, these structural elements are usually covered up by drop ceiling panels, and the "nominal" ceiling height would be measured from the floor to under the thickest steel girders: The result is that thick steel girder beams will run across the ceiling in regular intervals. ![]() Then a reinforced concrete floor (or more usually, a concrete over metal deck floor) rests on top of the joists and the girders. Resting on top of these girder beams are joists that span the girder beams. Steel structures rely on the large girder beams resting on columns as the main support. Minimizing floor-to-floor height while maximizing ceiling height.įirst, we must understand the difference between steel structures and reinforced concrete. Why is this? My main hypothesis is that it comes down to two factors:ġ. Steel structures are designed for commercial office buildings, and reinforced concrete is designed for residential buildings. That's the case for most residential condo buildings here in NYC as well. I believe it's because the flexibility and swaying that's unavoidable in steel buildings during "minor" tremors would unnerve residents in buildings full of them. As a general rule of thumb, in San Francisco office towers are structural steel-framed with concrete elevator cores, of course, but residential buildings are nearly all reinforced concrete like the Millennium tower. ![]()
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