- Alamodome: This entertainment and sports arena is viewable from the Convention Center and is very intriguing from a load path perspective. Operating similar to a cable stayed bridge, the roof is suspected from four sets of cables. A simple statics analysis at the top of each tower indicates that the weight of the roof acting in the cables causes the towers to experience compression and the remaining two sets of cables carry tension forces (to balance the horizontal force component in the cables holding the roof) down to the foundation. Does anyone notice what happens to the load path when the cables intersect the exterior cantilevered roof member? I have a piece of conference swag for whoever can correctly answer. A series of photos from the construction of the Alamodome can be viewed here.
- Tower of the Americas:
This 750 foot tall tower immediately adjacent to the conference center houses a revolving restaurant on top. I saw this structure on a particularly windy day, and so I could help but think about it's structural dynamic response. Unlike an inverted pendulum with a lumped mass (which I'm sure you've considered in Seismic Analysis), the mass of this tower is likely too large to neglect, so it would need to be considered as a distributed mass pendulum, which means that when you are formulating the equation of motion, inertial effects due to angular acceleration of the distributed mass need to be considered. See Chapter 8 of the Chopra's Structural Dynamics textbook for a fuller explanation. - The Alamo: While not as structurally impressive as the other two, a trip to San Antonio simply wouldn't be complete without the Alamo!
Wednesday, April 19, 2017
Structures of San Antonio
Last month I had the opportunity to attend NASCC: The Steel Conference in San Antonio, Texas. While there, I observed three interesting structures I thought might be fun to share.
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So my answer to your question about the Alamodome... The cables coming down from the top of the pillar are in tension (cables can't really support compression). That tension has to pass through either the cantilever roof member or the vertical cables to the ground. Because the vertical cables cannot counteract the horizontal force from the cables above the roofline, the cantilever roof member must pass the force back off to the main column. The vertical component from the roof member into the column is countered by the tension in the upper cables and the rest is directed down through the column.
ReplyDeleteThank you Ben for this excellent response! You are now the proud owner of a NASCC water bottle! Yes, exactly, the vertical cables between the roof and the ground are two force members and thus they cannot carry the horizontal component of the load from the cables above. Instead, this horizontal component is carried as compression (must be compression in order for sum of the forces the horizontal direction to equal zero at the point of connection) in the roof framing member. Note that this occurs in three locations around each concrete column, all of which connect to the column at the same elevation. Presumably, the magnitudes of these forces are balanced, meaning that while they compress the column in the transverse direction at this location, there is no net transverse force and hence, no shear or moment would be induced into the column.
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