Comparison to Program

The  design proposed in the original building program was relatively simple in structural terms. Very few changes were therefore necessary.

The original program suggested a steel frame building with bays of approximately 25′ by 25′ to keep the office spaces open and light. As structural engineers, we agree that a steel frame building is the most efficient and elegant solution. As mentioned in the original program, the advantages of steel construction are numerous:

  • good span to depth ratio allowing for larger unobstructed spaces
  • cost efficient
  • facility and speed of construction
  • low deadload
  • aesthetically unobtrusive

We found that our calculations were a lot more simple than they would have been for a concrete building and in some cases, we were also able to exceed original expectations in terms of bay dimensions.  The final bay sizes are 40′ x 20′ and 20′ x 25′ compared to the requested 25′ x 25′. The larger areas are light and open offices as requested in the original program while the smaller interior spaces are reserved for common facilities such as bathrooms, copy rooms and elevators as requested by the architects.

The original program recommended the engineers use a snow load of 25 psf in their calculations. However, upon closer inspection of the IBC 2009 snow load maps, we found that Virginia is situated on the limit between a 25 psf zone and a 30 psf zone. We, therefore, decided to design for a 30 psf load, prefering to overdesign rather than risking underdesign.

 (source :IBC 2009)

 

On the contrary, the original program suggested we apply a maximum allowable deflection  ratio of  l/360 associated with plastered ceilings. Upon reflection, we decided that the ceilings would most probably be non plaster and therefore that our beam deflection ratio should be a more tolerant l/240.

(source: IBC 2009)

 

Although not particularly mentioned in the original proagram, the Architects in A2 specified that they wished the building to be state of the art in terms of its HVAC  systems, providing an excellent level of comfort for its occupants. As such, we used an interstitial load of 10 psf rather than the recommended 3-8 psf (IBC 2009), thus giving HVAC engineers extra freedom in their design.

Suggestions that would make the original program more helpful:
 

Overall, the original program was perfectly clear. The building is a simple steel frame building and therefore, not much guidance is needed for the structural engineers.

The original program should have perhaps given more thought to details such as ease of circulation and required fire exits but these issues were addressed in the architectural assignment. These changes transformed the internal structure fairly radically and should probably been thought of in the initial program.

Architectural finishes do not need to be thought through in detail at such an early stage. However, it is highly unlikely that plaster ceilings would be used in a typical modern office setting. Authors of the original program should therefore, refrain from providing unuseful limits.

 

 

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