Cable-stayed Technology

A cable-stayed support system was chosen for the design of the CSU Performing Arts Center. One reason for choosing this system was to allow for a more compact facility because the space available on campus was limited. Another reason was to give patrons an unobstructed view of events by eliminating the need for columns.

The original use of cable-stayed technology was seen in bridges. German engineers established the design of cable-stayed bridges in the 1950's and 1960's. This technology was eventually adapted to buildings, using cables to support the roof. Each tower is buttressed by two sets of cables, transferring the load into the ground. Without a roof load to support, columns are not needed in the complex and the space can be used in more ways.

The concept behind cable-stayed technology is to have the supporting reactions to the load directed in only vertical directions as opposed to vertical and horizontal. It also eliminates any tension and/or compression force (Figures 3.1 and 3.2) . For a building, the load of the roof is directed through the cables, to the towers, and down to the ground. The walls do not support the roof as they normally would; only the cables are used to hold up the roof. An example of a cable-stayed building is the Alamodome, a multipurpose stadium in San Antonio, Texas (Figure 3.3). Our model is based on this design.

Figures 3.1-3.2

Figure 3.3

Main Hall Acoustics

Background
One of the key characteristics of a concert hall that greatly influences sound quality, is its reverberation time (the time before the decay of the reflected sound ). For orchestral or band music, the ideal reverberation time is approximately two seconds. Any times approaching 1.6 seconds will lead toward a dry, dead sound ( Beranek 1962 ). The other extreme is a time that is too long. This causes the music to lose its clarity, an excessive loudness, and the blending of incompatible chords ( Beranek 1962 ). A hall's reverberation time can be affected by such things as the volume of the room or the number of people in the audience. In the construction of the main hall for the CSU Performing Arts Center a balance will be determined that will create a reverberation time of two seconds, as independent of audience size as possible.

Sound quality is also greatly determined by the warmth of the sound. Warmth is determined by the fullness of the bass tones. If the middle frequencies of a sound have longer reverberation times than the low tones, then the sound will become brittle (Beranek 1962 1).

Materials
Table 4.1 gives the absorption coefficients of different frequencies for common surfaces. It shows that materials such as heavy curtains or thick carpet absorb are the ideal choice for decreasing the intensity of higher frequencies. This leads to the production of a more full, warm sound. Retractable banners will be built into the ceiling, and can be lowered to create this effect. Cloth seats will be used as they best assimilate an occupied audience area ( Beranek 1962 ). This allows sound within the hall to be independent of audience size. The low sound absorbance of plaster also makes it ideal for the creation of the desired reverberation time of two seconds.

Design considerations
The intensity of the direct sound should not be too weak, but at the same time, it must not become uncomfortably loud. This problem will be dealt with by limiting the length of the room, and by designing the surfaces above and around the stage to project the sound evenly throughout the concert hall. Another problem arises with the seats placed under a balcony. To prevent a muddiness within the sound, the depth under the balcony should not exceed the height of the opening beneath the balcony, as shown in figure 4.1 ( Beranek 1962 ).

Table 4.1
Absorption coefficients of different frequencies for main hall surfaces

Table based on: Beranek, L. 1966. Music, Acoustics, & Architecture. John Wiley and Sons, Inc., New York.

Figure 4.1
Balcony design

Figure based on: Beranek, L. 1966. Music, Acoustics, & Architecture. John Wiley and Sons, Inc., New York.

Floor Plans

The Colorado State University Performing Arts Center consists of three levels. The total area of the complex is 56,500 square feet. The basement and ground floors consist of 20,500 square feet apiece. The second floor has a square footage of 15,500.

The basement level of this center (Figure 5.1 ) includes two main dressing rooms with shower facilities as well as four private dressing rooms with individual restrooms for guest performers. The mechanical room for the building will be in the basement, housing such devices as the heating, ventilating, and air conditioning equipment as well as the mechanics for the elevator. A spacious performers' lounge has also been added in to the basement to provide a relaxing environment for the center's performers.

The building's main floor (Figure 5.2 ) includes the main performance hall as well as a small rehearsal hall. The main hall is 5,000 square feet and has a seating capacity of 1,200. A coffee shop and art lounge have been included in this plan for the enjoyment and convenience of the patrons. A large classroom is provided for dance classes as well as rehearsals. Sufficient office space is included adjacent to the center's box office.

The top floor of the CSU Performing Arts Center (Figure 5.3 ) includes a walk- around balcony overlooking the main lobby as well as a balcony for the main performance hall. An elevator is provided for travel between the first and second floors. A recording studio is also located on this floor as an added bonus.

Figure 5.1
Basement level floor plan

Figure 5.2 Ground Level

Figure 5.3 Second level floor plan

Conclusion

In conclusion, MASK Engineering has carefully planned out the details of the proposed CSU Performing Arts Center. This facility will be a benefit to the performing arts programs at CSU, the students and faculty of CSU, as well as the members of the community. It will allow for the improvement of programs in the area and growth of interest in cultural events. The site of Green Hall will be accessible to both students and the community, and will use the space on campus most efficiently, preserving the green areas. A cable-stayed support system for the roof will allow for a compact facility and an unobstructed view for patrons. In order to achieve the best acoustical results in the main performance hall, we have designed a rectangular hall made of plaster. We have also designed the hall so that the depth under the balcony does not exceed the height of the opening beneath the balcony. The total area of the complex will be 56,500 square feet split into three levels. The main hall will have a seating capacity of 1,200. The facility contains necessary rooms to accommodate the performers, and several rooms to make the visit of the patrons more enjoyable.

Through our research and planning, MASK Engineering recommends that the construction of the proposed CSU Performing Arts Center begin as soon as plans have been finalized and conditions permit. We expect this complex to benefit not only the performers, but also CSU students and all residents of Fort Collins.