Floor system redesign April 5, 2005

Transcription

1 Nijad Rudy BOUKHALIL structural option Bellevue Arts Museum Bellevue WASHINGTON Floor system redesign April 5, 2005 The horizontal diaphragm is a composite steel deck with poured concrete. This is a cheap and light system that can span long distances and a good solution to the BAM floor system. To come up with a different solution for vibration caused by long spans, I propose to use a joist system. This will reduce the weight of the floors by a large amount and thus save on the cost of the building. The BAM has unusual and large floor openings. Open floor areas are most subject to vibration. To minimize vibration, I will decrease joist spacing to 2 ft. Comparing the new weight of the designed joist with the existing composite steel deck, considerable difference in weight is found that would reduce the cost of the building. Joist system using Vulcraft: Typical roof bay: In the picture below, you see a typical bay (of 50 by 30 ) of the roof of the BAM. The 14K1 joists are resting on the W 24 X 68 girders, that in turn are resting on the 4 respective columns of the bay. But there is an 8 by 8 opening on the left end of the bay that is filled by a frosted glass which shows the skylight. The joist above and below the opening are 10k1 s and 12k1 s that are resting on the small W 8X 12 girders, that are in turn resting 2 big joists: the right joist is a 18K3 and the left one is a 16K2. These two joists are of different sizes because the 16K2 is resting on the columns which reduce the loads on it.

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3 Typical 3 rd floor bay: On the north east edge of the 3 rd floor, the bay has a 16 by 12 opening for a staircase. The beam at the border of the staircase is a W 12 X 45 holding up eight 12k1 joists spaced 2 apart. This beam itself is supported by two 24K4 joists that span the width of the bay (30 ).

4 Typical 2 nd floor bay:

5 Stress contour for shells Stress analysis is an essential part of the design process, which ensures the structural integrity of the structures. It is also an indispensable tool for optimizing structural design and meeting performance requirements. Effective and efficient stress analysis results in lightweight and reliable structures. The areas to be concerned about were around the elevator core

6 While designing the floor system, a problem was spotted: The Forum is an elliptical interior atrium that rises two stories. A 5 1/2-foot wide staircase takes visitors to the second floor along the south wall. A suspended stairway transports the visitor to the third floor along the north wall over head Indeed, the elliptic staircase on the 3 rd floor is partially-cantilevered on its right side. And below it, on the 2 nd floor is a 45 X 20 opening and thus no means of supporting the staircase. See the next 2 figures 3 rd floor opening:

7 3 rd floor staircase above the 2 nd floor: Beam: The right side beam of the staircase is required to be a W 40 X 183. The columns at the left support of the beam are a W 14X145, and the column at the right support is a W10X45 as shown in the figure below.

8 Analysis of Etabs of the W 40 X 183: The beam is spanning 60 feet, and with the shear walls gone, a W beam less than a W 40 X 183 will deflect more that L/480 = 1.5 The beam is deflecting 0.93 which is acceptable compared to the limit of 1.5

9 Joist: The Joist members around the cantilevered side are a 16K3 s spanning from 24 feet up to 29 feet; 16K2 s spanning a length that ranges only from 19 feet to 24 feet; 14K1 s spanning from 18 feet to 14 feet and 12k1 ranging from 14feet to 10 feet.