Structural Concepts and Existing Conditions Report

Transcription

1 Daniel Chwastyk F.W. Olin Center Louis Geschwindner Advisor Structural Concepts and Existing Conditions Report Executive Summary The following report discusses many of the structural concepts that were used in creating the F.W. Olin Center. The building it self consists of five stories all using CMU wall construction. A tower in the front of the building rises an extra floor to provide a telescope room. As stated below the NYC Building code was used for original design of the building. Because this code was unavalaible to me at the time of my design i was forced to use the International Building Code (which NYCBC is based from). This difference in codes is the cause for many of the design numbers disagreeing with the original numbers. The major part of this involved researching the building plans and specifications to better get an understanding for this building. The biggest assumption which i made was that the original designers planned on the CMU walls to carry the lateral loads. This is understandable due to the low wind and seismic shear which the F.W. Olin center has to support. Included in this report are the following Code information Description of the overall structural System Calculated Dead and Live loads used in analysis Calculated wind and seismic loads acting on the building A spot checking of several elements in gravity loading -1-

2 Code Information The main code governing the construction of F.W. Olin Center was the New York State Building Code. This code is based on the 2000 International Building Code with slight moderations. Structural steel was designed according to the Load and resistance factor design philosophy. The joists conform to the Steel Joist Institute specifications and Load tables. Overall Structural System The F.W. Olin Center is a 5 story complex. The perimeter of the building is roughly 182 ft by 152 ft. The foundation of the building consists primarily of 1 by 2 4 continuous concrete footings on top of a 1 layer of crushed rock. These foundations have a bearing capacity of 4000 psi. These footings support the CMU load bearing walls which make up the building. The Foundation walls are made up of 14 CMU s, and all other walls consist of 8 or 12 CMU s depending on the locations. These larger cmu walls function as the shear resisting system in the science center. The following picture shows the building footprint with the shear walls included. -2-

3 The basement floor is made up of 4 concrete slab on grade. The compressive strength of the floor concrete is 5000 psi. This concrete is supported by 6x6 10/10 welted wire fabric. Form decking is made up of a 3 concrete fill resting on the same welted wire fabric on a 9/16 28 gauge metal form deck, while floor decking is 1 ½ 18 gauge decking. An 18 gauge metal decking covers the chemistry room where beams are used instead of k joists. A typical wall section with basement floor, first floor, and roof is shown below. The steel beams on the roof shown are W12 x 22 rafter -3-

4 beams. The roof trusses tie into these beams at interior points on the roof. -4-

5 The typical framing plan of the first three floors consists of different types of k joists in the classrooms. The larger classrooms have 2 4K12 Joists spaced at 2 on center. Bridging for these joists is provided at quarter points. The smaller classrooms have 14K3, 14K4 and 14K5 joists all spaced at 2 on center. Bridging for these joists is provided at third points. The corridors which must carry a larger live load are typically covered by W5 x 16 beams. These beams sit on typical 7 1 / 2 x 7 1 / 2 x ¾ bearing plates at each end. In the mechanical/penthouse floor 12K1 and 12K5, spaced at 2 f.o.c, support the two mechanical rooms on the north and south of the tower. W5 x 16, W6 x 25, and W8 x 10 beams support the floors of the corridors, storage areas, and telescope room respectively. The telescope equipment floor is supported by W8 x 10 beams all spaced 2 on center. -5-

6 There are a total of 19 steel columns in the whole building. Six of them are seen in the north laboratory. These are all W8 x 67 and W8 x 58 and span through the first floor into the second. The rest of the columns are 6 diameter SCH. 80 columns. These columns surround the central tower of the building. These columns are spaced radially with a 30 degree separation between each member. These tower colums exist primarily for aestetic purposes and serve little structural use. The F.W. Olin Center s roof is made up of a 1 1 / 2 steel deck covered -6-

7 by composite insulation, and ultimately covered by a slate roof. The roof is hipped consisting mainly of two different forms of trusses. These trusses have WT6 x 11 top and bottom. W10 x 15 beams surround the outside of the buildings roof. W12 x 22 beams come off from every corner of the roof. The middle of the roof covering the mechanical rooms is sunken down 2 from the rest of the roof. This is done to hide the various vents on this section of the roof. This roof is made up of gauge C Channels spaced at 2 on center. Dead Loads Concrete slab and decking self WT. (TYP. FLOOR) CMU WALL SELF WEIGHT SUPER IMPOSED DEAD LOAD MECHANICAL FLOORING PARTITIONS TOTAL SUPER IMPOSED DL ROOF WEIGHT (STEEL DECK, INSULATION, SLATE) 43 psf 61 psf 10 PSF 5 PSF 10 PSF 25 PSF 13 PSF LIVE LOADS (PER DRAWINGS) ROOF LOAD SNOW BATHROOMS OFFICES VESTIBULES AND CONTROL CORRIDOR AND STAIRS LIGHT STORAGE 35 PSF 35 PSF 40 PSF 50 PSF 100 PSF 100 PSF 125 PSF WIND ANALYSIS Wind analysis was performed using ASCE 7 98 for reference. The wind speed listed on the plans is 70 MPH. this wind speed is the fastest -7-

8 mile wind speed. To calculate wind loads in the IBC you must use the three second gust wind speed. This three second gust speed is found from a table in the IBC, and depends entirely on the fastest mile wind speed. The three second gust speed for the f.w. olin center is 85 MPH. The drawing below shows the adjusted loading diagram, with the actual loading numbers listed. Wind pressure windward (psf) Wind pressure leeward psf -8-

9 Seismic Loads Seismic loads were determined by using the international building code 2000 edition. The response modification coefficient was found from a table in the IBC and equals 2.5. The seismic factor is found in a table in the ibc and is From these numbers a base shear of 1,666 kips was calculated using an overall building weight of 20,000 kips. This base shear is the controlling shear load for the building. SHEAR ANALYSIS Shear analysis was performed assuming that the 8" x 8" x 16" CMU walls carry the shear loads on the building. This analysis was done by obtaining the Cross Sectional area of mortar from the National Concrete Masonry Association website. The maximum shear force on the building was found to be the shear force caused by seismic loads. Mortar fails in shear before the concrete itself so the maximum shear strength must be less the the shear strength of the mortar (140 psi in for mortar used). Shear loads were checked for the main east to west walls of the building. These walls can be found as the 4 main horizontal walls on the above footprint drawing. The lengths of these walls range from 50 2" to 98 0". These walls were found to adequately handle the shear load on the F.W. Olin Center. SPOT CHECKING Below are a listing of some structural members which i spot checked for gravity loadings. Most differences between actual members and -9-

10 calculated members can be attributed to the fact that in many cases a different code was used in the actual design of the building and in the spot checking. Structure Actual member Designed member Roof Deck 1 1/2" 20 Ga. Type NR 1 1/2" 20 Ga. Type F The loads used in analysis were a dead load of 13 psf, a live load of 35 psf, and a snow load of 35 psf. The difference of types of decks is due to type nr not being listed in the United Steel Decking Manual. Corridor Beam W 5 x 16 W 10 x 12 The loads used in analysis were a dead load of 73.3 psf and a live load of 100 psf. These beams support the narrow corridors of the building. THe beams are spaced at 3 feet on center and span a maximum of 6 6". A W 10 x 12 beam is more than sufficient for the loading. A smaller beam would definately work, but the AISC steel manual doesn t contain maximum uniform loadings for any beams smaller than the W 10 x 12. Roof Beam W 10 x 15 W 10 x 12 The loads used in analysis were a dead load of 15.5 psf, a live load of 35 psf and a snow load of 35 psf. These roof beams support the outer sections of the roof. The span length for the beams is /16". Although the smaller W 10 x 12 beam is capable of supporting the roof, the fact that this beem is non compact may have cause the designers to use the heavier beam. Typ Floor Slab 3" Conc. on 9/16" 3" Conc. on 9/16" 28 Gauge Deck 26 Gauge deck. The loads used in analysis were a dead load of 68 psf and a live load of 125 psf. This is the standard floor slab throughout the building. This difference in floor slabs is most likely due to the decking manual being 3 ksi concrete and the concrete used in the building is 5 ksi concrete. Typ K joist Floor 24K K9 2 The loads used in analysis were a dead load of 33 psf and a live load of 50 psf. This k joist floor is seen on all floors. The span length of the joists is /4" and is braced at quarter lengths. note: many calculations are omitted from this report. These calculations are in the possesion of Daniel Chwastyk and my be obtained upon request. -10-