111 MORGAN ST. Ryan Friis

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1 Technical Report No. 1 September 30, 2002 Executive Summary: 111 Morgan St. is a 9 story cast-in-place concrete condominium building being constructed in Chicago, Illinois. The building s floor system utilizes an 8 ½ 2-way concrete slab of 5,000 psi concrete with drop panels of varying depths at the columns. The columns are spaced at 25-8 in the N-S direction and in the E-W direction the spacing varies from to Shear walls are used to resist the lateral forces in both the N-S direction as well as the E-W direction. For this report numerous loads were researched or calculated such as building dead load, design live load, snow load, wind load, and seismic load. All of these loading conditions are calculated from either IBC 2000 or ASCE 7-98, and will be compared to the design loads used for 111 Morgan St. which used the Chicago Building Code 1999 Edition for its design loads. The results of this research is as follows: Required Live Loads (psf) Load Type IBC 2000 Actual General Balcony Lobby Parking Mechanical NA 150 Load Type ASCE 7-98 Actual Wind (windward + leeward) 7-12 psf psf Seismic Base Shear 1511 kips NA Snow 20 psf 25 psf 1

2 Summary of Overall System: As stated earlier 111 Morgan St. is a CIP concrete structure utilizing a 2-way flat slab floor system. The slab is 8 ½ thick on all of the condominium levels (3, 4, 5, 7, 8, & 9) and is 8 thick on the parking levels (1, & 2) and the roof. At the columns a typical 4 x 4 x 4 drop panel is used to compensate for the large shear forces exerted on the slab at the column connection. On the parking garage levels (Basement, 1, & 2) the 2- way slab is still used, however the ramps that join each of the levels use a 7 one way slab system. All of the slabs in the building use 5,000 psi normal weight concrete with 60 ksi steel reinforcing. The interior columns in 111 Morgan Street are 20 in diameter and use varying strength concrete along their length. Starting at their base and continuing up to the 4 th floor slab the columns use 8,000 psi normal weight concrete, between the 4 th and 7 th floors 6,000 psi normal weight concrete is used, and above the 7 th floor 4,000 psi normal weight concrete is used. At level 3 the east side of the building steps back one column line, and the new exterior columns are not located on the same grid as the interior columns. The reason the exterior columns are not on the grid is to provide openings for windows and access to the balconies. On levels 3 and up the exterior columns are rectangular in shape and vary in size depending upon location. The exterior columns also change concrete strength according to the same schedule as the interior columns. Below level 3, beams are used to transfer the loads to the underlying columns which are located on the standard grid. The building s standard column grid is continued down into the building s foundation, which consists of numerous caissons that vary in depth from 63-0 to The foundation is typical for many large buildings in Chicago and should not pose any problems on future design. 2

3 The lateral force resisting system utilizes shear walls in both directions. The primary shear walls run in the transverse direction (E-W) and are located along the exterior of the building. They are one bay in length (22-0 ) and run from the basement all the way up to the roof of the building. On the building s interior the elevator and stair shafts also serve as shear walls in both directions. Building & Design Codes: The building code used in the design of 111 Morgan Street was the 1999 edition of the Chicago Building Code. As implied by the name, the code is unique to the city of Chicago and is the required building code for all buildings within the city s limits. The Chicago Building Code has provisions for the design of all of a building s major systems the same as any of the more common codes such as IBC 2000 or BOCA. Of particular importance to this report is, the Chicago Building Code provides requirements for the structural loading of buildings including live loads and wind provisions. Since the Chicago Building Code was not available for use in this report, IBC 2000 was chosen to determine the required live loads on the building. From the information available it is unclear what provisions for wind and seismic loads are provided in the Chicago Building Code, therefore for the purpose of this report, wind and seismic design loads were calculated using ASCE The design code used, according to the structural plans, is the latest edition of the American Concrete Institute Building Code (ACI 318). At the time 111 Morgan Street was designed the latest edition of the ACI code was ACI , however since that time ACI has updated the code and released a new edition, ACI If the 3

4 building is analyzed using the new code discrepancies will most likely occur since the load factors, strength reduction factors, and ductility requirements have been changed. Also, when using computer programs modifications will have to be made to most of the loadings since most programs have not yet been updated for the changes in ACI Loads: To begin with the dead load was calculated from the weight of each slab plus the weight of the exterior façade. The weight was determined using 150lb/ft 3 as the weight of reinforced concrete and then multiplied by the slab thickness and square footage. The weight of the brick façade was estimated at 25 psf As previous noted the Chicago Building Code was unavailable for researching the required loads for this building and therefore IBC 2000 was used to determine the required live loads and ASCE 7-98 was used to calculate wind, seismic, and snow loads. The live load information shown was obtained from Ch. 16 of IBC 2000 for residential, multifamily dwelling units, and has been compared to the loads used in the actual design which were found on the structural plans. The wind, seismic, and snow loadings were all calculated from various chapters of ASCE 7-98, and the results are summarized in the following tables and diagrams. Required Live Loads (psf) Load Type IBC 2000 Actual General Balcony Lobby Parking Mechanical NA 150 4

5 Load Type ASCE 7-98 Actual Wind (windward + leeward) 7-12 psf psf Seismic Base Shear 1511 kips NA Snow 20 psf 25 psf 5

6 The loads researched for this report are similar to those used for the design of the building, with the exception of the wind load. The design wind load is significantly higher than the wind load calculated by ASCE 7-98, and is probably due to a difference in wind speed between the City of Chicago Building Code and ASCE 7. Another possible explanation is that localized wind pressures can be much higher than the averages shown in ASCE, and could result in a higher wind force acting on a particular building. Spot Checks: For this report several items were checked in order to verify member sizes. The first item that was checked was the floor slab. An imposed dead load on the floor slab was assumed to be 20 psf and live loads were taken from the IBC 2000 code book. These loadings were then factored using the ACI load factors and compared to allowable values given in the 1992 edition of the CRSI handbook. The calculated factored load was 112 psf and the value given by CRSI was 186 psf. This simplified analysis shows that the 8 ½ slab thickness is certainly within an acceptable range of what would be expected. The next item checked for this report was a typical column on the 2 nd level of the building. Since no frame analysis was performed for this report the moment being transferred into the column was unknown and therefore had to be neglected. For this reason an interior column was selected so that the moment being neglected would be smaller (compared to an exterior or corner column). Dead loads were determined per floor using a 20 psf imposed dead load and the weight of the slab. The live load was also calculated per floor using a 40 psf load for general areas and a 15 psf partition load. The live load was reduced according to IBC 2000, and then both the dead 6

7 and live loads were adjusted so that the PCA column program could be used. The results of this analysis show that the column had a nominal axial capacity of 1435 kip and a bending strength of 81 ft-kips. Since 111 Morgan St. has a non-sway frame which utilizes shear walls as the lateral resisting system, the columns will not be required to carry a great deal of moment and therefore neglecting moment in the columns is a reasonable assumption and the conclusion can be made that the columns are appropriately sized. The final item check in this report was a shear wall. To make the calculations easier a shear wall along the exterior of the building was selected because its cross section does not change as it progresses up the building. The distribution of forces was determined as a percentage of the total linear feet of shear wall in that direction. It was estimated that the wall analyzed will carry approximately 20% of the total shear load. To simplify the procedure, the shear wall was treated as a cantilever beam and the story forces from the earthquake loading were used to design the wall. The results of this design were a wall that was 17-4 long and 1-0 thick. Since the actual shear wall spans an entire bay in length (22-0 ) its width is slightly smaller than the estimated width given in the simplified design. 7

8 APPENDIX 8