The building on 250 West Street is a 7-story multi-use that provides space for parking,

Transcription

1 December 5, 2002 Thesis Executive Summary The proposal for the investigation of the building on 250 West Street will include an in depth look at the floor and lateral systems. A continuation of the Pro-Con Study of Alternative Floor Systems (S-2) will be completed to determine the best floor system for the structure. From previous studies of the floor systems, 3 different systems are still viable options: a redesign of the current system of composite beams and composite deck spanning in the east-west direction, composite beams and composite deck spanning in the north-south direction and non-composite beams and composite deck spanning in the east-west direction. An initial design will be completed by loading the entire floor with a uniform load similar to the actual loads it will face. To complete the initial design, the computer program RAM will be used. The designs will then be compared on economics, constructability and effects on other building systems. Once the best system is determined, a detailed design will take place for the system also using RAM using LRFD principles instead of the ASD principles in the original design. The current framing plan does not have any columns in the corners of the building. As a result, the beams that frame into the corners are field welded with full penetration welds to the columns adjacent to the corners. This creates a moment connection to give the beams stability. Since field welding is very expensive, alternative methods of making the connection will be analyzed. This includes different types of moment connections and cantilevering the beams over the columns adjacent to the corners. The braced frame lateral system will also be redesigned using LRFD. Another change to the building is that the seismic load will be increased. The original design used a seismic resistance factor of 5 which requires special design considerations. The redesign will use a seismic resistance factor of 3, so the members and connections do not have to be specifically designed for seismic loads. Once the redesign is completed, an estimate and schedule will be completed for the changed design. The estimate will be completed by hand and then compared to the current system. The estimate will be broken down into: material and labor cost for both the floor system and lateral system redesign. From the estimate data, a schedule will be developed for the redesigned features of the building and also compared to the current schedule. The final part of the investigation of the building will be to complete a lighting design for the office space on the first floor. The space will be designed as if it had an open office plan. For the design, typical office finishes will be assumed for the space since the interior spaces of the building are not designed yet. Building Background The building on 250 West Street is a 7-story multi-use that provides space for parking, storage, retail and offices. The basement of the structure ties into an existing parking deck and adds additional parking as well as an area for storage. The first floor of the building is

2 partitioned roughly in half and provides retail and office space. The remaining 6 stories have all been designed for office space. The unique feature of the building is the incomplete design to allow for customization by the future tenants. However, this presents the challenge of designing spaces to accommodate an unknown tenant and function properly and safely. The project sits on a city block in the Arena District of Columbus, Ohio that slopes roughly 6 feet from the northeast down to the southwest corner of the building footprint. To the north of the building rests an existing building labeled D, while to the east of the project is the existing cinema and parking garage. The south and west sides of the building are open with the site for future building F to the south and West Street and Arena Park to the west. The site for building F will be used as a staging area for the project. The building itself is approximately 155,000 square feet and has a footprint of roughly 194 feet by 100 feet. The exterior of the building is a combination of brick columns, glass, and metal panels. Each side of the building has narrow brick columns the full height of the building, giving the illusion that the building appears taller than it actually is. The columns have a slight recess in the middle that is accented with limestone squares at the top and bottom. Also, each column is stepped in on all three exposed sides at both the 6 th and 7 th floors with limestone accents. This again adds to the illusion the building is taller than it actually is. An exception to this is the west elevation where a cantilevered balcony/terrace occurs on the 7 th floor. The balcony is surrounded with a metal guardrail with glass in fills. As a result of the balcony, the columns beneath it are a little different than the rest of the columns. Instead of being stepped at the 6 th and 7 th floor, they are stepped at the 5 th floor and end beneath the balcony. To contrast the brick columns, painted metal panels are installed between each column that extend several feet below all the finished floors. The remaining exterior of the building is filled with glass windows. 2

3 To finish out the building, screen walls are installed around the roof top units in order to hide the mechanical systems. The screen walls are made up of painted corrugated panels that are attached to a steel tube frame. Overall, the use of different building material adds a unique look to the building. The entire building s loads are transferred to the ground by a concrete foundation and steel superstructure. The loads are transferred from the foundation to the ground by a strip footing around the perimeter of the building and spread footings under each column. The basement walls are a combination of masonry and concrete. On top of the foundation are wide flange steel columns. Each floor system is made up of steel beams, covered by composite metal deck, shear studs and light-weight concrete to form composite beams. The lateral restraint system comes from four braced bays in the center core of the building: two braced frames in the east/west direction and two in the north/south that span the full height of the building. This allows the floor system to be designed for only the gravity loads, making the design much easier. The mechanical system for 250 West Street is a combination of variable and constant air volume systems. Each floor is equipped with four VAV boxes that are equipped with 12 kw reheat coils, with the exception of the bathrooms. Each bathroom is controlled by a constant volume fan box for its air conditioning needs. On top of the building will be (2) 130 ton, (1) 75 ton and (1) 60 ton roof top units to condition the building s air. Along with the roof top units, a 122 ton cooling tower and several auxiliary electric heating coils will complete the major components of the system. In order to get fresh air into the building; intake ducts will be located on the roof with the units as well as on the first and fourth floor. Several fans will be installed to help circulate air, exhaust fumes and to pressurize the stairs. Also, a carbon monoxide controlled exhaust system will be installed in the parking area to prevent the build-up of harmful gases. 3

4 The electrical system for the building is shared with the other buildings on the block. This includes buildings B, C, D, the cinema, the parking garage as well as the multi-use project. To support all the electrical needs for these buildings a 480/277 volt, 2500 amp, 3 phase system is utilized. Buildings D, B & C and the cinema have 225 amp, 3 phase panels while the parking garage has a 100 amp panel. The remaining capacity of the system is used to run the multi-use project. Each floor is served by a 480/277 volt, 3 phase, 200 amp and 400 amp panel. Off of the 400 amp panel is a transformer that steps the voltage down to 208/120 and serves 2 panels. Having multiple voltages at each floor allows the lighting to be run at 277 volts in order to conserve energy and then step it down to 120 for receptacles. Each elevator and roof top unit is served by a 480 volt, 100 amp, 3 phase line. The lighting plan for the building is incomplete due to the fact that much of the space is currently being built as unfinished office space until tenants can be lined up. However, the public areas of the building have been finalized and have permanent lighting. The central corridor on the first floor of the building is lit by recessed cans, wall sconces and cove lighting. The recessed, low voltage cans provide the general lighting for the corridor and use a 12 volt lamp. The oval lobby area is accented with a cove rope light and wall sconces in addition to the low voltage general lighting. In the public spaces around the elevators and in the bathrooms, recessed fluorescent can lights are used. The basement lighting has also been finalized. The storage area and corridor will receive surface mounted fluorescent fixtures and metal halide pendent fixtures will be placed in the parking area. For the most part, this is the only permanent lighting to be installed in the building at this time. There are some temporary 1-lamp fluorescent strips in the unfinished spaces to provide a minimum lighting level for safety purposes. The exterior of the building is lit by metal halide wall mounted cylinders at each column. The 4

5 exterior columns on the front of the building cascade light both up and down accenting the columns. The cylinders on the middle columns only shine light down because of the covered entrance. Just like the rest of the building, the final lighting plan will be completed after tenants are locked into the spaces. The entire building is protected by a sprinkler system. The basement is protected by two different systems; a dry pipe system in the parking area because of the unconditioned space, and a wet pipe system protects the storage area. The rest of the building is protected by a wet pipe system that is divided into 7 zones with each floor being zoned separately. Problem Statement All the systems in the building must be designed to be functional, economical, according to code and within industry standards. The location of the building will determine what codes are appropriate and how the building must perform. The budget of the building must also be determined by the owner and will have a direct impact on the quality of the finished product. The floor system of the building was designed to resist the minimum design loads that are prescribed in ASCE 7-98 by using the Allowable Stress Design method. The office space was designed to resist a live load of 50 psf and an additional 20 psf partition load as well as serviceability issues such as deflection. The building was initially designed without complete floor plans; therefore the additional load corridors create on the floor system will have to be taken into account somehow. Also, there are several moment connections in the building because of the framing layout. These moment connections occur on each floor near the corners of the building. The framing plan doesn't have any columns in the corners of the building. To give the beams stability that frame into the corners a field welded, full penetration weld is used to cantilever the beams off of 5

6 the first column line. Field welds tend to increase the cost of the connection since field labor is much more expensive that shop labor. There are several other alternatives that could be used to shift some of the labor away from the field such as: continuous beams cantilevered over the column or several other types of connections that utilize field bolting instead of field welding. Finally, the building must resist all the lateral loads that are applied to it. The building currently uses braced frames to resist the lateral loads to the building. When the seismic loads were determined for the building a seismic resistance factor of 5 was used in the calculations. Using a seismic resistance factor above 3 requires special attention be given to the design of the members and connections. In order to determine the structural design s capability in coordinating with the entire building, it is important to know the cost and construction time for the structural system. This will help determine if the building will be within budget and how long construction will take. Depending on the estimate and construction duration of the structural system, changes may need to be made to the structural system either to reduce costs or decrease the construction duration. The current design documents for the building do not have any final lighting designs for the interior of the building since the building currently has no tenants. An exception to this is the central core and lobby interior spaces. However, the system for the rest of the floors is only temporary and has a few fluorescent channels to provide a minimal amount of light to allow safe viewing of the space by possible tenants. Proposed Problem Solutions As with every engineering problem, several solutions are available to solve the problem at hand. From previous analysis done this semester, several types of floor systems are more logical for 250 West Street: composite beams and composite deck framing in the north-south 6

7 direction, composite beams and composite deck framing in the east-west direction and noncomposite beams and composite deck. The lateral system will be designed as braced frames as in the current system. Once the design is completed, an estimate and construction timeline will be completed and compared to the current cost and construction time. Also, a lighting plan will be developed for an office area. Floor System Design In the new building on 250 West Street the floors have all been designed to be unfinished office space from the second floor to the sixth floor. Each floor is almost identical with the exception of some minor changes in floor penetration openings in the central core. As a result, the floor system is very repetitive between these floors, and determining the most economical floor system will reduce the costs of the building. However, despite being economical and safe for the occupants, the floor system must conform to the fire rating on its own. The reason for this is because the floors are unfinished until tenants lease the space and customize the ceiling and floor finishes. To determine the best framing for the floor system, a continuation of the Pro-Con Study of Alternative Floor Systems (S-2) will be completed. As a result of that study, three types of flooring systems were still viable for the building. These floor systems include the current framing system of composite beams and composite deck framing in the east-west direction, reversing the framing to span the beams in the north-south direction and using non-composite beams as the final alternative. Once the best floor system is determined, the system will be designed using a 60 psf live load, 20 psf partition load, miscellaneous dead load to account for mechanical, electrical and plumbing systems and all dead loads from the system itself using the LRFD design methodology. The minimum live load according to ASCE 7-98 is 50 psf for an 7

8 office space. Since the tenants for each floor was not known at the time of design, it is being increased to 60 psf to add flexibility to the floor system. Each floor system design will conform to the 3 rd Edition of the Manual of Steel Construction: Load and Resistance Factor Design. Along with the floor system design, different types of moment connections and cantilevered beams will be analyzed in order to determine the most economical way to accommodate the detail of not having any columns in the corners of the building. A full penetration field weld of the top and bottom flanges is very expensive because of the field labor. Alternatives to decrease the amount of field labor will be evaluated for each connection. A few of the possible alternatives include cantilevering a beam over the first column adjacent to the corner, bolted flange plates, moment end plates and flange angles. Lateral System Design Like the current building, the lateral system will consist of braced frames in the central core of the building. Each frame will be designed to resist a portion of the lateral load based on its relative stiffness. The wind and seismic loads will be determined using ASCE 7-98 for the building location in Columbus, Ohio. The wind loads will be based on a wind speed of 90 mph, steel braced frames and a Type II structure. The seismic loads will be determined and applied using the equivalent lateral force method. The loads will be determined for the following building properties: category II, seismic use group I, site class B and a seismic resistance factor of 3.0. Each member of the frame will be designed for the critical load case and each frame will be designed to have a story and total drift less than h/400. Estimate and Construction Schedule Once the design of the new systems is designed, an estimate and construction schedule will be completed for the new structural system. The estimate and schedule will focus on the 8

9 new steel system and how it compares to the existing system. However, any changes to the foundation and other portions of the building will be noted, along with how they affect the estimate and schedule of the entire building. Lighting System Since the building is mostly unfinished space, a complete lighting design has not been designed for the building. As a result, a lighting system will be designed for the office space on the first floor of the building. The system will be designed for an open office plan without any partitions. It will also assume that computers are not heavily used in the area. The design will conform to the National Electric Code in both performance and energy consumption. Solution Method Floor System As done in the Pro-Con Study of Alternative Floor Systems (S-2) each proposed floor system will be initially designed using a uniform load over the entire area. For each alternative, a computer model will be developed using RAM and the initial floor system designed. Since the three systems have already made it through the initial study done earlier this semester, the systems will only be looked at for economy and construction time. The cost and construction time of each floor system will be determined using hand methods learned during a summer internship working for a steel erector. Once the best floor system is determined it will be redesigned in a more detailed manor. The floor system most suited for 250 West Street will be redesigned to include all floor openings and gravity loads. Most of the floor system will only experience gravity loads with the few members of the braced frames being the ones subjected to lateral loads. Also, the spandrel 9

10 beams will include the wall loads that were neglected in the initial design. Once again the computer program RAM will be used to complete the design of the floor system. Another part of the floor system is how to carry the loads in the corners of the building where columns do not exist because of architectural reasons. Several different types of connections will be examined to reduce the cost of the currently field welded beams. Hand designs will be completed for bolted flange plates, flange angles, moment end plates and beams cantilevered over the columns adjacent to the corner of the building. Each design will be analyzed for cost and field installation to determine the most economical solution. Lateral System To design the lateral system all applicable loads will be determined using ASCE A computer model will be developed in STAAD using the frames in the current design of the building. A lateral load will then be placed at the top of each frame and an analysis run. From the results of the analysis, an approximate stiffness can be determined for each frame. The lateral loads will then be assigned to each frame by determining the relative stiffness of each frame. The total load on each frame will be a combination of the direct shear and resulting torque placed on the building because the center of rigidity, center of load and center of mass do not occur at the same location in the building. The load on each frame will be determined by a series of both hand calculations and Microsoft Excel spreadsheets. Once the load each frame will resist is determined, the computer model in STAAD will be loaded. An analysis will then be run to determine the forces in each member. Hand calculations will then be performed to design each member for strength based on the loads from the STAAD output. 10

11 Once the design is complete, a new computer model will be created with the new design and loads. Another analysis will be performed to determine the drift of each frame. The drift of each frame will then be compared to the industry accepted value of h/400. If the frames fail in drift, the stiffness of the frame will be increased until the drift falls within industry standard. Estimate and Schedule Once the design of the floor systems and lateral system is complete, an estimate and schedule will be completed for the changed steel system and compared to the existing structure. The estimate and schedule will be completed by hand methods learned during summer employment. The estimate will be completed by first adding up the weight of all the materials. Shop hours will then be assigned to each member for fabrication. The cost of materials per ton will then be determined based on cost of steel, shop hours, paint, bolts, detailing for shop drawings and freight. The cost of material will then be determined by multiplying the cost per ton by the tonnage in the building. Erection costs will then be determined by assuming a daily production of the erection crew and detailing crew. The time required for each crew will then be multiplied by the cost of each crew per day for the total cost of erection. The erection cost will then be added to the material costs for the total cost of the system. From the estimate data, the time of construction will be known for the erection crew and detailing crew. With this data a schedule can be made for the steel erection. Starting and ending dates for both crews will be determined so the two crews do not interfere with each other during the erection process. 11

12 Lighting Design A lighting plan will be developed for the 1 st floor office space which is approximately half of the building footprint. The system will be designed as if it was an open plan office. First the design requirements of the space must be determined. The code requirements, power limits of ASHRAE/IESNA 90.1, 1999 and recommendations of the IESNA Handbook will also be considered when determining the design requirements of the office space. Once the requirements are determined, fixtures, lamps and ballasts can be selected to accomplish the lighting needs of the office. Light loss factors will also be determined before layout of fixtures can begin. To aid in the design of the system, the computer program Luxicon will be used to layout the lighting fixtures. Once the lighting design is complete circuiting and controls for the space will be developed. Tasks and Tools 1) Determine all loads on the building according to ASCE ) Design floor system a) Determine best floor system i) Create computer model of all 3 systems in RAM ii) Apply uniform load over entire floor for each system iii) Complete initial design of each system iv) Compare systems for cost and constructability issues v) Pick best system b) Design floor system i) Create computer model of system in RAM ii) Apply all gravity loads to floor system 12

13 iii) Complete design of floor system for gravity loads c) Determine best solution for members framing into building corners, moment connections or cantilevered beams i) Design several solutions by hand ii) Complete cost analysis for each option iii) Pick best solution iv) Refine floor system design if applicable 3) Design lateral system a) Determine stiffness of current frames in building using STAAD b) Determine load on each frame by stiffness method and from gravity analysis c) Determine member forces on each frame by using STAAD d) Design members sizes by hand based on strength e) Create model in STAAD of redesigned frames f) Check story and total drift of frames g) Increase stiffness if required 4) Estimate and Schedule a) Estimate i) Perform take-off of changed portions of building ii) Complete material costs iii) Complete erection costs iv) Compare cost to current design b) Schedule i) Prepare schedule using estimate data 13

14 ii) Compare schedule to current design 5) Lighting Design a) Determine requirements of system b) Determine recommendations and code requirements from IESNA Handbook, NEC and ASHRAE c) Pick fixtures to meet system requirements d) Pick lamps and ballasts for fixtures e) Determine light loss factors f) Design system Timetable January First Day of Classes Loads Determined

15 February Floor System Designed March Spring Break 11 Spring Break 12 Spring Break 13 Spring Break 14 Spring Break 15 15

16 Lateral System Designed Estimate & Schedule Completed April Lighting Design Completed Thesis Presentations 15 Thesis Presentations 16 Thesis Presentations

17 Conclusion The building on 250 West Street is a 7-story multi-use building. It is currently designed as a build to suit building with much of the space unfinished. The current structural system uses composite beams and composite deck spanning in the east-west direction. To better explore the economics of the building, several different floor systems will be analyzed to discern if the most economic system is used in the building and the effects of using LRFD vs. ASD design. The lateral system will also be accessed and redesigned for the building. Once the two systems are redesigned, an estimate and schedule will be completed to determine the effects of the changes on the building. To complete the study of the building, a lighting plan will be developed for the office space on the first floor of the building since the original construction documents do not contain a design. 17