Introduction and Background - Pennsylvania State University · 2003. 4. 21. · The lobby is two...

Composite Vs. Non Composite Structural Steel Systems & Annandale, Virginia Options to Achieve Low Floor-to-Floor Heights

Shawn A. Graham Spring 2003 The Pennsylvania State University Structural Option Page 5 Architectural Engineering

Introduction and Background Heritage Center is located in Annandale, Virginia and currently consists of three office buildings and a parking structure. Heritage Center Building IV is the latest and final office addition to the site, and has recently become available for occupancy in February 2003. As seen in Figure 1, Annandale, Virginia is only about eight miles south west of Washington D.C.. Heritage Center IV is situated inside the Capital Beltway at 7619 Little River Turnpike (Route 236), and is easily accessible to and from I-495, I-95, and I-66. As a result, local traffic congestion is minimal.

Figure 1 – Maps of Annandale, Virginia

Heritage Center Building IV is a ten story structure consisting of 206,000 square feet (21,000 square feet per typical floor plate) that sits on four levels of parking below grade. In comparison, Buildings I, II, and III are all less than 100,000 square feet. Figure 2 shows how Building IV is integrated within the site. The campus is commuter friendly with landscaped pedestrian walkways and plazas connecting all four buildings and the parking garages. On-campus parking is available at three spaces per 1,000 rentable square feet.

Figure 2 – Heritage Center Site

Building IV



The primary project team members that brought Heritage IV to life are given below. The address for each member is also given to clarify their location in relation to Annandale, Virginia.

o Owner

Bourj, LTD. 7611 Little River Turnpike, Suite 304 West Annandale, Virginia 22003

o Development Manager Royal Management & Development, INC.

7611 Little River Turnpike, Suite 304 West Annandale, Virginia 22003

o Architect / Mechanical, Electrical Engineer / Fire Protection Burt Hill Kosar Rittelmann Associates

650 Smithfield Street, Suite 2600 Pittsburgh, Pennsylvania 15222

o Structural Engineer Atlantic Engineering Services

650 Smithfield Street, Suite 1200 Pittsburgh, Pennsylvania 15222

o Site / Civil Engineer Burgess & Niple, INC.

4160 Pleasant Valley Road Chantilly, Virginia 20151-1226

o General Contractor / CM Clark Construction

7500 Old Georgetown Road Bethesda, Maryland 20814



Existing Conditions Architectural The exterior materials of Heritage IV consist of black thermal finished granite cladding at the building base and stair/core towers, anodized aluminum curtain walls, windows, and metal spandrel panels. Also, low emissivity coated, heat reflective, butt jointed glass panels are used. These architectural aesthetics combine nicely, and can be seen in Figure 3a and Figure 3b.

Figure 3a – Architectural Rendering Figure 3b – Architectural Rendering at Night The lobby is two stories in height and polished with white granite flooring with polished black granite borders. Mahogany wood accents trims and panels. A monumental circular staircase has stainless steel railings and glass panels. Figures 4a and Figure 4b are architectural renderings of the elevator lobby and circular staircase, respectively.

Figure 4a – Elevator Lobby Figure 4b – Circular Staircase



Building IV’s office floors will be split up into two different types of architectural layouts. Figure 5 shows the projected layouts: single tenant floor on the left, and a multiple tenant floor on the right.

Figure 5 – Architectural Layouts of a Typical Floor

As seen in Figure 6, parking level A is located on the first floor, along with the lobby and a fitness center. The remaining four levels of parking are all below grade and specified as levels B, C, D, and E. All four and one half levels of parking are connected to, and match up with the existing parking garage, which consists of 6 levels (levels A-E and a top surface level). This existing parking garage is located east of Heritage Center Building IV and is designated by dashed lines in Figure 6.

North



Figure 6 – First Floor and Parking Level A Plan Lastly, one additional prominent architectural feature is that the tenth floor steps back from the rest of the building to provide two open roof top terraces for the tenants on that level.



Structural Heritage IV’s structural system is comprised of two-way reinforced, 150 Psi, cast-in-place concrete flat slab with drop panels. The building footprint is 163 feet by 155 feet. The building perimeter shrinks to 163 feet by 140 feet at the third floor, and continues up until the tenth floor, where as previously mentioned it steps back again to provide the two open roof top terraces. The typical bay is thirty feet by thirty feet. The slab is typically nine inches thick. There are also ten foot square, nine inch thick drop panels that help resist punching shear of the columns. Also as seen in Figure 7, there are continuous drop panels that cross over three spans. These are also ten feet wide and nine inches thick. Therefore at drop panel locations the total concrete depth is eighteen inches.

Figure 7 – Typical Structural Floor Plan Showing Drop Panels Lateral resistance is provided by the continuous drop panels which serve as rigid moment frames. On each floor there are four of these continuous drop panels, two in each direction. They are strategically placed symmetrical about the building’s center of gravity, to reduce torsional effects. These continuous drop panels were designed to take the full lateral load of the building. There are thirty eight columns on the typical floor plan and they range in size from eighteen inches by eighteen inches to eighty-two inches by thirty-six inches, with an average size of thirty inches by thirty inches. Figure 8, shows a cross-section through a column, drop panel, and slab.



Figure 8 – Typical Column Termination at Slab Detail

The structural components below grade consist of eighteen inch thick concrete load bearing walls around the border of building, cast-in-place drilled caissons, and grade beams. The grade beams span between the exterior caissons and support the perimeter load bearing walls, along with the stair and elevator walls. All caissons are thirty-six inches in diameter, and the average grade beam size is thirty six inches by thirty six inches. There is a penthouse that resides on the tenth floor roof that contains cooling towers. Steel joists frame the roof of the penthouse and are supported by load bearing masonry walls. The elevator and stair openings are also encompassed by masonry walls that support the stair and elevator loadings. Three different concrete strengths are used for the various structural components throughout the building. As seen in Table 1, 7000 Psi concrete with a maximum water cement ratio of 0.35 is used for the columns. This higher strength concrete and lower cement ratio will result in the design of smaller columns, which in turn gives more leasable square footage. The rest of the building uses 4000 Psi and 5000 Psi concrete, which is typical for most office buildings constructed of concrete. Concrete Strength

Location Minimum f’c Required at 28 Days

Maximum Water Cement Ratio

Foundations 4000 Psi 0.45 Interior Slabs 5000 Psi 0.40 Exterior Slabs 4000 Psi 0.45 Garage Level Walls 5000 Psi 0.40 Garage Level Slabs 5000 Psi 0.40 Slab on Grade 5000 Psi 0.40 Columns 7000 Psi 0.35

Table 1 – Various Concrete Strengths



The design gravity dead loads used for the design of this structural system consist of the slab self weight, the drop panel self weight, and a super imposed dead load of 25 Psf. Normal weight concrete weighing 150 Pcf is used. These dead loads are summarized in Table 2. Design Gravity Dead Loads Slab Load (9”Slab)*(150 Pcf Concrete) 112.5 Psf Typical Drop Panel (9”Deep)*(150 Pcf Concrete) 112.5 Psf Super Imposed 25 Psf

Table 2 – Design Gravity Dead Loads

The design gravity live loads were obtained from BOCA 1996 for that of an office building type. As shown in Table 3, the snow load includes drift, and the corridor load decreases from 100 Psf to 80 Psf after the first floor. Design Gravity Live Loads (BOCA 1996) Roof (21Psf Snow + 9Psf Drift) Base Ground Snow Load 30 Psf Office Floors (50 Psf + 20 Psf Partitions) 70 Psf Lobby, Fitness Area, Retail Spaces, First Floor Corridors 100 Psf Garage Levels 50 Psf Corridors Above First Floor 80 Psf Stairs 100 Psf Mechanical 150 Psf

Table 3 – Unreduced Design Gravity Live Loads

Live load reduction is permitted if the area of influence for the loaded member is greater than 400 square feet, using the equation L = Lo(0.25+15/(Ai)0.5)). The design wind and earthquake loads were computed using Microsoft Excel spreadsheets. Wind load calculations were based upon BOCA 1996, with an 80 MPH wind speed. Windward pressures range from 2.2 Psf at 15’-0” to 11.5 Psf at 120’-0”. Leeward pressures are 13.4 Psf. The spreadsheet used for the wind loading calculation is shown in Appendix A. Seismic Loads were computed using BOCA 1996. The seismic forces were calculated for seismic hazard exposure group I, and for a reinforced concrete moment frame. The spreadsheet used to obtain seismic forces can be seen in Appendix B. On the following page in Table 4, the variables specific to Heritage Center Building IV in computing the wind and seismic forces are listed.



Design Lateral Loads (BOCA 1996) Wind Loads (BOCA 1996) Basic Wind Speed 80 MPH Importance Factor 1.0 Wind Load Exposure B Wind Design Pressure – P (Windward) 13 Psf Wind Design Pressure – P (Leeward) 14 Psf

Seismic Loads (BOCA 1996) Velocity – Related Acceleration – Av 0.05 Peak Acceleration – Aa 0.05 Seismic Hazard Exposure Group I Seismic Performance Category B Basic Structural System Reinforced Concrete Seismic Resisting System Reinforced Concrete Moment Frame Soil – Profile Type S1 Response Modification Factor – R 3 Deflection Amplification Factor – Cd 2.5 Analysis Procedure Equivalent Lateral Force

Table 4 – Design Wind and Earthquake Variables



Mechanical The mechanical system for Heritage IV is a water based system. Water is chilled by two rooftop cooling towers located in the penthouse. From there it makes its way to each floor level through a riser. Self contained packaged water cooled units are located on each floor, and use fans to circulate air over the cooled water pipes. A pressurized duct loop then circulates the cooled air throughout the level. Each self contained packaged water cooled unit moves 18,000 Cfm of air with a thirty horsepower fan. 3,100 Cfm is the minimum required outside air. For heating, 315 kW heating coils heat the air in the ducts. VAV boxes located on smaller ducts then supply air to diffusers which are located on the ceiling around the perimeter of the building. Return air is brought back into the ducts and mixed with new outside air, with a fraction of the return air exhausted. Each floor is independent of others, and therefore can be controlled separately. Lighting and Electrical Heritage IV has its own supply line and a 2000 kVA, 480/270 V, 3 phase, 4 wire transformer. If a power outage would occur, a 600 kW oil based emergency generator can supply power for eight continuous hours. Each floor has its own lighting panels. Exterior flood lights illuminate the glass corner façade. Some fluorescent lighting is provided on each floor, but the main lighting scheme is decided upon by the tenant. The two story lobby consists of compact fluorescent recessed down lighting, and indirect fluorescent tubular luminaries as shown in Figure 4a and Figure4b.



Construction and Cost Heritage IV was a Design-Bid-Build project with a traditional delivery system. The owner contracted the architect, who then contracted the design team. The construction site was cramped due to the existing buildings, parking structure, and nearby roadways. Construction started on August 17, 2001 and was recently completed on February 15, 2003. The base lump sum bid for Heritage IV was estimated as $ 22,673,000. Table 5 breaks down this total cost into the Construction Specification Institute’s (CSI) sixteen divisions.

Division Cost Estimate 01 – General Requirements $ 1,300,000 02 – Site Work $ 1,500,000 03 – Concrete $ 6,200,000 04 – Masonry $ 1,850,000 05 – Metals $ 750,000 06 – Wood and Plastic $ 220,000 07 – Thermal and Moisture Protection $ 420,000 08 – Doors and Windows $ 3,150,000 09 – Finishes $ 1,150,000 10 – Specialties $ 150,000 11 – Equipment $ 10,000 12 – Furnishings $ 50,000 13 – Special Construction $ 350,000 14 – Conveying Systems $ 950,000 15 – Mechanical $ 2,300,000 16 – Electrical $ 2,323,000

Total $ 22,673,000

Table 5 – Cost Estimate for each CSI Division, Courtesy of Royal Management & Development, INC.



Proposal Heritage Center Building IV is currently a cast-in-place, concrete flat slab system, with continuous drop panels. A concrete structural system was used for Heritage IV, because it gives a low floor-to-floor height of eleven feet four inches. The floor-to-floor height of the building was an important design factor because it is in close proximity to Washington, D.C., which has a height limitation. The Virginia Building Code states that all buildings must be not exceed a height of 125 feet above grade. However, the cooling towers on the roof were permitted, and do, surpass the height constraint. With the height limitation previously mentioned in mind, and the generalization that concrete gives a smaller floor thickness than steel, the architect and structural engineer decided to design the building in concrete. The average grade elevation for Heritage IV is 293.50 feet (parking level B), and the elevation of the roof level is 415.79 feet. This gives a building height of 122.29 feet, which is less than the height cap of 125 feet. This senior thesis includes a complete structural redesign of Heritage IV’s above grade office space, in both composite and non composite structural steel. The parking structure below grade will be assumed unchanged and left as cast-in-place concrete, with load bearing walls.

• The first goal, in performing this redesign in steel, is to compare the floor thicknesses between the existing concrete system and the newly designed composite and non composite steel systems; and ultimately to compare the impact each system has on the total building height.

• The second goal of this senior thesis is two compare the composite and non composite

structural steel systems. A detailed cost analysis and duration of construction activities will be the basis for this comparison.

• The third goal is to provide a lighting layout and design for tenant office space C (Figure 5).

• The fourth goal is to present some research on alternative structural systems used to

maintain low floor-to-floor heights. The two systems I researched are SMI Steel Product’s SmartBeam® and the staggered steel truss system.

The aforementioned steel design was completed using RAM International’s RAM Analysis Integrated Structural Software. I used RAM Modeler to model the building three dimensionally, RAM Steel to design for gravity loads, and RAM Frame to design for wind and earthquake loads. I used a combination of moment frames and braced frames to resist lateral loads, as I will later discuss.



Structural Composite Structural Steel System Heritage IV was designed using RAM Analysis Integrated Structural Software. I will know take you through the steps I took in order to design Heritage IV in composite steel. The typical floor framing plan, shown in Figure 9, is provided to give a better understanding of each step.

• The column grid layout (on average 30’ X 30’ bays, labeled A-G & 1-7) was input into the program, followed by the column placement. This was done for floors one through ten, the main roof, and the penthouse roof.

• The composite girders were input to interconnect the columns, and the composite beams were input and spaced on average at 7’-6”.

• The stair and elevator openings were modeled using concrete beams and columns to represent the CMU walls that will be in those locations.

• The slab was placed around the perimeter of the floor framing with an 18” overhang (shown in green).

• The slab openings were defined at stair and elevator openings with a 2” overhang.

Figure 9 – Typical Floor Framing Plan



• USD 2” Lok-Floor decking (unshored) was assigned to span perpendicular to the beams. Other criteria assigned to the decking included: 4 Ksi, 115 Psi, 3.25” thick concrete; and 60 Ksi, 3.5”, 0.75” diameter shear studs. A composite steel detail is shown in Figure 10.

Figure 10 – Composite Steel Detail

• The gravity loadings were input into the program. There were two types of loadings, surface

and line, and they are summarized in Table 6. The surface loads were put on their respective floors, and the line loads were put on the perimeter beams in agreement with the exterior façade.

Dead Construction Dead Live Reduction Construction

Live Mass Dead

Surface (Psf) Typical Floor 59.0 48.0 80.0 Reducible 20.0 69.0

First Floor 59.0 48.0 100.0 Reducible 20.0 69.0 Roof 59.0 48.0 80.0 Roof 20.0 69.0

Line (Klf) Granite 0.00 0.00 1.060 Unreducible 0.00 1.060

Aluminum/Glass 0.00 0.00 0.165 Unreducible 0.00 0.165

Table 6 – Gravity Loads input into RAM • An alternate deflection criterion was entered into the perimeter beams, because they are

carrying the load of the curtain wall. Deflection is limited here to prevent damage to the façade.

• A preliminary story height, or floor-to-floor height, of 12’-0” was input. • Each floor was assigned as a rigid diaphragm, and ground level was set at the first

floor/parking level A. In actuality the average grade is at parking level B, but it was set at the first floor/parking level A in the model because this is where the steel system begins.

W X _



• The wind and earthquake loads were input using ASCE 7-95 Equivalent Lateral Force and the criteria from Table 4, with the exception of the R (response modification factor for seismic loading) changing to 4.5 (steel moment frame system). Two wind cases, North-South and West-East, were set up. Also, four seismic cases were set up using a 5% eccentricity, North-South +/– 5% e, and West-East +/– 5% e.

• Finally the structure was analyzed. After the structure was analyzed, a vast amount of trial and error went into the final design. The structure had to have a drift of less than the industry standard of H/400. An intricate lateral resistance system was derived and implemented to achieve this. The lateral system consists of a mix between moment frames and braced frames, as well as orientating the wide flange steel columns in two different configurations (Refer back to Figure 9, moment frame members shown in red). Figure 11 shows a three dimensional model of Heritage IV; the moment frame members appear in red, the gravity frame members appear in light blue and the upside down V braces appear in purple.

Figure 11 – Three Dimensional Model Showing Lateral Moment Frames and Braced Frames



There were only a limited number of spots to place the braced frames, since the exterior façade is mostly glass, and the interior of the building consists of open office space. Therefore, the braced frames were placed at four locations in the building, two at each stair opening. Once drift was satisfied the next task was to design the moment frame members for the AISC, ASD interaction equation for gravity and lateral loads combined. All members must have a value of less than 1.0. RAM steel shows members in red if there interaction equation value is greater than or equal to 1.0. A numerous number of members originally showed up with high interaction values. For each member that did not satisfy the interaction equation, I had to manually go into the steel database and find a section that worked. Figure 12 shows a three dimensional model of Heritage IV’s moment frame members and their corresponding interaction equation values.

Figure 12 – Three Dimensional Model Showing Interaction Equation Values of Lateral Members

In the above model there is one member in red; its value is 1.01 and an engineering decision was made to not change it, due to keeping uniformity of the lateral members per each floor. Lastly, the steel girder section with the largest depth on each floor had to be taken into consideration to make sure that the assumed story height of 12’-0” allowed for a 8’-6” finished floor

Key



to ceiling height. The largest section was a W 24 X 55 on the first and roof levels, and a W 21 X _ on the other floors, which meant that the story height must be changed to 12’-3”for the first floor and roof stories. All other stories can be left at a 12’-0” story height. A 12’-3” floor-to-floor height allows for 5.25” of concrete and decking, 24” of steel section, 12” of mechanical duct, and 3.75” for the fireproofing and suspended 2’ X 4’ acoustical tile ceiling grid. Therefore the finished floor above to finished ceiling below is 3’-9” thick, in maintaining the 8’-6” room height. Changing the story height in RAM did not result in any changes to the system, however if the initial story height estimate was not as close to the required story height as it was here additional trial and error design may have been needed. As previously mentioned each lateral member was designed with uniformity amongst the level in mind. Table 7 shows the progression of wide flange steel sizes of lateral beams and columns from the first floor to the roof, as well as the lateral bracing size.

Level Lateral Beams Lateral Columns Lateral Bracing First W 14 X 68 W 12 X 152 HSS 6 X 6 X ½

Second W 14 X 61 W 12 X 152 HSS 6 X 6 X ½ Third W 14 X 61 W 12 X 136 HSS 6 X 6 X ½ Fourth W 14 X 61 W 12 X 120 HSS 6 X 6 X ½ Fifth W 14 X 61 W 12 X 106 HSS 6 X 6 X ½ Sixth W 14 X 61 W 12 X 87 HSS 6 X 6 X ½

Seventh W 14 X 61 W 12 X 79 HSS 6 X 6 X ½ Eighth W 14 X 61 W 12 X 72 HSS 6 X 6 X ½ Ninth W 14 X 61 W 12 X 72 HSS 6 X 6 X ½ Tenth W 14 X 61 W 12 X 72 HSS 6 X 6 X ½ Roof W 14 X 67 W 12 X 87 HSS 6 X 6 X ½

Table 7 – Lateral Beam and Column Sizes per Level and Lateral Bracing



Figure 13 shows a south side frame elevation of the upside down V braced framing.

Figure 13 – Upside Down V Braced Framing

The story displacement with respect to the ground must not be more than H/400 = 132’-6”/400 = 1590”/400 = 3.98”. The story displacement of the roof level for each of the six loadings, two wind and four seismic, are listed below in Table 8

Load Case North-South ∆ (inches) West-East ∆ (inches) Wind BOCA 99 N-S 2.14776 0.42900 Wind BOCA 99 W-E 0.52138 1.97166

Seismic BOCA 99 N-S + e 0.99410 0.20677 Seismic BOCA 99 N-S – e 1.03219 0.21946 Seismic BOCA 99 W-E + e 0.20681 0.87484 Seismic BOCA 99 W-E - e 0.25323 0.89024

Table 8 – Story Displacement of Roof Level

The maximum drift is 2.15” for wind in the North-South direction, which is less than the allowable 3.98”. The lateral system seems over designed for drift, but this is due to the upsizing of the lateral members to meet the previously mentioned interaction equation. The total building height of this composite structural steel system with moment frames and braced frames is 132’-6”. This building would not be permitted by code to replace the existing concrete building. A leasable floor would have to be removed to meet the height requirements, thus making the owner lose money.



Figure 14 shows the composite steel gravity beam and girder sizes, with shear stud requirements in parenthesis, for a typical floor. This composite design requires 20,799 total shear studs.

Figure 14 – Composite, Gravity Beam and Girder Sizes with Shear Stud Requirements The gravity column designs for a typical composite floor can be seen in Appendix C. One drawback to composite steel systems is that it has an increased vibration frequency compared to non composite steel systems.



Non Composite Structural Steel System The non composite structural steel system was designed exactly the same as the composite steel system, with the exception that the system was specified to be non composite, which means no shear studs are involved in the design. Figure 15 shows a non composite steel detail.

Figure 15 – Non Composite Steel Detail

The lateral system layout and member sizes remain exactly the same as the composite system. The only thing that changes in this system is the gravity beam and girder sizes. Figure 16 shows the non composite steel gravity beam and girder sizes for a typical floor.



Figure 16 – Non Composite, Gravity Beam and Girder Sizes

The gravity column designs for a typical non composite floor can be seen in Appendix C. They are the same size as the composite system. A 12’-3” floor-to-floor height for all floors allows for 5.25” of concrete and decking, 24” of steel section, 12” of mechanical duct, and 3.75” for the fireproofing and suspended 2’ X 4’ acoustical tile ceiling grid. Therefore the finished floor above to finished ceiling below is 3’-9” thick, and maintains the 8’-6” room height. The total building height for the non composite system is 134’-9”. Again, this building would not be permitted by code to replace the existing concrete building. A leasable floor would have to be removed to meet the height requirements, thus making the owner lose money. The vibration frequency for this non composite system shows to be lower than the composite system. This shows that non composite systems are less prone to vibration problems. One drawback to the non composite system is the increased girder depth’s, resulting in a higher total building height. On the other hand, time of construction will be faster, since shear studs do not need to be welded to the decking.



Composite Vs. Non Composite Structural Steel Systems Cost Analysis and Time of Construction Detailed structural system takeoffs were completed using RS Means 2002 Heavy Construction Cost Data, and RS Means 2002 Square Foot Cost Data. Table 9 (composite) and Table 10 (non composite) show the construction days, labor hours, total cost, and required crew for each structural system component.

Days Labor Hours Total Cost Crew Gravity Beams 35.11 2073.02 $559,813.98 E-2, E-5

Shear Studs 20.19 332.78 $29,239.23 E-10 Roof Joists 0.23 17.99 $3,361.83 E-7

Gravity Columns 2.27 127.54 $83,932.40 E-2 Lateral Beams 11.99 671.78 $394,110.60 E-2

Lateral Columns 5.70 317.46 $264,402.12 E-2 Lateral Bracing 2.30 128.95 $26,344.79 E-2

Moment Connections 42.32 6771.30 $507,847.50 E-12 Fire Proofing 41.49 1254.78 $107,142.48 (3) G-2

Metal Decking 67.16 2175.90 $306,366.13 E-4 Concrete 82.99 15709.54 $641,611.45 (3) C-20

Nuts, Bolts, Washers, Connection Angles and Plates

Already Included

Already Included $81,350.50 E-2

SUM 311.76 29581.04 $2,924,172.51

Table 9 – Composite Structural Steel System Takeoff

Days Labor Hours Total Cost Crew

Gravity Beams 32.87 2066.99 $775,740.33 E-2, E-5 Shear Studs 0.00 0.00 $0.00 Roof Joists 0.23 17.99 $3,361.83 E-7

Gravity Columns 2.27 127.54 $83,932.40 E-2 Lateral Beams 11.99 671.78 $394,110.60 E-2, E-5

Lateral Columns 5.70 317.46 $264,402.12 E-2 Lateral Bracing 2.30 128.95 $26,344.79 E-2

Moment Connections 42.32 6771.30 $507,847.50 E-12 Fire Proofing 48.65 1471.13 $125,616.01 (3) G-2

Metal Decking 67.16 2175.90 $306,366.13 E-4 Concrete 82.99 15709.54 $641,611.45 (3) C-20

Nuts, Bolts, Washers, Connection Angles and Plates

Already Included

Already Included $121,297.70 E-2

SUM 296.48 29458.57 $3,129,333.15

Table 10 – Non Composite Structural Steel System Takeoff



Table 11 defines the required crews that are in Table 9 and Table 10.

E-2 E-5 E-7 1 Struc. Steel Foreman 2 Struc. Steel Foreman 1 Struc. Steel Foreman 4 Struc. Steel Workers 5 Struc. Steel Workers 4 Struc. Steel Workers 1 Equip. Oper. (Crane) 1 Euip. Oper. (Crane) 1 Equip. Oper. (Crane) 1 Equip. Oper. Oiler 1 Welder 1 Equip. Oper. Oiler 1 Crane, 90 Ton 1 Equip. Oper. Oiler 1 Welder Foreman

1 Crane, 90 Ton 2 Welders 1 Gas Welding Machine 1 Crane, 90 Ton 2 Gas Welding Machines

E-10 E-12 C-20 1 Welder Foreman 1 Welder Foreman 1 Labor Foreman 1 Welder 1 Equip. Operator (Light) 5 Laborers 4 Gas Welding Machines 1 Gas Welding Machine 1 Cement Finisher 1 Truck, 3 Ton 1 Equip. Oper. (med.) 2 Gas Engine Vibrators 1 Concrete Pump (Small)

G-2 1 Plasterer 1 Plasterer Helper 1 Building Laborer 1 Grouting Equipment

Table 11 – Crews

As you can see from Table 9 and Table 10, the non composite structural system takes 15.28 less construction days than the composite system. These construction days do not represent the construction time of the project; when scheduling the project the construction manager would more than likely choose to add more crews, like I did for fireproofing and concrete. These construction days can however be used to compare the two systems as I did. Basically, if time is an issue non composite construction would be somewhat advantageous. This is because no shear studs, which need to be welded, are required in the non composite system. However, more than often, money is the concern. The composite system saves $205,160.64 over the non composite system. This is due to the fact that when shear studs are taken away you no longer get the composite action of the slab and steel. Therefore, the concrete does not take as much of the loading in a non composite system, which in turn makes the cross section of the wide flange steel members bigger. Matthew Stewart, a professional engineer as well as one of my primary contacts, is quoted on this issue as saying, “Based on my experience, non composite is always going to be more expensive because stud costs are peanuts compared to the extra tonnage you spend on heavier non composite sections… Who designs non-composite? Old farts that don’t have any experience with the composite design.”



As already mentioned, the lateral system used in both the composite and non composite system, was a combination of moment frames and braced frames. As seen in Table 9 and Table 10 the moment connections cost more than four times that of nuts, bolts, washers, connection angles and plates combined. The unit price that I used to calculate the moment connection’s cost was given to me by a contact of mine with 31 years experience; moment connection cost is 75% of the total weight of the members that have moment connections. As far as how I arrived at each of the values in Table 9 and Table 10 go; I used a series of spreadsheets which are in Appendix D. A moment connection provides lateral stability in the structural frame by preventing rotation between the girders and the columns. Moment connections may be welded, bolted, or a combination of both. When both welds and bolts are used, the bolts are designed to carry the shear or vertical load, whereas the welds are used to resist the effects of bending. This is why moment connections cost considerably more than simple connections. The sequence of events to erect the structural system I redesigned would look something like this:

• Erect columns on level 1 • Erect beams and girders on level 1 • Place metal decking on level 1 • Weld shear studs on level 1 (if applicable) • Erect columns on level 2 • Erect beams and girders on level 2 • Weld moment connections on level 1 • Erect braced frames on level 1 • Place metal decking on level 2 • Weld shear studs on level 2 (if applicable) • Erect columns on level 3 • Erect beam and girders on level 3 • Weld moment connections on level 2 • Erect braced frames on level 2 • Place metal decking on level 3 • Spray fireproofing on level 1 • Etc.

Fireproofing will not start on the first level until decking is placed on level 3; the two tasks should also be going on at opposite sides of the building.



Lighting Design The lighting scheme in Heritage IV is not provided; it is left up to the tenant to decide upon. I took it upon myself to design the lighting for Tenant C’s space in Figure 5. I used the lighting design program Luxicon. First, I went to Lithonia.com and found a direct light, recessed fixture. I chose a 3" deep PARAMAX 2' X 4' 2LP T8 12 CELL LOW IR SPEC LVR. Table 12 shows the parameters for this parabolic troffer. This is ideal for an office space. Figure 17 shows the actual fixture.

Number Lamps 2 Lumens Per Lamp 2900 Photometric Type Type C Luminous Width 1.76 ft Luminous Length 3.77 ft Luminous Height 0 ft Ballast Factor 1 Input Watts 71 Efficiency (Total) 78.3 % Efficiency (Up) 0.0 % Efficiency (Down) 78.3 % Table 12 – Fixture Parameters Figure 17 – Paramax Fixture Figure 18 shows Tenant C’s space. Two sides of the wall are covered with windows, and two interior columns are present within the space. The dimensions are 58’ X 48’ X 8.5’. I used a 2’ X 4’ acoustical tile ceiling grid, which is typical for an office space. The lighting layout is comprised of 12’-0” on center spacing in the Y direction and 8’-0” on center spacing in the X direction.

Figure 18- Tenant C’s Space



The ceiling grid was strategically planned around the interior columns, and to give an average luminance of 30 – 50 foot candles on the 2.5’ work plane. In Figure 19 a rendering of Tenant C’s space at 7:30 am, on April 15, 2003, with a clear sky is shown. A desk and chair were placed in the room in order to give a sense of space.

Figure 19 – Rendering of Tenant C’s Space at 7:30 am with a Clear Sky Figure 20 shows the same space on the same day at 1:30 pm

Figure 20 – Rendering of Tenant C’s Space at 1:30 pm with a Clear Sky



The space reaches very high illuminance levels during the daytime. To combat this ambient light, blinds shall be provided so that the tenant can control the amount of day lighting. Yet again, Figure 21 shows the same space on the same day at 7:30 pm. This rendering illustrates the space’s illuminance level when there is no day lighting.

Figure 21 – Tenant C’s Space at 7:30 pm Figure 22 shows the light distribution on the work plane, which is 2.5’ above the floor, at night. The distribution is not completely uniform when there is no ambient light. A solution is to provide each tenant with their own task light; so they have more control over their own individual lighting.

Figure 22 – Night Time Work Plane Light Distribution



The average illuminance for the space with no ambient light is 40.5 foot candles, which meets the requirements for an office space (30 – 50 foot candles). The maximum is 56.5 foot candles, and the minimum is 18.4 foot candles; the minimum occurs in the corners of the space. A horizontal grid of illuminances for the space can be seen in Appendix E. Also, the Lithonia specification for the parabolic troffer used in this lighting layout is in Appendix E. The next step was to pick an actual luminaire and ballast for the fixture. I completed this task using Sylvania.com. The lamp I chose was a Fluorescent Octron, 32 watt, T8. As shown in Table 13 it has a Color Rendering Index (CRI) of 82, and a Correlated Color Temperature (CCT) of 3500 K.

Product Information Abbrev. With Packaging Info. FO32835 30/CS 1/SKU Actual Length (in) 47.78 Actual Length (mm) 1213.6 Average Rated Life (hr) 20000 Base Medium Bipin Bulb T8 Color Rendering Index (CRI) 82 Color Temperature/CCT (K) 3500 Diameter (in) 1.10 Diameter (mm) 27.9 Family Brand Name Octron® 800 Industry Standards ANSI C78.1 - 1991 Initial Lumens at 25C 2950 Mean Lumens at 25C 2714 Nominal Length (in) 48 Nominal Wattage (W) 32.00 Value Added Product YES Unit EA

Table 13 – Product Information for FO32835 lamp

Figure 23 illustrates the FO32835 lamp, which is compatible with an instant start or rapid start ballast. The compatible ballast that I chose to use with this lamp is 2-lamp 277V electronic ballast for a 32W T8 lamp. Its order number off the Sylvania web page is QT2X32/277PAL. Figure 23 - FO32835 lamp



Options to Achieve Low Floor-to-Floor Heights SMI Smart Beam® SMI Steel Products is a division of Commercial Metals Company, based in Dallas, Texas. Commercial Metals Company and its subsidiaries manufacture, recycle, and market steel and metal products and related materials through a network of over 120 locations worldwide. Commercial Metals Company is one of the largest recyclers of steel in the country. With over 44 recycling operations across the Sunbelt, Commercial Metals Company is committed to providing sustainable steel products for the commercial construction industry. Capitalizing on the internal vertical integration of CMC, SMI Steel Products utilizes 100% recycled steel in their products.

SmartBeam® offers versatility, reliability and economy for all types of floor and roof structures. These new beams are good looking, lightweight and structurally strong.

SMI Steel Products is the exclusive cellular beam manufacturer for the Americas. A hexagonal design is also offered. Both start with a standard beam, which is cut in half longitudinally.

The two halves are separated, staggered, and welded together to form a SmartBeam® that weighs the same but is much stronger and deeper than the original. This procedure can be seen in Figure 24 and Figure 25, for hexagonal and cellular beams respectively.

Figure 24 – Hexagonal SmartBeam® Procedure

Figure 25 – Cellular SmartBeam® Procedure



The beams are cut along the cut lines electronically as shown in Figure 26. The only man labor involved is the welding of the beam back together as shown in Figure 27.

Figure 26 – Beam being Cut Electronically Figure 27 – Beam being Welded Back Together

SmartBeam® is ideally suited for composite floor beams. The most efficient span for SmartBeam® is typically 30'-60'. Spans less than 30' are most often better adapted to traditional wide flange beams. The most common building types for SmartBeam® are low to mid-rise office buildings, parking garages, mezzanines in distribution centers or any structure with a suspended floor. SmartBeam’s superior vibration characteristics and ability to accommodate mechanical equipment (duct work, wiring, and fire protection) make it an ideal product.

Figure 28 shows an integration of the mechanical system with a cellular SmartBeam® floor layout.

Figure 28 – Integration of Mechanical System and SmartBeam®



Figure 29 displays how a regular W 18 X 35 is made deeper and then labeled as a CB 27 X 35.

Figure 29 – W 18 X 35 becomes a CB 27 X 35

Advantages of SmartBeam®:

• Asymmetric composite design increases stiffness of floor, therefore improving vibration characteristics.

• Eliminates the need for intermediate columns since SmartBeam® economically spans the same width as wide bay systems.

• Less bridging to install compared to joist floor systems. • Faster erection due to fewer pieces with long span SmartBeam® system. • Lowers floor-to-floor height by passing ductwork and utilities through openings. • Asymmetric sections produce most economical composite design. • Architecturally pleasing when exposed. • SmartBeam® can be painted, galvanized or fireproofed. • Web opening geometry is variable in both hexagonal and cellular configurations. • Spans and depths to your specifications are available.

Three design checks must be performed to design a SmartBeam®. These checks include: vierendeel bending of the tees, web post bucking, and horizontal or vertical shear.

Vierendeel bending occurs when shear transfer through the holes introduces a bending stress into the top and bottom tees along with the axial stress from the moment couple forces. The tee sections are designed for combined stresses according to chapter H of the 9th Edition ASD Manual. A schematic of a SmartBeam® in vierendeel bending is shown in Figure 30.



Figure 30 - Vierendeel Bending in a SmartBeam®

As seen in Figure 31, Change in axial force between holes causes horizontal shear through the web post. Web post strength is determined using equations developed from destructive research and finite element analysis.

Figure 31 – Web Post Buck Buckling in a SmartBeam®

Using the shearing force from the web post design, horizontal shear through the web post is checked. Vertical shear is checked through the open portion of the beam.

Appendix F includes a project profile, courtesy of SMI Steel Products, of CNF Transportation; which is an office building located in Portland, Oregon. 27” SmartBeams® were used for this project.



Staggered Truss System The staggered truss system is a new concept in structural steel framing for high rise buildings. The system consists of a series of story-high trusses spanning the total width between two rows of exterior columns and arranged in a staggered pattern on adjacent column lines. The system was developed to achieve a more efficient structural frame to resist wind loads, and at the same time provide versatility of floor layout with large column-free areas. The staggered truss system consists of a story high truss that spans the entire width of the building. The system works together with precast plank that provides a smooth floor and ceiling while achieving the desired low floor-to-floor height. The composite truss and plank system provides a safe and efficient structural system that resists both gravity and lateral loads. Figure 32 shows a typical staggered truss system. Vierendeel Openings in the trusses provide corridor openings.

Figure 32 – Typical Staggered Truss System

The basic concept of the staggered truss system is that the total frame behaves as a cantilever beam when subjected to lateral loads. In this context, all columns are placed on the exterior wall of the building and function as the flanges of the beam, while the trusses which span the total transverse width between columns function as the web of the cantilever beam. Advantages of Staggered Truss:

• Significant cost saving due to a lighter frame and fewer foundations • Low floor-to-floor heights • Provides more column free open space.

Appendix G includes a project profile, courtesy of AISC, of The Embassy Suites Hotel; which is a hotel located in New York, New York.



Conclusions Heritage Center Building IV was originally designed in concrete because of a height restriction set by the Virginia Building Code. A concrete system allowed for a low floor-to-floor height of 11’-4”, and thus squeezed an additional leasable floor on the site. This unique structural system provides lateral resistance by means of rigid continuous drop panes. In this senior thesis, Heritage IV was redesigned in both a composite and non composite structural steel system. This structural redesign was done in order to compare the floor thicknesses between the existing concrete system and the newly designed composite and non composite steel systems; and to ultimately compare the impact each system has on the total building height. Table 14 compares the floor thicknesses and heights for theses three options. Keep in mind that the maximum allowable height is 125’-0”.

Structural System Floor Thickness Total Building Height Cast in Place Concrete 2’ -10” 122’- 3 ½”

Composite Steel 3 ’ 6” & 3’ - 9” 132’ - 6” Non Composite Steel 3’ - 9” 134’ - 9”

Table 14- Floor Thickness and Height Comparison

The composite system is 7’-6” over the height cap, while the non composite system is 9’-9” over. Steel systems are usually cheaper than concrete systems, but it depends upon the region. In and around Washington D.C. the cost is about the same, due to the fact that the region has a large number of concrete workers who are efficient at what they do. The detailed cost analysis and duration of construction activities, shown in Table 9 and Table 10, show interesting points as well. The construction time of a non composite system over a composite system is shorter by 5%. The cost of the composite system is cheaper than the non composite system by $205,160.64 or 6.5%. Also, the cost differential between the composite and non composite system would have been greater if the steel systems were designed for gravity loads alone and had a different lateral system, like shear walls. Additionally, both systems will save money over traditional concrete systems when it comes to the foundations. Steel buildings weigh less than concrete buildings, thus putting less axial load on the foundation, which in turn make them smaller (less cost). RAM steel was a very helpful, accurate, and relatively quick design tool. In the real world, every structural consulting firm has this program. In the real world design time equals money, and saving the littlest bit of design time is very desirable. However, it is very crucial that one understands enough about structural design in order to verify the outputs of the program. The lighting design of Tenant C’s space was designed using the program Luxicon. Linear T8 bulbs in a recessed fixture were placed at 12’-0” on center and 8’-0” on center, within a 2’ X 4’ ceiling



grid. The average illuminance on the work plane (2.5’ above ground level) was 40.5 foot candles, which is in the acceptable range of 30 – 50 foot candles for a typical office space. Blinds will be provided over the windows in order to control ambient light, and task lights will be placed at each tenant’s work station to give them extra control over their illuminance levels. SMI Steel Products SmartBeam® and the staggered truss system are just two of the many systems available to give low floor-to-floor heights. The SmartBeam® has many advantages, as previously listed, but does have one major drawback. It requires extraordinary cooperation between the structural engineer and mechanical engineer, as well as the architect. This coordination needs to begin early in the project’s life. This coordination would be easier in an AE firm, where the structural and mechanical engineers work in the same building. The staggered truss system has many advantages, like column free spaces and low floor-to-floor heights, but it also has a coordination disadvantage. I’m not saying coordination is a disadvantage, but it does not happen all enough in the industry, making it a disadvantage. The staggered truss system requires vast coordination between the architect and structural engineer. The vierendeel openings in the trusses have to be strategically placed at corridor openings or vise versa. My research proves that while new innovative systems like staggered steel trusses are being invented, older systems like non composite steel are becoming out dated, especially when there is composite steel systems.



References

1. AISC, Manual of Steel Construction. Load & Resistance Factor Design, Volume 1, Second Edition.

2. American Concrete Institute. ACI 318-02 - Building Code Requirements for Structural

Concrete.

3. Arthur H. Nilson. Design of Concrete Structures, Twelfth Edition.

4. Building Officials & Code Administrators International, Inc. 1996. The Boca National Building Code.

5. Cameron K. Andres and Ronald C. Smith. Principles and Practices of Commercial

Construction, Sixth edition.

6. Francis D.K. Ching. Building Construction Illustrated, Second Edition.

7. Louis F. Geschwinder, Robert O. Disque, Reidar Bjorhovde. Load and Resistance Factor Design of Steal Structures.

8. RS Means. 2002. Heavy Construction Cost Data.

9. RS Means. 2002. Square Foot Construction Cost Data.

10. www.aisc.org

11. www.lithonia.com

12. www.mapquest.com

13. www.royalontheweb.com

14. www.smisteelproducts.com

15. www.sylvania.com



Acknowledgements Special thanks to the following groups who gave me help with my Senior Thesis:

• Atlantic Engineering Services o D. Matthew Stuart, P.E., S.E., P.Eng. o Robert S. Bertocchi o John M. Schneider, P.E.

• Bourj, LTD.

• Royal Management & Development

• Burt Hill Kosar Rittelmann Associates

• Clark Construction

Special Thanks to the following professional who have taught me so much:

• The Architectural Engineering Faculty and Staff

Special Thanks to all of my friends who helped me along the way:

• The Architectural Engineering Class, Especially “The Late Night Crew” And lastly, a Special Thanks to my girlfriend and family for everything they have done:

• Julie Ream

• Randy, Roseann, and Nathan Graham



List of Appendices

Appendix Courtesy of: A Spreadsheet Used for the Wind Loading Calculations Shawn B Spreadsheet Used to Obtain Seismic Forces Shawn

C Gravity Column Designs for a Typical Composite and Non Composite Floor Shawn

D RS Means Cost Spreadsheets Shawn

E Horizontal Grid of Illuminances & Lithonia Specification for Troffer Luxicon &Lithonia

F Project Profile of CNF Transportation SMI G Project Profile of the Embassy Suites Hotel AISC

Construction Photos on Appendices Dividers Courtesy of: A Existing Parking Garage and New Slab on Grade AES B Front Elevation AES C Back Elevation – Stairs Well AES

D Front Elevation from Nearby Intersection and Existing Buildings AES

E Back Elevation and Existing Buildings AES F Front Elevation with Glass and Aluminum Façade AES G Back Elevation with Granite Façade AES

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