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Technical Assignment #2 Pro/Con Structural Survey of Alternative Floor Systems Executive Summary
Technical Assignment #2
Pro/Con Structural Survey of Alternative Floor Systems
Executive Summary:
The purpose of this report is to compare the advantages and disadvantages of various alternative floor system designs against the existing floor system in the Hyatt Center. Many factors can be used for comparison such as weight, costs, ease of construction, material benefits, structural benefits and setbacks as well as impacts on other systems within the building and compliance with the design criteria. Alternate systems will be designed and compared to the existing to establish which systems are viable as alternative gravity systems.
The existing composite floor system and Alternative #1 – Open-web steel joist with composite
deck; and Alternative #4 – One-way concrete slab and beam; are feasible options. Alternative #2 – Non-composite beams with form deck; and Alternative #3 – One-way concrete pan-joist; are not viable alternatives.
Alternatives:
Existing: Composite beams with composite metal deck Smallest member depths, but susceptible to vibration problems. Highly efficient system for long-spans and heavy loading.
Alternative #1: Open-web steel joist with composite deck
Lightest system weight of survey, however very susceptible to vibration problem. Speed and ease of erection but many joists increase crane movement and possibly
construction time.
Alternative #2: Non-composite beams with form deck Deep members required to span long direction to maintain deflection criteria. Lightweight system however imposes on mechanical and wiring systems.
Alternative #3: One-way concrete pan-joist
Large deep girders required to resist pan reactions also imposes on mechanical system.
Lease susceptible to vibration however was found to be heaviest system in survey which greatly effects foundation and gravity columns size.
Alternative #4: One-way concrete slab-and-beam
Ability to conform to unique bay configurations, but a heavy system which impacts foundation and column sizes which may become architecturally unacceptable.
Deep beams and girders result in increased floor heights and overall building height.
Patrick L. Hopple Faculty Consultant : Dr. Linda Hanagan Date: Wednesday, October 27, 2004 H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
1 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Introduction - Technical Assignment #2 – Pro/Con Structural Survey of Alternative Floor Systems
The purpose of this report is to compare the advantages and
disadvantages of various alternative gravity floor systems against the
existing gravity floor system. Many factors can be used for comparison of alternative
systems such as weight, costs, ease of construction, material benefits, structural benefits and
setbacks we well as impacts on other systems within the building. Alternative systems will
be chosen by typical industry use in commercial office high-rises, conservatively designed
with baseline loads and bay dimensions then measured against existing systems before
conclusions will be made on whether a system is to be investigated further or if the existing
flooring system is the best viable alternative.
Overall Structure: (An overview)
Composite System: The Hyatt Center is a 49-story commercial office
building in the center of the Chicago business
district. The entire building is composed of a 49-
story tower and a 7-story mezzanine.
The mezzanine structure and the tower have
some similar characteristics in terms of employed
gravity structural systems. The mezzanine is
comprised typically of rectangular bays (36’x46’)
and use specially detailed open-web steel trusses
and wide-flange beams with web-openings in the
retail areas to accommodate ducts and overhead
electrical runs. The trusses are comprised of
back-to-back angles for the diagonals and
verticals with chords of “WT” sections which
support an 11-inch slab on composite metal deck
2 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
and 4 ½” – ¾” diameter shear studs. Lateral loads in the mezzanine
are resisted by rigid moment frames in both directions. My focus for
this report is primarily on the tower of the Hyatt Center.
The tower structure consists of an oval-shaped footprint on the
site which produces some difficulty when trying to find a square bay.
However, the tower was designed to allow for a constant span dimension from the core to
the perimeter spandrels. This was accomplished by designing the central core walls to
mimic the profile of the curved façade, in doing so a constant beam span (varying from 40’
at the base to 43’ in upper levels) can be obtained across the floor plate, resulting in the
same beam spans. A constant perimeter span of 38’-3 ¾” was also upheld by the radial grid
dimensioning.
Alternative Floor Systems: Four alternate floor systems were chosen based on common practice in commercial
high-rise design:
1. Open-web joist system with composite metal deck 2. Non-composite wide flange beams with non-composite form deck 3. One-way concrete pan joist system (ribbed slab) 4. One-way concrete slab-and-beam system
The systems chosen above were selected based on a most practical/feasible approach in terms of constructability and least weight for the existing building layout. Because the Hyatt Center has typical bays which are trapezoidal-shaped reaching 42ft in the N-S direction and ranging 31ft-38ft in the E-W direction, many systems can be ruled out as possible solutions. One such floor system is a waffle slab which is common in high-rise applications for its less weight and easy of construction. Waffle slabs typical are utilized in square bays upwards of 38ft, but without square bays the two-way action becomes quite complex to analyze which causes the system to be dropped. The issue of long spans also becomes and issue when dealing with concrete construction. To be economical and a feasible alternative, a two-way slab can be placed in a relatively square bay with typical bays of no further than 30ft. After this point the slab and reinforcement become quite heavy which eliminates the advantages of using a two-way slab in the first place. In conclusion, although bays could be squared and minimized the architecture would discourage this approach as much of the expansive view would be obstructed causing vast differences in the aesthetics appearance.
3 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Design Methodology: To simplify the design process and promote consistency in the
structural survey between floor systems a simplified bay was used
instead of the actual trapezoidal bay as seen below. Since various
loading is present throughout the structure, a typical plan was used
to find the typical bay and limit loading on the bay. This typical plan was repeated
numerous times in the upper 35th through 46th floors of the Hyatt Center and is
representative of a large portion of the building. The simplified bay was squared-off
providing 36ft x 42ft spans and assumed to be representative of each bay throughout the
entire building. This assumption results in highly conservative design methodologies
however, with the unique bays and massive size of the Hyatt Center this approach will be
consistent among each system. Design loads were also kept relatively similar (and limited)
between each system to provide a baseline measurement for comparing member sizes.
Design Superimposed Dead Loads:
Raised Floor 15 psf
Ceiling/MEP 5 psf
Office 40 psf
Design Live Loads (ASCE 7-02):
Office 50 + 20 psf partitions
4 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Once the loading was determined to be fairly consistent across
the design of each system, members were arranged according to two
design methods. One was to keep the N-S (radially-away-from the
central core) arrangement of the members to ensure that in-plane
stiffness of the horizontal diaphragm was similar and adequate to the
existing system which provides transmission of lateral force to the central core. The second
method was to arrange members along the least span dimension (38 ft E-W) and assume
that shear wall-frame interaction of the columns and girders contributed to most of the
lateral load distribution along with the rigid diaphragm. Both arrangements have their pros
and cons which were taken into consideration which affected member sizing. Concrete
beams are typically not efficient in long-span conditions such as in the Hyatt Center;
therefore, design of pan joists in the short direction was implemented and one-way slab-
and-beam were arranged in the long direction.
The first alternative system, open-web joists with composite deck, was assumed to be
spaced equally along the 38’ bay which resulted in a spacing of 4’-9”. Such a close spacing
ensured that the joists could span the 42ft dimension while having adequate capacity to
hold the heavy loads. Hand calculations of required loads and stresses as well as the design
of the deck and joists can be found in Appendix B of this report.
The second alternative system design, non-composite wide-flange beams with form
deck, can be found in Appendix C of this report. The controlling factor in designing non-
composite systems is meeting deflection criteria. A limit of L/360 was set for each design
and required member properties were found and checked against the applied loading.
Non-composite sections do not have the versatility of concrete slab-and-composite beam
interaction to resist heavier loads; therefore the depth of members will most likely be
greater.
The last alternative systems, concrete pan-joists and one-way slab-and-beam, can be
found in Appendix D and E of this report, respectively. To ensure sufficient fire
protection, a 5” minimum slab was checked for stresses from the applied loads and
members were designed using the CRSI Design Handbook 2002. Member sizes were
5 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
checked using ACI 2002 load factors as compared to ACI 1998 load
factors in the handbook.
Detailing such as reinforcement placement, shear stud quantities,
connections and slab reinforcement were neglected in the overall
design of each system due to the broad focus of this report. Once
members systems were finalized, the advantages and disadvantages of each system were
compared and conclusions were formed about the validity of each system as a viable
alternative.
Issues addressed in determining validity include overall constructability, weight
increase/decrease, impact of each system on other building elements (foundation,
mechanical, electrical, etc.). Also a large concern in recent years, especially in new
commercial offices is vibration issues caused by lighter systems. Each system will be
discussed and a summary will conclude with which systems warrant further investigation by
a more refined analysis as an alternative floor system.
6 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Alternative Flooring System Survey
Existing Composite Flooring System: System Description: Slab: 5 ½” (2 ½” cover) LWC (115pcf) f ’c= 4 ksi Deck: USD 3” LOK-FLOOR, 20 gage Beams: A992 composite wide-flange sections W18x50 (40), cambered 1 ¼” Girders: A992 composite wide-flange sections W18x50 (40), cambered 1 ¼”
Perimeter Beams: A992 composite wide-flange sectionsW27x84
Depth: 23.5” total depth interior; 32.2” total depth exterior spandrel
Design Results: (Wt./SF = 18.13psf) Design Loads: 72psf (DL), 112psf (LL) Member Sizes: (# shear studs) Beams: W18x50 (40), cambered 1 ¼” Girders: W18x50 (40), cambered 1 ¼”
Perimeter Beams: W27x 84 (30) (due to L/600 deflection criteria)
Pros/Cons: The versatility of a composite floor system is due to
the inherent strength of the concrete slab in compression and the ability of the steel member to span long distances which are prevalent in the Hyatt Center. Advantages of composite systems include reduction in material cost, on-site labor, and construction time as well as simple repetitive connections, reduced structural depth of members and lower building mass. The combination of a composite steel deck with composite beams provides for a highly efficient system which can be repeated several times and become very cost effective, especially in a high-rise building where reductions in floor depths can result in cumulative savings in curtain walls, wiring, ductwork, plumbing, etc. which can be quite considerable.
Composite sections have greater stiffness than the individual (slab-and-beam) and therefore load resistance is higher, vibration issues are minimal and the beam arrangement in composite floor systems creates a very rigid horizontal diaphragm which provides stability for the overall building as well as distributing lateral loads to the core.
7 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Alternative #1 – Open-web steel joist with composite deck: System Description: Slab: 4” (2 ½” cover) LWC (115pcf) f ’c= 4 ksi Deck: USD B LOK, 20 gage Joists: Vulcraft Open-web joist Perimeter Beams: Vulcraft Joist-Girder Depth: 32”+4”=36” total
Design Results: Design Loads: 86psf (DL), 70psf (LL) Member Sizes: (depth (in)) Joists: 32LH13 (32”+4”) @ 4’-9” o.c.
Joist-Girder: 38G8N20K (32”+4”) USD: 5’span = 400psf LL > 70psf (service) Max single span = 5.14’ > 4.75’ Max 3-span = 6.91’ > 4.75’ Overhang = 2’-3” > 2’-1” (20 gage) TLAPPLIED= 874plf < TLALLOW = 974plf LLAPPLIED= 532plf < LLALLOW = 710plf Wt/S.F. = 7.17psf
Pros/Cons: A main advantage of an open-web joist system is the overall light weight of the system. A
light floor system will ultimately have the least impact on foundation and column requirements for a high-rise as well as crane sizing since heavier beam loads will not have to be lifted. The typical weight per area of this system is comparable to composite systems. Mechanical ductwork can be integrated through openings within the truss webs.
Construction and erection of joists can be quick and very repetitive if no unusual circumstances arise such as irregular bays or framing, such a fast erection can speed installation of composite deck behind the erection and individual trades can work almost immediately after erection is complete, therefore, construction time is minimized.
Disadvantages of open-web joists include issues pertaining to fireproofing. Also close spacing of joists may possibly hinder crane placement and slow the erection process.
Vibration is a major concern with this system. The lack of weight able to contribute to damping as compared to a wide-flange section causes light-framed floor systems to vibrate excessively with simple movement of just one person if additional partitions and other heavy loads such as file systems are not considered.
Connection into core wall will require extensive detailing of embedded plates.
8 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Alternative #2 – Non-composite beams with form deck: System Description: Slab: 6” (4” cover) NWC (145pcf) f ’c= 4 ksi Deck: USD UF2X, 18 gage (44- W4.0 x W4.0) Beams: A992 Wide-flange sections (non-composite) @ 9.5ft o.c. Perimeter Girder: A992 Wide-flange sections (non-composite) Depth: Interior (35.9” total); Spandrel
(44.2” total)
Design Results: Design Loads: 75psf (DL), 70psf (LL) Member Sizes: (depth (in)) Beams: W30x90 (29.5”)
Perimeter Girder: W40x149 (38.2”) USD: 9.5’span Max 3-span = 253psf TL >202psf TL BEAM: MU= 423.4k’ < ΦMN = 1060k’ GRD: MU= 868.2k’ < ΦMN = 3620k’ Wt/S.F. = 23.0 psf
Pros/Cons: Main advantages of non-composite
wide-flange beams include long-span efficiency, a good strength to weight ratio and fast erection with minimal foundation requirements due to lighter system densities as compared with concrete systems.
Non-composite systems have the ability to be custom-fit for use in irregular bays such as the trapezoidal bays in the Hyatt Center. The efficiency of this system is in repetitive member use and connection designs to provide quick erection around the central core.
A non-composite system however lacks the advantages of composite action between the concrete slab in compression and inherent long-span efficiency of structural steel causing member depths to be greater than a composite system.
Vibration can be a concern with a non-composite floor system. The lack of stiffness found in composite systems as well as less weight able to contribute to damping as compared to concrete floor systems may cause non-composite wide-flanges beams promote vibration issues if additional issues like partitions and other heavy loads such as file systems are not considered.
Spray-on fireproofing or a rated ceiling assembly is needed unlike the fireproofing which concrete systems provide.
9 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Alternative #3 – One - way concrete pan-joist: System Description: Slab: 5” Slab NWC (145pcf) f ’c= 4 ksi fy= 60ksi Forms: 30” forms = 6” ribs @ 36” o.c. Pans: 20” Deep pans + 5” slab = 25” deep (36’ span) Girder (h x b): 42” x 20” f ’c= 4 ksi fy=
60ksi
Design Results: Design Loads: 60psf (DL), 70psf (LL) Reinforcement: Ext. Span (int. span) Slab: AsMIN= #3 @ 12” o.c. Joist: Top bars: #6 @ 11” (#5 @ 8”) Bot. bars: 2 - #7 (2 - #6)
Girder: Top: 7-#14 2 layers Bottom: 4-#11 2 layers JOIST: LDALLOW= 195psf > LDAPPLY =
184psf GRD: MU= 1158k’ < ΦMN = 1818k’ LDALLOW= 11.3klf > LDAPPLY = 11.12klf Wt/S.F. = 125psf
Pros/Cons: Pan-joist floor systems have the advantage of being the most effective for reducing dead
weight of floors for long spans. Pan-joist construction can be quite fast and efficient when similar forms can be replicated and reused over and over again which reduces costs and saves on construction time.
Concrete construction in general has advantages of having no lead time, late changes can be made without much impact on schedules or costs and no additional fireproofing is needed unlike in steel construction.
A major disadvantage, evident in this system is the inefficiency in long spans. Girder depths of 42” provide no space for ductwork or wiring unless floor height is increased. Use of such a heavy system will have drastic impacts on foundation designs, crane and hoisting demands during construction and also cause column sizes to become so massive, they become architecturally unfeasible unless high-performance concrete is used.
This system will definitely impact the column and foundation requirements causing use of deep foundations and high-performance concrete to be used in the Hyatt Center.
Complex framing and bay sizes cause slow onsite construction because custom forms are needed which also congest site space during construction.
10 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Alternative #4 – One - way concrete slab-and beam: System Description: Slab: 6” Slab NWC (145pcf) f ’c= 4 ksi, fy= 60ksi (spacing = 10ft) Beams (h x b): 32” x 18” f ‘c=4ksi, fy= 60ksi Girder (h x b): 32” x 20” f ’c= 4 ksi, fy = 60ksi
Design Results: Design Loads: 75psf (DL), 70psf (LL) Reinforcement: Slab: AsMIN= #3 @ 12” o.c. Beam: Top bars: 4 - #14 Bot. bars: 2 - #11
Girder: Top: 4 - #14 Bottom: 3-#14 JOIST: LDALLOW= 6.2klf > LDAPPLY = 2.74klf +MU= 337.8k’ < ΦMN = 736k’ --MU= 602.8k’ < ΦMN = 1002k’ GRD: LDALLOW= 7.8klf > LDAPPLY = 7.2klf +MU= 611.3k’ < ΦMN = 795k’ --MU= 860k’ < ΦMN = 1019k’ Wt./SF = 107.7 psf
Pros/Cons: A big advantage of one-way slab-and-beam is
the ability to span long and short dimensions as well as form non-square configurations which are typical in the Hyatt Center. Vibration is typically not an issue with one-way concrete slab-and-beam systems due to the overall increase in weight as compared to the existing system.
Concrete construction in general has advantages of having no lead time, late changes can be made without much impact on schedules or costs and no additional fireproofing is needed unlike in steel construction.
The main disadvantage of this system is the required depth of members to resist the given loads. An increase of 14.5” compared to the existing system will cause conflicts in ductwork and wiring configurations unless the floor height is increased. Increases in building height will also impact the lateral load resisting system and increase the required sizes of gravity columns used to support such a heavy flooring system. Further analysis into use of high-performance concrete in flooring and column designs would have to be performed
11 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
This system will definitely have an impact upon the column and foundation requirements possibly causing use of deep foundations and high-performance concrete to be used in the Hyatt Center.
Conclusions:
Of the systems surveyed I left many flooring options out of the survey which are typically used in high-rise design. Waffle slab, post-tensioned concrete slab, and pre-cast hollow plank were considered in the initial stages of this report but research into each system and my design methodology helped weigh each as viable alternatives.
First, a waffle slab is typically a very efficient flooring system which has the advantage of
reducing the overall weight of the system by incorporating square pans as the formwork. The two-way action of a waffle slab is best suited for use in long-spans and heavy loading conditions, both of which are design criteria for this report. I chose not to explore this system due to the irregular bay which is present in the Hyatt Center. Logically no easy way to construct the waffle slab can be found. Instead of each waffle section being aligned with the end girders as in normal square bays, the trapezoidal bay will result in conflicting rib alignment. The lack of constructability in a “real-case” scenario leads me to neglect a waffle-slab in my evaluation.
Next, a post-tensioned slab system was initially considered as an alternative due to its
ability to span long dimensions and relatively small slab depth and reduced weight which
12 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
fit the design criteria of this survey. However, due to limited
knowledge and research of post-tensioned slabs I chose to neglect
this type of floor system. One drawback of using a system would be
tendon location around the central core. If tendons were to be radial
offsets about the curvilinear profile, then this system warrants further
investigation as a possible solution. Tendon orientation
perpendicular to the core wall may involve construction issues such as where tendons
would need to be placed in the core and what sequence would be needed to minimize the
impact on other trades, especially the jump-form used in the core wall construction.
The last alternative system I chose to neglect in my evaluation was pre-cast hollow
planks on steel wide-flange beams. The design of the Hyatt Center, with the central core
resisting all lateral loads, relies heavily on the horizontal diaphragms to distribute lateral
loads to the core shear walls. By incorporating pre-case planks into the floor design, we no
longer can assume a rigid diaphragm in the plane of the floor. Drastically reducing the in-
plane stiffness of the rigid diaphragm causes the structure to behave differently than
originally analyzed. A complete redesign of the lateral force resisting system would result if
pre-cast planks were used in place of a rigid floor slab.
After considering the four alternative floor systems I believe the best system to be used
in the Hyatt Center would be the existing composite steel beams with composite deck.
Looking into each alternative I found that many of the designed members were very deep
and large which resulted in heavier systems.
A one-way concrete slab-and-beam system is a feasible option to be investigated further
due to the ability to accommodate irregular bay configurations. Investigating use of high-
performance concrete for gravity structural members may provide the key element to
enable a switch to an all concrete building. One high-rise in particular, 311 South Wacker
Drive, is amongst the world’s tallest buildings. What makes this building unique is the use
of high-performance concrete in the building columns with compressive strengths in the
order of 8000-15,000psi. Concrete of this high-strength leads to a very brittle failure mode
which has to be considered during further investigation, however, the combination of high-
13 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
performance concrete with a one-way slab and beam system warrants
further investigation as a viable alternative.
An open-web steel joist system with composite decking is also
another system that should be analyzed in-depth. Many high-rise
buildings designed today are designed with long-spanning joists due
to the lightweight and ease of erection. Issues such as stiff girders between core wall and
exterior columns to transmit lateral loads may have to be addressed since the relative
stiffness of the rigid diaphragm will be reduced with use of light framed joists. Given the
design criteria, the open-web joist system with composite decking may work and warrants
further investigation into feasibility as an alternative system.
And lastly, the existing composite floor system is the best possible solution for the
flooring system considering the design criteria. Considering the grand scale of the Hyatt
Center, 50 stories (1.7 million gross square feet), a need for the most efficient floor system
needs to be utilized so costs of construction are the most economical. The slightest change
in the number of shear studs in a bay for example, which when replicated over 50 stories
on the same bay of 3 beams, has the possibility to drastically change cost figures. Also the
reduction in beam depths which results from the use of a composite system allows
mechanical ducts and other systems to be run in the ceiling plenum space, resulting in an
efficient floor sandwich.
14 of 14 Technical Assignment #2 Pro/Con Structural Survey of Alternate Floor Systems
Patrick L. Hopple Faculty Consultant - Dr. Linda Hanagan Date: Wednesday, October 27, 2004
H y a t t C e n t e r ( 7 1 S o u t h W a c k e r D r i v e : C h i c a g o , I L )
Appendix: Appendix: Pages: Description:
A 1-2 Design Bay and Loads
B 3-4 Alternative #1: Open-web steel joist with composite deck
C 5-6 Alternative #2: Non-composite beams with form deck
D 7-9 Alternative #3: One-way concrete pan-joist
E 10-12 Alternative #4: One-way concrete slab-and-beam
F 13 Project Grid Dimensions and Floor plan