Residence Inn by Marriott, Stamford CT · RESIDENCE INN BY MARRIOTT, STAMFORD CT Figure 1 –...

Residence Inn by Marriott, Stamford CT

DEPTH STUDY: FLAT PLATE CONCRETE SYSTEM

RESIDENCE INN BY MARRIOTT, STAMFORD CT

DEPTH STUDY - FLAT PLATE CONCRETE SYSTEM Design Goals As previously stated, the construction of the Stamford Residence Inn was delayed five months in order to redesign certain building elements to lower the overall cost of construction. One system included in the reevaluation is the superstructure. By changing portions of, or the entire structural system, the potential exists to cut the cost of the hotel significantly. Therefore, the primary goal of this redesign is to create a lower cost system than the original steel structure. As an intern in the summer of 2003 I participated heavily in the design of the original structural system of the Residence Inn. Because of my previous involvement in the design of the hotel I have a special interest in seeing this building constructed. As a result, it is a goal of mine here to design this system and thus be exposed to two completely different designs for the same building. First hand comparison of two completely different structural systems for the same building will provide valuable real experience. System Background In Technical Assignment #2, the Pro-Con Study of Alternate Structural Systems, flat plate concrete construction was determined to be the best alternative of the ones studied to redesign the Residence Inn and to potentially offer a better design solution than the original steel system. Flat plate concrete construction is characterized by its uniform depth achieved over an entire floor area and is generally the easiest concrete system to form. This method typically results in a shallower depth system than steel schemes and other concrete systems such as waffle slab or concrete joist systems. Since flat plate systems typically produce shallower depths is it often possible to have a lower floor to floor height than what would be required of different system. The typical floor to floor height of the Residence Inn’s original design is 10’-6” with a 1’-5” plenum in the guest suites and a 2’-3” plenum in the corridors. This plenum is occupied by ductwork and other mechanical equipment. In the mechanical breadth portion of this thesis the mechanical system is redesigned and the ductwork within the guest suites is eliminated, easily making it possible to reduce the floor to floor height of the hotel. Should the results of the mechanical redesign conclude that the original system should not be changed; the 10” plenum provided in the redesign will be able to accommodate the 6” deep ductwork of the original design. See Figure 1 below for a section illustrating the redesigned floor to floor height and plenum space changes. In all, the overall height of the hotel has been reduced by slightly over 8 feet.

AE SENIOR THESIS 10 DAVID WALENGA – SPRING 2004


Figure 1 – Plenum Section Code Change and Loads -Code Change Currently, the governing building code in the state of Connecticut is BOCA 1996. Connecticut plans on updating their governing code to IBC 2003 sometime in 2005. For the purposes of this project it is appropriate to use IBC 2000 as the design code. IBC 2000 has been selected as the design code for this study because it is currently the most used design standard in the United States. By changing from BOCA 1996 to IBC 2000 the most significant changes are in the lateral loading of the building. BOCA 1996 references the provisions in ASCE 7-95 and IBC 2000 references ASCE 7-98. The most noteworthy differences in ASCE 7-95 and ASCE 7-98 are the base wind speed and seismic acceleration factors for Stamford Connecticut. Changing codes increased the base wind speed from 80 mph to 110 mph. The acceleration factors and the method for determining the seismic response coefficient (Cs) are the primary differences in the seismic provisions of ASCE 7-95 and 98. There are other subtle differences in the seismic portion, but the basic methods are the same. See the wind and seismic load portions of this section for the results of the load calculations using IBC 2000. -Dead Loads Section 1606 of the 2000 edition of the International Building Code governs the application of dead loads in structural system design. The code specifies that the building’s material weights be used in design. Below is listed material weights used in design here as well as additional superimposed loads. Dead loads are based on industry standards and assumptions. Applied loads of known materials and finishes are as follows:



Reinforced concrete slab – 9” 110 psf

Reinforced concrete 150 pcf MEP, miscellaneous, ceiling: 10 psf Partitions: 20 psf Stone flooring system (ground floor): 150 psf Miscellaneous balcony weight: 5 psf Roof ballast: 13 psf Roof membrane and insulation: 7 psf Metal roof deck: 2 psf Mechanical roof top units: 25 psf (applicable bays only) Exterior slenderwall assembly: 36 psf of wall Elevator machine room 10” slab: 125 psf

Superimposed dead loads: Roof: 10 psf Floors: 10 psf -Live Loads Section 1607 of IBC 2000 includes the provisions governing live loads and live load reduction. Listed below are the applicable live loads for the Residence Inn. Balcony-100 psf Lobbies -100 psf Corridors-100 psf Guest rooms-40 psf Stairs-100 psf Live load reduction – 1607.9 (Equation. 16-1)

⎟⎟⎠

⎞⎜⎜⎝

⎛+=

TLLo AKLL 1525.0

AT is the tributary area of the column.

KLL is: 4 for interior columns 4 for exterior columns without cantilevered slabs 3 for exterior columns with cantilevered slabs 2 for corner columns with cantilevered slabs L is limited to 0.5Lo for columns supporting only one floor and to 0.4 Lo for columns supporting more than one floor.



-Snow Load Snow loads are governed by chapter 7 of ASCE 7-98 and Section 1608 of IBC 2000. The hotel’s roofs are flat and there are no sloped roofs on the project, therefore no sloped roof calculations need to be performed. Factors and values as per code: Ground snow load: 30 psf Flat roof snow load: 30 psf Snow exposure factor (Ce): 0.7 Thermal factor (CT): 1.0 Snow importance factor (I): 1.0 Flat roof snow load used for drifting calculations (Pf =CTCeIPg): 21 psf Average drifted snow loads: Penthouse roof to main roof (25’):

Pd= 40 psf hd= 1.68 feet wd= 4.5 feet

Main roof to 6th floor roof (86’): Pd= 54.2 psf hd= 3.2 feet wd= 8.9 feet

Main roof to loading dock roof (126’): Pd= 59.8 psf hd= 3.8 feet wd= 10.6 feet

-Wind Loads Wind loading is determined following the requirements of IBC 2000, Section 1609, as well as data from the 1999 Connecticut Supplement to BOCA. Site-location specific factors governing the design are as follows:

1. Basic wind speed, V: 110 mph 2. Importance factor, I: 1.0 3. Building Exposure Class: B



East - West Wind Loading

Figure 2 –E-W Pressure Profile

Figure 3 –E-W Shear Loading



North – South Wind Loading

Figure 4 –N-S Pressure Profile

Figure 5 – N-S Shear Loading



Total base shears: East-West Direction: 422 kips North-South Direction: 633 kips Compared to the wind loads of the original design determined using BOCA 1996, the wind loading using IBC 2000 is higher. This increase is mostly caused by changing the base wind speed from 80 miles per hour to 110 miles per hour. In terms of a percentage, the east-west total base shear increased by 8% while the base shear in the north-south direction increased by 30%. Wind loading significantly increased despite lowering the overall height of the building by fifteen feet. -Seismic Loads By changing design codes from BOCA 1996 to IBC 2000, the seismic loading on the Residence Inn increased. The increase is due in part to changing from a steel structure to a concrete structure because concrete structures weigh more than steel structures. The building weight of the steel structure was about 19,000 kips, while the weight of the concrete structure is roughly 24,200 kips, a 27% increase. Table 1 below summarizes the results of the seismic load calculations.

Level H (ft) hx wx wxhxk Cvx Fx (kip)

14 18.0 155.8 292 119194 0.03 26.76 13 12.5 137.8 1432 504993 0.13 113.37 12 9.75 125.3 1547 487286 0.13 109.40 11 9.75 115.5 1547 442456 0.12 99.33 10 9.75 105.8 1547 398343 0.11 89.43 9 9.75 96.0 1547 355001 0.09 79.70 8 9.75 86.3 1547 312492 0.08 70.16 7 9.75 76.5 1508 264042 0.07 59.28 6 9.75 66.8 1508 224472 0.06 50.39 5 9.75 57.0 1626 200506 0.05 45.01 4 9.75 47.3 1739 171483 0.05 38.50 3 9.75 37.5 1739 130224 0.03 29.24 2 9.75 27.8 1739 90983 0.02 20.43 1 18.0 18.0 2125 66425 0.02 14.91

∑wihi

k = 3767899 1.00 846

Table 1 – Seismic Story Shears

Total base shear (V): 846 kips Base shear of the original design: 665 kips Percent Increase: 27%



-Load Combinations

Load combinations are found in Section 1605 of IBC 2000. 1.4D 1.2D+1.6L+0.5(Lr or S or R) 1.2D+1.6(Lr or S or R) + (fL or 0.8W) 1.2D+ 1.6W +fL+0.5(Lr or S or R) 1.2D+1.0E+fL+f2S 0.9D+(1.0E or 1.6W)

Gravity System -Slab Design In Technical Assignment #2, it was determined that an eight in slab would be sufficient for a flat plate system, in the typical bays. However, after further investigation it has been determined that a nine inch slab would be required. For this thesis, the design of the typical bays is being performed and non-typical slabs are only checked for minimum slab depth. The typical bays that have been designed here account for roughly 60% of the structure’s floor area. Several slabs on the eastern end of the structure, in the area of the larger two bedroom suites and near the cantilevered balconies on the ninth through thirteenth floors, need a nine inch slab. Larger bays are also found on the north east side of the structure; the ‘short-leg’ of the structure. Applying a nine inch slab over the entire floor area simplifies forming and also eliminates the need for supplemental shear reinforcement, such as shear rails, from being required. It is more expensive to need additional shear reinforcement than to have a slab one inch thicker in depth. To design the slab for the Residence Inn, ADOSS was used to obtain design moments. ADOSS does not calculate all positive moments, so those were calculated separately, by hand. Design Assumptions:

f’c = 3000 psi Fy = 60 ksi Weight of concrete = 150 pcf Applied loads: Dead load: 50 psf Live load: 100 psf – required only in corridor but applied everywhere Wall load: 342 plf



-Typical 19’ Wide Bay

Mu b d As Min. As Reinforcement Span Location (ft-kips) (in) (in) (in2) (in2) End Spans

Ext. Neg 19 88 7.75 0.61 1.43 8 No. 5 @ 12" Column Strip Positive 86 88 7.75 2.77 1.43 9 No. 5 @ 10"

Int. Neg 143 88 7.75 4.61 1.43 8 No. 7 @ 10" Ext. Neg 0 140 7.75 0.00 2.27 12 No. 5

Middle Strip Positive 60 140 7.75 1.94 2.27 12 No. 5 Int. Neg 48 140 7.75 1.55 2.27 12 No. 5

Interior Span Column Strip Positive 72 88 7.75 2.32 1.43 8 No. 5 @ 12" Middle Strip Positive 163 140 7.75 5.26 2.27 12 No. 5 @ 12"

Table 1 - !9’ Wide Bay Design Summary

Moments were calculated using 40 psf live load in the suites and 100 psf live load in the corridor and the design was found to be mostly controlled by minimum steel. Therefore, moments were calculated using 100 psf live and found that only a minimal amount of steel had to be added over the previous trial design. Designing for 100 psf live load over the area of the floor adds value to the building in case someday the floor plan of the structure is changed. The design summary of the typical 19’-0” wide bays is summarized above in Table 1. As shown in Table 1, reinforcement in the end spans is governed by minimum reinforcement. For constructability reasons, No. 4 bars are not used because they are not capable of supporting the load of construction workers walking on the reinforcing mats. Additionally, bar sizes are skipped in order to make differing sizes obvious to the workers in the field. It is easier to visually tell the difference between a No. 5 and a No. 7 than the difference between a No. 5 and a No. 6. Spacing is not specified for the end spans’ middle strip because it is assumed the bars will be distributed evenly.



-Typical 22’ Wide Bay

Mu b d As Min. As Reinforcement Span Location (ft-kips) (in) (in) (in2) (in2) End Span

Ext. Neg 14 88 7.75 0.45 1.43 8 No. 5 @ 12" Column Strip Positive 60 88 7.75 1.94 1.43 9 No. 5 @ 10"

Int. Neg 99 88 7.75 3.19 1.43 8 No. 7 @ 10" Ext. Neg 0 177 7.75 0.00 2.87 12 No. 5

Middle Strip Positive 44 177 7.75 1.42 2.87 12 No. 5 Int. Neg 33 177 7.75 1.06 2.87 12 No. 5

Interior Span Column Strip Positive 58 88 7.75 1.87 1.43 8 No. 5 @ 12" Middle Strip Positive 112 177 7.75 3.61 2.87 15 No. 5 @ 12"

Table 2 – 22’ Wide Bay Design Summary

In table 2 above the design of the typical 22’-0” wide bays is summarized. The same design assumptions and processes were followed here as before with the 19’-0” wide bay. -Edge Beam Design The design of the edge beams is assumed to be controlled by lateral loading, as the edge beams are the beam portion of the hotel’s moment frames. Inspection of the output produced by ADOSS and a quick hand calculation check shows moments, torsion and shear loading from the gravity slab system will not control the design of the beams. The reinforcement required to sustain lateral loading is greater than what will be needed for gravity loads alone. The cross sectional area used in calculations is 14” x 14”.



-Column Design To design the columns of the gravity system a load takedown table was created using an Excel spreadsheet to obtain the axial loads at each floor height. Column moments are obtained from the ADOSS models of the slab design. For simplicity, and to obtain a relatively accurate representation of the columns needed for the hotel, columns are not designed for every floor but for the thirteenth, ninth, fifth and ground floors. Performing the design in this manner quickly shows how column sizes will vary with floor height. Exterior columns are designed here for gravity loading and will be checked for lateral loading when the lateral system is designed; the final design of the exterior columns will be determined once lateral effects are taken into account. To perform the design of the columns, axial loads are imputed into PCA Column along with moments obtained from ADOSS. Similar to ADOSS, the load factors in PCA Column have to be updated to current design code. The designs of PCA Column were cross-check with the 2002 CRSI design handbook. The design of typical interior and exterior columns is shown below in Tables 3 and 4.

Typical Exterior Column

Floor Design 13th 14" x 14" 8 #5 w/ #3 T @ 16" 9th 16" x 16" 8 #6 w/ #3 T @ 16" 5th 18" x 18" 8 # 8 w/ #4 T @ 16" Ground 22" x 22" 8 #10 w/ #4 T @ 16"

Table 3 – Typical Exterior Column Design

Typical Interior Column

Floor Design 13th 14" x 14" 8 #5 w/ #3 T @ 16" 9th 18" x 18" 8 #6 w/ #3 T @ 16" 5th 20" x 20" 8 #8 w/ #4 T @ 16" Ground 22" x 22" 12 #10 w/ #4 T @ 16"

Table 4 – Typical Interior Column Design



Typical 22’ Wide Bay Plan

9” Slab Edge Beam Figure 1 – 22’ Wide Bay Plan Foundation System In almost all cases, comparison of a steel framed structure to a concrete framed structure for the same building usually yields the result of either a larger or sometimes a different foundation system needed to support the concrete system versus the steel system. This is simply due to the fact that concrete systems weigh more than steel systems. The foundation for the Residence Inn is indeed affected by the increased weight of the concrete structure. By changing the structure to concrete, the overall weight of the hotel increased by 27%. As discussed in the Building Background portion of this report, the majority of the foundation system of the original design is a spread footing system. The remaining portions of the foundation are mat foundations. The three mat foundations are location in the regions of the steel braced frames. One mat foundation is located at the west stair/elevator tower and another is located at the west elevator bank. Columns are closely spaced here and by simple inspection it is fair to assume that even without the presence of the steel braced frames that mat foundations would still be required here. The third mat foundation supports frame No. 8, see Figure on Page 7, and will not be needed for the redesigned structure since the frame is removed. Inspection of the original design shows that there is adequate room to increase the area of the footings, if necessary, in order to transfer the additional concrete system load. To get an idea of the changes necessary to support the concrete structure, a typical interior and exterior spread footing were designed and compared to the original design.



-Interior Column Spread Footing

Original Design Redesign Size 11' x 11' x 3' Size 12' x 12' x 3' Reinforcement 10 #9, each way Reinforcement 11 #9, each way

Table 1 – Typical Interior Column Footing Design

-Exterior Column Spread Footing

Original Design Redesign Size 10' x 10' x 3' Size 11' x 11' x 3' Reinforcement 9 #9, each way Reinforcement 10 #9, each way

Table 2 – Typical Exterior Column Footing Design

Allowable soil pressure: 6 ksf Concrete design strength (f’c): 3 ksi The results of the redesign, shown in Tables 1 and 2, show that the increased load onto the spread footings does not significantly change the design of the spread footings. Adding 69 and 63 cubic feet of concrete to a spread footing is not a huge increase in material or labor costs to the system as a whole. However, the footings are still slightly larger. The design of the exterior column footings may change once lateral loads are applied; the exterior footings support the hotel’s moment frames. Lateral System From inspection of the shear distribution profiles of both wind load directions and the seismic loading it is determined that seismic loading controls the design of the lateral system for the Residence Inn. The seismic shears are higher on almost every floor than the shears for wind loading in both directions. In lieu of performing the extensive full design of the hotel’s lateral force resisting system only the story drifts are checked based on a method outlined in the Seismic Design Handbook by Naeim. This method determines story drifts based on the lengths and moments of inertia of a frame’s beams and columns. The drifts determined through this method are called bent displacements. Bent displacements usually cause the majority of story drift and are caused by the end rotation of beams and columns. For mid-rise buildings like the Residence, almost all of the story drift is caused by bent displacements. In taller structures, axial deformation of columns contributes significantly to story drift.



The decision use this method of analysis was made because story drifts almost always control the design of a lateral resisting system. Obviously, a more extensive study will have to be performed to obtain the final design of the lateral system. The purpose of this study is to determine if the cross sectional areas of the previously designed columns and edge beams are sized appropriately to control story drifts. Table 9.5.2.8 in ASCE 7-98 outlines the limitations for allowable story drifts. According to Table 9.5.2.8 the allowable story drift for the Residence Inn is 0.02hsx, where hsx is the height of the floor below the floor in question. Table 1 below shows the allowable story drifts for the Residence Inn.

h (ft) ∆a (in) Col. Size Penthouse Roof 18.00 4.32 14 x 14 Penthouse Floor 12.50 3.00 14 x 14 13th Floor 9.75 2.34 16 x 16 12th Floor 9.75 2.34 16 x 16 11th Floor 9.75 2.34 16 x 16 10th Floor 9.75 2.34 16 x 16 9th Floor 9.75 2.34 16 x 16 8th Floor 9.75 2.34 18 x 18 7th Floor 9.75 2.34 18 x 18 6th Floor 9.75 2.34 18 x 18 5th Floor 9.75 2.34 22 x 22 4th Floor 9.75 2.34 22 x 22 3rd Floor 9.75 2.34 22 x 22 2nd Floor 18.00 4.32 22 x 22

Table 1 – Allowable Story Drifts and Column Sizes

Based on the previously performed design of the columns a distribution of column cross-sectional size has been assumed and is shown in Table 1 above. The equation used to determine the bent drift per story is:

( )( ) ( ) ⎥

⎥⎦

⎤

⎢⎢⎣

⎡

∑+

∑∑

=∆icig

iibi KKE

hV 1112

2

Equation 1

Where: ( )igK∑ is the summation of gigi LI for all beams.

is the summation of ( icK∑ ) ici hI for all columns. I denotes the moment of inertia of either the columns or beams.



Table 2 – Bent-Action Drift Calculation

he bent-action story drifts are calculated and summarized in Table 2 below.

V (kips) Lg t) I Bms. ∑ ) ∑ . ∑

T

h h ∑V (f (Ig/Lg I Cols (Ic/h) ∆bi Drift (ft.) (in.) Story (kips) (in4) (in3) (in4) (in3) (in.) (in.) 14 18.00 216 26.8 26.8 445 3201 437 86436 400 0.1222 6.77 13 12.50 150 113.4 140.1 445 3201 437 86436 576 0.2594 6.65 12 9.75 117 109.4 249.5 445 3201 437 147456 1260 0.2153 6.39 11 9.75 117 99.3 348.9 445 3201 437 147456 1260 0.3009 6.18 10 9.75 117 89.4 438.3 445 3201 437 147456 1260 0.3781 5.88 9 9.75 117 79.7 518.0 445 3201 437 147456 1260 0.4469 5.50 8 9.75 117 70.2 588.1 445 3201 437 147456 1260 0.5074 5.05 7 9.75 117 59.3 647.4 445 3201 437 236196 2019 0.5045 4.54 6 9.75 117 50.4 697.8 485 3201 401 236196 2019 0.5839 4.04 5 9.75 117 45.0 742.8 485 3201 401 236196 2019 0.6216 3.46 4 9.75 117 38.5 781.3 485 3201 401 527076 4505 0.5940 2.83 3 9.75 117 29.2 810.6 485 3201 401 527076 4505 0.6162 2.24 2 9.75 117 20.4 831.0 485 3201 401 527076 4505 0.6318 1.62 1 3201 401 527076 3660 0.9925 0.99 18.00 144 14.9 845.9 485 * 2/3 of the first floor height is used in

. Had

imensions of the members may have to be increased to meet flexural and ductility requirements.

calculation.

Based on the calculations above, the story drifts of every level of the Residence Inn are within the allowable range governed by ASCE 7-98. By keeping within the allowable limits of story drift the primary goal of this study has been achieved. The intention here was to ensure that the designed and assumed column sizes, as well as the edge beam size, are adequate to determine story drifta more extensive analysis been performed, the reinforcement and possibly the cross sectional d



Mezzanine Hanger Anchor Mezzanine Tension Member Anchors The mezzanine level of the Residence Inn is hung from the second floor. The original design for the structure designed the mezzanine level as composite steel construction to achieve a lightweight and shallow system. To achieve the same properties, the mezzanine level will remain composite steel in the redesign. One side of the mezzanine rests on a concrete wall and the other is suspended by HSS members to the second floor. See Figure 1 for a partial plan. In the original design, the HSS tension members were connected to the second floor beams via a tab welded into the column and to the beam. Here, anchor bolts will have to be cast into the second floor slab and plates will be welded to the top of the HSS mto receive the bolting.

embers

Appendix D of ACI 318-02 governs the design of tensile anchorage to concrete. Following the provisions in Appendix D, it is determined that geometry of the HSS section controls the design. Assuming four, 5” hooked anchor bolts and a 10” x 10” plate, the breakout strength of the concrete is on the order of 90 kips. A tensile load of about 10 kips is applied to the connection, which is about nine times less than the breakout strength. In order to achieve proper edge distances and meet design requirements of the steel plate, the plate has to be 10” x 10”.

Figure 1 – Partial Mezzanine Plan

Design summary: 10” x 10” x ½” A36 plate (4) 5” ½ φ anchor bolts 3/16” fillet weld See Figure 2 at right for connection detail. Figure 2 – Anchor Connection Detail



Structural System Cost Two of the biggest issues that must be considered in the determination of what type of structural system to use for a project are time of construction and cost. System cost will be analyzed here; and scheduling and construction time are discussed in the Project Sequencing and Scheduling Analysis portion of the report. Many factors go into determining the cost of a building and its structural system. Location of the project influences the costs of both labor and material. Stamford Connecticut is a city with a population of 120,000 people located within 40 miles of New York City. According to R.S. Means, a construction cost reference series, the cost of construction, including labor and material, is 11% higher than the national average in Stamford. Given the close proximity to New York, it is not at all surprising that the cost of construction in Stamford is higher than the national average. To keep continuity between the original estimate and the new estimate, the cost of: slabs on grade, basement and foundation excavation, and basement construction were kept the same as the original but with 1% added for the cost of inflation since the original estimate was made. As reported in the Foundations portion of the redesign, the size of the foundations increased somewhat from the original design. The cost of this increase was estimated using the original cost’s unit prices; once this was done the increase was added to the original cost. The estimation of the concrete superstructure was performed using the MC^2 software package. An estimate of column length, beam length and slab area was performed and all necessary material data was entered. Specifically, concrete design strengths, steel grades, common reinforcing sizes were entered into MC^2. Once a price was obtained a rough check was performed using RS Means. This was done to ensure that the estimation is relatively accurate. The total cost of the flat plate system is summarized in Table 1 below.

Basement Excavation $225,092 Foundations $391,215 Miscellaneous Steel $3,000 Slabs on grade and Basement construction $271,510 Flat plate system cost $2,650,000 Total $3,540,817

Table 1 – Flat Plate System Cost



The cost difference summary between the steel system and the redesigned flat plate system is summarized below in Table 2. Taking into account the current volatile state of the cost of steel the flat plate system is almost $600,000 less than steel system. Removal of the steel surcharge would decrease the difference in cost by 22% to roughly $480,000.

Original Total Structure Cost $3,982,192 Original Plus 1% Inflation $4,022,014 Plus Steel Surcharge of $100/ton $104,200 Total Original Cost $4,126,214 Flat Plate Cost $3,540,817

Cost Difference $585,397

Table 2 – Cost Difference of Flat Plate System Clearly, based on the estimations performed, the flat plate concrete system is more cost efficient than the steel system. A portion of the cost difference can be attributed to the elimination of supplementary fire-proofing needed in the flat plate concrete system. The cost associated with fireproofing the steel system is estimated at just over $360,000. The cost of fireproofing coupled with the steel surcharges accounts for 62% of the cost difference between systems. To determine if the actual cost difference between the two a more detailed and professional estimate should be performed. However, based on the assumptions made and the methods of estimation, this estimate is accurate enough to show that the flat plate system costs less than the original design. System Advantages and Disadvantages Advantages

Simple, reusable formwork Simple reinforcement layout Only 9 inches total depth Less vibration and walking impact noise than concrete plank system No fireproofing required Not affected by recent steel surcharges Significantly cheaper than the steel system

Disadvantages

Heavier than steel system – Increased foundation size and seismic loads Shoring required Concrete construction heavily effected by weather More field labor required than steel system



Conclusions and Recommendation Conclusions A point by point list of conclusions:

The flat plate concrete system is considerably cheaper, almost $600,000, than the original steel with precast plank design. Much of this cost difference is due in part to the recent trends in the cost of steel and need for supplemental fireproofing on steel.

Despite being heavier than the steel system, the flat plate concrete system does not have

considerably larger foundations than the original design.

Although the weather can affect the progress of concrete construction it has been concluded through preliminary schedules that the construction of the concrete structure will be completed prior to the arrival of project delaying cold weather in Connecticut.

Recommendation

Based on the conclusions above and the research performed here, it is concluded that the flat plate concrete structural system is a better design alternative than the steel system. Therefore, it is recommended that flat plate concrete be the structural system for the Residence Inn by Marriott in Stamford, Connecticut.


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