Xyston Inn. NY. Proposal. Xiaodong Jiang. Structure Option. Advisor: Dr. Linda Hanagan

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1 Proposal Xiaodong Jiang Structure Option Advisor: Dr. Linda Hanagan December 12, 2014

2 Executive Summary Xyston Inn is a 17-story hotel building that will be located in Brooklyn, New York. The design of Xyston Inn is inspired by the varied character of the developing part of the city. This 65,000 sq. ft. hotel will provide a comfortable spot for the people visiting New York. To create a blight and commodious lounge space, the first floor is designed to be 20-feet tall. The building also includes 16 hotel floors and a mechanical floor which are all 10-feet in height. The overall height of the building is about 215 feet. Beside the floors above ground level, the building also contains a 12-feet-high cellar floor. The structural systems are two-way reinforced concrete slab for gravity and reinforced concrete shear wall for lateral. Xyston Inn is built on bedrock, which has great allowable bearing capacity values. Due to the large gravity load and wind load of this building, the foundation system is designed to be a mat foundation with thickness varies from 3 feet to 4 feet. To transfer building load to foundation, 20 x 24 reinforced columns are commonly used as the cellar and first floor level columns. The lateral system employs a reinforced concrete shear wall system at several locations, throughout the building. To balance the architectural needs with the great torsional force and moment, the structure adopts a 1 x 75 shear wall on the west to east direction. The concrete compressive strength of the shear walls also vary along the height of the levels. In the north to south direction, the lateral system consists of several separate shear walls which have varying lengths from 10 feet to 26 feet. To design the building structural system, the loads considered in this building design include live loads, building dead loads, snow loads, wind loads, seismic loads, and lateral soil loads. The live load, dead load and snow load are also known as gravity loads which are caused by gravity, and act in the vertical direction. The wind load and seismic load are known as lateral loads, which is the load caused by wind or ground motion; both loads are acting directly in the lateral direction, but they also have some effect in the vertical direction. The building structural design is based on 2008 New York City Building Codes for general structural requirements. The building loads are determined by using ASCE 7-10, and the details of concrete elements are designed by using ACI The following report will cover and explain the details of the existing structural conditions. Proposal 1

3 Table of Contents Executive Summary Table of Contents Purpose General Description of Building Structural System Structural System Overview Foundation System Gravity System Lateral System Joints Details Design Codes and Standards Material Design Loads Proposed Redesign Scenario Proposed Methods MAE Requirements Breadth Studies Tasks and Tools Thesis Schedule Conclusion Proposal 2

4 Purpose The purpose of this report is to propose a feasible scenario that includes the redesigns of gravity and lateral system of Xyston Inn. This report will go through the overview of the existing building conditions, proposed redesign scenario, and comparisons between them. This report also includes the tasks and tools that will be used to complete the proposed redesign of the building structural systems. Other objects included in this report are a spring semester calendar schedule, an introduction of breadth topics, and MAE requirements for graduate students. Proposal 3

5 Proposal 4

6 Structural System Overview Xyston Inn is a 17 story reinforced concrete building. The building system is supported by a mat foundation with thickness varying from 3 to 4 feet. The building floor system is supported by a two-way concrete flat slab with thickness varying from 8 to 10 inches. To resist lateral wind and seismic load, this building includes reinforced concrete walls with thickness varying from 8 to 1-2. Foundation System Pilllori Associates performed a geotechnical report of the proposed building site on November 29, The geotechnical investigation was to explore the subsurface conditions in order to determine the soil parameters for the building design and the construction of new foundations for the proposed construction. They recommended footings bearing on bedrock subsurface should be designed for an allowable bearing pressure of 20 tons per square foot. More details can be found in the lateral soil loads section of this report. The building mat foundation with varying thickness and reinforcing is designed by the following recommendations. The reason for choosing a mat foundation system is because the mat foundation reduces the soil and concrete pressure due to gravity loads and overturning moment from wind. Instead of having a lot of individual spread footings with varying foundation construction conditions, a mat foundation creates a flat level and makes construction easier and safer. The variation of mat foundation thickness is shown on Figure 4, next page. The mat foundation variation details are provided in Figure 5. As the figure shows, shear walls, which carry the lateral load, are supported on a 4 foot mat foundation region due to the larger load the shear walls were designed to carry. Proposal 5

7 3 mat foundation Figure 4: Mat Foundation Thickness 4 mat foundation Proposal 6

8 Concrete column reinforcements are continuous into the mat foundation to provide a rigid connection, transfer gravity load, and overturning moment loads due to wind and seismic. Figure 6 shows a typical connection between a column and the foundation. The column schedule and details will be shown in the gravity system section. Figure 6: Typical Column Connecting to foundation Gravity System Floor System Overview Xyston Inn hotel is a 48 x 100 rectangular slender building. The building floor is a two-way flat slab system supported by columns. The floor slab thicknesses vary depending on the different levels and keeps consistent on the same levels. The shape of the floor also varies depending on the levels. Figure 7 shows the first floor two-way slab with a thickness of 10.In comparison to Figure 8 which shows a typical floor with 8 two-way slab. In addition, Figure 9 shows the varied shape of the floor plan with respect to the floor level on the next page. (Note: tendon sizes are also shown on those plans) Proposal 7

9 Figure 7: First Floor Plan Figure 8: Second Floor Plan Proposal 8

10 Figure 8: Second Floor Structural Plan Figure 9: Sixteenth Trough Seventeenth Floor Plan Beside the tendons, the slabs have their own reinforcement based on ACI , and as required, the reinforcing of slabs cannot exceed the limit of 18 inches spacing limit. Table 1 shows the typical reinforcement of the slabs. Basic Slab Reinforcing Schedule Floor # Slab thickness Top Bottom each way 2 to each way 16 to each way each way Table 1: Basic Slab Reinforcing Schedule Proposal 9

11 Typical Floor Bay A typical floor bay is shown in Figure 10. This 12-9 x 23 bay is reinforced by #4 each way on the bottom of the slab. The bottom reinforcement will provide the minimum strength required for slab to resist the tension due to the positive moment. The design also include the details of the slabs top reinforcement, and more details of the two-way slab are shown on Figure The columns that support this bay are labeled as, C4, C5, C7 and C8, the details are described in the next section Typical x 23 Bay Figure 10 1: Typical Bay Proposal 10

12 Figure 10 2: Two way slab Reinforcement The greatest concern about the impact of the columns to the floor slab is punching shear. When the slab is loaded too much, the shear stress around the columns would exceed the limit of the concrete shear capacity and result in slab cracking and dropping from the column. Figure 11 shows a sample example of punching shear failure. To protect the slab from punching shear while limiting the slab thickness, the engineer used 6,000 psi concrete instead of 4,000 psi and continuous reinforcements of slab through the columns. Figure 11: Punching Shear Failure Unlike simply changing the concrete strength, the reinforcement to resist punching shear provides much more complicated details. Figure 12-1 and 12-2 shows the punching shear reinforcement schedule of this project. Proposal 11

13 Figure 12 1: Punching Shear Reinforcement Drawing Figure 12 1: Punching Shear Reinforcement Schedule Parameters Proposal 12

14 Gravity Columns The columns in this project are reinforced concrete columns. To transfer the gravity load into foundation, the reinforcements of the columns are continuous to the foundation. The most challenging part of the column design is the large number of floors. The first floor columns need to carry all of the load from above, it is not a big issue when the building has a small number of floors; however, Xyston Inn consists of 17 hotel floors, a mechanical floor and extremely heavy mechanical equipment on the roof level. Besides the huge gravity loads, the first floor column lengths are 20 feet, which might cause a column buckling issue. To solve those problems, this design calls for 8,000 psi concrete for the 1st floor to the 8th floor and 7,000 psi concrete for the levels above. Therefore, the size of the columns can be limited to the maximum of 20 x 24. Figure 13 shows the column designs for the first and second floors. Figure 14 shows a section of a column. All other floor to floor column heights are 10 feet. Figure 13: Column Schedule of the First and Second floor. Proposal 13

15 Lateral System Figure 14: Column drawing The lateral system is a challenging task for this building. Xyston Inn hotel has a height of 215 feet. This height will result into large wind loads. A possible problem to consider is the first floor column buckling due to the large lateral moment and ground overturning. The lateral load of this design follows 2008 New York City Building codes, the concrete element requirements of ACI , and AISC 14 th edition Specification for Structural Steel Buildings. Shear Wall This buildings lateral system consists of several shear walls with high strength concrete. The concrete strength also varies from floor to floor as shown in Figure 15, the highest strength concrete used in this project is 8,000 psi concrete. Floor Cellar through 8 th floor f c (Compressive Strength of Concrete) 8,000 psi 8 th floor through 15 th floor 7,000 psi 15 th floor through roof 5,000 psi Figure 15: Shear Wall Concrete Compressive Strength Proposal 14

16 The shear wall layout of the 2 nd floor is shown on Figure 16. The concrete shear wall system tends to be located on the south part of the building, due to the architecture features on the north façade and the varied shape of floor plans. In the north-south direction, the lateral system consists of five separate 1-0 thick shear walls which are shown in blue. In the west-east direction, the lateral system consists of two 1-2 shear walls around stair shaft and one 1-0 x 75-0 shear wall extending all the way to the roof. Due to differing locations of the COF (center of Force) and COR (center of rigidity) in the north to south direction, a large value of torsion will occur when winds are blowing. This design takes advantage of the solid south wall, and use 75% of the south wall s length for the shear wall system. With a length of 75, this shear wall is adequate to resist a large proportion of the lateral shear and torsion. 12 SW, W E 14 SW, W E Figure 16: Lateral System Shear Wall Layout 12 SW, N S To stabilize and resist possible loads, the shear walls need to be moment connected to the mat foundation. The typical connection is to use embedded dowels in the shear wall to hook and connect shear wall into the foundation. Figure 17-1 and 17-2 shows the #4 o.c. serving as the dowels. Proposal 15

17 Figure 17 1: Column to mat foundation Figure 17-2 Typ. Interior/ Exterior CMU Wall Reinforcement Joint Details In Xyston Inn hotel, the typical connections are slab-to-wall, slab-to-column, column-tofoundation, and shear wall-to-foundation. To connect two or more members together the joint detail is extremely important. If a joint is not capable of transferring the designed loads, the structure would behave quite differently, because if one part fails, the adjacent joint might also fail due to the increased load. Eventually, one joint failure might result into a progressive building failure. In previous sections, the reinforcing bar dowel is introduced. In this project, there are much more different joint details. Figure 18-1 shows the typical concrete wall construction joint detail, the water stop is important for the rebar protection. Figure 18 1 Typ. Concrete Wall Construction Joint Proposal 16

18 As Figure 18-2 shows, the gap between the walls shall not be less than 14 days after the second adjacent section is cast, it is important for gap control, drift control and water proof. Figure 18-2 Typ. Concrete Wall Construction Gap Detail. Design Codes and Standards Structural Codes and Standards Overall: 2008 New York City Building Code Concrete: ACI Steel: AISC 14 th edition o Specification for Structural Steel Buildings (Commentary and Supplements) Materials Concrete (Normal Weight) Project Concrete Columns Shear Walls Slabs Foundation 5,000 psi; 7,000 psi; 8,000 psi 5,000 psi; 7,000 psi; 8,000 psi 6,000 psi 6,000 psi Table 2: Normal Weight Concrete Usage and Strength Proposal 17

19 Steel Steel Reinforcement Typical Reinforcing Bars ASTM A-615, Grade 60 Welded Wire ASTM A 82 and ASTM A 185 Table 3: Reinforcing Steel and Standards Design loads This section describes the determination of the structural loads based on national codes. The load path analysis is also included in this section. National Code for Live Loads and Lateral Loads Load National Code Section Live ASCE 7-10, Chapter 4 4.3, 4.7 & 4.8 Lateral ASCE 7-10, Chapter 12& & Table 4: National Codes Gravity Load Live Loads The live loads in this building were determined by ASCE 7-10 Chapter 4 section 4.3, 4.7 and 4.8. The building live loads are listed on drawing S-500 of the structural drawing. Dead Loads Proposal 18

20 The designed dead loads and total ASD design loads are also listed on drawing S-500 of the structural drawing. Snow Loads The snow load is calculated based on ASCE 7-10, the design criteria of snow are listed on drawing S-500 of the structural drawing. Lateral Loads Wind Loads The designed wind loads of this project were determined by ASCE 7-10 Chapter 27 part 1, which is for enclosed, partially enclosed, and open buildings of all heights. The wind load criteria is also listed on drawing S-500 of the structural drawing. Seismic Loads The designed seismic loads of this project were determined by ASCE 7-10 Chapter 12.8, which outlines the equivalent lateral force procedure. The seismic load criteria is also listed on drawing S-500 of the structural drawing. Lateral Soil Loads Pollori Associates determined the unit soil weight to be 125 pcf. To resist the lateral soil loads, the designer needs to consider both at-rest earth pressure, active earth pressure, and passive earth pressure. The lateral soil loads on the foundation walls are a function of wall height. By considering the wall boundary condition as pin-pin, the moment and shear on the foundation can be determined. The Figure 19 below shows the equivalent lateral soil pressure. Figure 19: Lateral soil pressure Proposal 19

21 Load Path The function of load path is to ensure that any loading on the structural system is eventually transmitted into the foundation and distributed to the ground. Due to the different types of loads, there are generally two types of load paths which are gravity and lateral. Gravity The gravity loads of the building consist of live loads and dead loads. The load of the occupied spaces are supported by the two-way reinforced concrete slabs. Then, the gravity moments and loads are transferred from slab into columns and shear walls. The most of the slab gravity load moments are almost canceled by each other, except the exterior columns and shear walls in which the moment is accumulated along the building height and eventually dissipated to the foundation and bedrock. The vertical gravity loads also accumulate along the building height and eventually transferred to the foundation and transferred to bedrock. Lateral Wind Wind blows onto the building and creates wind pressure on the exterior façade. The façade transfers the load into the floor diaphragm which distributes it into the shear wall system. While this lateral load transferring along the wall height, the moment is being accumulated. Then the shear walls transfer the lateral shear and the great amount of moment to the foundation. Then the foundation transfers the shear and moment to bedrock. Eventually, the shear and moments are dissipated into the earth. On the roof level, wind creates a large uplift pressure across the surface of the roof. The uplift force is transferred from the aluminum cover to the roof slab. And at certain heights below the roof top, the uplift force will be canceled by the roof s dead load. The roof plan is shown below. Figure 20-1: Roof Plan Proposal 20

22 Figure 20-2: Roof Elevation Seismic The seismic loads are the loads due to ground shifting, when the ground shifts, the buildings inertia makes it want to stay in place. But due to the displacement, the stiffness of the building creates a response of internal forces. This response makes the building start moving. However, the motion is damped as long as the building is moving. Eventually, the energy of the ground motion is absorbed and dissipated to earth. In the structural field, the load path of seismic load is the same as wind load path. Soil The lateral soil loads are acting on the foundation wall and transferred through the cellar floor and first floor diaphragm. There are two possible paths. The first one is the loads transfer from one side to the other and dissipate into bedrock. The second one is the load transfers directly to the shear walls and goes down, eventually being dissipated into bedrock. Proposal 21

23 Proposed Redesign Scenario Technical Reports II, III and IV analyzed the existing structural reinforced concrete design. The redesign scenario will focus on the alternative of a composite steel structural design, and investigate the effects of a composite steel structure on the buildings lighting system, construction schedule, and cost as compared to the existing reinforced concrete structure. Due to the change in the structural system, it is important to re-evaluate building loads, floor vibration, deflection, and other building serviceability requirements. The first intention of the building redesign scenario of the composite steel structure is to create a lighter building with a faster structural construction schedule. Because the real cost of a hotel building shall also consider the profit, which a hotel can make in the reduced number of days of construction schedule. The second intention is to take advantage of multiple choices of available lateral systems for the composite steel structure to try to move the center of rigidity toward the center of mass. By doing so, the lateral design shear and story drift can both be reduced. Proposed Methods Gravity System The existing structural layout of the floor plan has no grid system because of the irregular layout of the columns, which supports the two-way flat slab system. The proposed composite steel floor layout will have a regular grid system, and the location of columns will be adjusted to fit the architectural floor plan and interior design drawings (see Figure P-2). Figure P 2: Alternative Composite Steel System, Grid layout (Partial) Proposal 22

24 By changing the floor system from two-way reinforced concrete into composite steel system, a floor vibration check is required to be proved by Design Guide 11. Therefore, floor vibration issues must be researched and the redesign of composite steel gravity system shall be proved to pass the vibration requirements. Lateral System The existing lateral system consists of reinforced concrete shear walls with a large eccentricity with respect to the center of mass. To be able to compare the existing system with a different structural system, the proposed lateral system is also made up of steel. To support the lateral load as well as reduce the lateral eccentricity, the steel lateral system design could include the following options: 1. Using steel plate shear walls in the exactly the same locations of the existing reinforced concrete shear walls, which will also result in large torsional shear in those shear walls. 2. In addition to option 1, adding regular brace frames on the north part of the building floor plan to move the center of rigidity close to the center of mass. 3. In addition to option 1, adding eccentrically braced frames or other specially braced frames to the structural system on the north part of the building floor plan to move the center of rigidity closer to the center of mass without interrupting the architectural features. Those three options will be researched and the most feasible option will be chosen as the new lateral system for the Xyston Inn. To analyze those steel lateral systems, ETABS 2013 will be used to process the base reactions, building drifts, and finite element analysis. The design of each single element of each lateral system will follow the requirements of AISC Steel Construction Manual 14 th edition. Additional study of designing steel lateral system by using AISC Steel Construction Manual 14 th edition will also be processed. Proposal 23

25 MAE Requirement The future thesis report will use the graduate level coursework to proceed with the design and analysis of proposed structural system. ETABS 2013, which is one of the most useful computer modeling software introduced in AE 530, will be used to process the loading responses of the redesigned structural system. Steel connection design, which was introduced in AE 534, will also be used for designing the steel connections. Breadth Studies 1- Lighting System Analysis As an important intention of the project architect, the building is designed to take advantage of its orientation to bring indirect sunlight into the building and create comfortable day-lighting conditions. However, in order to move the center of rigidity closer to the floors center of mass, the most efficient design is to add specially braced frames to the north exterior of the building. Therefore, an efficient redesign of the lateral system would probably affect the glazing and lighting design of this building. The lighting breadth will involve the general daylighting quality, lighting system solution, and the cost of lighting energy consumption. A study of solar angles, solar gain, envelop energy losses, and lighting quality will be performed to understand the new structural system s impact on the lighting conditions. 2 - Construction Schedule and Cost Analysis The new structural design of Xyston Inn uses steel as the major structural material. The construction schedule of a steel structure is typically faster to be erected than a reinforced concrete structure. By changing the building structural system from reinforced concrete system into steel structural, the construction period of the building can be significantly reduced. In the future, a comparison of construction time schedule between reinforced concrete and steel structure will be included. Even though the cost of two-way slab system is the cheapest one compare to other types of structure system, the steel structure is faster to be erected. As a hotel building, the faster it is erected, the sooner owner can start making profit and reduce the real cost of construction. In addition to steel construction, because the more and more steel suppliers are involved into pre- Proposal 24

26 fabricated steel connection business. If this project can take advantage of using pre-fabricated steel connection, the consuming time of construction can also be significantly reduced. In the future research study, a study of pre-fabricated steel connection will also be included into construction breadth. Tasks and Tools 1. Research and process floor vibration design a) Floor vibration design requirements based on Design Guide Research and compare lateral system a) Research the three options of steel lateral system designs b) Compare feasible and cost of each system c) Chose the best steel lateral system 3. Research various computer modeling programs a) Computer modeling program for chosen steel gravity system b) Computer modeling program for chosen steel lateral system c) Computer modeling program for chosen steel gravity and lateral system under specific loading cases 4. Breadth Topic 1 -Lighting System a) The effects to day-lighting if brace frame is used b) Analysis any possible change to lighting system. c) Cost of daily lighting consumption change d) Lighting quality change due to structural brace frame 5. Breath Topic 2 - Construction Schedule and Cost a) Possible effects of steel structure to construction schedule. b) The updated schedule date and the cost of gravity system c) The updated schedule date and the cost of lateral system d) Pre-fabricated steel connection Proposal 25

27 Proposal 26

28 Conclusion This report introduce the background statement of the existing structural design, which includes the gravity and lateral systems of the Xyston Inn hotel. A scenario has been created based on the results from Technical Reports II, III, and IV. Due to the large eccentricity between the center of mass and center of rigidity, the existing designed shear walls have to resist both directly lateral shear and torsional shear. The redesign of building lateral system will use steel plate shear wall for resisting major lateral loads, and the redesign will also try to design additional braced frame in the north exterior wall to make the center of rigidity closer to the center of mass and reduce torsional shear. In order to complete this thesis project in spring 2015, two breadth topics of redesigned structures impacts on the lighting and construction fields. A lighting study will be performed to analyze the effects of structure redesign to the light conditions and lighting energy consumption. The construction breadth will include the schedule change and evaluated cost difference due to the redesigned steel structure. This report also includes the tasks and tools for completing the structural redesign of the Xyston Inn hotel. According to the tasks and tools, a schedule of spring semester is also provided in this report. The graduate level course work will be reference from AE 530, Computer Modeling of Building Structure, to perform the ETABS structural analysis. Another graduate level course work will be reference from AE 534, Advanced Steel Connection Design, to perform a complete and detailed steel design of the Xyston Inn hotel. Proposal 27