Structural Option Faculty Consultant – Dr. Linda Hanagan ... Assignment 1...Structural Option...

Michael Gray Structural Option Faculty Consultant – Dr. Linda Hanagan Arlington Gateway Hotel Arlington, VA

Rendering courtesy of WDG Architecture

Arlington Gateway Hotel - Technical Assignment 1 - 1 -

Structural Concepts/Structural Existing Conditions Report Resubmitted November 5, 2004

Executive Summary

The Arlington Gateway Hotel is a 15 story cast-in-place reinforced concrete

structure totaling 240,000 square feet. The hotel also includes three levels of

below grade parking under the structure. The flooring system is a mix of two

way flat plate and flat slab design depending on floor loading conditions.

The exterior precast cladding is non load bearing and supported by each

floor. The structure uses moment frames to resist lateral forces due to wind.

The loading on the structure was calculated using BOCA 96 and ASCE 7-95.

The calculated loadings used throughout this report are current codes of

ASCE 7-02 and IBC 2003. Calculations are limited do to the nature of the

building being a two way slab and not having an in depth study of this

subject in classes at this time. Through simplified calculations, no significant

differences in member sizes have been found. It will take much

understanding of the structure to accurately define the lateral systems of the

building and this calculation has been omitted from this assignment to be

completed at a later date.

Through this analysis, wind and seismic forces were calculated. A maximum

base shear of 710 kips was found for combined wind forces. Maximum base

shear of 895 was found due to seismic forces. These forces were not used in

checking members in this report, but will need to be checked as part of

future investigations.




Building Description

The Arlington Gateway Hotel is a 240,000 square

foot structure located in Arlington, Virginia. The

hotel is part of Arlington Gateway, a mixed use

development. The height of the building is 170’

from ground level to the top of the mechanical

penthouse. There are 336 units in the 15 story

building. The break down

of each floor total area is

shown in the figures on the left. There is also an

additional 3 levels below grade that is the parking

garage. The lowest level of the parking garage is 30’

below ground level. The exterior of the building is

composed of non load bearing precast concrete

panels. Structural steel is used on the north east face

and for the roofing system of the ballroom and pool

areas.

Summary of the Overall Structural System

The overall structural system of the building is a two

way flat plate. The slabs are generally 8” thick with

#4@12” on center, each way. 4000 psi concrete is

used in all floor slabs. The building bears on spread footings and continuous

wall footings. Column dimensions are generally 32”x32” in the lower levels

and require 6000 psi concrete. On the second through eighth floor, columns

require 5000 psi concrete and 4000 psi concrete is used on the rest of the




building. Reinforcing steel is to be grade 60, except for column ties and

beam stirrups which are to be grade 40, minimum.

Foundation

The foundation of the building bears on decomposed rock. The structure

uses spread footings that were designed for two different bearing

conditions, 40ksf and 80ksf. The soil bearing conditions needs to be checked

by a geotechnical engineer for each footing, to determine what design to

use. The footings are to use 4000 psi normal weight concrete. For design of

foundation walls, an equivalent fluid pressure of 60 pcf should be used

above the water table and an additional 62.5 pcf below the water table.

Codes

The hotel’s structural members were designed using ACI 318-97 and AISC –

8th Edition. ACI 318-97 was used to design minimum requirements of

concrete members along with calculating loading using the equation of

1.4D + 1.7L for factored loads. AISC – 8th Edition is the manual for Allowable

Stress Design (ASD), this was used for the steel members in the pool and

ballroom areas. Through my analysis I will use ACI 318-02 and AISC – 3rd

Edition (LRFD). ACI 318-02 uses a loading equation of 1.2D + 1.6D for

factored loads.

Loading on the building was determined using BOCA 96 and ASCE 7-95.

These codes were used to define the loading on the lateral systems due to

wind and seismic forces. Also they define the minimum required gravity

loads, such as live loads. The live loads include snow loading and loading




due to objects that can be moved such as people and furniture. To

determine design loads for this assignment I used ASCE 7-02.

Lateral Systems

The lateral load resisting system uses moment frames to resist the forces of

wind. The whole structure acts as a moment frame. There were only

calculations of forces in the lateral system at this time. No lateral load

resisting members were checked due to the complexity of the structure and

the use of a two way flooring system. This will be accomplished in a later

report.

Wind

Wind loads for the structure were calculated by the engineer using BOCA 96

and ASCE 7-95. I calculated wind loads using ASCE 7-02. For simplicity of

calculations, I based my buildings shape on a rectangle equal to that of the

floor area of the upper floors.

The dimensions of the

rectangle are 73’ x 217’. On

the left are the Wind Pressure

Diagrams for the hotel. The

red area is the windward

pressure (+) and the blue

represents leeward pressure

(-). The max pressure in the N-




S direction is 15.9 psf at the top on the windward side with 9.8 psf acting on

the whole face of the leeward side. In the E-W direction the max wind

pressure is 17.04 psf at the top on the

windward side and 5.25 psf on the

leeward side. The tables provided on this

page show the exact breakdown of wind

pressure per height of building. In

Appendix E there is a diagram of the wind

pressure broken down into story forces

acting on each floor. I found the total

base shear in the N-S direction to be 710

kips. The N-S direction diagram reflects the

load at each floor for the 27’ bay believed

to be part of the lateral system. This was

done to aid in the 2-D calculation of the

lateral system in this direction that I will

compute at a later date. The E-W wind

loading diagram in Appendix E has the total

forces acting on each floor and a total base

shear of 195 kips.

Seismic

ASCE 7-02 was the code I used for my seismic

analysis. I first found the snow load for the

building to be 19.25 psf which is less than 30 psf; therefore, it was not

required to be used in the accumulation of loads on the structure. I used

N-S Direction

Height (ft)

Windward

(psf) Leeward

(psf)

Total MWFRS

(psf) 0-15 8.04 -9.82 17.86

15-20 8.75 -9.82 18.57 20-25 9.31 -9.82 19.13 25-30 9.88 -9.82 19.70 30-40 10.72 -9.82 20.54 40-50 11.43 -9.82 21.25 50-60 11.99 -9.82 21.81 60-70 12.56 -9.82 22.38 70-80 13.12 -9.82 22.94 80-90 13.55 -9.82 23.37

90-100 13.97 -9.82 23.79 100-120 14.67 -9.82 24.49 120-140 15.38 -9.82 25.20 140-160 15.94 -9.82 25.76

E-W Direction

Height (ft)

Windward (psf)

Leeward (psf)

Total MWFRS

(psf) 0-15 8.60 -5.25 13.85

15-20 9.35 -5.25 14.60 20-25 9.95 -5.25 15.20 25-30 10.56 -5.25 15.81 30-40 11.46 -5.25 16.71 40-50 12.21 -5.25 17.46 50-60 12.82 -5.25 18.07 60-70 13.42 -5.25 18.67 70-80 14.02 -5.25 19.27 80-90 14.48 -5.25 19.73

90-100 14.93 -5.25 20.18 100-120 15.68 -5.25 20.93 120-140 16.44 -5.25 21.69 140-160 17.04 -5.25 22.29




the values from seismic use group III and site

classification C. Through my calculations of seismic

shear I found the base shear to be 895 kips, which is

actually greater than my calculated base shear for

wind. There is no significant fault line in the area; the

large value for seismic base shear could be a result of

a very conservative approach I took in calculating

seismic story forces. The diagram on the left displays

the magnitude of seismic forces at each floor.

Loads

The building’s roof was designed using a live load of 16 psf. This varies a little

with my calculated snow load of 19 psf. The slight difference could be

because of a change in code or because some of the load goes to the

penthouse floor that was designed for 150 psf. The building’s roof was

designed using a live load of 16 psf. This varies a little with my calculated

snow load of 19 psf for this area. The slight difference could be because of

a change in code or because some of the load goes to the penthouse floor

that was designed for 150 psf. Typical floors were designed using 40 psf + 15

psf for partitions. 40 psf is the value I found in ASCE 7-02 for live floor loads for

a hotel. Corridors were designed using a live load of 70 psf, which is the

same value as found in ASCE 7-02. The 15 psf load for partitions is usually

taken as dead load, but in this case the engineer may have thought about

future remodeling of the floors. This would change locations of walls and a

new distribution of loads. Other live loads include 150 psf for mechanical

penthouse floor, 100 psf first floor and stairs, and 250 psf for the loading




dock. Wind and seismic loading on the structure is stated in the analysis of

the lateral system.

The accumulation of dead loads includes the weight of the building

materials and miscellaneous mechanical, electrical, and plumbing fixtures.

The 8” flat slab has a dead load of 100 psf. I have assigned 10 psf to MEP

and other miscellaneous being applied to each floor. The total loading on

each floor is shown in the diagram on the next page. For quick analysis a

live load of only 40 psf

was used in the table,

corridors make up a

small percentage of

floor area so it was not

included at this time.

Spot Checking

Through my

calculations, I

checked the design of

the two way slab

between columns. I had to simplify the design and treat this section as a

thin beam. My results were similar to the design; calculations can be seen in

Appendix A. For the one foot wide and 8” deep beam I found that

minimum steel requirements governed. To meet minimum steel

requirements I needed to use a #5@12”. The slab called for #4@10”. The

difference is due to the wider spacing of my design. Using the minimum

Level Total Live Load (psf)

Total Dead Load (psf)

Dead Weight

Live Weight

Factored Total

Weight 15(roof) 170 110.0 1742510 2692970 6399764

14 40 125.0 1980125 633640 3389974 13 40 125.0 1980125 633640 3389974 12 40 125.0 1980125 633640 3389974 11 40 125.0 1980125 633640 3389974 10 40 125.0 1980125 633640 3389974 9 40 125.0 1980125 633640 3389974 8 40 125.0 1980125 633640 3389974 7 40 125.0 1980125 633640 3389974 6 40 125.0 1980125 633640 3389974 5 40 125.0 1980125 633640 3389974 4 40 125.0 1980125 633640 3389974 3 40 125.0 1980125 633640 3389974 2 40 125.0 1980125 633640 3389974 1 40 125.0 1980125 633640 3389974

Sum 29464260 11563930 53859400




reinforcing provides a member to have a capacity of 88 foot kips. Using ACI

moment coefficients I found a maximum moment of 5.8’k (negative

moment). The extra capacity of the slab would take moments from lateral

forces, which will be calculated later. This will have to be checked to see if

82.8’k is more than the moments caused by the lateral forces.

Columns are now to be checked for capacity of gravity loads. There are 30

columns in the area of the above loading table. Through quick analysis

total building weight was divided between the 30 columns, each column

roughly supports 1795 kips. At this time only gravity loads have been found,

later lateral forces will need to be checked with the chosen column to see if

it will still be adequate. Columns under the first floor use 6,000 psi concrete

and 60,000 ksi steel and have a common dimension of 24” x 36”. Using CRSI

Handbook 2002, the maximum capacity for this column is 11079”k of

moment and a vertical load of 3043 kips. Due to the nature of the moment

frame design, I believe moments acting on each column will have a major

impact on the final design and sizing of the column. Checks on lateral

system are not yet complete

Miscellaneous Loading and Conditions

Through inspection and the building having cast-in-place concrete roof

slab, uplift due to wind does not need to be checked on the slab due to the

weight of the slab. Extra load due to the precast façade needs to be

checked on exterior members. The slabs of the below grade parking area

aid in retaining the lateral earth pressure applied to the basement walls.

Also loading due to mechanical units will need checked.




Appendix Title Pages

A. Member Check - Slab 10-11

B. Snow Load Calc. 12

C. Seismic Design 13-14

D. Wind Design 15-17

E. Wind Loading Diagram 18

Structural Option Faculty Consultant – Dr. Linda Hanagan ... Assignment 1...Structural Option...

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