analysis ii – façade redesign: architectural precast panels be posted/v analysis ii.pdf ·...

Analysis II – Façade Redesign: Architectural Precast Panels

Shawn Sambol Construction Management Goizueta Foundation Center for Research and Doctoral Education Emory University, Atlanta, GA

21

Analysis II – Façade Redesign: Architectural Precast Panels

Overview:

This analysis covers the comparison of the current EIFS façade and my

proposed change to architectural precast panels. It compares several important

factors and shows the results of a structural analysis showing that the existing

building can support the heavier façade. The precast is a higher quality and

more durable system that will last the life of the building. It has a greater cost

associated with it, but is well worth having confidence in the performance of the

façade when it needs to last for the life of the building.

Background:

The façade of a building is the main barrier between the outside weather, and the

interior of the building. It is crucial that the façade can keep water and moisture

out of the building, and that it can handle the type of weather it is going to be

exposed to. In the case of the Goizueta Foundation Center, the façade chosen

was an exterior insulating finish system, which I will refer to as EIFS from here

on. This system consists of several layers, shown in Figures 5 and 6 below.

A. Substrate/Sheathing

B. Adhesive

C. EPS Insulation Board

D. Reinforcing Mesh

E. Base Coat

F. Finish Coat

Figure 6: Isometric section of EIFS layers Figure 5: Layers of the EIFS system used on the Foundation Center


22

EIFS has several benefits, but also many drawbacks. Mainly, it is not a good

system to install in an area that receives a moderate amount of rainfall. This is

the case with Atlanta. The average annual rainfall in Atlanta is 51”. For a system

that can have problems in wet areas, Atlanta does not seem to be a good place

to be installing it. Not to say that EIFS may perform well in its initial testing for

moisture penetration, but over the life of the building it will certainly need

maintenance and/or repair. Moisture damage to a building with an EIFS façade

can be extremely expensive to repair and replace. In some cases, the

remediation costs more than the initial construction itself. The drawbacks of

EIFS certainly validate a redesign of the façade. The foundation center is an

educational building on a university campus. Universities build buildings that are

going to be in use for 100 years or more. With this in mind, the building must

then be exposed to 100 years of weather and storms. EIFS was first used in the

United States in 1969. It is barely more than 35 years old. There is no

guarantee that it can withstand 100 years of weather and storms because it

hasn’t been around even half that time for it to be tested. A university wants a

building with a high quality façade, and that is why I chose architectural precast

panels. I have compiled a list of factors that I feel are important when choosing a

façade (see Table 4 below).

Factors EIFS Precast Panels

Cost EIFS is very cost effective, at

about $10/sf.

More expensive, Architectural

Panels costing roughly $40/sf

Weight Second advantage, EIFS is a

very light façade system

Architectural Panels weight

62.5lb/sf

Insulation Value

The insulating board in the

EIFS system has an R-value

of 3.8 per inch thickness.

Concrete suffers here with an

R-value of only .1 per inch

thickness.

Ease of Installation

Labor intensive, requires

scaffolding and all work is

done from the exterior.

Panels are placed by crane,

and insulation is done from the

inside.

Water Tightness

Entirely dependent on the

quality of the installation.

Water tightness can be

achieved through sealants and

is very effective.


23

Time of Installation

In this case, 115 days, and

requires steel construction to

be completed before it can

begin.

Can be placed at a rate of 12

panels per day. Does not

require steel structure to be

complete to hang panels on

lower levels.

Maintenance Can be very costly, and is also

labor intensive.

Little to no maintenance

required.

Durability

EIFS has only been around for

35 years, no guarantee it can

last for the typical life of a

university building. Also only

comes with a 5 year warranty,

10 year was purchased for this

project.

Extremely durable, can easily

last 100 years under normal

weather conditions.

Fire Resistance Tested for fire resistance, but

materials are still combustible.

Concrete is noncombustible.

Quality Control

Left up to field installation.

Must be installed 100% per

specifications or water

penetration becomes a serious

issue.

All Panels are made in the

factory in a quality-controlled

environment.

Proposed Solution:

Through the use of a precast panel façade, I hope to show that it would be a

higher quality building that will last as long as the building will be expected to.

Precast concrete is an extremely durable material, withstands all types of

weather, and will be able to protect a building for 100 years. There are many

other advantages that precast has over EIFS. EIFS is a labor intensive system

to install. It requires scaffolding which increases the time it takes to install. Not

only does the scaffolding make the installation time longer, but the fact that the

steel erection must be completed before the EIFS can be installed. The

foundation center was erected in two sequences. After sequence A was

complete, the EIFS started installation there while the crane erected sequence B

(see Figure 7 on the following page).

Table 4: Comparison between EIFS and Precast Panels


24

The entire steel sequence was approximately 85 days, 40 for the first sequence,

and 45 for the second. The entire EIFS installation took a total of 115 days. This

is 115 days after the first steel sequence was completed (see Figure 8 on the

next page). Please refer to the schedule on the next page. The exterior skin

installation lasted from October through March, so the building was exposed for

the entire winter. If precast were being installed, there is no need for the steel

structure to be complete for panels to be hung. There are a few opportunities to

save schedule time here. First, a smaller crane could be used to hang panels on

the lower levels of the building until it is out of reach, at which time the tower

crane could take over placing panels. Second, the tower crane could set steel in

the morning and panels in the evening. Either way, the building would be

enclosed much sooner than in the case of the EIFS. It would likely be enclosed

by the end of the year, being that there is no wait for the structure to be

complete, and the precast would be insulated from the inside (see Table 5).

EIFS Precast Panels

115 Days 60 Days – 35, 25

Sequence A: 9/6/2004 – 10/22/2005 10/11/2004 – 3/18/2005

Sequence B: 10/25/2004 – 11/26/2004

Figure 7: Steel erection and building skin sequence

Table 5: EIFS and Precast Panel schedule comparison


25

Figure 8: Detailed schedule of structural steel and EIFS construction sequences


26

Cost:

Now to speak of the downsides of precast; its cost, weight, and insulation value.

For the cost comparison, Table 6 shows the difference between the systems:

Material Quantity Unit Unit Cost Total Cost

EIFS façade 57000 sf $9.73 $554,610.00

Architectural Preacast 57000 sf $40.00 $2,280,000.00

This is a substantial increase in cost. Not only does the material itself cost more

than the EIFS, but precast also requires additional framing and insulation. I have

added the rough cost of the framing and insulation into the per square foot cost

of the precast panels.

Insulation:

For insulation, the precast system will use R-19 batt insulation. This will have a

U-value around 0.05 vs. 0.04 for the EIFS system. To increase the efficiency of

the precast system, a thicker insulation could be used, such as R-22. This is an

important aspect of the façade because of its direct affect on heating and cooling

costs.

Structural Analysis:

Lastly, I will discuss the weight issue. The architectural precast panels I have

proposed to use are a solid 5” panel, made of normal weight concrete, and

weighing 62.5 lb/sf. I analyzed a column on the NW (rear) elevation (see

highlighted section in Figure 9 below).

Table 6: EIFS and Precast Panel cost comparison

Figure 9: NW (Rear) Elevation with the analyzed column and surrounding precast panels highlighted


27

The panel connections are column bearing, so the spandrel beams do not

require testing. I calculated the loads from the floor deck, beams and girders,

façade, and roof that are carried by that column. The specifications state that the

combined dead and live load carried to the columns from the floor deck is

225lb/sf. The composite deck is 3” 18 gage with 6-¼” lightweight structural

concrete and wwf 6x6 w1.4xw1.4. Using this information, I drew a model in the

structural program RAM Advanse, and applied the loads I calculated at each floor

level (see Table 7). I drew the column, defined the steel type and section sizes,

and then analyzed it. After analyzing, I ran the check for code compliance, and

the column was labeled ‘OK’ under the applied load scenario. Screenshots from

this analysis, as well as analysis reports can be found in the appendix of this

document. Figure 10 (on the following page) shows the column, beams, and

girders that were involved. Note that the column was spliced between the 3rd

and 4th levels, as the drawing is not clear in showing this.

Floor Level Load Type Loads Unit Total

Load

Roof 17.5

Façade 17.0 kip Lower Roof

Members 1.9

19.4

Slab 105.0

Façade 15.7 kip Level 5

Members 2.1

17.8

Slab 105.0


Members 1.9

1.9

Slab 105.0


Members 2.4

24.2

Slab 105.0


Members 1.9

1.9

Table 7: Summary of loads from each level of the building transferred to the analyzed column


28

The column I selected to analyze was the smallest in the rear elevation that was

under the typical load I determined. Being that it was successful under the

additional load of the precast, the remainder of the exterior columns would be as

well.

Conclusions:

This analysis has brought to light the shortcomings of an EIFS façade and the

benefits of using precast panels. After comparing all the important factors that

are a part of façade selection, I feel that the precast panels would be a much

smarter choice for this building. The main reasons being that it is a university

building that will be standing and in use for the next 100 years, and precast is

more than capable of protecting a building for this amount of time. The additional

cost is a substantial increase, but to avoid repair and maintenance costs that will

come in due time with EIFS, it will be a very wise decision to pay the greater

initial cost.

W14x99

W14x99

W14x99

W14x61

W14x61

W21x68

W21x44

W21x44

W18x35

W21x44

W21x44

W21x44

W21x44

W18x35

W24x55

W24x55

W21x44

W24x55

W24x6815’-6”

18’-6”

16’

13’

14’

Level 2

Level 3

Level 4

Level 5

Lower Roof

Figure 10: Diagram of the analyzed column, with beams, girders, and floor heights shown

analysis ii – façade redesign: architectural precast panels be posted/v analysis ii.pdf ·...

Documents