behavior of itech composite beam in fire - experimental study

50 S.Kim, M.Kim and S.Kang

Behavior of iTECH Composite Beam in Fire- Experimental Study

1Myeong-Han Kim, 2Sang-Dae Kim and 2Seong-Deok Kang1Department of Architectural Engineering, Daejin University, Korea

2Department of Civil and Environmental System Engineering, Korea University, Korea

This paper presents the resul ts o f an experimental investigation into the fire performances of simply supported iTECH composite beams using an ISO834 standard fire. To evaluate the fire resistance performance of the iTECH beam, a test was conducted for 4.7m-span-length iTECH beams under given conditions in a laboratory. The fire resistance performance of unprotected coatings of the iTECH beam has been examined, and a longer period of fire resistance was achieved by increasing the section size and decreasing its load ratio. Coating for the fire protection of iTECH beams reduce the rate of temperature rise of the beam in case of fire, and the required thickness of spray-on fire protection coatings can be determined by means of tests.

Before reviewing the fire test, I will present the basic concepts of the iTECH composite beam. Then, I will present the fire-resistance test overview and test results.

The name of this composite beam is " iTECH", which means " Innovat ive" , "Technical", "Economical", "Convenient" and "Hybrid System". This composite beam was developed mainly for the purpose of reducing the story height of high-rise residential steel buildings. This figure compares the "conventional composite beam" and the "iTECH composite beam". By adopting this floor system, a story height reduction of about 200 mm can be obtained. The advantages of a reduced story height are : First, increased number of stories and more lease area, second, reduced exterior and interior wall space, and third, reduced air conditioning and heating space.

Figure 1.2.1

Figure 1.2.2

Figure 1.2.3

Fire Science and Technology Vol.26 No.2(2007) 51-60 51

52 M.Kim, S.Kim and S.Kang Behavior of iTECH Composite Beam in Fire - Experimental Study 53

The important structural components of the iTECH beam are the asymmetric H section of steel, web opening, light-weight steel channel, and web concrete.

The top flange of the asymmetric H section is / for resisting the negative moment during the construction stage. Placement of the web opening is important for the following reasons.

(1) Stronger composite action between concrete and steel

(2) Duct Space(3) Placement of bottom rebars in the slab(4) Role as a shear stud. Light-weight

s tee l channels are at tached for supporting the deck plate and web concrete during the construction stage.Web concrete will increase the fire resistance, lateral torsional buckling strength, and shear strength of this composite beam.

The important merits of the iTECH composite beam can be summarized as follows:

Reduced story height, improved fire resistance, excellent constructability, and sufficient duct space.

These figures show the steel fabrication process for the iTECH composite beam.

Step 1 involves cutting the steel beam into a honeycomb shape. Thus, one steel beam is divided into two pieces of honeycomb-shaped steel.

Step 2 involves welding the upper flange and channel to the cut honeycomb-shaped steel.

There are some similar floor systems to the iTECH system, such as the "Slim Floor System", which was developed in Europe. It is expected that the iTECH system when compared with other floor systems can be applied to longer spans with good

Figure 1.2.4

Figure 1.2.5

Figure 1.2.6

Figure 1.2.7


constructability and lower costs. Four patent rights, three domestic patents and one patent from the United States, have been obtained.

For an application in real world projects, experimental and analytical studies were performed.

Some recent projects, / in which the iTECH composite beam was applied in a floor system, are shown.

The fire-resistance of the iTECH composite beam has been studied by experimental and analytical approaches.

N o w, I w i l l b r i e fl y d i s c u s s t h e experimental study. A total of 6 specimens were manufactured in full-scale section size. In the first column of the table, the front two-characters indicate the "fire test specimen of the iTECH beam". And the second two digits indicate the depth of the beam in centimeters. The selected three sizes for depth are the most general cases in real projects. The width of the beam was set to be 300 mm, as in the real design process of the iTECH beam. The last two digits indicate the thickness of fire-protection in the bottom steel flange. A thickness of 44 mm is suggested by the material manufacturer to provide 3 hours of fire-resistance for steel members. According to Korean building code, 3 hours of fire-resistance is required for structural members of a high-rise building. Load ratio, which means the ratio of the applied moment to moment strength, was selected to be 100%, 70%, and 40%. The installation of the thermocouples is shown.

This figure shows the location in the span length. And this figure shows the location in the section. Furnace and loading devices

Figure 1.2.8

Figure 1.2.9

Figure 1.2.10

Figure 1.2.11


are shown here. An adopted standard for fire-resistance testing is Korean Industrial Standard, KS F 2257.

This standard has many similar terms to those in ISO 834, especially in the failure criteria and standard time-temperature curve.

The specimen, horizontal furnace, and test setup are shown here.

These are the pictures captured immediately after the test.

You can see here that temperature changes with time in each of the locations of the section for the specimens without fire-protection.

Temperature changes for the specimens with fire-protection as shown.In the case of fire-protection at the bottom flange, all of the specimens exhibited very low temperatures for 3 hours duration.

Figure 1.2.12 Figure 1.2.13




In the test under appl ied load, the fire-resistance rating would not be determined by temperature. However, the temperature is a very important factor in the member strength. And, some standards prescribe the temperature limit for steel members in the fire-resistance test without applied load. In this study, the time to temperature limitation for steel members was compared for reference. In specimens without fire-protection, the time to temperature limitation moderately increased as the cross-section size increased. Whereas, specimens with fire-protection exhibited very low temperatures regardless of cross-section size.

Deformation and deformation rate for the specimens without fire-protection are shown in the left figures. Deformation and deformation rate for the specimens with fire-protection are shown in the right figures. (In the case of fire-protection all the specimens exhibited very little deformation for 3 hours duration.)

Fire-resistance rating was determined based on the deformation and deformation rate. In specimens without fire-protection, fire resistance increased considerably as the load ratio decreased. (39 minutes in 100% load ratio, 46 minutes in 70% load ratio, and 95 minutes in 40% load ratio) Specimens with fire-protection showed excellent fire resistance regardless of the load ratio. (Referring to temperature and deformation, a fire-protection thickness slightly less than 44 mm could be used for 3 hours of fire-resistance.)

In this study, the fire resistance of the iTECH composite beam was evaluated by experimental testing using the ISO standard fire. The conclusions are as follows: In specimens without fire-protection, the time

Figure 1.2.18

Figure 1.2.19

Figure 1.2.20

Figure 1.2.21

56 M.Kim, S.Kim and S.Kang 57

to temperature limitation moderately increased as the cross-section size increased. Whereas, specimens with fire-protection exhibited very low temperatures regardless of cross-section size. In specimens without fire-protection, fire resistance increased considerably as the load ratio decreased. Whereas, specimens with fire-protection showed excellent fire resistance regardless of the load ratio.

56 M.Kim, S.Kim and S.Kang 57

Q&A session with invited speakers

Dr. SuzukiI realize now that Japanese and Korean high rises are somewhat different from each

other. In Korea, the lateral forces created by earthquakes are not as large as they are in Japan. Korean superhigh rises predominantly have an RC or SRC structure, while most of these types of buildings in Japan have an S structure. There's probably a difference in how we build our frameworks too. We also use different materials and structural modalities depending on the intensity of seismic forces that we design these buildings to. In turn, these differences lead to different approaches to fire resistant designs. I feel that these differences make for interesting discussions between our two countries.

Dr. KimIn Korea, requirements for high rises with 50 or more stories focus more on

withstanding wind loads than earthquakes. There's also a great interest in performance design from the perspective of rationalized design and economic efficiency. I think it's a great idea to compare and study the different methods used in our two countries.

Dr. SuzukiTo take this topic a bit further, I think there's more flexibility in Korea in terms of

how materials are used. The current situation in Japan is very rigid. I get the feeling that, in the area of performance design, we'll be seeing more interesting things come out of Korea than from Japan. I sincerely hope that Korea also pursues the path of performance designs.

Dr. KimThere's a great deal of interest in performance design in Korea. I hope to work with

the Architectural Institute of Korea to initiate some action.

Dr.OkaI've heard that your building law was amended in 2000 and that the new law requires

buildings to withstand fire for 3 hours. Why was this change made?

Dr. KimKorea experienced a large number of fires in the 1990s. These fires not only

caused property damage but great loss of human life. This was one of the reasons our government included the 3-hour fire resistance requirement in the new law.

Dr. IkedaDoes Korea have performance requirements as well as utility requirements? Do you

have standards for taking a mid-point between these two, albeit by reducing the factor of safety somewhat, as a way to ensure economic efficiency? If not, it would seem that you could run into some problems in the future.

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Dr. KimWhile the building law amendment of 2005 allows for performance requirements,

no specific groundwork has been laid for implementation and there are no cases where certification has actually been granted. We would like to investigate approaches taken in other countries to ensure that the amendment of 2008 allows for performance designs.

Dr. IkedaJapanese organizations have been doing quite a bit of research on CFT columns, so I

think we will be able to offer you information in this area.

Dr. SugaharaWhat I hear from Dr. Kim is that fire resistance is an issue that's close to the hearts

of the Korean people. What sort of discussions do you have in your country on this issue? Have you established any basic strategies? Also, my understanding is that Korea has a robust environmental strategy. What are your requirements in this area? Are buildings simply seen as a way to create space? Or would it be enough that they can be repaired, reinforced and reused to meet environmental requirements? Based on how the issues of environment and fire prevention are related, how do you envision the future?

Dr. KimWhile we do have basic frameworks in place for fire, seismic and wind resistance, we

have yet to create specific strategies in Korea, particularly in the area of fire resistance because we don't have enough researchers. In terms of the environment, there is an impetus towards finding ways to ensure both environmental friendliness and economic efficiency, but in reality, the environment often seems to take a back seat.

Dr. WakamatsuWe see that you are now working to establish performance requirements. Are there

any movements within the Korean government's construction related agencies or the executive branch to drive a concerted approach to rationalize fire safety programs?

Dr. KimMany people are working in this area. While meetings with government officials

at the operations level as well as various seminars and investigative trips to other countries have allowed us to share a common awareness, most people are still extremely cautious and reticent to take action. This is why we have yet to realize an amendment to the law.

Dr. WakamatsuJapan experienced a wave of building fires from around 1965 and these obviously

caused considerable damage. In response, the Ministry of Construction initiated a 5-year project to fundamentally reform our fire safety programs. This was then followed up with another 5-year project. So the performance design regime that we currently

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implement in Japan was developed over a period of 10 years. I get the impression that you've been through something similar in the early stages of your efforts.

Dr. KimI look forward to learn more on this subject through input and collaborations mainly

through the COE to advance fire research in Korea. I would like to thank you and look forward to your continued support.

behavior of itech composite beam in fire - experimental study

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