Shake table test to examine the seismic performance of unit houses

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Hokkaido University

Shake table test to examine the seismic performance of unit houses

Ryosuke Matsuda, Taichiro Okazaki

Sapporo, Japan

Abstract

Recently in Japan, unit houses are considered to be used for various purpose like normal buildings. The purpose of this study is to examine the seismic performance of unit houses. 3 universities and 4 companies constituted a team for this test. We set two specimens on the shake table in Large-scale Earthquake Simulator in Japan National Research Institute for Earth Science and Disaster Resilience. We input seismic waves, 2 times larger than Japan Building Standard level 2 earthquake. That earthquake is defined as the largest estimated earthquake in the area. We measured acceleration, story drift, and strain of columns. Moreover, damages were observed after shaking. From the damage result, we confirmed that unit houses satisfy Japan Building Standards.

Keyword: shake table test, unit house, light-gauge steel.

Аннотация

ИСПЫТАНИЕ В СИМУЛЯТОРЕ ЗЕМЛЕТРЯСЕНИИ ДЛЯ ИЗУЧЕНИЯ СЕЙСМИЧЕСКИХ ХАРАКТЕРИСТИК МОДУЛЬНЫХ ЗДАНИЙ

Мацуда Рёсукэ, Таисиро Окадзаки. Университет Хоккайдо, Саппоро, Япония

В последнее время в Японии модульные дома используются для различных целей, как обычные здания. Целью данного исследования является изучение сейсмических характеристик этих зданий. Для проведения этого теста была собрана команда из 3 университетов и 4 компаний. Мы установили два образца на поверхность для встряхивания в Большом Симуляторе Землетрясений в Японском Национальном Исследовательском Институте Наук о Земле и Противодействии Катаклизмам. Мы воздействовали на образцы сейсмическими волнами, в 2 раза превышающими землетрясение 2 уровня в Японии. Такое землетрясение определяется, как самое большое оценочное землетрясение в этом районе. Мы измерили ускорение, движение этажей и напряжение колонн. Более того, повреждения наблюдались после встряски. По итогам разрушения мы подтвердили, что модульные дома соответствуют строительным нормам Японии.

Ключевые слова: тест в симуляторе землетрясений, модульный дом, легированная сталь.

Introduction

Unit houses are built up easily, because most of construction is done in factories. Main purpose of use is temporary building. Now, more type of use is considered in Japan. In this study, we did shake table test for unit houses which is already sold in Japan, and verified whether unit houses have enough resistance to earthquake, similar to normal buildings.

Test plan

We used SK 5700 [4.0 tsubo model], Unispace Series from FUJI SASH corporation, as specimens. This can be fordable and easy to move. Fig. 1 shows how to build up the unit. Putting up the roof part by crane, beam and column on the short side rotate and stand. The structure is rigid light steel frame with rectangular steel columns and cold forming beams. We can create larger buildings, connecting units to horizontal and vertical direction. After adding some parts and panels, it stands as a building, as shown in Fig. 2. Each panels are not included members to the structural calculation.

The shake table test was held in Large-scale Earthquake Simulator in Japan NationalResearch Institute for Earth Science and Disaster Resilience. The specimens are constituted 4 units connected 2 units horizontally and 2 units vertically. We put weight on second floor. That weight is 86% of building design load. We rotate specimens 90 degrees to verify the seismic performance of each direction. Fig. 3 shows setting condition of specimens. One has the long side in the shaking direction, another has the short side. We call former one house NE, and latter one house SW. Excitation tests ware done 9 times. The shaking wave was JMA Kobe NS. This earthquake occurred in Hyogo, Japan in 1993, causing great damage to various buildings. We changed the amplification in each shaking in the order of 10, 25, 10, 50, 10, 100, 10, 100, 10%. Fig. 4 shows the response spectrum to the shaking. 50% wave was a little larger than Japan Building Standard level 2 earthquake. Therefore 50% wave was equivalent to level 2 earthquake. This earthquake is defined as a rare and large earthquake which occurs once in building's lifetime or less. 100% was about 2 times larger than level 2. We put accelerometers on 1st floor, 2nd floor, 2nd ceiling, strain gages on each column on 1st floor to analyze shear force, and displacement transducers to measure the story drift. seismic column earthquake building

Results

The results of first 100% shaking are shown in Fig. 5. House NE's results are shown (a) and (b) They are results of relation between story drift angle and inertial force calculated from response acceleration and between story drift angle and column shear force from strain. Same results of house SW are shown in (c) and (d). When the story drift angle is smaller than about 0.01 rad, the response is linear. However, when the story drift become large, stiffness increases rapidly. About column shear force, columns in house SW resist only half of lateral force. On the other hand, in house NE, columns resist most of lateral force. Stiffness in house NE is higher than that in house SW.

In light steel structure, contribution of members, not of main frame such as panels, to resist force cannot be ignored. Speaking about the panel setting, top side was inserted to the gap of top beam. Bottom side was attached to bottom beam by screws. Panels do not resist force when there is no deformation. However, when the deformation of columns becomes larger, they start to resist lateral force. For this reason, the change of stiffness is explained.

Fig. 6 shows maximum story drift angle in each shaking

1st floor always deform more than 2nd floor. The reason is the difference of weight and similar stiffness of 1st layer and 2nd layer. Second 100% shaking caused larger deformation than first one. Focusing on house SW, north side deformed more than south side, because of the difference of opening area.

No damage was observed until after 50% shaking. After all shakings, there were several damages shown in Fig. 8. Particularly, sheet steel buckled around openings, and was tom off around screws. In addition, the damage of frame structure was observed in house SW. there were local deformation in top beams on short side, and welding cracks between bottom beam and column on short side. Fig. 7 shows the images of damage.

Figure 7. Damage (a) window panel, (b) wall panel, (c) short top beam, (d) short long beam to column connection, (a)~(d) corresponds to (l)~(4) in Fig. 8.

Conclusion

We did shake table tests to 2 specimens, connecting 4 units for each. There was no damage in the shaking equivalent to level 2 earthquake of Japan Building Standards. It is demonstrated that the unit houses satisfy the condition to be used for long term like normal buildings. However, after shakings which is 2 times larger than level 2, several damages were observed. Specifically, in frames on short side and panels. In addition, frames on short side resist less lateral force than frames on long side. For this reason, I conclude there is room for improvement of resistance mainly on short side structures.

References

1. FUJI SASH corporation. Unispace Series: SK Series,

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