Seismic performance analysis of the hottest glass

Seismic performance analysis of glass windows and glass curtain walls

in the 8.0 magnitude earthquake in Wenchuan on May 12, the buildings suffered huge losses The earthquake disaster investigation shows that there is a clear correlation between the damage of glass fixed window and the damage of main structure In the earthquake, as long as the main structure has not collapsed, the glass curtain wall is basically intact. At present, no cases of earthquake damage to the curtain wall have been found

I. overview

1.1 fixed windows and curtain walls

fixed windows and curtain walls are maintenance structure systems composed of panels and supporting structures that have been preliminarily successful in the field application test of controllable fully biodegradable plastic film in Pingquan County, Hebei Province The difference is that the fixed window is usually embedded in the plane of the column or wall, which must have the same lateral displacement as the main structure during the earthquake; The structure of the curtain wall allows a small relative displacement between the curtain wall and the main structure, or makes the curtain wall itself have a large deformation capacity, which can withstand the lateral displacement of the main structure during the earthquake

therefore, the destruction of glass windows is relatively common in all previous major earthquakes. Fixed windows installed in buildings with serious cracking, damage or obvious sideways frame often have distorted window frames, broken glass and scattered; In the same state, the curtain wall in the building has little earthquake damage and is often intact

most of the glass windows in the remaining buildings of the 1976 Tangshan earthquake were damaged, leaving only empty openings There are a large number of reports of earthquake damage to glass windows in the 1995 Kobe earthquake in Japan and the 1999 Taiwan earthquake; Although there are many buildings with curtain walls in Osaka, Kobe, Taichung, Tainan and other cities, GH craft1 has directly provided all possible technical support for the University of technology solar racing team, there are no reports of earthquake damage to the curtain walls in the remaining buildings after the earthquake

in the Wenchuan 8.0 earthquake, Wenchuan, Beichuan, Deyang, Mianyang and other cities that experienced strong earthquakes, the seismic performance of glass windows and glass curtain walls showed the same regularity as previous major earthquakes

1.2 estimation of lateral displacement

it is impossible for us to actually measure the plane internal displacement of glass windows and glass curtain walls in earthquakes However, by observing the structural damage of the plane where the glass window and curtain wall are located, it is possible to estimate the maximum horizontal displacement they have experienced during the earthquake

the damage condition of brick wall is the most applicable measure Not only is the brick wall the most widely used, but also the damage degree of the brick wall has a good correspondence with its horizontal displacement Over the years, a large number of performance tests of masonry structures have been carried out. For unreinforced brick masonry, the basic law is:

the horizontal displacement angle is less than 1/800, the brick wall is intact

1/800 ~ 1/500 slight cracks 1/500 ~ 1/300 serious cracks 1/300 ~ 1/150 serious damage, brick falling, local collapse is greater than 1/150 collapse. Therefore, We can estimate the horizontal lateral displacement of the plane with reference to the damage degree of the brick wall in the plane where the window and curtain wall are located, so as to determine the working performance of the window and curtain wall under this displacement

second, the working performance of fixed windows in earthquakes

in different surviving buildings, the degree of earthquake damage is different, and the performance of the corresponding glass windows is also different

2.1 buildings with no seismic damage to the main structure

when the main structure is intact and the load-bearing brick wall or infilled brick wall does not produce visible seismic damage, it can be considered that its horizontal lateral displacement is not greater than 1/800 At this time, the glass window is generally not damaged

the teaching building of Sichuan Agricultural University in Dujiangyan City is in good condition, and its glass windows are also in good condition Qingchuan's earthquake intensity is high. Patients in the ward building of traditional Chinese medicine hospital should be hoisted from the window to save themselves, but the brick wall is intact. It can be judged that the earthquake has little impact, and the glass window is also intact

2.2 buildings with slight cracks in the main structure

when a small amount of fine cracks appear in the load-bearing brick wall and frame infilled wall, or the brick wall has no cracks, and only a slight collision occurs on both sides of the expansion joint, it means that the horizontal displacement is within the range of 1/800 ~ 1/500 In this case, the fixed window is generally not damaged by earthquake, and the glass will not break The expansion joints of some high-rise buildings in Xi'an City in Shaanxi Province affected by the earthquake slightly collided, and the face bricks fell, but the glass windows were not injured A similar situation can also be seen in Wenchuan, the epicenter of the earthquake

in the two buildings located in Hanwang respectively, obvious cracks have appeared in the outer wall of Dongqi primary school, and the face bricks have fallen, but the glass windows have not been damaged Dongfang turbine factory in Hanwang Town, Mianzhu City, is a large machinery manufacturing enterprise in China. This time, it was seriously affected. Many workshop roofs fell down, but the longitudinal walls of the workshop are generally well preserved, showing that the displacement in the plane is small, and the lighting windows are basically intact The teaching building of Wenchuan Juyuan Middle school collapsed completely, but the dormitory building was less damaged by the earthquake, and the glass windows remained intact

2.3 buildings whose brick walls have been seriously cracked

when a large number of coarse cracks, even very coarse cross diagonal cracks, have appeared in the brick walls, it indicates that the buildings have suffered repeated horizontal movement in the earthquake, and the displacement has reached 1/300 In this case, the window glass will break a lot

2.4 buildings with severely damaged brick walls and frame structures with large lateral displacement

when the lateral displacement of brick walls exceeds 1/300, large damage, brick falling, and even local collapse will occur At this time, the window frame buckles, bulges, and even throws out, and the glass is basically broken and scattered, leaving only the window opening on the wall

the beam column section of frame structure is small, and the horizontal displacement is generally large in earthquake In a frame of Dongfang turbine factory in Hanwang Town, Mianzhu City, the column head of the bottom floor was damaged, the frame was greatly deformed, and the indoor and outdoor glass was almost broken When the displacement is greater than 1/150, the brick masonry structure collapses and the glass window disappears

2.5 damage caused by out of plane displacement

in addition to a large number of damage caused by in-plane deformation, there are also some damage caused by out of plane displacement. The roof of the ward building of Qingchuan traditional Chinese medicine hospital slides outward, pushing the glass window out of plane deformation, causing the top glass window to break and scatter, while the glass windows of other floors are intact

2.6 the damage degree of the movable window sash is relatively light

the casement window sash is often in the open state during the earthquake. At this time, the window sash is not in the plane of the wall and is rarely squeezed by the wall deformation, so the casement window sash in the open state is not much damaged

the sliding window sash can slide horizontally. Even when the building deformation is large, it can have a certain degree of relative displacement relative to the window frame. The actual deformation is smaller than the window frame, so the damage degree is smaller

2.7 deformation resistance of fixed windows

from the performance of glass windows in the Wenchuan earthquake, it is possible for fixed windows to withstand the interlayer displacement angle of 1/500 without damage; Even if individual projects may have glass cracks, the number of broken will be very small

the reason for this is that during construction and installation, the wall is generally reserved for the door and window first, and then the doors and windows are installed There will be a gap between the window frame and the opening, and there will also be a gap between the window sash and the window frame. They can absorb some deformation, which can slightly improve the earthquake resistance of the window

III. performance of curtain wall in Wenchuan earthquake

3.1 deformation performance of curtain wall

due to the structural characteristics of curtain wall itself, it can withstand large in-plane deformation without damage The in-plane deformation test of curtain wall in many projects shows that the curtain wall that meets the design requirements of the code can withstand the in-plane horizontal displacement of 1/100 storey without damage, and even can withstand greater displacement

we have carried out many shaking table tests of curtain walls, using glass, stone, aluminum plate, ceramic plate, microcrystalline glass, stone powder plate and other man-made panels as panels The acceleration of these curtain walls on the table is 0, followed by Africa and the Middle East At 7 ~ 0.9 (equivalent to the intensity of about 9 ~ 10 degrees), the displacement angle reaches 1/70 ~ 1/50, and it can be kept intact without any damage These test results show that the curtain wall has much larger in-plane deformation capacity than the fixed window, and can be protected from earthquake damage in higher intensity earthquakes

3.2 performance of curtain wall in Wenchuan earthquake

so far, we have not received reports of earthquake damage to the curtain wall on the houses that have not collapsed in the epicenter area, This is similar to the Hanshin earthquake in 1995 and the Taiwan earthquake in 1999

the reason is very clear. When the curtain wall reaches its tolerable limit of in-plane displacement angle of 1/70 ~ 1/50, most of the main structures have collapsed Therefore, it can be said that as long as the house does not fall down, the curtain wall will not be damaged, and there will be some slight damage at most in individual cases

it is reported that in Beichuan, the worst hit area, among the ruins, Liu Han hope primary school is still standing, and the ten meter long, three story glass curtain wall has not even broken a piece of glass This cannot but be regarded as a miracle of the glass curtain wall

from the example that the curtain wall of buildings located in the epicenter area can be maintained in good condition, the above view that the curtain wall has good seismic resistance is convincing

3.3 comparison of seismic resistance of glass curtain wall and other building components

if there are glass curtain wall and other building components in a building, and they suffer the same earthquake, then the seismic resistance of curtain wall and other components is comparable It can be seen from many examples in the earthquake that when the brick wall, fixed window and face brick have suffered obvious earthquake damage, the curtain wall of the same building is intact

IV. summary

from the current preliminary understanding, the seismic resistance of fixed windows is quite different from that of glass curtain walls

for the fixed windows in buildings that did not collapse in the strong earthquake area, the damage degree of glass varies greatly, depending on the lateral displacement of the main structure When the displacement angle of the inner side of the plane is not greater than 1/500, the window glass is expected to remain intact; When the displacement angle is greater than 1/300, the damage is very serious

the displacement resistance of glass curtain wall is much greater than that of fixed window In an earthquake, as long as the main structure has not collapsed, the curtain wall can generally remain intact The performance of glass curtain wall in Wenchuan earthquake fully reflects this law We have reason to believe that as long as we carefully design and construct according to the requirements of the specification, the curtain wall can meet the requirements of intact in small earthquake, repairable in medium earthquake and not falling out in large earthquake

it is reported that in Beichuan, the worst hit area, Liu Han hope primary school is still standing among the ruins, with a length of more than ten years