the earthquake and curtain walls

7/28/2019 The Earthquake and Curtain Walls

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THE EARTHQUAKE AND THE CURTAIN WALLS


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Introduction

We are all aware o the extent o devastation caused by major earthquakes to the constructions

and particularly to the buildings, as well as o the impact o such devastation on a personal or nationallevel resulting rom the loss o human lie and rom the material and economic damages

This is the reason why such great numbers o Scientic Organizations, Universities, Research

Centers and Institutes are studying the seismic protection o buildings, aiming mainly at the

construction o buildings whose the structural elements are capable o resisting the loads o major

earthquakes, thus reducing the risk o collapse

The problem o efectively reducing the seismic risk by the construction o earthquake resistant

buildings is particularly complex, since it is afected by large numbers o parameters and many

other actors

To begin with, there is the earthquake with its characteristics (range, distance, direction, depth o

epicenter), which, combined with those o the soil on which the building is ounded (composition,

condition, moisture) result in the earthquake magnitudes charging the building (acceleration,

speed, duration, requency o vibration) On the other hand, there is the building itsel receiving

the seismic orces and resisting to them depending on the characteristics o its structure (building

geometry, orm, mass, structural elements arrangement, rigidity, undamental period o vibration

etc)



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The structural rame o a building is the main load bearing element It is this structural rame

which rst receives all seismic orces and reacts to them The degree o the building’s survival over

an earthquake depends on the reaction and the overall behavior o the structure to the loads

created by the earthquake orces

Besides the building structural rame there are additional building components which are

placed onto the structure reacting parallel with it to the earthquake orces according to their own

characteristics It is widely accepted that the unctional capability o the building ollowing an

earthquake and its rating as habitable or not requently depends on the extent o damage caused

to such additional building components, irrespectively o the act that the structure may have

been unharmed

Among the non structural components o a building the most important are considered to be

the building envelope components and specially the glass curtain walls, which compared with all

other components, present the greatest degree o vulnerability during an earthquake

This high vulnerability o glass curtain walls is due to the act that glass panes are unable to

ollow the deormations imposed to the building structure by seismic orces in the course o an

earthquake and to adjust to the interstate drit More specically, they are unable to adjust to

displacements parallel to their surace, since the glass panes cannot deorm to this direction

However, and irrespectively o the act that the building structure may have survived

undamaged ater an earthquake, as already mentioned, the ragility o glass panes particularly

against hits and pressure applied onto their edges, makes them being the rst among the other

açade components that are destroyed

The elements more strained by the seismic orces due to seismic acceleration and the interstorey

drit are the anchoring o the curtain wall rame on the structure o the building




General picture of deformation

and the interstorey drift (δ)

Figure 1A shows the deormation and the

interstorey drit (δ) caused to the building

structure between two adjacent storeys in

the course o an earthquake It shows the

oor slab o the storey reerred to (11), the

roo slab o the said storey or oor slab o the

storey above (12) and the columns o storey

(13) under conditions o calm (no tremor)

Figure 1B presents the deormation

o elements and the interstorey drit (δ)

between slabs o the two storeys (14) under

conditions o seismic impact

Figure 1C presents the same section o the

building structure along with the structural

rame o a conventional curtain wall system,

under conditions o calm (no tremor), while

Figure 1D reers to the same elements as

above under earthquake conditions, during

which the structure o the curtain walls

ollows the deormation o the building

structure

Figure 1E presents the same structure asthat o Figure 1C, with the addition o glass

panels, under conditions (no tremor), while

Figure 1F reers to conditions o seismic

impact and shows that the glass panels ail

to ollow the deormation o the curtain

walls structure supporting them



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NOTE

Whatever will be described

below for interstorey drifts

during an earthquake, it also

applies in high rise buildings

for displacement due to high

wind loads during hurricane.

Figure 1F indicates why the glass panes are

susceptible to break, as they cannot ollow the

deormation o the curtain wall structure in adirection parallel to the surace o a conventional

curtain wall system which consist o continuous

vertical beams (mullions) and o short horizontal

beams (cross-beams) xed in-between the

vertical ones

The problem becomes more

serious when the glass panes are

bonded directly to the mullions,

a usual application in structural

glazing.

In this case there is no margin

for movements of the glass panes

in respect to the mullions resulting

in glazing breakage even in minor

earthquakes.




The confrontation of Seismic problem

To be earthquake resistant, a glass curtain wall should be capable of totally absorbing the

interstorey drift (δ) occurring in all directions between the adjacent storeys, while its components

should be capable of withstanding, without any permanent deformation, the accelerations (g)

developed in the course of the earthquake, irrespectively of the tremor spectrum.

This capability should be a requirement o all glass curtain walls at any level and in any direction, o

corner walls at any corner, edge or setback, corner walls between buildings, as well as o curtain walls

carrying unied glass panels rom one oor to the other oor

In addition, the seismic resistance o the glass curtain wall should not afect its unctional capacity

or its air- and water-tightness and it should not reduce its strength against wind pressure and other

external orces ater the termination o the earth tremor

All the above may be achieved by means of a functional separation of the glass curtain wall of

each storey from those of adjacent storeys, upper or lower, in a way ensuring that the drift of the

curtain wall in each storey will be independent of that of curtain walls over the other storeys.


the earthquake and curtain walls

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