Over the past years, many buildings have been collapsing and thus causing financial crisis because many earthquakes have been occurring around the world (USGS, 2013). For example, in the 11 March 2011 Japan earthquake, almost 300,000 buildings were destroyed and a further one million were damaged. The financial cost of the damage was 10.4 trillion Yen (approximately 132 billion Singapore Dollars) for just the destruction of the buildings. (BBC, 2012). Thus, the purpose of this experiment is to prevent the destruction of buildings and the resulting financial costs.
1.1 Background Research
Most buildings, even poorly-designed or poorly-built buildings, are able to withstand vertical load (“up-and-down loads”) so that they can carry their own weight and stay upright. However, buildings are usually unable to withstand horizontal load (“side-to-side loads”). (Reid, n.d.).
During an earthquake, there are both surface and body waves. Body waves are almost entirely responsible for destruction caused by earthquakes. Body waves include both primary waves or p-waves (longitudinal waves), which are compressional waves travelling faster than other waves through earth, and secondary waves or s-waves (transverse waves), which are shear waves and are slower than p-waves (about 60% the speed of p-waves). (UPSeis, n.d.). This means that the ground and the buildings shake both vertically and horizontally. As most buildings cannot withstand a lot of horizontal load, it causes the most damage to buildings and causes them to collapse.
Thus, there have been many measures put into place for buildings to be more earthquake resistant, such as using base isolation bearings, dampers such as the Taipei 101 Ball Bearing etc. Do existing measures actually work? Instead of adding additional things to the building, can the “skeleton” of a building be altered so that it can withstand more horizontal load?
Beams are often used in building architecture to withstand vertical gravitational forces. The loads carried by a beam are transferred to structural compression members (such as a column or a wall, etc.) which are connected it. The force is then transferred to adjacent structural compression members. During a large earthquake it is anticipated that the beams will undergo significant inelastic deformations and it is important for these beams to have a high energy dissipation capability and good stiffness retention. (Wight & Lesquesne, 2011).
Structural control through energy dissipation systems has been increasingly implemented internationally in the last years and has proven to be a most promising strategy for earthquake safety of the structures (Sophocleous, Phocas, 2012). Bracings are structures utilised in every building to support the weight of the buildings and can increase the capability to withstand the seismic forces during the earthquake whether it is by absorption of energy or holding the building in place. (Sarno, Elnashai, 2007).
Damper systems are designed to protect the internal structure and to prevent damages and injuries to the occupants by reducing the impact of the earthquake in the building. (Imad, n.d.). These systems are frequently used to dissipate the horizontal forces caused by an earthquake and stabilise the building by countering the vibration of the building. (Housner et al.,1997). For example, during an earthquake, as the building shakes to the left, the damper stays still as it has inertia. However, as the building shakes to the right, the damper will move to the left, countering the movement of the building. This counterbalances the vibrations of the structure.
An earthquake-resistant structure has been put to the test in a Mexican city. On 21 January 2003, the coastal region of the State of Colima, Mexico experienced a 7.6 magnitude earthquake. No damage was done to the building and occupants reported a far less severe quake while in the building. (Scot Forge, 2008).
1.2 Research Question
1. How do different types of bracings used in the construction of buildings reduce the horizontal load and damage to each floor during an earthquake?
2. How does the number of horizontal beams used for each floor affect the earthquake resistance of a building?
3. How does the damper affect the shake of the building on each floor?
Hypothesis 1: The greater the number of beams used to make up each floor, the less the acceleration of the horizontal shake of the tower.
Hypothesis 2: The “X” bracings work the best (least acceleration of the horizontal shake of the tower) as compared to no bracings and the “SLASH” bracings.
Hypothesis 3: If the damper is present, the acceleration of the horizontal shake of the tower should decrease.
1.3.1 Independent variable(s)
The 3 independent variables are:
1. The number of horizontal beams used to make each floor (“beam sets”)
Fig. 1. The beam sets that have been built.
2. The type of vertical bracings (sides of the tower)
Fig. 2. The bracings that have been built.
3. The presence of a damper
1.3.2 Dependent variable
The dependent variable is the acceleration of shake of the tower, recorded by the QCN software and sensors in the form of a graph.
The constants are
1. The position of the sensors on the tower
2. The amount of voltage (12 V) used to power the shake table
3. The direction that the shake table shakes (y-axis)
4. The materials used to make the towers and the height of the towers.