The building was built in 1989. It used the old code and was never improved accordingly to the new code. The new Taiwanese building code has more stringent earthquake requirements, since it was updated after the 921 earthquake (The 921 earthquake occurred on 1999 with a 7.6 magnitude earthquake, which caused over 2300 deaths). Since the 17 storey building was still based on the old code, the collapse explains the fact that surrounding buildings, which might have used the new code for construction or retrofit, are still standing. Therefore, the lack of adapting to the new code made the 17 storey building more susceptible to seismic forces.
Another engineering design issue was in the superstructure. The building was taller than other buildings surrounding it. The taller the building, the higher the moment will be when lateral seismic inertial forces are acted onto higher levels. Starter bars connecting the reinforced concrete columns and shear walls to the foundation must be designed for that additional stress. The building is also U-shaped and does not have a fourth shear wall “to hold the ends of the “U””. The asymmetrical layout of the shear walls can possibly induce torsional effects on the overall structure. However, torsional failure was not the main culprit as seen in these pictures. The whole building just overturned and collapsed. There was no twisting effect. But it is not to say that missing a shear wall is structurally acceptable. In the pictures, we can see that there are horizontal cracks on the walls. This is caused by lateral stresses from the seismic forces being localized in these walls. If we have that missing wall in the building, stresses can be distributed more evenly.
- Resist brittle failure, in particular vertical shear forces and diagonal shear cracks
- Prevent concrete aggregates from bursting out of the beam due to flexure
- Prevent flexural buckling of main longitudinal bars
And something is fishy here… Why would anyone want to enlarge pillars for decorative purposes? Enlarging pillars means reducing floor space, which most clients and architects hate. I rarely hear a client or architect request engineers to enlarge column sizes. It is usually the other way around for load bearing functions.
Although Taiwan has learned to put more stringent requirements for buildings after the 921 earthquake, it is not enough to make a law. They need to enforce it for each and every single suspicious building. Structural inspections should be consistent. Safety awareness should be promoted for earthquake damage prevention. Upgrades should be done to buildings to adhere to the current code, in order to retrofit the older buildings. Seismic retrofitting can include post-tensioning of high steel tendons, installing dampers, or slosh tanks. They are expensive but safety is always first!