Earthquakes occur far more regularly than you realise: There is at least one earthquake somewhere in Asia everyday. Thankfully most passed without any incident, because they were small, occurred deep beneath the earth’s surface or in some remote corner of the region. But once in a while a nasty one strikes causing widespread death and destruction.
But it doesn’t have to be this way. Through improved design and construction of buildings and transport infrastructure, countries can avert the worst. As Jo da Silva, Head of Arup International Development, remarked at a public lecture, “Earthquakes don’t kill people, collapsed buildings do.”
Quake prone Japan knows this at first hand. Stringent building regulations were put in place after the devastating Kobe earthquake of 1995 that killed 6,400 people. By making buildings earthquake proof, even skyscrapers in Tokyo were spared when the 8.9 magnitude earthquake – the world’s fifth largest quake since 1990 – rocked Japan on March 11, 2011. While the buildings swayed causing several heart-stopping moments, no major damage was reported. The widespread destruction around the Fukushima region was caused by the tsunami triggered by the earthquake.
Keeping racks intact
For warehouses operating in seismic zones, it is prudent to take the added step of ensuring that racks stay intact even in an earthquake, though it is not a statutory requirement. The movement of the earth surface from the quake will apply additional pressures to the racking system, laterally side to side, from front to rear and with upward forces causing the racks to collapse and contents to be lost, it would be damaging for businesses and could be deadly for employees.
What do you have to do to secure the racking system? Broadly, you need:
Chemical anchors for all posts with deeper penetration
Reinforced uprights to withstand the added stress from ground motion with additional cross bracing
Bolted beams to reinforce the fixability of the connection to the racking system
A central independent bracing tower which absorbs the forces from the 3 directions
Diagonal bracing using wire rope cables for lateral movement of racks fixed to the bracing tower.
Front to rear additional bracing to the tower to help absorb front to rear forces
Fitment of wire mesh decking or pallet support bars to prevent pallet from falling which will add to the risk of rack collapse.
How much reinforcement the rack needs to withstand seismic activity depends on the location of the warehouse, whether it is in the low risk zone UBC 1 or in the high risk zone UBC 4. Other safety considerations for seismic design rack is the warehouse floor to which it is anchored which must also be design to the relevant seismic conditions and the type of soil underneath the concrete floor. Typically the acceleration force is dictated by the UBC code or in some cases by the countries building code.
Dollars and sense
Needless to say, the added reinforcements to cushion racking systems from the adverse effect of an earthquake come at a cost. But the cost of picking up the pieces after an earth-shattering experience is often much higher once you factor in the loss of inventory, downtime during the clearing up process, adverse effect on the supply chain and damage to the company’s reputation. Taking all these forces into the structural design of the rack, requires detailed knowledge of the properties of the racking system, with qualified engineers to undertake the study.
Past experience has shown some companies simply by adding some rear bracing or portalizing as “seismic protection”. We always recommend that customers employ a 3rd party to check designs and calculations to ensure that their additional investment is well spent.
As prevention is always better than cure, check out with your rack supplier what’s best for your warehouse.