Thursday, June 6, 2013

Water Cooler Talk

As an office building owner, tenant or employee, you may have questions about the seismic safety of your building or work environment.  This may have been the topic of a water cooler conversation.  You may have asked, “Will my filling cabinet fall on me during an earthquake?"  Predicting a building and its contents response to an earthquake is nearly impossible.  In order to insure safety to building occupants, state building codes provide minimum guidelines for equipment and furniture anchorage.

2011 Tohoku Earthquake, Japan

ASCE 7 is the code that governs the seismic design of nonstructural components and their anchorage.  Specifically, Chapter 13, Seismic Design Requirements for Nonstructural Component.  As a minimum, the items listed in table 13.5-1 shall have positive anchorage to protect the life/safety of the building occupants.  These items include but are not limited to walls, ceilings, cabinets, equipment and fire sprinkler piping.

1994 Northridge Earthquake
Past earthquakes have shown that unanchored office file cabinets can present a major life/safety hazard during an earthquake.  File cabinets can topple over injuring people and trapping occupants inside the building.  The codes require that any permanent floor-supported storage cabinet, library shelving, book stacks and book selves over 6ft tall, including contents shall be properly anchored to prevent sliding and toppling during a seismic event.  Our recommendation is that any of these items over waist high should be properly secured.
1994 Northridge Earthquake
Some general FEMA guidelines for file cabinets are as follows;
1.       Do not locate file cabinets where their failure could block an exit door or exit corridor.
2.       Anchor file cabinets to the floor and/or wall to prevent toppling during a seismic event.
3.       Provide strong drawer latches to prevent drawers from sliding open.
4.       Do not place objects on top of file cabinets as they may be thrown off during a seismic event.
FEMA also provides anchorage details for cabinets up to 6 ft tall.  See below.  We recommend that you consult with your Structural Engineer to insure proper anchorage, especially for cabinets taller than 6ft.    
Wall-mounted file cabinets

Base-anchored file cabinets

Wall-mounted and base-anchored lateral file cabinets

Thursday, April 4, 2013

Seismic Safety - Water Heater Welfare

Every year we do several structural assessments of commercial and residential buildings.  Often, we see hot water heaters that do not have adequate seismic restraint.  This is something that is easily overlooked during construction or water heater replacement.  Unrestrained water heaters have broken loose or toppled creating serious threats of fire, explosion and electrocution in past earthquakes.

Unanchored Water Heaters Overturned During a Seismic Event
California has adopted Health and Safety Code Sections 19210-19217 to address these life safety threats.  The code states that:
  • Any new or replaced water heater sold on or after July 1, 1991 shall be braced, anchored or strapped to resist falling or horizontal displacement due to earthquake forces. 
  • The seller of any real property containing a water heater shall certify to the prospective purchaser that this section has been complied with. 
  • All water heaters manufactured for sale in California on or after July 1, 1991, shall include a statement in the instructions that the water heater must be braced, anchored or strapped to resist falling or moving. 
  • The front of the water heater shall have a label that states:                                               Warning: This water heater must be braced, anchored, or strapped to avoid falling or moving during an earthquake.  See instructions for correct installation procedures.

Since this issue affects every building owner and tenant in California, the Division of State Architects (DSA) has prepared some generic seismic restraint details.  The DSA details utilize two methods of bracing material:
  • Plumbers Tape Bracing
  • EMT Conduit Bracing
Water Heater Bracing Example, Division of State Architects
See DSA installation instructions

 The DSA details do not apply to every situation, but they are a minimal guide to start with.  There are other manufactured systems available.  Their installation instructions should be complied with.  We also suggest that you consult with a licensed Structural Engineer for any atypical situations or if you questions/concerns regarding your current water heater seismic restraint.  Remember, a loose water heater is a dangerous water heater!


Tuesday, March 5, 2013

Don’t Fear the Quicksand!

If you live in Newport Beach, CA, you may be living in a liquefaction zone.  Soil liquefaction is a phenomenon where saturated soil temporarily loses shear strength during an earthquake causing it to behave as a liquid.  (USGS has an animation that you can view here.) The liquefaction zones in Newport Beach include Balboa Peninsula, in and around Newport Bay and Upper Newport Bay, and in the lower reaches of major streams and the floodplain of the Santa Ana River.  The City of Newport Beach has recently developed minimum building standards to be followed if you own in one of these areas and want to build or remodel a home.  This policy is called “Minimum Liquefaction Mitigation Measures”.  It can be found on the City of Newport Beach website or click on the link above. 

Effects of liquefaction during the 1964 Niigata Earthquake
For a new home or an addition, the new foundation system must comply with these regulations.  An alternate solution is to arrange for a geotechnical investigation/report that directly addresses liquefaction and its mitigation.  The City regulations provides for five prescriptive mitigation solutions, as well as the option for a geological/engineered system, which will require approval by the City Building Official.
The five approved methods are as follows:

1.       Strengthened Slab-on-Grade Foundation System
2.       Structural Mat Foundation

3.       Post-tension Foundation System

4.       Caisson or Pile Foundation System

5.       Modified Soil Mat
In our experience, “Method 1. Strengthen Slab on Grade Foundation System” has been the most cost effective method to comply with these prescriptive regulations.  
These liquefaction requirements are often overlooked in the initial design phase of a project.  This oversight can lead to excessive delays in the permit process as well as construction cost overruns.   Moreover, for those owners that want to remodel or add on to an existing home, they need to be aware of the City’s “75% Rule”.  If the area of an addition, remodel and reconstruction is less than 75% of the area of the existing structure, the mitigation regulation is not applicable for the existing structure.  The existing foundations need not be modified.  Should you exceed this 75 % limit, there are two options.  One, use Methods 1 through 5 listed above, which means shoring the existing structure and constructing new foundations.  Two, use “Method 6 - Other Engineered Systems”.  Under this provision, LBSE has had success by underpinning and adding grade beams to an existing foundation system.
Our advice, retain Architects, Engineers and Contractors that understand the City of Newport Beach Liquefaction Mitigation Policy.  Experienced design professionals will always save time, cost and frustration during the construction of your dream house.