Summer 2006 Forward to a Friend




Traveling the Crooked Road
Subaru Ring Shaped Reinforcement Frame
By Ron Moore



Sunset
B-pillars (the pillars between the front and rear doors) in today’s Subaru Forester feature short reinforcement rods (colored orange) mounted along the mid section. The reverse side is reinforced by a high-strength, high-tension steel plate (colored blue). These add to strength and rigidity, enhancing occupant protection.





Sunset
A B-pillar from a Forester involved in a collision shows eight layers of high-strength, high-tension steel.
Photo: Ron Moore






When I saw the pillar, it was clear that something was different about the Forester B-pillar construction. It was eight layers thick!

As an emergency service responder, I’ve noticed that occupants of late-model Subaru vehicles are surviving some pretty severe side-impact collisions with relatively minor injuries, if any at all. Although the doors may be jammed, the side of the vehicle probably held up really well.

During an extrication seminar I was conducting, several members of an area fire department approached me with a question and a challenge. They had encountered a Subaru Forester involved in a crash and were unable to cut through the B-pillar with any of their extrication tools. Their cutter and their reciprocating saw were both unable to sever the pillar. They actually went back to the junkyard the next day and used a gasoline-powered rotary saw with an abrasive blade to totally remove the B-pillar. They brought it to the seminar to show me.

When I saw the pillar, it was clear that something was different about the Forester B-pillar construction. It was eight layers thick! One of the layers was a round steel rod that resembled a concrete reinforcement bar (rebar). That B-pillar had more layers of steel than I had ever seen in a vehicle.

Another incident involved a four-door Subaru WRX STi. The Subaru collided with a minivan at an estimated speed of 75 miles per hour. The broadside impact required the rescue team to remove the roof. The Subaru A-pillars were cut through, but the B-pillars again resisted every effort by the fire department to cut them.

I was able to study this Subaru vehicle-construction feature in more depth. I learned that the reinforced B-pillars are actually just one component of what Subaru calls its Ring-Shaped Reinforcement Frame body structure.

RINGS OF SAFETY

The innovative Ring-Shaped Reinforcement Frame body structure provides certain Subaru models manufactured since model-year 2002 with some unique crash protection. It also presents us rescue workers with some unique extrication challenges.

The Ring-Shaped Reinforcement Frame is part of a structural body construction in which body side panels and the pillars around them are connected and reinforced to form three rings. The A-pillars and the front firewall structure make up one ring. Both B-pillars along with two structural frame members in the floorboard and two specially shaped structural members running across the roof area make up the center ring. The third ring is formed by the C-pillars and a strengthened lower rocker sill area. This construction design resists collision failure quite well and helps maintain passenger compartment integrity by dispersing the impact forces of the crash away from the occupants.

Rings of SubaruThe Subaru Forester Ring-Shaped
Reinforcement Frame body structure
includes the A-, B- and C-pillars.
The pillars appear perfectly normal, but their designs and the choices of steel used in manufacturing make them very substantial components for vehicle crashworthiness.








The rescuers in the previously mentioned incidents unknowingly attempted to cut the B-pillars at the point where they are intentionally the thickest and the strongest.
  SUBARU B-PILLARS

The Subaru Impreza, WRX, WRX STI, Forester, Legacy, Outback and Baja models all feature heavily reinforced B-pillars. The pillars appear perfectly normal, but their designs and the choices of steel used in manufacturing make them very substantial components for vehicle crashworthiness.

All the metal in the B-pillars is made of high-strength, high-tension steel. Boron is an example of this type of exotic metal. In addition, the individual roof pillars are made from metal pieces of varying thickness called tailored blanks. The B-pillars are cut and welded with a laser, then welded along their edges to form the eight-layer pillar.

The rescuers in the previously mentioned incidents unknowingly attempted to cut the B-pillars at the point where they are intentionally the thickest and the strongest. The round rebar steel rod is only a little over 12 inches long. It begins at dashboard level and ends at almost the height of the roof rail. In this same middle portion of the B-pillar are extra layers of exotic-metal steel – one on the inside surface and another on the outside. They further reinforce and strengthen the pillar.

A LOOK INTO THE FUTURE

The federal government is encouraging better vehicle side-impact performance and standards requiring better roof crush performance. So we’ll see more of these types of reinforced pillars as well as the increased use of exotic martensite (boron) high-strength, high-tension steels. Extrication techniques are constantly evolving to handle improved construction methods.
 

Editor’s Notes:

Ron Moore’s article first appeared in Firehouse Magazine. We reprint it here by permission of the magazine and Ron Moore.

This article was written before or shortly after the introduction of the 2006 Subaru B9 Tribeca, which is why it isn’t included.