Looking at the many photos online of the Oroville Spillway collpase that has been in the news, there’s one major component of concrete that should be there, but is blatantly absent:
Rebar (short for reinforcing bar), collectively known as reinforcing steel and reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and hold the concrete in tension. Rebar’s surface is often patterned to form a better bond with the concrete. Source
If there was REBAR in the spillway concrete, you’d see a mesh lattice of it left behind in the hole, or at least a few sticking out at odd angles. here are several photos, I don’t see any REBAR, do you?
ADDED: Here is a closeup view from our local newspaper,
clearly no REBAR visible:
(Upon magnification of this image it appears there is some in the debris, so the question is now, was it enough, or was the problem due to some other factor)
Source: http://media.chicoer.com/2017/02/08/photos-oroville-dam-spillway-dwr/#7 (h/t to commenter TonyL)
If REBAR was present, we likely would not see such a dramatic collapse as it would have prevented water pressure cavitation from eroding more and more concrete. Concrete is a material that is very strong in compression, but relatively weak in tension. To compensate for this imbalance in concrete’s behavior, rebar is cast into it to carry the tensile loads. This means concrete pulls apart much easier than it is crushable, but with REBAR the tensile force required to pull the concrete apart is greatly increased.
One wonders if that lack of REBAR on the spillway was by design, accident, negligence, or some cost-cutting measure like the lack of life-boats and cheap steel on the Titanic. REBAR in concrete was invented in 1849. It seems incredible to me that it seems to be missing from this very important structure.
OROVILLE, Calif. (AP) — State engineers on Thursday discovered new damage to the Oroville Dam spillway in Northern California, the tallest in the United States.
Earlier this week, chunks of concrete went flying off the emergency spillway, creating a 200-foot-long, 30-foot-deep hole.
Department of Water Resources spokesman Doug Carlson said officials will ramp up the outflow from the damaged site Thursday so officials can drain Lake Oroville.
Meanwhile, reservoir levels continued to climb behind the critical flood-control structure. Officials said it is at 90 percent of its capacity.
They said the dam is still safe and doesn’t threaten communities downstream.
“The integrity of the dam is not jeopardized in any way because the problem is with the spillway and not the dam,” said Eric See, a spokesman for the Department of Water Resources.
As a contingency, state officials are preparing to use the emergency spillway at the dam.
Crews have been clearing trees, rocks, and other debris from the hillside near the dam where water will flow.
Lake Oroville would naturally flow over this ungated concrete crest, into a mostly unlined emergency spillway if the reservoir reaches 901 feet elevation. This would be the first time the spillway has been used in the dam’s 48-year history although the reservoir came within 1 foot of flowing over in January 1997.