Appeal from the Circuit Court of Cook County; the Hon. John A.
Nordberg, Judge, presiding.
JUSTICE LINN DELIVERED THE OPINION OF THE COURT:
Plaintiff, Paul Gabrenas, brought a tort action in strict liability against defendant, R.D. Werner Company, Inc., seeking to recover damages for injuries caused by a defectively designed ladder stabilizer that was designed, manufactured, and sold by defendant. Following a jury trial in the circuit court of Cook County, a verdict for plaintiff in the amount of $89,292.96 was returned and judgment was entered thereon. Defendant appeals, arguing that (1) the trial judge erred in permitting plaintiff to present testimony during rebuttal that did not in fact rebut testimony of any defense witnesses but did present a new theory concerning the defect in the ladder stabilizer, and (2) the verdict was contrary to the manifest weight of the evidence.
Plaintiff worked as a janitor in the building where he lived in LaGrange, Illinois. He purchased an R.D. Werner aluminum extension ladder in 1968. In 1970, he purchased a Model 75 Mark I Sta-Safe Stand-Off ladder stabilizer, which was designed, manufactured, and sold by defendant. He assembled the stabilizer, and never took it apart. He used the ladder with the stabilizer twice a year to install and remove window screens.
On June 18, 1974, plaintiff attached the stabilizer to the ladder and installed 34 to 36 window screens. After a dinner break he went to the courtway of his building to install two remaining screens. He placed the ladder against the building with the base five feet away on ground that was soft on the surface but hard just beneath the surface. Two feet to the right was a wall perpendicular to the wall against which the ladder was leaning. The arms of the ladder stabilizer rested immediately below the window sill where plaintiff was going to work, a little more than 10 feet above the ground.
Plaintiff tested the ladder by stepping on the first two rungs to make sure both legs were resting firmly and evenly on the ground. He climbed the ladder and cleaned the sill, descended to get a silicone spray, climbed up again to spray the screen track, and descended again. He picked up two screens in his left hand and climbed the ladder a third time, stopping on the third or fourth rung from the top. As he began to install the screen on the left he felt a sensation of movement to the right, forward toward the building, and downward. He turned to look; the next thing he remembered was lying on his back on the ground with the ladder on top of him, the stabilizer arms up in the air.
Plaintiff suffered a comminuted fracture of the right humerus near the shoulder. A physician who had examined plaintiff testified that at the time of trial the fracture site had healed, but there was considerable overriding of bone and a resulting 3/4-inch shortening of the arm, a one-third loss of normal movement, chronic pain, and severe degenerative arthritis.
After he came home from the hospital, plaintiff examined the ladder stabilizer. "It was broke, bent up, sheared through at the top bolt hole on the right-hand side, but still confined to the rest of the unit by a crossbar."
On June 18, 1976, plaintiff filed a strict liability suit against defendant. As amended, the complaint alleged that the stabilizer was defective and unreasonably dangerous because it failed to stabilize the ladder when used in a reasonably foreseeable manner; it failed to support reasonably foreseeable loads and stresses; the tubing was severely weakened by bolt holes; the bolt holes were placed in an area where stresses are concentrated; the bolts did not fit the bolt holes adequately; the bolt holes were ragged and bolt fittings loosened with use, thereby increasing stress concentrations; the bolts and nuts faced directly into the tubing, thereby increasing weakness; bracing was inadequate; there was no clamp to keep the stabilizer centered on the ladder; the stabilizer lacked an adequate safety factor; and the stabilizer forced the user to lean to one side of the ladder. The complaint further alleged failure to warn that the stabilizer had a propensity to become distorted, bend, break, or otherwise fail.
At trial, plaintiff called Marvin Salzenstein, a mechanical engineer, to give expert testimony about the defective condition of the ladder stabilizer. In November 1981, Salzenstein had examined the fractured stabilizer, a new model 75 stabilizer, all the drawings that defendant had provided for that model, a metallurgist's report on the strength of the material, and a Werner model 77 stabilizer. He also photographed the fractured stabilizer. The purpose of his examination was to determine where and how the failure occurred and whether the stabilizer was adequately designed for its anticipated use. He concluded that the stabilizer design was inadequate; while the ladder was in an upright position the right arm bent toward the user of the ladder and then fractured across two of the bolt holes that held the arm to the bracket. The fracture caused an instability that permitted the ladder to collapse. He stated that the appearance of the fracture surface was inconsistent with the theory that the ladder slipped and slid down the wall to the right and that the stabilizer fractured when the arm hit the ground. He stated further that because of the wall beside the window where plaintiff was working, it would have been impossible for the ladder to slip to the right and fall in that manner.
Salzenstein testified that when a ladder stabilizer is in use the weight of the user and the reaction force from the stabilizer bearing against the wall create stress forces that are transferred entirely through the structure of the stabilizer and the ladder. The presence of bolt holes reduces the area available to carry the load and also concentrates stress factors around the holes. The stress concentration in the stabilizer in question was three or four times greater near the edge of the hole than in an area unaffected by the hole. Using a metallurgist's report on the yield strength of the aluminum of the stabilizer and applying a safety factor of four, Salzenstein had determined that the maximum allowable stress at the bolt holes was 7,500 pounds per square inch. After correcting an earlier error in his calculations, Salzenstein testified that the actual stress at the bolt holes had been 10,000 pounds per square inch, which exceeded the maximum safe amount.
A further problem, Salzenstein stated, was that the stabilizer design included space between the bolts and the holes. Where cyclic loading occurs, the loose fasteners will "rack," or wobble, causing "fretting," which will lead to microscopic cracking and ultimate failure. Another design defect was the use of threaded bolts, which increased the friction between the surfaces and hastened destruction. Salzenstein had found evidence that racking and fretting had occurred at the bolt holes on the stabilizer in this case. His opinion was that the stabilizer was in an unreasonably dangerous condition as a result of its design, that this condition was the proximate cause of the fracture of the arm at the bolt hole, and that this fracture was the cause of plaintiff's fall.
Defendant called two expert witnesses. Gene Litwin, a mechanical engineer, stated that he had examined the broken stabilizer and a new stabilizer of the same model, and reviewed defendant's design specifications. Litwin testified that he had found errors in Salzenstein's calculations and conclusions that discredited Salzenstein's opinions. He challenged Salzenstein's stress calculations, stating that a stress concentration factor of 1.25 should have been used. He admitted on cross-examination that this factor would be substantially increased if the bolt did not fit the hole. His "best estimate" was that under the conditions at the time of plaintiff's accident the maximum stress concentration would be 7,321.5 pounds per square inch. Litwin's calculations indicated "a proper and adequate safety factor" and led him to "the conclusion that the product is adequately and safely designed and one would not expect failures in normal usage." His opinion was that "the fracture was ...