Building Flaws Cited in Report on Quake : Seismic standards: Better enforcement of current codes could have prevented much damage, engineers find.

A team of engineers commissioned by the state to examine the effects of the Northridge earthquake has found that in many cases, failures of design, construction and inspection caused more damage than building code deficiencies.

Despite the widespread calls for tougher codes immediately after the Jan. 17 earthquake, case studies of 27 buildings yielded evidence that much of the typical damage could have been prevented by inexpensive measures to better enforce the current code, state officials said.

Faults pinpointed in the study included missing joint reinforcement, gaps in wood framing, discrepancies between a designer’s assumptions and actual field conditions, and a design that did not allow the proper distribution of seismic forces.

The report also shows that retrofitting helped prevent damage in some cases and not in others, depending on how well it was done.

Drawn in part from that study, recommendations being presented to the state Seismic Safety Commission today in Sacramento will focus primarily on how to ensure that the code is followed.

“Overall, the recommendation is that quality control--doing what we do, but doing it better--is the fundamental recommendation, rather than change the code,” said L. Thomas Tobin, executive director of the Seismic Safety Commission.

“We believe a good portion of the damage in the earthquake was due to a failure of quality control, either through design by the engineer or architect or plan checking, construction or inspection,” Tobin said.

Among the proposals will be a requirement that architects and engineers identify all seismic features in their plans and that local building officials specifically inspect those features.

Also, the commission staff will recommend that the architect or engineer personally inspect the project during construction.

“We have to get the best pair of eyes out on the job, the individual who designs the building,” said Fred Turner, the commission’s staff structural engineer. “Quite often, when you get out in the field, you may see the opportunity for improvements. You can resolve construction difficulties. You can even learn so your construction process is better.”

The study was coordinated by consulting engineers Rutherford & Chekene of San Francisco, which retained other engineers for the 27 case studies. A draft was shown to the Seismic Safety Commission in October.

Its findings, incorporated into staff recommendations that are expected to be adopted early next year, shed light on some of the most spectacular--and unexpected--building failures.

The team investigating the Bullock’s department store in Northridge Fashion Center, for example, found that it was designed with “an inadequate lateral system consisting of discontinuous shear walls” which, in effect, bounced up and down independently, punching through the concrete floor beneath.

The engineers concluded that had the earthquake lasted longer, the Broadway department store in Northridge Fashion Center could have collapsed because of the failure of columns around the escalators.

Those columns, which were not part of the building’s seismic apparatus, were unable to sway with the exterior frame and broke instead.

Other problems at the Broadway store included masonry walls that were poorly fastened to the building frame because of the difficulty of grouting such walls, causing them to move independently.

One code deficiency was noted in the separation of the Broadway’s roof from its walls. The engineers said the forces were great enough to have caused the failure even if the 1970 building had been designed to current code.

The incompatibility between systems that carry the weight of a structure and those designed to resist the lateral force of the earthquake noted at the Broadway was also responsible for the collapse of the Cal State Northridge parking structure, the report said. Non-seismic columns breaking in the interior of the garage pulled the exterior frame inward.

In several cases, engineers found that retrofitting proved ineffective.

The team investigating the Broadway store in Topanga Plaza said that a retrofitting project helped to keep damage within the design criteria of the building, but that “the inadequate attachment of the original construction walls to their foundation reduced the total resistance provided and led to significantly greater damage than would otherwise have occurred.”

In the case of the Bullock’s at Northridge Fashion Center, the engineer singled out an inadequate retooling of the plan improvised just after the 1971 Sylmar earthquake, while the building was under construction.

Extra shear walls were added, but consisted of “shotcrete,” concrete sprayed between existing columns. The walls were not fastened to those columns, causing the discontinuous load path.

One of the most perplexing findings was that damage often could not be explained by current seismic theoretical models.

The seven-story Holiday Inn in Van Nuys, for example, was most heavily reinforced in the lower floors, based on the assumption that they would be subject to the greatest seismic forces. However, damage to the red-tagged building was concentrated on the fourth and fifth floors.

The same pattern showed up in the Sherman Oaks Towers, a 12-story concrete frame building whose fifth floor was most seriously damaged.

Turner, staff structural engineer for the commission, called it “disconcerting” that the actual performance of buildings--including some that should have failed but did not--cannot be replicated by currently accepted theory.

“We can say that the general performance objectives of the building code were met,” Turner said.