Design of CSUN’s Library Blamed for Quake Losses : Aftermath: Consultant says the facility’s two new wings lacked sufficient bracing to resist forces unleashed by the 6.7-magnitude temblor.

NORTHRIDGE —  The design of Cal State Northridge’s signature Oviatt Library was to blame for the heavy earthquake damage sustained by its two new wings, according to a consultant’s report that helps explain why the 1991 additions fared worse than the original library built in 1973.

Although the steel-frame wings complied with state building codes, they lacked sufficient bracing to resist the forces of the 6.7-magnitude quake, according to the report by John A. Martin & Associates of Los Angeles. In addition, the report questions why a series of crucial connections at the buildings’ foundations were designed to be their weakest link.

Officials at the hard-hit campus have adopted a $5- to $7-million plan to repair the library wings, the least expensive of 19 possible remedies outlined in the report. That course of action, which should take 18 months to complete, involves reinforcing dozens of key connecting points where the wings’ vertical steel columns join their foundations.

The Northridge campus suffered an estimated $350-million loss in the Jan. 17, 1994, earthquake, including damage to virtually every major building. Many have been repaired and reopened, including the original library that houses most of the stacks. But Oviatt’s new, four-story wings--the library’s main study space--are among half a dozen major facilities that remain closed.

The Martin report, completed in December but only recently released in response to repeated requests from The Times, is the second such survey to link severe earthquake damage at campus buildings to problematic design. In a report released last month, another consultant called the design of a collapsed parking structure on campus “conspicuously flawed.”

Although the library’s new wings did not collapse like the Zelzah Avenue parking deck, they were left perilously unstable when the earthquake’s forces snapped many connections at their key “base plates,” the thick, steel squares that held its girders in place.

As a result, city and campus building officials deemed them unsafe for public use, and their popular work stations have remained off limits for the last 15 months.

“It is apparent that a combination of high base plate stresses and lack of redundancy in braced frame overturning elements permitted the failures observed,” the Martin report said.

Martin engineers refused to comment on their report without the approval of campus administrators, who declined to give them permission. Likewise, the firm that designed the library wings, the Leo Daly Co. of Los Angeles--CSUN’s master-plan architects--did not return repeated phone calls seeking comment.

The Martin firm elaborated on the library damage in simpler terms in a separate report it prepared for the state Seismic Safety Commission.

“Current design codes allow the column base plates to be the highest stressed elements in the system, which also makes them the weakest link. Unfortunately, the base details utilized on this building . . . are not inherently ductile in nature and cannot absorb a great deal of energy before failure,” that report said.

Both Martin reports conclude that the design of the wings did not have adequate bracing elements meant to absorb earthquake forces. So when the powerful quake hit, the damage occurred in the weakest area--the foundation connections.

Other structural engineers interviewed by The Times also said the wings should have been designed with better bracing to absorb earthquake forces and relieve stress on the key base plate areas.

“Many engineers, including ourselves, have been making the base plates not the weak link for a while now,” said Mark Saunders, a San Francisco-based structural engineer. Saunders is part of a statewide group of professionals that has been studying the earthquake’s effect on steel-frame buildings.

Engineers scouring buildings throughout Los Angeles discovered that more than 120 steel-frame structures suffered cracked or broken welds during the temblor, raising questions about a contemporary method of construction that was previously thought impervious to earthquake damage.

The CSUN library, however, is the only building so far in which damaged base plates have been identified, according to state officials and private structural engineers studying the quake’s aftermath.

Several structural engineers interviewed said most of the documented problems occurred in “moment frame” steel buildings, which are different from the braced frame design used in the CSUN wings.

In the more flexible, moment frame buildings, the weld cracks were found in the walls, at the points of connection between vertical columns and horizontal beams that were meant to flex in a quake.

But at CSUN, the library wings were built according to a less-common, “braced frame” design that is more rigid because it relies on X-shaped steel bracing to connect vertical columns. Engineers said other braced-frame buildings sustained earthquake damage but none like the library wings.

Beefing up the bracing is the goal of the school’s repair plan, according to engineer Charles Thiel Jr., who is chairman of the Cal State University system’s Seismic Review Board and has been serving as the chief building official for the Northridge campus in the wake of the earthquake.

The repair plan calls for installing a continuous ring of steel bracing inside each wing’s fourth-floor wall to limit potential earthquake forces on the foundation connections. Campus officials also intend to re-weld the cracked, horizontal base plates and add vertical, steel reinforcing plates to bolster the columns’ connections to the foundations.

Although the approach is the cheapest of the consultants’ menu of recommendations, Thiel maintained that cost did not influence campus officials’ choice and that the plan of repairs was sound. “We wouldn’t have done a thing differently,” Thiel said.

The consultant estimated the cost of repairs at $4.2 million. But Bill Chatham, CSUN’s associate vice president in charge of facilities, predicted the total cost for the 90,000-square-foot wings would run about $5 million to $7 million.

Immediately after the earthquake, it appeared to campus officials that the original library-- designed under building codes that predated the 1971 Sylmar earthquake--had suffered more serious damage than the newer wings.

But within several weeks, as workers tore into the buildings, officials discovered the wings’ unusual structural problems.

The original concrete-frame core of the library, a four-story, 130,000-square-foot structure, sustained about $12 million damage in the quake, largely because of required asbestos cleanup. But there was no serious structural damage, and campus officials were able to reopen the building in time for classes to start last fall.

Nonetheless, the Martin report also noted that the repairs to the original library did not bring it into compliance with current building codes. The core building meets only 70% of the current requirements for resisting lateral earthquake forces. Yet Thiel and outside engineers contacted by The Times said that should pose no great reason for concern.

Because of the age of the original building, Thiel said it would have to be rebuilt to comply with the current code. For now, there is no state law requiring that older buildings meet new seismic-safety requirements.

Whether the library’s wings will comply with current, earthquake-safety standards is unclear. Although campus officials maintained the planned construction would bring them up to date, the Martin report says that only the immediate areas of repair will be brought into compliance “whereas the balance of the structure will not be affected in any way.”

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Repairing Failed Steel Columns

Officials at Cal State Northridge have settled on a plan to repair the steel-frame wings of the campus’ Oviatt Library, which suffered unique damage in the Northridge earthquake.

The Damage

Engineers were surprised to discover extensive disruption where the building’s vertical steel structural columns connected to its foundation. Main areas of damage identified by the engineers:

Bracing

Gusset Plates

Grout

Concrete

Anchor Bars

Base Plate

Nuts and Washers

Column

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The Fix

The repairs will cost an estimated $5 million to $7 million, and will completed in 18 months.

Columns: They will remain in place

Bracing: Existing bracing will remain. New bracing will be added to the 4th floor of library wings along their entire perimeter.

Gusset Plates: Existing undamaged gusset plates remain in place

Base Plate: Cracked areas in base plates will be rewelded

Grout: All grout will be removed and replaced

Concrete: Cracked or damaged concrete removed and replaced

New Gusset Plates: Steel plates will be welded on both sides of the column and base plate assembly, reinforcing the joint and helping transfer future stress and pressure to the base plate.

Anchor Bars: Bent bars straightened or replaced

Shear Key

Nuts and Washers: Damaged items to be replaced

Source: CSUN