nisee

National Information Service for Earthquake Engineering
University of California, Berkeley

      The importance of construction aspects has been discussed in Importance of Construction and Maintenance and in Refs. 12 and 13.  Field inspection of the performance of structures during earthquakes has revealed that a large percentage of damage and failure has been due to poor quality control of structural materials and/or poor workmanship - problems which could have been corrected if the buildings had been carefully inspected during construction.  Examples of observed damage due to poor workmanship are illustrated in Slides J102-J109.

      For the main building column and shear walls a normal weight concrete was specified using natural aggregates with f’c = 345 kilograms per square centimeter.  The concrete for the floor slab was specified to have f’c = 210 kilograms per square centimeter and to be a lightweight concrete using expanded shale lightweight aggregates.  In the actual construction the lightweight concrete specified for the slab was also cast through the normal weight concrete of the shear wall, thus creating a discontinuity in the equality of concrete over the height of the shear wall.  The weaker layer of lightweight concrete was crushed by the harder and stronger normal weight concrete, inducing the failure shown in this slide.

      Note the large distortion of the first soft story columns (one of the corner columns underwent 0.81 meters of lateral displacement in a clear height of about 4.27 meters, resulting in an interstory drift index of 0.19) and the complete disruption of the concrete in the poorly tied (confined) corner column, while the concrete in the spirally reinforced concrete core of the other columns remained intact for most of the height.  However, as illustrated in the close-up of Slide J104 and particularly J105, as a consequence of poor workmanship and poor (or complete lack of) inspection, the lateral resistance capacity and particularly the energy dissipation capacity of a large percentage of these spirally reinforced concrete columns was greatly reduced due to a premature ending of the spiral reinforcement at the top of the columns.  The spiral was ended before reaching the spandrel girder, leaving this critical region of the column (the top and here the plastic hinge formed) without any lateral confinement and therefore greatly reducing its energy dissipation capacity.

      The structural system (used in Slide J106) consisted of thick (0.25 meters) reinforced concrete flat plates used as the floor system, supported on reinforced concrete columns and shear walls.  The building was almost square in plan, but the arrangement of the effective shear resisting walls was asymmetrical [in the upper stories they were located chiefly in the south and west faces (walls); and in the bottom three stories shear walls were also added in the two south bays of the east facade as illustrate in this slide].  As a consequence of the large eccentricities between the center of mass and center of rigidity (which was accentuated by the use of very heavy precast concrete non-structural panels on the north and east walls), large torsional forces and deformations were induced during the earthquake.  These torsional forces and deformations (which can be seen in this slide) caused the failure of the shear walls at floor level due to poor detailing and workmanship of the anchorage for the non-structural precast panels.  Note the weakness introduced in the shear walls at the second and third floor levels of the east facade, and how this weakness led to the failure and significant shift of the second story wall with respect to the first story.  Although some of the panels were still attached to the building after the earthquake, as can be seen in this slide, most of them broke loose from the building and fell into the sidewalk and street, killing two people and destroying several cars [7].

      The dramatic collapse of the upper four stories of the building in Slide J107 was a consequence of poor selection of the structural layout (large eccentricity), the use of unnecessary masses (heavy precast panels at the east and north facades), and poor detailing and particularly poor workmanship in the anchoring of the precast elements to the structural system.

Considerable honeycombing was observed with complete lack of mortar in many of the columns of the buildings in Slide J108.  It was possible to break away large parts of concrete with just a screwdriver or a kick with a boot as was the case illustrated in this slide.  Adequate attention was not given to concrete mixing, placement, consolidation, and/or curing and in the placement of the steel reinforcement.  This poor quality control of materials and poor workmanship contributed significantly to the catastrophic collapse of these buildings [4].

The University of California, Berkeley
Copyright 1997, The Regents of the University of California.
Structural Engineering Slide Library, W. G. Godden, Editor
Set J: Earthquake Engineering, V. V. Bertero

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