A large-scale model of a nonductile concrete frame with columns susceptible to shear failure was retrofitted with two strengthening schemes. In the first scheme, full-height concrete piers were added to the original columns. Tests showed that the strengthened column section behaved monolithically and the failure mode was shifted to hinging of the spandrel beams. Large increases in frame strength and stiffness were also realized. In the second scheme, a steel X-bracing system was attached to the frame's exterior face. Lateral capacity was governed by yielding and buckling of the braces. The system exhibited substantially increased frame stiffness and strength. Both systems were quite constructable and relied extensively on epoxy-grouted dowels. The pier system required a lower level of construction skill but was somewhat more labor intensive. The bracing system required a higher level of construction skill due to local variations in fit-up requirements and the need for field welding.

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The December 23, 1972, earthquake in Managua, Nicaragua caused extensive damage to structures throughout the city of Managua. There was damage to virtually every building in Managua, a city of approximately 400,000 inhabitants. An estimated 10,000 people were killed, mostly in the collapse of homes built of native taquezal construction. The city contained numerous reinforced concrete structures designed to recent standards. Although many of these buildings were heavily damaged, with some collapses, some had only minor damage. There were also several structures of structural steel. The paper provides an overview of structural effects and discusses the performance of selected buildings in Managua illustrating the range of performance of modern construction. Damage to numerous other buildings will be discussed. The paper, while emphasizing the structural effects on buildings, also discusses the performance of non-structural elements, mechanical equipment, etc.

The use of terra cotta as a cladding material emerged in the 1880s and began to decline in the late 1930s. During this period, high-rise buildings employing terra cotta cladding included no provisions for differential movement between the cladding and structural framing. Numerous terra cotta clad buildings are showing signs of distress due to weathering and induced stresses from frame shortening under load. Determination of residual compressive stresses within the terra cotta cladding is often necessary for evaluation and repair of the distressed material. The level of stresses induced in the cladding of a high-rise building in San Francisco was measured by performing strain relief tests. Uniaxial strain gauges were adhered vertically to the face of the terra cotta blocks and initial balance readings were obtained. The mortar bed joints were sawn along the terra cotta units and the strains monitored during and after the cutting. Samples of the terra cotta block were cut, instrumented, and tested in compression to determine elastic properties and ultimate compressive strength. Having obtained the physical properties of the terra cotta, compressive stresses due to frame shortening in the structure were determined. Strain data obtained indicated stress levels which were low enough to eliminate the need for stress relief. Optimum saw cutting locations were determined had stress levels been high enough to require stress relief.

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