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Next: 3.0 EXPERIMENTAL RESULTS Up: Seismic Cladding of Walls Previous: 1.0 INTRODUCTION

2.0 DESIGN OF EXPERIMENT

This project was motivated by the owner's desire to seismically upgrade the Rivera Library Building on the campus of the University of California at Riverside. A photograph of this four story building is shown in Fig. 2.

  
Figure 2: Rivera Library at UCR
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This building has a 41 $\times$ 73 m (135 $\times$ 240 ft.) footprint and throughout the exterior walls are clad by over 300 reinforced concrete panels. The cross-section of a typical panel is shown in Fig. 3(a).

  
Figure 3: Cross Sections of (a) Existing Wall and (b) Test Specimen
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At the middle the panel is 165 mm (6.5 in.) thick, and is 102 mm ( 4 in.) thick along the longitudinal edges. For experimental purposes, the thickness of a panel was simplified to be 127 mm (5 in.) thick throughout, Fig. 3(b), resulting in an equivalent shear capacity as in the actual building. The height of the experimental panel was reduced from the design height of 4.0 m (13 ft.) to 3.5 m (11.5 ft.) for ease of installation into the test frame and the clear height remained the same as in the prototype. A photograph of the test panel is shown in Fig. 4.

  
Figure 4: Test Panel Under Construction
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It was cast using lightweight concrete with the ultimate strength of 28 MPa (4 ksi). A general view of the cladding panel in the test frame is shown in Fig. 5. The essential features of the panel attachments to the test frame consist of three elements: (a) bottom supports, (b) three energy dissipating devices at the top, and (c) hydraulic load actuator for applying cyclic load shown on the right near the top of the wall.

  
Figure 5: Test Setup.
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A more detailed illustration of the bottom supports is shown in Fig. 6. The two vertical steel assemblies are largely for resisting the overturning force caused by the application of the inplane horizontal force at the top of the panel by the actuator.

  
Figure 6: Bottom Supports (a) Front View, (b) Vertical Section.
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The horizontal plate at the bottom is mainly for resisting shear. Note that there were 32-14 mm (9/16 in.) diameter holes for attaching the wall panel to the steel details. In that regard, the initially specified Hilti Kwik Anchor Bolts, Fig. 7, were found to be inadequate.

  
Figure 7: Hilti Kwik Anchor Bolt
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As during the application of the cyclic load by the actuator, an unpermissible movement between the wall and the steel details took place. This can be readily explained by noting the following. The expansion end of a bolt had to pass through 14 mm (9/16 in.) diameter holes in the steel plates, requiring the same size of holes in the concrete wall. As a result, beyond the bolt expansion end toward the bolt nut, a void in the shape of an annulus was formed allowing the bolt shank to move freely back and forth. By changing the bolts to a Hilti Hit HY-150 type, Fig. 8, and injecting epoxy around the bolts, the bolts remained solidly embedded during repeated tests.

  
Figure 8: Hilti Hit HY-150 Bolt
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For both sizes of bolts the drilled bolt-holes were 57 mm (2.25 in.) deep. When the bolt sizes were changed, the panel was turned upside down and turned around through 90o in order to attach the steel details to the unmarred side of the panel.

The basic detail of an energy dissipating device near the top of the wall is shown in Fig. 9.

  
Figure 9: Cross Section of the Energy Dissipator.
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In this assembly a 152 $\times$ 102 $\times$12.7 mm (6 $\times$ 4 $\times$ 0.5 in.) angle that is 660 mm (26 in.) long is attached to an ``existing'' concrete beam. (In the experiment it was attached to a steel beam.) Whereas a 102 $\times$ 76 $\times$ 7.9 mm (4 $\times$ 3 $\times$ 5/16 in.) TS tube is bolted to the precast concrete panel. The brass washers rubbing during motion against the TS steel tube dissipate energy. The low friction shims made of Teflon accommodate the needed vertical motion of the panel between the parts. There were three such details for the panel. This method of dissipating energy is related to the earlier report and paper by Grigorian and Popov (1993, 1994).

The test wall made-up in the above manner was then extensively instrumented particularly for measuring displacements.


next up previous
Next: 3.0 EXPERIMENTAL RESULTS Up: Seismic Cladding of Walls Previous: 1.0 INTRODUCTION
10/30/1997