Research Program

The main objective of the research project discussed in this paper was to de­velop new experimental data to evaluate the behavior of structural silicone

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under simulated seismic-induced deformation conditions. Although consider­able tension and shear test data on structural silicone coupons is available, test data on a continuous sealant bead under four-sided SSG configuration is very limited. In particular, for the coupon test results to be more useful for applica­tion to assess seismic performance of structural sealants, some correlation needs to be developed between the continuous bead sealant behavior in a full – scale four-sided SSG mock-up under cyclic racking conditions and coupon tests on isolated short length sealant beads. Such full-scale racking test results can also help evaluate the proposed 50psi (345 kPa) allowable sealant stress for seis­mic application. Another objective of the research was to use the results of full – scale testing to evaluate the accuracy of linear elastic FE modeling of the mock – up in predicting sealant deformation/stresses.

In designing the test mock-up configuration, it was important to note that in unitized systems, the corner condition poses the most unknown behavior, as most prior mock-up tests have considered only planar conditions. The reason for the importance of the corner condition has to do with the interaction of the two perpendicular panels at the corner, which leads to vertical shear transfer between the intersecting panels. Such vertical shear actually is expected to have more influence on the corner mullion especially if it is of a split mullion type. The test mock-ups were designed to evaluate the behavior of one type of unit­ized system developed by Bagatelos Architectural Glass Systems. It should be noted that unitized systems are custom designed and each designer will provide framing and connection details different from others. To develop a more com­plete understanding of the seismic response of the particular framing system developed by Bagatelos Architectural Glass Systems, the boundary condition of the vertical mullion stack joints was chosen as a variable. This allowed compari­son of the behavior of a complete unitized system with sliding vertical mullions to the behavior of a system that emulated a stick-built condition with restrained vertical sliding. The details of the mock-up construction and boundary condi­tions are explained in the next section.

The racking tests followed the AAMA 501.6 [7] testing protocol that requires full-scale mock-ups be constructed and attached to a racking facility and be sub­jected to the pre-determined displacement cyclic history. In this study, the rack­ing facility at the Pennsylvania State University, shown in Fig. 1 with a typical mock-up attached to the facility, was used. Mock-ups were attached to the slid­ing steel tubes of the facility. A computer-controlled actuator applies a given dis­placement at a given frequency (per the AAMA 501.6 test protocol) to the bottom sliding tube, and through the fulcrum arm, the top tube displaces an equal amount in the opposite direction. This motion simulates the drift a given story may experience during an earthquake. Each applied racking displacement step includes: a ramp-up period that builds within four cycles to the peak dis­placement at that step, four constant-amplitude cycles at the peak displace­ment, and a four-cycle ramp-down period. Each racking step increases in magnitude by 1/4 in. (6.4 mm) until facility capacity is reached (6 in. (152 mm) displacement) or complete mock-up failure occurs. Concatenation (joining) of the steps yields the AAMA 501.6 specified cyclic displacement protocol as shown in Fig. 2. The drift a specific building structure can be expected to experience

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Top boundary condition, steel angles

pm mockup to nonz. sliding tubes.

Bottom boundary condition varies from ”free" (ВСІ) to "pinned* (BC3)

FIG. 1—Typical mockup mounted on the racking test facility.

during a design level seismic event is a function of the building primary lateral force-resisting system and the seismic ground motion expected to occur at the site. It is typical for building codes to restrict the buildings expected drift to between 1.25 % and 2.00 % of building story height.