Chapter 5. Seismic Performance Evaluation of Ceiling Systems Based on
5.2. Shake-Table Test of Non-Seismic Ceiling Systems
5.2.2. Test specimens and measurements
Figure 5.10 shows the coherence function measured from the recorded signals on the top of the square frames 1 and 2. It can be observed that the coherence function maintains almost unity in the whole frequency range except for around 20 Hz, where the coherence function highly fluctuated. Such a high fluctuation, around 20 Hz, is speculated to be caused by the local vibration of the beam members at the top frame and will not affect the global response of the ceiling specimens. Therefore, it can be concluded that the large-scale test frame installed on the two isolated shake tables was perfectly synchronized, and the whole suspended ceiling specimen installed on the large-size test frame is expected to be subjected to the same floor motions.
All the boundaries of the test specimens were treated to have a 15 mm clearance between the grid members and the wall-attached perimeter closure channel to satisfy a minimum gap requirement (10 mm) for SDC C according to ASTM E580 (ASTM- E580-E80 2017). The key specimen information is summarized in Table 5.1.
In this experimental program, direct- and in-direct-hung T-bar ceiling systems (DTL and ITL specimens) were tested and compared to investigate the differences in their dynamic characteristics and seismic performance resulting from the differ- ence in hanger members. Testing was conducted under more severe pounding con- ditions in the case of continuous panel ceilings, considering the robust restraint pro- vided by the screw-attached ceiling panels as reported in previous studies (Gilani et al. 2015; Magliulo et al. 2012; McCormick et al 2008). The ceiling size (or the ceil- ing mass) was significantly increased in this case such that more sever pounding forces can be applied to ceiling systems. Two large-size ceiling specimens (IMC-L- Figure 5.11 Configuration of indirect-hung suspended ceiling system (T&H-bar) (Lay-in panel)
Table 5.1 Ceiling types and key properties of test specimens
Specimen Ceiling type Ceiling size, m Input
direction
Boundary type (clearance, mm)
Plenum depth,
m Panel type
DTL-FS Direct-hung suspended
T-bar ceiling 9.0 × 4.07 x Free floating (15) 0.79 Lay-in
DTL Direct-hung suspended
T-bar ceiling 3.87 × 3.87 x, y, z Free floating (15) 0.80 Lay-in
ITL Indirect-hung suspended
T-bar ceiling 3.87 × 3.87 x, y, z Free floating (15) 0.75 Lay-in
ITL-R1 Indirect-hung suspended
T-bar ceiling 3.87 × 3.87 x, y, z Free floating (x-dir.
410, y-dir. 15) 0.75 Lay-in
ITL-R2 Indirect-hung suspended
T-bar ceiling 3.87 × 3.87 x, y, z Free floating (410) 0.75 Lay-in
ITHL Indirect-hung suspended
T&H-bar ceiling 3.87 × 3.87 x, y, z Free floating (15) 0.75 Lay-in
IMC-L-M Indirect-hung suspended
M-bar ceiling 12.9 × 12.8 x Free floating (15) 1.00 Screw-attached
IMC-L-C Indirect-hung suspended
M-bar ceiling 12.9 × 12.8 x Free floating (15) 1.00 Screw-attached
IMC Indirect-hung suspended
M-bar ceiling 3.87 × 3.87 x, y, z Free floating (15) 0.75 Screw-attached
M, IMC-L-C) were fabricated and uniaxially tested in the longitudinal direction us- ing the test frame described in the preceding section (see Figure 5.1). IMC-L-M specimen was fabricated to evaluate the ceiling seismic performance along the M- bar direction. IMC-L-C specimen has same configuration with IMC-L-M specimen, but it was 90° rotated from IMC-L-M specimen to exert pounding forces on the car- rying channel members. In addition, in order to evaluate the 3-dimensional input effects and the interaction with a nonstructural element installed within the ceiling, a small-size test specimen was also prepared by installing the air conditioner within the ceiling grid. The specimen and measurement plan for the tested ceilings are sum- marized in Figures 5.12 – 5.14.
While measuring the natural frequency and damping ratio of the ceiling systems by the since sweep or white noise test, the magnitude of the input acceleration (0.1
± 0.05 g) was observed to be generally too low for generating enough dynamic forces that could overcome the initial frictional forces existing in the perimeter of the sus- pended ceilings. When a higher input was applied to overcome the friction, the ac- celeration data was disturbed, wherein undesired acceleration spikes caused by pounding upon the perimeter closure channels occurred. Therefore, a specimen with a sufficiently wide clearance (410 mm) in both the horizontal directions was fabri- cated (ITL-R2). Furthermore, another specimen with a 410 mm clearance (ITL-R1) in one horizontal direction was also fabricated to measure the additional damping effect caused by the friction between the ceiling grids and perimeter closure channels (see Figure 5.12(c) and 5.12(d)).
Various measuring devices including accelerometers, LVDTs, and strain gauges were installed to monitor the global and local responses of the test frame and specimen. The installation locations are shown in Figure 5.12 – 5.14.
(a) Direct-hung T-bar ceiling specimen (DTL)
(b) Indirect-hung T-bar ceiling specimen (ITL)
(c) Indirect-hung T-bar ceiling specimen with large clearance (ITL-R1)
(d) Indirect-hung T-bar ceiling specimen with large clearance (ITL-R2)
(e) Indirect-hung T&H-bar ceiling specimen (ITHL)
(f) Indirect-hung M-bar ceiling specimen (IMC)
(g) Measurement plan at the top of test frame
Figure 5.12 Configuration of small-size shake table test ceiling specimens
(a) Indirect-hung M-bar ceiling specimen excited along M-bar direction (IMC-L-M)
(b) Indirect-hung M-bar ceiling specimen excited along Carrying-channel direction (IMC-L-C)
(c) Measurements plan at the top of large-size test frame
Figure 5.13 Configuration of large-size shake table test ceiling specimens
Specimen DTL-FS is a lay-in T-bar ceiling system which was installed on the full-scale 2-story steel moment frame which was discussed in Chapter 4 (see Figure 4.1). The specimen was fabricated to have a plan dimension of 9.0 m × 4.07 m. This specimen was specially prepared for evaluating the interaction effects that could be probable when the ceiling is installed with various nonstructural elements. For DTL- FS specimen, partition walls and fire sprinklers were incorporated to assess their interactions with the ceiling specimen. Full- and partial-height partition walls, with two cross-sectional types (rectangular and T-section), were installed at the side and center of the ceiling specimen, respectively. The top of the partial-height partition walls was connected to ceiling grids using ceiling screws (d = 3.0 mm), and concrete nails (d = 3.5 mm) were used to fix the wall base on the concrete floor slab (see Figure 5.14(b)). Fire sprinklers were provided above the ceiling specimen, penetrat- ing the ceiling panels through flexible sprinkler drops. The sprinkler drops were branched from the water pipes that were suspended to the floor above by hanger bolts. No extra clearances were introduced around the sprinkler drops (see Figure 5.14(c)).
(a) Measurements plan for DTL-FS ceiling specimen
(b) Configuration of full- and partial-height partition walls
(c) Configuration of water pipes and fire sprinklers installed above ceiling specimen Figure 5.14 Details of DTL-FS and nonstructural elements installed within ceiling specimen