Summary and Observations
(1) The seismic performance of an SSG curtain wall alone cannot be treated as an isolated system as its performance depends upon its interaction with the super structure and the super structure’s response to an event. From this standpoint, the behaviour of many SSG systems in the vicinity of the event (2010 mega-earthquake) performed favorably with little or no damage. This is a result of the inherent flexibility of the split-mullion modern SSG curtain wall systems coupled with the
FIG. 18—Load displacement curves: standardized strain rate.
FIG. 19—Load displacement curves: high strain rate.
FIG. 21—Load displacement curves: standardized strain rate.
FIG. 22—Load displacement curves: high strain rate.
restrictions and requirements imposed on building structures in the national seismic code.
(2) Of the buildings reviewed in this paper, both “stick" and “unitized" type and both two-side and four-side SSG systems performed favorably, including most of these without any reported damage, with one approaching 30 years of age.
(3) All of the SSG projects reviewed in this paper that performed favorably utilized the 6.4 mm (0.25 in.) minimum thickness of the structural seal recommended by the ASTM C1401 industry guide. In SSG systems where there is no contribution from split mullions and sliding anchors,
FIG. 26—Load displacement curves: highest strain rate.
the thickness of the sealant becomes more important in its ability to absorb lateral displacements from interstory drifts.
(4) Shear stresses imposed into the structural silicone will vary according to the specific product utilized (high modulus versus medium modulus, etc.) but also according to the strain rate that the sealant is subjected to. Thus, SSG designers ought to carefully select the material for use in designs in seismic regions.
(5) The majority of the buildings reviewed in this paper were designed and fabricated utilizing two-part high modulus shop applied structural silicone by three experienced companies in conjunction with proper technical support and overview. It is believed that the experience provided by these fabricators contributed to the success of the SSG systems reviewed.
Black -» 1.1 m/s (43.3 in/s)
200 Blue->0.5 m/s (19.7 m/s)
Red -» 0.00085 m/s (
FIG. 27—Load displacement curves, all three strain rates superimposed.
Copyright by ASTM Int’l (all rights reserved); Tue May 6 12:07:08 EDT 2014
(6) The high rigidity and low interstory drifts of buildings imposed by the seismic code NCh433 contributes to reduced actual shear strains into structural seals when compared to building codes of outer countries.
(7) Site review of a damaged SSG curtain wall (MTS Building) showed glass fragments retained by the silicone. This supports the ASTM notion that the structural seal and weatherseal can contribute to retaining broken glass during the event, minimizing fallout hazard to pedestrians (Fig. 14).