An adhesively-bonded cast glass system for the Crystal Houses façade
Chapter 4 provided an overview of the three structural systems utilizing cast glass components in architecture, including a brief overview of the work presented in this dissertation. This chapter presents the design principles and experimental work for the first of the two systems explored in this work: a transparent, adhesivelybonded glass block system designed for self-supporting envelopes. The proposed system was developed for the Crystal Houses façade in Amsterdam, designed by MVRDV Architects. The system is exclusively constructed by solid cast glass blocks, bonded with DELO Photobond 4468, a colourless, UV-curing adhesive. This allows for a system of an increased transparency, sparing the necessity of an opaque substructure. In contrast with previous realized projects, solid soda-lime glass blocks are used rather than borosilicate ones.
Initially, several architectural prototypes, comprising glass elements of different tolerance ranges, are built to evaluate the visual performance and the thickness of the adhesive that allows for an even spread. The prototypes indicate that a homogeneous bond thicker than 0.3 mm cannot be obtained by the selected adhesive due to the latter’s flow properties and low viscosity. Based on the adhesive’s optimum application thickness, it is determined that the glass blocks’ top and bottom surfaces should be flat within 0.25 mm for guaranteeing an even adhesive layer of the highest strength.
The structural verification of the system is demonstrated by physical testing of prototypes in compression, 4-point bending, hard-body impact and thermal shock. Compressive tests on individual blocks highlight the need for proper detailing and uniform load distribution of the system. Compressive tests on columns made of adhesively bonded glass blocks further confirm that strict size tolerances are essential for maximizing the load-bearing capacity of the system: specimens with larger size deviations fail in considerably lower stress values than specimens with smaller size deviations. Furthermore, series of 4-point bending tests on adhesively bonded glass beams demonstrate that the chosen adhesive enables the glass brick wall to behave monolithically under such loading when the adhesive is applied in a constant layer of the optimum thickness.
Overall, the results show that the adhesively bonded glass block structure can provide the required structural performance, but only if strict tolerances are met in the geometry of the glass blocks so that the chosen adhesive can be evenly spread in a constant thickness.