Thermo-mechanical modeling of thermal breaks in structural steel point transmittances.

摘要

Thermal bridging through structural steel members in building envelopes poses issues with heat loss and condensation in cold regions. Structural steel thermal breaks, taking the form of low-thermal conductivity, high-strength and stiffness materials placed between the faying surfaces of a steel connection, serve to reduce heat flow through the steel element and have seen extensive use in the construction industry. However, current steel construction code provisions in the US prohibit the use of compressible materials in a steel connection. While the practical benefits of thermal breaks in structural steel beams and columns have been well demonstrated, there is a lack of guidance on the structural design of these thermal breaks, as well as a yet undetermined thermal efficacy of thermal break design parameters.;The objective of this thesis was to determine the thermal and mechanical behavior of structural steel beam thermally broken connections and continuous beam thermal bridges. Heat flow through a thermally broken steel end-plate connection was determined experimentally using a calibrated hot box. Results were used to validate a finite element heat transfer model, which was used to perform a parametric analysis on the thermal break using different break and bolt materials. From the analyses, it was determined that the thickness of the break is effective in reducing heat flow and condensation potential. The use of stainless steel or fiber-reinforced bolts provides a significant reduction in heat flow and condensation potential. The mechanical behavior of the thermally-broken connection was analyzed using cantilever bending tests and shear tests on an identical set of connections using three different thicknesses of neoprene pad. Results showed that the rotational stiffness of the connection was reduced approximately linearly with increasing neoprene pad thickness. Shear deflection stiffness was reduced exponentially with increased pad thickness. Structural experimental results were validated against a finite element model which was used to investigate stresses in the end-plate and the bolt. Bolt rupture was found to occur at a reduced applied bending moment due to the increased rotation of the end-plate due to the soft intermediate layer of neoprene between the end-plate and the connection member.