Evaluation of the Allowable Design Stress of 3M™ VHB™ Structural Glazing Tape B23F –

Experiments and Simulation

Fay Salmon, Steve Austin and Brent Bystrom

3M Company

Abstract

In the construction industry, 3M™ VHB™ Structural Glazing Tape (VHB Tape) is used for

attaching glass panels to metal frames in curtain wall, window and door, and skylight/canopy

systems. The design of VHB Tape bonds for such applications, specifically the bond width or bite

required to support the load caused by negative wind pressure, follows the industry practice of

employing the trapezoidal load distribution equation together with an allowable design bond stress.

For more than 30 years, designers and engineers have used the trapezoidal load distribution

equation to design safe and secure structural glazing systems with silicone sealants and VHB Tape.

An allowable design stress for the VHB Tape is therefore needed to enable its bond design. In

the work described here, the results of a finite element analysis and a third party mock-up

performance test are presented to assess an allowable design stress for the VHB Tape.

The experimental work involves a full-scale mock-up test on a curtain wall system bonded by

VHB Tape following ASTM E330 Standard Test Method for Structural Performance of Exterior

Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference. The

VHB Tape bond width was predefined based on the curtain wall system design. ASTM E330

pressure loads were then chosen to evaluate an allowable design stress of 15 psi (103.4 kPa) based

on the trapezoidal load distribution design equation, and was shown in the tests to withstand 150%

of the design pressure loads following the ASTM E330 requirement. The finite element analysis

was performed to simulate the full-scale mock-up test and to evaluate the VHB Tape bond

performance, in particular, to determine the stress, strain, and strain rates of VHB Tape under the

specific wind loads and loading rates used in the test. Because the VHB Tape bond strength is

strain rate dependent, the simulation results of the strain rates as well as the stress enable the

assessment of the VHB Tape bond strength. The finite element analysis results showed that due

to the out-ward arching deflection of the glass panel under negative wind pressure, VHB Tape is

strained such that it experiences tensile strain along its inside bond edge, and compressive strain

along the outside edge. Though the simulation results indicated that the highest tensile stress

along the inside edge may exceed the design value of 15 psi, it is within the VHB Tape bond

strength of the corresponding strain rates. This is confirmed by the full-scale mock-up test where

no debonding along the inside or the outside edge of the VHB Tape bond was observed. Both the

experimental and finite element analysis results therefore give consideration to a 15 psi allowable

design stress for VHB Tape to be used in conjunction with the trapezoidal load distribution

equation methodology to determine the VHB Tape bond width.