Many of the newly constructed buildings are becoming intelligent, thus required equipment for building service such as air conditioning, electrical and information lines is diversified. In addition, for the sake of reducing construction costs, planning a floor height as low as possible is a common practice. In order to cope with this, circular holes are widely provided on the web of a beam composed of H-shaped steel to maximize the efficiency of ceiling spaces. In such a case, it is more likely that more holes will be installed to accommodate design changes during construction or future facility renewal than the minimum requirements of the initial design. Perforated beams may have lower strength and stiffness than ordinary non-perforated beams because parts of the cross section of the web are cut off. In the general structural design at normal temperature, some measures have been taken to prevent an excessive reduction in strength and stiffness.
On the other hand, a perforated beam that is heated during a fire demonstrates a different deformation behavior from that at normal temperature due to the deterioration in yield strength and elastic modulus, thermal expansion and thermal stress. Regarding the fire resistance of beams, although the fire resistance test method based on the ISO 834 series is specified, test method specialized for perforated steel beams is not established. For rational fire resistance design of steel buildings, sufficient knowledge on the fire resistance of perforated beams especially having circular opening in the web is essential.
In this study, two full-scale protected perforated steel beams with different opening spacing were used for fire resistance test to grasp the behavior of H-shaped steel beam with circular holes at high temperature. The hole spacings of two specimens were 1.5D (1.5 times the diameter of hole) and 2.5D (1.5 times the diameter of hole) on center respectively. Collapse behaviors of the steel beams including collapse time, distribution of steel temperatures, vertical deflection and out-of-plane deformation were reported and comparatively discussed.
The following findings were obtained.
(1) At high temperature, the shear yield of web posts affected the beam collapse in both the 1.5D and 2.5D specimens. Also, the deformation of holes occurred due to local buckling by the shear yield. It was found that the 1.5D specimen had more clear local buckling and larger deformation of the hole than the 2.5D specimen, thus the narrower the hole spacing, the greater the collapse of the perforated beam were affected by the shear yield.
(2) At collapse, the average temperatures of the web were 570 Deg.C for the 1.5D specimen and 660 Deg.C for the 2.5D specimen. The difference was about 90 K. The 1.5D specimen with the narrow hole spacing and the larger area loss of the web due to holes collapsed at a lower temperature.
(3) The perforated H-shaped steel beams showed collapse behavior due largely to shear buckling of the web, which was different from the general collapse behavior of non-perforated beams.
