We have developed the new hybrid structure of CLT infill and steel frame for middle-rise and high-rise buildings. This structural system can achieve the high structural potential of the CLT panel by holding around the CLT panel with steel frame. Steel frame can support sustained load of a high-rise building without CLT panels and can build long-span beams reasonably. Compression stress of CLT seismic panel can be transmitted to the upper and bottom steel beams through high strength mortal layer, and the steel beams can secure high shear strength as boundary beams. Shear of the CLT panel is transmitted by drift pined joints with insert-steel gusset plate. And tension stress balanced with compression stress of CLT is supported by steel tie bar.
To clarify the performance of this structural system, we have conducted the structural experiment series with seven test frames in 1/2 scale. The result of the structural experiment series provided the following findings.
Firstly, all of the CLT specimens reached compressive or shear failure, and performed to their full structural potential. Because of that, it has been found that it is possible to perform structural design that takes advantage of full CLT performance. The structural performance has increased up to max. 3.48 times for the horizontal stiffness and up to max. 2.67 times for the horizontal bearing capacity, by inserting CLT panels into the streel frames.
All CLT panel showed slip type restoring force characteristic. In case of shear failure, the decreases in shear force were caused at story deformation angle greater than 1/71 radian. In case of compression failure, the decreases of shear force were gradual, and their deformation performances were excellent.
It has been found by the experiment series that these failure modes of CLT depend on aspect ratio (H/L) of CLT, and in case of low H/L, shear failure tends to occur. The shear strength and elastic shear modulus of test frame CLTs in shear failure could be reduced to about 70% of the material shear test.
When the story deformations of the CLTs are separated into the deformation components of shear deformation, slip displacement of the joints, and rotational deformation of the CLTs, the rotational deformations of the CLTs are the largest. And the rotational deformation ratio of story deformation tends to increase by H/L of CLT
Based on the above findings, a subsequent paper will show the detail study on compressive stress transfer in the upper and bottom surfaces of CLT with analytical studies, and propose structural design and stress analysis method of the structural system.
