Effect of Frictional Force on Lateral Resistance of Wall-Floor Joints of Wooden Light Frame Constructions

Abstract

In wooden light frame constructions, wind or earthquake forces are transmitted through the boundaries between upper floors and walls, walls and lower floors, floors and sills, or sills and foundations. At the boundary between the bottom plate of a shear wall and a floor diaphragm sheathed with plywood or another wood based panel, for example, the lateral force borne by this shear wall is transmitted by both nailed or other mechanical joints and friction between the bottom plate and the floor sheathing panel. In this study, static cyclic tests were conducted to estimate the effect of frictional force on the lateral resistance at this boundary. The observed apparent frictional coefficient between SPF bottom plates and softwood plywood sheathing panels averaged 0.285 and varied in a wide range from 0.2 to 0.35. The minimum value, 0.2, is roughly close to the dynamic frictional coefficient obtained from pure frictional tests of the same combination of materials. The wide variation of apparent frictional coefficient seems to result from irregular contact conditions between bottom plates and sheathing panels or eccentricity of lateral forces. Static cyclic tests showed a great effect of friction on hysteretic damping capacity.

Dynamic response of wall-floor joints of wooden light-frame constructions under forced harmonic vibrations

“…2. This slight change in resonance frequency shows that dynamic lateral forces are transmitted by friction through the wall-floor joints with little contribution from the nailed joints in load share if they are sufficiently below the frictional limits [1,2]. This test result indicates that the responsive characteristics of timber constructions during strong earthquakes cannot be directly correlated with the resonant frequencies observed under free or forced vibrations at very low accelerations, which are regarded as an index of the earthquake resistance of structures.…”

“…1. These three specimens were selected from the six specimens used in the previous static tests and were undamaged except for the nail holes [1]. The average air-dry specific gravity and moisture content of the SPF 204 frame members of the specimens were 0.47 (0.41-0.52) and 12.6% (11.6-13.2%) and those of the floor-sheathing plywood (15-mm thick Karamatsu plywood) were 0.57 (0.54-0.59) and 9.8% (8.7-10.6%), respectively.…”

“…The current design standards for timber structures, however, do not stipulate the allowable lateral resistance of nailed wallfloor joints with bottom plates that are nailed to joists through plywood sheathing. In this study, therefore, the allowable lateral resistance of a standard timber-to-timber joint with six CN90 nails adjusted to the average specific gravity of the frame members was calculated according to the Japan standard for timber structures [4] as an approximation, where the contribution of frictional resistance to the actual lateral resistance was not taken into account [1,2]. The resultant static allowable lateral resistance was 5797 N per six nails, which roughly corresponded to the acceleration of 0.6 G for the given mass.…”

“…The average air-dry specific gravity and moisture content of the SPF 204 frame members of the specimens were 0.47 (0.41-0.52) and 12.6% (11.6-13.2%) and those of the floor-sheathing plywood (15-mm thick Karamatsu plywood) were 0.57 (0.54-0.59) and 9.8% (8.7-10.6%), respectively. The apparent frictional coefficient obtained from the previous static tests between the bottom plates of the walls and the floor-sheathing plywood was 0.29 on average and ranged from 0.23 to 0.35 [1].…”

“…At these boundaries, nailed wall-floor joints mainly resist the lateral forces occasionally in concert with other supplementary resisting elements. The authors, in previous studies [1,2], showed the effect of frictional resistance on the lateral resistance of the wallfloor joints of wooden light-frame constructions under static forces. In this study, the authors conducted shaking table tests with the same wall-floor joints to observe their responsive characteristics under dynamic forces.…”