No abstract

Impact hammer tests were conducted to demonstrate the vertical dynamic characteristics of light frame joist floor and effect of human load on it. The specimen was 3.64m-long-span and 4.55m-wide joist floor consisted of eleven 2" by 8" dimension lumbers and 15 mm-thick plywood subfloor. Furniture and/or human (in four types of posture, respectively) loads were applied to investigate the influence on natural frequencies and damping factors. The test results indicate, i) Human-load hardly affects natural frequencies,ii) The value of damping factor increases with the body area in contact with the floor,iii) The first natural frequency of joist floor is roughly estimated according to the theory of free vibration equation of motion for bending beam.

Shuzo SUZUKI and Yukitaka IHARA Impact hammer tests and analyses by finite element method were conducted to demonstrate the effects of support condition and uneven distributed load on the vertical dynamic characteristics of light frame joist floors with 3.64m-long-span and from 0.91m to 7.82m-wide joist floor consisted of 2" by 8" dimension lumbers and 15 mm-thick plywood subfloor.The results indicate, i) Support condition slightly affects the natural frequencies when the width/span ratios exceed 2; ii) In addition to the mass-ratio of human-load, both the placement and the stand position of persons onto the joist floor give influence on the damping factor of 1st natural frequency; iii) The joist subjected to uneven distributed load generates locally deformed vibrational mode and also determines the 1st natural frequency of the joist floor; iv)Finite element analysis employed the appropriate models is effective to predict the natural frequencies and mode shapes of joist floor subjected to uneven distributed load.

Dynamic tests and direct transient response analyses of finite element method were carried out to demonstrate the vertical dynamic response of light frame joist floor subjected to various impact forces (impact-hammer, heel-drop, clay-drop). The specimen was 3.64m-long-span and 3.64m-wide joist floor consisted of eleven 2" by 8" lumbers and 15 mm-thick T&G plywood subfloor. The test results indicate, i) Dynamic maximum displacement of mid-span of the joist placed in the center of the floor obtained by the finite element method agree with those by experiments, ii) Dynamic maximum displacements closely relate to both the natural frequency of the joist floor and the processing time of impact force. iii) The static calculation using the coefficient (1.4) derived from the direct transient response analyses predicts the dynamic maximum displacements of the joist accepted the impact force.