Abstract
Lath mortar wall is one of the typical fire proof walls for wooden houses in Japan. But this wall has a lot of problems, such as crack of mortar due to drying shrinkage, separation from sheathing due to lack of fastening, degradation of timbers for sheathing and framing due to immersion of water, which impose possible damage in earthquake. Thus, nondestructive testing to evaluate the degree of degradation for mortar and timber of building elements is needed. So, in this study, a nondestructive testing method and its criteria for field survey using frequency analysis of sound when hitted by steel hammer have been developed. The results obtained are as follows.
(1) The characteristic patterns for mortar were classified into categories A, B and C by the high, medium and low frequency at the peak of sound level and into I, II and III by the shape of distribution. Examinations of defects of mortar and degradation of timber sheathings and framing in actual use indicated that these categories were related to the degree of cracks in mortar or the degree of degradation of timber due to fungi and termites. Category AI was sound and CIII was the lowest. Mortar had higher possibility of defects and degradation, when it was closer to C and III. Simulating tests in which sheathing and frame of timbers were assumed to be lost also led to the same trend.
(2) The characteristic patterns for sill of timber were classfied into categories A, B and C by the shape of distribution although the frequency at the peak of sound pressure level was not so different. The characteristic pattern for non-degradative timber was ranked into category A independent of moisture content although the peak was little bit different. The sill with mortise and joints, which was newly constructed on site, was ranked into category A or B.
