DYNAMIC EMBEDMENT OF METAL PLATE CONNECTIONS

Metal plate connectors (MPCs) are a critical component of prefabricate d wood trusses in that they provide an effective and efficient means o f transferring chord and web forces across the joint. Key to this proc ess is the proper embedment of the connector plate into the wood. Impr oper embedment is generally manifested in either the compressive stren gth of the wood being exceeded, or in plate rejection, where the plate springs partially back out of the wood after pressing. Keyed, in part , off the findings of several independent researchers, a technique was investigated in which the MPCs were pressed into dense southern pine 2 by 4's under a low amplitude vibratory load at frequencies of 30, 50 , and 70 Hz. Data for these so-called ''dynamic'' connections were col lected on both the mean force necessary for pressing and on the degree of plate embedment. Comparisons were then made to similar ''static'' connections fabricated in a traditional manner using equivalent lumber . Both the static and dynamic connections were tested in tension to de termine their comparative strengths and stiffnesses. Results showed so me indications of reduced press load at the 30-Hz frequency. At the 50 -Hz level, an increase in plate embedment was observed, although this was attributed to an accompanying increase in mean press loads. The 70 -Hz and control groups behaved quite similarly and showed only small v ariations between static and dynamic connections due to material varia bility. Tension test results were consistent throughout all MPC config urations and showed no marked differences in either capacity of stiffn ess as a result of the dynamic embedment.