Johnn P. Judd

Tensile Strength of Varied-Angle Mortise and Tenon Connections in Timber Frames

AbstractThe tensile strength of varied-angle mortise and tenon connections in timber frames is discussed in this paper. Twelve full-size mortise and tenon connections (four 90°, four 67.5°, and four 45°) were tested under monotonic tensile loading. Initial yield modes observed during testing included peg bending, peg shear, tenon tear out, and mortise splitting. Decreased connection angle corresponded to equal or increased tensile strength but decreased ductility. A theoretical method to calculate the tensile strength of mortise and tenon connections is also developed. The method uses a modified set of yield-limit equations supplemented with local-stress-effect (mortise splitting and row tear out) equations to predict tensile strength. The governing theoretical yield modes agree well with yield modes observed during testing. The theoretical tensile strength is reasonably accurate, averaging 14% higher to 9% lower compared with test results. The findings indicate that mortise and tenon connections are sign...

Retrofit of Steel-Frame Buildings Using Enhanced Gravity-Frame Connections

This paper presents a new retrofit method that employs gravity-frame connections to improve the seismic performance of buildings by enhancing the lateral-force resisting capacity of conventional shear-tab connections. In the retrofit method, proprietary Tstub flange connectors used in the Simpson Strong-Tie ® Strong Frame ® Special Moment Frame are installed adjacent to the shear tab connections to create a ductile partially restrained beam-to-column connection. Beam flanges and buckling restraint plates are used to force the reduced-width segment of the T-stub stem into high-mode buckling and to act as a “structural fuse” in an earthquake. The collapse safety and seismic serviceability performance was predicted for a set of archetypical office buildings with ductile or non-ductile (pre-Northridge) moment connections by employing the FEMA P-695 and FEMA P-58 methodologies. The results indicated that the seismic collapse safety and serviceability performance of retrofitted buildings was generally superior compared to conventional buildings. The retrofit method decreased interstory drifts and reduced repair cost and downtime, although retrofitted buildings were stiffer and experienced higher roof accelerations in some scenarios.

Radio-Frequency Identification Triggering System for Structural Health Monitoring of Highway Bridges

One challenge with structural health monitoring (SHM) for highway bridges is managing large amounts of response data. This paper discusses a proposed SHM system that was developed to collect, store, and prioritize excitation data caused by traffic loads, especially overweight trucks. In the proposed system, a microcontroller is used to trigger the release of data. A radio-frequency identification (RFID) reader and antenna combinations are installed on the truck and at the bridge of interest. The truck information, including axle weights and configuration, is assigned to the RFID tag and placed on the windshield. The transponder at the bridge detects the approaching RFID tag and triggers the data acquisition system to release the response (strain) data from a sensor interrogator through a microcontroller to a network portal (such as a cellular modem or Ethernet radio) while the truck passes over the bridge. Field tests were conducted to validate the proposed system. The optimal position of the vehicle relative to the transponder, the height and horizontal position of the transponder, and the location of the RFID tag were investigated for a vehicle travelling at 105 kph (65 mph). The tests results indicated that the triggering system was successful, but it was sensitive to the position of the tag relative to the transponder.