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This research investigation explores the feasibility of implementing a laser welded sandwich steel panel bridge deck system as a viable alternative to standardized reinforced concrete bridge decks. Generally used in naval ship building applications, steel sandwich panels possess attractive characteristics towards the integration with bridge infrastructure such as service life in excess of 100 plus years, dead load reduction, rapid construction, decreased closure time, and automated mass production. The lack of fatigue data for the laser "stake" welds used to create the enclosed sandwich panel geometry raised concerns with respect to fatigue life. The primary focus of this study was to determine whether or not infinite fatigue life was possible. Two different laser welding technologies were investigated, Laser Beam Welding (LBW) and Hybrid-Laser Arc Welding (HLAW). Test specimens were fabricated and tested in order to examine fatigue resistance based on a localized load effect between adjacent core stiffeners. Finite element models were used to obtain the stress range for each individual test due to complex geometry and partially restrained boundary conditions. In order to assess the fatigue performance of the overall deck system, additional finite element models were created to study the local and global behavior of different sandwich panel configurations. As a whole the investigation yielded promising results. Infinite fatigue life is achievable due to outstanding fatigue performance. The HLAW stake welds demonstrated superior fatigue resistance in comparison to the LBW process. Localized load effects can be minimized through the modification of different panel parameters. Pushing forward, full scale testing is essential to the future employment of this innovative bridge deck system. / Master of Science

The Sandwich Plate System (SPS) is created by bonding two steel plates together with an elastomer core that is injected into a cavity formed by the steel plates and perimeter bars. The result is a stiffer and lighter panel that can be used for plate-like structures such as bridge decks, stadium risers or ship decks. For more versatility, the effects of welding post-injection to the SPS panels were investigated. Three post-injection welded joints were tested to determine fatigue resistance and the effects of cyclic loading on the localized debonding of the heat affected zone at the post-injection welded joint of a SPS bridge deck. Seven panels containing one of three post-injection weld configurations were investigated. Each panel was fatigue tested to ten million cycles or until failure, by applying remote bending to the post-injection welded joint. Experimental deflections and strains were compared to finite element analyses. Fatigue-life predictions were made using code based S-N curves, and a relatively new mesh-insensitive structural stress method with a master S-N curve approach. The post-injection welded joint demonstrated good fatigue resistance to recommended AASHTO loading when shims were used under the middle support to offset the camber in the SPS panels. It was also found that stresses caused by draw down of the camber had an adverse affect on the post-injection welded joint and greatly reduced its fatigue resistance. / Master of Science

An innovative approach to possible construction or rehabilitation of bridge decks can be found in a bridge construction system called the Sandwich Plate System (SPS). The technology developed and patented by Intelligent Engineering Canada Limited in conjunction with an industry partner, Elastogran GmbH, a member of BASF, may be an effective alternative to traditional bridge rehabilitation techniques. Although the system's behavior has been studied the connection of the SPS deck to the supporting girders has not been investigated. Two types of connection are presented in this research. The use of a bent plate welded to the SPS deck and subsequently bolted to the supporting girder utilizing slip-critical connections has been utilized in the construction of a SPS bridge. A proposed SPS bridge system utilizes the top flange of the supporting girder welded directly to the SPS deck as the deck-to-girder connection. The fatigue performance of a deck-to-girder connection utilizing a bent plate welded to the deck and bolted to the supporting girder using slip-critical connections was tested in the Virginia Tech Materials and Structures Laboratory. The testing concluded that the fatigue performance of the welded and bolted bent plate connection was limited by the weld details and no slip occurred in the slip-critical connections. Finite element modeling of the two types of deck-to-girder connections was also used to determine influence of the connections on the local and global behavior of a SPS bridge system. A comparison of the different connection details showed that the connection utilizing the flange welded directly to the SPS deck significantly reduces the stresses at location of the welds in the connections, but the connection type has a limited influence on the global behavior of a SPS bridge. / Master of Science