Search

There is a need to modify structural elements of buildings and bridges in order to improve the response to blast loads. Testing the modifications has been a major stumbling block to advances. Failure modes resulting from a 1 to 10 ms blast impulse are substantially different from the failure modes obtained with conventional laboratory structural tests. Field tests using actual explosions are expensive, are not repeatable, and the fireball makes visual and video viewing impossible and reliable real-time data very difficult to obtain. The University of California, San Diego and MTS Systems Corporation were funded to design and build a system able to perform laboratory blast simulations. The system, which was completed in 2005 at UCSD, has been used to test modified and unmodified reinforced structures including: concrete columns 355 mm square by 3 m high; and concrete block walls 200 mm thick by 3 m high. By January 2006, over 20 specimens were tested, with specimen failure modes matching the failure modes from field tests. The system uses impact loading to produce a 2 ms pulse with a typical peak pressure loading of 35 MPa and an impulse of 14 kPa-s over the surface of the column. The system allows observation of the test in person and by high-speed video, as well as successful instrumentation of the specimen. This paper describes the blast simulation system and its capabilities.

The current approach for seismic retrofit of bridge columns in California involves extensive use of steel jacketing, which has been shown to be very effective in enhancing the flexural and shear performance of deficient bridge columns. In this paper, an analytical model is developed for the first-yield limit state and the ultimate limit state of flexurally dominated steel-jacketed circular bridge columns. Lateral stiffening of column is taken into account by considering the effective bond transfer between the steel jacket and column. Two possible ultimate limit states are identified: (1) A limit state that corresponds to the ultimate compressive strain of concrete; and (2) a limit state that corresponds to low-cycle fatigue fracture of the longitudinal steel. An equation based on the energy balance method is proposed for predicting the ultimate compressive strain of concrete confined by the steel jacket. The ultimate limit state governed by low-cycle fatigue fracture of the longitudinal steel is assessed using an energy-based damage model. The proposed model is shown to correlate well with the lateral response of tested steel-jacketed columns.

Full‐depth structural concrete overlays in bridge deck rehabilitation require special interface design and construction joint preparation between the old bridge deck and the overlay in order to ensure monolithic structural action of the overlaid bridge superstructure under all loading conditions. The effectiveness of interface dowels for horizontal shear transfer in connection with clean and speciallyroughened contact surfaces is investigated. Preliminary analytical studies of the horizontal shear‐transfer behavior of overlaid reinforced concrete bridge decks and experimental results on the effects of interface preparations and dowels from shearblock tests, full‐scale transverse bridge deck slab panel tests, and a full‐scale prototype bridge deck test are presented. The full‐scale prototype bridge deck test was performed on a section of a reinforced concrete T‐girder bridge that had been in service for 25 years. A detailed account of analytical and experimental investigations of the horizontal load‐transf...

The horizontal loadtransfer behavior of fulldepth structural concrete overlays used in bridge deck rehabilitation is investigated with a specially developed analytical model and compared with test ...

In order to provide experimental background for current seismic design of bridge footings, a 0.4:1 scale circular column footing model was tested. The model was designed and constructed based on a footing of an actual prototype bridge which was built following current bridge design standards. The model pier was tested in a vertical cantilever condition with cyclic horizontal displacements and constant axial load applied to the top of the column. The pier was supported on rubber pads simulating the compressive flexibility of pile foundation, with high tensile strength bars simulating the uplift stiffness of the piles. Under imposed horizontal displacement, the pier developed a satisfactory hysteretic response with a full plastic hinge formed at the bottom of the column. However, test results and theoretical analyses revealed potential problems in current bridge footing design, in particular, the lack of the column/footing joint shear design as well as non-conservative flexural and shear designs which are based on full effectiveness of the entire footing.

Until recently, bridge design specifications in California permitted longitudinal column reinforcement to be terminated in monolithic cap beam/column joints with straight bar development not extending fully up the joint height. Since the development length could be construed not to comply with ACI 318 requirements, it was suspected that the anchorage length provided for the column bars was insufficient to develop the full moment capacity of the column at the joint interface. considering that this detailing was widely used in bridges in California an experimental investigation was initiated at the University of California, San Diego, where response of a bridge knee joint incorporating as-built reinforcement details was examined under simulated seismic loading. Following inadequate performance of the test unit, the behavior of the knee joint was investigated based on the experimental readings, giving consideration to bond slip of the longitudinal column reinforcement. The response of the test unit indicated that the bond conditions developed when anchoring the longitudinal reinforcement of circular bridge columns is unlike that developed along the beam reinforcement anchored into building joints.

The paper describes tests carried out on large scale reinforced concrete test units, with details modeling those encountered in sections of Los Angeles' I-10 Santa Monica Viaduct. Lap-splices of column longitudinal reinforcement and joint details including inadequate development of column reinforcement in the cap beam, and a total absence of special joint reinforcement, would be considered unacceptable in new designs. The purpose of the tests was to obtain verification of analytical predictions that, despite the poor detailing of the bents, could be expected to survive the design level earthquake without collapse. Test results confirmed that the lap splices should perform adequately under seismic attack, and the column/cap beam connections would maintain gravity load capacity after joint degradation.

This paper describes theoretical and experimental studies related to seismic evaluation and retrofit of bridge column footings. One "as-built" model column footing and three retrofit model column footings were tested under simulated seismic actions. Test results of the "as-built" footing showed that column/footing joint shear failure is a potential danger to existing bridge structures. Test results also revealed that if there is no dependable tensile capacity in the pile/footing connection, a rocking behavior may dominate pier response, minimizing damage to footing and column. Model column footings retrofit using current retrofit standards developed relatively stable hysteretic responses up to moderate ductility levels. However, experimental observations and theoretical analyses based on a strut-and-tie model and yield-line theory indicated that with current footing retrofit design, which lacks the consideration for joint shear design, the reinforced concrete overlay may not develop a fully effective postcracking mechanism. Improved retrofit details including long dowels to ensure development of an effective joint shear-resisting mechanism are proposed and confirmed by experimental results.

The difficulties in assessing the probable deformation and force states of structural wall buildings under lateral earthquake forces are evaluated by means of laboratory test results from a five-story full-scale reinforced masonry structural wall research building tested to failure at the University of California, San Diego under simulated seismic loads.