Sarah Orton

Carbon Fiber-Reinforced Polymer for Continuity in Existing Reinforced Concrete Buildings Vulnerable to Collapse

Carbon fiber-reinforced polymer (CFRP) can provide continuity in reinforced concrete beams and thereby reduce the likelihood of progressive collapse if a supporting column were lost due to extreme loading (blast or impact). Seven half-scale specimens representing two spans of a reinforced concrete (RC) frame with a center supporting column removed were tested. The capacity of vulnerable RC building beams with discontinuous reinforcing steel were evaluated and compared with beams using CFRP to provide continuity, and with beams designed with continuous reinforcing steel. It was found that CFRP is capable of providing sufficient continuity to withstand the loss of a supporting column through either catenary (or cable) action, which reduces material usage, or flexural action, which reduces deflections. Furthermore, beams with continuous reinforcement may not be able to withstand the loss of a center-supporting column due to limited rotational ductility of the beam.

Experimental Evaluation of Disproportionate Collapse Resistance in Reinforced Concrete Frames

ACI Structural Journal, V. 110, No. 3, May-June 2013. MS No. S-2011-220 received July 12, 2011, and reviewed under Institute publication policies. Copyright

Calibration of Live-Load Factor in LRFD Bridge Design Specifications Based on State-Specific Traffic Environments

In this paper, the live load factor in the Strength I Limit State in the AASHTO LRFD Bridge Design Specifications is calibrated based on state-specific traffic environments and bridge configurations. As the initial development of the live load factor in the LRFD specifications was intended to be applied at the national level, state-specific traffic conditions, such as traffic volume, truck load, or bridge configurations, were not considered in the development process. In addition, due to the lack of reliable U.S. truck weight data in the early 1990s, truck data from Ontario, Canada, collected in the 1970s were used for the initial AASHTO calibration. Hence, the application of the live load factor in the LRFD specifications may result in over- or under-designed bridges for a specific state. Through reliability analysis of bridges based on state-specific traffic and bridge conditions, the live load factor can be recalibrated to achieve both reliable and economical bridge design. In this study, the traffic d...

Resistance of Flat-Plate Buildings against Progressive Collapse. II: System Response

AbstractUsing a macromodeling approach and alternate path method, dynamic and static analyses are performed to assess the progressive collapse resistance of a multistory reinforced concrete flat-plate building lacking structural integrity reinforcement in the slabs. Two loading scenarios, instantaneous removal of an exterior column and interior column, are considered. The dynamic analyses examine the potential of progressive collapse of the building, the dynamic demands on global and local nonlinear deformations, the effects of strain rate in materials, and the development of compressive membrane action. The effectiveness of an energy-based nonlinear static analysis procedure is examined for equivalently estimating the peak dynamic global and local responses caused by sudden column removal. The analyses indicate that older flat-plate buildings are vulnerable to progressive collapse; the combined effects from strain rate and compressive membrane action can significantly increase punching resistance; energy...

Resistance of Flat-Plate Buildings against Progressive Collapse. I: Modeling of Slab-Column Connections

AbstractA macromodel for slab-column connections is created for use in the system-level progressive collapse analyses of reinforced concrete flat-plate structures. The proposed model jointly uses shell and connector elements to simulate the complex behavior of slabs. Shell elements are used to simulate the flexural response of slab and the load redistribution over floor slabs. The connector elements, which permit simulating separation of slab from column on a punching failure, are defined with nonlinear responses for primary bending moment and torsion. A deformation-based punching failure criterion is defined for connector elements to simulate the punching failure at a slab-column connection and failure propagation. Parameters defining concrete tension stiffening behavior under static loading, including the peak tensile stress and the tensile strain when stress degrades to zero, are calibrated from two experiments. To ensure applicability, the proposed model is validated by 24 large-scale tests conducted ...

Experimental Testing of CFRP-Strengthened Reinforced Concrete Slab Elements Loaded by Close-In Blast

Strengthening reinforced concrete slab or wall structural elements with carbon fiber-reinforced polymer (CFRP) can improve their blast resistance. However, close-in blasts (blasts with a scaled range of less than 0.4 m/kg1/3) may undermine the effectiveness of the CFRP strengthening. This paper presents an experimental testing program on CFRP-strengthened reinforced concrete slab specimens that utilized fiber anchors. Two CFRP mitigation designs were tested under blast loads with a scaled range of 0.4 and 0.6 m/kg1/3. Tests on unmitigated reinforced concrete slab specimens provided baseline comparisons. The experimental results showed that the use of CFRP strengthening improved the blast resistance of reinforced concrete slab specimens. For a larger scaled range, 0.6 m/kg1/3, the CFRP successfully prevented flying debris and reduced the overall deflections of the slab specimens. However, for the closer scaled range, 0.4 m/kg1/3, the high shock blast pressures shattered the concrete through the thickness of the slab specimen and tore through the back-face CFRP. However, back-face velocity and overall deflections were reduced by about 75% compared to the baseline test slab specimen.

Live Load Effect in Reinforced Concrete Box Culverts Under Soil Fill

AbstractThe effects of live load in box culverts may be nearly negligible compared with the effects of dead loads when significant fill is placed above the crown of the culvert. The objective of this study was to determine the effects of live load (truck loads) on reinforced concrete box culverts classified as bridges [spans greater than 6 m (20 ft)] under soil fills of different thicknesses. The study considered the field testing of 10 existing reinforced concrete box culverts with fill depths ranging from 0.76 m (2.5 ft) to 4.1 m (13.5 ft). Instrumentation of the culverts consisted of 12 reusable strain transducers and 12 linear variable displacement transducers. The instrumentation was designed to be applied, used, and removed in one day of testing. Loaded trucks were driven over the culvert to provide live load. The results of the testing show that the live-load effect does diminish with increasing fill depth. The 2012 AASHTO LRFD bridge design specifications are overly conservative in predicting stra...

Effects of In-Plane Lateral Restraint and Post-Punching Capacity on Load-Carrying Capacity of Slab-Column Connections against Disproportionate Collapse

The overall goal of this research is to evaluate the potential of disproportionate collapse in older reinforced concrete flat plate buildings subjected to the loss of a supporting column. The research program considers testing of isolated slab-column connections that represent the connection near the lost supporting column. The goal of the tests is to evaluate the effects of in-plane lateral restraint and post-punching capacity. The experiments provide critical data for validating the mechanical model of slab-column connections used to examine the disproportionate collapse resistance of flat plate system. Five tests of restrained and unrestrained isolated slab column tests have been conducted at reinforcement ratio of 1.0% and 0.67%. The tests show that there is a marginal increase in punching shear capacity (2 to15%) due to the inplane restraint, but is highly dependent in the level of lateral restraint. The tests also show that there can be significant post-punching capacity if the top bars are well anchored into the slab.

Experimental Study of Dynamic Progressive Collapse in Flat-Plate Buildings Subjected to Exterior Column Removal

AbstractThis paper documents the findings from a dynamic collapse experiment carried out on a single-story two-by-two bay reinforced concrete flat-plate substructure. The test specimen had a 0.4 sc...

Effects of In-Plane Restraint on Progression of Collapse in Flat-Plate Structures

AbstractThis paper presents experimental and numerical studies of reinforced concrete flat-plate structures. Experiments were performed on six interior slab-column connections without structural in...