Joseph W. Tedesco

Strengthening of Reinforced Concrete Beams with Externally Bonded Composite Laminates

A particularly challenging problem confronting engineers in the revival of U.S. infrastructure is the rehabilitation of concrete structures. This paper summarizes the results of experimental and analytical studies concerning the flexural strengthening of reinforced concrete beams by the external bonding of high-strength, lightweight fiber reinforced plastic (FRP) plates to the tension face of the beam. Twenty-four large-scale beams were tested experimentally to evaluate the strength enhancement provided by the FRP plates. An inelastic section analysis procedure was developed that accurately predicts the load displacement response of the retrofitted beams. A nonlinear finite element method analysis was also conducted that corroborates the results from the experimental study and inelastic section analysis.

Strain-Rate-Dependent Constitutive Equations for Concrete

This paper summarizes the results of a comprehensive experimental study to quantify the effects of strain rate on concrete compressive and tensile strengths. Direct compression and splitting tensile tests were conducted at quasi-static rates (between 10{sup {minus}7}/s and 10{sup {minus}5}/s) in a standard MTS machine to establish the static properties. These same tests were conducted at high strain rates (between 10{sup {minus}1}/s and 10{sup 3}/s) on a split-Hopkinson pressure bar (SHPB) to determine the dynamic material properties. A statistical analysis was performed on the data and strain-rate-dependent constitutive equations, both for compression and tension, were developed. These constitutive equations were subsequently employed to modify an existing quasi-static, nonlinear concrete material model.

EXPERIMENTAL AND NUMERICAL ANALYSIS OF HIGH STRAIN RATE SPLITTING TENSILE TESTS

Splitting tensile concrete specimens were tested at strain rates of 10 to the power -7/sec to 10 to the power 2/sec in a low speed material test machine and in a 50.8-mm diameter Split Hopkinson Pressure Bar (SHPB). A comprehensive finite element method (FEM) analysis was conducted on the same test speciments. A high-speed framing camera was used to record the gross deformation and cracking during the fracture process in the SHPB tests. In addition, an ultra high speed image converter camera with equivalent framing rates of 10,000 to 1,000,000 frames per sec was used to record some of the early crack formations during the fracture process in the SHPB tests. Results of tensile strength versus strain rate are presented and compared with compressive strength at similar strain rates. These same tensile data are compared with strength data obtained using a fracture mechanics model. Computer generated crack patterns are presented and compared to experimentally observed crack patterns in the fracture of concrete at high strain rates.

Prediction of Anchorage Failure for Reinforced Concrete Beams Strengthened with Fiber-Reinforced Polymer Plates

This paper examines the anchorage failure mode of fiber-reinforced polymer (FRP)-strengthened reinforced concrete beams. An improved analytical procedure for calculating shear and normal stresses at the plate curtailment is presented. The analytical expressions are developed from linear elastic theory and statistical analyses of experimental results. The procedure is validated by comparisons with experimental results reported in the literature. Simplified, closed-form expressions to estimate the anchorage failure load for FRP-strengthened beams subjected to either concentrated or uniform loads are provided.

A strain-rate-dependent concrete material model for ADINA

Abstract The analysis, design and/or evaluation of protective structures and facilities for military use demands the accurate determination of material and structural response to high-intensity, short-duration impulse loadings. There currently exists a preponderance of data supporting increased strength characteristics in concrete, the primary construction material for protective facilities, at high strain rates. This paper summarizes the modification of the nonlinear concrete material model currently employed in the ADINA finite-element computer programs to account for high strain rate effects. The resultant strain-rate-dependent concrete material model encompasses the strain-rate range from 10 −7 s −1 (quasi-static) to 10 3 s −1 , in both compression and tension.

Numerical analysis of high strain rate splitting-tensile tests

Abstract Experimental splitting-tension tests were conducted on 2-in. diameter concrete specimens in a Split Hopkinson Pressure Bar at strain rates of 4.4, 10.6, and 14.7/sec. The specimens were instrumented with electrical resistance strain gages and break circuits to detect crack initiation and growth. Experimental results indicate that there is a shift of crack initiation time relative to the peak stress. Also, experimental strength vs strain rate data reveal that the dynamic tensile strength of concrete is significantly higher than the static tensile strength. A comprehensive numerical analysis was conducted on the splitting-tensile experiments to investigate the effects of varying the uniaxial tensile strength of the concrete on the crack initiation time, stress state, crack growth characteristics, and failure mode in the concrete specimens. The results of the numerical analyses are used to enhance the understanding of concrete tensile strength strain rate sensitivity.

Numerical analysis of high strain rate concrete direct tension tests

Abstract Direct tension tests of plain concrete specimens were conducted on a split-Hopkinson pressure bar (SHPB) to investigate the effects of increasing strain rate on the tensile strength of concrete. A comprehensive finite element method (FEM) study was performed on the SHPB experiments. Both linear and nonlinear analyses were conducted. The results of the numerical analyses disclose the dynamic states of stress in the specimen prior to failure as well as the mode of failure

Numerical simulation of high strain rate concrete compression tests

Abstract Dynamic direct compression tests of plain concrete specimens were conducted on a split-Hopkinson pressure bar (SHPB) to investigate the effects of increasing strain rate on the compressive strength of concrete. A comprehensive finite element method study was performed on the SHPB experiments. Both linear and nonlinear analyses were conducted. The results of the numerical analyses disclose the dynamic states of stress in the concrete specimen prior to failure as well as the modes of failure.

Numerical analysis of dynamic split cylinder tests

Abstract To investigate the effects of strain rate on the tensile strength of concrete, split cylinder tests of plain concrete specimens were conducted on a Split-Hopkinson Pressure Bar (SHPB). To ascertain the stress condition in the material specimens at failure, a comprehensive finite element method (FEM) study was conducted on the SHPB experiments. Both linear and nonlinear analyses were performed. From the results of the numerical analyses, the dynamic states of stress occurring in the split cylinder prior to failure as well as the mode of failure are revealed.

FINITE ELEMENT METHOD ANALYSIS OF A CONCRETE BRIDGE REPAIRED WITH FIBER REINFORCED PLASTIC LAMINATES

Abstract Many reinforced concrete bridges throughout the United States on county and state highway systems are deteriorated and/or distressed to such a degree that structural strengthening of the bridge or reducing the allowable truck loading on the bridge by load posting is necessary to extend the service life of the bridge. The structural performance of many of these bridges can be improved through external bonding of fiber reinforced plastic (FRP) laminates or plates. This paper summarizes the results of a comprehensive finite element method (FEM) analysis of a deteriorated reinforced concrete bridge repaired with externally bonded FRP laminates. Static and dynamic analyses of the bridge were conducted for conditions both before and after the FRP repairs, with loading by two identical test trucks of known weight and configuration. The results of the FEM analyses were corroborated with field test data. The results of a parametric study to assess the effects of altering the cross sectional dimensions and material properties of the FRP laminates upon bridge girder deflections and reinforcing steel stresses is also presented.